Method and device for treating tail gas of dryer

Abstract

The present invention belongs to the technical field of dryer tail gas treatment methods. The dryer tail gas treatment method: uses the cooling end of a heat pump to cool down the high-temperature and high-humidity tail gas of the dryer, so that the moisture therein condenses and becomes low-temperature and low-humidity tail gas; uses the heating end of the heat pump to heat the low-temperature and low-humidity tail gas into high-temperature and low-humidity tail gas, and then returns it to the dryer. The dryer tail gas treatment device includes a cyclone dust collector, a heat recovery device, and a heat pump. The present invention is used to solve the technical problem that the existing heat pump technology-based dryer waste heat recovery system cannot be implemented.

Description

Technical Field

[0001] The present invention belongs to the technical field of dryer tail gas treatment methods, and particularly relates to a dryer tail gas treatment method and a dryer tail gas treatment device for implementing the above method. Background Art

[0002] The heated air flow inside the dryer is used for drying feed pellets. During this process, a large amount of tail gas is discharged to the outside. After fresh air is supplemented at the air supply opening of the dryer, the reheated air flow is used for drying feed pellets again. The tail gas discharged from the dryer is mostly high-temperature, high-humidity gas with a strong odor. At present, the treatment methods for the tail gas discharged from dryers by feed manufacturers are mostly: directly discharging it into the atmosphere and discharging it into the atmosphere after deodorizing with a deodorizing device. Direct discharge will affect the living environment of surrounding residents and seriously pollute the environment. Due to the high price of the deodorizing device, its economy is not high.

[0003] A heat pump is a device that transfers the heat energy of a low-temperature heat source to a high-temperature heat source. It only needs to consume a small amount of electric energy to obtain low-grade heat energy from the air in nature, and then provide high-grade heat energy that can be utilized to people. Heat pumps are mostly used in the HVAC industry and are often used in combination with heat recovery devices to play the roles of heating, cooling, diverting, and circulating hot and cold air.

[0004] The Chinese utility model patent specification with the publication number CN21785761U and the publication date of November 11, 2022 discloses a dryer waste heat recovery system based on heat pump technology. In this scheme, the dryer tail gas is dust-removed and then passes through the condensation end, mixes with the supplemented air, and then enters the dryer after passing through the heat pump heating end. The tail gas of the dryer enters the dryer after adding the newly supplemented air. Obviously, the air volume at the air inlet and outlet of the dryer is different, and this scheme cannot be implemented. Summary of the Invention

[0005] The first object of the present invention is to provide a dryer tail gas treatment method to solve the technical problem that the existing dryer waste heat recovery system based on heat pump technology cannot be implemented.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions. The dryer tail gas treatment method is characterized by including the following steps:

[0007] (1) 1 / 6 to 1 / 3 of the tail gas of the dryer enters the high-efficiency cyclone dust collector to remove dust with a particle size of 50 - 300 μm, and then enters the heat recovery device through the circulating fan. After heat exchange with the low-temperature air flow in the heat recovery device, it is cooled to below 50°C and the specific humidity is 80 g / kg.

[0008] (2) The tail gas after heat exchange by the heat recovery device enters the cooling end of the heat pump, is cooled to 32 - 38 °C, the specific humidity drops to 32.0 - 38.0 g / kg, and the condensed moisture is discharged from the cooling end of the heat pump;

[0009] (3) The air flow cooled by the cooling end of the heat pump in step (2) converges with fresh air to obtain a mixed gas, forming the low-temperature air flow described in step (1). The volume ratio of fresh air to the air flow in step (2) is 2:1 - 5:1; the low-temperature air flow enters the heat recovery device for preheating;

[0010] (4) The preheated gas is transported along the pipeline to the heating end of the heat pump, heated to 70 - 75 °C, and then returns to the dryer along the pipeline by the circulation fan.

[0011] 1 / 6 - 1 / 3 of the total emissions of the drying tail gas passes through the high-efficiency cyclone dust collector, and the remaining 2 / 3 - 5 / 6 of the tail gas goes to the original environmental protection dust removal system. The reason why the air volume of the tail gas entering the heat pump in step (1) is 1 / 3 - 1 / 6 of the total air volume is: this ratio mainly depends on how many degrees Celsius the tail gas is expected to be cooled to. If this air volume is greater than 1 / 3, for example, 1 / 2, then due to the conservation of air volume, the supplementary air volume should also be 1 / 2 of the tail gas air volume. Then the air volume ratio between the cooling end and the heating end of the heat pump becomes 1:2. This ratio increases the cooling temperature of the heat pump and cannot meet the demand for condensation and moisture removal.

[0012] The tail gas after cyclone dust removal in step (1) is introduced into the heat recovery device containing a filter and exchanges heat with the tail gas that has been processed by the heat pump and has become low-temperature and low-humidity. There are two purposes: First, the energy can be initially exchanged through heat transfer, which not only reduces the temperature of the high-temperature and high-humidity tail gas but also preheats the processed low-temperature and low-humidity tail gas. Second, due to the limitation of the compressor of the heat pump, the temperature of the gas entering the cooling end of the heat pump cannot be higher than 50 degrees, otherwise, a high-temperature alarm will be triggered, causing the heat pump to stop working.

[0013] The tail gas obtained in step (1) is sent to the cooling end of the heat pump for cooling, reducing the tail gas temperature to 32 - 38 °C. At this time, the temperature is lower than the dew point temperature of the tail gas, so that the moisture in the tail gas is condensed and discharged, thus achieving the purpose of dehumidification and drying. Through calculation, it is known that when the tail gas is reduced to 32 - 38 °C, the specific humidity can be reduced to 32.0 - 38.0 g / kg.

[0014] Mix the fresh outside air with the cooled tail gas obtained in step (2). The air volume ratio of the fresh air to the cooled tail gas is 2:1 to 5:1. The mixed gas enters the heat recovery device for preheating, which has two functions: one is to absorb the heat of the high-temperature and high-humidity tail gas in step (10) for preheating, reducing the burden of heating the low-humidity tail gas in the next step; the other is to reduce the temperature of the high-temperature and high-humidity tail gas in step (10) to a range acceptable to the heat pump.

[0015] The reason for the air volume ratio of the fresh air to the cooled tail gas being 2:1 to 5:1 is as follows: In step (1), only 1 / 3 to 1 / 6 of the total air volume of the tail gas enters the heat pump system, and the remaining air volume is directly discharged to the environmental protection deodorization system. In step (3), the fresh air is 2 to 5 times that of the tail gas, that is, the fresh air is equal to 2 / 3 to 5 / 6 of the total air volume. After the two converge in step (3), it is equal to the total air volume of the original tail gas, and then returning to the dryer can make the dryer achieve air volume balance.

[0016] The tail gas preheated by the heat recovery device obtained in step (4) enters the heating end of the heat pump, is heated to 70 - 75 °C, and under the action of the circulating fan, returns to the dryer again.

[0017] For further improvement of the technical solution of the present invention, the heat recovery device is a plate heat exchanger for gas-to-gas heat exchange.

[0018] For further improvement of the technical solution of the present invention, the outside dry bulb temperature of the fresh air is 35 °C, and the specific humidity is 21.4 g / kg; the dry bulb temperature of the converged gas becomes 36 °C, and the specific humidity becomes 30.6 g / kg.

[0019] For further improvement of the technical solution of the present invention, the preheating temperature in step (3) is 43 °C.

[0020] The second object of the present invention is to provide a dryer tail gas treatment device, including a cyclone dust collector, a heat recovery device, and a heat pump;

[0021] The cyclone dust collector is connected to the high-temperature gas flow channel inlet of the heat recovery device via a circulating fan;

[0022] The cooling end inlet of the heat pump is connected to the high-temperature gas flow outlet of the heat recovery device; the cooling end outlet of the heat pump is connected to the low-temperature gas flow channel inlet of the heat recovery device via a pipeline; the pipeline is connected to the outside air via a circulating fan;

[0023] The heating end inlet of the heat pump is connected to the low-temperature gas flow outlet of the heat recovery device, and the heating end outlet of the heat pump is connected to the dryer via a circulating fan.

[0024] The third object of the present invention is to provide another method for treating the tail gas of a dryer, so as to solve the technical problem that the existing waste heat recovery system based on heat pump technology for dryers cannot be implemented.

[0025] To solve the above technical problems, the present invention adopts the following technical solutions. The method for treating the tail gas of a dryer is characterized by including the following steps:

[0026] (1) All the tail gas of the dryer enters a high-efficiency cyclone dust collector to remove dust with a particle size of 50 - 300 μm. The tail gas after dust removal enters a first heat recovery device with a filter through a first circulation fan, and is cooled to below 50°C after heat exchange with a low-temperature air flow in the first heat recovery device, and the specific humidity is still 80 g / kg.

[0027] (2) The tail gas treated by the first heat recovery device enters the cooling ends of a first heat pump and a second heat pump respectively along a ventilation duct for cooling. The cooling end of the first heat pump cools the tail gas to 29 - 35°C, and the cooling end of the second heat pump cools the tail gas to 29 - 38°C; the condensed water precipitated from the tail gas due to cooling flows out from the heat pump; the cooling air volume ratio of the cooling end of the first heat pump to the cooling end of the second heat pump is (1 / 8 - 1 / 4) : (3 / 4 - 7 / 8).

[0028] (3) The tail gas cooled by the cooling ends of the first heat pump and the second heat pump converges, and enters the first heat recovery device with a filter along the ventilation duct for heat exchange to perform primary preheating; the specific humidity of the converged tail gas is 25.6 - 36.5 g / kg.

[0029] (4) The tail gas preheated by the first heat recovery device enters a second heat recovery device with a filter along the ventilation duct, and performs secondary preheating through heat exchange with a high-temperature air flow in the second heat recovery device.

[0030] The high-temperature air flow in the second heat recovery device comes from: the heating end of the second heat pump absorbs external fresh air for heating, the ratio of the air volume of the cooling end of the second heat pump to the air volume of the heating end of the second heat pump is between 1:4 and 1:8, and the heated fresh air enters the second heat recovery device through a circulation fan to form the high-temperature air flow.

[0031] (5) The tail gas after secondary preheating enters the heating end of the first heat pump along the ventilation duct and is heated to 70 - 75°C by the heat pump, and then returns to the dryer under the action of a circulation fan.

[0032] All the exhaust gas generated by the dryer is passed through a high-efficiency cyclone dust collector to remove dust particles with a size of 50 - 300 μm in the exhaust gas, preventing the reduction of heat exchange efficiency caused by the accumulation and residue of dust on the heat recovery device and the heat pump fins, and even preventing the heat pump from failing due to consequences such as high-temperature alarms of the heat pump caused by poor heat conduction of the heat pump fins. However, over time, there will inevitably be some residue on the fins. Doing so can also reduce the frequency of cleaning the heat recovery device and the heat pump fins by the operating workers;

[0033] The filtered and cleaned exhaust gas is introduced into the heat recovery device to exchange heat with the exhaust gas that has been processed by the heat pump and has become low-temperature and low-humidity. There are two purposes. Firstly, energy can be preliminarily exchanged through heat exchange, which not only reduces the temperature of the high-temperature and high-humidity exhaust gas but also preheats the processed low-temperature and low-humidity exhaust gas. Secondly, due to the limitation of the compressor of the heat pump, the temperature of the gas introduced into the cooling end of the heat pump cannot be higher than 50 degrees, otherwise, it will cause a high-temperature alarm and lead to the heat pump stopping working;

[0034] Send 1 / 8 - 1 / 4 of the exhaust gas volume in step (2) to the cooling end of the first heat pump for cooling, so that the exhaust gas temperature is reduced to 29 - 35 °C. At this time, the temperature is lower than the dew point temperature of the exhaust gas, so that the moisture in the exhaust gas is condensed and discharged, thus achieving the purpose of dehumidification and drying. When the exhaust gas is reduced to 29 - 35 °C, the specific humidity can be reduced to 25.6 - 36.5 g / kg.

[0035] Send 3 / 4 - 7 / 8 of the exhaust gas volume in step (3) to the cooling end of the second heat pump for cooling, also reducing the exhaust gas temperature to 29 - 38 °C, and merging with the exhaust gas obtained from the first heat pump. The specific humidity of the merged exhaust gas is 25.6 - 36.5 g / kg.

[0036] Taking the air flow distribution ratios of the first heat pump and the second heat pump as 1 / 8 and 7 / 8 as an example, explain the reason for distributing the air flow in the above ratio:

[0037] The enthalpy value of the high-temperature and high-humidity exhaust gas is much higher than that of the low-temperature and low-humidity exhaust gas. Therefore, to achieve the energy balance at both ends of the heat pump, the air volume at the heating end of the heat pump should be 4 - 8 times that at the cooling end, and specifically how many times depends on the target cooling temperature at the cooling end, that is, the target moisture value. Therefore, if the air flow distribution ratios of the first heat pump and the second heat pump are 1 / 8 and 7 / 8, then after merging, the air flow rate becomes 8 / 8 (i.e., 1) again. This part of the air flow then all enters the heating end of the first heat pump. For the first heat pump, the air volume at its heating end is 8 times that at its cooling end. Similarly, the air volume at the heating end of the second heat pump is also 8 times that at its cooling end;

[0038] The combined exhaust gas is sent to a heat recovery device for preheating, which serves two purposes: one is to absorb the heat of the high-temperature and high-humidity exhaust gas in step (2) for preheating, reducing the burden of heating the low-humidity exhaust gas in the next step; the other is to reduce the temperature of the high-temperature and high-humidity exhaust gas in step (2) to a range acceptable to the heat pump, i.e., below 50°C.

[0039] The heating end of the second heat pump absorbs external fresh air for heating. The ratio of the air volume of the refrigeration end of the heat pump to the air volume of the heating end of the heat pump is between 1:4 and 1:8. The specific ratio depends on the target cooling temperature of the heat pump, but this ratio should be equal to the corresponding ratio of the first heat pump. Otherwise, the refrigeration temperatures of the first heat pump and the second heat pump will become different, making the system temperature control complex and introducing more uncertain factors.

[0040] The reason for setting two heat pumps in the present invention is as follows: The air volumes of the heating end and the refrigeration end of the heat pump are different, but the amounts of gas discharged and replenished by the dryer should be the same. Therefore, no matter how many heat pumps are used, if the gas volume flowing through the refrigeration end of the heat pump is the amount of all the exhaust gas of the dryer, the gas volume of the heating end of the heat pump will necessarily be greater than the amount of replenished gas required by the dryer. Suppose we only use 1 heat pump to complete this task. Similarly, assuming the exhaust gas volume of the dryer is 1, 3 - 7 parts of fresh air need to be replenished to make the ratio of the air volume of the refrigeration end to the heating end of this heat pump meet 1:4 - 1:8. However, since the dryer only needs air equal to the exhaust gas volume as a supplement, the heated exhaust gas has to discharge 3 - 7 parts of hot air again, and only 1 part of hot air is recycled into the dryer. At this time, the 3 - 7 parts of hot air discharged have been mixed with the exhaust gas and belong to polluted air. Whether it goes directly to the deodorization system or is directly discharged into the atmosphere, this solution is no longer meaningful.

[0041] For further improvement of the technical solution of the present invention, the temperature of the external fresh air in step (4) is 35°C, and the specific humidity is 21.4 g / kg.

[0042] For further improvement of the technical solution of the present invention, the high-temperature gas flow of the second heat recovery device in step (4) is subjected to condensation treatment after heat exchange. The gas heated by the second heat pump will enter the second heat recovery device to continue preheating the cooled exhaust gas, and then this gas flow will enter another device in the feed mill - the cooler for continued use. The cooler is usually used as a subsequent drying device for the granulator in the feed mill. Since the overall cost of the granulation line is relatively low and the initial moisture value of the granulated product is not high, the feed mill usually uses normal-temperature air to dry the granulated material. However, when the weather is humid or the temperature is low in autumn and winter, the drying effect will deteriorate. Therefore, introducing the gas heated by the second heat pump into the cooler will greatly improve the production efficiency of the feed mill.

[0043] For further improvement of the technical solution of the present invention, the heat recovery device is a plate heat exchanger for gas-to-gas heat exchange.

[0044] The fourth object of the present invention is to provide a dryer tail gas treatment device, which is characterized in that it includes a cyclone dust collector, a first heat recovery device, a second heat recovery device, a first heat pump, and a second heat pump;

[0045] The cyclone dust collector is connected to the high-temperature air flow channel inlet of the first heat recovery device via a circulation fan;

[0046] The cooling end inlet of the first heat pump is connected to the high-temperature air flow outlet of the first heat recovery device; the cooling end outlet of the first heat pump is connected to the low-temperature air flow channel inlet of the first heat recovery device;

[0047] The cooling end inlet of the second heat pump is connected to the high-temperature air flow outlet of the first heat recovery device; the cooling end outlet of the second heat pump is connected to the low-temperature air flow channel inlet of the first heat recovery device; the heating end inlet of the second heat pump is connected to external air via a circulation fan; regulating pneumatic air volume control valves are provided on the connecting pipes between the cooling end inlet of the first heat pump and the high-temperature air flow outlet of the first heat recovery device and between the cooling end inlet of the second heat pump and the high-temperature air flow outlet of the first heat recovery device;

[0048] The high-temperature air flow inlet of the second heat recovery device is connected to the heating end outlet of the second heat pump via a circulation fan; the high-temperature air flow outlet of the second heat recovery device is connected to a condenser; the low-temperature air flow inlet of the second heat recovery device is connected to the low-temperature air flow outlet of the first heat recovery device; the low-temperature air flow outlet of the second heat recovery device is connected to the heating end inlet of the first heat pump; the heating end outlet of the first heat pump is connected to a dryer via a circulation fan.

[0049] Through the pre-cooling of the high-temperature and high-humidity tail gas by the heat recovery module of the present invention, the pre-cooled tail gas is shunted and sent to the cooling end of the heat pump for condensation, the obtained low-temperature and low-humidity air is sent to the heat recovery module for pre-heating, the pre-heated air is sent to the heating section of the heat pump for re-heating, and finally the high-temperature and low-humidity air is sent to the dryer for drying the feed. By recycling the tail gas discharged from the dryer, the technical advantages of the heat pump cooling and heating and the heat recovery device are fully utilized. Compared with the current situation of directly discharging the dryer tail gas into the atmosphere and discharging it into the atmosphere through a deodorization device, during the operation of the dryer, the energy consumption is significantly reduced, and the treated tail gas will not cause destructive effects on the environment. It is a low-energy-consumption and low-cost method for treating high-temperature and high-humidity tail gas of a dryer, and has good market application prospects. Description of the Drawings

[0050] Figure 1 is the process flow chart of the dryer tail gas treatment of the present invention;

[0051] Figure 2 It is a schematic structural diagram of the tail gas treatment device of the dryer in Embodiment 1;

[0052] Figure 2 In it: 1 - dryer; 2 - cyclone dust collector; 3 - centrifugal fan; 4 - first heat recovery device; 5 - ventilation duct; 6 - air volume regulating valve; 7 - first heat pump; 701 - first heat pump cooling end; 702 - first heat pump heating end; 8 - second heat pump; 801 - second heat pump cooling end; 802 - second heat pump heating end; 9 - ventilation duct; 10 - condensate water; 11 - ventilation duct; 12 - second heat recovery device; 13 - centrifugal fan; 14 - fresh air; 15 - ventilation duct; 16 - centrifugal fan; 17 - cooler;

[0053] Figure 3 It is a schematic structural diagram of the tail gas treatment device of the dryer in the comparative example;

[0054] Figure 4 It is a schematic structural diagram of the tail gas treatment device of the dryer in Embodiment 2;

[0055] Figure 4 In it: 18 - dryer; 19 - environmental protection treatment system; 20 - cyclone dust collector; 21 - centrifugal fan; 22 - heat recovery device; 23 - heat pump; 2301 - heat pump cooling end; 2302 - heat pump heating end; 24 - condensate water; 25 - fresh air; 26 - centrifugal fan; 27 - ventilation duct; 28 - centrifugal fan; 29 - ventilation duct. Specific embodiments

[0056] Embodiment 1

[0057] In this embodiment, the dryer can dry 10 tons of feed with an initial moisture content of 22% (wet basis moisture content, the same below) to 8% per hour. The temperature of the high-temperature and high-humidity tail gas discharged from the dryer is 65 °C, the specific humidity is 80 g / kg, and the air volume is 30000 m 3 / h.

[0058] As Figure 2 shown, a tail gas treatment device for a dryer includes a high-efficiency cyclone dust collector 2, a first heat recovery device 4, a second heat recovery device 12, a first heat pump 7, and a second heat pump 8. The first heat recovery device 4 and the first heat recovery device 12 are preferably air-to-air plate heat exchangers containing filters.

[0059] The cyclone dust collector 2 is connected to the high-temperature gas flow channel inlet of the first heat recovery device 4 via a circulation fan 3.

[0060] The inlet of the first heat pump cooling end 701 is connected to the high-temperature air flow outlet of the first heat recovery device 4, and the outlet of the first heat pump cooling end 701 is connected to the inlet of the low-temperature air flow channel of the first heat recovery device 4. An air volume regulating valve 6 for adjusting the pneumatic air volume is provided on the ventilation duct 5 between the inlet of the cooling end of the first heat pump and the high-temperature air flow outlet of the first heat recovery device. The air volume regulating valve 6 is preferably a pneumatic air volume regulating butterfly valve.

[0061] The inlet of the second heat pump cooling end 801 is connected to the high-temperature air flow outlet of the first heat recovery device 4, and the outlet of the second heat pump cooling end 801 is connected to the inlet of the low-temperature air flow channel of the first heat recovery device 4 via the ventilation duct 9. The inlet of the second heat pump heating end 802 is connected to the fresh air 14 from the atmosphere. An air volume regulating valve 6 for adjusting the pneumatic air volume is provided on the ventilation duct 5 between the inlet of the cooling end of the second heat pump and the high-temperature air flow outlet of the first heat recovery device. The air volume regulating valve 6 is preferably a pneumatic air volume regulating butterfly valve.

[0062] The high-temperature air flow inlet of the second heat recovery device 12 is connected to the outlet of the second heat pump heating end 802 via the circulation fan 16, and the high-temperature air flow outlet of the second heat recovery device 12 is connected to the cooler 17. The low-temperature air flow inlet of the second heat recovery device 12 is connected to the low-temperature air flow outlet of the first heat recovery device 4 via the ventilation duct 11. The low-temperature air flow outlet of the second heat recovery device 12 is connected to the inlet of the first heat pump heating end 702. The outlet of the first heat pump heating end 702 is connected to the dryer 1 via the circulation fan 13.

[0063] Refer to Figure 1 、 Figure 2 , the method for treating the exhaust gas of the dryer is as follows:

[0064] (1) The exhaust gas of the dryer 1 enters the high-efficiency cyclone dust collector 2 to remove dust with a particle size of 50 - 300 μm. The centrifugal fan 3 is behind the high-efficiency cyclone dust collector 2. Further, the exhaust gas enters the first heat recovery device 4, and after heat exchange with another low-temperature air flow in the first heat recovery device 4, it is cooled to 49.5 °C, and the specific humidity is still 80 g / kg;

[0065] (2) After the exhaust gas comes out of the first heat recovery device 4, it enters the first heat pump cooling end 701 and the second heat pump cooling end 801 along the ventilation duct 5 respectively. The ratio of the air volume entering the first heat pump cooling end 701 and the second heat pump cooling end 801 can be realized by adjusting the air volume regulating valve 6. Preferably, the air volume entering 701 is 3750 m 3 / h, and the air volume entering 801 is 26250 m 3 / h;

[0066] (3) The first heat pump cooling end 701 and the second heat pump cooling end 801 both cool the tail gas to 29°C with a specific humidity of 25.6 g / kg. The tail gases merge and enter the first heat recovery device 4 along the ventilation duct 9. The condensed water 10 separated from the tail gas due to cooling flows out from the drain openings at the bottoms of the first and second heat pumps;

[0067] (4) The tail gas in step (3) is preheated to 44°C with a specific humidity of 25.6 g / kg by the first heat recovery device 4; the tail gas enters the second heat recovery device 12 along the ventilation duct 11 and is further heated to 55°C with a specific humidity of 25.6 g / g; then, the tail gas enters the heating end 702 of the first heat pump along the ventilation duct 11 and is heated by the heat pump to 71.3°C with a specific humidity of 25.6 g / kg; then, the tail gas returns to the dryer 1 after passing through the centrifugal fan 13;

[0068] At the same time, fresh air 14 with a volume flow rate of 186000 m 3 / h, a temperature of 35°C, and a moisture content of 21.4 g / kg (from the atmosphere) enters the heating end 802 of the second heat pump and is heated to 78°C, then enters the second heat recovery device 12 along the ventilation duct 15 and passes through the centrifugal fan 16, and is cooled to 68°C and then leads to the cooler 17.

[0069] In Example 1, compared with the prior art, the present invention has the following remarkable advantages:

[0070] For a dryer that can dry 10 tons of feed with an initial moisture content of 22% to 8% per hour, its tail gas temperature is 65°C, the moisture content is 80 g / kg, and the emission volume is 30000 m 3 / h; at the same time, the dryer needs to supplement fresh air from the surrounding environment into the dryer. Preferably, the temperature of the surrounding fresh air is 35°C and the moisture content is 21.4 g / kg.

[0071] (1) The prior art needs to discharge all the tail gases to the environmental protection deodorization equipment, and the initial investment of this equipment is about 800,000 - 1,000,000 yuan (RMB, the same below), and the later use cost is about 0.4 cents per cubic meter. Calculated based on 3000 hours of production time per year, the use cost is 360,000 yuan / year. However, if the present invention is implemented, the initial investment and the later annual use cost can be eliminated;

[0072] (2) The prior art needs to heat the supplemented fresh air through the steam heat exchanger in the dryer, while the present invention can heat the supplemented fresh air to 71.3°C and then supplement it into the dryer. Through experimental detection, the steam heat exchanger heats 26500 m 3 / h, the steam flow rate required to heat 21.4 g / kg of fresh air from 35°C to 71.3°C is 942 kg / h. Taking the market average price of steam as 0.4 yuan / kg, it costs 377 yuan per hour; the power of all additional power-consuming equipment such as the heat pump and fan used in the present invention is 350 kW. Taking the weighted electricity cost as 0.6 yuan / kWh, the present invention costs 210 yuan per hour. Calculated based on 3000 hours of production time per year, it can save 500,000 yuan per year;

[0073] (3)Generally speaking, for the dryer under the aforementioned preconditions, Example 1 can save the feed mill an initial investment cost of 800,000 - 1,000,000 yuan, and can additionally save 860,000 yuan per year.

[0074] Control example of Example 1

[0075] As Figure 3 shown, all the tail gas of the dryer enters the high-efficiency cyclone dust collector, and only 1 heat pump is used to treat the tail gas of the dryer. Assuming the tail gas volume of the dryer is 1, 3 - 7 parts of fresh air need to be supplemented to make the air volume ratio of the refrigeration end and the heating end of this heat pump meet 1:4 - 1:8. However, since the dryer only needs the same amount of air as the tail gas as a supplement, the heated tail gas has to discharge 3 - 7 parts of hot air again, and only 1 part of the hot air is recycled into the dryer. At this time, the 3 - 7 parts of hot air discharged have been mixed with the tail gas and belong to polluted air. Whether it goes directly to the deodorization system or is directly discharged into the atmosphere, this solution is no longer meaningful.

[0076] The reason for setting two heat pumps in this embodiment is that the air volumes of the heating end and the refrigeration end of the heat pump are different, but the gas volumes discharged and supplemented by the dryer should be the same. Therefore, no matter how many heat pumps are used, if the gas volume flowing through the refrigeration end of the heat pump is the total tail gas volume of the dryer, the gas volume at the heating end of the heat pump will inevitably be greater than the gas volume required for the dryer to be supplemented.

[0077] Example 2

[0078] Considering that some feed mills have already completed the initial investment in environmental protection deodorization, they do not want to spend a large amount of money to choose Example 1 to achieve the zero-emission effect of the dryer, but only hope to spend less money and save money by reducing the tail gas emissions of the dryer and saving energy consumption. Therefore, Example 2 is aimed at this type of demand.

[0079] As Figure 4 shown, a dryer tail gas treatment device includes a cyclone dust collector 20, a heat recovery device 22, and a heat pump 23.

[0080] One end of the cyclone dust collector 20 is connected to the dryer tail gas via a ventilation duct, and the other end of the cyclone dust collector 20 is connected to the high-temperature gas flow channel inlet of the heat recovery device 26 via a circulation fan 21.

[0081] The inlet of the heat pump cooling end 2301 is connected to the high-temperature air outlet of the heat recovery device 22; the outlet of the heat pump cooling end 2301 is connected to the inlet of the low-temperature air flow channel of the heat recovery device 26 via a pipeline. The pipeline between the outlet of the heat pump cooling end 2301 and the inlet of the low-temperature air flow channel of the heat recovery device 26 is connected to the fresh air 25 via a circulation fan.

[0082] The inlet of the heat pump heating end 2302 is connected to the low-temperature air outlet of the heat recovery device 22 via a pipeline 27, and the outlet of the heat pump heating end 2302 is connected to the air supply inlet of the dryer via a circulation fan 28 and a ventilation pipeline 29.

[0083] In this embodiment, the dryer can dry 10 tons of feed with an initial moisture content of 22% (wet basis moisture content, the same below) to 8% per hour. The temperature of the high-temperature and high-humidity tail gas discharged from the dryer is 65 °C, the specific humidity is 80 g / kg, and the air volume is 30000 m 3 / h.

[0084] Referring to Figure 4 , the method for treating the tail gas of the dryer is as follows:

[0085] (1) 2 / 3 of the tail gas of the dryer 18 (i.e., 20000 m 3 / h) does not pass through the heat pump system and directly enters the environmental protection treatment system 19 of the feed mill. The remaining 1 / 3 (i.e., 10000 m 3 / h) enters the high-efficiency cyclone dust collector 20 to remove dust with a particle size of 50 - 300 μm; then, under the action of the centrifugal fan 21, the tail gas enters the heat recovery device 22 and is cooled to 49 °C after heat exchange with another low-temperature air flow in the heat recovery device 22, and the specific humidity remains 80 g / kg;

[0086] (2) The tail gas preliminarily cooled in step (1) enters the heat pump cooling end 2301 and is cooled to 38 °C, and the specific humidity drops to 43.5 g / kg. The condensed water 24 condenses and flows out from the drain outlet at the bottom of the heat pump;

[0087] (3) Fresh air 25 (from the atmosphere) with an outside dry-bulb temperature of 35 °C and a specific humidity of 21.4 g / kg is sucked into the heat pump system by the centrifugal fan 26 and merges with the air flow obtained in step (2). The ratio of the fresh air to the air flow in step (2) is 2:1. The dry-bulb temperature of the merged gas becomes 36 °C, and the specific humidity becomes 30.6 g / kg;

[0088] (4)The mixed gas obtained in step (3) enters the heat recovery device 22, is preheated to 43°C, and is conveyed along the ventilation duct 27 to the heat pump heating end 2302 and heated to 70.5°C. Then it is driven by the centrifugal fan 28 and returns to the dryer 18 along the ventilation duct 29.

[0089] In Example 2, compared with the prior art, the present invention has the following remarkable advantages:

[0090] For a dryer that can dry 10 tons of feed with an initial moisture content of 22% to 8% per hour, its tail gas temperature is 65°C, the moisture content is 80 g / kg, and the emission is 30000 m 3 / h; at the same time, the dryer needs to supplement fresh air in the surrounding environment into the dryer. Preferably, the temperature of the surrounding fresh air is 35°C and the moisture content is 21.4 g / kg.

[0091] (1) In the prior art, all tail gases need to be discharged to the environmental protection deodorization equipment, and the use cost of this equipment is about 0.4 cents per cubic meter. However, in this Example 2, the tail gas emission can be reduced by 10000 m 3 / h. Calculated based on 3000 hours of production time per year, 120,000 yuan can be saved annually in the use cost of environmental protection deodorization;

[0092] (2) In the prior art, the supplemented fresh air needs to be heated by the steam heat exchanger in the dryer, while the present invention can heat the supplemented fresh air to 70.5°C and then supplement it into the dryer. Through experimental detection, the steam heat exchanger needs to consume a steam flow rate of 905 kg / h to heat 26500 m3 / h of fresh air at 35°C and 21.4 g / kg to 70.5°C. Taking the market average price of steam as 0.4 yuan / kg, it costs 362 yuan per hour; the total power of all additional power-consuming equipment such as the heat pump and fan used in the present invention is 72 kW. Taking the weighted electricity cost as 0.6 yuan / kWh, the present invention costs 30 yuan per hour. Calculated based on 3000 hours of production time per year, 950,000 yuan can be saved annually;

[0093] (3) Generally speaking, for the dryer under the foregoing preconditions, Example 2 can save 1.07 million yuan for the feed factory annually.

Claims

1. Method for treating tail gas of dryer, characterized in that, it includes the following steps: (1) All the tail gas of the dryer enters the high-efficiency dust removal device to remove dust with a particle size of 50 - 300 μm. The tail gas after dust removal enters the first heat recovery device with a filter through the first circulation fan, and is cooled to below 50 °C after heat exchange with the low-temperature air flow in the first heat recovery device, and the specific humidity is still 80 g / kg; (2) The tail gas treated by the first heat recovery device enters the cooling ends of the first heat pump and the second heat pump respectively along the ventilation duct for cooling. The cooling end of the first heat pump cools the tail gas to 29 - 35 °C, and the cooling end of the second heat pump cools the tail gas to 29 - 38 °C; the condensed water precipitated from the tail gas due to cooling flows out from the heat pump; the cooling air volume ratio of the cooling end of the first heat pump to the cooling end of the second heat pump is (1 / 8 - 1 / 4) : (3 / 4 - 7 / 8); (3) The tail gas cooled by the cooling ends of the first heat pump and the second heat pump converges, and enters the first heat recovery device with a filter along the ventilation duct for heat exchange for primary preheating; the specific humidity of the converged tail gas is 25.6 - 36.5 g / kg; (4) The tail gas preheated by the first heat recovery device enters the second heat recovery device with a filter along the ventilation duct, and undergoes heat exchange with the high-temperature air flow in the second heat recovery device for secondary preheating; The high-temperature air flow in the second heat recovery device comes from: the heating end of the second heat pump absorbs external fresh air for heating. The ratio of the air volume of the cooling end of the second heat pump to the air volume of the heating end of the second heat pump is between 1:4 and 1:

8. The heated fresh air enters the second heat recovery device through the circulation fan to form the high-temperature air flow; (5) The tail gas after secondary preheating enters the heating end of the first heat pump along the ventilation duct and is heated by the heat pump to 70 - 75 °C, and then returns to the dryer under the action of the circulation fan.

2. The method for treating tail gas of dryer according to claim 1, characterized in that, the external fresh air temperature in step (4) is 35 °C, and the specific humidity is 21.4 g / kg.

3. The method for treating tail gas of dryer according to claim 1, characterized in that, the high-temperature air flow in the second heat recovery device in step (4) is subjected to condensation treatment after heat exchange.

4. The method for treating tail gas of dryer according to claim 1, characterized in that, the heat recovery device is a plate heat exchanger for gas-to-gas heat exchange.

5. Device for realizing the method for treating tail gas of dryer according to any one of claims 1 - 4, characterized in that, it includes a dust removal device, a first heat recovery device, a second heat recovery device, a first heat pump, and a second heat pump; the dust removal device is connected to the high-temperature air flow channel inlet of the first heat recovery device via a circulation fan; the cooling end inlet of the first heat pump is connected to the high-temperature air flow outlet of the first heat recovery device; the cooling end outlet of the first heat pump is connected to the low-temperature air flow channel inlet of the first heat recovery device; The inlet of the cooling end of the second heat pump is connected to the high-temperature air flow outlet of the first heat recovery device; the outlet of the cooling end of the second heat pump is connected to the inlet of the low-temperature air flow channel of the first heat recovery device; the inlet of the heating end of the second heat pump is connected to the external air via a circulation fan; regulating pneumatic air volume valves are provided on the connecting pipeline between the inlet of the cooling end of the first heat pump and the high-temperature air flow outlet of the first heat recovery device and on the connecting pipeline between the inlet of the cooling end of the second heat pump and the high-temperature air flow outlet of the first heat recovery device; The high-temperature air flow inlet of the second heat recovery device is connected to the heating end outlet of the second heat pump via a circulation fan; the high-temperature air flow outlet of the second heat recovery device is connected to the condenser; the low-temperature air flow inlet of the second heat recovery device is connected to the low-temperature air flow outlet of the first heat recovery device; the low-temperature air flow outlet of the second heat recovery device is connected to the heating end inlet of the first heat pump; the heating end outlet of the first heat pump is connected to the dryer via a circulation fan.

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