A low-temperature flue gas waste heat recovery system for molten salt furnaces in chlor-alkali production
By designing a low-temperature flue gas waste heat recovery system in chlor-alkali production, the waste heat of low-temperature flue gas is used to heat brine and wastewater, solving the problem of unutilized latent heat of low-temperature flue gas, improving hydrogen combustion efficiency and brine temperature, and achieving energy saving and emission reduction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- LANZHOU HEWEI ENVIRONMENTAL PROTECTION TECH CO LTD
- Filing Date
- 2025-02-11
- Publication Date
- 2026-05-26
AI Technical Summary
In existing technologies, the latent heat of water vapor in low-temperature flue gas is not effectively utilized, resulting in low brine temperature during chlor-alkali production, which affects process stability and efficiency, and requires a large amount of steam replenishment.
A low-temperature flue gas waste heat recovery system for molten salt furnaces in chlor-alkali production was designed. The system utilizes the waste heat from the low-temperature flue gas through primary and secondary recovery devices to heat brine and wastewater, thereby increasing their temperatures and recovering condensate, thus achieving efficient utilization of waste heat.
It improves hydrogen combustion efficiency, saves energy, increases brine temperature, extends resin regeneration cycle, reduces energy waste, and achieves energy conservation and emission reduction.
Smart Images
Figure CN224285469U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of low-temperature waste heat recovery technology, and in particular to a low-temperature flue gas waste heat recovery system for molten salt furnaces in chlor-alkali production. Background Technology
[0002] The molten salt furnace uses hydrogen as fuel, excess air as an oxidizer, and sodium nitrate, potassium nitrate, and sodium nitrite as heat transfer media. The heat generated by the complete combustion of hydrogen is transferred to the final concentrator through the heat transfer media, where 61% of the water in the alkali is evaporated to produce 98% molten alkali.
[0003] The flue gas produced by the molten salt furnace at 400°C, after heat exchange in the air heat exchanger, still has a temperature of 230°C. Using a waste heat boiler to produce steam, the flue gas temperature can only be reduced to 130°C, meaning the latent heat carried by the water vapor in the low-temperature flue gas cannot be released, resulting in resource waste.
[0004] In the chlor-alkali industry, processes such as salting and chelating resin adsorption require brine temperatures of 55-65℃. Lower brine temperatures lead to problems such as reduced salting rate, lower salt concentration, slower precipitate formation rate, and slower precipitate settling rate. Lower brine temperatures also reduce the penetration capacity of chelating resins and their ability to adsorb calcium ions, resulting in process instability. However, industrial water, hydrogen-based washing solutions, and salt mud washing solutions are used as brine at only room temperature; the primary refined brine temperature is only 50℃. Raising the brine temperature to 65℃ and the primary refined brine temperature to 60℃ requires a large amount of steam to meet production demands.
[0005] Further effective solutions are needed to further utilize the latent heat carried by water vapor in low-temperature flue gas and improve the efficiency of hydrogen combustion. Utility Model Content
[0006] Purpose of the utility model: To address the problems existing in the prior art, this utility model provides a low-temperature flue gas waste heat recovery system for molten salt furnaces in chlor-alkali production. By utilizing the heat of wet flue gas and the latent heat of steam to heat heat-consuming fluids such as brine, the system recovers the waste heat of low-temperature flue gas from the molten salt furnace, thereby improving the efficiency of hydrogen combustion.
[0007] Technical Solution: This utility model provides a low-temperature flue gas waste heat recovery system for molten salt furnaces in chlor-alkali production, comprising: a molten salt furnace and a primary recovery device and a secondary recovery device connected to the flue gas exhaust port of the molten salt furnace via pipelines; the inlet of the primary recovery device is connected to a primary refined brine storage tank, and the outlet of the primary recovery device is connected to a resin tower; the inlet of the secondary recovery device is connected to a wastewater recovery storage tank, and the outlet of the secondary recovery device is connected to a brine storage tank.
[0008] The first-stage recovery unit uses convection heat transfer to heat the primary refined brine using the waste heat from the low-temperature flue gas of the molten salt furnace, raising the temperature of the primary refined brine to 60°C, thereby increasing the resin penetration capacity, extending the resin regeneration cycle, and reducing energy waste. The second-stage recovery unit uses convection heat transfer to heat the wastewater (chemical brine) in the wastewater recovery storage tank using the waste heat from the low-temperature flue gas of the molten salt furnace, raising the temperature of the chemical brine to 65°C, thereby controlling the NaCl concentration of the crude brine.
[0009] In the first and second stage recovery units, during the convective heat exchange process, water vapor in the low-temperature flue gas of the molten salt furnace condenses to produce condensate. The first and second stage recovery units recover the water vapor condensate and transport it through pipelines to the brine storage tank to recover the condensate and avoid wasting water vapor.
[0010] The first-stage recovery unit is equipped with a diversion mechanism and DCS automatic control. The diversion mechanism controls the temperature of the primary refined brine to 60±1℃. The second-stage recovery unit is equipped with a diversion mechanism and DCS automatic control. The diversion mechanism controls the temperature of the wastewater to 63-65℃.
[0011] Furthermore, a brine transfer pump is installed at the outlet of the primary refined brine storage tank. The primary refined brine in the primary refined brine storage tank is transferred to the intermediate brine tank via the brine transfer pump.
[0012] Furthermore, the system also includes a transfer brine tank, which is located between the primary refined brine storage tank and the first-stage recovery device. The transfer brine tank is connected to both the primary refined brine storage tank and the first-stage recovery device via pipelines. The transfer brine tank provides a buffer for water supply, increasing the system's fault tolerance.
[0013] Furthermore, a brine booster pump is installed at the outlet of the intermediate brine tank. The primary refined brine in the intermediate brine tank is pressurized by the brine booster pump and then enters the first-stage recovery unit to exchange heat with the flue gas. The first-stage recovery unit is connected to the resin tower, where the primary refined brine, after heat exchange, absorbs calcium and magnesium ions from the primary refined brine.
[0014] Furthermore, a wastewater transfer pump is installed at the outlet of the wastewater recovery storage tank. The wastewater in the wastewater recovery storage tank is transferred to a transfer tank by the wastewater transfer pump.
[0015] Furthermore, the system also includes a transfer tank, which is located between the wastewater recovery storage tank and the secondary recovery device. The transfer tank is connected to both the wastewater recovery storage tank and the secondary recovery device via pipelines. The transfer brine tank provides a buffer for water supply, increasing the system's fault tolerance.
[0016] Furthermore, a booster pump is installed at the outlet of the transfer tank. The wastewater in the transfer tank is pressurized by the booster pump and then enters the secondary recovery unit to exchange heat with the flue gas. The secondary recovery unit is connected to a brine storage tank; the wastewater undergoes heat treatment and is sent to the brine storage tank, where it is mixed with dilute brine and used as brine.
[0017] Furthermore, the outlet of the resin tower is connected to the wastewater recovery storage tank via a pipeline. The wastewater in the wastewater recovery storage tank consists of waste acid, waste alkali, wastewater, and waste brine generated by the resin tower; hydrogen scrubbing liquid generated by the hydrogen scrubbing tower; and concentrated water generated by the pure water station.
[0018] Preferably, the wastewater transfer pump is also equipped with a return flow meter, a pressure gauge, a thermometer, and a pipe diameter reducer.
[0019] Preferably, the brine delivery pump is also equipped with a reflux valve, a pressure gauge, a thermometer, and a pipe diameter reducer.
[0020] Beneficial effects: Compared with the prior art, the specific beneficial effects of this utility model are as follows:
[0021] This invention utilizes the heat of wet flue gas and the latent heat of steam to heat heat-consuming fluids such as brine, and recovers the waste heat of low-temperature flue gas from molten salt furnaces. It can make greater use of the latent heat carried by water vapor in low-temperature flue gas, thereby improving hydrogen combustion efficiency. Through technical improvements, the hydrogen combustion efficiency is increased by 26.23%, and 4.77 t / h of water vapor is recovered from the flue gas, achieving the goal of energy conservation and emission reduction. Attached Figure Description
[0022] Figure 1 A flowchart of a low-temperature flue gas waste heat recovery system for molten salt furnace in chlor-alkali production is provided for this utility model;
[0023] Illustrations: 1. Molten salt furnace; 2. Stage I recovery unit; 3. Stage II recovery unit; 4. Primary refined brine storage tank; 5. Transfer brine tank; 6. Resin tower; 7. Brine transfer pump; 8. Brine booster pump; 9. Wastewater recovery storage tank; 10. Transfer water tank; 11. Chemical brine storage tank; 12. Wastewater transfer pump; 13. Booster pump; 14. Hydrogen scrubbing tower; 15. Pure water station. Detailed Implementation
[0024] The present invention will now be described in detail with reference to the embodiments.
[0025] Implementation method 1:
[0026] This embodiment provides a low-temperature flue gas waste heat recovery system for molten salt furnaces in chlor-alkali production, such as... Figure 1 As shown, the details are as follows:
[0027] It includes: a molten salt furnace 1 and a primary recovery device 2 and a secondary recovery device 3 connected in sequence to the flue gas exhaust port of the molten salt furnace 1 via pipelines.
[0028] The primary brine recovery unit 2 is sequentially connected to the intermediate brine tank 5 and the primary refined brine storage tank 4. The outlet of the primary refined brine storage tank 4 is connected to the inlet of the intermediate brine tank 5 via a pipe, and the outlet of the intermediate brine tank 5 is connected to the inlet of the primary recovery unit 2 via a pipe. The primary recovery unit 2 is also connected to a resin tower 6; the outlet of the primary recovery unit 2 is connected to the inlet of the resin tower 6 via a pipe. A brine transfer pump 7 is installed at the outlet of the primary refined brine storage tank 4, and the brine transfer pump 7 is also equipped with a reflux valve, pressure gauge, thermometer, and pipe reducer. A brine booster pump 8 is installed at the outlet of the intermediate brine tank 5. The primary recovery unit 2 is equipped with a diversion mechanism and DCS automatic control.
[0029] The secondary recovery unit 3 is sequentially connected to the transfer tank 10 and the wastewater recovery storage tank 9. The outlet of the wastewater recovery storage tank 9 is connected to the inlet of the transfer tank 10 via a pipe, and the outlet of the transfer tank 10 is connected to the inlet of the secondary recovery unit 3 via a pipe. The secondary recovery unit 3 is also connected to a brine storage tank 11; the outlet of the secondary recovery unit 3 is connected to the inlet of the brine storage tank 11 via a pipe. A wastewater transfer pump 12 is installed at the outlet of the wastewater recovery storage tank 9, and a reflux valve, pressure gauge, thermometer, and pipe reducer are also installed at the wastewater transfer pump 12. A booster pump 13 is installed at the outlet of the transfer tank 10. The secondary recovery unit 3 is equipped with a diversion mechanism and DCS automatic control. The outlet of the resin tower 6 is connected to the inlet of the wastewater recovery storage tank 9 via a pipe.
[0030] Optionally, the inlet of the secondary recovery unit 3 can also be connected to the outlet of the hydrogen scrubbing tower 14 and the outlet of the pure water station 15.
[0031] Working Principle: The primary refined brine is pumped to a transfer brine tank via a brine transfer pump. Upon arrival at the transfer tank, the primary refined brine is pressurized by a brine booster pump and then enters the Stage I recovery unit for heat exchange with the low-temperature flue gas generated by the molten salt furnace. The Stage I recovery unit uses convective heat exchange, automatically controlled by a DCS system, and utilizes a flow distribution mechanism to maintain the temperature of the primary refined brine at 60±1℃. After heat exchange, the primary refined brine is transported to a resin tower, where it absorbs calcium and magnesium ions. Simultaneously, the condensate generated from the low-temperature flue gas heat exchange in the Stage I recovery unit is piped to the Stage II recovery unit, and then from there to the brine storage tank for recovery. The wastewater recovery storage tank recovers waste acid, waste alkali, wastewater, and waste brine from the resin tower, hydrogen scrubbing liquid from the hydrogen scrubbing tower, and concentrated water from the pure water station. The wastewater recovered from the storage tank is pumped to a transfer tank, where it is further pressurized by a booster pump before entering the secondary recovery unit for heat exchange with the low-temperature flue gas from the molten salt furnace. The secondary recovery unit uses convective heat exchange, is automatically controlled by a DCS system, and utilizes a diversion mechanism to maintain the wastewater temperature at 63-65℃. The heat-exchanged wastewater is then transported to a brine storage tank, mixed with dilute brine, and used as brine. Simultaneously, the condensate generated from the low-temperature flue gas heat exchange in the secondary recovery unit is piped to the brine storage tank for recovery. This completes the recovery of waste heat from the low-temperature flue gas from the molten salt furnace.
[0032] calculate:
[0033] Producing 1 ton of caustic soda flakes consumes 2,388,424.38 kJ of heat and approximately 371.3 Nm3 of hydrogen. The heat generated by the complete combustion of hydrogen is 3,886,397.1 kJ, resulting in a hydrogen utilization efficiency of only 57.45%.
[0034] The flue gas produced during the production of 1 ton of caustic soda flakes has a temperature of approximately 230°C and a volume of approximately 1205.46 Nm3. The flue gas contains 377.49 Nm3 of water vapor, 803.17 Nm3 of N2, and 24.76 Nm3 of O2. The flue gas carries a total of 1,372,266.2 kJ of heat.
[0035] The annual production capacity is 150,000 tons of caustic soda flakes, with an annual production time of 8,000 hours. On average, it consumes 6,961.9 Nm³ of hydrogen per hour and produces 22,602 Nm³ of flue gas per hour. The heat generated by the complete combustion of hydrogen is 72,869,945.6 kJ / h, the heat absorbed by the molten salt is 44,782,957.5 kJ / h, and the heat carried in the flue gas is 25,729,991.3 kJ / h.
[0036] The wastewater temperature before heating is taken as 25℃, and the temperature after heating is taken as 65℃. The wastewater flow rate is 55m3 / h, the specific heat capacity of the wastewater is taken as 4.22kJ / (kg*℃), and the cumulative recovered heat is 9,284,000kJ / h.
[0037] The temperature of the purified brine before heating is 50℃, and the temperature after heating is 60℃. The brine flow rate is 255 m3 / h, the brine density is 1.189 g / cm3, the brine specific heat capacity is 3.243 kJ / (kg*℃), and the cumulative recovered heat is 9832613.9 kJ / h.
[0038] It recovers 19,116,613.9 kJ of heat per hour, saves 8.01 tons of medium-pressure steam per hour, generates 4.77 tons of steam condensation per hour, and increases hydrogen utilization by 26.23%.
[0039] The above embodiments are only for illustrating the technical concept and features of this utility model, and are intended to enable those skilled in the art to understand the content of this utility model and implement it accordingly. They should not be construed as limiting the scope of protection of this utility model. All equivalent transformations or modifications made in accordance with the spirit and essence of this utility model should be included within the scope of protection of this utility model.
Claims
1. A low-temperature flue gas waste heat recovery system for a molten salt furnace in chlor-alkali production, characterized in that, include: Molten salt furnace and a primary recovery unit and a secondary recovery unit connected to the flue gas exhaust port of the molten salt furnace via pipelines; The inlet of the first-stage recovery device is connected to a primary refined brine storage tank, and the outlet of the first-stage recovery device is connected to a resin tower. The inlet of the Level II recovery device is connected to a wastewater recovery storage tank, and the outlet of the Level II recovery device is connected to a brine storage tank.
2. The low-temperature flue gas waste heat recovery system for molten salt furnace in chlor-alkali production according to claim 1, characterized in that: A brine delivery pump is installed at the outlet of the primary refined brine storage tank.
3. The low-temperature flue gas waste heat recovery system for molten salt furnaces in chlor-alkali production according to claim 1, characterized in that: It also includes a transfer brine tank, which is located between the primary refined brine storage tank and the first-stage recovery device. The transfer brine tank is connected to the primary refined brine storage tank and the first-stage recovery device via a pipeline.
4. The low-temperature flue gas waste heat recovery system for molten salt furnace in chlor-alkali production according to claim 3, characterized in that: The outlet of the transfer brine tank is equipped with a brine booster pump.
5. The low-temperature flue gas waste heat recovery system for molten salt furnaces in chlor-alkali production according to claim 1, characterized in that: The outlet of the wastewater recycling storage tank is equipped with a wastewater transfer pump.
6. The low-temperature flue gas waste heat recovery system for molten salt furnace in chlor-alkali production according to claim 1, characterized in that: It also includes a transfer tank, which is located between the wastewater recycling storage tank and the secondary recycling device. The transfer tank is connected to the wastewater recycling storage tank and the secondary recycling device via a pipeline.
7. The low-temperature flue gas waste heat recovery system for molten salt furnace in chlor-alkali production according to claim 6, characterized in that: A booster pump is installed at the outlet of the transfer water tank.
8. The low-temperature flue gas waste heat recovery system for molten salt furnace in chlor-alkali production according to claim 1, characterized in that: The outlet of the resin tower is connected to the wastewater recovery storage tank via a pipe.
9. The low-temperature flue gas waste heat recovery system for molten salt furnace in chlor-alkali production according to claim 5, characterized in that: The wastewater transfer pump is also equipped with a return flow meter, pressure gauge, thermometer, and pipe diameter reducer.
10. The low-temperature flue gas waste heat recovery system for molten salt furnace in chlor-alkali production according to claim 2, characterized in that: The brine delivery pump is also equipped with a return flow meter, pressure gauge, thermometer, and pipe diameter reducer.