A heat pump system and process for recovering waste heat of ion-exchange membrane caustic soda to heat primary brine

Abstract

The present invention discloses a heat pump system and process for recovering waste heat from ion-exchange caustic soda to heat primary brine. The system includes a heat pump unit, the condensing end of which is connected to a steam tank, the steam outlet of which is connected to a steam pipe network, and the steam outlet of the steam pipe network is connected to a brine heater; the evaporating end of the heat pump unit is connected to a caustic soda pipeline from an electrolyzer. The present invention utilizes the waste heat of caustic soda, a low-grade heat source, to generate steam through the heat pump unit to heat the primary brine. Excess steam can be incorporated into the steam pipe network, and when insufficient steam is available, it can be supplemented by steam from the pipe network, thus saving a large amount of energy. The temperature of the primary brine is adjusted by the steam flow rate, and the temperature of the caustic soda is adjusted by the heat pump unit, making temperature control relatively simple.

Description

Technical Field

[0001] The present invention relates to the technical field of waste heat recovery of ion-exchange membrane caustic soda, and in particular to a heat pump system and process for recovering waste heat of ion-exchange membrane caustic soda to heat primary brine. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Currently, caustic soda is primarily produced using the ion-exchange membrane process, which sequentially consists of steps including primary brine, secondary brine, electrolysis, dechlorination of the desalinated brine, and chlorine-hydrogen treatment. The primary brine obtained after primary refining has a temperature of approximately 50°C. Before entering the resin tower for secondary refining, the primary brine needs to be heated to 60°C. The current process uses steam passing through a plate heat exchanger to heat the primary brine. After electrolysis in the electrolytic cell, the caustic soda product reaches a temperature of 85 to 88°C and needs to be cooled to 40°C using circulating cooling water before being delivered to the product tank farm.

[0004] Patent CN 214502169 U provides a device for heating brine using the waste heat of ion-exchange caustic soda. The brine is heated using alkaline solution through a heat exchanger. However, this method has the following problems: 1. Due to the temperature difference limit for heat exchange, the caustic soda temperature can only be reduced to a limited extent, requiring it to be cooled again with circulating water before being sent to the product tank area; 2. In winter, the temperature of the primary brine is relatively low, and the waste heat provided by the caustic soda product may not be sufficient to heat the brine; 3. There is a risk of leakage in the heat exchanger, which could result in contamination of the primary brine and alkaline solution; and 4. Temperature control is relatively complex. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a heat pump system and process for recovering the waste heat of ion-exchange membrane caustic soda to heat primary brine, which can reasonably utilize the waste heat of caustic soda products and reduce energy consumption.

[0006] The technical solutions of the present invention are as follows:

[0007] In a first aspect of the present invention, a heat pump system for recovering waste heat from ion-exchange membrane caustic soda to heat primary brine is provided, comprising a heat pump unit, wherein the condensing end of the heat pump unit is connected to a steam tank, the steam outlet of the steam tank is connected to a steam pipe network, and the steam outlet of the steam pipe network is connected to a brine heater; and the evaporating end of the heat pump unit is connected to a caustic soda pipeline from an electrolyzer.

[0008] In some embodiments of the present invention, the heat pump unit includes a high-temperature refrigeration cycle and a low-temperature refrigeration cycle.

[0009] In some embodiments of the present invention, the high-temperature refrigeration cycle includes an evaporative condenser, a high-pressure compressor, a condenser, and a high-pressure throttle valve connected in sequence.

[0010] In some embodiments of the present invention, the low-temperature refrigeration cycle includes an evaporator, a low-pressure compressor, an evaporative condenser, and a low-pressure throttle valve connected in sequence.

[0011] In some embodiments of the present invention, the desalted water outlet of the steam tank is connected to the condenser of the heat pump unit, and the steam outlet of the condenser is connected to the steam tank.

[0012] In some embodiments of the present invention, the steam inlet of the brine heater is connected to the steam network, a solenoid valve is provided on the pipeline between the brine heater and the steam network, and the condensate outlet of the brine heater is connected to the steam tank.

[0013] In some embodiments of the present invention, the brine heater is provided with a primary brine inlet and a primary brine outlet.

[0014] In some embodiments of the present invention, a temperature sensor is provided on the primary brine outlet pipeline of the brine heater.

[0015] In a second aspect of the present invention, a process for recovering waste heat from ion-exchange membrane caustic soda to heat primary brine is provided, which is achieved by utilizing the heat pump system for recovering waste heat from ion-exchange membrane caustic soda to heat primary brine as described in the first aspect. The caustic soda produced by the electrolyzer enters the evaporator of the heat pump unit for cooling, and the temperature is reduced to below 40°C; the desalted water in the steam tank enters the condenser of the heat pump unit for heating, and the heated gas-liquid mixture enters the steam tank, and the steam is drawn out from the top of the steam tank and enters the steam pipe network, and then the steam in the steam pipe network enters the brine heater to heat the primary brine.

[0016] In some embodiments of the present invention, the outlet temperature of the primary brine is obtained by a temperature sensor, and the steam flow rate entering the brine heater is regulated by a solenoid valve according to the outlet temperature.

[0017] One or more technical solutions of the present invention have the following beneficial effects:

[0018] In the ion-exchange membrane caustic soda process, the caustic soda at the outlet of the electrolyzer needs to be cooled before being pumped into the finished product tank area, and the primary brine needs to be heated before secondary refining. The present invention utilizes a heat pump system to recover the waste heat of the caustic soda at the outlet of the electrolyzer to heat the primary brine, thereby saving both the circulating cooling water used for cooling the caustic soda and the steam required for heating the primary brine, thereby saving a large amount of energy.

[0019] This invention utilizes the waste heat of caustic soda, a low-grade heat source, to generate steam through a heat pump unit to heat the primary brine. Excess steam can be fed into the steam network, and steam from the network can be used to supplement insufficient steam. The primary brine temperature is regulated by the steam flow rate, while the caustic soda temperature is regulated by the heat pump unit, making temperature control relatively simple.

[0020] The heat pump system of the present invention adopts a high-temperature and low-temperature cascade system, which enables the condenser side to generate a higher temperature. The condenser can heat the desalted water in the steam tank into steam for use. Compared with the existing technology, the system of the present invention is simple, easy to implement, and improves energy utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of a heat pump system for recovering waste heat from ion-exchange membrane caustic soda to heat primary brine according to the present invention.

[0022] In the figure: 1. Heat pump unit; 1.1. Condenser; 1.2. High-pressure compressor; 1.3. Evaporative condenser; 1.4. High-pressure throttle valve; 1.5. Low-pressure throttle valve; 1.6. Evaporator; 1.7. Low-pressure compressor; 2. Steam tank; 3. Brine heater; 4. Solenoid valve; 5.1. First temperature sensor; 5.2. Second temperature sensor. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0024] Example 1

[0025] In a typical embodiment of the present invention, a heat pump system for recovering waste heat of ion-exchange membrane caustic soda and heating primary brine is proposed. Figure 1 As shown, it includes a heat pump unit 1, the condensing end of the heat pump unit 1 is connected to the steam tank 2, the steam outlet of the steam tank 2 is connected to the steam pipe network, and the steam outlet of the steam pipe network is connected to the brine heater 3; the evaporating end of the heat pump unit 1 is connected to the caustic soda pipeline from the electrolytic cell.

[0026] The heat pump unit 1 includes a high-temperature refrigeration cycle and a low-temperature refrigeration cycle. The high-temperature refrigeration cycle includes an evaporator condenser 1.3, a high-pressure compressor 1.2, a condenser 1.1, and a high-pressure throttle valve 1.4 connected in sequence, forming a closed circulation loop for the high-temperature refrigerant. The low-temperature refrigeration cycle includes an evaporator 1.6, a low-pressure compressor 1.7, an evaporator condenser 1.3, and a low-pressure throttle valve 1.5 connected in sequence, forming a closed circulation loop for the low-temperature refrigerant. The high-temperature refrigeration cycle and the low-temperature refrigeration cycle are coupled via the evaporator condenser 1.3.

[0027] The working principle of the heat pump unit is as follows: low-temperature stage part: the low-temperature refrigerant gas from the evaporator 1.6 is compressed by the low-pressure compressor 1.7 and then enters the condenser evaporator 1.3. In the condenser evaporator 1.3, the heat released by the low-temperature refrigerant is absorbed by the high-temperature refrigerant. While the high-temperature refrigerant evaporates, the low-temperature refrigerant condenses. The condensed low-temperature refrigerant passes through the low-pressure throttle valve 1.5 and enters the evaporator, completing a refrigeration cycle; high-temperature stage part: the high-temperature refrigerant gas that evaporates after absorbing heat in the condenser evaporator 1.3 is sucked in and compressed by the high-pressure compressor 1.2 and then enters the condenser 1.1 for condensation, releasing heat to the cooling medium. The condensed high-temperature refrigerant liquid passes through the high-pressure throttle valve 1.4 and enters the condenser evaporator 1.3, completing a refrigeration cycle.

[0028] The desalted water outlet of the steam tank 2 is connected to the condenser 1.3 of the heat pump unit 1, and the steam outlet of the condenser 1.3 is connected to the steam tank 2. The desalted water enters the condenser of the heat pump unit for heating, becomes a gas-liquid mixture, and then enters the steam tank. In the steam tank, the steam is drawn out from the top of the steam tank and enters the steam pipe network. The steam condensate remains in the steam tank for recycling.

[0029] The brine heater 3 is provided with a primary brine inlet, a primary brine outlet, a steam inlet and a condensate outlet, wherein the steam inlet is connected to the steam network, and the condensate outlet is connected to the steam tank. In the brine heater, the primary brine and the steam exchange heat, the temperature of the primary brine increases, and the steam is condensed into condensate. The heated primary brine is sent to refining, and the condensate is returned to the steam tank for recycling.

[0030] Furthermore, the brine heater is a shell and tube heat exchanger or a sleeve and tube heat exchanger, which uses a countercurrent method for heat exchange.

[0031] Furthermore, a solenoid valve 4 is provided on the pipeline between the brine heater 3 and the steam network, and a first temperature sensor 5.1 is provided on the primary brine outlet pipeline of the brine heater 3. The solenoid valve can control the amount of steam entering the brine heater according to the outlet temperature of the primary brine monitored by the first temperature sensor, and the control process is simple.

[0032] Furthermore, the caustic soda from the electrolytic cell enters the evaporator for cooling, and the cooled caustic soda is sent to the caustic soda tank. A second temperature sensor 5.2 is provided at the outlet of the caustic soda to monitor the outlet temperature of the caustic soda.

[0033] In this embodiment, the condensing temperature of the condenser is 140°C, the evaporating temperature of the evaporator is 35°C, and both the high-temperature refrigerant and the low-temperature refrigerant are R365mfc. A heat pump unit with two refrigeration cycles cascades, which can generate a very high temperature on the condenser side, can heat the desalted water in the steam tank into steam, and can be used as supplementary steam for the steam network and steam for heating the primary brine. At the same time, the evaporator can also directly reduce the temperature of the caustic soda to below 40°C.

[0034] The working principle of the heat pump system of this embodiment that recovers the waste heat of ion-exchange membrane caustic soda to heat primary brine is as follows:

[0035] The caustic soda produced by the electrolyzer enters the evaporator of the heat pump unit for cooling, reducing the temperature to below 40°C. The desalted water in the steam tank enters the condenser of the heat pump unit for heating. The heated gas-liquid mixture enters the steam tank, and steam is drawn from the top of the steam tank and enters the steam pipe network. The steam in the steam pipe network then enters the brine heater to heat the primary brine. The outlet temperature of the primary brine is measured by a first temperature sensor, and the steam flow entering the brine heater is adjusted based on the outlet temperature via a solenoid valve. The outlet temperature of the caustic soda is monitored by a second temperature sensor to ensure that the outlet temperature meets the requirements, eliminating the need for secondary cooling.

[0036] Taking a 240,000 ton / year caustic soda plant as an example, the plant can generate 11.4 tons of steam per hour (pressure 0.2 MPaG, temperature 134°C), of which 6.1 tons are used to heat the primary brine, and the remaining 5.3 tons of steam are incorporated into the steam network. At the same time, the circulating cooling water volume is saved by about 424m3 per hour. 3 The caustic soda product from the electrolytic cell is cooled from 85°C to 40°C before being sent to the product tank farm. The steam generated by the heat pump unit is used to heat the brine in the existing brine heater, raising its temperature to 60°C. The excess steam is then fed into the steam network.

[0037] Example 2

[0038] In a typical embodiment of the present invention, a process for recovering the waste heat of ion-exchange membrane caustic soda to heat primary brine is proposed, and the process is implemented using the heat pump system for recovering the waste heat of ion-exchange membrane caustic soda to heat primary brine as described in Example 1. Specifically, the caustic soda produced by the electrolytic cell enters the evaporator of the heat pump unit for cooling, and the temperature is reduced to below 40°C; the desalted water in the steam tank enters the condenser of the heat pump unit for heating, and the heated gas-liquid mixture enters the steam tank, and the steam is drawn out from the top of the steam tank and enters the steam pipe network, and then the steam in the steam pipe network enters the brine heater to heat the primary brine.

[0039] Furthermore, the outlet temperature of the primary brine is obtained by a temperature sensor, and the steam flow entering the brine heater is adjusted through a solenoid valve according to the outlet temperature.

[0040] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A heat pump system for recovering waste heat from ion-exchange membrane caustic soda to heat primary brine, characterized in that: It includes a heat pump unit, the condensing end of the heat pump unit is connected to a steam tank, the steam outlet of the steam tank is connected to a steam network, and the steam outlet of the steam network is connected to a brine heater; the evaporating end of the heat pump unit is connected to a caustic soda pipeline from an electrolyzer; a solenoid valve is provided on the pipeline between the brine heater and the steam network; a primary brine inlet and a primary brine outlet are provided on the brine heater; a temperature sensor is provided on the primary brine outlet pipeline of the brine heater; the desalted water outlet of the steam tank is connected to a condenser of the heat pump unit, and the steam outlet of the condenser is connected to a steam tank; the steam inlet of the brine heater is connected to the steam network, and the condensate outlet of the brine heater is connected to the steam tank.

2. The heat pump system for recovering waste heat of ion-exchange membrane caustic soda to heat primary brine according to claim 1, characterized in that: The heat pump unit includes a high-temperature refrigeration cycle and a low-temperature refrigeration cycle.

3. The heat pump system for recovering waste heat of ion-exchange membrane caustic soda to heat primary brine according to claim 2, characterized in that: The high-temperature refrigeration cycle includes an evaporative condenser, a high-pressure compressor, a condenser, and a high-pressure throttle valve connected in sequence.

4. The heat pump system for recovering waste heat of ion-exchange membrane caustic soda to heat primary brine according to claim 2, characterized in that: The low-temperature refrigeration cycle includes an evaporator, a low-pressure compressor, an evaporative condenser, and a low-pressure throttle valve connected in sequence.

5. A process for recovering waste heat from ion-exchange membrane caustic soda to heat primary brine, which is achieved by using the heat pump system for recovering waste heat from ion-exchange membrane caustic soda to heat primary brine as claimed in any one of claims 1 to 4, characterized in that: The caustic soda produced by the electrolytic cell enters the evaporator of the heat pump unit for cooling, and the temperature drops to below 40°C; the desalted water in the steam tank enters the condenser of the heat pump unit for heating, and the heated gas-liquid mixture enters the steam tank, and the steam is drawn out from the top of the steam tank and enters the steam pipe network, and then the steam in the steam pipe network enters the brine heater to heat the brine once.

6. The process for recovering waste heat of ion-exchange membrane caustic soda for heating primary brine according to claim 5, characterized in that: The outlet temperature of the primary brine is obtained by the temperature sensor, and the steam flow entering the brine heater is adjusted through the solenoid valve according to the outlet temperature.

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