Kiln waste gas and waste heat recovery process and system

Abstract

The present invention discloses a process and system for recovering waste heat from kiln exhaust gas. The high-temperature exhaust gas from the kiln realizes waste heat utilization through a waste heat refrigeration device and a heat exchanger. The waste heat can be used for waste gas condensation and water removal, heat exchange of inlet furnace oxygen, and regeneration of a rotary dehumidifier. The exhaust gas from a first firing kiln can obtain oxygen with a concentration greater than 95% after wet impurity removal and secondary water removal, and can be directly used for secondary sintering of high-nickel ternary materials. The exhaust gas from a second firing kiln can be used for heating oxygen for primary sintering. The remaining exhaust gas can obtain oxygen with an oxygen concentration greater than 97% after dust removal by a dust filtration device and water and carbon dioxide removal by a purification device, and can be directly used for primary sintering, thereby realizing the cyclic regeneration of oxygen. The present invention realizes the multiple utilization of waste heat and the cyclic regeneration of oxygen, making the production process consume less gas and be highly energy-efficient.

Description

Technical Field

[0001] The present invention relates to the technical field of recovery and utilization of kiln tail gas, and particularly relates to a process and system for recovering waste gas and waste heat from a kiln. Background Art

[0002] With the rise of the new energy lithium-ion battery industry, high-nickel ternary materials have attracted much attention due to their high energy density and long cycle life. How to reduce the production cost of high-nickel ternary cathode materials is an unchanged theme. Considering the current situation of the pure oxygen sintering process in long kilns, there is still a large room for cost reduction in the recycling of waste gas and waste heat. Related technologies have recorded an oxygen recovery and utilization device for a kiln for sintering high-nickel ternary materials, which only removes part of the water vapor by condensation. In addition, other dust carried out by the exhaust gas will greatly affect the oxygen concentration, and it is very likely that the oxygen concentration required for sintering, which is more than 95%, cannot be achieved, thus affecting the sintering effect of high-nickel ternary materials. In addition, a system for recovering and utilizing the tail gas of a high-nickel kiln has also been recorded. This solution only removes impurities from the discharged waste gas and then re-oxygenates it to further improve the air oxygen production efficiency, rather than efficiently recycling the oxygen after kiln sintering. Therefore, it is very necessary to develop a process that can directly recycle and utilize oxygen and waste heat. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides a process and system for recovering waste gas and waste heat from a kiln, which can efficiently recycle oxygen and waste heat during the sintering process of high-nickel ternary cathode materials to reduce production costs.

[0004] According to a first aspect embodiment of the present invention, a process for recovering waste gas and waste heat from a kiln includes the following steps:

[0005] S1. Fresh gas is heated by a heat exchanger and then enters a first firing kiln for reaction. The high-temperature waste gas generated by the reaction enters a waste heat refrigeration device for heat exchange and then is introduced into a wet dust collector.

[0006] S2. The waste gas after dust removal is dehumidified by a condensation device and then introduced into the moisture absorption area of a rotary dehumidifier for deep water removal to obtain a primary recycled gas.

[0007] S3. The primary recycled gas is introduced into a second firing kiln for reaction. The high-temperature waste gas generated by the reaction first passes through the heat exchanger to use part of the heat to heat the fresh gas, and then enters a dust filtration device for dust removal.

[0008] S4. The waste gas with waste heat after dust removal is introduced into the regeneration area of the rotary dehumidifier and finally enters a purification device to obtain a secondary recycled gas.

[0009] S5. The secondary recycled gas is reintroduced into the first firing kiln for reuse.

[0010] Among them, the waste heat refrigeration device can be used for refrigerating the condensation device.

[0011] In the present invention, the waste heat recovery process of kiln exhaust gas is used in the sintering process of high-nickel ternary cathode materials. The required gas is oxygen, and the ternary cathode materials are ternary nickel cobalt manganese lithium (NCM622, 712, 811, 955), lithium nickel cobalt aluminate (NCA), nickel cobalt manganese aluminum lithium, or lithium-rich manganese-based.

[0012] The waste heat recovery process of kiln exhaust gas according to the embodiments of the present invention has at least the following beneficial effects:

[0013] 1. The high-temperature exhaust gas from the kiln realizes waste heat utilization through the waste heat refrigeration device and the heat exchanger. The waste heat can be used for exhaust gas condensation and water removal, heat exchange of inlet oxygen, and regeneration of the rotary dehumidifier, so that the waste heat can be efficiently utilized.

[0014] 2. The exhaust gas from the first firing kiln can obtain oxygen with a concentration greater than 95% after wet impurity removal and secondary water removal, and can be directly used for the secondary sintering of high-nickel ternary materials.

[0015] 3. The exhaust gas from the second firing kiln can be used for heating the fresh gas for the first sintering, further saving energy. The remaining exhaust gas can obtain oxygen with an oxygen concentration greater than 97% after dust removal by the dust filtration device and water and carbon dioxide removal by the purification device, and can be directly used for the first sintering, thus realizing the recycling and regeneration of oxygen.

[0016] 4. The operating power of this waste heat recovery process of exhaust gas is mainly the induced draft fan and the water pump. Therefore, the energy consumption of this process is extremely low, greatly saving the operating cost. In addition, the oxygen recovery of this process is mainly purification rather than pure oxygen production, so the recovery efficiency is high. Compared with the conventional roller hearth kiln sintering process, the present invention combines the sintering characteristics of high-nickel ternary cathode materials, realizes the multiple utilization of waste heat and the recycling and regeneration of oxygen, making the production process consume less gas and be highly energy-efficient.

[0017] According to some embodiments of the present invention, the waste heat refrigeration device can also be used for refrigerating the wet dust collector and / or the cooling zone of the first firing kiln and / or the cooling zone of the second firing kiln.

[0018] According to some embodiments of the present invention, this process is used in the sintering process of high-nickel ternary cathode materials, the fresh gas is fresh oxygen, and the high-temperature exhaust gas is high-temperature oxygen-rich exhaust gas.

[0019] According to some embodiments of the present invention, the high-temperature exhaust gas generated by the first firing kiln is directly discharged into the waste heat refrigeration device, and the high-temperature exhaust gas generated by the second firing kiln is directly discharged into the heat exchanger. The direct discharge means that no air is supplemented in the exhaust gas pipeline. Since the existence of the air supply port will reduce the temperature of the exhaust gas and the oxygen concentration in the exhaust gas, the direct discharge method can completely collect all the exhaust gas and waste heat from the kiln.

[0020] According to some embodiments of the present invention, the temperature of the high-temperature waste gas generated by the first firing kiln is 400 - 600 °C; the temperature of the high-temperature waste gas generated by the second firing kiln is 200 - 400 °C.

[0021] According to some embodiments of the present invention, the secondary recycled gas and the fresh gas are introduced into the first firing kiln at a volume ratio of 10:(1 - 10).

[0022] The waste heat recovery system for kiln waste gas according to the second aspect embodiments of the present invention includes a heat exchanger, a first firing kiln, a waste heat refrigeration device, a wet dust collector, a condensation device, a rotary dehumidifier, a second firing kiln, a dust filtration device, and a purification device. The rotary dehumidifier includes a moisture absorption area and a regeneration area. The gas enters the first firing kiln through the heat exchanger. The waste gas of the first firing kiln sequentially passes through the waste heat refrigeration device, the wet dust collector, the condensation device, and the moisture absorption area and then enters the second firing kiln. The waste gas of the second firing kiln is introduced into the heat exchanger as a heating medium, and then sequentially passes through the dust filtration device, the regeneration area, and the purification device. The outlet of the purification device is communicated with the inlet of the first firing kiln. Among them, the waste heat refrigeration device can be used for refrigerating the condensation device.

[0023] According to some embodiments of the present invention, the waste heat refrigeration device is a lithium bromide water chiller. The lithium bromide water chiller includes a generator and an evaporator. The first firing kiln is communicated with the generator. The condensation device includes a cooling water chamber, a condensation gas chamber, and a first circulating cooling water pipe. The condensation gas chamber is arranged in the cooling water chamber. The water in the cooling water chamber can flow through the evaporator through the first circulating cooling water pipe to achieve heat exchange. The bottom of the condensation gas chamber can hold condensed water and is provided with a drain valve.

[0024] According to some embodiments of the present invention, the first firing kiln and / or the second firing kiln includes a temperature reduction area. The condensation device further includes a second circulating cooling water pipe. The water in the cooling water chamber can flow through the temperature reduction area through the second circulating cooling water pipe to achieve heat exchange.

[0025] According to some embodiments of the present invention, the condensation device further includes a third circulating cooling water pipe. The wet dust collector is a water curtain dust collector. The water curtain dust collector includes a water tank. The water in the cooling water chamber can flow through the water tank through the third circulating cooling water pipe to achieve heat exchange.

[0026] According to some embodiments of the present invention, the purification device is a molecular sieve purifier.

[0027] According to some embodiments of the present invention, a gas storage tank is further communicated between the moisture absorption area and the second firing kiln.

[0028] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. Brief Description of the Drawings

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0030] Figure 1 is a schematic diagram of waste gas and waste heat recovery of the sintering process of the high-nickel ternary cathode material in the embodiment of the present invention;

[0031] Figure 2 is a schematic diagram of the structure of the rotary dehumidifier in the embodiment of the present invention.

[0032] Reference numerals: heat exchanger 100, first firing kiln 200, cooling zone 210, induced draft fan 300, lithium bromide water chiller 400, generator 410, evaporator 420, water curtain dust collector 500, water tank 510, condensation device 600, condensation gas chamber 610, cooling water chamber 620, first circulating cooling water pipe 630, second circulating cooling water pipe 640, third circulating cooling water pipe 650, rotary dehumidifier 700, moisture absorption zone 710, regeneration zone 720, gas storage tank 800, second firing kiln 900, dust filter 1000, molecular sieve purifier 1100, waste gas port 1110. Detailed Description of the Embodiments

[0033] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, in which the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

[0034] Referring to Figure 1 , a waste gas and waste heat recovery system for a kiln includes a heat exchanger 100, a first firing kiln 200, a waste heat refrigeration device, a wet dust collector, a condensation device 600, a rotary dehumidifier 700, a second firing kiln 900, a dust filtering device and a purification device. The rotary dehumidifier 700 includes a moisture absorption zone 710 and a regeneration zone 720. Gas enters the first firing kiln 200 through the heat exchanger 100. The waste gas of the first firing kiln 200 sequentially passes through the waste heat refrigeration device, the wet dust collector, the condensation device 600 and the moisture absorption zone 710 and then enters the second firing kiln 900. The waste gas of the second firing kiln 900 is introduced into the heat exchanger 100 as a heating medium, and then sequentially introduced into the dust filtering device, the regeneration zone 720 and the purification device. The outlet of the purification device is communicated with the inlet of the first firing kiln 200. Among them, the waste heat refrigeration device can be used for refrigeration of the condensation device 600.

[0035] In some of these embodiments, the waste heat refrigeration device is a lithium bromide water chiller 400, which includes a generator 410 and an evaporator 420. A kiln 200 is communicated with the generator 410; the condensation device 600 includes a cooling water chamber 620, a condensation gas chamber 610, and a first circulating cooling water pipe 630. The condensation gas chamber 610 is arranged in the cooling water chamber 620. The water in the cooling water chamber 620 can flow through the evaporator 420 through the first circulating cooling water pipe 630 to achieve heat exchange. The bottom of the condensation gas chamber 610 can hold condensed water and is provided with a drain valve.

[0036] In some of these embodiments, the first kiln 200 and / or the second kiln 900 includes a cooling zone 210. The condensation device 600 further includes a second circulating cooling water pipe 640. The water in the cooling water chamber 620 can flow through the second circulating cooling water pipe 640 through the cooling zone 210 to achieve heat exchange.

[0037] In some of these embodiments, the condensation device 600 further includes a third circulating cooling water pipe 650. The wet dust collector is a water curtain dust collector 500, which includes a water tank 510. The water in the cooling water chamber 620 can flow through the third circulating cooling water pipe 650 through the water tank 510 to achieve heat exchange.

[0038] In some of these embodiments, the purification device is a molecular sieve purifier 1100.

[0039] In some of these embodiments, a gas storage tank 800 is further communicated between the moisture absorption zone 710 and the second kiln 900.

[0040] Embodiment

[0041] Refer to Figure 1 , a waste heat recovery process for the exhaust gas of a kiln for sintering high-nickel ternary cathode materials, comprising the following steps:

[0042] S1. Fresh oxygen enters from the inlet valve, is heated by the heat exchanger 100 and then enters the first kiln 200. The high-temperature oxygen-rich exhaust gas (400 - 600 °C) after the reaction is directly discharged from the kiln exhaust port under the action of the induced draft fan 300, and then enters the generator 410 of the lithium bromide water chiller 400 for heat exchange. Then the exhaust gas is introduced into the water curtain dust collector 500, and the dust such as lithium oxide in the exhaust gas is adsorbed and dissolved by the water curtain.

[0043] S2. The exhausted gas after dust removal is then introduced into the condensation gas chamber 610 of the condensation device 600. Since the condensation gas chamber 610 is surrounded by cooling water, the temperature of the condensation gas chamber 610 is very low, thereby condensing and dehumidifying the water vapor in the exhausted gas. It should be noted that the cooling water in the cooling water chamber 620 is cooled by the evaporator 420 of the lithium bromide chiller 400. The specific principle is as follows: After the lithium bromide aqueous solution is heated by the high-temperature exhausted gas in the generator 410, the water in the solution continuously vaporizes. As the water continuously vaporizes, the concentration of the lithium bromide aqueous solution in the generator 410 continuously increases and enters the absorber. The water vapor enters the condenser and is condensed after being cooled by the cooling water in the condenser, becoming high-pressure and low-temperature liquid water. When the water in the condenser passes through the throttle valve and enters the evaporator 420, it rapidly expands and vaporizes. When the water in the cooling water chamber 620 enters the evaporator 420 through the first circulating cooling water pipe 630, a large amount of heat of the water in the evaporator 420 is absorbed during the vaporization process, and the cooled water returns from the evaporator 420 to the cooling water chamber 620, enabling the condensation device 600 to have the function of cooling and refrigeration. In addition, the cooling water also passes through the second circulating cooling water pipe 640 and is introduced into the water tank 510 of the water curtain dust collector 500 to cool the exhausted gas, and the cooling water also passes through the third circulating cooling water pipe 650 and is introduced into the cooling area 210 of a firing kiln 200 to cool the materials in the cooling area 210. The exhausted gas after condensation and dehumidification enters the moisture absorption area 710 of the rotary dehumidifier 700 for deep water removal, and the primary recycled oxygen with a purity greater than 95% is obtained after coming out.

[0044] S3. The primary recycled oxygen enters the gas storage tank 800 for buffering, and then directly enters the second firing kiln 900 through the inlet valve, and is used for the secondary sintering process of the high-nickel ternary cathode material. The high-temperature oxygen-rich exhausted gas (200 - 400 °C) after secondary sintering is directly discharged as a heating medium and introduced into the heat exchanger 100 to use a part of the waste heat of the second firing exhausted gas to heat the fresh oxygen, and then the material dust carried out is removed by the dust filter 1000.

[0045] S4. The oxygen-rich exhausted gas with heat (80 - 200 °C) after dust removal is introduced into the regeneration area 720 of the rotary dehumidifier 700 to restore the activity of the moisture absorption area 710. The structural schematic diagram of the rotary dehumidifier 700 is as Figure 2 shown. Finally, the oxygen-rich exhausted gas enters the molecular sieve purifier 1100 for adsorption and purification of carbon dioxide and water, and the secondary recycled oxygen with a purity greater than 97% is obtained. The carbon dioxide and water adsorbed by the molecular sieve purifier 1100 are directly discharged from the exhaust gas port 1110.

[0046] S5. The secondary recycled oxygen and fresh oxygen are re-introduced into the first firing kiln 200 in a volume ratio of 10:(1 - 10) through the inlet valve for recycling.

[0047] Comparative Example 1

[0048] Taking the production process of conventional high-nickel ternary cathode materials as a reference, only waste gas filtration and dust removal are carried out during either the first firing or the second firing process, and then it is directly discharged into the air.

[0049] Comparative Example 2

[0050] Taking the patent (CN110836608A) as Comparative Example 2, in this recycling process, the oxygen generation device is a pressure swing adsorption oxygen generation device, and then recycling is carried out according to this process.

[0051] Comparative Example 3

[0052] Taking the patent (CN110836608A) as Comparative Example 3, in this recycling process, the oxygen generation device is a cryogenic air separation oxygen generation device, and then recycling is carried out according to this process.

[0053] The economic benefits of the above-mentioned examples and Comparative Examples 1-3 were calculated for the energy-saving recycling during the sintering process of 400 kg / h of high-nickel ternary cathode materials, as shown in the following table:

[0054]

[0055] By comparing and analyzing the data in the above table, it can be clearly found that with different equipment investments, the equipment prices and oxygen recovery rates will also be different, and the corresponding operating costs and revenues will also have huge differences. From the perspective of the benefit return period and the economic benefits over 10 years, the recycling process of the present invention is far superior to Comparative Examples 1-3. The main reason is that the oxygen recovery in the present invention is mainly purification rather than oxygen generation, so it is more efficient and economical.

[0056] The embodiments of the present invention have been described in detail above with reference to the drawings. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. A waste heat recovery process for kiln furnace exhaust gas, characterized in that, it includes the following steps: S1. Fresh gas is heated by a heat exchanger and then enters a firing kiln for reaction. The high-temperature exhaust gas generated by the reaction enters a waste heat refrigeration device for heat exchange and then is introduced into a wet dust collector; S2. The exhaust gas after dust removal is dehumidified by a condensation device and then introduced into the moisture absorption area of a rotary dehumidifier for deep water removal to obtain a primary recovered gas; S3. The primary recovered gas is introduced into a second firing kiln for reaction. The high-temperature exhaust gas generated by the reaction first passes through the heat exchanger to use part of the heat to heat the fresh gas, and then enters a dust filtration device for dust removal; S4. The exhaust gas with residual heat after dust removal is introduced into the regeneration area of the rotary dehumidifier and finally enters a purification device to obtain a secondary recovered gas; S5. The secondary recovered gas is re-introduced into the first firing kiln for reuse; wherein, the waste heat refrigeration device can be used for refrigerating the condensation device.

2. The process according to claim 1, characterized in that, the waste heat refrigeration device can also be used for refrigerating the wet dust collector and / or the cooling area of the first firing kiln and / or the cooling area of the second firing kiln.

3. The process according to claim 1, characterized in that, the high-temperature exhaust gas generated by the first firing kiln is directly discharged into the waste heat refrigeration device; the high-temperature exhaust gas generated by the second firing kiln is directly discharged into the heat exchanger.

4. The process according to claim 1, characterized in that, the secondary recovered gas and the fresh gas are introduced into the first firing kiln at a volume ratio of 10:(1 - 10).

5. A waste heat recovery system for kiln furnace exhaust gas, characterized in that, it includes a heat exchanger (100), a first firing kiln (200), a waste heat refrigeration device, a wet dust collector, a condensation device (600), a rotary dehumidifier (700), a second firing kiln (900), a dust filtration device and a purification device. The rotary dehumidifier (700) includes a moisture absorption area (710) and a regeneration area (720). Gas enters the first firing kiln (200) through the heat exchanger (100). The exhaust gas of the first firing kiln (200) sequentially passes through the waste heat refrigeration device, the wet dust collector, the condensation device (600) and the moisture absorption area (710) and then enters the second firing kiln (900). The exhaust gas of the second firing kiln (900) is used as a heating medium to enter the heat exchanger (100), and then sequentially passes through the dust filtration device, the regeneration area (720) and the purification device. The outlet of the purification device is communicated with the inlet of the first firing kiln (200). Wherein, the waste heat refrigeration device can be used for refrigerating the condensation device (600).

6. The waste heat recovery system for kiln furnace exhaust gas according to claim 5, characterized in that, The waste heat refrigeration device is a lithium bromide water chiller (400). The lithium bromide water chiller (400) includes a generator (410) and an evaporator (420). The first kiln furnace (200) is communicated with the generator (410). The condensation device (600) includes a cooling water chamber (620), a condensation gas chamber (610) and a first circulating cooling water pipe (630). The condensation gas chamber (610) is arranged in the cooling water chamber (620). The water in the cooling water chamber (620) can flow through the evaporator (420) through the first circulating cooling water pipe (630) to realize heat exchange. The bottom of the condensation gas chamber (610) can hold condensed water and is provided with a drain valve.

7. The waste heat recovery system of the kiln exhaust gas according to claim 6, characterized in that, the first kiln furnace (200) and / or the second kiln furnace (900) includes a cooling zone (210). The condensation device (600) further includes a second circulating cooling water pipe (640). The water in the cooling water chamber (620) can flow through the cooling zone (210) through the second circulating cooling water pipe (640) to realize heat exchange.

8. The waste heat recovery system of the kiln exhaust gas according to claim 6, characterized in that, the condensation device (600) further includes a third circulating cooling water pipe (650). The wet dust collector is a water curtain dust collector (500). The water curtain dust collector (500) includes a water tank (510). The water in the cooling water chamber (620) can flow through the water tank (510) through the third circulating cooling water pipe (650) to realize heat exchange.

9. The waste heat recovery system of the kiln exhaust gas according to claim 5, characterized in that, the purification device is a molecular sieve purifier (1100).

10. The waste heat recovery system of the kiln exhaust gas according to claim 5, characterized in that, a gas storage tank (800) is also communicated between the moisture absorption zone (710) and the second kiln furnace (900).

Images