Systems and methods for drying liquid or solid substances

Abstract

A system and method for drying liquid or solid substances. The system comprises a drying apparatus for removing water from a substance to be dried by evaporation, a moisture collection system for absorbing the product moisture into a liquid absorbent, and a liquid absorbent drying apparatus for separating and discharging the absorbed product moisture from the liquid absorbent. The drying system is near-insulated because the temperature of the substance to be dried and the removed water are the same before and after the drying process, and the physical state of the removed water is the same before and after the drying process. The system further avoids the discharge of moist air from the enclosure of the drying apparatus.

Description

Technical Field

[0001] The present invention relates to a system and method for drying liquid or solid substances, such as food, chemicals, agricultural products, paper, and wood.

Background Art

[0002] The drying process typically involves the removal of water from a liquid or solid substance by evaporation of water, for example, to adapt the consistency of the product or to extend its shelf life. The drying process can be carried out, for example, inside a belt dryer, a fluidized bed dryer, on a cylindrical drum, inside a screw conveyor, or inside a spray dryer. After removal, the evaporated product moisture is usually dissolved in an excess amount of air that is high enough to achieve a sufficiently low relative humidity for the drying process. The air, dissolved product moisture, and optionally other volatile and odor components are usually discharged directly to the atmosphere from the enclosure of the dryer or indirectly via an air treatment system if necessary. The energy consumption of the dryer consists of various contributions such as sensible heat to the drying temperature of the incoming substance, latent heat for the evaporation of the product moisture, heating of the fresh air supply, and heat insulation losses. This energy can be supplied by convective heat transfer from relatively warm drying air to the substance being dried, by radiation from an infrared heating device or a burner, by microwave heating, and / or by conduction from a heated drum or a heated closed conveyor belt transporting the dried product. The total amount of energy for the drying process is typically in the range of 1.2 to 2.5 times the latent heat for the evaporation of the product moisture (typically 2258 kJ / kg). Thus, the drying process typically requires 2700 to 5600 kJ of energy per kg of evaporated water and is therefore known as an energy-intensive process, on the one hand, due to the high latent heat for evaporating the product moisture and, on the other hand, due to the usually significant losses associated with the discharge of relatively warm moist air.

[0003] Various attempts have been made to reduce the energy demands of the drying process. Quijano et al. [Reference 1] describe, for example, a spray drying process in which moist air discharged from the drying process is dehumidified and reused for the drying process, i.e., in a closed loop, avoiding energy losses associated with the discharge of warm air. Air dehumidification is performed inside a column in which the air is in direct contact with a hygroscopic liquid absorbent that absorbs product moisture from the air. The diluted liquid absorbent is then heated to 400°C inside a regenerator, a temperature high enough to boil the dissolved product moisture and produce steam that can be recovered elsewhere. A drawback of this method is that a suitable combination of high-temperature resistant liquid absorbent and corrosion-resistant constituent materials for the regenerator has not been found. Ko et al. [Reference 2] describe a batch drying process involving dry air in a closed loop, reuse of a liquid absorbent that absorbs product moisture from the dry air for a certain period, and a subsequent regeneration step of the liquid absorbent in a separate loop in which the liquid absorbent is heated to a sufficiently high temperature to discharge the absorbed moisture again by evaporation.

[0004] Both methods described require a heating step of the diluted liquid absorbent to evaporate the product moisture from the liquid absorbent. Therefore, the theoretical minimum energy requirement for these optimized drying processes is at least equal to the latent heat for evaporation of product moisture plus the enthalpy of dissolution, i.e., the bond energy between water and the absorbent salt, together typically at least 2500 kJ per kg of product moisture removed. This is still quite high, considering the fact that the specific energies of water and the drying liquid or solid substance do not change significantly when water is mixed with (or dissolved in) this liquid or solid substance, respectively. Similarly, a drying process that essentially means separating water from a substance should also require no significant amount of energy, provided that the temperature of the substance being dried and the removed water are the same before and after the drying process, the physical state of the removed water is the same as that of the product being dried, i.e., the liquid, and no warm, humid air is discharged into the environment from the drying process enclosure.

[0005] Other examples of drying systems are known from CN111947443, CN212362660U, and FR939336. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The objective is to provide a drying system and / or method for drying liquid or solid substances that eliminates, or at least reduces, the aforementioned drawbacks. More generally, the objective is to provide an energy-efficient drying system and / or method for drying liquid or solid substances without discharging moist, foul-smelling air into the environment. In this specification, drying can also be defined as dehumidification, and vice versa. [Means for solving the problem]

[0007] The present invention is defined by the claims. According to a first aspect, a product drying system, - A product drying apparatus comprising a product inlet for receiving a wet product, wherein the product drying apparatus is configured to remove moisture from the received wet product by evaporation, and the product drying apparatus comprises a product outlet for discharging the dried product and a first moisture outlet for discharging the evaporated product moisture, - A moisture collection system comprising a moisture inlet for receiving product moisture from a product drying apparatus and a liquid absorbent inlet for receiving a concentrated liquid absorbent, wherein the moisture collection system has a control device configured to absorb product moisture into the liquid absorbent, specifically to generate a diluted liquid absorbent, - A liquid absorbent drying apparatus configured to receive a diluted liquid absorbent from a moisture collection system and separate the absorbed moisture from the liquid absorbent, wherein the liquid absorbent drying apparatus includes a second moisture outlet for discharging the separated moisture into the environment, and the liquid absorbent drying apparatus is preferably configured to discharge the product moisture in a liquid state to, for example, a drain, The product drying system is -The product drying apparatus, moisture collection system, and liquid absorbent drying apparatus are arranged relative to each other to provide near-thermal drying of the product. and / or A product drying system is provided, wherein the product drying system has a fluid sealing system boundary surrounding each of the product drying apparatus, a moisture collection system, and a liquid absorbent drying apparatus, and the fluid sealing system boundary is configured to intersect only by the product inlet of the product drying apparatus, the product outlet of the product drying apparatus, the moisture outlet of the liquid absorbent drying apparatus, and an optional outlet of the vacuum pump of the liquid absorbent drying apparatus.

[0008] In this way, it has been found that an energy-efficient drying system for drying products can be achieved, specifically without releasing humid, foul-smelling air into the environment. Specifically, the system boundary can be a sealed (e.g., gas-sealed) enclosure or housing (e.g., defined by its respective closed outer wall), as understood by those skilled in the art.

[0009] The fluid-sealed system boundary specifically does not include any gas inlets or outlets. One or more gas lines (if any), for example, one or more gas ducts for transporting heated gas or heated air (if any), and / or one or more vapor ducts for transporting evaporated moisture (vapor), are located only within the enclosure of the system boundary. In a preferred embodiment, the moisture collection system includes a diluent liquid absorbent outlet for discharging the diluent absorbent.

[0010] Therefore, during operation, the system preferably does not emit any gas or gas mixture.

[0011] According to the embodiment, a near-insulating drying system for dehumidifying liquid or solid substances, - A product drying apparatus for removing moisture from the substance to be dried, - A moisture collection system for collecting product moisture and transferring the collected product moisture to a liquid absorbent, - A near-insulating drying system can be provided, comprising a liquid absorbent drying system for separating the collected product moisture from the liquid absorbent and discharging this liquid moisture.

[0012] According to one embodiment, the system comprises a drying device for removing water from a substance to be dried by evaporation, a moisture collection system for absorbing the resulting moisture into a liquid absorbent, and a liquid absorbent drying device for separating and discharging the absorbed resulting moisture from the liquid absorbent.

[0013] During operation, the product drying system preferably receives the wet product through the product inlet at a specific product temperature, and the product drying system preferably discharges the removed water (in a liquid state) through a second water outlet so that the discharged water has substantially the same temperature as the product temperature.

[0014] The system preferably further avoids the discharge of moist air from the enclosure of the drying device.

[0015] For example, product drying equipment can include belt dryers, fluidized bed dryers, cylindrical drum dryers, screw conveyor dryers, or spray dryers.

[0016] According to the embodiment, the entire system is envisioned to have an enclosure (i.e., the system boundary) comprising a product inlet for supplying the material to be dried and a product outlet for discharging the dried material. During system operation, moisture dissolved in the material to be dried is at least partially evaporated inside the enclosure (i.e., the system boundary), and the resulting vapor can then be dissolved and diluted, for example, in a certain amount of air present inside the enclosure to achieve a sufficiently low relative humidity in this moist gas for the drying process, to form a moisture-containing gas mixture. The moist gas can be discharged from the drying apparatus (e.g., from the enclosure of the drying apparatus), and a similar amount of fresh, dry air can be supplied to the drying apparatus enclosure (specifically, the dry air is generated inside the system boundary).

[0017] It should be noted that air is not required for drying the product (by a drying apparatus). Specifically, in drying processes at relatively high temperatures, usually above 100°C, the evaporated product moisture can not be diluted in the air. A wet gas is formed only when product moisture is present and is discharged directly from the drying apparatus to a downstream moisture collection system. These processes also do not require any supply of fresh air to the drying apparatus (e.g., to the drying apparatus enclosure).

[0018] Specifically, the present invention provides a product drying system and method comprising the adiabatic chemical absorption of product moisture by a liquid absorbent and the near-adiabatic removal of moisture from the liquid absorbent. More specifically, the present invention provides a near-adiabatic system and method for drying liquid or solid substances. Specifically, aspects of the present invention provide a closed feature of the drying process that avoids the discharge of damp, odorous air into the environment.

[0019] For example, a moisture collection system may include a control device configured to absorb the generated moisture vapor into a liquid absorbent. The liquid absorbent may be, for example, a concentrated salt solution of lithium chloride, calcium chloride, and / or lithium bromide in water, as will be apparent to those skilled in the art.

[0020] The wet gas outlet of the product drying apparatus can be connected to the wet gas inlet of the control apparatus. During operation, the wet gas can be brought into contact with a liquid absorbent inside the enclosure of the control apparatus, thereby absorbing the moisture from the wet gas.

[0021] According to the embodiment, the control device may include a dry air outlet for discharging any remaining air after at least a portion of the dissolved moisture has been transferred to the liquid absorbent. This dry air is then preferably returned to the product dryer, for example, through a dry air inlet on the enclosure (e.g., housing) of the dryer.

[0022] The regulating device can include, for example, a packed tower to enlarge the surface of the moisture exchange interface between the wet gas and the receiving liquid absorbent. Specifically, it is assumed that the regulating device is provided with a liquid absorbent outlet for discharging the diluted liquid absorbent containing dissolved product moisture to a liquid absorbent drying device. It can also be assumed that the regulating device is provided with a liquid absorbent inlet for returning the concentrated liquid absorbent from the liquid absorbent drying device after removing at least a part of the dissolved product moisture from the liquid absorbent. The moisture collection system can further include means for transferring energy from the diluted liquid absorbent to the dry air (if present).

[0023] The liquid absorbent drying system is preferably configured to evaporate the product moisture absorbed by the liquid absorbent into evaporated moisture from the liquid absorbent. The liquid absorbent drying system can include one or more liquid absorbent spraying devices and a packed tower to enlarge the moisture release surface area of the diluted liquid absorbent where the dissolved product moisture can evaporate.

[0024] The liquid absorbent drying system preferably includes a condensing device configured to condense the evaporated moisture. The condensing device can include a surface area for condensing the product moisture, for example, the surface area provided by the surface of at least one heat transfer tube and / or one heat transfer plate.

[0025] The condensing device can also include a condensate pan for collecting the condensed product moisture discharged from the condensing surface. This condensate pan can be connected to the condensate outlet of the liquid absorbent drying system.

[0026] The liquid absorbent drying system preferably includes a heat transfer medium flow circuit arranged such that the heat removed from the evaporated moisture during its condensation in the condensing device is absorbed by the heat transfer medium, and the absorbed heat is used for the evaporation of the moisture absorbed from the liquid absorbent.

[0027] According to the embodiment, the temperature, volume, and / or pressure of one or more fluids in the liquid absorbent drying system can be selected so that absorbed moisture evaporates from the liquid absorbent in the liquid absorbent drying system, and / or the evaporated moisture condenses on the condensation surface of each condenser. The temperature, volume, and / or pressure of the heat transfer fluid in the heat transfer medium flow circuit (if present) can be selected so that the heat transfer medium condenses indirectly with respect to the diluted liquid absorbent in the heat exchanger, and / or the heat transfer medium evaporates in the condenser. The heat transfer medium flow circuit preferably includes a compressor (e.g., at least downstream of the condenser, e.g., one cooling tube and / or cooling plate) arranged to increase the pressure of the heat transfer medium to the internal pressure of the heat exchanger.

[0028] Optionally, the first heat exchanger is installed at the outlet of the dilution liquid absorbent of the moisture collection system (i.e., the outlet of the dilution liquid absorbent of the moisture collection system may include the first heat exchanger).

[0029] Optionally, a second heat exchanger is installed at the dry air outlet of the moisture collection system (if any) (i.e., the dry air outlet may include the second heat exchanger).

[0030] Optionally, the heat exchanger at the outlet of the diluted liquid absorbent in the moisture collection system is connected to the heat exchanger at the outlet of the dry air in the moisture collection system to exchange energy (i.e., heat) between the diluted liquid absorbent (flowing along or through the first heat exchanger during operation) and the dry air (flowing through or along the second heat exchanger during operation).

[0031] Optionally, the (second) heat exchanger installed at the dry air outlet of the moisture collection system is located inside the enclosure of the product dryer.

[0032] Furthermore, aspects of the present invention provide a method characterized by the features of claim 16. In this way, the above-mentioned advantages can be achieved.

[0033] Specifically, according to the embodiments, a method is provided for near-thermal drying of liquid or solid substances such as food, chemicals, agricultural products, paper, and wood. This method includes removing product moisture from a liquid solid substance by evaporation of the moisture. The method further includes absorbing the moisture removed from the product into a liquid absorbent, i.e., preferably, for example, a concentrated salt solution of lithium chloride, calcium chloride, and / or lithium bromide in water. The method includes separating the absorbed product moisture from the liquid absorbent by evaporation of the product moisture (by a liquid absorbent drying apparatus).

[0034] Specifically, this method involves concentrating the evaporated product moisture (specifically by a liquid absorbent drying apparatus), and the heat released during the concentration of the evaporated moisture is preferably absorbed by a heat transfer medium, and the absorbed heat is preferably used for the evaporation of the absorbed product moisture from the liquid absorbent. Therefore, the energy required to dehumidify the liquid absorbent, that is, to remove the product moisture absorbed by evaporation, can be minimized by reusing the energy released by the condensation of the product moisture vapor.

[0035] Optionally, this method further includes heat exchange from the diluted liquid absorbent to dry air (if present). Optionally, this heat exchange takes place inside the enclosure of the product drying apparatus.

[0036] It will be understood that any of the embodiments, features, and options described in consideration of a (near-thermal) product drying system are equally applicable to methods for (near-thermal) product drying, and vice versa. It will also be clear that one or more of the above embodiments, features, and options can be combined. In the drawings, similar or corresponding features are indicated by similar or corresponding reference numerals. [Brief explanation of the drawing]

[0037] Non-limiting embodiments of the present invention are described in detail with reference to the accompanying drawings.

[0038] [Figure 1] This diagram shows the current state of affairs in this field, system boundaries, and a typical drying system for liquid or solid substances, following the flow that crosses these system boundaries. [Figure 2] Examples of external boundaries and functional elements within a near-insulated drying system for drying liquid or solid substances are shown, along with schematic diagrams of the flow intersecting each element boundary. [Figure 3] A schematic diagram illustrating the operating principle of a further embodiment of a near-insulated drying system combined with a belt-type product drying apparatus is shown. [Figure 4A] The drying apparatus portion of the embodiment shown in Figure 3 is shown in more detail. [Figure 4B] The moisture collection system of the embodiment shown in Figure 3 is illustrated in more detail. [Figure 4C] The absorbent drying system of the embodiment shown in Figure 3 is shown in more detail. [Modes for carrying out the invention]

[0039] Figure 1 illustrates an example of a drying system in accordance with the current state of the art, which has some drawbacks that the present invention seeks to mitigate. The system comprises elements within an external boundary 1, such as an enclosure 2 having a feed opening 3 for supplying the wet product 4 to be dried, and a discharge opening 5 for discharging the dried product 6. The enclosure 2 may also be assumed to have an air feed opening 6A for supplying air 7, and a discharge opening 8 for discharging a product moisture-containing gas 9. This wet gas 9 consists of a mixture of evaporated product moisture 10 and the supplied air 7. It is also possible that no fresh air is supplied to the enclosure 2. In that case, the wet gas 9 consists only of product moisture 10. Drying of the product is carried out by evaporation of product moisture 10 from the interfacial product surface 11. The latent heat for the evaporation of product moisture can be supplied to the product surface 11 by convection, i.e., heat transferred from the airflow 7. In this case, the airflow 7 is first brought to a sufficiently high temperature inside the heat exchanger 12 by means of an energy source 13, such as electricity, steam, hot water, or hot oil. The heat exchanger 12 can be located outside or inside the enclosure 2. Alternatively, the latent heat for the evaporation of product moisture can be supplied by conduction, by direct contact between the product and a relatively high-temperature surface below it (i.e., a heated surface, a heated support surface). In this case, the heat exchanger 12 can be part of a transport device that transports the product through a drying apparatus, such as a cylindrical internal heating drum or a transport belt with a heat supply below. Another option for heat supply is radiation from a gas combustion or electrically heated radiating surface located inside the enclosure 2.

[0040] The driving force for moisture transfer from the product surface 11 to the receiving gas 14 is the positive difference in the partial pressure of moisture within the product surface 11 and the receiving gas 14. This positive difference is usually maintained by minimizing the partial vapor pressure of the receiving gas 14 to a value sufficiently lower than the partial vapor pressure of the evaporated product surface 11. This can be achieved by two measures, namely, by increasing the mass ratio of the fresh air supply 15 to the recirculated air 16 by adjusting the flow rates of the exhaust fan 17 and the recirculation fan 18, thereby reducing the moisture concentration in the receiving gas, or by increasing the temperature of the supplied air 7 in the drying process, or by a combination thereof. The energy required for the drying process usually consists of two main components: the latent heat for the evaporation of product moisture, and the sensible heat associated with heating the fresh air supply 15 from the inlet temperature of the flow 15 to the outlet temperature of the flow 19. The thermal energy consumption of the drying process typically reaches 1.2 to 2.5 times the latent heat of evaporation for product moisture alone (2258 kJ / kg), i.e., 2700 to 5600 kJ per kg of evaporated water. This thermal energy demand is supplied by a heating circuit 13 via a heating device 12. The drying process also typically involves discharging humid, foul-smelling air 19 into the environment 20, which can cause nuisance to neighbors.

[0041] For example, various attempts to reduce the energy requirements of the drying process have been described in the literature, such as transferring moisture from the exhaust gas 19 to a liquid absorbent, and thus reusing the dehumidified gas as fresh replenishment in a closed loop toward the inlet 15. This measure can reduce the energy loss associated with the net heating of fresh air and the emission of odors from the drying process into the environment, but what remains is a considerable amount of energy for the evaporation of the product moisture.

[0042] The specific energy of water and a liquid or solid substance does not change significantly when water is mixed with (or dissolved in) a liquid or solid substance. Similarly, a drying process that essentially means (partially) separating water from a liquid or solid substance does not require a considerable amount of energy if the following conditions are met: the temperature of the substance being dried and the removed water are the same before and after the drying process, and the physical state of the removed water after the drying process is the same as before, i.e., it is liquid, and no warm, humid air is discharged into the environment from the drying process enclosure.

[0043] Figure 2 shows an overview of the main components of a drying system and their interconnections according to a non-limiting embodiment of the present invention that satisfies these requirements.

[0044] Specifically, Figure 2 shows a product drying system comprising a product dryer 22 including a product inlet for receiving wet products. The product dryer 22 is configured to remove moisture from the received wet products by evaporation and includes a product outlet for discharging dried products and a first moisture outlet for discharging evaporated product moisture. The product dryer 22 can be installed, for example, inside each dryer enclosure 2 (e.g., a housing or similar), or each dryer enclosure 2 may be provided.

[0045] The system includes a moisture collection system 23, which includes a moisture inlet for receiving product moisture from the product drying apparatus 22 and a liquid absorbent inlet for receiving a concentrated liquid absorbent. The moisture collection system has a control device 28 configured to allow the product moisture to be absorbed by the liquid absorbent, specifically to produce a diluted liquid absorbent.

[0046] Furthermore, the system includes a liquid absorbent dryer 24 configured to receive a diluted liquid absorbent from a moisture collection system 23 and separate the absorbed moisture from the liquid absorbent. The liquid absorbent dryer 24 includes a second moisture outlet 58 for discharging the separated moisture into the environment. Preferably, the liquid absorbent dryer 24 is configured to discharge the productive moisture in the liquid state 25 to, for example, a drain.

[0047] As described below, the product drying systems 22, 23, and 24 are: The product drying apparatus 22, the moisture collection system 23, and the liquid absorbent drying apparatus 24 are arranged relative to each other to provide near-thermal drying of the product, and / or The product drying system has a fluid sealing system boundary 21 surrounding each of the product drying apparatus 22, the moisture collection system 23, and the liquid absorbent drying apparatus 24, and the fluid sealing system boundary 21 is configured to intersect only at the product inlet of the product drying apparatus 22, the product outlet of the product drying apparatus 22, and the moisture outlet of the liquid absorbent drying apparatus 24.

[0048] Specifically, the near-insulated drying system comprises, within its enclosed system boundary 21, a product drying device 22 for removing moisture from the substance to be dried, a moisture collection system 23 for collecting product moisture and transferring the collected product moisture to a liquid absorbent, and an absorbent drying system 24 for removing product moisture from the liquid absorbent. A characteristic feature of this near-insulated drying system is that the system boundary 21 is intersected only by an inwardly oriented mass flow of the product 4 to be dried, an outwardly oriented mass flow of the dried product 6, and an outwardly oriented mass flow 25 of product moisture in a liquid state.

[0049] Preferably, the product dryer 22 may be a belt dryer, a fluidized bed dryer, a cylindrical drum dryer, a screw conveyor dryer, or a spray dryer. The product dryer 22 may have an enclosure 2 provided with a product inlet 3 for supplying the substance 4 to be dried and a product outlet 5 for discharging the dried substance 6. The enclosure 2 of the dryer 22 may have a wet gas outlet connection 8 for discharging wet gas 9, which may consist of product moisture 10 in pure form or product moisture dissolved in air. The dryer enclosure 2 may have an optional inlet connection 6A for supplying dry air 7 (into the interior of the dryer). The embodiment shown in Figure 2 includes several items having the same names and functions as the embodiment shown in Figure 1. These similar items are indicated by the same reference numerals. For brevity, the description of the operating principle of the embodiment shown in Figure 2 will be limited to the differences from Figure 1.

[0050] During the operation of the drying apparatus 22, the driving force for moisture transfer from the product surface 11 (of the product in the drying apparatus 22) to the receiving gas 14 (for receiving moisture) is preferably a positive difference between the partial pressure of moisture on the product surface 11 and the partial pressure in the receiving gas 14. This positive difference is preferably maintained by a downstream moisture collection system 23, which is connected to the moisture (i.e., wet gas) discharge section of the drying apparatus 22 at a connection point 26 (the connection 26 is located internally within the external boundary 21 of the system).

[0051] The moisture collection system 23 preferably includes a dry air outlet connected to the dryer 22 via a transfer point 27 (internally within the external boundary 21 of the system) to return relatively dry air 7 to the product dryer enclosure 2 (after collecting at least a portion of the product moisture 10).

[0052] It will be understood that the energy required for the drying process essentially consists of the latent heat for evaporating the product moisture, i.e., 2258 kJ of energy per kilogram of evaporated water, plus, in some cases, some energy for heating the incoming product 4 to the drying temperature. Another preferred characteristic embodiment is that this energy is provided by the moisture collection system 23 rather than via an external energy source (i.e., an energy source located outside the boundary 21). Preferably, the drying process itself is adiabatic and therefore, according to the present invention, does not involve an external thermal energy supply sourced from outside the external boundary 21.

[0053] The moisture collection system 23 preferably includes a so-called adjustment device 28 configured to absorb product moisture 10 onto the receiving interface surface 29 of the liquid absorbent, a diluted liquid absorbent outlet 30, and a concentrated liquid absorbent inlet 31. In addition, the product moisture vapor inlet 26 of the moisture collection system can be connected to the wet gas outlet 9 of the drying apparatus.

[0054] The moisture collection system 23 may also be provided with a dry air outlet 27 to return dry air 7 to the product drying apparatus enclosure 2 after transferring at least a portion of the dissolved product moisture 10 to the receiving liquid absorbent 29. Preferably, the driving force for this moisture to be transferred from the wet gas 32 to the receiving interface surface area 29 of the liquid absorbent is the positive difference between the partial pressure of moisture in the wet gas 32 and the partial pressure of moisture in the receiving liquid absorbent 29.

[0055] According to the embodiment, the liquid absorbent may include one or more salt solutions, such as a lithium chloride solution, a calcium chloride solution, and / or a lithium bromide solution. Once the chemical composition of the liquid absorbent is selected, it will be understood that the partial pressure of the latter can be reduced to a sufficiently low value by either increasing the mass fraction of the dissolved salt or by lowering the temperature of the receiving liquid absorbent.

[0056] Specifically, the absorption of product moisture 10 into the liquid absorbent 29 is an exothermic process (with heat dissipation from two sources: latent heat from the phase change of product moisture from vapor to liquid, and dissolution energy, i.e., chemical bonding energy of product moisture to salt ions). Preferably, the moisture transfer process within the moisture collection system 23 is adiabatic, i.e., there is no external energy supply or release from the external boundary 21. A preferred embodiment of a near-adiabatic drying system is that the heat generated within / released by the moisture collection system 23 is reused by the drying apparatus 22, i.e., as a heat source for the drying process 22, for example, by transferring energy to the dry air 7 flowing out from the diluting liquid absorbent 30, or, in the case of a belt drying system of a drum drying apparatus, as a direct contact conduction heat source below the surface 11.

[0057] Preferably, during operation, the moisture concentration in the liquid absorbent in the moisture collection system 23 is maintained at a constant and sufficiently low level by the downstream liquid absorbent drying system 24. The absorbent drying system 24 is preferably connected to the diluted liquid absorbent outlet of the moisture collection system via a connection point 30 (located internally within the external system boundary 21) to receive the diluted liquid absorbent. The absorbent drying system 24 is also preferably connected to the concentrated liquid absorbent inlet 31 of the moisture collection system 23 (located within the external boundary 21) to send the concentrated liquid absorbent to the moisture collection system 23.

[0058] The liquid absorbent drying system 24 is preferably configured to evaporate the product moisture 10 (absorbed by the liquid absorbent) from the liquid absorbent to become evaporated moisture, and the evaporation process is preferably carried out inside the enclosure 32 (e.g., housing) of the liquid absorbent drying system 24.

[0059] The liquid absorbent drying system 24 may include one or more liquid absorbent sprayers and packed columns to increase the interfacial surface area 33 of the diluted liquid absorbent on which the dissolved product moisture 10 can evaporate.

[0060] The liquid absorbent drying system preferably includes a condenser 34 configured to condense evaporated water and collect and discharge the formed condensate 25 into an external drain 35. As understood, during the operation of the system, the driving force for evaporating water from the diluted liquid absorbent is the positive difference between the partial pressure of water at the evaporation surface 33 of the liquid absorbent and the partial pressure of water at the condenser surface 34. The first partial pressure depends on the combination of the water activity of the liquid absorbent and its temperature at the evaporation surface 33. The latter partial pressure depends on the temperature of the condenser surface 34. The positive difference between each of these surfaces is preferably maintained by transferring the latent heat released at the condenser surface 34 to the latent heat required for evaporation at the evaporation surface 33. The remaining net heat demand, after subtracting condensation from evaporation, is the chemical bonding energy of the dissolved product water in the diluted liquid absorbent, which can potentially be recovered from the heat dissipation energy released in the water absorption process inside the control unit 28. This means that if the temperatures of the substance to be dried 4, the dried substance 6, and the removed water 25 are the same before and after the drying process, and the physical state of the removed water 25 is the same as that of the product to be dried, i.e., the liquid, then the combined process within the boundaries 21 of the entire system may require no net energy demand. In addition, the process is substantially closed off without releasing moist air or odors into the atmosphere.

[0061] Figures 3, 4A, 4B, and 4C illustrate further embodiments, including, for example, a belt drying apparatus according to the present invention. The embodiment shown in Figure 3 includes several items having the same names and functions as the embodiments shown in Figures 1 and 2. These similar items are indicated by the same reference numerals. For the sake of brevity, the description of the operating principle of the embodiment shown in Figure 3 is limited to the differences from Figure 2.

[0062] The product drying apparatus 22 may include a product conveyor 37 configured to transport the product (liquid or solid) along a product drying path between a product inlet and a product outlet. Preferably, the product conveyor 37 is configured to support the product along the product drying path.

[0063] In the embodiment shown in Figure 3, the product to be dried 4 is supplied to the drying apparatus enclosure 2 on a transport belt 37 (e.g., an open transport belt 37 or an open mesh transport belt 37) and transported through the drying apparatus enclosure 2, and the transport belt 37 also transports the dried product 6 from (outside) the drying apparatus enclosure 2. An airflow 7 from the moisture collection system 23 (see Figure 4B) can be supplied to the drying apparatus 22 (see Figure 4A) and the drying apparatus enclosure 2 via one or more inlets 6A at a relatively high temperature, for example, 50-90°C, and a relatively low absolute humidity ratio, for example, 10-20 g / kg.

[0064] In this embodiment, where the product conveyor is a belt conveyor 37 (e.g., a belt dryer), air can be transported upward through the porous product layer, thereby adiabatically taking moisture from the product and convectively transferring energy to the product. The dryer 22 is configured such that the resulting moist gas flow 9 can leave the dryer enclosure 2, for example, through one or more outlet openings 8, at a temperature in the range of 35-50°C, for example, with an elevated absolute humidity ratio of 30-50 g / kg, for example, by means of an exhaust fan 17. The resulting moist gas flow 9 can then be directly transferred to a downstream moisture collection system 23. Therefore, the combination of processes within the boundaries 22 of the dryer is preferably adiabatic, i.e., there is no external heat energy supply from any external source.

[0065] As can be seen from the drawing, from the internal connection point 26 with the moisture collection system, the wet gas flow can be divided into a portion 37 supplied to the control device 28 after being mixed with, for example, the dry air flow 38 (if present) from the exhaust fan 39 of the control device, and a portion 16 redirected toward the dryer 22. This measure allows the volumetric flow rate of air that passes through the dryer and through the product layer and is discharged from the dryer by the fan 17 to be larger (or smaller) than the flow rate from the control device and from the fan 39.

[0066] The control device 28 is preferably equipped with a spray device 46 for dividing the concentrated liquid absorbent 49 supplied on top of the packed tower 47 to increase the surface area of ​​the moisture-receiving interface of the liquid absorbent, and a demister 48 for preventing liquid absorbent droplets from being carried over to the dry air 38 from the control device and exhaust fan 39.

[0067] The system can be configured such that a moist gas flow 37 is supplied to a control device 28 below the packed column 47, and that the moist gas flow 37 flows in reverse with a moisture-receiving liquid absorbent and is transported upward through the packed column. During operation, moisture from the moist gas flow is preferably transferred to the liquid absorbent by a heat dissipation adiabatic process, thereby the released latent heat and bound energy are absorbed mainly by the diluted liquid absorbent 45 and partially by the dry air 38 (if present). In this embodiment, a preferred liquid absorbent is lithium chloride dissolved in water, supplied to the control device 28 at a concentration of, for example, about 40-44%, and the supply temperature to the control device is, for example, 20-60°C. The diluted liquid absorbent is preferably discharged after absorbing some moisture from the air flow at a concentration of, for example, 36-40%, and at a temperature of, for example, 60-130°C.

[0068] According to one aspect of the present invention, a heating device 40 and a cooling device 41 can be assumed to be located at the dilution liquid absorbent outlet 45 of the control device 28 and the drying air supply unit 7 to the drying device, respectively. The heating and cooling devices can be connected via a heat transfer loop 42 to regenerate heat from the absorption process inside the control device 28 as a heat source for the drying process inside the enclosure 2. The heat transport medium in this heat transfer loop can be a liquid such as water circulated by a liquid pump 43.

[0069] The heat transfer medium can also be a refrigerant that evaporates in a cooling device 41 (i.e., the cooling device is an evaporator) and condenses in a heating device 40 (i.e., the heating device is a condenser) at appropriately selected temperature and pressure, and is made possible by a compressor 43 (i.e., the pump is a compressor) for transporting the refrigerant gas from the lower pressure in the cooling device 41 to the higher pressure in the condenser 40, and by a throttle valve 44 for flow and pressure regulation. According to the present invention, the heating device 40 can also be located inside the enclosure 2 of the drying device. Furthermore, the latent heat for the evaporation product can be supplied by conduction, by the product coming into direct contact with a relatively hot surface below it. In that case, the heat exchanger 40 can be part of a transport device 37 that transports the product through the drying device, such as a cylindrical internal heating drum or a transport belt with a heat supply below.

[0070] Therefore, during system operation, the combination of processes within the (boundary) of the moisture collection system 23 is also preferably adiabatic, i.e., there is no external thermal energy supply from any external source supplied from the external boundary 21.

[0071] The regeneration of the liquid absorbent is preferably carried out within (or within) the liquid absorbent drying system 24 (see Figure 4C), where diluted liquid absorbent can be supplied at an internal transfer point 31 and concentrated liquid absorbent can be returned via an internal transfer point 30. Such a drying system itself, applied to an air dehumidification process, is described in International Patent Application PCT / NL2022 / 050195, which is by reference deemed to be incorporated in its entirety into this application.

[0072] The diluted liquid absorbent 45 can be supplied to the holder 32 (e.g., a container or vessel), and the liquid absorbent can be distributed, for example, by means of a spraying device 50 over a packed column 51 on the interface surface where the liquid absorbent drying process is carried out. The resulting concentrated liquid absorbent 52 can be discharged from the holder 32 of the liquid absorbent drying system 24 by means of a pump 36, preferably with respect to the portion that goes toward the transmission point 31 to the control device 28, and with respect to the portion that is returned to the inlet of the holder 32 via a throttle valve 53.

[0073] The water vapor from the liquid absorbent is preferably condensed on the outer surface of a vapor condenser 34, which may be located, for example, above the holder 32 of the liquid absorbent drying system 24. This vapor condenser 34 may comprise a bundle of multiple internal cooling tubes and / or multiple internal plates. The heat transfer medium 54, usually a refrigerant, is preferably evaporated inside the tubes and / or plates of the vapor condenser 34 so that the latent heat released by the condensation of moisture from the liquid absorbent is discharged from the condenser. The refrigerant vapor is transported from the condenser to a refrigerant compressor 55, which pressurizes it to a sufficiently high pressure so that a second phase change of the refrigerant from vapor to liquid can occur inside the heat exchanger 56. The heat exchanger 56 is preferably configured to preheat the diluted liquid absorbent before it enters the holder 32, thereby transferring energy from the moisture evaporated during condensation in the condenser 34 to the diluted liquid absorbent as an energy source for evaporating the moisture absorbed from the liquid absorbent. To reiterate, this drying process is highly energy-efficient, requiring no energy whatsoever except for a limited amount of electricity for, for example, the drive motor of the compressor 55 and the optional vacuum pump 60 (typically 5-25% or less of the energy normally required to evaporate a unit mass of water). In this embodiment, the condensate formed in the condenser 34 is collected on an inclined condensate pan 57 below the tube bundle and discharged to the condensate drain 35 via the condensate outlet pipe 58 and the condensate pump 59.

[0074] The pressure inside the holder 32 is preferably less than atmospheric pressure, specifically in the range of 20 to 200 mbar, depending on the partial pressure of the condensed water on the condenser 34. The holder can be connected to a vacuum pump 60 to achieve a pressure below atmospheric pressure. During operation, non-condensable gases can be discharged to the atmosphere (i.e., the system environment) by the vacuum pump 60. Apart from some electrical energy for the drive motor of the compressor, the combination of processes within the boundary 24 of the liquid absorbent drying system is adiabatic, i.e., there is no external heat energy supply from any external source supplied from the external boundary 21. Given the limited electrical energy for the drive motor of the compressor (and, for example, the vacuum pump), the processes within the boundary of the liquid absorbent drying process are therefore almost adiabatic, requiring only 5 to 25% of the energy normally required per unit mass of evaporated water.

[0075] Therefore, the combination of processes within boundaries 22, 23, and 24 is highly efficient, requiring only 5-25% of the energy normally needed per unit mass of evaporated water, which is substantially less than the coefficient of 1.2-2.5 normally required for drying processes.

[0076] In this specification, the present invention is described with reference to specific embodiments of the present invention. However, it will be apparent that various modifications and changes can be made herein without departing from the essence of the invention. For the purposes of clarity and concise description, features are described herein as part of the same or distinct embodiments, but alternative embodiments having all or some combinations of the features described in these distinct embodiments are also conceivable.

[0077] However, other modifications, variations, and substitutions are possible. Therefore, the specification, drawings, and examples should be considered illustrative rather than restrictive.

[0078] For the purposes of clarity and concise description, features are described herein as part of the same or distinct embodiments, but it will be understood that the scope of the invention may include embodiments having all or some combinations of the described features.

[0079] In the claims, no reference numerals enclosed in parentheses should be construed as limiting the claims. The word “equipped with” does not preclude the existence of any other features or steps not listed in the claims. Furthermore, the words “one (a)” and “one (an)” should not be limited to “only one,” but rather used to mean “at least one,” and not to exclude plurals. The mere fact that certain measures are listed in different claims does not imply that combinations of these measures cannot be used advantageously.

[0080] References [1] DP Quijano et al., Heat recovery in milk powder drying by using a liquid sorption process, Proceedings of the 12th IEA Heat Pump Conference, 2017. [2] U.S. Patent No. 4,189,848, Suk M. Ko, August 4, 1977 日 To apply

Claims

1. A product drying system, - A product drying apparatus (22) including a product inlet for receiving a wet product, wherein the product drying apparatus (22) is configured to remove moisture from the wet product received by evaporation, and the product drying apparatus (22) includes a product outlet for discharging the dried product and a first moisture outlet for discharging the evaporated product moisture, - A moisture collection system (23) comprising a moisture inlet for receiving product moisture from the product drying apparatus (22) and a liquid absorbent inlet for receiving a concentrated liquid absorbent, wherein the moisture collection system has a control device (28) configured to absorb the product moisture into the liquid absorbent, specifically to generate a diluted liquid absorbent, - A liquid absorbent drying apparatus (24) configured to receive a diluted liquid absorbent from the moisture collection system (23) and separate the absorbed moisture from the liquid absorbent, wherein the liquid absorbent drying apparatus (24) includes a second moisture outlet (58) for discharging the separated moisture into the environment, and the liquid absorbent drying apparatus (24) is preferably configured to discharge the product moisture in a liquid state (25) to, for example, a drain (35), The aforementioned product drying systems (22, 23, 24) are: - The product drying apparatus (22), the moisture collection system (23), and the liquid absorbent drying apparatus (24) are arranged relative to each other to provide near-thermal drying of the product. and / or - A product drying system having a fluid sealing system boundary (21) surrounding each of the product drying apparatus (22), the moisture collection system (23), and the liquid absorbent drying apparatus (24), wherein the fluid sealing system boundary (21) is intersected only by the product inlet of the product drying apparatus (22), the product outlet of the product drying apparatus (22), the moisture outlet of the liquid absorbent drying apparatus (24), and an optional outlet of the vacuum pump (60) of the liquid absorbent drying apparatus (24).

2. The product drying system according to claim 1, wherein the product drying apparatus (22) includes a product conveyor (37) configured to transport liquid or solid products along a product drying path between the product inlet and the product outlet, and the product conveyor (37) is preferably configured to support the products along the product drying path.

3. The product drying system according to any one of the prior claims, wherein the product drying apparatus (22) includes a belt dryer, a fluidized bed dryer, a cylindrical drum dryer, a screw conveyor dryer, or a spray dryer.

4. A product drying system according to any one of the prior claims, comprising a first heating device (40) for generating heat for the product drying device (22) for drying the wet product.

5. The product drying system according to claim 4, comprising a first heat transfer medium flow circuit (42) located downstream of the control device (28) and arranged to transfer heat from a liquid absorbent to the first heating device (40), wherein the first heat transfer medium flow circuit (42) preferably comprises a compression device (43) for compressing the heat transfer medium of the heat transfer medium flow circuit (42).

6. The product drying system according to claim 4 or 5, wherein the first heating device (40) is configured to heat a gas or gas mixture (7), such as air, for the drying of the product by the product drying device (22), and the control device of the moisture collection system preferably includes an outlet for supplying a drying gas or drying gas mixture to the first heating device (40).

7. The product drying system according to any one of the prior claims, wherein the adjusting device (28) is configured to divide the supplied concentrated liquid absorbent (49) on the packed column (47) in order to increase the surface area of ​​the moisture-receiving interface of the liquid absorbent, and the adjusting device (28) is configured to transport the supplied product moisture upward through the packed column (47) in a backflow with the liquid absorbent (49).

8. The product drying system according to any one of the prior claims, wherein the liquid absorbent drying apparatus (24) includes a condenser (34) disposed for condensing the liquid from the absorbent received from the moisture collection system (23), the condenser (34) is preferably part of a second heat transfer medium flow circuit (54, 55, 56), and the second heat transfer medium flow circuit (54, 55, 56) is preferably configured to transfer heat to dilute the liquid absorbent upstream of the condenser (34).

9. The product drying system according to claim 8, wherein the liquid absorbent drying apparatus (24) includes a condensate collector, for example, a condensate pan (57), disposed below the condensing apparatus (34) for collecting the condensed liquid and sending the liquid to the second moisture outlet (58).

10. The product drying system according to any one of the prior claims, wherein the liquid absorbent drying apparatus (24) includes a holder (32), the holder (32) comprises a packed column (51) for receiving the liquid absorbent to be dried, and the liquid absorbent drying apparatus (24) is preferably configured to maintain the pressure inside the holder (32) at a pressure below atmospheric pressure, for example, in the range of 20 to 200 mbar.

11. The product drying system according to any one of the prior claims, wherein the system boundary is a sealed, for example, gas-sealed enclosure or housing defined by the respective closed outer walls of the system.

12. The product drying system according to any one of the prior claims, wherein the system boundary (21) is configured such that it is intersected only by an inwardly oriented mass flow of the product to be dried (4), an outwardly oriented mass flow of the dried product (6), and an outwardly oriented mass flow (25) of the product moisture in the liquid state.

13. The product drying system according to any one of the prior claims, wherein the system is configured such that the heat generated inside or by the moisture collection system (23) is reused by the product drying apparatus (22).

14. Product drying system, for example, the system described in any one of the prior claims, - A product drying apparatus (22) including a product inlet for receiving a wet product, wherein the product drying apparatus (22) is configured to remove moisture from the wet product received by evaporation, and the product drying apparatus (22) includes a product outlet for discharging the dried product and a first moisture outlet for discharging the evaporated product moisture, - A moisture collection system (23) comprising a moisture inlet for receiving product moisture from the product drying apparatus (22) and a liquid absorbent inlet for receiving a concentrated liquid absorbent, wherein the moisture collection system has a control device (28) configured to absorb the product moisture into the liquid absorbent, specifically to generate a diluted liquid absorbent, - A liquid absorbent drying apparatus (24) configured to receive a diluted liquid absorbent from the moisture collection system (23) and separate the absorbed moisture from the liquid absorbent, wherein the liquid absorbent drying apparatus (24) includes a second moisture outlet (58) for discharging the separated moisture into the environment, and the liquid absorbent drying apparatus (24) is preferably configured to discharge the product moisture in a liquid state (25) to, for example, a drain (35), The product drying system (22, 23, 24) has a fluid-sealed system boundary (21) surrounding each of the product drying apparatus (22), the moisture collection system (23), and the liquid absorbent drying apparatus (24), wherein the system boundary is a sealed, for example, gas-sealed enclosure or housing defined by the closed outer walls of each of the systems.

15. Product drying system, for example, the system described in any one of the prior claims, the system is - A product drying apparatus (22) including a product inlet for receiving a wet product, wherein the product drying apparatus (22) is configured to remove moisture from the wet product received by evaporation, and the product drying apparatus (22) includes a product outlet for discharging the dried product and a first moisture outlet for discharging the evaporated product moisture, - A moisture collection system (23) comprising a moisture inlet for receiving product moisture from the product drying apparatus (22) and a liquid absorbent inlet for receiving a concentrated liquid absorbent, wherein the moisture collection system has a control device (28) configured to absorb the product moisture into the liquid absorbent, specifically to generate a diluted liquid absorbent, - A liquid absorbent drying apparatus (24) configured to receive a diluted liquid absorbent from the moisture collection system (23) and separate the absorbed moisture from the liquid absorbent, wherein the liquid absorbent drying apparatus (24) includes a second moisture outlet (58) for discharging the separated moisture into the environment, and the liquid absorbent drying apparatus (24) is preferably configured to discharge the product moisture in a liquid state (25) to, for example, a drain (35), The product drying system includes a first heating device (40) for generating heat for the product drying apparatus (22) for drying the wet product. The system includes a first heat transfer medium flow circuit (42) located downstream of the regulating device (28) and arranged to transfer heat from the liquid absorbent to the first heating device (40), wherein the first heat transfer medium flow circuit (42) preferably includes a compression device (43) for compressing the heat transfer medium in the heat transfer medium flow circuit (42). The liquid absorbent drying apparatus (24) includes a condenser (34) provided for condensing the liquid from the absorbent received from the moisture collection system (23), the condenser (34) being part of a second heat transfer medium flow circuit (54, 55, 56), the second heat transfer medium flow circuit (54, 55, 56) preferably configured to transfer heat to dilute the liquid absorbent upstream of the condenser (34). The aforementioned product drying systems (22, 23, 24) are: - The product drying apparatus (22), the moisture collection system (23), and the liquid absorbent drying apparatus (24) are arranged relative to each other to provide near-thermal drying of the product. and / or - A product drying system having a fluid sealing system boundary (21) surrounding each of the product drying apparatus (22), the moisture collection system (23), and the liquid absorbent drying apparatus (24), wherein the fluid sealing system boundary (21) is intersected only by the product inlet of the product drying apparatus (22), the product outlet of the product drying apparatus (22), the moisture outlet of the liquid absorbent drying apparatus (24), and an optional outlet of the vacuum pump (60) of the liquid absorbent drying apparatus (24).

16. For example, a method for drying a wet product using a system described in any one of the prior claims, wherein the method is: - The process involves sending the wet product to the product drying apparatus (22), the product drying apparatus (22) removing moisture from the received wet product by evaporation, discharging the dried product, and the product drying apparatus (22) discharging the evaporated product moisture to the moisture collection system (23). - The adjustment device (28) of the moisture collection system (23) absorbs the generated moisture into the liquid absorbent, thereby specifically generating and absorbing the diluted liquid absorbent. - Includes separating the absorbed moisture from the liquid absorbent using a liquid absorbent drying apparatus (24), The liquid absorbent drying apparatus (24) discharges the separated moisture into an environment in a liquid state (25), for example, into a drain (35). The aforementioned method, - Near-thermal drying of the product is achieved, and / or - A method in which a fluid sealing system boundary (21) is utilized, and the fluid sealing system boundary (21) encloses each of the product dryer (22), the moisture collection system (23), and the liquid absorbent dryer (24), and the fluid sealing system boundary (21) is intersected only by the product inlet of the product dryer (22), the product outlet of the product dryer (22), the moisture outlet of the liquid absorbent dryer (24), and the outlet of the vacuum pump (60) of the liquid absorbent dryer (24).

17. The method according to claim 16, wherein the heat is released inside the moisture collection system (23), and the heat is reused by the product dryer (22) as a heat source for the drying process, or as a direct contact conductive heat source for and / or below the surface (11) of the product conveyor (37) of the product dryer (22), for example, by transferring energy from the flowing diluent absorbent (45) to the flowing dry air (7).

18. The method according to claim 16 or 17, comprising reusing heat from the absorption process inside the control device (28) as a heat source for the drying process inside the enclosure (2) of the product drying apparatus (22).

19. The method according to claim 18, wherein, in reusing the heat from the absorption process, a heat transfer loop having a liquid heat transfer medium, for example, water or a refrigerant.

20. The method according to any one of claims 16 to 19, wherein the process inside the liquid absorbent drying apparatus (24) is near-thermal, specifically requiring 5 to 25% of the energy normally required per unit mass of evaporated water, preferably less than the latent heat of water, and specifically less than 1.2 to 2.5 times the amount of energy normally required.

21. The method according to any one of claims 16 to 20, wherein the drying process itself is not equipped with any external thermal energy supply.

22. The method according to any one of claims 16 to 21, wherein the product is a liquid or solid substance, and the product sent to the drying apparatus is not specifically a gas or a mixture of gases.

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