Apparatus and method for solvent recovery from a drying process

Abstract

A method and apparatus for condensing a majority of the solvent in a process gas stream at low temperatures, e.g., about -5°C below the freezing point of water. The gas stream exiting the condensation step can be further treated in one or more emission control devices, such as a single or multi-stage series of concentrator devices, such as a zeolite concentrator device. One or more emission control operations can be performed downstream of the single-step or multi-step concentrator. The above-described condensation process allows the one or more concentrators to operate in a preferred temperature range, removing 99% or more of the VOCs, and meeting or exceeding stringent environmental regulations.

Description

Technical Field

[0001] This application is a continuation-in-part of U.S. application Ser. No. 16 / 508,482, filed Jul. 11, 2019, the disclosure of which is incorporated herein by reference.

Background Art

[0002] In the manufacture of lithium ion batteries and the like, wet coating can be applied to a substrate in the form of a slurry or paste and is composed of fine powder mixed with a binder material, typically a polymer that can be water-soluble. In some cases, the binder is dissolved in an inorganic solvent such as N-methyl-2-pyrrolidone (NMP), acetone, various alcohols, or a similar industrial solvent selected to dissolve an organic binder to form a coatable liquid. These web-based products can be coated on at least one side (lateral side) of a substrate web. In these cases, the wet coating is applied continuously or discontinuously on a moving web and dried in an oven or dryer to remove the solvent, thereby solidifying the applied coating. Through this application, a continuously applied coating applies the coating to a substrate such as a web, foil, etc. in a continuous process, regardless of the presence or absence of coating parameters (e.g., thickness, chemical composition, and / or physical parameters of the coating material, etc.) that change timely and / or locally. Thus, in this continuous process, it should be understood that the coating process also includes coatings in regular or irregular patterns on a continuously moving substrate.

[0003] In some cases, both sides (lateral sides) of the aforementioned web-based product are coated. In a typical case where both sides of the substrate web are coated, a first web coating is continuously applied on the moving web, dried in an oven or dryer, followed by the application of a second wet coating, followed by drying in a second drying step.

[0004] In a preferred embodiment for manufacturing a battery electrode, a wet slurry is applied to both sides of a foil web and then dried in an oven or dryer. This arrangement is called simultaneous double-sided coating-drying. In the case of manufacturing a lithium-ion electrode, this arrangement is particularly advantageous for enhancing productivity because only one drying step is required after applying the wet coating slurry on both sides.

[0005] For the recovery of VOC solvents from these and other industrial processes (such as solvents condensable at the operating temperature of a common cooling system (e.g., N-methyl-2-pyrrolidone (NMP), triethyl phosphate (TEP), dimethylacetamide (DMAc)), or other condensable fluid emissions from industrial activities such as the manufacture of lithium-ion battery electrodes, or for the drying and curing of polymer films, a mist removal device is typically used after condensing volatile organic compounds (VOCs) together with water and other potential contaminants on a low-temperature dehumidifier or the condenser coils of a finned surface. In most web drying operations, at least a portion of the air exiting the condensation step is discharged to the atmosphere as a sidestream, and the remaining air can be returned to the dryer. The flow rate of the sidestream is at least equal to the fresh air entering the drying device, particularly the permeating air of the web slots. For many commonly used solvents such as NMP, the concentration at the end of the condensation operation far exceeds the allowable limit for discharge to the atmosphere. Furthermore, the recovery of such solvents can be cost-effective and may be desirable. Therefore, generally, an additional downstream emission control operation (emission control device) is required to reduce the VOC concentration to an acceptable level. Methods for capturing and / or destroying VOCs include thermal (catalytic and direct thermal) oxidizers, scrubbers, carbon adsorption, and adsorption onto a concentration medium such as zeolite. The allowable emission concentration of VOCs to the atmosphere is usually in the range of 10 - 20 mg / Nm 3 as carbon, but in many locations, these concentrations are set at lower limits more frequently.

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the current market situation regarding the production of green energy products such as electrodes for batteries, VOC emissions at much lower concentration levels on the order of 1 mg / Nm 3 are required. Conventional emission control devices are an unrealistic option for reaching these low levels. Further, energy consumption is high with most conventional emission control methods, and some or all of these devices currently configured in the market cannot reach such low outlet emission concentrations. In VOC capture operations using condensation coils, very low temperatures are required to reach the equilibrium vapor pressure necessary to release a sufficiently low VOC concentration from the condensation unit. For example, if there is NMP in the incoming air stream, for the outlet stream to reach 1 mg / Nm 3 , the condensation coil needs to operate with a coil surface temperature of less than -35°C. In most drying processes, water vapor is included in the dryer exhaust gas along with VOC species. At such temperature conditions, often the water in the coil fins and tubes freezes to form ice. This ultimately blocks the air flow between the fins within the heat exchange core of the tubes and the condensation coil, and thus it is necessary to thaw to melt and remove the ice clogging the coil. To operate continuously, some systems may arrange two or more condensation coil sets in parallel. Additional valves, heaters, and air moving hardware are provided, and while one or more condensation coil paths are online in the condensation operation mode, at least one condensation coil path is isolated from the drain flow path and operates in the thawing mode. The issues of reliability and energy efficiency often plague such systems as to how to completely avoid them.

[0007] Therefore, devices and methods for reducing or eliminating such VOCs that are not troubled by the drawbacks of the prior art would be highly beneficial.

Means for Solving the Problems

[0008] The problems of the prior art are addressed by the embodiments disclosed herein. This provides a method and apparatus for overcoming the limitations of the prior art in an innovative and useful way by condensing a majority of the solvent in the process stream at low temperatures (e.g., even below the freezing point of water, about -5 °C) compared to conventional thermal coil condensers. The remaining solvent in the gas stream can be less than 50 mg / Nm 3 by the low temperature condensation step. In this temperature range, solvents such as NMP and DMAc exhibit the behavior of antifreeze liquids that lower the freezing point of the water and solvent mixture and prevent the accumulation of ice. In certain embodiments, the gas stream exiting the condensation step is further processed by one or more emission control devices such as a single-stage or multi-stage series of concentrator devices such as a zeolite concentrator device. By the aforementioned condensation process, one or more concentrators operate in a preferred temperature range, removing 90 - 99% or more of the VOCs, meeting or exceeding strict environmental regulations.

[0009] The flow capacity of the concentrator per given volume of the adsorption medium generally increases with a low removal rate and decreases with a high removal rate. Thus, the optimal design point of the removal rate of VOCs in the air stream containing a specific solvent at each stage processed using two or more emission control devices (the first being of the concentrator type) in series may be below the 90 - 99% removal range. In one example embodiment, the first stage concentrator removes 90% or more of the VOCs, leaving less than 10% of the inflow. For example, if the inflow is 50 mg / Nm 3 , 5 mg / Nm 3 is left. The optional second stage concentrator also removes 90% or more of the VOCs coming in from the first stage concentrator. Thus, the resulting outlet concentration is on the order of about 0.5 mg / Nm 3 and meets strict environmental regulations including, for example, new targets in the battery industry.

[0010] Accordingly, the specific embodiments disclosed herein relate to a circulating air conditioner such as one or more recirculating air dryers that produce recirculating air containing at least one condensable fluid (such as NMP), wherein the circulating air conditioner a. At least one main condenser having a supply port, an exhaust port, and at least one main condensation stage, wherein: i. A condensation chamber to which the circulating air is accessible or permeable; ii. A cooling coil disposed at least partially within the condensation chamber and penetrated by a cooling medium, iii. Thereby, the cooling coil of the main condenser operates at a main cooling medium temperature of 0 °C or lower. The main condenser; b. A circulating air supply line connected to the supply port of the main condenser and connectable to an air source containing a condensable fluid such as an exhaust circulation air duct for the one or more dryers to carry the circulating air; c. A circulating air exhaust line connected to the exhaust port of the main condenser and connectable to a supply circulation air duct of the one or more dryers; d. A secondary off-gas extraction line fluidly connected to at least the condensation chamber of the main condenser; Including: i. Thereby, the volumetric flow rate of the circulating air flowing through the condensation chamber is split into a large recirculation flow exiting the condenser through the circulating air exhaust line and a small off-gas side flow.

[0011] In a specific example, the secondary flow and the recirculation flow are split in volume by a split ratio of 0.1% to 20%, preferably 0.5% to 10%, and more preferably 1% to 5%.

[0012] In a specific aspect, the circulating air conditioner further includes at least a preliminary condenser having at least one preliminary condensation stage, the preliminary condenser being disposed in the circulating air flow upstream of the main condenser and including a preliminary condensation chamber to which the circulating air is accessible or permeable and a cooling coil disposed at least partially within the preliminary condensation chamber and penetrated by a preliminary cooling medium, whereby the preliminary cooling medium has a temperature higher than the main cooling medium temperature.

[0013] The preliminary condenser and the main condenser can be enclosed in a common condenser housing.

[0014] Any of the circulation air conditioners of the foregoing embodiments may further include, alone or in combination, a preliminary cooling heat exchanger disposed upstream of the preliminary condensation stage or at least upstream of the main condensation stage to already lower the temperature of the circulation air flow, and / or a reheating heat exchanger disposed downstream of the main condensation stage. The preliminary cooling heat exchanger and the reheating heat exchanger may be thermally coupled by exchange of a heat transfer medium such as water, brine, or a suitable heat fluid, and / or may be thermally coupled by a thermocouple or a heat pipe. In some examples, the preliminary cooling heat exchanger and the reheating heat exchanger are additionally or alternatively thermally coupled via at least one thermocouple or heat pipe.

[0015] Any of the circulation air conditioners of the foregoing embodiments, alone or in combination, as a first pollution prevention stage, includes an air pollution control unit having at least one adsorption concentrator fluidly connected to the secondary off-gas extraction line and having gas exhaust and desorption exhaust, and may further include at least a second pollution prevention stage selected from the group that may include an adsorption concentrator supplied by the gas exhaust of the first pollution prevention stage and having gas exhaust and desorption exhaust. At least one desorption exhaust of the absorption concentrator can be connected to desorption consisting of a filtration device, an absorption concentrator, a thermal oxidizer, and a catalytic device.

[0016] The second pollution prevention stage line is connected to a desorption condenser, whereby the gas exhaust of the desorption condenser is refluxed to the secondary off-gas extraction line. The second pollution prevention stage may include at least one activated carbon filter.

[0017] Any of the circulation air conditioners of the foregoing embodiments, alone or in combination, may include one or more suitable sensors and one or more injectors for introducing humidity into a gas stream containing a solvent such as a circulation air supply line. The one or more sensors and the one or more injectors may be part of a control system that may include a PID controller to dynamically control the humidity of the gas stream containing the solvent.

[0018] In terms of aspects of the method, embodiments disclosed herein relate to a method for conditioning recirculating air comprising at least one condensable fluid, a. introducing the recirculating air into a main condenser having at least one main condensation chamber at a first volumetric flow rate and an intake temperature level well above 0 °C, b. gradually cooling the recirculating air until a main temperature level in the main condensation chamber reaches 0 °C or below, c. after reaching a second temperature level, splitting the volumetric flow of the circulation into a large recirculation flow and a small off-gas sidestream, and d. providing the large recirculation flow to an intake of recirculating air of a dryer are included.

[0019] In certain aspects, this method may further include providing a condenser that includes at least one cooling coil containing a cooling medium for cooling the recirculated air of step b), whereby the cooling medium enters the cooling coil at the distal side of the recirculated air inlet at an inlet temperature of 0 °C or lower and is heated while moving countercurrently to the recirculated air through the cooling coil. The flow rate and temperature of the incoming cooling medium are preferably measured using a suitable flow meter device and a temperature sensor such as a resistance temperature detector (RTD). The temperature of the discharged cooling medium is preferably measured using a suitable temperature sensor such as an RTD. The recirculation flow can be driven by a fluid pump in communication with the fluid inlet connection of the cooling coil. Further, the temperature of the air exiting the cooling coil is preferably measured using an array of one or more temperature sensors spaced across the cross-section of the outlet face of the coil. The air temperature sensor can be, for example, an RTD or a thermocouple. The flow rate and temperature of the coolant of the incoming cooling medium can be controlled to respective predetermined set points by a suitable PID controller in control communication with a flow control device (preferably a variable speed centrifugal pump and a temperature control valve, preferably a set of three-way flow distribution valves arranged by an actuator). The coolant is introduced into the recirculation flow conduit from a cooled salt water source, typically a water-cooled or air-cooled centrifugal chiller. The set of three-way flow path valves allows fresh cooling medium from the cooling medium source to enter the recirculation flow path through the coil, while an equivalent flow of heated cooling medium exiting the cooling coil return connection is discharged to the cooling medium source. In some embodiments, the temperature of the air exiting the cooling coil can be controlled to a predetermined set point by a suitable PID controller in control communication with a valve and actuator arranged in a conduit that receives fresh coolant from the cooled salt water source.The predetermined setpoint of the air exiting the cooling coil is selected by the operator to reach the desired target concentration of the solvent or aqueous humidity of the air exiting the coil, as determined from theoretical and / or empirical vapor pressure equations (such as the Antoine Equation or Raoult’s Law, or engineering simulation model tools such as ChemCad, ASPEN, or other theoretical or empirical methods known in the art, or preferably from experimental test measurements). Alternatively, in a preferred embodiment, the output from the outlet air temperature measurement is input to a first PID controller configured by a control algorithm to calculate the temperature setpoint of the incoming cooling medium. Thus, the output of the first PID controller communicates with a second PID controller, which receives the temperature setpoint from the first PID controller in a cascade control configuration between the two respective PID controllers. The second PID controller output arranges the actuator of the three-way flow path valve to control the measured temperature of the cooling medium entering the coil to the input setpoint of the first PID controller. In this cascade configuration, the output of the first controller, and thus the setpoint of the second controller, can be used in temperature units as an engineering parameter, which can be limited between acceptable minimum and / or maximum setpoints depending on the functional capabilities of the coolant system. This parameter can also be converted by calculation to other engineering parameters, which includes, but is not limited to, the concentrations of solvent and water expected at the air film boundary of the coil fins and tube surfaces according to the vapor-liquid equilibrium (VLE) relationship (from the Antoine Equation and Raoult’s Law, or other theoretical or empirical methods known in the art, or experimental test measurements). These parameters are preferably used to set the values of the minimum and / or maximum setpoints of the second PID controller to reduce the formation of solvent mist. Without cascade, the first controller can directly set the valve position (e.g., in this case, a 4 - 40 mA position signal to the actuator of the mixing valve for controlling the temperature of the mixed coolant entering the coil).Alternatively, when an optional second controller is incorporated (in a cascade-like fashion), the output of the first controller is in temperature units (e.g., °C) and is the setpoint input to a second controller that outputs a position signal. There are advantages to the intermediate temperature signal in a cascade arrangement. For example, the upper and lower limits of the setpoint temperature of the second controller can be established based on the operation of engineering parameters or physical characteristics, as opposed to simply a rote positioning without a cascade arrangement.

[0020] In any embodiment for reducing fog formation, the temperature of the cooling medium exiting the coil is measured and input to a third PID controller having an output that communicates with the aforementioned flow control device (preferably a variable speed centrifugal pump that sets the speed and thereby the flow of the cooling medium through the coil). The setpoint temperature (an operator input parameter determined as described below) input to the third PID controller is compared with the measured temperature, and the output of the third PID controller adjusts the speed of the pump and thus the flow rate of the coolant medium to reach the desired target temperature.

[0021] Optionally, in an alternative embodiment, the output from the outlet coolant temperature measurement is input to a third PID controller configured to calculate a flow rate setpoint for the coolant entering the coil by a control algorithm. Thus, the output of the third PID controller communicates with a fourth PID controller, which receives the flow rate setpoint from the third PID controller in a cascade control configuration between the two respective PID controllers. The output of the fourth PID controller sets the speed of the circulation pump to control the measured flow of coolant entering the coil to the input setpoint of the third PID controller. In this cascade configuration, the output of the third controller, and thus the setpoint of the fourth controller, can be used as an engineering parameter that can be limited between the allowable minimum and / or maximum setpoint values depending on the functional capacity of the coolant system, in flow rate units (such as liters per minute). This flow rate parameter can also be converted to other engineering parameters by calculations including but not limited to the cooling load of the coil by theoretical or empirical heat and mass balance methods known in the art, or from experimental test measurements. These parameters are optionally used in setting the values of the minimum and / or maximum setpoints of the fourth PID controller to reduce the formation of solvent mist.

[0022] Therefore, the output of the third controller can directly set the pump speed, for example, by a 4 - 20 mA signal. Alternatively, by incorporating a fourth controller, the output from the third controller regarding the fluid flow rate (e.g., gpm or lpm) can be input into the fourth controller, which sets the pump speed, for example, by a 4 - 20 mA signal and makes the measured flow rate match the value of the flow rate set point. The input to the third controller can be set to a value below the outlet air, for example, a value 0 to 12 degrees Celsius lower than the temperature of the air exiting the coil. The set point of the flow input to the fourth controller can be restricted from the perspective of the flow rate and is of engineering / physical importance in optimizing the coil performance. The set point of the input flow rate to the fourth controller is resolved by the interaction of the third and fourth controllers when meeting the temperature set points of the first and third controllers.

[0023] The desired target temperature of the coolant medium at the coil outlet can be selected to reduce fog formation according to various film fog formation models found in the literature or by experiment.

[0024] In the case of an example of condensing NMP from vapor at a specific flow rate of air entering the condensation step, the experimental results obtained in a pilot-scale test showed that by operating the condensation coil while maintaining the outlet temperature of the coolant medium at a value lower than the outlet air temperature from the coil, the formation of fog can be significantly reduced and even eliminated. To achieve the condition that the outlet coolant temperature is lower than the air outlet temperature of each coil, first the outlet air temperature was selected and the inlet temperature of the coolant medium was adjusted to reach the outlet air temperature. Next, the outlet temperature of the coolant medium was measured and the flow rate of the coolant medium was adjusted, whereby the temperature rise of the coolant medium changed from the inlet to the outlet of the coil and the outlet temperature of the coolant was 0 to 12 °C lower than the outlet air temperature of the coil, most preferably 1 to 5 °C lower than the outlet air temperature of the coil. The results of the settings in the first step and the second step interact, and these steps need to be repeated until the temperature conditions of both the outlet air and the outlet coolant medium are satisfied. Similarly, this process can be carried out starting from the second step and then proceeding to the first step. Preferably, the steps are continuously executed by a PID controller loop as described above.

[0025] In addition to the aforementioned flow rate and temperature settings of a given coil, the design of a coil or set of coils for performing a condensation operation needs to be selected to match the heat load for cooling the sensible heat of the air flow and the heat of phase change while meeting the currently described air outlet temperature, coolant media temperature, and flow conditions. A common approach to coil design typically focuses on the efficient utilization of the coolant media from the plant cooling facility (typically by a row of finned tubes and the flow on the fluid side, typically by a multi-pass array of tubes) while minimizing the physical coil size and the pressure loss of the air-side flow. The multi-pass tube array is typically manifolded and piped to direct the fluid media in successive passes that flow countercurrent to the direction of the air-side flow. In conventional coil designs, often the coolant outlet temperature exceeds the air-side outlet temperature of the coil, resulting in a reduction in coolant flow rate and pump cost and an improved return temperature of the coolant returning to the plant cooling facility. However, in the case of the formation of solvent mist in the condenser coil, higher coolant outlet temperatures are associated with test results for conditions that result in greater mist formation. Therefore, as a coil load specification, it is advantageous to specify that the desired outlet temperature of the coolant media is in the range 0 to 12 °C lower, preferably 1 to 5 °C lower, than the specified air outlet temperature. This specification typically results in an improved design velocity of the coolant flow compared to conventional selections for a given cooling load.

[0026] Furthermore, when meeting the coolant outlet temperature conditions described for a condensation operation with a significant air-side temperature drop, it is advantageous to divide the cooling load among two or more coils or stages that process the air flow in series (each coil having a separate coolant media flow circuit with control as described above for a single coil). This makes it easier to reach a reduced coolant outlet temperature for each coil stage with respect to the air outlet temperature.

[0027] Another aspect of coil design for reducing fog formation is the choice of fin spacing on the air side and air velocity. Manipulating the coil so that the channel flow between fins is predominantly turbulent, rather than laminar or transitional, is advantageous for reducing fog formation. A common fin arrangement can include straight parallel fins of a thin conductive material such as aluminum, copper, or alloy steel, equally spaced to form a straight flow path from the air inlet face to the air outlet of the coil. In another preferred arrangement, the fins are formed in a wavy shape, equally spaced, and the airflow follows a meandering or sinusoidal path between the fins, increasing turbulence. In a conventional coil design for typical loads, the fin spacing and air velocity are selected to achieve a compact coil size with low pressure loss and efficient utilization of the coolant medium from the plant cooling facility. In contrast, for fog reduction or elimination, higher air velocities and / or larger fin spacings are advantageous for reducing or eliminating fog formation. When the fin spacing is 3.2 mm or more, an air velocity exceeding 1.5 m per second is recommended. The dimensionless fin Reynolds number, Re L is represented as, where Re L =(fin spacing)(air velocity) / (kinematic viscosity), and the fin spacing and air velocity need to be selected such that Re L > 400. As a result of this air velocity and fin spacing, the coil dimensions in the flow direction tend to increase, and special consideration of the coolant flow rate is necessary to meet the load specifications and the desired low coolant outlet temperature. In some cases, it may be necessary to increase the diameter of the coil tubes. Again, these design features tend to conflict with conventional coil design parameters, so careful specification is required in the selection of coils to avoid fog formation.

[0028] One or more controllers used in any of the embodiments disclosed herein may have a processing unit and a storage element. The processing unit may be a general-purpose computing device such as a microprocessor. Alternatively, it may be a special processing device such as a programmable logic controller (PLC). The storage element can utilize any memory technology, such as RAM, DRAM, ROM, flash ROM, EEROM, NVRAM, magnetic media, or other media suitable for holding computer-readable data and instructions. The controller unit may be in electrical communication (e.g., wired, wireless) with one or more operating units within the system, including one or more of valves, actuators, sensors, etc. The controller may also be associated with a human-machine interface or HMI that displays or otherwise indicates to an operator one or more parameters related to the operation of the system described herein and / or the execution of the method. The storage element may contain instructions that, when executed by the processing unit, enable the system to perform the functions described herein. In some embodiments, two or more controllers can be used.

[0029] Any of the methods of the foregoing embodiments, alone or in combination, may further include supplying the recirculated air at the first volumetric flow rate to a pre-condenser upstream of the main condenser at a pre-condensation temperature level lower than the first temperature level and significantly exceeding the main temperature level, gradually cooling the recirculated air to the pre-condensation temperature level within the pre-condenser, and supplying the cooled recirculated air to the inlet of the main condenser. The recirculated air can be pre-cooled upstream of the main condenser and / or reheated downstream of the main condenser.

[0030] Any of the methods of the foregoing embodiments, alone or in combination, may further include supplying the offgas sidestream to at least a two-stage air pollution prevention device, collecting and concentrating the residual condensable fluid in the adsorption concentrator as a first pollution prevention stage, and then, as a second stage further downstream of the first stage, treating the remaining offgas stream in a second air pollution prevention device to a level of residual condensable concentration in the air well below a predetermined limit (1 mg / Nm 3 etc.). The second air pollution prevention device may be a filtration device such as a second adsorption concentrator or an activated carbon filter.

[0031] Any of the methods of the foregoing embodiments, alone or in combination, may further include adding humidity to the recirculated air supply line.

[0032] By operating a single-stage or multi-stage condenser in combination with one or more emissions control devices such as two VOC concentrator foils in series, a target emissions rate of less than 1 mg / Nm 3 is achieved. In some embodiments, the recovery of VOC solvents results in the removal of substantially all VOC waste from the environment without the need for thermal combustion products or other secondary pollutants. Valuable solvents such as NMP can be recovered and purified, for example, for reuse in the battery electrode manufacturing process by a closed-loop system.

[0033] The embodiments disclosed herein may be formed in various component and component arrangements, as well as in various process operations and process operation arrangements. The drawings are for the purpose of illustrating only the preferred embodiments and are not to be construed as limiting. This disclosure includes the following drawings.

Brief Description of the Drawings

[0034]

Figure 1

Figure 1a

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

[0035] A more complete understanding of the components, processes, and devices disclosed herein can be obtained by reference to the accompanying drawings. These drawings are merely schematic diagrams for the convenience and ease of demonstration of the present disclosure, and thus are not intended to show the relative sizes and dimensions of the device or its components, and / or to define or limit the scope of the exemplary embodiments.

[0036] In the following description, specific terms are used for clarity, but these terms are intended to refer only to the specific structures of the embodiments selected for illustration in the drawings and are not intended to define or limit the scope of the present disclosure. It should be understood that in the following drawings and the following description, like reference numerals refer to components of like function.

[0037] The singular forms "a", "an", and "the" include plural referents unless the context clearly indicates otherwise.

[0038] As used herein, various devices and components may be described as "including" other components. The terms "including", "comprising", "having", "can", "containing", and variations thereof, as used herein, are intended to be open transitional phrases, terms, or words that do not preclude the possibility of additional components.

[0039] All ranges disclosed herein include the recited endpoints and can be combined independently (e.g., the range "2 inches to 10 inches" includes the endpoints, 2 inches and 10 inches, as well as all intermediate values).

[0040] As used herein, approximating language may be applied to modify any quantitative representation that could vary without resulting in a change in the basic function to which it is related. Accordingly, values modified by terms such as "about" or "substantially" may not be limited to the precise values specified. The adjective "about" can also be considered to disclose a range defined by the absolute values of two endpoints. For example, the expression "about 2 to about 4" also discloses the range "2 to 4".

[0041] Note that many of the terms used herein are relative terms. For example, the terms "upper" and "lower" are relative to each other, i.e., an upper component is located at a higher position than a lower component, and should not be construed as requiring a particular direction or position of the structure. As a further example, the terms "interior", "exterior", "inner", and "outer" are centered-based and should not be construed as requiring a particular direction or position of the structure.

[0042] The terms "top" and "bottom" are based on an absolute reference, i.e., the earth's surface. In other words, in the direction towards the earth's surface, the location of the top is always arranged at a higher elevation than the location of the bottom.

[0043] The terms "horizontal" and "vertical" are used to indicate absolute reference, i.e., relative directions with respect to the horizon. However, these terms should not be construed as requiring that the structures be perfectly parallel or perpendicular to each other.

[0044] Referring to FIGS. 1, 1a and 2 (like numerals indicate like parts), a condenser 10 is shown having a supply port 12 and an exhaust port 14 spaced from the supply port 12. A portion of the process gas exiting the condenser 10 is directed through a flow 30 to a pollution control unit 40. In the embodiments shown in FIGS. 1 and 2, the inlet of the condenser 10 optionally includes an air particle removal filter 18, one or more pre-cooling regions 15 (each having a pre-cooling chamber 15a), one or more cooling or condensation regions or stages 16 (each having a condensation chamber 16a) downstream of the one or more pre-cooling regions 15, a mist coalescing panel (i.e., a demister) 28, and one or more re-heating regions 17 (each having a re-heating chamber 17a) downstream of the one or more cooling or condensation regions 16. Each of the aforementioned chambers is accessible or permeable to circulating air. In certain embodiments, the cooling or condensation region 16 can be a single-stage condenser (FIG. 1) or can include multiple cooling stages (FIG. 2), each being effective to further cool the incoming gas stream to a temperature lower than the temperature at which the gas stream was cooled in the immediately upstream cooling stage.

[0045] In some embodiments, two cooling or condensation regions 16, 16' are present (FIG. 2). In some embodiments, three, four, five, or more condensation regions are present (not shown). The number of condensation regions depends in part on the characteristics of the VOC and how much the process stream containing the VOC needs to be cooled stepwise to avoid fog formation, i.e., at least in part, is a function of the rate of temperature decrease or temperature cooling profile of the VOC.

[0046] In certain embodiments, each cooling or condensation region or stage 16 may include a condensation chamber 16a having a cooling coil 20 disposed therein through which a cooling medium may be circulated. Suitable cooling media are not particularly limited and include water and brines such as water mixed with propylene and / or ethylene glycol, respectively. Each cooling coil 20 may be partially or fully disposed within its cooling or condensation region 16. As shown in FIG. 1, preferably, the flow of the cooling medium through the cooling coil 20 is in a countercurrent direction to the flow of the process gas through the condensation chamber 16a. In some embodiments, the flow of the coolant may be configured in parallel flow, as shown by the flow streams 116a and 116b of FIGS. 3 and 4.

[0047] Alternatively, a spray condenser can be used to spray the coolant from one or more nozzles into the condensation chamber to condense the VOCs in the process stream. As shown in FIG. 5, the direct contact condenser 510 can be arranged in place of the condenser 10 of FIGS. 1 - 4. The gas stream 70 containing the solvent from the drying operation is pre-cooled in the economizer heat exchanger 101 and then directed towards the direct contact condenser vessel 505. The cooled stream 70a is optionally pre-filtered in the air filter unit 569, pressurized by the blower 502, and blown into the port in the lower section of the vessel 505. The air 570 containing the solvent enters the lower chamber of 505 and is directed vertically through the flow distributor 516 into the region of the media packing 515. The flow distributor 516 includes structural elements to support the weight of the packing and the weight of the liquid adhering to the packing. The packing can be selected for its optimal surface contact area with the upward flowing air stream per unit volume and low pressure drop characteristics. Common packing shapes include Raschig rings, saddles, pall rings, or other suitable packing shapes. The packing is typically made of corrosion-resistant materials such as stainless steel, ceramic, polymeric materials, etc. The air stream 570 containing the solvent passes through the packing media and comes into direct contact with the cooled condensed solvent flowing downward by gravity, wetting the surface of the packing. To uniformly disperse the cooled solvent across the entire upper horizontal cross-section of the packing 515, the cooled condensed solvent is supplied to the upper part of the vessel 505 via the flow distribution manifold or header 513 and can optionally be further distributed by the fluid tray 514. The cooled solvent 538 is used directly as the condensation medium by direct contact between the air stream 570 containing the solvent and the wet surface of the packing media in the packing contact region 515. The cooled solvent picks up the solvent condensed from the counter-flowing air and drips downward through the packing, eventually reaching the bottom of the packing region 515 and being discharged as a sample through the distributor 516 to the lower part of the vessel 505 that functions as a sump. The level of the solvent 536 collected in the sump is maintained by a level sensor and control that directs the solvent through the conduit 537 to the primary storage container 38.

[0048] The outlet gas flow 571 passes through the demister element 528, and most of the flow moves through the exhaust line 72a and is reheated by the economizer 101 before being carried to the dryer operation in the flow or conduit 72b. The split ratio of the flow occurring within the conduit 30 is preferably in the range of 0.5% to 10% of the flow within the exhaust line 572. In an unsteady operating state, this split ratio can be as high as 20%. The flow within the conduit 30 is preferably reheated by the heat exchanger 580 to bring the temperature of the flow stream 30b entering the concentrator 50 to a range of 10°C to 20°C, most preferably 15°C.

[0049] In the case of direct contact condensation, the cooling and condensation surface is, in effect, a cooled solvent liquid that functions as a cooling medium, wets the surface of the packing, and drips in a downward countercurrent to the airflow containing the solvent. Since the cooled solvent has a lower vapor pressure than the air containing the solvent, the cooled solvent absorbs more solvent from the air and its temperature is raised by the air. Therefore, in the continuous steady state, operating energy must be removed from the condensed solvent stream 539 by the liquid-liquid heat exchanger 591. The temperature of the cooled solvent supplied to the direct condenser must be measured and accurately controlled before distributing the cooled solvent to the vessel 505 via the supply manifold 513. Most of the solvent collected at 536 in the sampling region of 505 is led through the conduit 539, optionally filtered by the liquid filter 518, further pumped by the centrifugal pump 592, cooled through the liquid-liquid heat exchanger 591, and further transported to the distribution header 513 near the top of the tower vessel 505. The split ratio of the flow in the conduit 537 is in the range of 5% to 30% of the flow in the conduit 539. The flow rate of 539 is measured by a suitable liquid flow meter and controlled to a set point by a controller that adjusts the speed of the electric pump 592 by variable frequency motor speed control. The temperature of the cooled solvent is measured by a suitable temperature element such as an RTD when it enters the distributor manifold 513 and is controlled to a set point temperature, preferably in the range of -10 to 0 °C, most preferably -4 °C, by the plant facility coolant salt water source of the heat exchanger 591. The actuated flow control valve 520 in the coolant flow conduit from the salt water source is adjusted to obtain the desired measured temperature supplied to the distribution header 513. The said temperature set point is such that, in the case of NMP, the vapor pressure of the solvent in the gas phase exiting the packing region 515 results in a solvent concentration level in the range of 1 to 500 mg / Nm 3 , preferably 1 mg / Nm 3 of the solvent.

[0050] In certain embodiments, the pre-cooling zone 15 and the re-heating zone 17 can be brought to and / or maintained at their respective operating temperatures using a pre-cooling heat exchanger and a re-heating heat exchanger, as shown in FIGS. 1, 2, 3, and 4. In certain embodiments, these heat exchangers are a closed-loop heat exchange recirculation system 35 that can function as an economizer. The recirculation system 35 can include a first coil 35a disposed at least partially within the pre-cooling chamber 15a and a second coil 35b disposed at least partially within the pre-heating chamber 17a. The loop of the recirculation system 35 can include a suitable heat exchange medium, such as water or brine, for transferring heat to and / or from the process gas in the pre-cooling and pre-heating zones. An air-to-air economizer heat exchanger 101 can also be used, as shown in FIGS. 1a, 5, 7, and 8. The exhaust flow 70 from the drying operation is pre-cooled in the economizer 101 by the cooler return air flow in the exhaust line 72a. The economizer 101 is selected to provide a heat exchange effect in the range of 40 - 60% and brings the appropriate post-pre-cooling temperature value in the range of 80 - 100 °C to the temperature of the flow stream 70a. Thus, the exhaust return air 72a is re-heated to the desired temperature in the range of 40 - 60 °C within the economizer 101 with the energy from the exhaust flow 70. The temperature of the heat exchange medium can optionally be adjusted with the help of an additional heat exchanger 291, as shown in FIG. 3. In certain embodiments, the temperature of the coolant within the loop of the recirculation system 35 is higher than the temperature of the coolant within one or more coils within the condensation zone 16. Excess thermal energy can be removed and the temperature of the coolant within the loop of the recirculation system 35 can be controlled by circulating a portion of the coolant through the liquid-liquid heat exchanger 291 via the pump 292 from the loop of the recirculation system 35 in a split ratio range of 10 - 50% of the flow stream. A portion of the fluid thus cooled is returned from the conduit 293 to 35 before entering 35b.

[0051] In certain embodiments, the pre-cooling region 15 and the condensation region 16 have a common housing. In certain embodiments, the condensation region 16 and the re-heating region 17 have a common housing. In certain embodiments, the pre-cooling region 15, the condensation region 16 and the pre-heating region 17 have a common housing.

[0052] In some embodiments, a first coil 35a for pre-cooling may be disposed upstream of the pre-cooling region to lower the temperature of the circulating air exhaust flow 70. In some embodiments, a second coil 35b for re-heating may be disposed downstream of the condensation region 16. In some embodiments, both coils may be so disposed. The pre-cooling coil and the re-heating coil can be thermally coupled by exchange of a heat transfer medium such as water, brine, or a suitable heat transfer fluid.

[0053] In certain embodiments, the sidestream off-gas extraction line 30 may be provided to be in fluid communication with the condensation region 16. When a plurality of condensation regions are provided, the sidestream off-gas extraction line preferably communicates directly in fluid with the most downstream condensation chamber 16a' (i.e., the chamber immediately upstream of the reheating region 17). The sidestream gas extraction line 30 may be configured to communicate with the operation of downstream units such as one or more VOC concentrators and / or one or more emission control units, as will be discussed in more detail below. A portion of the sidestream off-gas may also be extracted following the reheating region through line or conduit 29 and added to the sidestream flowing through extraction line 30. The control system 31 consists of a temperature sensor and a controller arranged to measure the mixing temperature of the flows from extraction lines 29 and 30 and to adjust the operating flow dampers of flow lines 29 and 30. Thus, an optimum temperature in the range of 10 to 18 °C, preferably 15 °C, is obtained by closed-loop control of the flow distribution when the flow stream 30b enters the condenser 50. The recirculated air exhaust line 72 may be provided to be in fluid communication with the exhaust port 14 of the condenser 10. The recirculated air exhaust line 72 may be configured, for example, to connect to the supply recirculated air duct of one or more industrial dryers (Figure 3). The distribution of the split flow through flow or conduit 30a is preferably in the range of 0.5% to 10% of the flow in the exhaust line 72. During non-steady state operating conditions, this split ratio can be as high as 20%.

[0054] In some embodiments, the supply port 12 of the condenser 10 is in fluid communication with, or is adapted or configured to be in fluid communication with, the exhaust from one or more industrial dryers 200 (FIG. 3), such as via a circulating air supply line 70. That is, the source of the process gas supplied to the condenser 10 can be the exhaust from one or more industrial dryers, such as one or more dryers that dry a coating on a web. For example, in the manufacture of battery electrodes, a wet process is used to apply battery electrode components to a current collector web, such as copper or aluminum foil. Typically, a polymer binder, graphite, and an active material are mixed with a solvent or water and applied to the web. The solvent or water is removed in one or more dryers to produce a dry battery electrode material for use in a battery cell. The exhaust from such one or more dryers is a suitable supply stream to the condenser 10.

[0055] In some embodiments, the exhaust port 14 of the condenser 10 is in fluid communication with, or is adapted or configured to be in fluid communication with, a recirculation supply to one or more industrial dryers 200 (FIG. 3), such as via a circulating air discharge line 72. A suitable driving force, such as a suction fan disposed in the recirculation line 72, can be used to drive the flow of process gas that flows into and through the condenser 10.

[0056] The dryer or dryers 200 can be conventional convective air web dryers, such as those in which hot air is used to dry a coating on a web that moves through the dryer. For example, an air bar or nozzle can be used to direct a jet of air against the surface of the material to perform a heat and / or mass transfer function. Convective air drying of battery electrode materials typically involves a drying air temperature in the range of 80 to 160 °C and 30 to 100 watts / m per side of the web. 2It is carried out with the convective heat transfer coefficient of the air nozzles to the web at ℃. As is known to those skilled in the art, a plurality of air nozzles can be arranged in an array or a plurality of arrays to direct the impact of air onto a large surface of the web-shaped material on one side of the web or on both sides simultaneously. In some embodiments, heat transfer to the web can be enhanced by the addition of an infrared emitter or emitting surface. The optimum temperature of the emitting surface ranges from 260 to 425 °C. The web materials generally processed in this way include paper, plastic film, metal foil, woven and non-woven fabrics, mats, and porous membrane materials. The floating air bar is a type of air nozzle used in industrial dryers and ovens, and it floats and transports a continuous web that is processed by heat treatment including any combination of drying, heating, curing, and cooling of the web. A coating is applied to the surface of the web, or a volatile material is present within the base web material and must be dried and / or heated to a specific temperature to promote the thermal curing of the polymer material during the coating. In many processes, the volatile material in the web or coating after being released from the web surface is carried away from its surface by the used nozzle air and directed to the exhaust by the air treatment system. Next, this exhaust is directed to the condenser 10 according to a specific embodiment.

[0057] Alternatively, the dryer can be a so-called "inert" dryer, and the interior of the dryer contains an inert gas such as nitrogen, for example, to limit the oxygen content of the dryer atmosphere (e.g., 2% or less) to reduce the possibility of explosion. The nitrogen can be vaporized from a liquid nitrogen storage tank or continuously generated from a nitrogen generator system having a membrane separator or a pressure swing adsorption module.

[0058] The recovered condensate can be removed from the condenser 10 and stored in a suitable container or storage container 38. Each condensation stage 16 and 16a' and the combined demister 28 can be configured to discharge the condensed solvent by gravity and discharge it into the sample pot 36. The discharge line 37 can include an air lock (S trap or other suitable device) to prevent the passage of air from the condenser 10 to the container 38 and vice versa.

[0059] In certain embodiments, the pre-cooling stage 15 of the condenser 10 functions as a pre-condenser. It operates at an appropriate temperature (and / or pressure) such that little or no VOC condenses when the process gas flows through one or more pre-cooling chambers 15a.

[0060] Most preferably, the cooling coil 20 in the condensation region 16 is operated such that the gas exiting the condensation chamber 16a has a main temperature of 0 °C or less. In some embodiments where multiple condensation regions 16 are used, the cooling coil located in the most downstream stage is operated such that the chamber in which it is located has an outlet temperature of 0 °C or less (for example, 0 °C, -1 °C, -2 °C, -3 °C, -4 °C, -5 °C), or is lowered to -20 °C if the behavior of the antifreeze by the solvent in the mixture of solvent and water is favorable against freezing and ice formation in the condensation coil. In such cases of low-temperature condensation, it is particularly important to place the cooling coil in one or more upstream condenser stages and operate such that the temperature of each chamber increases such that only a very small portion of the VOC in the upstream stage condenses.

[0061] The goal of the design and operating conditions of each condenser coil is to maximize condensation by wetting of the solvent on the tube and finned surface to promote capture and gravity drainage. When air containing the solvent is rapidly cooled below the equilibrium vapor pressure of the solvent, the formation of small droplets in the bulk air flow is promoted as it moves between the condenser coil tubes and the finned surface. After nucleation, the small droplets tend to remain very small and further condensation and growth due to the Kelvin effect can be ignored. Thus, in certain embodiments, the cooling rate is carefully controlled so as not to cool the VOC-containing stream too rapidly in order to reduce or eliminate harmful fogging. The formation of fog, or very small droplets of liquid (generally on the order of 1 μm or less), is problematic in that it involves the formation of small droplets that tend to be entrained in the air flow and thus hinders their removal or recovery. In fact, a significant portion of such aerosol droplets not only pass through the demister panel but also through the core of the condenser coil. As a result, the formation of fog or aerosol results in an undesirable loss of product. In embodiments where the VOC contains NMP, such as in the manufacture of lithium battery electrodes, for example, these small droplets of NMP are ultimately returned to the dryer, which is highly undesirable. Thus, the one or more pre-cooling zones 15 and condensation zones 16 should be operated such that the process stream is gradually cooled to avoid the formation of fog. In many cases, it is optimal to do this by gradually cooling and dividing the cooling load among two or more coils (each with an individual coolant media flow circuit with its own controls) or stages that process the air flow in series.

[0062] For the purpose of characterizing and quantifying the cooling rate, the residence time of air containing the solvent while it is within the core of a specific condenser coil (i.e., during cooling) is determined on a surface-volume basis. That is, the volume space occupied by the tubes and fins within the overall dimensions of the core is ignored when calculating the surface residence time. The specific volume airflow Q through the coil is expressed in cubic meters per normal unit of time. The volume V is calculated in cubic meters using the area of the coil surface and the depth in the flow direction. Thus, the surface residence time within the core is determined as t = V / Q. Additionally, the temperature drop ΔT in degrees Celsius of the air and solvent driven by the cooling coil (this parameter is a temperature difference value, not an absolute temperature value) can be measured directly during operation or calculated from the supplier's dimensional data at the design stage. Finally, the cooling rate R can be expressed as R = ΔT / t. For example, the area of the surface of the cooling coil core is 4.5 square meters and the depth of the flow path is 0.3 meters. The specific volume airflow is 25,000 Nm 3 / h. Thus, the residence time is t = (4.5 × 0.3) m 3 / 25,000 m 3 / hour = 5.4 × 10 -5 hours and can be calculated as such. Converting to milliseconds, t = 5.4 × 10 -5 hours × 3,600,000 milliseconds / hour = 194 milliseconds. If the air temperature entering the coil is 56°C and the exiting temperature is 28°C, the cooling rate R = ΔT / t = (56°C - 28°C) / 194 = 0.144°C / millisecond.

[0063] For NMP capture with minimized fog formation in the condensation coil region where solvent condensation occurs while the gas flow travels the distance between the condensation coil tubes and the finned surface, the cooling rate needs to be less than 0.30 °C per millisecond, preferably 0.15 - 0.22 °C per millisecond. For minimizing fog formation in the condensation coil region where solvent condensation occurs while the gas flow travels the distance between the condensation coil tubes and the finned surface, the typical design criteria cooling rate for water-miscible organic solvents needs to be less than 0.3 °C per millisecond, preferably 0.1 - 0.2 °C per millisecond. In most cases, the maximum acceptable cooling rate for a particular solvent needs to be determined experimentally.

[0064] During operation, a method for accurately controlling the cooling rate can be described with reference to FIG. 2 for the exemplary case of chamber 16a and coil 20. This same method is applicable to a plurality of cooling coils represented as 22 within condensation chamber 16'. It should be understood that the circulation flow loops and controls described below will apply to additional coils in a similar manner. All such flow loops will include the temperature control circuitry and hardware shown for chamber 16a and coil 20.

[0065] The flow rate and temperature of the cooling medium 20a entering the coil 20 are preferably measured using a suitable flow meter device and a temperature sensor such as a Resistance Temperature Detector (RTD), respectively. The circulating flow is driven by a fluid pump 21a communicating with the fluid inlet connection of the cooling coil 20. Further, the temperature of the air entering the cooling coil is preferably measured using an array of one or more temperature sensors 21d spaced across the cross-section of the inlet face of the coil, and the temperature of the air exiting the cooling coil is preferably measured using an array of one or more temperature sensors with a controller 21c spaced across the cross-section of the outlet face of the coil. The air temperature sensor can be an RTD or a thermocouple. The temperature of the incoming cooling medium is measured by a suitable sensor equipped with a PID controller 21b that communicates with a valve and actuator 21 arranged in conduit 20c from a cooled salt water source (typically a water-cooled or air-cooled centrifugal chiller), and is controlled to a predetermined set point. An actuated three-way flow path valve 21 functioning as a flow distribution valve allows fresh cooling medium from the cooling medium source to enter the circulation path through the coil, while the heated cooling medium fluidly communicating with the cooling coil return connection 20b is discharged and returned to the cooling medium source. In a preferred control configuration, the temperature of the air exiting the cooling coil is controlled to a predetermined set point by a suitable PID controller 21c that communicates with a valve and actuator 21 arranged in the conduit as a flow distribution valve from a cooled salt water source. In the most preferred embodiment, the output from the outlet air temperature measurement and controller 21c is calculated by a control algorithm and configured to transmit the temperature set point to an inlet cooling medium control loop PID controller equipped with a temperature sensor 21b in a cascade control configuration. The predetermined set value of the air exiting the cooling coil is selected by the operator to reach the desired target concentration of the solvent or aqueous humidity of the air exiting the coil, which is determined from theoretical and / or empirical vapor-liquid equilibrium (VLE) equations such as Antoine's equation or Raoult's law, or engineering simulation model tools such as ChemCad, ASPEN, or other theoretical or empirical methods known in the art, or preferably from experimental test measurements.

[0066] The specific test result conditions discussed in the following example relate to the third coil, i.e., the final condensation coil of a series of four coils within the condenser system 10 according to FIG. 2. The first coil is a pre-cooling coil where no condensation occurs, the second is the first condensation coil, the third is the final condensation coil, and the fourth is a re-heating coil. It should be understood that the general methodology and elements of the condensation region 16 are similarly applicable to subsequent condensation regions 16' and subsequent condensation regions of a condenser system with additional condensation regions. In this example, when condensing NMP from dry air, the setpoint value of the outlet air temperature to the controller 21c for a vapor pressure of dry air equal to 45 volume ppm is approximately -2 °C based on an empirical correlation. Naturally, there is a certain degree of uncertainty in such empirical predictions, and as a result, it is optimal to experimentally verify the actual requirements through operation in a pilot or prototype condenser unit. In some cases, to address the uncertainty, the setpoint outlet air temperature is set lower than the temperature determined by the VLE. To meet the target solvent concentration in the coil outlet air, a setting 0 - 5 °C lower than the VLE prediction may be required.

[0067] In the preferred embodiment shown in FIG. 2, the output from the outlet cooling medium temperature sensor and the PID controller 20e is input to the drive control of the pump motor 20f, which in turn sets the speed of the circulation pump to adjust the flow of the cooling medium entering the coil to the input setpoint of the PID controller 20e. The setpoint of the controller 20e is determined from the analysis of fog mitigation.

[0068] The potential impact of aerosol mist formation is also considered when determining the set points for the inlet and outlet temperatures and flow rates of the coolant medium. Even if a phase change occurs, the mist droplets that cannot be captured by the demister element of the condenser remain in the outlet air stream and re-evaporate after the outlet gas of the condenser is reheated for use in a dryer or other downstream operation. In the experiment of condensing NMP, the outlet concentration value was measured by a flame ionization detector (FID) device in the sampled air after being aspirated through a PTFE membrane filter to remove submicron mist particles, and then it was found to be consistent with the vapor-liquid equilibrium calculation after heating. Furthermore, the air sample was collected and measured without filtration and measured after sample heating. The unfiltered values were in the range of up to 80 ppm, while the filtered values were in the range of 45 - 50 ppm. The difference between the two measured values represents the magnitude of mist formation. By examining the technical literature and conducting experiments with the goal of reducing or eliminating the magnitude of mist formation, additional parameter sets were investigated. The experimental results showed that the preferred set point outlet temperature of the coolant medium for the controller 20e is 0 - 12 °C lower, preferably in the range of 1 - 5 °C lower than the specified air outlet temperature. In an example before the coil outlet air temperature was set to -2 °C, the wind speed between the coil fins was 2.1 meters per second, the coolant medium inlet temperature was set to -7 °C, and the coolant flow rate was adjusted so that the coolant medium outlet temperature was -4 °C, which is 2 °C lower than the coil outlet air temperature. The filtered outlet concentration of NMP in the coil outlet air was 45 ± 5 ppm, while the unfiltered outlet concentration of NMP was 48 ± 5 ppm, and the 3 ppm difference in NMP represents a low mist formation rate.

[0069] In an alternative cascade configuration, the output of controller 20e is communicated as the input setpoint of controller 20h to set the flow setpoint of the flow rate measured by flow sensor 20g. The output of controller 20h is input into the drive control of pump motor 20f, and pump motor 20f sets the speed of the circulation pump accordingly to adjust the flow of the cooling medium entering the coil to the input setpoint of PID controller 20h. In this alternative configuration, the output of controller 20e can be utilized in flow rate units (such as liters per minute) as an engineering parameter that can be restricted between the allowed minimum and / or maximum setpoint values according to the functional specifications of the pump capacity of the coolant system. This flow rate parameter can also be converted to other engineering parameters by calculations including, but not limited to, the cooling load of the coil by theoretical or empirical heat and mass balance methods known in the art, or from experimental test measurements. These parameters are optionally used in setting the values of the minimum and / or maximum setpoints of PID controller 20h to reduce the formation of solvent mists.

[0070] In certain embodiments, when the process gas flow from condensation region 16 reaches 0 °C or below and VOC condensation is complete or substantially complete, the gas flow is split into a relatively large recirculation gas flow (e.g., line 72) and a relatively small off-gas sidestream (e.g., extraction line 30). In the example shown in Figure 3, these amounts are split at a split ratio of approximately 2%.

[0071] In certain embodiments, the blend of off-gas side stream extraction lines 29 and 30 coupled to 30a is adapted or configured to be disposed in fluid communication with one or more downstream emission control operations 40. For example, the emission control operation may include at least one adsorption concentrator with gas exhaust and desorption exhaust, such as one or more VOC adsorption concentrators 50 used to concentrate the VOCs extracted by the condenser 10. The type of VOC concentrator used is not particularly limited and may be a rotary gas adsorption concentrator sold by SG America, Inc. or Nichias Corporation of Japan. For example, a honeycomb rotor may be used to support the VOC adsorption medium, and the rotor may be divided into at least an adsorption zone and a desorption zone. Air containing the solvent to be treated passes through the adsorption zone, where the VOCs are adsorbed by the adsorption medium (such as zeolite). Next, the VOCs can be desorbed, for example, by passing heated air through the desorption zone. In some cases, such a concentrator may include an adsorbent substrate such as a hydrophobic zeolite, or a rotor wheel having a combination of adsorbents. The rotor wheel can be rotated continuously, and the air stream passes through the rotor wheel concentrator, where the VOCs are removed from the air and can be adsorbed onto the adsorbent substrate. Most of this cleaned air can be discharged to the atmosphere. A small portion of the air stream can be heated to a high temperature and used as desorption air. As the wheel rotates continuously, this portion of the wheel with the adsorbed solvent moves to the desorption region, where the VOCs are heated and desorbed into the heated desorption air stream, and then collected from the desorption air by a subsequent solvent removal device such as a condenser coil. Purge air can be used to cool the adsorption medium, and in turn, the heated purge air can be recycled to the desorption region. Thus, one or more adsorption concentrators 50 have gas exhaust and desorption exhaust and can function as an emission or pollution control stage.

[0072] In certain embodiments, a single VOC concentrator 50 can be used. In other embodiments, two or more VOC concentrators 50 and 50' arranged in series can be used. In some embodiments, one or more additional emission or pollution control stages 52 can be used downstream of one or more VOC concentrators 50, such as one or more filtration devices (e.g., activated carbon-based filtration devices), absorption concentrators, thermal oxidizers (e.g., regenerative thermal oxidizers), catalytic oxidizers, and / or biofilters.

[0073] In some embodiments, a two-stage air pollution control unit 500 as shown in FIG. 6 can be arranged downstream of the condenser 10, similar to the pollution prevention unit disclosed in JP 2011-031159 A. The unit includes an organic solvent recovery device, and the adsorbent includes an adsorbent body including an adsorption element, which is composed of at least an adsorption region, a regeneration region, and a cooling region. The organic solvent-containing gas (e.g., the gas in the secondary flow 30 from the condenser 10) is continuously supplied to the adsorption region of the adsorbent body (the adsorption element adsorbs the organic solvent in the adsorption region), sent to the regeneration region, and the heated gas desorbs the organic solvent adsorbed from the adsorption element. The organic solvent-containing gas is adsorbed again in the adsorption region by the regenerated adsorption element, and a condensation part is provided for recovering the organic solvent desorbed in the regeneration region. A backup treatment device capable of continuously adsorbing and desorbing the organic solvent-containing treated gas that has passed through the adsorption region without being adsorbed is provided, and continuous solvent adsorption and desorption treatments are performed in the adsorption region and the regeneration region by the adsorption element formed in a columnar or cylindrical shape.

[0074] Figures 3 and 4 illustrate exemplary embodiments of the operation of the condenser and the discharge control device. In the exemplary embodiment shown in FIG. 3, an exhaust gas stream 70 containing VOCs such as NMP exiting one or more dryers 200 can generally have a temperature of about 80-130°C, more typically about 120-130°C, and can generally have a solvent concentration of about 500-3000 ppmV, more typically about 1800-2500 ppmV. In the illustrated embodiment, the concentration of the solvent in the exhaust stream is 1800 ppmV and the temperature is 130°C. Using a driving force such as a fan 201, the exhaust stream can be introduced into the supply port 12 of the condenser 10. Alternatively, or in addition, a suction fan 202 can be disposed downstream of the condenser exhaust port 14.

[0075] In line with the objective of gradually reducing the temperature of the exhaust gas flow, it first enters the pre-cooling region 15 of the condenser 10, which has a coil 35a with a cooling medium having a temperature sufficient to lower the temperature of the gas flow to about 83°C. The residence time of the gas flow in the pre-cooling region must be sufficient to cool the temperature of the flow to a desired value such as 83°C. Since no condensation occurs at this stage, a cooling rate in the range of 0.6°C or more per millisecond is tolerated. Preferably, the conditions in the pre-cooling region 15 are such that little or no solvent condensation occurs. Next, the gas flows into the first cooling or condensation stage 16a, where it is cooled by a coil 116a containing a cooling medium having a temperature sufficient to lower the temperature of the gas flow to 29°C (for example, 18°C). At this stage, most of the heat exchange is sensible heat, and little solvent condensation occurs at this stage, but the cooling rate is important in this initial stage of the condensed solvent. A cooling rate not exceeding the range of 0.15 - 0.30°C per millisecond is preferred. Next, the cooled gas flows into a second cooling or condensation region or stage 16' (main condensation stage) equipped with a coil 116b containing a cooling medium having a temperature sufficient to lower the temperature of the gas flow below 0°C, for example, to -2°C (for example, -10°C), where a large phase change occurs and all or substantially all of the remaining solvent condenses. Also in this case, at this stage, as in the initial stage of condensing the solvent, the cooling rate becomes important. A cooling rate not exceeding the range of 0.15 - 0.30°C per millisecond is preferred. This gradual cooling of the gas flow helps to minimize or prevent the formation of harmful mists.

[0076] Next, most of the gas flows into the reheating region 17. The embodiment shown here has a coil 35b containing a cooling medium having a temperature sufficient to raise the temperature of the gas flow to 45°C. Thereafter, the gas is recirculated to one or more dryers 200 via the exhaust line 72. As shown at 73, ambient air can be added to the exhaust line 72.

[0077] A small portion of the gas stream (e.g., by mass flow balance corresponding to the flow of gas entering the web slots of one or more dryers) is extracted from the air exiting the final cooling or condensation region or stage 16' via the sidestream off-gas extraction line 30. In the example shown in FIG. 4, the volumes of the recirculation air stream 72 and the off-gas sidestream 30 are split at a split ratio of approximately 1.1%. This extraction is preferably carried out upstream of the preheating region 17. This is because the relatively low temperature of this extracted stream moderates the air stream 30a and enhances the efficiency of the downstream concentrator. A portion of the gas within the reheating region 17 can be extracted within the conduit 29 and mixed with the gas within the sidestream off-gas extraction line 30 extracted from the second cooling or condensation region 16'. The amount of gas reheated in region 17 that is mixed with the gas in the sidestream off-gas extraction line can be mixed with the temperature controller and damper control system 31 to adjust the temperature of the gas entering the downstream concentrator (or other downstream emission control device) to optimize the performance of the downstream unit (e.g., adjust the gas within the sidestream off-gas extraction line 30a to a temperature of about 10 - 20 °C, preferably about 15 °C).

[0078] Thus, the condenser apparatus 10 can be used to generate a feed stream to a downstream emission control unit such as one or more VOC concentrators, and the feed stream is at a temperature optimal for the performance of the emission control unit or units. Off-gas sidestream flows extracted from multiple condenser apparatuses equivalent to the condenser apparatus 10 are preferably combined in a common conduit 700 and supplied to a single VOC polishing concentrator system as shown in FIGS. 3 and 4. This enables better capacity matching of the sidestream flows from a large-scale operation with, for example, eight or more condenser units. The combination of the off-gas sidestream flows improves the economies of scale of the VOC polishing operation.

[0079] The gas in the secondary off-gas extraction line enters a first VOC polishing concentrator 50 containing an adsorbent such as zeolite or carbon. This first concentrator 50 typically removes about 90-99% of the VOC (e.g., NMP) from the gas stream. Next, the adsorbed VOC can be desorbed by reheating and, as shown, directed to a cooler or desorption condenser 80 etc. and recycled to the inlet stream to the first VOC polishing concentrator. The VOC condensate is collected from the condenser 80 via line 81 and can be stored or recycled to the coating process.

[0080] In the embodiment shown in FIG. 3, the concentrated gas stream then enters a second VOC polishing concentrator 50', which also typically removes about 90-99% of the VOC (e.g., NMP) remaining in the stream. In certain embodiments, the second VOC polishing concentrator 50' is the same as the first VOC polishing concentrator 50. The collected air stream can be condensed in condenser 80 as shown.

[0081] A bypass line 85 can be provided to enable interruption of the concentrator unit. The bypass line 85 directs the flow (e.g., with the help of fan 88) to one or more backup carbon filters 87 so that the VOC content discharged to the atmosphere does not exceed the regulatory limit (e.g., <1 mg / Nm 3 ).

[0082] An emergency purge system 90 is provided, which includes a purge line 91 having a damper 92 that directs the flow of gas from condenser 10 to one or more discharge control units such as one or more carbon filters 95.

[0083] NMP can be recovered from condenser 10 via line 117 and stored as shown.

[0084] Figure 4 (like numerals indicate like parts as above) shows a similar process in which only a single VOC polishing concentrator 50 is used. In this embodiment, two carbon filters 87, 87' are disposed downstream of the single VOC polishing concentrator 50 to achieve a target VOC emission concentration of <1 mg / Nm 3 This embodiment also eliminates the emergency purge system 90 and instead, as shown, a purge fan 190 is fluidly connected to the exhaust line 72 to provide an emergency purge.

[0085] Referring to FIG. 5, in the case of the coil condenser 10, avoidance of fog formation in the direct contact condenser 510 depends on the gradual cooling of the air stream containing the solvent in the condensation region within the height of the packing region 515. The cooling rate is first considered in the design selection of the volume of the packing region 515. The condenser vessel 505 preferably has a circular cross-section. Alternatively, it may have a square or rectangular cross-section in plan view to accommodate the site layout requirements. As in the case of the coil type condenser, the volume is determined on a surface area basis. That is, the volume space occupied by the packing within the overall dimensions of the packing region 515 is ignored when calculating the surface residence time. The specific volume air flow Q through the coil is expressed in cubic meters per normal unit of time. Using the area of the packing surface and the depth in the flow direction, the volume V is calculated in cubic meters. Thus, the surface residence time in the core is determined as t = V / Q. Further, the temperature drop DT in degrees Celsius of the air and solvent driven by the cooling coil (this parameter is a temperature difference value, not an absolute temperature value) can be measured directly during operation or calculated from the supplier's dimensional data at the design stage. Finally, the cooling rate R can be expressed as R = DT / t. For example, the area of the face of the direct contact condenser vessel is 4.0 square meters and the height of the packing is 1.5 meters. The specific volume air flow is 25,000 Nm 3 / h. Thus, the residence time can be calculated as t = (4.0 × 1.5) m 3 / 25,000 m 3 / hour = 2.4 × 10 -4 hours. Converting to milliseconds, t = 2.4 × 10 -4The time multiplied by 3,600,000 milliseconds / hour equals 864 milliseconds. When the air temperature entering the packing is 83°C and the outlet temperature is -4°C, the cooling rate R = DT / t = (83°C - (-4)°C) / 864 = 0.1°C / millisecond.

[0086] For minimizing the generation of fog in the condensation packing region where solvent condensation occurs while the gas stream travels the distance within the packing for NMP capture, the cooling rate should be less than 0.20°C per millisecond, preferably 0.07 - 0.15°C per millisecond. The typical design criteria for organic solvents such as DMAc containing water vapor for minimizing the generation of fog in the condensation coil region where solvent condensation occurs while the gas stream travels the distance within the packing is that the cooling rate must be less than 0.15°C per millisecond, preferably 0.05 - 0.12°C per millisecond. In most cases, the maximum allowable cooling rate for a specific solvent has to be determined experimentally.

[0087] During operation, a method for accurately controlling the cooling rate can be described with reference to FIG. 5 for an exemplary case of the packing 515. The flow meter 524 and the temperature sensor 521 monitor the flow rate and temperature of the cooled solvent medium entering the manifold 513. The circulation flow 539 is driven by a fluid pump 592 that communicates with the fluid inlet connection of the cooling coil 591. Further, the temperature of the air entering the packing region 515 is preferably measured using an array of one or more temperature sensors 522 spaced across the cross-section of the outlet face of the coil, and the temperature of the air exiting the demister 528 is preferably measured using an array of one or more temperature sensors 523 spaced across the cross-section of the outlet face of the demister. The above-mentioned air temperature sensors can potentially be RTDs or thermocouples. The temperature of the incoming cooling medium is measured by a suitable sensor equipped with a PID controller 521 that communicates with a valve and actuator 520 arranged in a conduit from a cooled salt water source (typically a water-cooled or air-cooled centrifugal chiller) and is controlled to a predetermined set point. The measured air temperature drop of the air entering the packing and the air 571 exiting the condensation tower is controlled to a predetermined set point by a second suitable PID controller 523 that communicates with the variable frequency motor control drive pump 592. In this way, the target rate of temperature drop within the condensation unit 510 is controlled, for example, to 0.15 °C per millisecond for NMP.

[0088] Figure 6 shows a different type of adsorption device for replacing the single VOC polishing concentrator of Figure 4. The main adsorption occurs on path A1 through the first segment of carousel-type adsorption concentrator 610. Desorption is performed with reference to Japanese Patent Application Laid-Open No. 2011-031159. The main desorption cycle is executed by path B2 in which condenser 620 and heating coil 625 are installed. Further, Figure 6 shows a closed-loop auxiliary adsorption-cooling-desorption cycle having a path “A2” (adsorption)-“C” (cooling)-heating-“B1” (desorption)-cooling. This configuration has the advantage that two cycles can be operated under inert conditions (if necessary) and can result in a higher desorption concentration in the main desorption cycle. As described in Figure 4, an additional carbon filter can be installed before the gas is released into the stack. The described process is also possible with a disk-type concentrator.

[0089] The foregoing description does not include consideration of the condensation of organic solvents such as NMP in which high humidity (e.g., water) coexists within the gas (usually air) stream. In the previously discussed embodiments, the humidity in the gas stream containing the solvent is sufficiently low so that the vapor-liquid equilibrium conditions do not result in the condensation of water along with the solvent. For example, if the dew point humidity level (water vapor) of the gas flowing into the condenser is lower than the surface temperature of the condenser coil, little water will condense. On the other hand, if the dew point humidity exceeds the surface temperature of the condenser coil, both water and solvent can condense depending on factors such as vapor-liquid thermodynamics, contact time, droplet nucleation behavior, etc. Such condensation often cannot be predicted based solely on thermodynamic properties, often requires dynamic experiments, and unexpected results may be found regarding the capture of organic solvents in the condensate.

[0090] When condensing an organic solvent miscible with water such as NMP, especially at a temperature lower than the aqueous dew point of a humid gas stream, the vapor pressure of the solvent typically decreases as the water content of the incoming air increases, and as a result, the vapor pressure of the solvent exiting the condenser decreases. Therefore, compared to the case where the water humidity is very low (condenser temperature exceeding the dew point of the water vapor phase), when water also condenses together with the organic solvent, the outlet concentration of the organic solvent is lower. In certain cases, it is advantageous to add water vapor to the incoming gas stream to reduce the concentration of the organic solvent in the outlet gas stream. This may allow, due to the change in the operation of the VLE, the final condensation temperature, i.e., the outlet air temperature of the last condensation coil, to be set at a higher temperature. Under the dry air conditions for battery electrode treatment, the equivalent concentration of NMP in the outlet air is obtained at a condensation coil outlet air temperature in the range of 0 - 5 °C with injection compared to an air outlet temperature in the range of -5 to -2 °C without water injection. This can be advantageously used for the operating cost and capital cost of the plant cooling facility.

[0091] Therefore, in some cases, it may be advantageous to adjust the aqueous humidity conditions of the gas going into the condenser in order to obtain the desired outlet concentration of the solvent and / or water in the gas exiting the condenser. For example, instead of lowering the temperature of the condenser (even to a temperature lower than the freezing point of water) to reduce the solvent concentration (as discussed in the previous embodiment), in certain cases, water (e.g., by spraying or injection), steam or gas containing a high water content can be introduced, water can be vaporized by spraying it into the air stream, or the water humidity of the gas entering the condenser can be increased by heating a water source such as a water container (e.g., a boiler) in the duct before the condenser. This additional water vapor can promote the condensation of the solvent and water at a higher condenser operating temperature within the condenser. Thereby, not only does the outlet concentration of the solvent decrease, but from the perspective of reducing the refrigeration power load, the energy efficiency of the condensation operation step can be improved.

[0092] FIG. 7 shows an exemplary embodiment of vapor injection for adding aqueous humidity in accordance with the foregoing description. The condensation effect of an organic solvent species such as NMP in the condensation coil 20 can be enhanced by co-condensing a certain amount of water, which advantageously reduces the concentration of the solvent leaving the condenser 16 in streams 30 and 72a. In the embodiment shown, a gas temperature sensor with a controller 21c is disposed at the outlet of the condensation chamber 16a. If there are two or more condensation coils as described in any embodiment having a plurality of condensation coil stages as described above, the sensor with the controller 21c can similarly be disposed at the outlet of each condensation coil. The sensor with the controller 21c provides a temperature value for the condensation operation representing the saturated vapor concentration in the form of the aqueous dew point temperature leaving the condenser. The aqueous dew point sensor 310 provides a dew point temperature value of the incoming process gas stream 70a representing the water vapor concentration entering the condenser 10. In the embodiment shown, pressurized vapor is introduced into the duct carrying the gas stream 70a, such as by an injector 303, to raise the aqueous humidity of the stream 70a before it enters the condenser 10. The desired dew point at the sensor 301 is set to a value higher than the condensation temperature sensed by the sensor with the controller 21c within the closed loop controller 302, and the closed loop controller 302 then opens the operating injector valve 306 to add sufficient water vapor through the injector 303 to promote the condensation of water vapor within the condensation chamber 16a. The discharge of the injector 303 into the stream 70a can consist of a pipe or an array of pipes with drill orifices for discharging the vapor, or preferably, an injector array having one or more pipes with a plurality of nozzles distributed along each pipe length (such as those available from Armstrong International or other suitable vapor dispersion elements).

[0093] Alternatively, instead of measuring the aqueous dew points of streams 70a and 72a to control steam injection at injector 303, steam injection can be continuously controlled by an alternative closed-loop control operation of controller 302 by determining the molar fraction of water in gas stream 72a. An optional solvent concentration sensor or analyzer 304 provides a value of the concentration of the organic solvent in gas stream 72a exiting the condensation unit 10. Suitable gas-phase solvent concentration analyzers can be selected from available instruments including flame ionization detectors (FID), Fourier Transform Infrared spectroscopy (FTIR), mass spectrometry, or other suitable instruments. An optional aqueous dew point sensor or analyzer 305 provides a value of the concentration of aqueous humidity in gas stream 72a exiting the condensation unit 10 instead of the value provided by the temperature sensor with sensor and controller 21c. Suitable aqueous dew point analyzers can be selected from available instruments including capacitive elements, Fourier Transform Infrared spectroscopy (FTIR), mass spectrometry, or other suitable instruments. The molar fraction of water in the gas phase is determined by dividing the volume fraction reported by sensor 305 by the sum of the volume fractions reported by solvent concentration sensor 304 and aqueous dew point sensor 305. The resulting measured molar fraction value is then compared to a setpoint of controller 302 to determine the output position value of electric valve 306 by a conventional control loop method (such as proportional (P) control action, or proportional + integral (PI) control action, or proportional + integral + derivative (PID) control action). A preferred setpoint for the gas-phase molar fraction of water has been found to be in the range of 0.95 to 0.995, and for the NMP solvent, most preferably in the range of 0.98 to 0.99.

[0094] Alternatively, the control of the injection of steam or water spray to increase the humidity of the stream 70a can be based on the measurement of the composition of the condensed liquid stream in the discharge line 37 by the analyzer 37a. The injection of steam or water into the air entering the condenser increases the proportion of water contained in the condensate stream while reducing the solvent concentration of the air exiting the condenser coil. Thus, the proportion of water in the condensed liquid correlates with the concentration of the solvent exiting the condenser coil as determined by VLE prediction or preferably by experimental results. The composition of the condensed solvent can be measured in continuous or batch unit samples for the water content along with the organic species recovered. The continuous measurement device can include analytical instruments such as Fourier transform infrared (FTIR), mass spectrometry, electrical conductivity, or other suitable instruments. In addition to the above instruments, the batch unit measurement of the water content can include Karl Fischer titration.

[0095] As described above, the condensation effect of organic solvent species such as NMP in the condensation coil 20 can be enhanced by co-condensing a certain amount of water, which advantageously reduces the concentration of the solvent leaving the condensation region 16 in the streams 30 and 72a. Steam or water is injected through the injector 303 and co-condensed on the coil 20. The condensate containing both water and the organic solvent is collected in the sample bowl 36 and discharged into the discharge line 37. The analyzer 37a measures the water content of the condensed liquid stream. The desired water content in the condensate has been found to be in the range of 0.1 to 0.8 mole fraction to enhance the condensation effect, and most preferably 0.2 to 0.5 mole fraction of water.

[0096] In some cases, it is not desirable to raise the water content of the outlet gas 72a above a certain level, such as in the case of the stream 72a that provides dry air for the drying operation of the lithium-ion battery electrode. In such cases, it may be necessary to remove at least a portion of the water content by means of the stream 72b, more preferably a desiccant adsorbent of the stream 72a. For example, the removal of water in a continuous stream is easily achieved by passing the gas through a desiccant adsorbent foil unit such as that provided by Nishi Giken. For example, the removal of water in a continuous stream is easily achieved by passing the gas through a desiccant adsorbent foil unit such as that provided by Nishi Giken. FIG. 7 shows a preferred embodiment in which the gas stream 72a enters the continuously rotating adsorbent foil 750 and removes a portion of the water vapor. The pie-shaped portion of the desiccant adsorbent foil 750 adsorbs water from the stream 72a and is subsequently rotated to the desorption zone, where the heated stream 784 passes through the adsorption medium to desorb the water captured from the stream 72a before. Next, the desorbed water in the stream 782 passes through the condenser device 780, where the cooling medium passes through the coil 790 to condense the water vapor on the coil. The cooling medium can be water or an aqueous salt solution of water and glycol from a cooling unit, as is known in the process cooling industry. In continuous operation, the condensed water is discharged from the coil 790, collected in the lower housing of the condenser 780, and discharged through the discharge pipe 781. The condensed water can be disposed of as wastewater or recycled to the process, for example, to provide a water spray or steam supply injector 303. The gas stream 783 exiting the condenser 780 is reheated by the heater 785 to provide a temperature favorable for desorption with the heated stream 784 when passing through the desorption section of the desiccant foil 750. The heater 785 can be an electric resistance coil, a hot water or steam coil, or other suitable heat transfer fluid. The pie-shaped sector of the dried adsorbent medium receives the wet stream 72a and rotates to the sorption zone that removes a portion of its moisture. The aqueous dew point of the outlet stream 730 can optionally be measured by an aqueous dew point measuring device 310. The preferred aqueous dew point of the stream 730 is typically in the range of -60°F to -20°F, returning dry air to the drying process.

[0097] The described water injection method can also be used in any of the condensation configurations of FIGS. 1-5 described above. Other condensation plenum arrangements are possible instead of the condensation chamber 10, and the described water injection method can be benefited from.

[0098] Next, referring to FIG. 8, the pollution prevention section 40 consists of one or more concentrator units 50 and 50' in series, followed by one or more passive (static) bed adsorbent units 52 and 52a in series. Although two exemplary concentrator units and two exemplary static bed units are shown, it is understood that additional concentrator units and passive bed units can be added to the pollution control section 40 to meet the discharge requirements in the exhaust stream 30f. The stream 30 exits the condenser section 10 and is adjusted by introducing it into the heated gas flow line 29 via the mixing valve set and control system hardware 31 to obtain the desired set point temperature in the stream 30a before entering the first concentrator unit 50 of the pollution control section 40. The first concentrator unit 50 removes most of the solvent in the stream 30a, and the second concentrator unit 50' additionally removes the solvent. Additional concentrators can be optionally added to this sequence until the level of the solvent remaining in the stream 30d drops to the preferred level. The preferred design level of the solvent in the stream 30d is determined by specifying the optimal economic operation of the solvent recovery step related to the consumption of the adsorbent medium in the ongoing operation of the fixed bed adsorbers 52 and 52a. Generally, the operating cost of the concentrator unit is mainly the energy cost of the fan, heater, and coolant. When the value of the recovered solvent is high, additional concentrator units are preferably selected. On the other hand, the main operating cost of the passive adsorbent bed is the cost of replacing the adsorbent, typically activated carbon. For example, the capture and recovery of the solvent in the concentrator unit may preferably reduce the outlet concentration to 1 ppm to 10 ppm. When the solvent concentration in the gas stream drops below 10 ppm, preferably below 1 ppm, the life of the adsorbent in the fixed bed carbon adsorption device downstream of the last concentrator is often very long and is therefore a preferred choice. Furthermore, the passive adsorbent bed can surely meet the strict environmental discharge requirements by adding additional adsorbent containers in series. In an embodiment of a plurality of adsorbers arranged in series, a final emission level of less than 1 ppm can be achieved.

[0099] In one example, the concentration of the solvent in the gas stream 30 exiting the condensation region 16 at a temperature of -2°C is 50 ppm on a volume basis. The stream 30a consists of the stream 30 and the heated stream line 29, and is adjusted to a preferred mixing temperature in the range of 10 to 20°C, most preferably 15°C, by controlling the split ratio of the stream lines 29 and 30. The adjustment control system 31 consists of a temperature sensor that senses the gas temperature of the mixed stream 30b and a temperature controller that receives a sensor signal from the temperature sensor. The controller communicates with the respective adjustment flow valves of the gas stream lines 29 and 30, and the controller positions the adjustment valves to provide a mixing temperature of the stream 30a equal to the setpoint value of 15°C. The heated stream line 29 is drawn from the outlet of the reheating region 17 at a temperature of 45°C or from the heated stream 72b exiting the economizer heat exchanger 101. The split ratio of the flow in line 30 to the flow in line 29 is 2:1 on a normal volume flow rate basis at 0°C and 1 atmosphere. In normal dynamic process control operations, the split ratio can range from 1:2 to a maximum of 10:1. The stream 30a merges with the return stream 83 from the concentrator condenser 80 as the stream 30b and is supplied to the concentrator 50 at a nominal 15°C and a solvent concentration of 50 ppm. The adsorbent foil of the concentrator 50 adsorbs the solvent, the solvent is concentrated in the stream 82, and while passing through the condenser 80 to condense and recover the solvent, the solvent concentration of the stream 30c decreases to 5 ppm. In this example, in order to extend the life of the adsorbent in the downstream passive bed vessel, it is desirable to further reduce the solvent concentration of the stream 30c by the concentrator before the final wash in the passive adsorbent bed. Therefore, the stream 30c passes through a second concentrator 50' after being combined with the return stream 83a from the condenser 80a. The adsorbent foil of the concentrator 50' adsorbs the solvent, the solvent is concentrated in the stream 82a, and while passing through the condenser 80a to condense and recover the solvent, the solvent concentration of the stream 30d decreases to 0.5 ppm. In this way, multiple steps of concentration can be performed until the outlet concentration from the last condenser no longer saturates the adsorbent of the next passive adsorbent bed too quickly. In this example, 0.5 ppm is low enough so that the desired operating life of the adsorbent in the bed 52 can be maximized to 1 year before replacing the adsorbent to avoid solvent breakthrough.The adsorbent bed 52 reduces the solvent concentration of the stream 30e to 0.05 ppm. Before discharging the stream 30f to the atmosphere, it is desirable to further reduce the solvent. The second adsorbent bed 52a receives the flow stream 30e from the bed 52 and further reduces the solvent concentration to less than 0.01 ppm. The operating life until the adsorbent of the bed 52a is replaced is several years. If a lower outlet concentration is required, additional adsorbent beds can be placed after the beds 52 and 52a in a similar manner.

Example

[0100] Example 1 Referring to FIG. 7, the stream 70a is composed of air containing 2000 volume ppm of NMP vapor and has an aqueous moisture dew point of -40° C. corresponding to 190 volume ppm of water. The target outlet concentration of NMP is slightly below 50 ppm. The condenser temperature 21c is set to operate at a condensation temperature of 2° C. In the absence of steam injection, the outlet concentration is 66 ppm of NMP. By operating the control loop 302 and adjusting the setpoint, steam is injected to obtain an outlet concentration of less than 50 ppm of NMP from the condenser. To be slightly below 50 ppm of NMP, the dew point setting to the controller is adjusted to a dew point of -11° C. by trial and error, and the concentration measured by the analyzer 304 is 47 ppm. Thus, in this process, steam is added to the stream 70a via the injector 303 through the electric control valve 306 that communicates with the controller 302 at a rate necessary to reach an aqueous dew point of -11° C. at the sensor 301. The resulting outlet concentration of NMP in the stream 72a is 47 volume ppm, and 15% of the injected water vapor is condensed with the condensed NMP.

[0101] For comparison, without steam injection into the stream 70a with an aqueous dew point of -40° F. containing 2000 volume ppm of NMP, to achieve less than 50 ppm of NMP, the condensation temperature required to obtain 47 ppm of NMP in the outlet stream 72a is -2° C. This requires 15% - 20% more cooling wattage in the plant cooling facility.

[0102] Example 2 Referring again to FIG. 7, stream 70a is composed of air containing 2000 volume ppm of NMP vapor, and has an aqueous moisture dew point of -40° C. corresponding to 190 volume ppm of water. The target outlet concentration of NMP is slightly below 50 ppm. The condenser temperature 21c is set to operate at a condensation temperature of 2° C. In the absence of steam injection, the outlet concentration is 66 ppm of NMP. By operating valve 306 and adjusting the injection rate, steam is injected to obtain an outlet concentration from the condenser slightly less than 50 ppm of NMP at analyzer 304. Thus, the steam injection rate is manually adjusted until a value of 47 ppm is observed at analyzer 304. Under these conditions, the concentration of water in the condensate in discharge pipe 37 measured by analyzer 305 is 0.19 mole fraction of water (3.9 wt %). Just as analyzer 304 is for occasional (infrequent) measurements, analyzer 305 is used frequently for process quality control, but the data available from analyzer 305 can now be used as a process set point. Thus, steam is added to stream 70a via injector 303 through operating control valve 306 at a rate necessary to reach a mole fraction value of 0.19 measured at analyzer 305. The resulting outlet concentration of NMP in stream 72a is expected to be maintained at approximately 47 ppm by volume according to VLE physics, but the above process parameters are maintained without the need to directly measure the outlet concentration with additional equipment.

[0103] Conditions such as in this example are best determined by experimental tests, especially when targeting very low (e.g., <100 ppm) solvent concentrations in the outlet air stream. Calculations based only on thermodynamic vapor-liquid equilibrium data are often inaccurate for the condensation and formation of aerosol droplets as described above. Injection of steam or water by other means described can have the positive effect of reducing the tendency to form fine aerosol droplets that are not easily collected on the condenser coil or the demister in the condensation region 16.

[0104] Although various aspects and embodiments are disclosed herein, other aspects, embodiments, modifications, and variations will be apparent to those of ordinary skill in the art upon reading and understanding the foregoing detailed description. The various aspects and embodiments disclosed herein are for illustrative purposes only and are not intended to be limiting. This disclosure is intended to be construed to include all such aspects, embodiments, modifications, and variations as long as they are within the scope of the appended claims or their equivalents.

Claims

1. A circulation air conditioner for a recirculating air dryer that generates recirculating air containing at least one condensable fluid, a. At least one main condenser having a supply port, an exhaust port, and at least one main condensation stage, i. A condensation chamber where the recirculating air is accessible or permeable, ii. A cooling coil at least partially disposed within the condensation chamber and penetrated by a cooling medium, iii. Thereby, the cooling coil of the main condenser operates at a main cooling medium temperature of 0 °C or lower, The main condenser, b. A recirculating air supply line connected to the supply port of the main condenser and connectable to an air source containing a condensable fluid for carrying the recirculating air, c. A recirculating air exhaust line connected to the exhaust port of the main condenser, d. A secondary off-gas extraction line fluidly connected to at least the condensation chamber of the main condenser, iv. Thereby, the volumetric flow rate of the recirculating air flowing through the condensation chamber is divided into a large recirculation flow exiting the main condenser through the recirculating air exhaust line and a small off-gas side flow by the secondary off-gas extraction line, e. At least a pre-condenser having at least one pre-condensation stage, e-1. The pre-condenser is disposed in the recirculating air flow upstream of the main condenser, e-2. The pre-condenser, A pre-condenser condensation chamber where the recirculating air is accessible or permeable, And a cooling coil at least partially disposed within the pre-condenser condensation chamber and penetrated by a pre-cooling medium, e-3. Thereby, the pre-cooling medium has a temperature higher than the main cooling medium temperature, the pre-condenser, f. As a first anti-pollution stage, an air pollution control unit having at least one adsorption concentrator fluidly connected to the secondary off-gas extraction line and having gas exhaust and desorption exhaust, and at least a second anti-pollution stage selected from the group consisting of a filtration device, an absorption concentrator, a thermal oxidation device, and a catalytic device, Including, each of the cooling coils has a coil tube and a finned surface, and is configured to maintain the cooling rate at less than 0.30 °C per millisecond while the recirculating air moves between the aggregated coil tubes and the finned surface. The circulation air conditioner.

2. The circulation air conditioner according to claim 1, wherein the pre-condenser and the main condenser are enclosed in a common condenser housing.

3. A pre-cooling heat exchanger disposed upstream of the pre-condensation stage and / or a re-heating heat exchanger disposed downstream of the main condensation stage to lower the temperature of the circulating air flow, and The pre-cooling heat exchanger and the re-heating heat exchanger are thermally coupled by exchange of a heat transfer medium selected from water, brine or a suitable heat fluid, and / or are thermally coupled by a thermocouple or a heat pipe. The circulating air conditioner according to claim 1.

4. The second anti-pollution stage is supplied from the gas exhaust of the first anti-pollution stage and includes an adsorption concentrator having gas exhaust and desorption exhaust. The circulating air conditioner according to claim 1.

5. The desorption exhaust of at least one of the adsorption concentrators is connected to a desorption line connected to a desorption condenser, whereby the gas exhaust of the desorption condenser is refluxed to the sub-stream off-gas extraction line. The desorption exhaust of at least one of the adsorption concentrators is connected to a desorption line connected to a desorption condenser, whereby the gas exhaust of the desorption condenser is refluxed to the sub-stream off-gas extraction line. The circulating air conditioner according to claim 1.

6. The second anti-pollution stage includes at least one activated carbon filter. The circulating air conditioner according to claim 1.

7. The circulating air conditioner according to claim 1 further includes an injector in fluid communication with the circulating air supply line.

8. The injector has a valve, The circulating air conditioner includes a dew point sensor for sensing the aqueous dew point temperature value of the air containing the condensable fluid entering the circulating air supply line, a temperature sensor for sensing the temperature of the fluid exiting the at least one main condenser, and a controller that communicates with the dew point sensor and the temperature sensor and controls the valve so that the injector injects water or steam into the circulating air supply line when the dew point sensor senses an aqueous dew point lower than a predetermined value of -51 °C (-60 °F). The predetermined value is based on the temperature of the fluid exiting the at least one main condenser sensed by the temperature sensor. The circulating air conditioner according to claim 7.

9. The injector has a valve, The circulation air conditioner further includes a solvent concentration analyzer for analyzing the solvent concentration of the fluid in the circulation air exhaust line, a dew point sensor for sensing the humidity of the fluid in the circulation air exhaust line, and a controller that communicates with the solvent concentration analyzer and the dew point sensor to calculate the mole fraction of water in the fluid exiting the at least one main condenser, and operates to control the valve so that the injector injects water or steam into the circulation air supply line when the mole fraction is lower than 0.

95. The circulation air conditioner according to claim 7.

10. The circulation air conditioner according to claim 1, further including a desiccant adsorber that is in fluid communication with the circulation air exhaust line.

11. A method for conditioning circulation air containing at least one condensable fluid, comprising: a. Introducing circulation air into a main condenser having at least one main condensation chamber and at least one cooling coil penetrated by a cooling medium at a first volumetric flow rate and an intake air temperature level well above 0°C. b. Gradually cooling the circulation air with the cooling coil until the main temperature level in the main condensation chamber reaches 0°C or lower. c. After reaching a temperature level of 0°C or lower, dividing the volumetric flow rate of the circulation air into a large recirculation flow and a small off-gas sidestream. d. Providing the large recirculation flow to the circulation air intake of a dryer. including, the method further comprising: e. Supplying the circulation air at the first volumetric flow rate to a pre-condenser upstream of the main condenser, which has at least one cooling coil penetrated by a cooling medium, at a pre-condensation temperature level lower than the first temperature level and well above the main temperature level. f. Gradually cooling the circulation air with the cooling coil to the pre-condensation temperature level in the pre-condenser. g. Supplying the cooled circulation air to the intake of the main condenser. h. Supplying the off-gas sidestream to at least two air pollution prevention devices. i. As a first pollution prevention stage, collecting and concentrating the residual condensable fluid in an adsorption concentrator. j. Subsequently, as a second stage further downstream of the first stage, treating the remaining off-gas flow in a second air pollution prevention device to a level of residual condensable concentration in the air well below 1 mg / Nm3. Further comprising, wherein the cooling coil has a coil tube and a finned surface, and maintaining the cooling rate at less than 0.30 °C per millisecond while the circulating air travels the distance between the agglomerated coil tube and the finned surface. **Claim 12**: The method according to claim 11, wherein the cooling medium enters the cooling coil at the distal side of the circulating air inlet at an inlet temperature of 0 °C or lower and is heated while moving in a countercurrent direction to the circulating air through the cooling coil. **Claim 13** The method according to claim 11, further comprising pre-cooling the circulating air upstream of the main condenser. **Claim 14** The method according to claim 11, further comprising reheating the circulating air downstream of the main condenser. **Claim 15** The method according to claim 11, further comprising reheating the circulating air downstream of the main condenser. **Claim 16** The method according to claim 11, wherein the second air pollution prevention device is a second adsorption concentrator. **Claim 17** The method according to claim 11, wherein the second air pollution prevention device is a filtration device. **Claim 18** The method according to claim 17, wherein the filtration device includes an activated carbon filter. **Claim 19** The method according to claim 11, further comprising adding humidity to the circulating air before gradually cooling the circulating air. **Claim 20** The method according to claim 19, further comprising sensing the dew point of the circulating air before being supplied to the main condenser and sensing the temperature of the large recirculation flow, and the amount of humidity added to the circulating air is based on the sensed temperature of the large recirculation flow. **Claim 21** The method according to claim 19, further comprising sensing the dew point temperature value of the circulating air before introducing the circulating air into the main condenser, sensing the temperature of the fluid exiting the at least one main condenser, and controlling the introduction of humidity in response to the sensed dew point temperature and the sensed temperature of the fluid exiting the at least one main condenser. **Claim 22** The method according to claim 19, further comprising analyzing the solvent concentration of the fluid in the circulating air discharged from the main condenser, sensing the humidity of the fluid in the circulating air discharged from the main condenser, calculating the mole fraction of water in the circulating air discharged from the main condenser, and introducing humidity into the circulating air before entering the main condenser in response to the mole fraction being lower than 0.

95. **Claim 23** Using a first controller that controls and communicates with a valve, an actuator, and a control disposed in a conduit that receives fresh cooling medium into the cooling coil, further comprising controlling the temperature of the air exiting the cooling coil to a set point that reaches a desired target humidity concentration of the air exiting the cooling coil, the method of claim 12.

24. Using a first controller configured to calculate a temperature set point of the incoming cooling medium, further comprising controlling the temperature of the air exiting the cooling coil to a set point that reaches a desired target humidity concentration of the air exiting the cooling coil, the first controller communicating with a second controller that receives the set point from the first controller in a cascade control configuration, the second controller controlling and communicating with an actuator and a valve to control the measured temperature of the cooling medium entering the cooling coil to the set point of the first controller, and / or Measuring the temperature of the cooling medium exiting the cooling coil and inputting the measured value to a controller that communicates with a flow control device, and comparing the measured value with a value of a set point that reaches a desired target humidity concentration of the air exiting the cooling coil, and adjusting the flow control device in response to the comparison, thereby controlling the flow rate of the cooling medium, and / or Measuring the temperature of the cooling medium exiting the cooling coil and including inputting the measured value to a third controller, the third controller communicating with a fourth controller that receives a flow rate set point from the third controller in a cascade control configuration, the fourth controller controlling the speed of the flow control device to control the measured flow rate of the cooling medium entering the cooling coil to the input set point of the third controller, the method of claim 12.

25. The method of claim 11, wherein the outlet temperature of the coolant medium is maintained at a value lower than the outlet air temperature from the cooling coil.

26. A method of conditioning recirculating air that includes at least one condensable fluid, a. Introducing water into the recirculating air, where the water includes steam, b. introducing the circulating air into a main condenser having at least one main condensation chamber and at least one cooling coil containing a cooling medium, at a first volumetric flow rate and an intake temperature level well above 0 °C, where the main temperature level of the main condenser is higher than the main temperature level required to condense an equal amount of the at least one condensable fluid in the absence of addition of vapor to the circulating air; c. gradually cooling the circulating air within the main condensation chamber; d. after reaching the main temperature level, splitting the volumetric flow rate of the circulating air into a large recirculation flow and a small off-gas side flow; e. providing the large recirculation flow to the circulating air intake of a dryer; which includes; f. supplying the circulating air at the first volumetric flow rate to a pre-condenser upstream of the main condenser, at a pre-condensation temperature level lower than a first temperature level and well above the main temperature level, the pre-condenser having at least one cooling coil penetrated by a cooling medium; g. gradually cooling the circulating air with the cooling coil to the pre-condensation temperature level within the pre-condenser; h. supplying the cooled circulating air to the intake of the main condenser; i. supplying the off-gas side flow to at least a two-stage air pollution prevention device; j. as a first pollution prevention stage, collecting and concentrating the residual condensable fluid within an adsorption concentrator; k. subsequently, as a second stage further downstream of the first stage, treating the remaining off-gas flow within a second air pollution prevention device to a level of residual condensable concentration in the air well below 1 mg / Nm3. which further includes, the cooling coil having a coil tube and a finned surface, and a method of maintaining a cooling rate below 0.30 °C per millisecond while the circulating air travels the distance between the agglomerating coil tube and the finned surface. **Claim 27** The method according to claim 11, wherein the cooling medium enters the cooling coil at the far end side of the circulating air inlet at an inlet temperature of 0 °C or below, and is heated while moving through the cooling coil in a countercurrent direction to the circulating air. **Claim 28** The method according to claim 27, wherein the cooling rate is maintained at 0.15 - 0.22 °C per millisecond.

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