Methanol synthesis recycle gas waste heat utilization system and method

Abstract

The invention relates to the technical field of methanol synthesis processes, and discloses a methanol synthesis recycle gas waste heat utilization system and method.The methanol synthesis recycle gas waste heat utilization system comprises a heat exchange unit and a refrigeration unit, a gas outlet and a water inlet are formed in the top of the heat exchange unit, and a gas inlet and a water outlet are formed in the bottom of the heat exchange unit; a water inlet and a water outlet of the heat exchange unit are communicated with the refrigeration unit through pipelines; the refrigeration unit is provided with a refrigerant inlet and a refrigerant outlet; and the heat exchange unit is a tubular heat exchanger. According to the scheme, the heat in the low-pressure synthesis recycle gas (about 85-120 DEG C) is transferred to the refrigeration unit, and the refrigerant product is produced in the circulation operation process in the refrigeration unit, so that the heat in the low-pressure synthesis recycle gas is effectively utilized, and the energy utilization efficiency of methanol synthesis is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of methanol synthesis processes, and specifically relates to a system and method for utilizing the waste heat of methanol synthesis recycle gas. Background Art

[0002] The main methods for synthesizing industrial methanol at home and abroad are the low-pressure method, the medium-pressure method, and the high-pressure method. The production of methanol involves multiple processes, not only including the preparation of raw material gas, but also gas purification and compression, methanol synthesis, and crude methanol rectification. In methanol production, the chemical equation for methanol synthesis is:

[0003] CO + 2H 2 → CH 3 OH + 90.58 KJ / mol

[0004] CO 2 + 3H 2 → CH 3 OH + H 2 O + 49.32 KJ / mol

[0005] With the synthesis of methanol, a large amount of heat is by-produced. At present, only the heat in the medium-high pressure and medium-pressure synthesis recycle gas generated during the methanol synthesis process is utilized, such as using it to preheat the methanol synthesis raw materials, or like the low-pressure methanol synthesis process of the British DPT company, using the heat generated during the methanol synthesis process to by-produce medium-pressure saturated steam to drive the synthesis compressor turbine and improve the energy utilization rate of the process.

[0006] However, the medium-low pressure synthesis gas (about 85 - 120 °C) after the low-pressure steam in the methanol synthesis stage is mostly directly cooled to below 45 °C through the industrial circulating water process, resulting in the energy in the medium-low pressure synthesis gas (about 85 - 120 °C) not being utilized and causing energy waste.

[0007] In summary, developing a system and method for utilizing the waste heat of medium-low pressure synthesis recycle gas is of great significance for the full utilization of energy during the methanol synthesis process, achieving energy conservation and carbon reduction, and reducing the energy consumption of the methanol process. Summary of the Invention

[0008] The present invention aims to provide a system and method for utilizing the waste heat of methanol synthesis recycle gas to solve the technical problem that the waste heat in the existing medium-low pressure synthesis recycle gas is not utilized.

[0009] To achieve the above object, the present invention adopts the following technical solution: A system for utilizing the waste heat of methanol synthesis recycle gas includes a heat exchange unit and a refrigeration unit. The top of the heat exchange unit is provided with an air outlet and a water inlet, and the bottom is provided with an air inlet and a water outlet; the water inlet and the water outlet of the heat exchange unit are both connected to the refrigeration unit through pipelines; the refrigeration unit is provided with a refrigerant inlet and a refrigerant outlet.

[0010] The principle of this solution is as follows:

[0011] The low-pressure synthesis recycle gas (about 85 - 120°C) generated during the methanol synthesis process enters the heat exchange unit through the inlet, and undergoes flow heat exchange with the heat exchange medium entering the heat exchange unit from the water inlet. The heat-exchanged synthesis recycle gas returns to the methanol system from the outlet; while the heat-exchanged heat exchange medium enters the refrigeration unit, and after transferring heat to the absorbent in the refrigeration unit, it returns to the heat exchange unit to repeat heat exchange with the synthesis recycle gas. The absorbent in the refrigeration unit evaporates the refrigerant after absorbing heat, and the refrigerant completes heat exchange with the refrigerant during the circulation process in the refrigeration unit to produce refrigerant products.

[0012] In the initial stage of designing the waste heat utilization system, the applicant tried to use a plate heat exchanger with a small footprint and higher heat exchange efficiency as the heat exchanger for the synthesis recycle gas and the heat exchange medium. However, the applicant found that when the inlet gas volume is large or the heat exchange temperature difference is large, the volume change of the synthesis recycle gas before and after heat exchange is large, resulting in a large pressure change of the synthesis recycle gas before and after heat exchange, which easily damages the plate heat exchanger and causes the heat exchange to be unable to proceed continuously. Subsequently, the applicant adjusted the synthesis gas inlet flow rate many times. However, no matter how much the synthesis gas inlet flow rate is reduced, the temperature of the heat-exchanged medium will be too low to reach the heat required by the refrigeration unit. Specifically, the temperature of the refrigerant prepared cannot meet the user's requirements.

[0013] By chance, the applicant used a shell-and-tube heat exchanger as the heat exchanger for the synthesis recycle gas and the heat exchange medium, and found that it can effectively balance the continuity of heat exchange production and the refrigerant production requirements of the refrigeration unit. On the one hand, the shell-and-tube heat exchanger has strong pressure-bearing capacity, which is convenient for balancing the inlet flow rate of the synthesis recycle gas and the pressure difference of the synthesis recycle gas before and after heat exchange, realizing safe production and continuous production; on the other hand, the shell-and-tube heat exchanger has good heat exchange efficiency, which can meet the heat requirements during the production of refrigerant in the refrigeration unit, continuously produce high-quality refrigerant products, and make full use of the heat in the low-pressure synthesis recycle gas.

[0014] The advantages of this solution are as follows:

[0015] 1. Compared with the prior art where the low-pressure synthesis recycle gas generated during the methanol synthesis process is directly cooled and reserved, resulting in energy loss, this solution transfers the heat in the low-pressure synthesis recycle gas (about 85 - 120°C) to the refrigeration unit, and produces refrigerant products during the circulation process in the refrigeration unit, realizing the effective utilization of the heat in the low-pressure synthesis recycle gas and improving the energy utilization efficiency of methanol synthesis.

[0016] 2. Compared with the prior art where a large amount of cooling water resources are consumed to reduce the temperature of the synthetic recycle gas by continuous flowing cooling water, in this solution, during the waste heat utilization process of the synthetic recycle gas, a closed loop is set up to realize the reuse of the heat transfer medium, absorbent and refrigerant, effectively reducing the cost in the waste heat utilization process of the low-pressure synthetic recycle gas and improving production efficiency.

[0017] 3. This solution makes full use of the waste heat in the methanol synthesis recycle gas and produces high-value low-pressure refrigerant through heat exchange and lithium bromide refrigeration process. From the overall perspective of the enterprise, it reduces the overall energy consumption of the enterprise and reduces the carbon emissions of the enterprise.

[0018] Preferably, the refrigeration unit includes a generating device, a cooling device, an evaporation device and an absorption device connected in sequence through pipelines; a forward conveying pipe and a reverse conveying pipe are connected between the absorption device and the generating device; the cooling device is provided with a cooling inlet and a cooling outlet, and the cooling device is provided with a refrigerant inlet and a refrigerant outlet; the water inlet and outlet of the heat exchange unit are both connected to the generating device through pipelines.

[0019] Beneficial effects: In this solution, the heat transfer medium after heat exchange transfers heat to the solution composed of absorbent and refrigerant in the generating device, causing the refrigerant in the solution to evaporate and form a high-concentration refrigerant solution. The high-concentration refrigerant solution enters the absorption device through the forward conveying pipe; while the evaporated refrigerant enters the cooling device and is cooled down under the action of cooling water. The cooled refrigerant enters the evaporation device and absorbs the heat of the refrigerant to form a low-pressure steam refrigerant. The low-pressure steam refrigerant then enters the second generating device and mixes with the high-concentration absorbent solution to form a low-concentration absorbent solution. The low-concentration absorbent solution enters the generating device through the reverse conveying pipe to complete the cycle of absorbent and refrigerant. During this process, the absorbent, refrigerant and cooling water are recycled, reducing the cost in the waste heat utilization process.

[0020] This solution also provides a method for waste heat utilization of methanol synthesis recycle gas, which is completed based on the above waste heat utilization system of methanol synthesis recycle gas, and includes the following steps:

[0021] Step 1: Primary heat exchange, the synthetic recycle gas exchanges heat with the heat transfer medium in the heat exchange unit to obtain the heat transfer medium after heat exchange;

[0022] Step 2: Refrigeration heat exchange, the heat transfer medium after heat exchange transfers heat to the first absorbent solution in the generating device to obtain desalted water, the first refrigerant steam and the second absorbent solution; the second absorbent solution enters the absorption device along the forward conveying pipe;

[0023] Step 3: Refrigerant heat exchange, the generated refrigerant steam is cooled by cooling water in the cooling device to form a refrigerant, and the refrigerant then exchanges heat with the refrigerant in the evaporation device to obtain the second refrigerant steam and the refrigerant product;

[0024] Step 4: Circulation heat exchange, the heat exchange medium in step 2 repeats steps 1 and 2 to realize the recycling of the heat exchange medium; the second absorbent solution in step 2 is mixed with the evaporated refrigerant vapor obtained in step 3 in the absorption device to form a first absorbent solution, the first absorbent solution returns to the generating device along the reverse transport pipe, and repeats steps 2 to 4 to realize the recycling of the absorbent solution.

[0025] Beneficial effects: This solution uses the circulating heat transfer of the heat exchange medium (taking desalted water as an example) and the refrigerant (taking water as an example) to enable the heat in the synthetic cycle gas at 85 to 120°C to be used to produce low-temperature refrigerant products. On the one hand, the temperature of the low-pressure synthetic cycle gas is reduced to the subsequent use temperature range of the methanol system. On the other hand, this part of the heat energy is fully utilized to produce commercial product refrigerants, effectively improving the energy utilization efficiency of industrial production. In the process of waste heat utilization, the heat exchange medium (taking desalted water as an example), absorbent (lithium bromide) and refrigerant (taking water as an example) can all be recycled, effectively reducing the cost of waste heat utilization.

[0026] Preferably, the heat exchange medium is any one of water, oil or desalted water.

[0027] Beneficial effect: This solution uses water, desalted water or oil to achieve heat exchange with the synthetic cycle gas, and transfers the waste heat in the synthetic cycle gas to the refrigeration unit for utilization.

[0028] Preferably, the heat exchange medium is desalted water, the absorbent is lithium bromide, and the refrigerant is water.

[0029] Beneficial effects: This scheme uses desalted water to absorb heat from the synthetic circulating gas and then convert it, which can effectively reduce the probability of scaling or corrosion in the pipeline during the repeated circulation of the heat exchange medium, thereby saving the cost of pipeline cleaning and replacement, and achieving continuous production. In addition, desalted water can be made by desalting the circulating water in the methanol synthesis process, which can effectively reduce production costs. This scheme uses lithium bromide as an absorbent and water as a refrigerant to form a binary solution of lithium bromide-water, which is convenient for using various low-potential thermal energy and the heat energy in waste gas and waste heat as power, without consuming a large amount of electricity, and can produce a large number of refrigerant products, with good power saving and energy saving effects and high economic benefits.

[0030] Preferably, the temperature of the desalted water entering the heat exchange unit is 50-55°C, and the temperature of the desalted water entering the generating device is 75°C-110°C.

[0031] Beneficial effect: This scheme uses a heat exchange medium with a temperature of 75°C to 110°C to exchange heat with a low-concentration lithium bromide solution, which is convenient for evaporating water in the low-concentration lithium bromide solution and realizing the operation of the lithium bromide refrigerant to produce refrigerant products.

[0032] Preferably, the inlet water temperature of the cooling water in the cooling device is 20 to 35 °C.

[0033] Beneficial effects: In this solution, water at normal temperature (the temperature in Chongqing area varies greatly) can be used to cool the refrigerant vapor in the cooling device to a relatively low temperature, so that the refrigerant can exchange heat with the refrigerant medium under the low-pressure condition of the evaporation device at a relatively low temperature, thereby producing a high-quality refrigerant medium product, converting the heat in the synthetic circulating gas into the output of the actual refrigerant medium product, and fully demonstrating the industrial utilization value of the energy in the synthetic circulating gas.

[0034] Preferably, the inlet water temperature of the refrigerant medium in the evaporation device is 10 to 22 °C.

[0035] Beneficial effects: In this solution, by adjusting the inlet water temperature of the refrigerant medium, it is convenient to produce low-pressure refrigerant medium products according to the temperature requirements of users for the refrigerant medium products. Specifically, when users need to produce low-pressure refrigerant medium products at 5 to 7 °C, refrigerant medium with an inlet water temperature of 10 to 18 °C can be used; when low-pressure refrigerant medium products at 10 to 11 °C are needed, refrigerant medium with an inlet water temperature of 18 to 22 °C can be used, realizing the flexible utilization of the production of refrigerant medium products. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic structural diagram of the methanol synthesis circulating gas waste heat utilization system in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The following is further detailed through specific embodiments:

[0038] The reference numerals in the accompanying drawings of the specification include: heat exchange unit T, refrigeration unit R, shell-and-tube heat exchanger 1, generating device 2, cooling device 3, evaporation device 4, absorption device 5, air inlet 6, air outlet 7, water outlet 8, water inlet 9, generating tube 10, cooling inlet 11, cooling outlet 12, cooling tube 13, evaporation inlet 14, evaporation outlet 15, evaporation tube 16, reverse conveying pipe 17, forward conveying pipe 18.

[0039] Embodiment

[0040] This embodiment is basically as Figure 1 shown: A methanol synthesis circulating gas waste heat utilization system includes a heat exchange unit T and a refrigeration unit R. In this embodiment, the heat exchange unit T is specifically a shell-and-tube heat exchanger 1. The top of the shell-and-tube heat exchanger 1 is provided with an air outlet 7 and a water inlet 9, and the bottom is provided with an air inlet 6 and a water outlet 8. The water inlet 9 and the water outlet 8 of the shell-and-tube heat exchanger 1 are both connected to the refrigeration unit R through pipelines.

[0041] The refrigeration unit R includes a generating device 2, a cooling device 3, an evaporation device 4, and an absorption device 5 that are connected in sequence through pipelines; a forward delivery pipe 18 and a reverse delivery pipe 17 are connected between the absorption device 5 and the generating device 2; the cooling device 3 is provided with a cooling inlet 11 and a cooling outlet 12, and the evaporation device 4 is provided with a refrigerant inlet and a refrigerant outlet; the water inlet 9 and the water outlet 8 of the shell-and-tube heat exchanger 1 are both connected to the generating device 2 through pipelines. In this solution, the refrigeration unit R is specifically a lithium bromide refrigeration unit, the generating device 2 is specifically a generator, the cooling device 3 is specifically a cooler, the evaporation device 4 is specifically an evaporator, and the absorption device 5 is specifically an absorber. A generating pipe 10 is connected between the generator and the cooler, a cooling pipe 13 is connected between the cooler and the evaporator, and an evaporation pipe 16 is connected between the evaporator and the absorber.

[0042] The specific implementation process is as follows:

[0043] The low-pressure synthesis recycle gas in the methanol synthesis process enters the shell-and-tube heat exchanger 1 from the inlet 6, and the low-temperature heat exchange medium enters the shell-and-tube heat exchanger 1 from the water inlet 9. The two exchange heat during the flow in the shell-and-tube heat exchanger 1 to form a high-temperature heat exchange medium and a low-temperature synthesis recycle gas. The low-temperature synthesis recycle gas returns to the methanol synthesis system from the outlet 7; while the high-temperature heat exchange medium enters the generator and exchanges heat with the low-concentration lithium bromide solution in the generator to evaporate the water in the low-concentration lithium bromide solution, forming generated steam, high-concentration lithium bromide solution, and low-temperature heat exchange medium. The low-temperature heat exchange medium returns to the shell-and-tube heat exchanger 1 along the pipeline between the generating device 2 and the water inlet 9 of the shell-and-tube heat exchanger 1 to continue exchanging heat with the low-pressure synthesis recycle gas. The high-concentration lithium bromide solution enters the absorber along the forward delivery pipe 18, and the generated steam enters the cooler along the generating pipe 10 to exchange heat with the cooling water and then condense. The cooling water is discharged from the cooling outlet 12, and the cooled refrigerant enters the evaporator along the cooling pipe 13, evaporates into low-pressure steam after absorbing the heat in the refrigerant, and the refrigerant forms a low-pressure refrigerant product with a lower temperature and is output. The low-pressure steam enters the absorber along the evaporation pipe 16 and is absorbed by the high-concentration lithium bromide solution to form a low-concentration lithium bromide solution. The low-concentration lithium bromide solution then returns to the generator through the reverse delivery pipe 17 to continue absorbing the heat in the high-temperature heat exchange medium to evaporate the refrigerant steam and form a high-concentration lithium bromide solution, recycling the waste heat in the synthesis recycle gas to produce a refrigerant product.

[0044] The present invention makes full use of the waste heat in the methanol synthesis recycle gas and produces high-value low-pressure refrigerant products through heat exchange and lithium bromide refrigeration processes. From the overall perspective of the enterprise, it effectively reduces the overall energy consumption of the enterprise, and thus reduces the carbon emissions of the enterprise.

[0045] This solution also provides a method for utilizing the waste heat of the methanol synthesis recycle gas, which is completed based on the above-mentioned system for utilizing the waste heat of the methanol synthesis recycle gas, and specifically includes the following steps: includes the following steps:

[0046] Step 1: Primary heat exchange. The synthetic recycle gas exchanges heat with the heat exchange medium in the shell-and-tube heat exchanger 1 to obtain the heat exchange medium after heat exchange.

[0047] In this solution, the components and characteristics of the low-pressure methanol synthesis recycle gas in the methanol synthesis process are as follows: the pressure is 6 - 9.5 Mpa.G, the temperature is 85 - 120 °C, the molar composition is hydrogen content 50% - 70%, methane content 3% - 15%, nitrogen content 3% - 15%, methanol content 1% - 6%, carbon monoxide content 3% - 10%, and the rest contains a small amount of water, carbon dioxide, etc. In this solution, the heat exchange medium is specifically any one of water, oil, or demineralized water. In this embodiment, it is specifically demineralized water, which is convenient for reducing pipeline scaling and the number of cleaning times, and can also reduce costs.

[0048] This stage is carried out in the shell-and-tube heat exchanger 1. In this embodiment, the synthetic recycle gas specifically enters the shell-and-tube heat exchanger 1 at a flow rate of 240 - 242 m 3 / h and exchanges heat with the demineralized water entering the shell-and-tube heat exchanger 1 from the generator at 50 - 55 °C to form a synthetic recycle gas at 60 °C - 65 °C and demineralized water at 75 °C - 110 °C. The synthetic recycle gas after heat exchange returns to the methanol system from the outlet 7.

[0049] This solution adopts the above intake flow rate of the synthetic recycle gas, which is convenient for providing sufficient heat to the heat exchange medium and ensuring that the heat contained in the heat exchange medium after heat exchange can fully meet the operating requirements of the lithium bromide refrigerant during the flow process. The applicant's experiment found that when the flow rate of the low-pressure synthetic recycle gas is 240 - 242 m 3 / h, about 32 m 3 of refrigerant products can be produced per hour, and the temperature difference before and after the refrigerant products is as high as 8 - 12 °C, effectively improving the energy utilization efficiency of the methanol synthesis process.

[0050] Step 2: Refrigeration heat exchange. The heat exchange medium after heat exchange transfers heat to the first absorbent solution in the generating device 2 to obtain demineralized water, the first refrigerant steam, and the second absorbent solution; the second absorbent solution enters the absorption device 5 along the forward conveying pipe 18.

[0051] The absorbent is specifically lithium bromide, the refrigerant is specifically water, the first absorbent solution is a low-concentration lithium bromide solution, the second absorbent solution is a high-concentration lithium bromide solution, and the first refrigerant steam is generated steam. In this stage, the demineralized water after heat exchange enters the generator and transfers heat to the low-concentration lithium bromide solution to re-obtain demineralized water at 50 - 55 °C and return to the shell-and-tube heat exchanger 1 to re-exchange heat to obtain high-temperature demineralized water; while the low-concentration lithium bromide solution absorbs the heat in the demineralized water and evaporates the first steam to obtain a high-concentration lithium bromide solution; the high-concentration lithium bromide solution enters the absorption device 5 along the forward conveying pipe 18.

[0052] Step 3: Refrigerant heat exchange. The refrigerant vapor is cooled by cooling water in the cooling device 3 to form refrigerant, and then the refrigerant exchanges heat with the refrigerant in the evaporation device 4 to obtain the second refrigerant vapor and the refrigerant product; the second refrigerant vapor is the second water vapor and enters the absorption device 5 along the evaporation tube 16.

[0053] In this stage, the first water vapor enters the cooler to exchange heat and condense with the cooling water at 20 - 35°C. The cooling water absorbs the heat in the first water vapor and forms the cooling water at 30 - 43°C and is discharged; the condensed water then enters the evaporator to absorb the heat of the refrigerant and evaporates into the second water vapor, while the refrigerant cools down to form the refrigerant product. Specifically, in this solution, the inlet water temperature of the refrigerant in the evaporator is 10 - 22°C, the inlet water flow rate is 30 - 35 m 3 / h, and the obtained refrigerant product is 5 - 11°C, fully meeting the different refrigerant product requirements of different producers.

[0054] In this solution, by adjusting the temperature of the refrigerant inlet water, it is convenient to produce low-pressure refrigerant products according to the temperature requirements of users for the refrigerant product. Specifically, when users need to produce low-pressure refrigerant products at 5 - 7°C, refrigerant at 10 - 18°C can be introduced; when they need to produce low-pressure refrigerant products at 10 - 11°C, refrigerant at 18 - 22°C can be introduced, realizing the flexible utilization of refrigerant product production.

[0055] Step 4: Circulating heat exchange. In step 2, the demineralized water returns to the shell-and-tube heat exchanger 1 along the water inlet 9 of the generator 2 and the shell-and-tube heat exchanger 1, repeating step 1 and step 2 to realize the recycling of demineralized water; in step 2, the high-concentration lithium bromide solution is mixed with the second water vapor in the absorption device 5 to form a low-concentration lithium bromide solution, and the low-concentration lithium bromide solution re-enters the generator along the reverse conveying pipe 17, repeating step 2 to step 4 to realize the recycling of the lithium bromide solution.

[0056] In different operating times of the methanol synthesis recycle gas waste heat utilization system of this solution, it operates with different synthesis recycle gas inlet flow rates, cooling water inlet temperatures, refrigerant inlet temperatures and flow rates. Among them, Examples 1 - 5 show the values within the scope of the claims of this solution, and Comparative Examples 1 - 2 show the values outside the scope of the claims of this solution, fully demonstrating the effect differences of the methanol synthesis recycle gas waste heat utilization methods under different parameter conditions of this solution. The results are shown in Table 1.

[0057] Table 1 Results under different operating times

[0058]

[0059]

[0060] Experimental data show that, in this solution, a waste heat utilization system for methanol synthesis recycle gas is formed by connecting the pipelines of a shell-and-tube heat exchanger and a lithium bromide refrigeration unit, and the flow rates and temperatures of the methanol synthesis recycle gas and the refrigerant are limited to make the most of the waste heat in the synthesis recycle gas. It not only effectively utilizes the waste heat in the low-pressure methanol synthesis recycle gas and converts this waste heat into a refrigerant product for output, fully improving the energy utilization efficiency and production benefits of methanol synthesis, but also can reduce the overall energy consumption and carbon emissions of the enterprise, achieving a double harvest of environmental protection and benefits.

[0061] Specifically, in Examples 1 to 5, within different operating times, by adjusting the flow rates and temperatures of the synthesis recycle gas and the refrigerant, the waste heat in the synthesis recycle gas can be effectively utilized. In this solution, the temperature of the refrigerant inlet water is also adjusted to facilitate the production of low-pressure refrigerant products according to the temperature requirements of users for the refrigerant products. Specifically, when users need to produce low-pressure refrigerant products at 5 - 7°C, the refrigerant with a temperature of 10 - 18°C can be introduced; while when they need to produce low-pressure refrigerant products at 10 - 11°C, the refrigerant with a temperature of 18 - 22°C can be introduced, realizing the flexible utilization of the production of refrigerant products. In Comparative Example 1, since the temperature of the synthesis recycle gas dropped to 50°C, the higher alcohols in the synthesis gas solidified into solids and adhered to the surface of the heat exchanger, affecting the heat exchange of the lithium bromide heat exchanger and further resulting in a decrease in the refrigeration capacity. In Comparative Example 2, the temperature of the synthesis recycle gas only dropped to 70°C, the available heat was reduced, and the refrigeration capacity decreased.

[0062] The above are only the embodiments of the present invention. Specific technical solutions and / or common knowledge such as characteristics that are well-known in the art are not described in detail here. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can still be made, and these should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation manners described in the specification can be used to explain the content of the claims.

Claims

1. A waste heat utilization system for methanol synthesis recycle gas, characterized in that: It includes a heat exchange unit and a refrigeration unit. The top of the heat exchange unit is provided with an air outlet and a water inlet, and the bottom is provided with an air inlet and a water outlet; the water inlet and water outlet of the heat exchange unit are both connected to the refrigeration unit through pipelines; the refrigeration unit is provided with a refrigerant inlet and a refrigerant outlet; The heat exchange unit is a shell-and-tube heat exchanger.

2. The waste heat utilization system for methanol synthesis recycle gas according to claim 1, characterized in that: The refrigeration unit includes a generating device, a cooling device, an evaporation device and an absorption device connected in sequence through pipelines; a forward conveying pipe and a reverse conveying pipe are connected between the absorption device and the generating device; the cooling device is provided with a cooling inlet and a cooling outlet, and the cooling device is provided with a refrigerant inlet and a refrigerant outlet; the water inlet and water outlet of the heat exchange unit are both connected to the generating device through pipelines.

3. A waste heat utilization method for methanol synthesis recycle gas, which is completed by using the waste heat utilization system for methanol synthesis recycle gas according to any one of claims 1-2, characterized in that: It includes the following steps: Step 1: Primary heat exchange, the synthesis recycle gas exchanges heat with the heat exchange medium in the heat exchange unit to obtain the heat exchange medium after heat exchange; Step 2: Refrigeration heat exchange, the heat exchange medium after heat exchange transfers heat to the first absorbent solution in the generating device to obtain desalted water, the first refrigerant steam and the second absorbent solution; The second absorbent solution enters the absorption device along the forward conveying pipe; Step 3: Refrigerant heat exchange, the generated refrigerant steam is cooled by cooling water in the cooling device to form a refrigerant, and the refrigerant then exchanges heat with the refrigerant in the evaporation device to obtain the second refrigerant steam and the refrigerant product; Step 4: Circulating heat exchange, the heat exchange medium in step 2 repeats steps 1 and 2 to realize the recycling of the heat exchange medium; the second absorbent solution in step 2 is mixed with the evaporated refrigerant steam obtained in step 3 in the absorption device to form the first absorbent solution, and the first absorbent solution returns to the generating device along the reverse conveying pipe and repeats steps 2 to 4 to realize the recycling of the absorbent solution.

4. The waste heat utilization method for methanol synthesis recycle gas according to claim 3, characterized in that: The heat exchange medium is any one of water, oil or desalted water.

5. The waste heat utilization method for methanol synthesis recycle gas according to claim 4, characterized in that: The heat exchange medium is desalted water, the absorbent is lithium bromide, and the refrigerant is water.

6. The waste heat utilization method for methanol synthesis recycle gas according to claim 5, characterized in that: The temperature of the desalted water entering the heat exchange unit is 50-55°C, and the temperature of the desalted water entering the generating device is 75°C-110°C.

7. The waste heat utilization method for methanol synthesis recycle gas according to claim 6, characterized in that: The inlet temperature of the cooling water in the cooling device is 20-35°C.

8. The waste heat utilization method for methanol synthesis recycle gas according to claim 7, characterized in that: The inlet temperature of the refrigerant in the evaporation device is 10-22°C.

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