Method for operating plant for drying material to be dried with superheated water vapor

Abstract

An apparatus for drying material using superheated water vapor comprises a downwardly open chamber (10) having an inlet (61) for material to be dried, an outlet (62) for dried material, an inlet (71a, 71b) for superheated water vapor and an outlet (73a, 73b) for vapor. Also included is a delivery system (60) for introducing material into the chamber (10), transporting dried material in the chamber (10) during drying, and discharging the dried material from the chamber (10), and a vapor compressor (40) and a heat exchanger (30) for compressing a first portion returned from the chamber (10), and a heat exchanger for transferring heat from the compressed first portion by condensing a volumetric flow of the compressed first portion supplied to the heat exchanger. The apparatus is operated so as to form a vapour atmosphere in the upper region of the chamber (10), which vapour atmosphere floats on the ambient air in the lower region of the chamber (10), forming a transition layer (66) between the upper and lower regions. The steam generator (15) is arranged and operated such that water vapor is supplied to the chamber (10) and / or water vapor is generated in the chamber (10) by determining the current height, maintaining the height of the transition layer (66) within a predetermined range, and controlling the volumetric flow rate of the first portion of compression supplied to the heat exchanger (30) or the volumetric flow rate of the steam generator (15) in accordance with the determined height.

Description

[0001] The invention relates to a method for operating a device for drying a material to be dried using superheated water steam and a corresponding device. Prior Art

[0002] Industrial material drying consumes 12%-25% of the total industrial energy demand in industrial countries, of which the drying process is the most energy-intensive one. Because drying is usually based on fossil energy, CO 2 Therefore, reducing the energy demand for drying is essential to reduce CO 2 It is crucial.

[0003] In a method that is energy-friendly, superheated steam is used for drying instead of hot air. U.S. Pat. No. 5,711,086 (Heat-Win Ltd.) proposes a device for this purpose, in which the moist material is continuously fed into a chamber through an opening, passes through the chamber and is discharged from the chamber through the opening. An atmosphere of superheated steam prevails in the chamber, which is caused by the moisture of the material to be dried and / or supplied from the outside. In this case, a transition layer is formed between the steam atmosphere and the opening and the ventilation duct surroundings, which prevents the steam from escaping from the chamber, but at the same time allows the supply and removal of material.

[0004] The system thus allows simple material supply and removal. Excess steam condenses. By keeping constant the material mass flow, the residence time, the superheated steam mass flow and its temperature, a constant dry matter content can be obtained in a simple manner. However, energy losses occur due to the condensation of excess steam and the return of the correspondingly removed heat by reheating.

[0005] WO 2012 / 140125 A1 (EPCON Evaporation Technology) describes a method with a closed chamber in which a mixing system is provided, in which the wetted material is contacted with superheated steam. The excess steam is mechanically compressed and supplied to a heat exchanger, making energy recovery possible, thereby increasing efficiency.

[0006] Also considering the closed chamber, process control is guaranteed. However, there are also some challenges in the supply and removal of materials. Summary of the invention

[0007] The object of the invention is to provide a method which belongs to the technical field mentioned at the outset for operating an apparatus for drying material to be dried by means of superheated steam and a corresponding apparatus which allows high energy efficiency with simple material supply and removal.

[0008] The solution to the object is defined by the features of claim 1. According to the invention, for drying the material to be dried with superheated steam, a device is operated, which comprises:

[0009] a) a chamber open downwards, the chamber having an inlet for the material to be dried, an outlet for the dried material, an inlet for superheated water steam and an outlet for the steam;

[0010] b) a conveying system for introducing the material to be dried into the chamber, conveying the material to be dried in the chamber, and discharging the dried material from the chamber during the drying process;

[0011] c) a steam compressor for compressing a first portion of said steam recirculated from said chamber;

[0012] d) A heat exchanger for transferring heat from the compressed first part by condensing the volume flow of the compressed first part.

[0013] The device operates as follows:

[0014] e) forming a steam atmosphere in the upper region of the chamber, the steam atmosphere floating on the surrounding air in the lower region of the chamber, wherein a transition layer (stratification layer) is formed between the upper region and the lower region;

[0015] f) maintaining the height of the transition layer within a predetermined range by determining the current height, and according to the determined height:

[0016] f1) regulating the volume flow of the compressed first portion supplied to the heat exchanger; or

[0017] f2) regulating a volume flow of a water steam generator, wherein the water steam generator is arranged and operated such that water steam can be supplied to the chamber and / or water steam can be generated in the chamber.

[0018] Accordingly, the device for drying the material to be dried with superheated water steam according to the present invention comprises:

[0019] a) a chamber open downwards, the chamber having an inlet for the material to be dried, an outlet for the dried material, an inlet for superheated water steam and an outlet for the steam;

[0020] b) a conveying system for introducing the material to be dried into the chamber, conveying the material to be dried in the chamber, and discharging the dried material from the chamber during the drying process;

[0021] c) a steam compressor for compressing a first portion of said steam recirculated from said chamber;

[0022] d) a heat exchanger for transferring heat from the compressed first portion by condensing the volume flow of the compressed first portion; and

[0023] e) A controller for acquiring and processing the measured values ​​and for generating control signals.

[0024] In this case, the controller operates in particular as follows:

[0025] f) forming an atmosphere of superheated water vapor in the upper region of the chamber, the atmosphere floating on the surrounding air in the lower region of the chamber, wherein a transition layer is formed between the upper region and the lower region;

[0026] g) maintaining the height of the transition layer within a predetermined range by determining the current height, and according to the determined height:

[0027] g1) regulating the volume flow of the compressed first portion supplied to the heat exchanger; or

[0028] g2) regulating a volume flow of a water steam generator, wherein the water steam generator is arranged and operated in such a way that water steam is supplied to the chamber and / or water steam is generated in the chamber.

[0029] The materials to be dried are in particular bulk materials, such as products or by-products of the food or feed industry, combustible or building materials, basic materials of the chemical or paper industry and biomass in general. The technology can also be used for drying textiles (including laundry). In principle, the method is best suited for drying materials that require drying temperatures between 100°C and 200°C and do not allow other organic substances to be gasified.

[0030] The steam is in particular water steam, but other solvents such as ethanol may also be used.

[0031] Since there is no oxygen during the drying process, oxidation of the material to be dried is avoided. Thus, for example, fats in food or animal feed do not go rancid. At the same time, the risk of fire and explosion is reduced.

[0032] The loss of aroma is minimized through the circulation process. No odor or dust is emitted to the surrounding environment. Since the temperature is always above 100°C, the material to be dried is pasteurized or even sterilized.

[0033] The chamber is closed at the top and completely or partially open at the bottom. It can have one or more openings at the lower end, which are arranged on the main chamber boundary or on an inward or outward point, such as a tubular extension. Accordingly, the main volume of the chamber can be completely filled with a steam atmosphere, that is, completely located in the upper area of ​​the chamber, and the transition layer can be formed in the tubular extension or multiple tubular extensions. The size of the opening or openings is particularly such that on the one hand, pressure equalization and a certain gas flow between the chamber and the surrounding environment are possible, and on the other hand, it is possible for the dry material to be introduced and discharged through the opening or at least one opening. In particular, all the dry material eventually enters the chamber and is discharged from the chamber through one or more such openings. Therefore, the inlet for the material to be dried and the outlet for the dry material are formed by one or more of these openings. Therefore, the material can be introduced and discharged in a cost-effective design without a large amount of air being conveyed into the water vapor in the process.

[0034] The vapor atmosphere contains a residual proportion of air; this is preferably less than 4% by volume.

[0035] Steam is water vapor, the properties of which change due to interaction with the material to be dried and the chamber atmosphere compared to the introduced superheated steam. Steam is usually more saturated and has a lower temperature than the introduced superheated steam. Steam may also contain other components, in particular small amounts of the material to be dried or dust, such as aerosols and other vapors from the material, such as aromas.

[0036] The conveying system allows the continuous operation of the device in particular. In a preferred embodiment, it comprises a rising conveyor for introducing the material to be dried through an opening on the lower side of the chamber, a belt conveyor for transmitting the material to be dried in the chamber, and a gravity remover for unloading through the same or preferably further openings on the lower side of the chamber. In an optional embodiment, the conveying system comprises one or more rotors, and the device operates as a disc dryer. Further conveying systems, such as fluidized beds or paddle conveyors, can be used within the scope of the present invention. The device can also be used with, for example, a spray drying tower. The conveying system can be partially formed by upstream equipment components, for example, if the material to be dried is directly introduced into the steam atmosphere through the component, such as an extruder, or blown in by a steam flow. The conveying system can include one or more conveyors (e.g., belts or ropes). The chamber itself can be part of the conveying system, such as in the case of a paddle mixer. In each case, introduction, transmission in the chamber and / or discharge can be carried out completely or partially by gravity. Thus, for example, the dried material can fall through an opening located at the bottom.

[0037] In the context of the method according to the invention, the height, ie the vertical position, of the transition layer is now kept within a predetermined range, which is equivalent to keeping the volume of the steam atmosphere in the chamber constant.

[0038] The current altitude can be determined directly or indirectly. Instead of the altitude, a quantity related to the altitude can also be used as a control variable for regulating the volume flow of the compressed first part supplied to the heat exchanger or the steam generator, such as the temperature measured at one or more specific points and / or the content of any gas contained in the air measured at one or more specific points, such as O 2 or N 2 .

[0039] In a first variant, the volume flow of the compressed first part supplied to the heat exchanger is preferably set by adjusting the volume flow of the steam compressor. This can be achieved by setting the rotation speed of the steam compressor and / or the opening of an adjustable hole arranged upstream or downstream of the steam compressor. In addition, an adjustable valve can also be installed downstream of the steam compressor to supply a (proportional) volume flow of the compressed steam to the heat exchanger, while the (possible) remaining part is recirculated back to the chamber. For example, this variant can be used in combination with a turbo compressor, which preferably operates at a certain constant volume flow. In principle, such a (bypass) valve can also be arranged downstream of the heat exchanger, in which case the first part of the compression is completely guided through the heat exchanger, but only a part is condensed there, and the remaining part is recirculated back to the chamber through the bypass valve. In addition, several variants can also be combined, in particular by adjusting the steam compressor to achieve a certain minimum flow, and the regulating valve is only used when it is necessary to further reduce the compressed part supplied to the heat exchanger.

[0040] In a first variant, in particular, the regulation is achieved by increasing the volume flow of the compressed first portion supplied to the heat exchanger when a drop in the transition layer is detected, and reducing the volume flow when an increase in the transition layer is detected. As a result, the volume flow of the first portion is ultimately set to increase or decrease the exhaust portion, thereby increasing or decreasing the volume of the steam atmosphere in the chamber.

[0041] In a first variant, the volume flow of the compressed first part which is to be supplied to the heat exchanger is preferably adjusted according to one of the following methods (wherein these methods can in principle also be combined with one another):

[0042] 1. The height of the transition layer is adjusted by setting the rotational speed of the steam compressor. By increasing the rotational speed, the first part of the steam recirculated from the chamber to be compressed is increased, i.e. a larger part is compressed and then supplied to the heat exchanger as a volume flow.

[0043] 2. The height of the transition layer is regulated by the volume flow rate returning to the chamber from the first compression section. To this end, the opening of the (bypass) valve downstream of the steam compressor is adjusted so that the height of the transition layer remains within the desired range. If the (bypass) valve is opened to a greater extent, the volume flow rate returning to the chamber will increase, and accordingly, the volume flow rate for condensation in the heat exchanger will also be smaller.

[0044] 3. The height of the transition layer is adjusted by setting the opening of the holes upstream or downstream of the steam compressor. Thus, when the rotation speed of the steam compressor remains constant, the first part of the steam recirculated from the chamber to be compressed can be adjusted.

[0045] In a second variant, the regulation is carried out in particular by reducing the volume flow of the water vapor generator when a drop in the transition layer is detected and increasing the volume flow of the water vapor generator when an increase in the transition layer is detected. Thus, the volume of the steam atmosphere in the chamber is ultimately directly influenced.

[0046] The return of process heat by compression and condensation in a heat exchanger increases efficiency, but causes all relevant process parameters to become interdependent, leading to nonlinear behavior of the system. This presents a particular challenge when operating systems with an open chamber, since it must always be ensured that the transition layer between the steam atmosphere and the surroundings remains stable and within the permissible height range. Operation according to the invention enables a stable process and a constant dry matter content to be achieved even in an open chamber.

[0047] In particular, the steam compressor can be run using electrical energy, which means that it can easily be operated using renewable energy and thus can significantly reduce carbon dioxide (CO) compared to conventional drying methods. 2 emissions.

[0048] Preferably, the current height of the transition layer is determined based on a measurement value of at least one temperature sensor, the at least one temperature sensor being arranged within a height range corresponding to the specified range.

[0049] At least one temperature sensor is preferably installed in a duct which extends downwards from the main volume of the chamber, in particular in vertical direction, and connects the chamber to the surroundings. Alternatively or additionally, the temperature sensor can also be installed at the opening for discharging the material to be dried.

[0050] The temperature sensor acts as a steam fill level sensor and ultimately determines the height of the steam-air transition layer (or a parameter directly related thereto). In a preferred embodiment, when the value provided by a particular temperature sensor exceeds a first threshold, the transition layer is considered to be falling, and when the value provided by the particular temperature sensor is below a second threshold, the transition layer is considered to be rising. The threshold values ​​are selected in the range of 90-100°C, preferably with a difference of 2-8°C. It is particularly preferred that the first threshold value is about 98°C and the second threshold value is about 96°C.

[0051] The temperature sensor can be installed in the area of ​​the inlet and / or outlet. The temperature sensor is preferably arranged below the chamber, especially in the area of ​​the outlet, because the interfering influence of the drying material on the temperature measurement is usually less than the interfering influence of the material to be dried at the inlet. Interference can be further reduced if the temperature sensor is installed in a pipe separated from the outlet near the outlet. Practice has shown that a pipe diameter of 1.5-6 cm is sufficient for this purpose. Preferably, the temperature sensor is installed at both the inlet and the outlet. This allows for optimal monitoring of the process and early detection of faults.

[0052] System parameters, in particular the speed of the steam compressor, can be controlled by means of a PID control, advantageously based on measured temperature values, wherein temperature values ​​measured by a plurality of temperature sensors arranged at different heights can be utilized, and thus in particular temperature gradients can be utilized. The controller can be integrated into a conventional machine controller (PLC) or can also be implemented by the machine controller.

[0053] If a different solvent is used instead of water, different temperature values ​​will result. The prevailing air pressure also has an influence, especially due to the altitude above sea level, and this must be taken into account when setting the temperature value. The above instructions refer to the drying method carried out at sea level.

[0054] In addition to temperature sensors, other measurements can also be used to determine the height of the transition layer, such as one or more lambda probes to determine the oxygen content or chemical sensors to determine the nitrogen content or the content of other gases in the air.

[0055] Advantageously, within the scope of the method of the invention, the drying temperature is maintained within a predetermined range by comparing the drying temperature with a set value and, based on the comparison result:

[0056] g1) regulating the volume flow of a water steam generator, the water steam generator being arranged and operated so that water steam can be supplied to the chamber or generated in the chamber, provided that the height of the transition layer is maintained within a predetermined range by regulating the volume flow of the compressed first part supplied to the heat exchanger; or

[0057] g2) adjusting the heating power of the heating device; or

[0058] g3) regulating the volume flow of the compressed first part supplied to the heat exchanger, provided that the height of the transition layer is kept within a predetermined range by regulating the volume flow of the steam generator.

[0059] Therefore, there are several variations in adjusting the height of the transition layer and the drying temperature:

[0060] Variants Height adjustment of transition layer Drying temperature adjustment 1A Compression section to heat exchanger Steam generator 1B Compression section to heat exchanger Heating device 2A Steam generator Heating device 2B Steam generator Compression section to heat exchanger

[0061] In variant 2A, the drying temperature is regulated by the heating power of the heating device, the transition layer is regulated by a water vapor generator, and the steam compressor has the task of extracting a first portion of the steam from the chamber, which is greater than in variant 1B but less than in variant 2B. Thus, the steam compressor ensures that a higher temperature is reached in the heat exchanger than in variant 1B, thereby reducing the heating power of the heating device.

[0062] The drying temperature is primarily the temperature of the superheated steam entering the chamber or, especially in the case of indirect drying, the temperature of the contact surface with the material to be dried. The corresponding setting value depends, among other things, on the material and the desired dry matter content.

[0063] The dry matter content of the processed material to be dried can be determined in the chamber, for example, by measuring the temperature of the surface of the material to be dried. Infrared temperature sensors are very suitable for this purpose. Based on the measured surface temperature, the dry matter content can be derived using a characteristic curve previously determined empirically. If the specifications are not met, the system parameters are adjusted, in particular the set drying temperature of the contact surface in the case of superheated steam or indirect drying and / or the conveying speed of the conveying system (and the residence time of the material to be dried in the chamber).

[0064] In a preferred embodiment, the apparatus comprises a piping system between the steam outlet and the superheated steam inlet, wherein the piping system is arranged with:

[0065] g) Steam compressor

[0066] h) Circulation fan

[0067] i) a heat exchanger for transferring heat of the compressed first portion by condensing a volume flow of the compressed first portion supplied to the heat exchanger, thereby heating a second portion of the steam recirculated from the chamber; and

[0068] j) A water vapor heating device is arranged between the heat exchanger and the superheated water vapor inlet.

[0069] The heat transfer in the heat exchanger takes place in particular in countercurrent, with the compressed water vapor stream flowing from top to bottom.

[0070] The circulation fan can be installed upstream or downstream of the heat exchanger. It serves to maintain the water vapor flow in the circuit and thus compensate for the resulting pressure drop. It has been shown that the required mass flow increases approximately linearly with the evaporation rate. The mass flow provided by the circulation fan should be at least 60 times the compressed mass fraction supplied to the heat exchanger. This ensures that, in addition to the actual evaporation of the liquid in the material to be dried, heat losses can be compensated and the material to be dried and its contained and surface moisture can be preheated. The mass flow rate is preferably set above 60:1 in order to provide a safety factor, since the expected dissipation resulting from the high mass flow rate is converted into heat in the system, thereby promoting the heating of the water vapor. Depending on the specific construction of the equipment, ratios of 100:1, 150:1 or even higher can be set. Thus, the circulation fan can support the heating device and in some cases even replace it.

[0071] A steam compressor is a mechanical compressor. It is used for heat recovery. The steam is supplied through a part of the pipe system or directly from the chamber. Steam compressors can be of multi-stage design, i.e. several compressor stages are arranged in series.

[0072] The volume flow of the first part of the steam supplied to the heat exchanger and compressed by the steam compressor is in particular proportional to the amount of water vapor released during the drying of the material, so that the mass flow in the circuit is constant. According to the compressor characteristic map, the first part is determined by the pressure ratio and the speed of the steam compressor. Therefore, the first part can be set by adjusting the speed. In each case, the volume flow of the compressed first part supplied to the heat exchanger is generally between 1:30 and 1:160 based on the circuit water vapor.

[0073] Besides the condensation of the compressed steam (and possibly water vapor from a steam generator), other heat sources may be present in the heat exchanger, such as waste heat or dedicated heating devices.

[0074] The heating device for the steam is independent of the heat exchanger. In particular, it is a resistance heater. Alternatively, a gas burner or the like can also be used. As mentioned above, the heating device can be integrated into the circulation fan, in particular to heat the water vapor by heat dissipation in the fan. If the heating device is separated from the fan, it should be arranged downstream of the fan in the circulation direction, preferably directly upstream of the chamber inlet. The desired dry matter content can ultimately be set by adjusting the heating device. Instead of (or in addition to) the resistance heater, waste heat can be used in the heating device, for example waste heat generated from the exhaust gas of a gas engine, which is transferred to the water vapor via an adjustable heat exchanger (for example a gas-to-gas heat exchanger using the hot gas waste heat).

[0075] The heating device may comprise one or more heating units. For example, in a belt dryer, each belt is assigned a separate heating device. Thus, the operation of the individual heating devices can be regulated individually or collectively.

[0076] Ultimately, a constant dry matter content is achieved. If the vapor compression rate is changed to set the height of the transition layer, the condensation temperature in the condenser changes mid-term, which also affects the evaporation rate in physics and thus leads to a change in the water vapor content. This effect can be compensated by adjusting the heating power.

[0077] Although hardly any air enters the system through an open lock, the possibility of trace amounts of air cannot be completely ruled out. Small amounts of air in the system can accumulate in the condenser and, over time, clog important heat transfer surfaces. To avoid this, the condenser must be ventilated continuously. Therefore, the heat exchanger is preferably equipped with an air vent valve on the condenser side and the opening of the air vent valve is adjusted depending on the air content determined on the condenser side. The air content can be determined based on the condenser pressure and condensing temperature, the saturation temperature deviation or directly using a lambda probe.

[0078] The exhaust valve is installed, in particular in the form of a needle valve, preferably above the condensate outlet. The latter allows excess condensate to be discharged. Advantageously, the regulation is based on the measured values ​​of one or more fill level sensors, which can be capacitive limit switches or the like. Finally, the water is recovered from the material to be dried, usually in a sterile and demineralized state.

[0079] Advantageously, the air content on the condenser side is adjusted to 0-50%, preferably 5-20%, in particular 7-12%. If this value is below the lower setting value, there will be a large amount of water vapor loss. If this value is too high, the efficiency of the steam compression will decrease.

[0080] Since the air mass flow rate into the condenser is not constant and depends greatly on the operating conditions of the unit, the exhaust valve must be constantly readjusted. This keeps the air content in the condenser at the desired percentage.

[0081] In a preferred embodiment, the pipe leading from the condenser leads to a branch (such as a T-type or a Y-type).

[0082] As a result, water and non-condensable gases can be reliably separated at the outlet of the condenser and the loss of water vapor to the surrounding environment can be minimized. One branch of the branch leads to a horizontal or slightly upward drain line, on which a vent valve is installed. The other branch leads downward (especially vertically) to a pipe section with an enlarged cross-section, in which a water column is formed. In this way, the discharge of condensed water can be regulated and delayed.

[0083] Two (e.g. capacitive) fill level sensors are arranged along the pipe section with the water column. A stop valve is connected at the bottom and is opened or closed according to the measured values ​​of the fill level sensors so that the water level of the water column is always between the fill level sensors.

[0084] A throttling valve (such as a needle valve) is installed downstream of the stop valve. This component ensures that the condensate is discharged more slowly and prevents the gas-air mixture from leaking downwards.

[0085] Due to the pressure drop across the stop valve with downstream throttle, water vapor is generated, and the condensate outlet thus forms a (further) water vapor generator. This water vapor can be fed back to the water vapor circuit, the drying chamber and / or the material to be dried via corresponding pipes and used for further drying and / or preheating of the material.

[0086] In this preferred embodiment, the exhaust valve is also adjusted according to the air content determined on the condenser side, which can be determined directly by a lambda probe as described above, or indirectly by the deviation of the static pressure from the water vapor pressure at the condensation temperature.

[0087] Advantageously, the inlet for the superheated steam is arranged in the chamber so that the superheated steam intersects the conveying path of the material to be dried in the chamber in a directional steam flow. Preferably, it is carried out in a cross-flow or counter-flow manner. The supply and discharge of the superheated steam are coordinated with the internal geometry of the chamber, in particular so that the steam atmosphere in the chamber is looped.

[0088] When the apparatus of the present invention is designed as a belt dryer, the inflow and extraction of superheated steam is preferably as close to the material as possible.

[0089] Preferably, an element for homogenizing the steam flow is installed on the chamber side of the inlet. In particular, the element forms a flow resistance, smoothes the steam flow, i.e., in particular eliminates large-scale eddies or secondary flows and standardizes the flow curve. The size of the resistance should be sufficient to coordinate the steam flow while avoiding unnecessary pressure losses and an increase in the power required by the circulation fan. The element can be designed in the form of a filter or made of a fine-porous material. For example, glass fiber mats are suitable. A diffuser can be installed upstream to distribute the steam flow over a larger cross section.

[0090] This element allows the circulation of superheated steam in the chamber to be controlled. It has also been shown to stabilize the transition layer.

[0091] When starting the device, the required steam atmosphere must first be formed in the upper region of the chamber. To this end, the device preferably includes a water steam generator and in particular performs the following steps:

[0092] - generating water vapor in a water vapor generator, introducing the generated water vapor into the chamber, and exhausting the air in the chamber downwardly out of the chamber;

[0093] During operation of the steam generator (after the steam atmosphere has been created or the air in the chamber has been evacuated) until the operating pressure is reached in the heat exchanger:

[0094] - Start the circulation fan,

[0095] - start the heating device and / or the steam compressor,

[0096] - introduction of the material to be dried via a conveying system, and

[0097] - Start the steam compressor.

[0098] In particular, the generated water vapor is introduced from above, preferably at the highest point of the chamber and / or the pipe system. The chamber is preferably preheated with air to 100° C. The introduced water vapor not only displaces the air from the chamber, but also from the pipe system.

[0099] In the last phase, both the steam generator and the steam compressor are started, the operating pressure in the heat exchanger increases, and the heat exchanger operates as a condenser while maintaining a steam atmosphere. In particular, it is 1.5-4 bar higher than atmospheric pressure, depending on other machine and process parameters. When the operating pressure is reached, the steam generator is shut down and switched to rated operation.

[0100] In another embodiment of the invention, the conveying system has a rotating hollow shaft, which is arranged in a chamber and has a plurality of disks, forming a heat exchanger, wherein a cavity is arranged inside the hollow shaft, to which cavity the steam compressor supplies a volume flow of a compressed first part of the steam for heating the disks; in this embodiment, the first part thus corresponds to the entirety of the recirculated steam; but in a corresponding embodiment, a part of it can be returned to the chamber via a (bypass) valve arranged downstream of the steam compressor. In this way, the hollow shaft acts as a condenser for the recirculated compressed steam. The cavity can extend to the disks or be limited to a central part of the hollow shaft.

[0101] The liquid material to be dried is supplied to the disc through the inlet, then dried, and finally removed from the disc after drying, such as scraped off, and discharged from the chamber through the material outlet. Therefore, in this embodiment, drying is performed indirectly.

[0102] In the embodiment with a rotating disk shaft, it is preferred that water vapor is supplied to the chamber from a water vapor generator. This supply is carried out (also) during the drying process, in particular in a continuous manner, the water vapor being compressed by a steam compressor and supplied to the hollow shaft, and finally used for drying the liquid material, heating the chamber and compensating losses.

[0103] The steam generator is arranged and operated in such a way that steam can be supplied to the chamber or generated in the chamber. The steam can be supplied directly to the chamber or indirectly, for example, via a pipe system. For example, water can be generated by injecting water into an atmosphere of superheated steam. Thus, the steam generator can also be installed directly in the chamber.

[0104] In one embodiment of the invention, the volume flow of the compressed first part supplied to the heat exchanger is then adjusted as a function of the current height of the transition layer. In this case, preferably, the volume flow of the water vapor generator is adjusted as a function of the measured condensation temperature in the cavity of the hollow shaft, so that the condensation temperature remains within a predetermined interval. This ultimately regulates the dry matter content of the material to be dried. This corresponds to variant 1A described above.

[0105] In another regulation method, similar to the variant with a rotating disk shaft, the height of the transition layer is maintained within a prescribed range not by regulating the volume flow of the compressed first part supplied to the heat exchanger, but by regulating the volume flow of the water vapor generator. In this alternative method, the volume flow of the compressed first part supplied to the heat exchanger is regulated, in particular, as a function of the measured condensation temperature in the cavity, so that the condensation temperature is maintained within a predetermined range. This corresponds to the above-mentioned variant 2B.

[0106] In all embodiments of the invention, the steam generator arranged in the device can be operated using waste heat. In this case, in particular, the condensate from the heat exchanger can be used as feed water. If the condensate does not meet the supply requirements, further water can be supplied, for example from a water tank.

[0107] In plants with a steam circuit, steam from a steam generator can be introduced into the circuit, thereby increasing the compressed first part supplied to the heat exchanger. This increases the condensation temperature and thus increases the heat output to the circuit flow via the heat exchanger. As a result, the power of the heating device can be reduced, thereby increasing the process efficiency.

[0108] Further advantageous embodiments and feature combinations of the invention emerge from the following detailed description and the entire patent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0109] The accompanying drawings for explaining exemplary embodiments show:

[0110] Figure 1A and Figure 1B is a schematic block diagram of an apparatus for drying a material to be dried by using superheated water steam according to a first embodiment and a second embodiment of the present invention;

[0111] Figure 2Ais a schematic cross-sectional view of an apparatus according to a first embodiment;

[0112] Figure 2B is a detailed view of an advantageous embodiment of a condensate outlet of the device according to the first embodiment;

[0113] Figure 3 is a schematic cross-sectional view of an apparatus according to a third embodiment;

[0114] Figure 4A and Figure 4B is a cross-sectional view of a drying chamber of an apparatus according to a fourth embodiment of the present invention;

[0115] Figure 5A and Figure 5B is a cross-sectional view of a drying chamber of an apparatus provided according to a fifth embodiment of the present invention;

[0116] Figure 6 is a diagram of actuators and controlled variables of a device according to the invention;

[0117] Figure 7 is a block diagram of a sensor system of an apparatus according to a first embodiment of the present invention;

[0118] Figure 8 is a profile of measured temperatures at three heights in a vertical duct near the outlet; and

[0119] Fig. 9 is an overview of the temperature and air content at the start-up of the device according to the invention;

[0120] In principle, identical parts are provided with the same reference symbols in the figures. DETAILED DESCRIPTION

[0121] Figure 1A , Figure 1B Schematic block diagrams of devices for drying materials to be dried by superheated water steam provided in the first embodiment and the second embodiment of the present invention respectively. Figure 2A A schematic cross-sectional view of an apparatus according to a first embodiment is shown. The first embodiment and the second embodiment differ in the positioning of the circulation fan in the water vapor circuit. In addition, the second embodiment comprises a further water vapor generator, which can be operated by waste heat. It should be considered that the use of such a water vapor generator is also possible when the circulation fan is positioned as in the first embodiment. Otherwise, all the following remarks apply to the first embodiment and the second embodiment.

[0122] The device comprises a chamber 10 into which a wet material 1 can be introduced and a dry material 2 can be discharged via a conveying system 60. In the device shown, the mass flow of the wet material 1 (dry matter content 50%, temperature 50-70° C.) is 36 kg / h. The chamber 10 is closed at the top and sides and open at the bottom; in the exemplary embodiment shown, it accordingly comprises:

[0123] - an inlet 61 designed as a pipe extending obliquely upwards to the upper region of the side wall of the chamber 10, wherein a bucket conveyor 65.1 is arranged in the conveying system 60 and serves as an ascending conveyor; the cross section A1 perpendicular to the longitudinal axis of the pipe is about 0.10 m 2 ;

[0124] - outlet 62, which is designed as an opening on the lower side of the chamber 10, through which the dry material 2 is discharged under the action of gravity; the cross-sectional area A2 of the opening is about 0.02 m 2 ;

[0125] A downwardly open measuring tube 63 (cf. FIG. 2 ), arranged in the region of the outlet 62 , containing a plurality of temperature sensors.

[0126] The bucket conveyor 65 . 1 comprises a tray for receiving the material to be dried, the tray being perforated so that air cannot be transported upwards during the transition to the chamber 10 .

[0127] During operation, the chamber 10 is filled with water vapor, which floats above the ambient air.

[0128] The feed line of the steam generator 15 opens into the upper side of the chamber 10 so that steam can be supplied directly to the chamber 10 when needed, especially during startup as described below. A steam exhaust valve can also be provided on the upper side of the chamber 10 to exhaust excess steam from the chamber 10 (not shown).

[0129] The bucket conveyor 65.1 slowly introduces the wet material 1 from the ambient air into the steam atmosphere from below at a speed of 10-30 mm / s without entraining air.

[0130] Two horizontal belt conveyors 65.2, 65.3 are arranged in the chamber 10 so that the first of these further belt conveyors 65.2 receives the moist material from the bucket conveyor 65.1, conveys it through the first drying stage and discharges it to the second belt conveyor 65.3, which conveys the material through the second drying stage. The area over which the water vapor flows in the region of the belt conveyors 65.2, 65.3 is in each case approximately 0.45 m 2 From the second belt conveyor 65 . 3 , the material falls out of the chamber 10 through the outlet 62 via the steam-air transition layer.

[0131] The residence time of the material in the chamber 10 is set by the conveying speed of the conveying system 60. In the apparatus shown, this is typically about 20-30 minutes.

[0132] A closed circuit water vapor conduit is connected to the chamber 10. The circuit is driven by a circulation fan 20. In the apparatus shown, the volume flow in the circuit is 2150 m 3 / h.

[0133] The treated superheated water vapor is divided into two partial flows when entering the chamber. Each partial flow first passes through a diffuser, where it is distributed over a larger cross section, and then passes through filter elements 72a, 72b. In the exemplary embodiment shown, these are designed to have a basis weight of 610 g / m 2 This results in a pressure loss coefficient ζ of 400 at a water vapor velocity of 1.3 m / s and a ζ value of 200 at a water vapor velocity of 7 m / s or more.

[0134] They serve to homogenize the steam flow. The steam flow is then discharged in a divided form via a first steam inlet 71a adjacent to the first belt conveyor 65.2 and a second steam inlet 71b adjacent to the second belt conveyor 65.3. In the device shown, the evaporation mass flow is approximately 16 kg / h (equivalent to 26.7 m 3 / h water vapor). The volume of water vapor in the water vapor chamber is 0.85m 3 , where the air content is less than 4%.

[0135] The steam flow passes through the conveying surface of the belt conveyors 65.2, 65.3 and is extracted again from the chamber 10 in each case through the water vapor outlets 73a, 73b on the opposite side. The water vapor provides heat to the material to be dried, resulting in evaporation of water. In this case, the dry matter content of the material is determined by analyzing the material after outflow to the ambient air, on the basis of which the water vapor temperature and the residence time are readjusted. Alternatively, the dry matter content can also be checked by (optical) temperature measurement of the material surface in the water vapor, wherein a plurality of corresponding sensors can be arranged along the conveying path in the chamber in order to monitor the drying process.

[0136] In order to introduce heat in the circulating steam conduit, the circulating water steam conduit comprises a heat exchanger 30 and a subsequent heating device 50. The heating device 50 advantageously comprises a first heating unit 51a for the water steam fraction supplied to the first water steam inlet 71a and a second heating unit 51b which can be independently adjusted for the water steam fraction supplied to the second water steam inlet 71b.

[0137] The heat exchanger 30 is a layered heat exchanger. Its external heat exchange area is about 95m 2 , the internal heat exchange area is about 0.3m 2 . A filter may be arranged upstream of the heat exchanger 30 to avoid contamination thereof by the entrained material fraction. The heat exchanger 30 is operated as a condenser by means of a steam compressor 40 which compresses a portion of the water vapor extracted from the chamber 10 and supplies it to the condenser, in which a portion of the steam is condensed at elevated pressure, typically at atmospheric pressure 2.5-4 bar, and in the process the enthalpy of evaporation is transferred to the circulating water vapor stream by means of the heat exchanger 30. In the exemplary embodiment shown, the installed power of the steam compressor 40 is 3.7 kW. During operation, the power is typically about 1.1 kW.

[0138] The subsequent heating device 50 further heats the circulating water vapor flow to the necessary drying temperature.

[0139] In order to drain the water, the condenser of the heat exchanger 30 has a condensate drain valve 31 which opens automatically depending on the water level. To this end, the water level is monitored by one or more capacitive water level sensors and the valve is opened for a predetermined time when the water level exceeds a certain desired level. If two water level sensors are used, the upper sensor can be used to start the emptying process, while the lower water level sensor responds during the emptying process, shortening the predefined time interval. This ensures that the condensate volume always remains within the height range between the lower sensor and the valve, so that the steam / air mixture cannot leave directly through the valve. In the device shown, the mass flow rate of the condensate is typically about 7.5 kg / h (equivalent to 1.6 m 3 / h water vapor).

[0140] In addition, an air discharge valve 32 for discharging non-condensable gases is installed above the water outlet. The proportion of these gases in the water vapor is determined by the temperature and pressure sensors at the condenser outlet.

[0141] Within the scope of the second embodiment, the condensate from the heat exchanger 30 is supplied to the steam generator 17. Waste heat (e.g., a temperature of about 170° C.) is supplied to the steam generator to evaporate the condensate. The generated steam is then supplied to the steam circuit downstream of the circulation fan 20 and upstream of the branch of the supply pipe to the heat exchanger 30 and the steam compressor 40.

[0142] Figure 2BA detailed view of an advantageous embodiment of the condensate outlet of the device according to the first embodiment is shown. A pipe 33 leaving the condenser of the heat exchanger 30 leads to a Y branch. One branch of this branch leads to a horizontal or slightly upward discharge pipe, which is provided with a vent valve 32. The other branch leads vertically downward into a pipe section 34 of enlarged cross section, forming a water column. Two (e.g. capacitive) filling level sensors 35.1, 35.2 are arranged along the pipe section 34 with the water column. At the bottom, a shut-off valve 36 is connected, which is opened or closed depending on the measured values ​​of the filling level sensors 35.1, 35.2, so that the water level of the water column is always between the filling level sensors 35.1, 35.2.

[0143] Another pipe section, a needle valve 37 as a throttle, is then connected to the stop valve 36. The water vapor generated due to the pressure drop at the stop valve 36 and the needle valve 37 is finally sent back to the water vapor circuit through a pipe 38 arranged downstream of the needle valve 37, into the drying chamber and / or to the material to be dried.

[0144] The vent valve 32 is then adjusted depending on the air content on the condenser side, which is determined directly via the lambda probe 39 or indirectly via the deviation of the static pressure from the water vapor pressure at the condensation temperature.

[0145] Figure 3 A schematic cross-sectional view of an apparatus according to a third embodiment is shown. The apparatus according to the third embodiment is used for indirect drying. It comprises a chamber 110 filled with water vapor, the chamber 110 being closed at the top and partially open at the bottom. The conveying system 160 in the chamber 110 has a rotating hollow shaft 167 with a plurality of disks 168, the hollow shaft being hollow and having the function of conveying the material and acting as a heat exchanger, i.e. acting as an internal condenser. The apparatus also has a steam compressor 40, a water vapor generator 115 and an inlet 161 for drying the liquid material.

[0146] The liquid material to be dried is supplied to the outside of the hollow shaft 167 with the disk 168 through the inlet 161. Steam from the chamber 110 is supplied to the steam compressor 40. To this end, the steam compressor 40 extracts steam from the chamber and supplies at least a part of it to the hollow disk condenser after compression. There, the compressed water vapor condenses and heats the hollow shaft 167 with the disk 168, thereby drying the material. In this case, the dry matter content of the material to be dried is set by the condensation temperature. The air content in the hollow shaft 167 as a condenser is adjusted to a predetermined content by a discharge valve. The dried material is scraped off the disk 168 by a scraper, which is ground on the hollow shaft 167 and discharged through the outlet 162 on the lower side of the chamber 110. In order to constantly heat the device and compensate for losses, water vapor is continuously sucked from the water vapor generator 115. According to the third embodiment, a water vapor blower is not required in the device.

[0147] The device according to the third embodiment can be adjusted in two basic ways:

[0148] - According to a first method, the volume flow of the water vapor generator 115 is regulated by measuring the condensation temperature of the hollow shaft so that this temperature is maintained within a predetermined gap. The volume flow supplied to the compression part of the disk condenser is regulated based on a temperature sensor in the area of ​​the water vapor / air separation layer so that this temperature is maintained within a predetermined range, whereby the transition layer is maintained at a predetermined height.

[0149] - According to a second method, the volume flow supplied to the compression part of the disk condenser is regulated by measuring the condensation temperature of the hollow shaft so that this temperature is maintained within a predetermined gap. The volume flow of the water vapor generator 115 is regulated based on a temperature sensor in the area of ​​the water vapor / air separation layer so that this temperature is maintained within a predetermined range, whereby the transition layer is maintained at a predetermined height.

[0150] Figure 4A and 4B Schematic cross-sectional view of a drying chamber of an apparatus according to a fourth embodiment of the invention and the corresponding supply and removal, wherein the figure does not show the rising conveyor formed according to the first three embodiments for introducing the material to be dried into the steam atmosphere of the chamber. Figure 4A shows a view of a vertical plane perpendicular to the axis of rotation of the blade, Figure 4B A view of a vertical plane through the axis of rotation is shown. As far as the sensor system and the controller are concerned, the other components of the device for the material supply, in particular the water vapor supply and the removal and handling, correspond essentially to one of the first three embodiments.

[0151] The chamber 210 forming the conveying duct has a substantially circular cylindrical shape. The paddles 267.1, 267.2 are rotatably mounted around the longitudinal axis of the chamber 210 and at a constant distance from the chamber wall. Depending on the material being conveyed, the distance is selected to be so small that clogging of the material is avoided. The paddles 267.3, 267.4, 267.5 with a larger wall distance are mounted near the paddles 267.1, 267.2 with a smaller wall distance, the paddles 267.1 to 267.5 always having the same wheelbase relative to each other. Here, depending on the material being conveyed, a gap size is also selected that is too large so that thicker sheets cannot be stuck, but the transport of the material is facilitated. The paddles 267.1 to 267.5 each have an axial setting angle of, for example, 30° in the conveying direction. A different number of paddles can also be used.

[0152] Two vertical channels lead into the chamber 210 at one end of the upper side, one serving as an inlet 261 for the material to be dried and the other serving as a water vapor discharge outlet 273. A transverse outlet 262 for discharging the dried material is provided at the other end of the upper region of the chamber 210. The height of the lower edge of the outlet 262 and the filling height of the conveying duct can be set by vertical adjustment of the weir 211. The filling degree is required to be more than 2 / 3.

[0153] The blades 267.1 to 267.5 rotate slowly at a speed of about 20-30 rpm. They can rotate in two directions, and the main direction of rotation (for conveying the material in the direction of the material outlet) is directed in such a way that the blades 267.1 to 267.5 move downwards where the water vapor enters.

[0154] The dried material falls through outlet 262 into a conveying conduit having a spiral 268 for controlled backup and controlled removal of the material. Once the material passes through the spiral 268, it falls into a vertical removal conduit where a transition layer 266 flows between the ambient environment and the steam atmosphere. Controlled backup ensures that the transition layer 266 is stable.

[0155] The water vapor is supplied from above the water vapor circuit via the corresponding inlet 271 and distributed over the length of the conveying duct and introduced laterally / horizontally into the mixer / conveying trough in the lower region of the chamber 210 via the inlets 274.1 to 274.3. In this case, the flow resistance of the material placed thereon is used to produce a uniform inflow, thereby producing a drying process that is as uniform as possible. At the same time, the water vapor feed design prevents the material from falling back into the water vapor circuit.

[0156] In this case, the water vapor inflow is arranged so that there is no inflow opening at the axial position of the blades 267.1, 267.2 with a small gap size. In each case, the width of the gap is the same as the width of the blade tip. At the position without or with shortened blades 267.3 to 267.5 with a large gap size, the water vapor enters the chamber 211 through the inflow opening.

[0157] The transverse openings can be of different sizes. They can be smaller the closer they are to the feed inlet or the steam outlet, depending on the desired distribution of the steam along the axis of the mixer. (Also, the steam will take the path of least resistance, and there will be little or no flow in most parts of the mixer.)

[0158] The temperature of the water vapor flowing transversely into the channel does not have to be uniform, but rather increases in an optimal manner along the conveying channel in the conveying direction. The closer the material is to the end of the process and the drier it is, the hotter the water vapor introduced.

[0159] The water vapor that flows in horizontally first roughly flows horizontally through the loose materials, and then flows in the opposite direction to the material flow direction. Finally, the water vapor beside the inlet 261 of the material is sucked upwards through the outlet 273, and the result is that the particles are not carried.

[0160] Figure 5A and Figure 5B is a schematic cross-sectional view of a drying chamber of an apparatus according to a fifth embodiment of the invention and the corresponding supply and removal. Figure 5A shows a view of a vertical plane perpendicular to the axis of rotation of the helix, Figure 5B A view of a vertical plane through the axis of rotation is shown. As for the sensor system and the controller, as for the material supply, the other components of the device, in particular the water vapor supply and the components for removal and treatment, correspond essentially to one of the first three embodiments.

[0161] The drying chamber of the fifth embodiment has many similarities to the fourth embodiment. The main difference is that a spiral is used as a mixing and conveying element in the chamber instead of a paddle. The chamber 310 forming the conveying duct has a generally circular cylindrical shape. The spiral 367 is rotatably mounted around the longitudinal axis of the chamber 310; the distance between each winding and the chamber wall is small.

[0162] Two vertical channels lead into the chamber 310 at one end of the upper side, one serving as an inlet 361 for the material to be dried and the other serving as an outlet 373 for the discharge of water vapor. A transverse outlet 362 for discharging the dried material is provided at the other end of the upper region of the chamber 310. The height of the lower edge of the outlet 362 and the filling height of the conveying duct can be set by vertical adjustment of the weir 311. The filling degree is required to be more than 2 / 3.

[0163] The spiral 367 rotates slowly at a speed of about 20-30 rpm. It can rotate in two directions, with the main rotation direction (for conveying material in the direction of the material outlet) pointing to move the windings of the spiral 367 downward to where the water vapor enters.

[0164] The dried material falls through outlet 362 into a conveying conduit with a spiral or screw 368 for controlled backup and controlled removal of the material. Once the material passes through the spiral 368, it falls into a vertical removal conduit where a transition layer 366 flows between the environment and the steam atmosphere. The controlled backup ensures that the transition layer 366 is stable.

[0165] The water vapor is supplied from above the water vapor circuit via a corresponding inlet 371 and distributed over the length of the conveying conduit, from which it is introduced transversely / horizontally via an inlet 374 into a mixer / conveying trough in the lower region of the chamber 310. In this case, the flow resistance of the material placed thereon is used to produce a uniform inflow, thereby resulting in a drying process that is as uniform as possible. At the same time, the design of the water vapor supply prevents the material from falling back into the water vapor circuit. The cross section of the inlet 374 decreases in the opposite direction of the material conveying direction. The inlet 374 is divided into different temperature zones in the feed, so that the water vapor temperature increases along the conveying conduit in the conveying direction: the closer the material is to the end of the process, the drier it is, and the hotter the water vapor is introduced.

[0166] The water vapor of the lateral inflow first roughly flows horizontally through the loose materials, and then flows in the opposite direction to the material flow direction. Finally, the water vapor beside the inlet 361 of the material is sucked upwards through the outlet 373, and the result is that the particles are not carried.

[0167] The operation of the device according to the invention will be described below in conjunction with the first two embodiments. However, the corresponding description can also be easily transferred to the other three embodiments.

[0168] Figure 6 The actuators and control variables of the device according to the invention, i.e. the device according to the first embodiment, are shown when operating according to variant 1B, wherein the volume flow of the compressed first part supplied to the heat exchanger 30 is set by adjusting the steam compressor 40. The control variable 82 can be influenced by the actuator 81. The actuator 81 comprises a circulation fan 20, which can be adjusted in particular by its rotation speed to set a circulation water vapor flow 82.3, an exhaust valve 32, a steam compressor 40, a heating device 50, and a conveying system 60, wherein the circulation fan 20 can be adjusted in particular by its rotation speed to set a circulation water vapor flow 82.3, the exhaust valve 32 can be selectively opened or closed to set an exhaust gas mass flow 82.5, the mass flow 82.4 of the steam compressor 40 can likewise be set by the rotation speed, the power of the heating device 50 can be set to adjust the water vapor temperature 82.2, and the conveying system 60 allows the conveying speed to be set, thereby setting the material throughput 82.1 and the residence time of the material to be dried in the chamber.

[0169] Variable material quantities 83 include dry matter content 83.1 at the inlet, material consistency 83.2, material form 83.3 and material-related adsorption isotherms 83.4. As control variables 84, dry matter content 84.1 at the outlet and height 84.2 (or position) of the transition layer are mainly predetermined.

[0170] The condenser pressure 85.1 and the specific energy consumption 85.2 (in kWh / kg water) result from the quantity 85 resulting from the operating parameters.

[0171] Figure 7The following quantities are continuously measured and provided to the device controller:

[0172]

[0173] Figure 8 The temperature sensors 91.8a, 91.8b, 91.8c ( Figure 7 ) is an overview of the measured temperatures at three heights in a vertical pipe near the outlet measured by the temperature sensor 91.8a. The top temperature sensor 91.8a is arranged at a vertical distance of 50 mm from the bottom of the chamber. The vertical distance between adjacent sensors is 50 mm in each case. The top curve 95a represents the value measured by the top temperature sensor 91.8a, the middle curve 95b represents the value measured by the middle temperature sensor 91.8b, and the bottom curve 95c represents the value measured by the lower temperature sensor 91.8c. The measurement series involves a drying operation requiring a balanced state by the regulation of the above-mentioned control variable 82. In this case, the temperature measured by the top temperature sensor 91.8a is used as the basis for regulating the control variable 82, in particular the basis for regulating the mass flow 82.4 of the steam compressor 40, so that the transition layer is maintained at its height 84.2 by regulation. The set value is 97.0°C. Alternatively, the middle temperature sensor 91.8b or a quantity derived from the measured values ​​of multiple sensors can be used. If the corresponding temperature or the amount determined from the corresponding temperature leaves a predetermined frequency band (e.g., a control temperature of ±1 K), the speed of the steam compressor 40 is adjusted upward or downward during operation according to variant 1A or 1B. Advantageously, a PID control known per se is used for the control. For example, the values ​​P=1, I=10 and D=0 can be selected for the speed control of the steam compressor 40.

[0174] refer to Fig. 9The start-up of the device according to the invention is described, and an overview of the temperature (top, in ° C.) and the air content (bottom, in %) during the start-up of the device according to the invention is shown. The start-up is divided into three phases: the heating phase with air (phase 1), the steam filling (phase 2) and the final material filling (phase 3). The chamber temperature 96 in the upper region of the chamber, the temperature 97.2 measured by the temperature sensor 91.2 downstream of the heat exchanger 30, the temperature 97.7 measured by the temperature sensor 91.7 downstream of the steam compressor 40, the temperatures 97.8a, 97.8b, 97.8c of the three temperature sensors 91.8a, 91.8b, 91.8c in the measuring tube 63 (temperature generally decreasing downwards) are shown. The air content 98.1 in the chamber 10 measured by the lambda probe and the air content 98.2 in the condenser, which is indirectly determined from the measured pressure of the water vapor at the condensate outlet downstream of the condenser and the measured temperature, are shown in the lower region. By these measured values, in combination with the temperature measurement, the steam filling can be accurately monitored.

[0175] Steam drying is carried out in a steam atmosphere at ambient pressure, where the air content in the steam atmosphere should not be greater than 4%. Therefore, the chamber of the device must first be preheated to a temperature of at least 100°C, where there must be an air and steam atmosphere. This is achieved in three stages.

[0176] In the first stage, the device is heated by hot air. To this end, the air is circulated by a circulating fan 20, and heat is provided by a heating device 50 in the process. Fig. 9 The steam compressor 40 is started in position A of 10°C and lasts for about 1 hour. At the end of this phase, the steam compressor 40 is started in idling (short circuit) (position B) in order to also preheat, thereby avoiding large thermal stresses and condensation in the steam compressor 40 during steam filling. This phase ends when the chamber 10 reaches a temperature exceeding 100°C. Since the air is directly heated, the temperature of the circulating air in the circulation duct at this time is already far above 100°C.

[0177] After reaching a chamber temperature of 100°C, steam filling begins (position C). For this purpose, the heating device 50, the steam compressor 40 and the circulating fan 20 are turned off, and the water vapor of the water vapor generator 15 enters the chamber 10 from above. In this case, the less dense air moves downward out of the chamber 10. This becomes apparent as the temperature sensor 91.8ac at the material outlet measures an increase in the temperature 97.8ac. At the end of this phase, the steam compressor 40 is turned on again to reach the operating temperature, resulting in a brief oscillation of the temperature 97.7 (position D).

[0178] In terms of air content, the air content in the chamber initially drops suddenly due to the downward movement of the hot air, and then the temperature 97.8a...c measured by the temperature sensor 91.8a...c rises slowly. When these reach 100°C, it means that the water vapor volume has reached the mounting base. It has been found that the air can move out of the chamber from the top downward without being affected by the lighter water vapor. Finally, the steamed water vapor floats above the cold air. Although the bottom side of the chamber is open, a stable transition layer 66 is formed between the water vapor and the air, the so-called stratified layer (see Figure 2). In the area of ​​this layer, a temperature profile is established in the range of about 50cm from ambient temperature to more than 100°C. In the area where the temperature gradient is from 100°C to 65°C, the temperature gradient is typically 0.13-0.26K / mm. In this case, the air content in the chamber 10 drops to less than 4%.

[0179] Once the steam atmosphere is generated, the material can enter the device (position E). At this stage, the water vapor generator 15 still needs to generate water vapor. This is necessary because water vapor condenses on the cold material, thereby heating the cold material. Since the drying process has not yet generated enough water vapor, it must be provided by the water vapor generator 15. At this process stage, the heating device 50 and the circulation fan 20 work again. When a large part of the receiving capacity of the chamber 10 is filled with material, the steam compressor 40 is further started, whereby the condenser pressure rises (position F). As a result, the condensation temperature in the condenser increases, so that heat can be output to the water vapor circuit again (position G). If the chamber 10 is completely filled with material within the scope of its receiving capacity and a sufficient water evaporation rate has been reached, the water vapor generator 15 can be turned off and the conventional drying process is started. In this case, the air content in the chamber 10 is maintained at less than 4%. During operation according to one of the variants 2A and 2B, the water vapor generator (usually at a reduced power) continues to operate to adjust the height of the transition layer.

[0180] Since, on the one hand, the target dry matter content of the material at the outlet depends on the relative pressure and therefore on the water vapor temperature (provided that the residence time is long enough), on the other hand, heat must be continuously supplied to the process of continuous preheating of the material, the heat is supplied at high temperature before the material is supplied, while the preheating of the material entering the water vapor atmosphere is affected by the steam at low temperature.

[0181] At this stage, the condenser must be further degassed. Although the air content of the plant is low, excess air accumulates in the condenser and needs to be continuously discharged (position I). In this case, the air content on the condenser side is adjusted by the controller of the exhaust valve 32 to less than 15% by volume, in particular 7-10% by volume. The air content is determined based on the measured values ​​of the temperature sensor 91.9 and the pressure sensor 92.9.

[0182] In the drying operation, the moisture of the material to be dried is evaporated in the chamber 10 by supplying heat from the superheated steam. The steam is superheated to exceed the saturation temperature at the inlet of the chamber 10. As the material to be dried passes through, the heat energy of the steam is transferred to the material and additional water evaporates.

[0183] At the outlet of the chamber 10, the water vapor mass flow increases as water evaporates from the material. The temperature in this case decreases depending on the dry matter content of the material or the state of the adsorption isotherm and the degree of heat transfer to the material, so that the water vapor remains superheated.

[0184] The main part of the loop steam then enters the heat exchanger 30 and is superheated again on the other side of said heat exchanger 30 by condensation of the higher temperature steam compression steam.

[0185] After the heat exchanger 30 is overheated, the heat loss is compensated by the heating device 50. Thus, the drying temperature and the desired dry matter content at the outlet can also be set accurately and quickly. Typically, a water vapor temperature of 140 to 170°C is very suitable for drying, while the material temperature is usually 105 to 130°C, depending on the adsorption isotherm.

[0186] After the water vapor leaves the drying chamber, part of the additional water vapor is withdrawn from the circuit and compressed to about 2.5 to 5 bar at atmospheric pressure by a steam compressor 40. Depending on the pressure in the condenser, the vapor is condensed at a saturation temperature of 130° C. to 150° C. In the process, the enthalpy of evaporation released during the condensation is returned to the water vapor circuit via a heat exchanger at an elevated temperature.

[0187] Demineralized sterile water above 100°C leaves the system through the condensate drain valve 31, retaining the loop water vapor. Finally, the 100°C water can be used for preheating, or to replace tap water.

[0188] During the drying process, the material to be dried or already dried is continuously introduced or discharged, wherein in each case the material is guided through the stratified layers and, on discharge into the ambient air, is re-dried due to the lower partial pressure of water vapor in the ambient air and the residual heat in the material to be dried. If the material flow rate increases, the compressed first part supplied to the heat exchanger must be increased accordingly. This works properly as long as the power of the circulation fan is sufficient to return the heat. It has been found that within this framework, the efficiency of the process even increases if the material flow rate increases.

[0189] Within the scope of the third embodiment, when the device is started, the steam atmosphere is mainly formed by the following steps:

[0190] 1. Air replacement by water vapor from a water vapor generator;

[0191] 2. Introduce the material to be dried;

[0192] 3. Start the steam compressor (drying process begins);

[0193] 4. After the operating pressure has been reached in the heat exchanger, the steam generator continues to operate with a reduced volume flow (and is regulated as described above).

[0194] The invention is not limited to the embodiments shown. In particular, the dimensions of the individual devices and the conveying systems used can be adapted to the type and amount of material to be dried.

[0195] The material can be introduced directly from a preceding process into the steam atmosphere. In addition, the material can be preheated before being introduced into the device. Thus, in particular, the amount of water vapor available for steam compression is increased. If waste heat, for example from upstream or downstream process steps, is available, this waste heat can be easily supplied to the device according to the invention, so that the energy requirement for the heating device can be reduced.

[0196] In summary, it should be noted that the present invention provides a method for operating a device for drying material to be dried by means of superheated water steam and a corresponding device which enable high energy efficiency with simple material supply and removal.

Claims

1. A method of operating an apparatus for drying a material to be dried using superheated steam, characterized in that: The device comprises: a) a chamber opened downward, the chamber having an inlet for the material to be dried, an outlet for the dried material, an inlet for superheated water steam and an outlet for the steam; b) a conveying system for introducing the material to be dried into the chamber, conveying the material to be dried in the chamber, and discharging the dried material from the chamber during the drying process; c) a steam compressor for compressing a first portion of said steam recirculated from said chamber; and d) a heat exchanger for transferring heat from the compressed first part by condensing the volume flow of the compressed first part; The device operates in the following manner: e) forming a steam atmosphere in an upper region of the chamber, the steam atmosphere floating on ambient air in a lower region of the chamber, wherein a transition layer is formed between the upper region and the lower region; and f) maintaining the height of the transition layer within a predetermined range by determining the current height, and according to the determined height: f1) regulating the volume flow of the compressed first portion supplied to the heat exchanger; or f2) regulating a volume flow of a water steam generator, wherein the water steam generator is arranged and operated such that water steam can be supplied to the chamber and / or water steam can be generated in the chamber.

2. The method according to claim 1, characterized in that The current height of the transition layer is determined based on a measurement value of at least one temperature sensor, wherein the at least one temperature sensor is arranged within a height range corresponding to the predetermined range.

3. The method according to claim 1 or 2, characterized in that: The drying temperature is maintained within a predetermined range by comparing the drying temperature with a set value, and based on the comparison: g1) regulating a volume flow of a water steam generator, wherein the water steam generator is arranged and operated so that water steam can be supplied to the chamber and / or water steam can be generated in the chamber, provided that the height of the transition layer is kept within the predetermined range by regulating the volume flow of the compressed first part supplied to the heat exchanger; or g2) adjusting the heating power of the heating device; or g3) regulating the volume flow of the compressed first part supplied to the heat exchanger, provided that the height of the transition layer is maintained within the predetermined range by regulating the volume flow of the steam generator.

4. The method according to any one of claims 1 to 3, characterized in that The device comprises a piping system between the outlet of the steam and the inlet of the superheated steam, wherein the piping system is arranged with: h) the steam compressor; i) Circulation fan; j) said heat exchanger for transferring heat from said compressed first portion by condensing said volume flow of said compressed first portion supplied to said heat exchanger for heating a second portion of said steam recirculated from said chamber; and k) A heating device for the water vapor, arranged between the heat exchanger and the inlet of the superheated water vapor.

5. The method according to any one of claims 1 to 3, characterized in that The conveying system has a rotating hollow shaft, which is arranged in the chamber and has a plurality of disks and forms the heat exchanger, wherein a cavity is arranged inside the hollow shaft, and the steam compressor can supply the volume flow of the compressed first part of the steam to the cavity for heating the disks.

6. The method according to any one of claims 1 to 5, characterized in that The heat exchanger has an exhaust valve on the condenser side, and the opening degree of the exhaust valve is adjusted based on the air content determined on the condenser side.

7. The method according to claim 6, characterized in that The air content on the condenser side is adjusted to 0-50%, preferably 5-20%, particularly preferably 7-12%.

8. The method according to claim 4, characterized in that The following steps are performed to form a steam atmosphere in the upper region of the chamber: - generating water vapor in a water vapor generator and introducing the generated water vapor into the chamber, wherein the air located in the chamber moves downwardly out of the chamber; During operation of the steam generator, until the operating pressure is reached in the heat exchanger: - starting the circulation fan; - starting the heating device and / or the steam compressor; - introducing the material to be dried through the conveying system; and - Starting the steam compressor.

9. An apparatus for drying materials to be dried using superheated steam, characterized in that: include: a) a chamber opened downward, the chamber having an inlet for the material to be dried, an outlet for the dried material, an inlet for superheated water steam and an outlet for the steam; b) a conveying system for introducing the material to be dried into the chamber, conveying the material to be dried in the chamber, and discharging the dried material from the chamber during the drying process; c) a steam compressor for compressing a first portion of said steam recirculated from said chamber; d) a heat exchanger for transferring heat from the compressed first portion by condensing the volume flow of the compressed first portion; and e) a controller for acquiring and processing the measured values ​​and for generating control signals; The controller can be operated in the following manner: f) forming an atmosphere of superheated water vapor in the upper region of the chamber, the atmosphere floating on the surrounding air in the lower region of the chamber, wherein a transition layer is formed between the upper region and the lower region; g) maintaining the height of the transition layer within a predetermined range by determining the current height, and according to the determined height: g1) regulating the volume flow of the compressed first portion supplied to the heat exchanger; or g2) regulating a volume flow of a water steam generator, wherein the water steam generator is arranged and operated in such a way that water steam is supplied to the chamber and / or water steam is generated in the chamber.

10. The device according to claim 9, characterized in that The device comprises a piping system between the outlet of the steam and the inlet of the superheated steam, wherein the piping system is arranged with: h) the steam compressor; i) Circulation fan; j) said heat exchanger for transferring heat from said compressed first portion by condensing said volume flow of said compressed first portion supplied to said heat exchanger, thereby heating a second portion of said steam recirculated from said chamber; and k) A heating device for the water vapor, arranged between the heat exchanger and the inlet of the superheated water vapor.

11. The device according to claim 10, characterized in that The inlet of the superheated water steam is arranged on the chamber so that the superheated water steam in the directional steam flow intersects with the conveying path of the material to be dried in the chamber.

12. The device according to claim 11, characterized in that Elements for homogenizing the steam flow are arranged on the chamber side of the inlet.

13. The device according to claim 9, characterized in that The conveying system has a rotating hollow shaft, which is arranged in the chamber and has a plurality of disks and forms the heat exchanger, wherein a cavity is arranged inside the hollow shaft, and the steam compressor can supply the volume flow of the compressed first part of the steam to the cavity for heating the disks.

14. The device according to any one of claims 9 to 13, characterized in that The water steam generator is arranged and operated such that water steam is supplied to the chamber and / or water steam is generated in the chamber.

15. The device according to claim 14, characterized in that The water steam generator is connected to the heat exchanger in such a way that the water steam generator can be operated at least partially with condensate from the heat exchanger.

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