CN114576944A - Low-cost drying technology for grains and agricultural and sideline products - Google Patents
Low-cost drying technology for grains and agricultural and sideline products Download PDFInfo
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- CN114576944A CN114576944A CN202210273562.8A CN202210273562A CN114576944A CN 114576944 A CN114576944 A CN 114576944A CN 202210273562 A CN202210273562 A CN 202210273562A CN 114576944 A CN114576944 A CN 114576944A
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B9/00—Machines or apparatus for drying solid materials or objects at rest or with only local agitation; Domestic airing cupboards
- F26B9/06—Machines or apparatus for drying solid materials or objects at rest or with only local agitation; Domestic airing cupboards in stationary drums or chambers
- F26B9/066—Machines or apparatus for drying solid materials or objects at rest or with only local agitation; Domestic airing cupboards in stationary drums or chambers the products to be dried being disposed on one or more containers, which may have at least partly gas-previous walls, e.g. trays or shelves in a stack
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/26—Drying gases or vapours
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/001—Drying-air generating units, e.g. movable, independent of drying enclosure
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/004—Nozzle assemblies; Air knives; Air distributors; Blow boxes
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/02—Circulating air or gases in closed cycles, e.g. wholly within the drying enclosure
- F26B21/04—Circulating air or gases in closed cycles, e.g. wholly within the drying enclosure partly outside the drying enclosure
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/06—Controlling, e.g. regulating, parameters of gas supply
- F26B21/08—Humidity
- F26B21/083—Humidity by using sorbent or hygroscopic materials, e.g. chemical substances, molecular sieves
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Abstract
The invention discloses a low-cost drying technology for grains and agricultural and sideline products, which comprises an air dehumidification technology and a low-energy-consumption concentration regeneration technology of a desiccant. The air dehumidification technology adopts hygroscopic concentrated solution as a drying agent to contact with wet air to obtain dry air and diluted desiccant solution; the dry air is used for drying and dehydrating grains and agricultural and sideline products. The low-energy-consumption concentration regeneration technology of the desiccant is to perform concentration regeneration treatment on a diluted desiccant solution, pump water vapor out of the diluted solution by utilizing the combination of a single-stage or two-stage steam compressor, compress and heat the diluted desiccant, use the obtained compressed steam for heating the diluted desiccant to realize the concentration regeneration of the diluted desiccant, and leave the water in a liquid water form. The dehumidification and regeneration processes of the invention recycle latent heat of gasification, save energy input of traditional drying and drying, are suitable for drying treatment of large-batch grains and agricultural and sideline products, can be started up in all weather, has extensive operation conditions, and is easy for engineering application.
Description
Technical Field
The invention belongs to the field of agricultural product processing, relates to drying of grains such as rice, corn, wheat and the like and agricultural and sideline products, and particularly relates to a low-cost drying technology for grains and agricultural and sideline products.
Background
The water content of the grain is usually higher during grain harvesting, the grain is more serious during the process of harvesting and rob, the grain can be mildewed due to the action of respiration and microorganisms during the high water content, and therefore drying treatment is needed, and the common drying forms include three types of natural drying, ventilation drying and mechanical drying. The harvested grains have timeliness, mechanical drying is needed in rainy days, the mechanical drying technology comprises a convection drying method, a heat conduction drying method, a radiation drying method, an electric field drying method, a combined drying method and the like, but the mechanical drying technology needs a large amount of energy input, the drying cost is high, the mechanical drying technology cannot bear grains with lower price, and although the grain drying technology is developed to the present, the proportion of the total mechanical drying quantity of the grains in all the grains is still not high.
Many agricultural and sideline products need to be dehydrated, such as processing of dried persimmons of fruits, drying of longan, pepper of spices, drying of anise and dehydrated vegetables of vegetables, drying of daylily, drying of nuts and the like, and different processing methods are needed in view of different process purposes, but the links needing dehydration are involved, the existing method needs a large amount of energy input, a heat pump technology appears in the dried persimmons processing, the progress is made, the COP (coefficient of performance) of the heat pump can reach 3.8, and the energy consumption is greatly reduced. However, the premise is that the steam leaves the drying system, the quantity of heat to be supplemented is large, and the equipment investment is high, so that the steam has advantages for specific occasions and high value-added products, and is not a preferable scheme for heavy-load drying.
Disclosure of Invention
The invention aims to provide a technical scheme for drying grains and agricultural and sideline products at low cost. The method is characterized in that the correlation between an air dehumidification technology and a low-energy-consumption concentration regeneration technology of a desiccant is utilized, an organic combination of the two technologies is constructed, moisture in humid air from a grain bin and a drying chamber of agricultural and sideline products is absorbed into the desiccant through the dehumidification technology, then the low-energy-consumption concentration regeneration technology is utilized for concentration, the moisture leaves a system in a liquid water form, latent heat of vaporization in the two processes is recycled in a closed loop, energy required by drying is greatly reduced, and the low-cost drying technology for the grains and the agricultural and sideline products is formed.
Various stoving processes are because moisture all leaves the system with the form of gaseous state water, take away a large amount of energy, consequently need supply, and also the heating, the power consumption is very high, and corresponding stoving cost is also high, has restricted cereal stoving total amount, if can retrieve the heat of taking away in the moisture, let moisture leave the system with the liquid form, then can the energy saving greatly. Assuming a drying temperature of 30 ℃, an enthalpy of 126.28KJ/Kg for liquid water and an enthalpy of 2559KJ/Kg for gaseous water, energy is saved (2559-126.28)/2559 =87.6% if the water vapor can leave the system as liquid water. Liquid water leaving the system can save 87.6% of energy consumption compared with gaseous water leaving the dry system.
Air dehumidification technology: the grains and agricultural and sideline products need low-humidity dry air for drying, the air is dehumidified, and then the drying capacity is obtained again. The liquid absorption dehumidification utilizes the property that the moisture absorbent has the capacity of absorbing moisture to dry air, has the advantages of good dehumidification effect, continuous work and air purification, treats the air to an air supply state in one treatment process, has large dehumidification amplitude of the air and can reach lower moisture content.
Low energy consumption concentration regeneration technology: the liquid solution adopts a vapor mechanical recompression (MVR) technology, which is an energy-saving technology for reusing the energy of secondary vapor generated by the liquid solution and reducing the requirement on external energy. The working process is that the steam at low temperature is compressed by a compressor, the temperature and the pressure are improved, the enthalpy is increased, and then the steam enters a heat exchanger for condensation, so that the latent heat of the steam is fully recovered. Except for preheating required for starting, no new energy is supplemented in the whole process, and after secondary steam is condensed, liquid water leaves the system. In the practical case of adopting MVR technology in the concentration process of biological fermentation liquor and various extraction liquid, only 28-39KWH of electric power is consumed for evaporating one ton of water, and 860KWH of electric energy is needed for electrically heating and evaporating one ton of water, so that the energy-saving effect is extremely remarkable. If the energy-saving drying method is used for dehydrating and recycling the grains and agricultural and sideline products, various conveying devices are added to consume energy, the total energy consumption for removing one ton of water is less than 200KWH, the water content is reduced by 5% for each ton of grains, one ton of water is removed from 20 tons of grains, the drying cost for each ton of grains is less than 10 degrees, and the cost is only one third to one fourth of that of the drying method because the drying energy input of the traditional drying method is saved.
The invention relates to a low-cost drying technology for grains and agricultural and sideline products, which consists of a grain bin or an agricultural and sideline product drying chamber, an air dehumidification technology and a low-energy-consumption concentration regeneration technology.
The invention has the following main characteristics:
1. the method changes the moisture discharge mode of the existing drying process of grains and agricultural and sideline products, changes the gaseous water vapor form into the liquid water form, leaves the system, and completely recovers the latent heat of vaporization. The whole drying process does not need heating equipment except the operation of power equipment, saves investment and greatly reduces unit energy consumption.
2. The selected dehumidifying agent has high dehumidifying capacity, and lithium chloride solution is preferably used as the dehumidifying agent; at 27 deg.C, relative humidity of 65%, and desiccant concentration of 25%, dry air with relative humidity of 31% can be obtained, and the desiccant can still have dehumidification capacity, and at 40% concentration, the dehumidification amount per unit air circulation is 18g/m3And the dehumidification efficiency is high.
3. Lithium chloride is not consumed, the problem of entrainment is solved, no consumption is caused in the whole process, and the lithium chloride is continuously recycled.
4. The dehumidification operation condition is extensive, is not influenced by weather conditions, can be started in all weather, and is easy to engineer.
Specifically, the invention is achieved by the following modes:
the utility model provides a low-cost drying technology of cereal and agricultural and sideline products, includes concentrated regeneration technique of low energy consumption of air dehumidification technique and desiccant, dehydrating unit which characterized in that: obtaining low-humidity dry air, diluted desiccant and latent heat of vaporization by an air dehumidification technology, and obtaining dry hot air after the dry air at an outlet obtains the latent heat of vaporization for drying and dehydrating grains and agricultural and sideline products; and (3) concentrating and regenerating the dilute dehumidifying agent by a low-energy-consumption regeneration technology to obtain a high-concentration dehumidifying agent and a heat source required by self concentration. The air dehumidification technology transfers the moisture in the grains into the dehumidification liquid, creates conditions for adopting the MVR technology, contributes to the process effect of low energy consumption for the whole drying process, is used for drying the grains and agricultural and sideline products, and forms a low-cost drying technology.
The invention comprises the following steps: firstly, absorbing moisture (wet air is used as a carrier) released by a material into a dehumidifying agent concentrated solution by an air dehumidifying technology to form a dehumidifying agent dilute solution; then, a low-energy-consumption concentration regeneration technology of the desiccant is used for providing a high-concentration desiccant solution and a heat source required by self evaporation for an air dehumidification technology; the combination of the air dehumidification technology and the low-energy-consumption concentration regeneration technology of the desiccant constructs an application channel of the MVR technology on drying of grains and agricultural and sideline products, the latent heat of vaporization in the processes of the air dehumidification technology and the low-energy-consumption concentration regeneration technology of the desiccant realizes closed cycle utilization, and the energy required by drying is greatly reduced.
The air dehumidification technology comprises a dehumidification device, wherein a dehumidification agent with strong moisture absorption characteristic is subjected to multistage countercurrent or cross-flow contact dehumidification with high-humidity air coming out of a material to be dried on a honeycomb paper wet curtain; the operation of the dehumidifying device is divided into three stages, and the specific process is as follows:
s11, the first stage uses the dilute solution of the desiccant to circulate and contact with the high humidity air spray at the inlet of the dehumidifier for moisture exchange;
s12, spraying and contacting the second-stage concentrated solution of the dehumidifying agent with the primarily dewatered air for further dehumidification;
s13, third-stage solution-free spraying for defoaming and purifying and preparation and replacement with a preceding-stage wet curtain;
and S14, when the concentration of the first-stage dilute solution is reduced to a certain amount, transferring the first-stage dilute solution to a concentration and regeneration link of a desiccant, transferring the second-stage concentrated solution to a first-stage dilute solution tank, injecting the regenerated concentrated solution into a second-stage concentrated solution tank, and sequentially circulating.
Wherein, the dehumidification links in the steps S11 and S12 can realize continuous countercurrent of the dehumidification solution if being subdivided into multiple stages, and are also regarded as two-stage circulation of the dilute and concentrated solution, which is the protection scope of the present invention.
The low-energy-consumption concentration regeneration technology of the dehumidifying agent is characterized in that a single machine or a two-stage steam compressor is combined to extract water vapor from a dehumidifying agent dilute solution, compress and heat up (MVR) the water vapor for heating the dilute dehumidifying agent, water leaves a system in a liquid water form, enthalpy is recycled, additional energy supplement is not needed, and the concentrated dehumidifying agent returns to an air dehumidifying device. The former stage vapor compressor selects a high-speed centrifugal compressor with a high pumping speed as a vacuum pump to reduce the boiling point of the dilute solution, and the latter stage adopts a Roots compressor with a large compression ratio to enlarge the temperature difference of heat exchange between the secondary vapor and the dilute solution in a vacuum system and strengthen the heat exchange.
The closed-loop recycling of the latent heat of vaporization comprises two aspects:
firstly, in the air dehumidification technology, a desiccant absorbs moisture to release latent heat of vaporization to obtain dry hot air with the temperature 2-4 ℃ higher than that of an inlet, and the dry hot air returns to a grain bin and a drying chamber for agricultural and sideline products to supplement energy consumption required by material dehydration in an equal amount;
secondly, in the low-energy-consumption concentration regeneration technology of the desiccant, the water vapor evaporated by the dilute desiccant is compressed by MVR to increase the temperature and then returns to be used for heating the dilute solution, and the heat energy input of the conventional evaporation is replaced by equal amount. The water leaves the system in the form of liquid water, and the enthalpy heat is recycled.
The invention has the following beneficial effects:
1. an application channel of the MVR technology on grain and agricultural and sideline product drying is constructed, a low-energy-consumption concentration regeneration technology is applied to a grain drying process through bridging of an air dehumidification technology, latent heat of vaporization is recovered in the whole process, a low-energy-consumption drying process is realized, and additional energy supplement is not needed. The organic combination of the air dehumidification technology and the low-energy-consumption concentration regeneration technology forms a low-cost drying technology for grains and agricultural and sideline products.
2. The technical device has relatively low manufacturing cost and low operation cost, is only one third to one fourth of a drying method, and is easy to popularize and apply.
3. In the period of emergency harvesting and planting, when the crops meet rainy weather, the moisture index of the purchased grains can be properly relaxed, the contradiction between farmers and purchasing parties is solved, the deterioration of the grains can be reduced, the waste of total social resources is reduced, and the method has great social significance.
4. For agricultural and sideline products, the dehydration and drying treatment can be carried out at low cost, the method has great advantages in vegetable dehydration, fruit dehydration and places needing low-temperature drying, and the deep processing of the agricultural and sideline products can be powerfully promoted due to great reduction of the dehydration cost, thereby providing an effective means for countryside vogue.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
FIG. 1 is a schematic view of a low-cost drying technique for grains and agricultural and sideline products.
Fig. 2 is a schematic structural diagram of the dehumidifying apparatus.
Fig. 3 is a flow chart of the regeneration process of the dilute solution of the desiccant, wherein, a is a section chart of an evaporation type, and b is a flow chart of the regeneration process.
Fig. 4 is a flow chart of a drying process for a high moisture grain bin in place, wherein the grain bin is fishbone shaped and is a ventilation and fumigation channel of a conventional configuration for either drawing moist air or blowing dry air.
Fig. 5 is a flow chart of a drying process suitable for agricultural and sideline products, wherein a drying tray is arranged in a drying chamber and used for placing materials to be dried.
In the figure: 201: a housing; 202: a honeycomb paper wet curtain; 203: a wind-shielding partition plate; 204: a desiccant spray nozzle; 205: a fan; 206 regeneration concentrated desiccant temporary storage tank; 207: a desiccant tank change valve; 208: a concentrated dehumidifying agent circulating pump; 209: a concentrated desiccant tank; 2010: a dilute desiccant circulating pump; 2011: a dilute desiccant tank; 2012: a dilute desiccant outlet (de-regeneration device); 301: an evaporation chamber; 302: a demister; 303: a sight glass; 304: a shell and tube heat exchanger; 305: an electric heating tube; 306: heat exchangers (condensate-low temperature dilute solution); 307: a dilute desiccant valve; 308: a steam trap; 309: a concentrated dehumidifying agent discharging pump; 3010: a compressed vapor chamber; 3011: a pre-compression vapor line; 3012: a centrifugal vapor compressor; 3013: a Roots vapor compressor; 3014: a compressed vapor line.
Detailed Description
All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in figure 1, a low-cost drying technology for grains and agricultural and sideline products comprises an air dehumidification technology, a low-energy-consumption concentration regeneration technology of a desiccant and a dehumidification device, wherein low-humidity dry air, a diluted desiccant and latent heat of gasification are obtained through the air dehumidification technology, and dry hot air is obtained after the dry air at an outlet obtains the latent heat of gasification and is used for drying and dehydrating the grains and the agricultural and sideline products; the dilute dehumidifying agent is subjected to concentration regeneration treatment by a low energy consumption regeneration technology (MVR steam mechanical recompression technology) to obtain a high-concentration dehumidifying agent and a heat source required by self concentration, and the organic combination of the two technologies forms a process with low energy consumption.
As shown in fig. 2, the dehumidifying apparatus includes a housing 201, a plurality of drying compartments are included in the housing 201, a honeycomb paper wet curtain 202 is disposed in each drying compartment, and a wind shielding partition 203 is disposed between each drying compartment; wherein, the drying cabin is divided into a first-level drying cabin, a second-level drying cabin and a third-level drying cabin, wherein, the first-level drying cabin and the second-level drying cabin are provided with dehumidifying agent nozzles 204, the rightmost end of the drying cabin is an air inlet and is provided with a fan 205 for air circulation, the first-level drying cabin is provided with a dilute dehumidifying agent groove 2011, the second-level drying cabin is provided with a concentrated dehumidifying agent groove 209, the third-level drying cabin is provided with a regeneration concentrated dehumidifying agent temporary storage groove, wherein, the dilute dehumidifying agents among the dilute dehumidifying agent grooves 2011 of a plurality of first-level drying cabins are communicated and circulated, the concentrated dehumidifying agents among the concentrated dehumidifying agent grooves 209 of a plurality of second-level drying cabins are communicated and circulated, the dilute dehumidifying agent groove 2011 is also provided with a dilute dehumidifying agent circulating pump 2010 and communicated with the dehumidifying agent nozzles 204 on the first-level drying cabin, the concentrated dehumidifying agent groove 209 is also provided with a concentrated dehumidifying agent circulating pump 208 and communicated with the dehumidifying agent nozzles 204 on the second-level drying cabin, the regenerated concentrated desiccant temporary storage tank is communicated with the concentrated desiccant tank and the diluted desiccant tank through separate pipelines, and the pipelines are provided with desiccant tank-changing valves 207 for recycling the desiccant among the regenerated concentrated desiccant temporary storage tank, the concentrated desiccant tank and the diluted desiccant tank; the concentrated solution inlet of regeneration has still been seted up on the concentrated desiccant of regeneration groove of keeping in, connects the low energy consumption regenerating unit of weak solution (MVR) to, weak desiccant groove 2011 has still seted up weak desiccant discharge port, and connects the low energy consumption regenerating unit of weak solution (MVR) through the pipeline. The invention selects the honeycomb paper wet curtain with low price and long service life as the filler, the honeycomb paper wet curtain is folded by a thin paper board with oblique ripples, is formed by reversely staggered and laminated at a certain angle to form a honeycomb structure, the surface of the honeycomb structure is mineralized by inorganic coating, the honeycomb structure has the characteristics of high wetting rate, uniform distribution, mildew resistance and the like, the dehumidifying agent is sprayed from the upper part, and the desiccant is contacted with high-humidity air at the inlet in a counter-current or cross-current spraying manner, and falls to a bottom liquid storage tank along the groove by means of gravity, then the circulation, the wet curtain of honeycomb divide into the tertiary, and the preceding two-stage lower part sets up solitary solution circulation groove, and the first grade is sprayed the contact with the high humidity air of import with weak solution circulation and is carried out the moisture exchange, and the second grade is sprayed the contact with the air of preliminary dewatering with concentrated solution and is further dehumidified, and the no solution of third level sprays for the defoaming purifies and with the preparation of preceding stage wet curtain trade. According to the air quantity requirement, a plurality of groups can be combined to adapt to different air quantity requirements. And after the moisture exchange, the dry air leaves the dehumidifying device and enters the lower part of the grain bin or grain pile for drying operation, the concentration of the dehumidifying solution is reduced, the dehumidifying solution is transferred to a regeneration link when the water absorption capacity is weakened, the second-stage concentrated solution is transferred to the first-stage dilute solvent tank, and the regenerated concentrated solution is injected into the second-stage concentrated solution tank and is circulated in sequence. The continuous countercurrent operation of the dehumidifying solution can be realized by subdividing the first two stages into multiple stages, and the dehumidifying solution is suitable for production places with large water removal amount and high moisture content, such as vegetable dehydration.
The dehumidifying agent of the invention is a solution with low water vapor partial pressure, difficult crystallization, small viscosity, no toxicity, no odor and moisture absorption. The grains and agricultural and sideline products are seasonally dried, the desiccant has long-term stability, and calcium chloride (CaCl) is selected2) Lithium chloride (LiCl), alone or in combination. LiCl is preferably selected, lithium chloride has extremely strong hygroscopicity, 1 lithium chloride molecule can be tightly combined with 2 water molecules in a completely dry environment, 26 water molecules can be absorbed in a 90% humidity environment, the strong hygroscopicity is shown, the hygroscopicity is high, and the current lithium chloride hygrometer utilizes the principle that the equilibrium humidity of a saturated lithium chloride solution and air is kept between 11% and 12% in a wide temperature range. Even if the concentration is reduced, the water-absorbing ability is maintained. The literature shows that the lithium chloride has the maximum moisture absorption capacity when the concentration is 30-40%, and the lithium chloride still has strong moisture absorption capacity in air with relative humidity of 65% (air humidity corresponding to safe moisture of grains) when the concentration is 25%. The lithium chloride solution has strong water removal capacity, the solubility of the lithium chloride is 83.5g/100g at 20 ℃, the concentration weight ratio is 45.5%, the initial concentration (also the regeneration concentration end point) of the dehumidification solution is set to 40% for preventing crystallization and destroying working conditions, and the regeneration concentration of the dilute solution is set to 25% for keeping relatively large water removal efficiency. Under the saturated solution working condition, the concentration of 83.5kg of lithium chloride saturated solution is reduced to 25% from 45.5%, the weight of the solvent water is 83.5/25% =334kg, and 234 kg of water can be removed in one cycle by removing 100kg of the base solvent. If 1 ton of lithium chloride concentrated solution is reduced from 40% to 25%, the moisture removed in one dehumidification cycle process is 40%/25% -1=0.6, namely 0.6 ton of water can be absorbed, the water removal efficiency is high, and the method has industrial value. From the above calculation, if the regeneration concentration is reduced, the concentration end point is increased, which will greatly improve the water removal efficiency. Extreme conditions have an effect on both the dehumidification and concentration processesAnd setting the regeneration concentration and the concentration end point according to the actual working conditions. The grain just harvested has large moisture, the air humidity circulated back is also large, the lower regeneration concentration can be adopted, and the higher regeneration concentration is adopted when the moisture approaches the safe moisture or the terminal moisture. The adjustment is carried out according to the acceleration of the rapid dehydration of the materials.
As shown in fig. 3, the regeneration process of the dilute solution of the desiccant comprises an evaporation chamber 301, a demister 302 and a sight glass 303 are arranged on the evaporation chamber 301, a tubular heat exchanger 304 is arranged inside the evaporation chamber 301, an electric heating tube 305 is further arranged below the evaporation chamber 301, one end of the evaporation chamber 301 is connected with a heat exchanger (condensate water-low temperature dilute solution) 306, the inlet end of the heat exchanger (condensate water-low temperature dilute solution) 306 is connected with a dilute desiccant inlet, a dilute desiccant valve 307 is arranged, the heat exchanger (condensate water-low temperature dilute solution) 306 is further provided with a water drain for discharging liquid condensate water and a steam trap 308, the evaporation chamber 301 is further connected with a concentrated desiccant outlet for discharging and reusing concentrated desiccant, a concentrated desiccant discharge pump 309 is arranged, and the evaporation chamber 301 is further connected with a steam compressor unit comprising a preceding-stage steam compressor and a subsequent-stage steam compressor, the front stage vapor compressor is a centrifugal vapor compressor 3012, and the rear stage vapor compressor is a roots vapor compressor 3013.
The low-energy-consumption concentration and regeneration technology is completed by an MVR unit, as shown in figure 3, the technology comprises an evaporator 301, a tubular heat exchanger 304 is arranged at the lower part of the evaporator, an evaporation chamber is arranged at the upper part of the evaporator, a stainless steel wire mesh filler 302 is arranged at the top of the evaporator and used for removing foam, an electric heating tube 305 is arranged at the bottom of the evaporator and used for preheating dilute solution, steam enters a centrifugal compressor 3012 for suction and compression and enters a Roots compressor 3013, compressed secondary steam enters a tubular heating side steam cavity 3010 and enters the interior of the tubular, the evaporation chamber is heated to form circulation, condensed liquid water is discharged from a steam trap 308, a heat exchanger 306 for recovering waste heat of condensed water is added at the front end of the steam trap and used for preheating dilute solution, and energy is further saved. The operation process is as follows: when the dilute solution which absorbs moisture to a certain degree and needs to be regenerated, the Roots compressor is started to form a certain negative pressure, the control valve 307 is opened to suck the dilute desiccant into the evaporation chamber, the valve 307 is closed to stop feeding when the solution in the evaporation chamber is observed to be higher than the uppermost tube from the sight glass 303, then the electric heating tube 305 is started to preheat the solution to 80-90 ℃, the bypass valve is arranged at the front end of the steam trap 308 and used for discharging non-condensable gas, when water flows out, the preheating is finished, the electric heating tube 305 is closed, the centrifugal compressor 3012 is started, the bypass valve is closed, the normal working condition is entered, after the evaporation is carried out for a certain time, the control valve 307 is partially opened to supplement the dilute solution, the water removal amount of the steam trap is about equal to the feeding amount, the temperature is equal to or higher than the temperature of the solution in the evaporation chamber due to the preheating of the dilute desiccant by the heat exchanger 306 (the vacuum causes the liquid boiling point in the evaporation chamber to be reduced), the stability of the evaporation working condition can not be damaged. And continuously operating and circulating, observing that the liquid level of the solution in the chamber to be evaporated rises to a certain degree from the sight glass 303 and the temperature rises to the set temperature, indicating that the concentration is increased, finishing concentration, closing 307, and starting a discharge pump 309 to pump out the concentrated solution. The dilute solution feed valve 307 is then opened and the next run is started.
The steam compressor unit consists of a centrifugal steam engine and a roots compressor which are connected in series in two stages, and the reason is that the evaporation boiling point of the lithium chloride concentrated solution is higher than the conventional evaporation temperature, which is also the dynamic basis for releasing latent heat of vaporization in the dehumidification process. The atmospheric boiling point of the 40% strength lithium chloride solution was 119 ℃ and the 25% strength was 109.5 ℃. MVR needs to be directly exhausted to the atmosphere through the steam trap 3-8, namely the atmospheric pressure, the temperature of water vapor leaving the liquid surface is 109 ℃, certain overheating exists, for compression, condensation after compression can be avoided, and howling is reduced, so that the MVR is favorable to one aspect, but the heat dissipation through a pipeline and the outlet pressure are the atmospheric pressure, and the temperature which can be effectively used for heating the dilute solution is the water vapor temperature corresponding to the atmospheric pressure, namely 100 ℃. The existing MVR equipment is a centrifugal or Roots type vapor compressor, the temperature of the single machine is raised by 20-28 ℃ through compression, and for the heat exchange of the lithium chloride concentrated solution, the temperature difference can be reduced, a larger heat transfer area is needed, and the economical efficiency is poor. The invention adopts a two-stage series method to solve the problem that the boiling point of a dehumidifying agent in a vacuum system can be reduced to enlarge the temperature difference between an inlet and an outlet, the former stage utilizes a high-speed centrifugal compressor with high pumping speed in a vacuum state to perform the compression of the former stage, the vacuum degree is improved, the boiling temperature of a solution is reduced, the latter stage is connected with a Roots compressor with large compression ratio in series, the compression ratio is improved, so that larger temperature difference between the inlet and the outlet is obtained, and the heat transfer is enhanced. The steam is connected to the hot side of the heat exchanger to heat the dilute dehumidifying agent in the vacuum system for concentration, and the condensed water is discharged as liquid water and leaves the system.
Example 1 drying for high moisture cereals:
the warehouse is divided into a storage warehouse, a reserve warehouse, a transfer warehouse, a port warehouse, a raw material finished product warehouse, a supply warehouse, a futures delivery warehouse, a comprehensive warehouse and the like; the storage warehouse and the storage warehouse are links of high-moisture grain dehydration and drying, and the requirement of the subsequent warehouse on drying is slightly low. The collecting storage is located the grain delivery area, it is direct to the peasant grain of purchasing, the oil is and transports the interim warehouse of other transfer storehouses or reserves, this stage is because grain, the oil has just been reaped soon, the moisture content is high, the microorganism is active, grain easily generates heat and mildenes and rot, consequently it needs control moisture to receive grain, and the peasant often weather of stage of robbing for harvest is not good, no dry condition, in time sell, form the contradiction, if the collecting storage possesses better dry condition, then can in time purchase high moisture grain, reduce the total waste. The existing mechanical drying method has high cost, and the cost is balanced by adopting a method of reducing the grain price. This conflict can be mitigated if the low cost drying techniques of the present invention are employed.
Most of the storage bins are horizontal warehouses, all the storage bins are generally provided with earthworm ventilation channels, have ventilation and fumigation conditions and certain sealing conditions, and can be dried in place by adopting the method provided by the invention. The turnover and the dumping of the warehouse are reduced. Taking 8000t of storage bin as an example, owing to a series of mechanical operations such as screening, edulcoration, detection are required in the purchase, 20 days can be full of, even many processing lines before the purchase work simultaneously, limit purchase volume does not exceed 500t every day, with 500t limit treatment capacity every day, cereal precipitation 5% (limit purchase moisture exceeds standard and expands to 5%), dewater to terminal moisture in 24h, need get rid of 25t moisture. The average concentration of the concentrated solution tank of the dehumidifying device is 35 percent, the atmospheric humidity is 70 percent, and at least 16.7g/m of air dehumidification amount per circulation unit is removed under the condition of 27 DEG C3,（Data of equipment merchant 18g/m3) Then more than 1.5x10 would be required6m3The circulating air volume of (1), i.e. 17.32 m/s3S, the dehumidifying device is controlled according to the optimized wind speed of 3m3Calculation of/s, 6m is required2The ventilation area of the wet curtain is 7.5m2The wet curtain ventilation area. The MVR has an evaporation rate (20% redundancy) of 1.5t/h of working load, and the heat exchange area is 20m2400m of a heat exchanger3Centrifugal compressor with/min pumping speed and 135m3The min Roots compressor performs working condition matching according to the compression ratio of the equipment on the principle that the outlet pressure of the former-stage compressed compressor is basically equal to the inlet pressure of the latter-stage compressor. The device for processing the amount can be integrated into a unit, can also be carried on a vehicle, and is suitable for different operation places.
As shown in fig. 4, an inlet of a dehumidifying device is connected to a earthworm ventilation channel of a fishbone structure at the bottom of a grain bin, high-humidity air in a grain pile is sucked out and enters the dehumidifying device, low-humidity air after dehumidification is connected to the upper end of the bin from the other side, the dehumidifying device is started, dry air with the relative humidity of 20-40% from the dehumidifying device is blown to the upper top of the bin to form a cycle, drying and dewatering operation is started, when the relative humidity difference between an inlet and an outlet is less than 10% and is less than 60%, dehumidification is stopped, grains are slowly heated, internal moisture is diffused to the outside, and then drying and dewatering are performed again. The large granary is large in size, the total diffusion speed of grain moisture can be higher than the dehumidification capacity of the dehumidifier, so that the drying operation can last for a long time, the grain moisture can be reduced to a position close to safe moisture in a drying process, and the phenomenon of heating and mildew is avoided.
Example 2: drying the grain bin of the large-scale storage warehouse:
the grain moisture transferred from the storage warehouse to the storage warehouse basically reaches the standard, the required water removal amount is small, but due to the damp-heat diffusion phenomenon, the problem of inconsistent moisture content can occur locally, and dry air can be introduced periodically according to a certain program at the initial stage of warehousing, so that the grain moisture is safe to store for a long time. Because the size of the dehumidification device is small, the dehumidification device can be moved to a specified place on a vehicle and then connected with an entrance for air dehumidification, and the air humidity in the grain stack and the air humidity in the upper space of the granary are kept to be less than 65 percent, or the dehumidification device can be used for dehumidifying airThe set humidity is selected as desired. The storage warehouse can share one dehumidifying device, a large storage warehouse of a plurality of storehouses can be processed by adopting a mode of dispersedly patrolling a plurality of vehicle-mounted dehumidifying devices, and concentrated regeneration treatment of dehumidifying agents is provided for a plurality of dehumidifying vehicles in one MVR regeneration treatment center. After air drying of one storehouse is completed, the high dehumidifying agent is replaced, the next storehouse is switched to, and the storage capacity of the storage storehouse is generally 8000m3The process scheme is the same as that of example 1, the dehumidification equipment is selected as that of example 1, the low-cost regeneration device selects a corresponding type according to the treatment capacity of the regeneration liquid, and the principle and operation are the same as those of example 1.
Example 3 is suitable for drying agricultural by-products:
the agricultural and sideline products are characterized by large water content of materials, large dehydration load, fixed production place and strong seasonality. In order to keep the flavor, the product can not be dried at high temperature, some products need to keep rehydration and other requirements, the drying can not be carried out under the condition of too low humidity, the drying is similar to the drying in the shade, the drying is carried out under the conditions of medium and low humidity and temperature, so that the dehumidifying agent can operate under the condition of lower concentration, and the drying characteristics are just more suitable for exerting the advantages of the invention.
As shown in fig. 5, the whole process is composed of a material drying chamber, a tray and tray rack, a heating source, a dehumidifying device and a dilute dehumidifying agent regenerating device, wherein the dehumidifying device and the MVR are both arranged in a drying area. Because of the material preheats and MVR starts required heat energy fewest, and the heat source grade requirement is not high, it is as starting the heat source to prefer high temperature heat pump, the material is at the indoor balance of drying chamber, it preheats the drying chamber air to the drying temperature of settlement to open the heat pump, stop the heat pump operation, material moisture evaporation, humidity is higher than and opens dehydrating unit behind the setting value, dewater, dehumidification solution concentration reduces after the certain degree, pump income MVR evaporating pot, the heat pump starts to heat the temperature that MVR can operate with rare dehumidification solution, stop the heating, open MVR and concentrate, concentrate the pump goes into dehydrating unit, continuous cycle operation. Because the moisture leaves the drying chamber in the form of liquid water, the whole heat consumption is extremely low, only various motors are consumed, boiler equipment is saved, the investment and operation cost is reduced, and various pollutions are avoided.
The drying has high dehydration strength, the environment humidity allows the operation under the condition of high relative humidity, therefore, the desiccant can be carried out under the condition of low concentration, and the steam compressor can select a Roots unit with larger single-stage compression ratio, thereby saving the investment.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the present invention shall fall within the protection scope of the present invention.
Claims (7)
1. A low-cost drying technology for grains and agricultural and sideline products comprises an air dehumidification technology and a low-energy-consumption concentration regeneration technology of a desiccant, and is characterized in that: obtaining low-humidity dry air, diluted desiccant and latent heat of gasification through an air dehumidification technology, and obtaining dry hot air after the dry air at an outlet obtains the latent heat of gasification for drying and dehydrating grains and agricultural and sideline products; the dilute dehumidifying agent is subjected to concentration regeneration treatment through a low-energy-consumption regeneration technology to obtain a high-concentration dehumidifying agent and a heat source required by self concentration, and the organic combination of the two technologies forms a process with low energy consumption.
2. The low-cost drying technique for grains and agricultural and sideline products as claimed in claim 1, wherein: the method comprises the following steps: firstly, absorbing moisture in wet air released by a material to be dried into a dehumidifying agent concentrated solution through an air dehumidifying technology to form a dehumidifying agent dilute solution, thereby creating conditions for a steam mechanical recompression technology; then, a high-concentration dehumidifying agent solution and a heat source required by self evaporation are provided for the air dehumidifying technology through the low-energy-consumption concentrating and regenerating technology of the dehumidifying agent, an application channel of the steam mechanical recompression technology on drying of grains and agricultural and sideline products is constructed through the combination of the air dehumidifying technology and the low-energy-consumption concentrating and regenerating technology of the dehumidifying agent, latent heat of vaporization in the processes of the air dehumidifying technology and the low-energy-consumption concentrating and regenerating technology of the dehumidifying agent is recycled in a closed loop, and energy required by material drying is greatly reduced.
3. The low-cost drying technique for grains and agricultural and sideline products as claimed in claim 1, wherein: the air dehumidification technology comprises a dehumidification device, wherein a dehumidification agent with strong moisture absorption characteristic is subjected to multistage countercurrent or cross-flow contact dehumidification with high-humidity air coming out of a material on a honeycomb paper wet curtain; the operation of the dehumidifying device is divided into three stages, and the specific process is as follows:
s11, the first stage uses the dilute solution of the dehumidifying agent to circulate and contact with the high humidity air at the inlet of the dehumidifying device for water exchange;
s12, spraying and contacting the second-stage concentrated solution of the dehumidifying agent with the primarily dewatered air for further dehumidification;
s13, third-stage solution-free spraying for defoaming and purifying and preparation and replacement with a preceding-stage wet curtain;
and S14, when the concentration of the first-stage dilute solution is reduced to a certain amount, transferring the first-stage dilute solution to a concentration and regeneration link of a desiccant, transferring the second-stage concentrated solution to a first-stage dilute solution tank, injecting the regenerated concentrated solution into a second-stage concentrated solution tank, and sequentially circulating.
4. The low-cost drying technique for grains and agricultural and sideline products as claimed in claim 3, wherein: the dehumidification links in the steps S11 and S12 are further divided into a plurality of dehumidification steps in the middle, and the concentration of the internal circulation dehumidification solution is increased in sequence.
5. The low-cost drying technique for grains and agricultural and sideline products as claimed in claim 1, wherein: the low-energy-consumption concentration regeneration technology of the desiccant is characterized in that a plurality of vapor compressors are combined to pump vapor out of a dilute solution of the desiccant, compress the vapor and raise the temperature of the vapor for heating the dilute desiccant, so that the moisture leaves a system in a liquid water form, the enthalpy is recycled without additional energy supplement, and the concentrated desiccant returns to a dehumidifying device.
6. The low-cost drying technique for grains and agricultural and sideline products as claimed in claim 5, wherein: the former stage vapor compressor selects a high-speed centrifugal compressor with a high pumping speed as a vacuum pump to reduce the boiling point of the dilute solution, and the latter stage adopts a Roots compressor with a large compression ratio to enlarge the temperature difference of heat exchange between the secondary vapor and the dilute solution in a vacuum system and strengthen the heat exchange.
7. The low-cost drying technique for grains and agricultural and sideline products as claimed in claim 2, wherein: the closed-loop recycling of latent heat of vaporization comprises the following steps:
firstly, in the air dehumidification technology, a desiccant absorbs moisture to release latent heat of vaporization, dry hot air with the temperature higher than the inlet temperature of a dehumidification device is obtained and returned to a grain bin and a drying chamber of agricultural and sideline products, and energy consumption required by material dehydration is supplemented in an equal amount;
secondly, in the low-energy-consumption concentration regeneration technology of the dehumidifying agent, water vapor evaporated by the dilute dehumidifying agent is compressed by a steam mechanical recompression technology to increase the temperature and then returns to be used for heating the dilute solution, the heat energy input of conventional evaporation is replaced by equal amount, and water leaves the system in a liquid water form, so that the enthalpy heat is recycled.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115682640A (en) * | 2022-10-12 | 2023-02-03 | 孙聪 | Energy-saving grain vacuum drying technology |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115682640A (en) * | 2022-10-12 | 2023-02-03 | 孙聪 | Energy-saving grain vacuum drying technology |
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Application publication date: 20220603 |