Waste heat utilization system and waste heat recovery method for carbonic ester production device

Abstract

The invention relates to a carbonic ester solvent production device, in particular to a waste heat utilization system for a carbonic ester production device and a waste heat recovery method.The waste heat utilization system comprises a carbonic ester device, a second-class lithium bromide absorption heat pump unit, an expansion compressor unit and a hot water circulation system, and a heat exchanger is arranged at the top of a rectifying tower of the carbonic ester device; the circulating water exchanges heat with tower top material steam in the heat exchanger and then enters the second-class lithium bromide absorption heat pump unit, and the cooled circulating water flows back into the heat exchanger; the second-class lithium bromide absorption heat pump unit utilizes heat of circulating water to produce steam exhaust, and the steam exhaust enters the expansion compressor unit to generate low-pressure steam; external high-pressure steam is connected into the expansion compressor unit to generate medium-pressure steam. By efficiently recovering latent heat of vaporization at the tower top of the carbonic ester production device, the requirement for additional energy is reduced, meanwhile, the consumption of cooling water at the tower top is reduced, and the purpose of saving energy in the rectification process is achieved.

Description

Technical Field

[0001] The invention relates to a carbonate solvent production device, in particular to a waste heat utilization system and a waste heat recovery method for a carbonate solvent production device. Background Art

[0002] Carbonate esters are important battery electrolyte solvents, and recent research on their production process conditions has been extensive. The reactive distillation process of the transesterification method is a major research and development focus. Its mild reaction conditions and pollution-free, environmentally friendly production process make it one of the most advanced methods for synthesizing carbonate esters. As the industry develops, carbonate ester plants within the industry are actively upgrading their technology to improve energy efficiency while continuously improving quality. With increasingly robust energy management systems and the petrochemical industry's move towards a green and low-carbon development path, accelerating energy-saving upgrades and emissions reductions is imperative.

[0003] Carbonate production equipment usually includes reaction distillation towers, purification distillation towers, etc., which require the consumption of a large amount of steam. The energy consumed in the distillation process accounts for a high proportion of the total energy consumed by the entire chemical enterprise. At the same time, the large amount of latent heat of vaporization at the top of the tower requires the consumption of a large amount of circulating cooling water.

[0004] Therefore, there is an urgent need to develop a waste heat utilization system to efficiently recover the latent heat of vaporization of the top steam. Summary of the Invention

[0005] To address the problems in the above-mentioned background technology, the present invention provides a waste heat utilization system and waste heat recovery method for a carbonate production device. By efficiently recovering the latent heat of vaporization at the top of the carbonate production device, not only the external energy demand is reduced, but also the cooling water consumption at the top of the tower is reduced, thereby achieving energy saving in the distillation process.

[0006] The first object of the present invention is to provide a waste heat utilization system for a carbonate production device, comprising a carbonate device, a second-type lithium bromide absorption heat pump unit, an expansion compressor unit and a hot water circulation system, wherein:

[0007] A heat exchanger is installed at the top of the distillation tower of the carbonate unit. The circulating water of the hot water circulation system exchanges heat with the steam of the tower top material in the heat exchanger and then enters the second type lithium bromide absorption heat pump unit through the water supply pipe. The cooled circulating water flows back to the heat exchanger through the return pipe.

[0008] The second type of lithium bromide absorption heat pump unit includes a gas-liquid separator. The heat of the circulating water is transferred to the gas-liquid separator, which heats the feed water in the gas-liquid separator to generate steam exhaust gas, which enters the expansion compressor unit.

[0009] The expansion compressor unit includes a steam compressor, a steam expander and a reducer. The steam exhaust gas enters the steam compressor to generate low-pressure steam; the steam compressor is connected to the steam expander through the reducer, and the external high-pressure steam is connected to the steam expander to generate medium-pressure steam.

[0010] Furthermore, the expansion compressor unit also includes a first separator and a second separator. The steam exhaust gas enters the steam compressor and then generates low-pressure steam through the first separator; the external high-pressure steam enters the steam expander and then generates medium-pressure steam through the second separator.

[0011] Furthermore, it also includes a constant pressure water replenishment device, the water inlet of the constant pressure water replenishment device is connected to the pure water network, and the water outlet of the constant pressure water replenishment device is connected to the return pipe of the circulating water through a pipe.

[0012] Furthermore, the hot water circulation system also includes a temperature sensor, which detects and feeds back the temperature of the circulating water, so that the temperature of the circulating water is controlled at 85-100°C.

[0013] Furthermore, the second type of lithium bromide absorption heat pump unit also includes an evaporator, an absorber, a generator and a condenser. The circulating water flowing out of the heat exchanger enters the evaporator so that the heat of the circulating water is absorbed. The cooled circulating water enters the generator to heat and concentrate the dilute lithium bromide solution in the generator. The cooled circulating water flows back to the heat exchanger.

[0014] Furthermore, there is condensed water in the condenser, and a condensation pump is also provided on the condenser, and the condensed water is sprayed out through the condensation pump.

[0015] The condensed water is sprayed on the outer surface of the heat exchange tube of the evaporator through the condensation pump, generating water vapor that enters the absorber; the lithium bromide concentrated solution in the generator is sprayed in the absorber through the solution pump to absorb the water vapor generated by the evaporator.

[0016] Furthermore, the heat exchanger is a fully welded plate heat exchanger.

[0017] Furthermore, the steam compressor is a screw compressor.

[0018] A second object of the present invention is to provide a waste heat recovery method for a carbonate production device, comprising the following steps:

[0019] S1: A heat exchanger is installed at the top of the distillation tower of the carbonate unit. Water is used as the heat exchange medium to exchange heat with the steam of the overhead material. The high-temperature hot water obtained by the exchange enters the second-type lithium bromide absorption heat pump unit to prepare steam exhaust gas; the cooled water flows back into the heat exchanger;

[0020] S2: The steam exhaust gas is passed into the steam compressor to further heat and pressurize it to the required pressure to form low-pressure steam, which is then introduced into the low-pressure steam network;

[0021] S3: The steam expander is connected to the steam compressor through a reducer, and the external high-pressure steam is connected to the steam expander to generate medium-pressure steam, which is then incorporated into the medium-pressure steam network. The medium-pressure steam network is connected to the carbonate device to provide driving force for the carbonate device.

[0022] Furthermore, the steam pressure generated by the steam compressor is in the range of 0.2 to 1.0 MPaG, and the steam pressure generated by the steam expander is in the range of 0.5 to 1.5 MPaG.

[0023] Preferably, the steam pressure generated by the steam compressor is in the range of 0.3 to 0.5 MPaG, and the steam pressure generated by the steam expander is in the range of 0.7 to 1.1 MPaG.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention adopts a hot water circulation system, in which hot water is used as a driving heat source by exchanging heat with high-temperature materials through a heat exchanger, and a second-class lithium bromide absorption heat pump unit is used to produce 0.2-0.22MPaG primary steam. The primary steam is then pressurized to the required steam by a steam compressor and supplied to a low-pressure steam network. At the same time, a steam expander is driven by high-pressure steam, and the high-pressure steam is adiabatically expanded to medium-pressure steam in the steam expander and supplied to a medium-pressure steam network, thereby meeting the various types of steam required by the carbonate production device. The waste heat recovery system of the present invention is used to return the steam prepared by recovering the waste heat of the process liquid of the carbonate production device to the steam network, which can minimize the total steam consumption and reduce the consumption of cooling circulating water in the device.

[0026] (2) The present invention has a short recovery period. The second-class lithium bromide absorption heat pump unit can produce steam without consuming high-grade energy. The steam pressurized by the expansion compressor unit can be directly used by the device, thereby saving the input of primary energy and achieving significant energy-saving effects. In addition, the second-class lithium bromide absorption heat pump unit and the expansion compressor unit basically do not consume electricity. The second-class lithium bromide absorption heat pump unit uses lithium bromide solution, and there is no pollution or waste during operation. There is no need to pile up fuel waste sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1This is a schematic diagram of the overall structure of the waste heat utilization system for the carbonate production device of the present invention;

[0029] Figure 2 This is a waste heat utilization flow chart of the waste heat utilization system for the carbonate production device of the present invention;

[0030] Figure 3 This is a schematic diagram of the overall structure of the expansion-compression unit of the waste heat utilization system for the carbonate production device of the present invention;

[0031] Figure 4 This is a schematic diagram of the second type of lithium bromide absorption heat pump unit in the waste heat utilization system for the carbonate production device of the present invention.

[0032] Among them: 1-carbonate unit, 11-heat exchanger, 2-second-type lithium bromide absorption heat pump unit, 21-gas-liquid separator, 22-evaporator, 23-absorber, 24-generator, 25-condenser, 26-solution pump, 27-solution heat exchanger, 3-expansion compressor unit, 31-steam compressor, 32-steam expander, 33-reducer, 34-first separator, 35-second separator, 4-hot water circulation system, 41-water supply pipe, 42-return pipe, 5-constant pressure water supply device. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0034] The following is combined with Figure 1 To the attached Figure 4 The present invention is described in detail with reference to specific embodiments.

[0035] like Figure 1-4As shown, the present invention provides a waste heat utilization system for a carbonate production device, comprising a carbonate device 1, a second-type lithium bromide absorption heat pump unit 2, an expansion compressor unit 3, and a hot water circulation system 4, wherein: a heat exchanger 11 is provided at the top of the distillation tower of the carbonate device 1, and the circulating water of the hot water circulation system 4 enters the second-type lithium bromide absorption heat pump unit 2 through a water supply pipe 41 after heat exchange with the steam of the tower top material in the heat exchanger 11. The water supply pipe 41 is connected to a hot water circulation pump, and the circulating water that absorbs the waste heat of the tower top steam is supplied to the second-type lithium bromide absorption heat pump unit 2 through the hot water circulation pump. The circulating water is cooled by heat exchange and heat conduction inside the second-type lithium bromide absorption heat pump unit 2, and the cooled circulating water is cooled by heat exchange and heat conduction. The circulating water flows back to the heat exchanger 11 through the return pipe 42; the second-type lithium bromide absorption heat pump unit 2 includes a gas-liquid separator 21, and the circulating water transfers the steam heat of the material at the top of the distillation tower to the gas-liquid separator 21, so that the feed water in the gas-liquid separator 21 is heated to produce steam exhaust gas, and the temperature of the steam exhaust gas is higher than the temperature of the circulating water. The generated steam exhaust gas enters the expansion compressor unit 3; the second-type lithium bromide absorption heat pump unit 2 of the present application uses waste heat as the driving source, and through internal heat exchange and heat conduction, it raises the low-temperature waste heat to medium and high temperature, and outputs higher-grade thermal energy. The hot water cools down after releasing heat in the second-type lithium bromide absorption heat pump unit 2, and the return pipe sends the low-temperature water back to the heat exchanger 11 to form a closed cycle.

[0036] The expansion compressor unit 3 comprises a steam compressor 31, a steam expander 32, and a speed reducer 33. Exhaust steam enters the steam compressor 31 and is compressed to produce low-pressure steam, which is then fed into a low-pressure steam network for the company's own use. The steam compressor 31 is connected to the steam expander 32 via a speed reducer. External high-pressure steam is fed into the steam expander 32, driving it to produce medium-pressure steam. This medium-pressure steam is then fed into the medium-pressure steam network, which is then connected to the carbonate unit 1, providing power for the unit. This system achieves a tower top waste heat utilization rate of approximately 80%, increasing steam self-sufficiency by 50%. This system, through the combination of a heat exchanger 11 and a second-type lithium bromide absorption heat pump unit 2, implements a closed loop of waste heat recovery, temperature elevation, and reuse, significantly improving energy efficiency.

[0037] This application utilizes a hot water circulation system, where circulating water exchanges heat with high-temperature materials through a heat exchanger 11. A second-class lithium bromide absorption heat pump unit 2 is used to produce 0.2-0.22 MPaG primary steam. This primary steam is then pressurized to the required level by a steam compressor 31 and supplied to the enterprise's low-pressure steam network. Simultaneously, a steam expander 32 is powered by high-pressure steam, which adiabatically expands to medium-pressure steam within the steam expander 32 and is then supplied to the enterprise's medium-pressure steam network, thereby meeting the various steam requirements of the carbonate production unit. By utilizing the waste heat recovery system of the present invention, steam generated by recovering waste heat from the process fluids of the carbonate production unit and returning it to the steam network can minimize total steam consumption and reduce the consumption of cooling circulating water within the unit.

[0038] The waste heat recovery system of the present invention can directly produce steam with a steam pressure of 0.2 to 1.5 MPaG and directly output steam with stable pressure and reliable quality (steam quality can reach over 98%). It utilizes the sensible heat of high-pressure steam, replacing the original temperature and pressure reduction device. Unlike conventional compressors that are directly driven by electricity, the present invention utilizes steam expansion work, significantly saving users the cost of laying cables for high-power electrical equipment. Furthermore, the present invention does not consume high-quality energy. The second-type lithium bromide absorption heat pump unit 2 consumes only low-grade waste heat, without consuming high-quality energy. Furthermore, the system can utilize a wide range of low-grade waste heat, such as waste heat generated by waste hot water, waste heat process gas, and waste heat process liquid, all of which can be fully utilized.

[0039] Furthermore, the waste heat recovery system of the present invention has low recovery costs. The second-type lithium bromide absorption heat pump unit 2 can produce steam without consuming high-grade energy. The steam, pressurized by the expansion compressor unit 3, can be directly used by the device, thereby saving primary energy input and achieving significant energy-saving effects. Furthermore, the second-type lithium bromide absorption heat pump unit 2 and the expansion compressor unit 3 consume virtually no electricity. The second-type lithium bromide absorption heat pump unit 2 uses a lithium bromide solution, resulting in zero pollution and waste during operation, and no fuel waste storage site is required.

[0040] In the specific embodiment, see Figure 2 and Figure 3The expansion compressor unit 3 also includes a first separator 34 and a second separator 35. The steam exhaust gas enters the steam compressor 31 and then generates low-pressure steam through the first separator 34. The first separator 34 can efficiently remove liquid water; the external high-pressure steam enters the steam expander 32 and then generates medium-pressure steam through the second separator 35. Since the steam pressure after expansion may flash due to the sudden pressure drop, a gas-liquid two-phase flow is generated. The second separator 35 is set to quickly separate the liquid phase and output medium-pressure steam with a dryness of ≥99% to supply other process units. This application increases the dryness of steam by more than 99% through the setting of the first separator 34 and the second separator 35, eliminates the heat exchange efficiency attenuation caused by liquid phase carryover, and increases the overall thermal efficiency of the system by 12%.

[0041] This application connects the steam compressor 31 and the steam expander 32 through a reducer 33, and uses the work generated by the expansion of high-pressure steam to drive the steam compressor 31 to operate, thereby reducing the external power consumption and ensuring efficient power transmission. At the same time, the reducer 33 can adjust the speed of the steam compressor 31 and the steam expander 32 to ensure that the two work in coordination. Through the linkage of the steam compressor 31 and the expansion compressor 32, the separated dry steam is redistributed to users of different pressure levels to achieve accurate matching of energy grades.

[0042] Specifically, this embodiment of the present application also includes a constant-pressure water replenishment device 5 , the water inlet of which is connected to the pure water network, and the water outlet of which is connected via a pipe to the circulating water return pipe 42 . Because hot water will experience certain losses during operation of the hot water circulation system 4 (such as loss of circulating water volume due to evaporation and leakage), constant-pressure water replenishment device 5 is required to ensure stable operation of the waste heat recovery system. Furthermore, pure water replenishment prevents the introduction of Ca²⁺ and Mg²⁺ ions from industrial water replenishment, which can cause heat exchanger scaling and lithium bromide solution contamination.

[0043] Specifically, the hot water circulation system 4 also includes a temperature sensor that detects and provides feedback on the temperature of the circulating water, ensuring that the temperature of the circulating water entering the lithium bromide unit is controlled at 85-100°C. Preferably, the temperature of the circulating water is controlled at 90-100°C. In this embodiment, the outlet water temperature is controlled by controlling the amount of circulating water used, and the temperature difference between the outlet and return water is generally set at 10°C.

[0044] For details, see Figure 2 and Figure 4 In the embodiment of the present application, the second type of lithium bromide absorption heat pump unit 2 also includes an evaporator 22, an absorber 23, a generator 24 and a condenser 25. The circulating water flowing out of the heat exchanger 11 enters the evaporator 22 so that the heat of the circulating water is absorbed. The circulating water after the initial cooling enters the generator 24 to heat and concentrate the dilute lithium bromide solution in the generator 24. The circulating water that has been cooled again flows back to the heat exchanger 11.

[0045] Furthermore, condenser 25 contains condensed water, which is sprayed onto the outer surface of the heat exchange tubes of evaporator 22 via a condensate pump, generating water vapor that enters absorber 23. The concentrated lithium bromide solution in generator 24 is sprayed into absorber 23 via solution pump 26, absorbing the water vapor generated by evaporator 22 and releasing a large amount of condensation heat to heat the feed water in gas-liquid separator 21. The concentrated solution (concentrated lithium bromide solution) in generator 24 and the dilute solution (dilute lithium bromide solution) in absorber 23 are exchanged via solution heat exchanger 27. The second type of lithium bromide absorption heat pump unit 2 of the present application has fewer operating parts, simple and reliable unit operation, low maintenance costs, and a high degree of automatic control.

[0046] See attached Figure 4 The working principle of the second type of lithium bromide absorption heat pump unit in the present invention is as follows:

[0047] (1) Extraction of waste heat

[0048] In the vacuum evaporator 22, the principle of lowering the boiling point of water under negative pressure is utilized, and the condensed water generated by the steam from the condenser 25 is sprayed on the outer surface of the heat exchange tube of the evaporator 22. The condensed water absorbs the heat of the low-temperature waste heat flowing inside the heat exchange tube, evaporates and vaporizes to generate steam which enters the absorber 23, completing the waste heat extraction process.

[0049] (2): Transfer of waste heat

[0050] In the absorber 23, the lithium bromide concentrated solution is distributed outside the heat exchange tube of the absorber 23 by utilizing its water absorption and heat release properties. The lithium bromide concentrated solution from the generator 24 absorbs the water vapor from the evaporator 22 and releases a large amount of condensation heat. The condensation heat is used to heat the feed water in the heat exchange tube of the gas-liquid separator 21 that needs to increase its temperature, thereby realizing the transfer of heat from the low-temperature heat source to the heated heat medium. At the same time, the lithium bromide solution changes from a concentrated solution to a dilute solution, no longer has water absorption, and needs to be concentrated before recycling.

[0051] (III): Working fluid concentration

[0052] The heat source water coming out of the evaporator 22 enters the generator 24, heats and concentrates the dilute lithium bromide solution from the absorber 23, and the concentrated solution continues to return to the absorber 23 to continue absorbing water vapor to heat the feed water. The refrigerant vapor generated by the concentrated solution goes to the condenser 25.

[0053] (IV): Cooling water cooling

[0054] In the condenser 25, the low-temperature cooling water condenses the refrigerant steam and releases heat. The steam condenses into condensed water and is transported to the evaporator 22 for further cyclic evaporation. The cooling water is heated and then enters the cooling tower for cooling and recycling.

[0055] In some embodiments, heat exchanger 11 is a fully welded plate heat exchanger. In the waste heat recovery system of a carbonate production unit, the efficiency of recovering waste heat from the distillation tower overhead gas phase directly depends on the performance of heat exchanger 11. Traditional shell-and-tube heat exchangers struggle to meet high recovery requirements due to low heat transfer efficiency, susceptibility to scaling, and bulkiness. Plate heat exchangers offer a large heat exchange area per unit volume, a compact structure, and a small footprint, significantly improving heat exchange efficiency and fully recovering waste heat from the overhead gas phase.

[0056] In some embodiments, the steam compressor 31 is a screw compressor. Screw compressors use a rotary motion design, unlike reciprocating components, resulting in low vibration and noise. They also offer better operating stability than piston compressors and are suitable for long-term continuous operation.

[0057] The present invention also provides a waste heat recovery method for a carbonate production device, comprising the following steps:

[0058] S1: A heat exchanger is installed at the top of the distillation tower of the carbonate unit. Water is used as the heat exchange medium to exchange heat with the steam of the overhead material. The high-temperature hot water obtained by the exchange enters the second-type lithium bromide absorption heat pump unit to prepare steam exhaust gas; the cooled water flows back into the heat exchanger;

[0059] S2: The steam exhaust gas is passed into the steam compressor to further heat and pressurize it to the required pressure to form low-pressure steam, which is then introduced into the low-pressure steam network;

[0060] S3: The steam expander is connected to the steam compressor through a reducer, and the external high-pressure steam is connected to the steam expander to generate medium-pressure steam, which is then incorporated into the medium-pressure steam network. The medium-pressure steam network is connected to the carbonate device to provide driving force for the carbonate device.

[0061] Furthermore, the steam pressure generated by the steam compressor is in the range of 0.2 to 1.0 MPaG, and the steam pressure generated by the steam expander is in the range of 0.5 to 1.5 MPaG.

[0062] Preferably, the steam pressure generated by the steam compressor is in the range of 0.3 to 0.5 MPaG, and the steam pressure generated by the steam expander is in the range of 0.7 to 1.1 MPaG.

[0063] The effects achieved by the recycling method of the present invention are described below with reference to two specific embodiments.

[0064] Example 1

[0065] A waste heat recovery method for a carbonate production device comprises the following steps:

[0066] S1: The crude carbonate product is fed into a distillation tower for refining, with the top temperature of the distillation tower being 100°C. A heat exchanger 11 is installed at the top of the distillation tower of the carbonate unit 1, using water as the heat exchange medium to exchange heat with the steam of the top material. The outlet temperature of the high-temperature hot water obtained by the exchange is 97°C. The high-temperature hot water enters the second-type lithium bromide absorption heat pump unit 2 to produce steam exhaust gas. The steam pressure of the steam exhaust gas is 0.21 MPaG. The circulating water is cooled to 87°C and then refluxed into the heat exchanger 11.

[0067] S2: The 0.21 MPaG steam exhaust gas is passed into the steam compressor 31 to further increase the temperature and pressure to 0.45 MPaG to form low-pressure steam, which is then introduced into the low-pressure steam network;

[0068] S3: The steam expander 32 is connected to the steam compressor 31 through the reducer 33, and the external high-pressure steam (steam pressure is 2.1 MPaG) is connected to the steam expander 32 to generate medium-pressure steam. The steam pressure of the medium-pressure steam obtained after expansion is 0.9 MPaG, and it is incorporated into the medium-pressure steam network. The medium-pressure steam network is connected to the carbonate device 1 to provide driving force for the carbonate device 1.

[0069] Example 2

[0070] A waste heat recovery method for a carbonate production device comprises the following steps:

[0071] S1: The crude carbonate product is fed into a distillation tower for refining, with the top temperature of the distillation tower being 100°C. A heat exchanger 11 is installed at the top of the distillation tower of the carbonate unit 1, using water as the heat exchange medium to exchange heat with the steam of the top material. The outlet temperature of the high-temperature hot water obtained by the exchange is 100°C. The high-temperature hot water enters the second-type lithium bromide absorption heat pump unit 2 to produce steam exhaust gas. The steam pressure of the steam exhaust gas is 0.22 MPaG. The circulating water is cooled to 90°C and then refluxed into the heat exchanger 11.

[0072] S2: The 0.22 MPaG steam exhaust gas is passed into the steam compressor 31 to further increase the temperature and pressure to 0.48 MPaG to form low-pressure steam, which is then introduced into the low-pressure steam network;

[0073] S3: The steam expander 32 is connected to the steam compressor 31 through the reducer 33, and the external high-pressure steam (steam pressure is 2.2 MPaG) is connected to the steam expander 32 to generate medium-pressure steam. The steam pressure of the medium-pressure steam obtained after expansion is 1.0 MPaG, and it is incorporated into the medium-pressure steam network. The medium-pressure steam network is connected to the carbonate device 1 to provide driving force for the carbonate device 1.

[0074] The specific data of Example 1 and Example 2 are shown in the following table.

[0075] Comparison Item Example 1 Example 2 Recovered hot water volume (t / h) 600 500 Waste heat recovery capacity (GJ) 25.080 20.900 Waste heat recovery rate (%) 96.5 96.4 Steam production (t / h) 5.450 4.542 Cost saving (yuan / h) 1386.3 1135.5

[0076] It can be seen from Examples 1 and 2 that the method of the present invention can fully recover the waste heat of the device, reducing the cooling water load of the original device. The waste heat recovery rate exceeds 95%. At the same time, a large amount of low-pressure steam is generated to enter the pipeline network, which can save costs of about 16 million per year.

[0077] In summary, the waste heat recovery method of the present invention recovers the energy that was originally wasted by circulating water in the distillation tower, and converts this part of heat into steam heat source for its own needs through the supplement of a small amount of energy from the second-type lithium bromide heat pump unit and the compression expansion unit, which not only saves the consumption of heat steam, but also reduces the use of cold circulating water.

[0078] The present invention is further described above with the aid of specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the essence and scope of the present invention. Various modifications made to the above embodiments by ordinary technicians in this field after reading this specification are all within the scope of protection of the present invention.

Claims

1. A waste heat utilization system for a carbonate production device, characterized in that: It includes a carbonate unit, a second-type lithium bromide absorption heat pump unit, an expansion compressor unit and a hot water circulation system, including: A heat exchanger is provided at the top of the distillation tower of the carbonate device. The circulating water of the hot water circulation system exchanges heat with the steam of the tower top material in the heat exchanger and then enters the second type lithium bromide absorption heat pump unit through the water supply pipe. The cooled circulating water flows back to the heat exchanger through the return pipe. The second type of lithium bromide absorption heat pump unit includes a gas-liquid separator, the heat of the circulating water is transferred to the gas-liquid separator, so that the feed water in the gas-liquid separator is heated to generate steam exhaust gas, and the steam exhaust gas enters the expansion compressor unit; The expansion compressor unit includes a steam compressor, a steam expander and a reducer. The steam exhaust gas enters the steam compressor to generate low-pressure steam; the steam compressor is connected to the steam expander through the reducer, and the external high-pressure steam is connected to the steam expander to generate medium-pressure steam.

2. The waste heat utilization system for carbonate production equipment according to claim 1, characterized in that: The expansion compressor unit also includes a first separator and a second separator. The steam exhaust gas enters the steam compressor and then generates low-pressure steam through the first separator; the external high-pressure steam enters the steam expander and then generates medium-pressure steam through the second separator.

3. The waste heat utilization system for carbonate production equipment according to claim 1, characterized in that: It also includes a constant pressure water replenishment device, the water inlet of the constant pressure water replenishment device is connected to the pure water pipe network, and the water outlet of the constant pressure water replenishment device is connected to the return pipe of the circulating water through a pipe.

4. The waste heat utilization system for carbonate production equipment according to claim 1, characterized in that: The hot water circulation system further comprises a temperature sensor, which detects and feeds back the temperature of the circulating water, so that the temperature of the circulating water is controlled at 85-100°C.

5. The waste heat utilization system for carbonate production equipment according to claim 1, characterized in that: The second type of lithium bromide absorption heat pump unit also includes an evaporator, an absorber, a generator and a condenser. The circulating water flowing out of the heat exchanger enters the evaporator so that the heat of the circulating water is absorbed. The cooled circulating water enters the generator to heat and concentrate the dilute lithium bromide solution in the generator. The cooled circulating water flows back to the heat exchanger.

6. The waste heat utilization system for carbonate production equipment according to claim 5, characterized in that: Condensed water is contained in the condenser, and a condensation pump is further provided on the condenser, through which the condensed water is ejected.

7. The waste heat utilization system for carbonate production equipment according to claim 1, characterized in that: The heat exchanger is a fully welded plate heat exchanger.

8. The waste heat utilization system for carbonate production equipment according to claim 1, characterized in that: The steam compressor is a screw compressor.

9. A waste heat recovery method for a carbonate production device, characterized in that: The following steps are involved: S1: A heat exchanger is installed at the top of the distillation tower of the carbonate unit. Water is used as the heat exchange medium to exchange heat with the steam of the overhead material. The high-temperature hot water obtained by the exchange enters the second-type lithium bromide absorption heat pump unit to prepare steam exhaust gas; the cooled water flows back into the heat exchanger; S2: The steam exhaust gas is passed into the steam compressor to further heat and pressurize it to the required pressure to form low-pressure steam, which is then introduced into the low-pressure steam network; S3: The steam expander is connected to the steam compressor through a reducer, and the external high-pressure steam is connected to the steam expander to generate medium-pressure steam, which is then incorporated into the medium-pressure steam network. The medium-pressure steam network is connected to the carbonate device to provide driving force for the carbonate device.

10. The waste heat recovery method of a carbonate production device according to claim 9, characterized in that: The steam pressure generated by the steam compressor is in the range of 0.3 to 0.5 MPaG, and the steam pressure generated by the steam expander is in the range of 0.7 to 1.1 MPaG.

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