System and method for producing steam through heating medium water by using low-temperature waste heat

Abstract

The invention relates to a system for producing steam by low-temperature waste heat through heat medium water, which comprises a heat medium water heat taking unit, a deoxygenated water steam producing unit and a steam compression unit, the heat medium water heat taking unit comprises a low-temperature waste heat outlet, a heat exchanger tube pass, a heat medium water tank, a heat medium water pump and a low-temperature waste heat inlet which are communicated in sequence through a pipeline; the deoxygenated water vapor generating unit comprises a heat exchanger shell pass outlet, a negative pressure flash tank, a deoxygenated water pump and a heat exchanger shell pass inlet which are sequentially communicated through pipelines, and the vapor compression unit comprises a negative pressure flash tank top outlet, a first compressor, a second compressor, a vapor-liquid separation tank and a vapor outlet system which are sequentially communicated through pipelines. According to the method for producing the steam from the low-temperature waste heat through the heating medium water, the 98-DEG C heating medium water is obtained from the low-temperature waste heat, the deoxygenated water is heated through the heat exchanger, the deoxygenated water subjected to temperature rising is subjected to negative-pressure flash evaporation, then low-pressure steam is generated through compression and boosting, high-quality conversion of low-temperature heat is achieved, working medium leakage is avoided, and the system safety and stability are good.

Description

Technical Field

[0001] The present invention relates to the technical field of low-temperature waste heat utilization, and in particular to a system and method for producing steam by using low-temperature waste heat through heat medium water. Background Art

[0002] Faced with increasingly severe energy and environmental issues, how to improve the comprehensive energy utilization efficiency of industrial enterprises, recycle various waste heat and reduce the pollution of waste heat to the environment has become the focus of people's attention. The chemical production process is continuous, multi-process, and multi-level, which consumes a lot of fuel and electricity, and produces abundant low-temperature waste heat resources (70-120℃), so there is huge energy-saving potential. However, except for a small part of this energy that is transferred to the product, most of the energy is discharged to the environment in the form of cooling water, cooling air, heating furnace exhaust, etc., which not only causes thermal pollution to the environment but also increases the energy consumption of enterprises.

[0003] Chemical plants are highly coupled and related in terms of materials and heat energy. Low-temperature waste heat resources cannot be sent back to the production process for utilization due to the wide distribution of heat sources and temperature positions, and the heat sources and heat sinks are quite dispersed. Most of this heat energy is discharged through heat exchange with air and circulating water, resulting in a large amount of waste of low-temperature waste heat resources. Therefore, how to combine heat between plants to reduce the generation of low-temperature waste heat, how to recover the low-temperature waste heat generated by process plants, and how to convert low-temperature waste heat with high quality are major key technical issues that need to be urgently solved in the chemical industry, and are also technical bottlenecks that restrict the development of enterprises.

[0004] Using low-temperature waste heat to produce steam is a very effective high-quality conversion method, especially in the petrochemical industry, which requires a large amount of steam, providing favorable conditions for using waste heat recovery to produce steam. Traditional heat pump technology can only produce hot water at a maximum temperature of 70 to 90°C, but industrial processes generally require high-temperature steam, which makes it difficult for traditional heat pumps to be used for low-temperature waste heat recovery. Summary of the invention

[0005] High-temperature steam heat pumps can generally generate high-temperature and high-pressure steam, and are therefore suitable for recovering low-temperature waste heat and generating steam for user production. In view of the deficiencies of the prior art, the present invention provides a system and method for generating steam using low-temperature waste heat through heat medium water based on high-temperature steam heat pump technology, which has the advantages of low circulating water consumption, good system safety and stability, and solves the problem that the existing heat pumps may have leakage or other failures, causing hot water to carry oil into the generated steam.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a system for producing steam from low-temperature waste heat heat medium water, comprising a heat medium water heat extraction unit, a deoxygenated water steam production unit and a steam compression unit which are connected in sequence through pipelines, the heat medium water heat extraction unit comprising a low-temperature waste heat outlet, a heat exchanger tube side, a heat medium water tank, a heat medium water pump and a low-temperature waste heat inlet which are connected in sequence through pipelines, the deoxygenated water steam production unit comprising a heat exchanger shell side outlet, a negative pressure flash tank, a deoxygenated water pump and a heat exchanger shell side inlet which are connected in sequence through pipelines, the negative pressure flash tank top outlet, a first compressor, a second compressor, a vapor-liquid separation tank and a steam outlet system of the steam compression unit are connected in sequence through pipelines, the lower part of the negative pressure flash tank is connected to a deoxygenated water supply pipeline, the upper section of the negative pressure flash tank is connected to a vacuum pump, and the bottom outlet of the vapor-liquid separation tank is connected to the inlet of the second compressor.

[0007] Furthermore, the heat exchanger is a plate heat exchanger to achieve heat exchange between the heat medium water and the deoxygenated water, and the negative pressure flash tank can generate low-pressure steam of 0.034 MPa (absolute pressure) from the deoxygenated water.

[0008] Furthermore, the first compressor is a two-stage centrifugal compressor, which can increase the low-pressure steam to 0.130 MPa (absolute pressure) low-pressure steam through two-stage centrifugal compression.

[0009] Furthermore, the second compressor is a screw compressor, which can increase the low-pressure steam to 0.7 MPa (absolute pressure) steam.

[0010] A method for producing steam by using low-temperature waste heat through heat medium water comprises the following steps: Step 1: Heat extraction with heat medium water. The heat medium water is pumped out from the heat medium water tank by a heat medium water pump and transported to each low-temperature waste heat system at a certain pressure. The low-temperature waste heat of 70-120°C generated by each production device is extracted by heat exchange with heat medium water. The heat exchange principle is from low temperature to high temperature, stepwise heat exchange, and the heat medium water is heated to 98°C. Step 2: Deoxygenated water heat exchange: deoxygenated water is pumped out from the negative pressure flash tank by a deoxygenated water pump to increase the pressure, and then transported to the heat exchanger to exchange heat with 98°C heat medium water. The 98°C heat medium water transfers heat to the deoxygenated water through a partition heat exchanger, and the heated deoxygenated water enters the negative pressure flash tank; Step 3: negative pressure flash evaporation to produce steam. The pressure of the negative pressure flash tank is reduced to a vacuum state by a vacuum pump. The heated deoxygenated water enters the negative pressure flash tank through a pressure reducing valve, flash steam vaporizes, and generates low-pressure steam of 0.034 MPa (absolute pressure). The unvaporized deoxygenated water is circulated for heat exchange to produce steam. The liquid level of the negative pressure flash tank is maintained by a deoxygenated water supply line. Step 4: The low-pressure steam of 0.034 MPa (absolute pressure) generated by steam compression is pressurized by two sets of compressors in series. The first compressor increases the low-pressure steam to 0.130 MPa (absolute pressure) low-pressure steam through two-stage centrifugal compression, and the second compressor increases the low-pressure steam to 0.7 MPa (absolute pressure) steam through screw compression; Step 5 Vapor-liquid separation The 0.7MPa (absolute pressure) steam boosted by the screw compressor enters the vapor-liquid separation tank for vapor-liquid separation. The gaseous part enters the steam outlet system for user use, and the liquid part is self-pressurized back to the screw compression inlet for reuse.

[0011] Furthermore, the transmission temperature difference loss of heat medium water is less than 1°C per kilometer, which realizes the recovery of low-temperature waste heat resources, eliminates some air coolers, and reduces the use of circulating water.

[0012] Compared with the prior art, the beneficial effects are: (1) Heat is taken from heat medium water, and steam is produced from deoxygenated water. Deoxygenated water is used as the working medium, and low-pressure steam is produced by indirect heat exchange between deoxygenated water and heat medium water. Compared with absorption heat pumps or compression heat pumps, this can ensure steam quality and is highly safe, avoiding the risks caused by the complex process of the working medium circulation system, leakage of the heat exchanger, and leakage of the working medium compressor. (2) Adopt negative pressure flash evaporation + double compression technology, consume a small amount of electricity, use low-temperature heat medium water to heat deoxygenated water, and then vacuum flash evaporate it into low-pressure steam, and then compress the steam twice to high temperature and high pressure to achieve high-quality conversion of low-temperature thermal energy, which can not only save energy and reduce consumption, but also alleviate the contradiction between the waste of low-temperature heat and the shortage of medium and low-pressure steam in enterprises; (3) The consumption of circulating water is small. Only a small amount of circulating water is required for lubricating oil cooling. The main process does not consume circulating water, which reduces the consumption of public works. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the structure of the present invention.

[0014] In the figure: 1. Low-temperature waste heat; 2. Heat medium water tank; 3. Heat medium water pump; 4. Heat exchanger; 5. Negative pressure flash tank; 6. Deaeration water pump; 7. Deaeration water supply pipeline; 8. Vacuum pump; 9. First compressor; 10. Second compressor; 11. Vapor-liquid separation tank; 12. Steam outlet system. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0016] See also Figure 1 In this embodiment, a system for producing steam through heat medium water using low-temperature waste heat includes a system for producing steam through heat medium water using low-temperature waste heat, including a heat medium water heat extraction unit, a deoxygenated water steam production unit and a steam compression unit which are sequentially connected through pipelines, wherein the heat medium water heat extraction unit includes a low-temperature waste heat 1 outlet, a heat exchanger 4 pipe side, a heat medium water tank 2, a heat medium water pump 3 and a low-temperature waste heat 1 inlet which are sequentially connected through pipelines, wherein the deoxygenated water steam production unit includes a heat exchanger 4 shell side outlet, a negative pressure flash tank 5, a deoxygenated water pump 6 and a heat exchanger 4 shell side inlet which are sequentially connected through pipelines, wherein the negative pressure flash tank 5 top outlet, a first compressor 9, a second compressor 10, a vapor-liquid separation tank 11 and a steam outlet system 12 of the steam compression unit are sequentially connected through pipelines, wherein the lower part of the negative pressure flash tank 5 is connected to a deoxygenated water supply pipeline 7, the upper part of the negative pressure flash tank 5 is connected to a vacuum pump 8, and the bottom outlet of the vapor-liquid separation tank 11 is connected to the inlet of the second compressor 10.

[0017] Furthermore, the heat exchanger 4 is a plate heat exchanger to achieve heat exchange between the heat medium water and the deoxygenated water, and the negative pressure flash tank 5 can generate low-pressure steam of 0.034 MPa (absolute pressure) from the deoxygenated water.

[0018] Furthermore, the first compressor 9 is a two-stage centrifugal compressor, which can increase the low-pressure steam to 0.130 MPa (absolute pressure) low-pressure steam through two-stage centrifugal compression.

[0019] Furthermore, the second compressor 10 is a screw compressor, which can increase the low-pressure steam to 0.7 MPa (absolute pressure) steam.

[0020] Furthermore, the low-temperature waste heat system, heat exchanger, flash tank, compressor, gas-liquid separation system, steam outlet system, liquid outlet system and heat medium water system are auxiliary equipment of the steam heat pump unit.

[0021] A method for producing steam by using low-temperature waste heat through heat medium water comprises the following steps: Step 1: Heat extraction with heat medium water. The heat medium water is pumped out from the heat medium water tank 2 by the heat medium water pump 3 and transported to each low-temperature waste heat 1 system at a certain pressure. The low-temperature waste heat of 70-120°C generated by each production device is extracted by heat exchange with heat medium water. The heat exchange principle is from low temperature to high temperature, stepwise heat exchange, and the heat medium water is heated to 98°C. Step 2: Deoxygenated water heat exchange: the deoxygenated water is pumped out from the negative pressure flash tank 5 by the deoxygenated water pump 6 to increase the pressure, and then transported to the heat exchanger 4 to exchange heat with the 98°C heat medium water. The 98°C heat medium water transfers heat to the deoxygenated water through the partition heat exchange, and the heated deoxygenated water enters the negative pressure flash tank 5; Step 3: negative pressure flash evaporation to produce steam. The pressure of the negative pressure flash tank 5 is reduced to a vacuum state by a vacuum pump 8. The heated deoxygenated water enters the negative pressure flash tank 5 through a pressure reducing valve, flash steam vaporizes, and generates low-pressure steam of 0.034 MPa (absolute pressure). The unvaporized deoxygenated water is circulated for heat exchange to produce steam. The liquid level of the negative pressure flash tank 5 is maintained by the deoxygenated water supply pipeline 7. The low-pressure steam of 0.034 MPa (absolute pressure) generated by steam compression and pressure boosting in step 4 is boosted by two sets of compressors in series. The first compressor 9 increases the low-pressure steam to 0.130 MPa (absolute pressure) low-pressure steam through two-stage centrifugal compression, and the second compressor 10 increases the low-pressure steam to 0.7 MPa (absolute pressure) steam through screw compression; Step 5 Vapor-Liquid Separation The 0.7 MPa (absolute pressure) steam boosted by the screw compressor enters the vapor-liquid separation tank 11 for vapor-liquid separation. The gaseous part enters the steam outlet system 12 for user use, and the liquid part is self-pressurized back to the screw compression inlet for reuse.

[0022] In the embodiment of the present invention, the transmission temperature difference loss of the heat medium water for heat extraction is less than 1°C per kilometer, thereby realizing the recovery of low-temperature waste heat resources, eliminating some air coolers, and reducing the use of circulating water.

[0023] The working principle of the above embodiment is: Heat is taken from heat medium water, steam is produced from deoxygenated water, and deoxygenated water is used as the working medium. Low-pressure steam is produced by indirect heat exchange between deoxygenated water and heat medium water. The main process flow is that 98°C heat medium water enters the heat exchanger 4 to heat the deoxygenated water, and the heated deoxygenated water enters the negative pressure flash tank 5 for flash evaporation, and then is compressed and pressurized twice to produce low-pressure steam, which can keep the system at a slightly positive pressure, easy to operate, and oil is not easy to enter the steam. Compared with absorption heat pumps or compression heat pumps, it can ensure the quality of steam and has high safety, avoiding the risks caused by the complex process of the working medium circulation system, leakage of the heat exchanger and leakage of the working medium compressor, etc.; the negative pressure flash evaporation + double compression technology is adopted to realize high-quality conversion of low-temperature thermal energy by consuming a small amount of electric energy, and the consumption of circulating water is small. Only a small amount of circulating water is required for cooling the unit lubricating oil, and the main process does not need to consume circulating water, which reduces the consumption of public works and improves the energy utilization efficiency.

[0024] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0025] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A system for producing steam using low-temperature waste heat through heat medium water, characterized in that: It includes a heat medium water heat extraction unit, a deoxygenated water steam production unit and a steam compression unit which are connected in sequence through pipelines. The heat medium water heat extraction unit includes a low-temperature waste heat outlet, a heat exchanger tube, a heat medium water tank, a heat medium water pump and a low-temperature waste heat inlet which are connected in sequence through pipelines. The deoxygenated water steam production unit includes a heat exchanger shell outlet, a negative pressure flash tank, a deoxygenated water pump and a heat exchanger shell inlet which are connected in sequence through pipelines. The steam compression unit includes a negative pressure flash tank top outlet, a first compressor, a second compressor, a vapor-liquid separation tank and a steam outlet system which are connected in sequence through pipelines. The lower part of the negative pressure flash tank is connected to a deoxygenated water supply pipeline, the upper section of the negative pressure flash tank is connected to a vacuum pump, and the bottom outlet of the vapor-liquid separation tank is connected to the inlet of the second compressor.

2. The system for producing steam by using low-temperature waste heat through heat medium water according to claim 1, characterized in that: The heat exchanger is a plate heat exchanger, which realizes heat exchange between heat medium water and deoxygenated water. The negative pressure flash tank can generate low-pressure steam of 0.034MPa (absolute pressure) from deoxygenated water.

3. The system for producing steam by using low-temperature waste heat through heat medium water according to claim 1, characterized in that: The first compressor is a two-stage centrifugal compressor, which can increase the low-pressure steam to 0.130MPa (absolute pressure) low-pressure steam through two-stage centrifugal compression.

4. The system for producing steam by using low-temperature waste heat through heat medium water according to claim 1, characterized in that: The second compressor is a screw compressor, which can increase the low-pressure steam to 0.7 MPa (absolute pressure) steam.

5. A method for a system for producing steam by using the low-temperature waste heat according to any one of claims 1 to 4 through heat medium water, characterized in that: The following steps are involved: Step 1: Heat extraction with heat medium water. Heat medium water is pumped out from the heat medium water tank by a heat medium water pump and transported to each low-temperature waste heat system at a certain pressure. The low-temperature waste heat of 65-120°C generated by each production device is extracted by heat exchange with heat medium water. The heat exchange principle is from low temperature to high temperature, stepwise heat exchange, and the heat medium water is heated to 98°C. Step 2: Deoxygenated water heat exchange: deoxygenated water is pumped out from the negative pressure flash tank by a deoxygenated water pump to increase the pressure, and then transported to the heat exchanger to exchange heat with 98°C heat medium water. The 98°C heat medium water transfers heat to the deoxygenated water through a partition heat exchanger, and the heated deoxygenated water enters the negative pressure flash tank; Step 3: negative pressure flash evaporation to produce steam. The pressure of the negative pressure flash tank is reduced to a vacuum state by a vacuum pump. The heated deoxygenated water enters the negative pressure flash tank through a pressure reducing valve, flash steam vaporizes, and generates low-pressure steam of 0.034 MPa (absolute pressure). The unvaporized deoxygenated water is circulated for heat exchange to produce steam. The liquid level of the negative pressure flash tank is maintained by a deoxygenated water supply line. Step 4: The steam is compressed and pressurized, and the low-pressure steam of 0.034 MPa (absolute pressure) is generated and pressurized by two sets of compressors in series. The first compressor increases the low-pressure steam to 0.130 MPa (absolute pressure) low-pressure steam through two-stage centrifugal compression, and the second compressor increases the low-pressure steam to 0.7 MPa (absolute pressure) steam through screw compression; Step 5: Vapor-liquid separation: the 0.7MPa (absolute pressure) steam boosted by the screw compressor enters the vapor-liquid separation tank for vapor-liquid separation. The gaseous part enters the steam outlet system for user use, and the liquid part is self-pressurized back to the screw compression inlet for reuse.

6. The method for producing steam by using low-temperature waste heat through heat medium water according to claim 5, characterized in that: The transmission temperature difference loss of heat medium water is less than 1°C per kilometer, which realizes the recovery of low-temperature waste heat resources, eliminates some air coolers, and reduces the use of circulating water.

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