Method for generating steam or hot water using waste heat from cooling water

Abstract

The present invention provides a method for producing steam or hot water, including the steps of: (S1) flowing process waste heat fluid supplied from a plurality of waste heat sources into heat exchangers, the number of which corresponds to the plurality of waste heat sources, and exchanging heat with cooling water; (S2) flowing the cooling water, which has been heated by heat exchange with the process waste heat fluid in each of the heat exchangers, into a refrigerant evaporator through an integrated pipe and vaporizing the refrigerant by heat exchange with the refrigerant; (S3) compressing the vaporized refrigerant stream in a refrigerant compressor; (S4) exchanging heat with water in a refrigerant condenser to produce a condensed refrigerant stream and steam or hot water; and (S5) passing the condensed refrigerant stream through a refrigerant expansion valve to reduce its pressure, and then circulating it in the refrigerant evaporator.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0050549 filed on April 18, 2023, and Korean Patent Application No. 10-2024-0021815 filed on February 15, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for generating steam or hot water using waste heat from cooling water, and more particularly to a method for generating steam or hot water by performing heat exchange between the cooling water and a plurality of waste heat sources generated in a petrochemical process, and then recovering the waste heat from the heated cooling water. [Background technology]

[0003] Petrochemical processes require a lot of energy to produce products, and the energy used can be disposed of or reused.

[0004] Steam used as an energy source in petrochemical processes is generally generated by burning hydrocarbon fuels in boilers (see Figure 1). However, this process is expensive and the fuel is released into the atmosphere in the form of carbon dioxide, contributing to global warming.

[0005] Therefore, in order to reduce carbon emissions and lower the manufacturing costs of petrochemical products, methods such as reducing the amount of steam used in the process and utilizing waste heat have been proposed.

[0006] Petrochemical products are typically produced through processes including reaction, separation, purification, etc., and the lower part of the column in which these processes take place is heated with steam, generating high-temperature process fluids at the top of the column.

[0007] Referring to Figure 2, high-temperature fluids generated in petrochemical processes can become waste heat (WH), and a large amount of heat is wasted as it is cooled by heat exchange with cooling water in heat exchangers (HE) such as condensers and coolers. The heated cooling water flows into a cooling tower (CT), where it is cooled while dissipating heat, and then is supplied to the heat exchanger again. The heat dissipated during this cooling process can be called waste heat within the process.

[0008] The cooling tower operates by contacting cooling water with atmospheric air to forcibly dissipate heat, and therefore the heat wasted in the cooling tower cannot be recovered, resulting in a significant heat loss.

[0009] Therefore, a method is needed to effectively recover and reuse waste heat from cooling water that has been heated by heat exchange with high-temperature fluids (waste heat sources) generated in various processes such as reactions, separation, and refining during the production of petrochemical products. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention is intended to solve the problems mentioned in the background of the invention, and provides a method for recovering waste heat by exchanging heat between cooling water and a plurality of waste heat sources generated in a petrochemical process, and then flowing the heated cooling water into a heat pump device, and using the recovered waste heat to generate large amounts of steam or hot water required in the process. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the present invention provides a method for generating steam or hot water, including the steps of: (S1) flowing process waste heat fluid supplied from a plurality of waste heat sources into heat exchangers, the number of which corresponds to the plurality of waste heat sources, and exchanging heat with cooling water; (S2) flowing the cooling water, which has been heated by heat exchange with the process waste heat fluid in each of the heat exchangers, into a refrigerant evaporator through an integrated pipe and vaporizing the refrigerant by heat exchange with the refrigerant; (S3) compressing the vaporized refrigerant stream with a refrigerant compressor; (S4) exchanging heat with water in a refrigerant condenser to generate a condensed refrigerant stream and steam or hot water; and (S5) passing the condensed refrigerant stream through a refrigerant expansion valve to reduce its pressure, and then circulating it to the refrigerant evaporator.

[0012] In the present invention, the integrated piping has a straight length of 5 to 5,000 m and can be controlled to maintain a flow velocity of 0.5 to 5 m / s.

[0013] The temperature of the compressed refrigerant stream may be 90 to 200°C, and the temperature of the refrigerant stream condensed by heat exchange with water in the refrigerant condenser may be 85 to 170°C.

[0014] In addition, the steam generated in the refrigerant condenser can be transferred to a steam compressor and further compressed to be converted into high-pressure steam.

[0015] Furthermore, the present invention provides a steam or hot water generation system for carrying out the above method, comprising a plurality of waste heat sources, a number of heat exchangers corresponding to the plurality of waste heat sources, and a heat pump device connected to the heat exchangers via an integrated pipe and branch pipes, wherein the heat pump device comprises a refrigerant evaporator, a refrigerant compressor, a refrigerant condenser, and a refrigerant expansion valve connected via pipes, and heated cooling water flowing out from each of the heat exchangers is integrated through the integrated pipe and flows into the refrigerant evaporator of the heat pump device, where the refrigerant is vaporized by heat exchange, and then circulated to each of the heat exchangers again via the branch pipes.

[0016] The system may include an additional steam compressor coupled to a refrigerant condenser of the heat pump unit. [Effects of the Invention]

[0017] According to the present invention, after heat exchange between each of a plurality of waste heat sources and cooling water, the heated cooling water is flowed into a heat pump device through an integrated pipe, and the waste heat of the heated cooling water is recovered by heat exchange with the refrigerant flow circulating in the heat pump device. The refrigerant flow is vaporized using the waste heat of the cooling water, and then compressed using electricity and heat exchanged with water to generate large amounts of steam or hot water required in the process.

[0018] In addition, when generating steam from the waste heat of cooling water recovered by the heat pump device, the temperatures of the compressed refrigerant and condensed refrigerant are controlled to maximize the temperature lift, and the generated steam is further compressed to convert it into final high-temperature and high-pressure steam, which can be used as an energy source in various process steps, thereby lowering the production costs of petrochemical products and reducing carbon emissions.

[0019] Furthermore, since the present invention is applied to multiple waste heat sources generated in various petrochemical processes, it is possible to recover waste heat from multiple cooling water heat exchangers (e.g., 10 to 100) within a petrochemical plant, and such waste heat recovery can be performed using a single heat pump device via an integrated piping. In particular, by controlling the flow rate of the integrated piping within a predetermined range so as to maintain a uniform mixture of heated cooling water, it is possible to simplify the steam generation equipment and improve operational efficiency, thereby reducing costs, minimizing maintenance, and stabilizing operation. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing a schematic diagram of a steam production process using a boiler. [Figure 2] This is a diagram showing a process in which waste heat sources generated in various petrochemical processes are heat exchanged with cooling water, and then the heated cooling water is cooled in a cooling tower. [Figure 3] FIG. 1 is a diagram illustrating a process in which multiple waste heat sources are each heat-exchanged with cooling water according to the present invention, and then the heated cooling water is cooled by a heat pump device to recover the waste heat and generate the steam or hot water required in the process. [Figure 4] 1 is a diagram illustrating a process of generating high-pressure steam by further connecting a steam compressor to a refrigerant condenser of a heat pump device according to the present invention. [Figure 5] FIG. 10 is a diagram illustrating a process in a comparative example in which a plurality of waste heat sources are heat-exchanged with cooling water, and then the heated cooling water is cooled in a cooling tower. DETAILED DESCRIPTION OF THE INVENTION

[0021] The terms and words used in the description of the present invention and the claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0022] As used herein, the meaning of "comprise" or "contain" is to embody a particular property, region, integer, step, operation, element, or component, and does not exclude the addition of other particular properties, regions, integers, steps, operations, elements, or components.

[0023] The term "stream" as used in the present invention can refer to the flow of fluid within a process, or the fluid itself flowing in a pipe. Specifically, the stream can simultaneously refer to the fluid itself flowing in the pipe connecting each device and the flow of the fluid. Furthermore, the fluid can contain one or more components of gas, liquid, and solid.

[0024] One embodiment of the present invention relates to a method for generating steam or hot water by recovering the waste heat of the heated cooling water after performing heat exchange with multiple waste heat sources, specifically including a step (S1) of heat exchange between multiple process waste heat fluids and cooling water, a step (S2) of combining the cooled water heated by the heat exchange and vaporizing the refrigerant by heat exchange with a refrigerant, a step (S3) of compressing the vaporized refrigerant stream, a step (S4) of heat exchange between the compressed refrigerant stream and water to generate a condensed refrigerant stream and steam / hot water, and a step (S5) of depressurizing the condensed refrigerant stream.

[0025] Hereinafter, the method for generating steam or hot water will be described in detail step by step with reference to the accompanying drawings.

[0026] Referring to FIG. 3, the method for generating steam or hot water by recovering waste heat from cooling water according to the present invention can be performed using a steam or hot water generation system including a plurality of waste heat sources 100, a number of heat exchangers 200 corresponding to the plurality of waste heat sources, and a heat pump device 300 connected to the heat exchangers via an integrated pipe and branch pipes.

[0027] The plurality of waste heat sources 100 may be high-temperature process waste heat fluids generated in various processes such as reaction, separation, and refining during the production of petrochemical products. The temperature of such high-temperature process waste heat fluids may vary depending on the conditions of each process and may be in the range of approximately 20 to 250°C, specifically 30 to 150°C.

[0028] On the other hand, treating the process waste heat fluid without separate heat recovery is not desirable from an energy perspective, so recovering the heat contained in the waste heat source 100, i.e., the high-temperature process waste heat fluid, and utilizing the recovered heat in other processes that require heat is essential to reducing the energy consumption of the entire process.

[0029] To this end, the process waste heat fluids WH1, WH2, WH3, etc. can be supplied to heat exchangers HE1, HE2, HE3, etc. that use cooling water. The process waste heat fluids exchange heat with the cooling water in the heat exchangers HE1, HE2, HE3, etc., so that the heat of the process waste heat fluids can be transferred to the cooling water. Furthermore, the cooling water, whose temperature has been increased by the transferred heat, can be supplied to a refrigerant evaporator, which will be described later, and used as a heat source for vaporizing the refrigerant.

[0030] Specifically, the process waste heat fluids WH1, WH2, WH3, etc. may have different fluid properties, such as their components and temperatures, and it may not be appropriate to supply such process waste heat fluids directly to the refrigerant evaporator. For the sake of operational stability and reliability of the refrigerant evaporator, it is preferable that the process waste heat fluid is first heat exchanged with cooling water in a heat exchanger (sometimes referred to as a cooling water heat exchanger), and then the high-temperature cooling water flowing out of the heat exchanger is supplied to the refrigerant evaporator.

[0031] In one embodiment of the present invention, the heat exchanger 200 is a component connected to a plurality of waste heat sources 100, through which cooling water circulates to cool or condense process waste heat fluids WH1, WH2, WH3, ..., and may be configured in a number (HE1, HE2, HE3, ...) corresponding to the number of the waste heat sources 100.

[0032] Generally, in a petrochemical plant, a large number of cooling water heat exchangers, for example, about 10 to 100 cooling water heat exchangers, are operated to cool or condense high-temperature process fluids generated in various processes. In order to simultaneously utilize such a large number of cooling water heat exchangers, the present invention connects a cooling water heat exchanger to each of a plurality of waste heat sources to recover heat by cooling or condensing the high-temperature process fluid, and uses the recovered heat to increase the temperature of the cooling water circulating through each heat exchanger, and supplies the heated cooling water to a single refrigerant evaporator, thereby simultaneously treating a large amount of process waste heat fluid.

[0033] The heat exchanger may include a cooler or condenser commonly used in petrochemical processes. The heat exchanger applicable to the present invention may be a shell and tube type, and to improve heat exchange efficiency, a plate type or a falling film evaporator may also be used, but is not limited thereto.

[0034] In one embodiment of the present invention, cooling water at 10 to 50°C, specifically 20 to 40°C, can be supplied to and circulated in each of the heat exchangers HE1, HE2, HE3, etc., at a pressure of 1 to 20 bar, specifically 2 to 10 bar, and a flow rate of 10 to 1,000,0000 ton / hr, specifically 20 to 100,000 ton / hr.

[0035] Specifically, when process waste heat fluids WH1, WH2, WH3, ... at high temperatures, for example, 20 to 250°C, supplied from a plurality of waste heat sources 100 flow into the respective heat exchangers HE1, HE2, HE3, ... through which the cooling water circulates, the cooling water can absorb heat from the process waste heat fluid through mutual heat exchange and increase in temperature. Here, it is advantageous to adjust the temperature increase range of the cooling water to 13 to 60°C, for example, 15 to 50°C, in order to maintain the temperature difference with the process waste heat within an appropriate range.

[0036] Meanwhile, the flow rate of the process waste heat fluid flowing into each of the heat exchangers HE1, HE2, HE3, etc. is not particularly limited, and may be, for example, 0.1 to 100,000 ton / hr, specifically 0.5 to 50,000 ton / hr or 1 to 40,000 ton / hr. The process waste heat fluid that has exchanged heat with cooling water in each of the heat exchangers HE1, HE2, HE3, etc. may exit each of the heat exchangers at a temperature lower than its initial temperature, for example, in the range of 15 to 200°C.

[0037] The cooling water heated in each of the heat exchangers HE1, HE2, HE3, etc. is then cooled after supplying heat in a refrigerant evaporator, and must be circulated to the heat exchanger (cooling water heat exchanger) for cooling or condensing the high-temperature process waste heat fluid within the process (i.e., to recover the heat from the process waste heat fluid).

[0038] In the present invention, the cooling water heated in each of the heat exchangers HE1, HE2, HE3, etc. is merged into a single integrated pipe 10, and the integrated cooling water stream in the integrated pipe 10 can then be supplied to the heat pump device 300, specifically, to the refrigerant evaporator EV.

[0039] For example, if each of the coolant streams is directly supplied to the refrigerant evaporator EV provided in the heat pump apparatus 300, the coolant streams heated in each of the heat exchangers HE1, HE2, HE3, etc. will not be uniform in temperature and flow rate, making it difficult to stably operate the refrigerant evaporator EV, and the cost of installing the refrigerant evaporator EV to resolve this issue may increase excessively. Furthermore, unstable operation of the refrigerant evaporator EV may cause the refrigerant to be overcooled or undercooled, which may in turn impair the operational stability of other equipment provided in the heat pump apparatus 300, such as the refrigerant compressor CP.

[0040] According to an embodiment of the present invention, uniformity in the flow rate and temperature of each heated coolant stream can be achieved by combining and supplying the respective heated coolant streams into a single integrated pipe 10. Specifically, the integrated pipe 10 may be a header-type pipe with caps on both ends to collect the heated coolant streams flowing out of the heat exchangers HE1, HE2, HE3, etc., which are arranged in parallel. In order for the coolant streams to be supplied to the refrigerant evaporator EV of the heat pump unit 300 while maintaining a uniform mixed state, the length of the integrated pipe and the flow velocity of the working fluid need to be designed within appropriate ranges.

[0041] Specifically, the linear length of the integrated pipe 10 can be 5 to 5,000 m, more specifically, 10 to 1,000 m. If the length of the integrated pipe is less than 5 m, the thermal mixing of the heated coolant becomes uneven, which changes the refrigerant evaporation rate due to heat exchange in the refrigerant evaporator EV of the heat pump unit 300, causing surges or cavitation in the downstream refrigerant compressor CP, which may render operation impossible. If the length of the integrated pipe is more than 5,000 m, heat loss may occur, resulting in a decrease in the amount of waste heat, or an increase in the pipe differential pressure, resulting in an increase in power consumption.

[0042] The flow velocity of the integrated pipe 10 may be in the range of 0.5 to 5 m / s, more specifically, 1 to 3 m / s. If the flow velocity of the integrated pipe is less than 0.5 m / s, the thermal mixing efficiency of the heated cooling water may decrease, and if it exceeds 5 m / s, erosion may occur inside the pipe.

[0043] By applying the integrated piping 10 as described above, it is possible to simplify the steam generating equipment, reduce costs by improving the operational efficiency, minimize maintenance, and stabilize the operation.

[0044] On the other hand, if a heat pump device is connected to each cooling water that has been heat exchanged with a single waste heat source to recover the waste heat from the cooling water, multiple heat pump devices must be used for heat exchangers corresponding to multiple waste heat sources, making it difficult to achieve the economical effect of replacing a cooling tower, which is a means of cooling cooling water that has been heated in the conventional method.

[0045] As in the present invention, when multiple cooling water streams that have been heated by heat exchange with multiple waste heat sources are integrated in an integrated pipe and then supplied to a heat pump device, advantages such as simplified control and operation, reduced number of abnormal operations, and increased replacement cycles can be obtained compared to operating multiple heat pump devices.

[0046] Furthermore, when a heat pump device is connected to each cooling water that has undergone heat exchange with a single waste heat source, there may be a waste heat source that cannot be recovered due to the limitations of small-capacity equipment. However, in the present invention, even a very small amount of waste heat can be recovered by supplying multiple heated cooling water streams to the heat pump device through an integrated piping.

[0047] Furthermore, when multiple heat pump devices are operated individually, it can be inconvenient to have to adjust the material balance of the entire facility. However, the present invention applies a single heat pump device through integrated piping, which allows for more efficient material balance adjustment, stabilizes operation, and reduces the number of maintenance operations.

[0048] The heat pump device 300 applied in the present invention performs a cycle of transferring a low-temperature heat source at a high temperature or transferring a high-temperature heat source at a low temperature using the heat of evaporation or condensation of the refrigerant, and the refrigerant evaporator EV, refrigerant compressor CP, refrigerant condenser CD, and refrigerant expansion valve (EP valve) are connected via piping, allowing the refrigerant to circulate.

[0049] The refrigerant evaporator EV is a component that vaporizes and evaporates the refrigerant by performing heat exchange between a high-temperature fluid and the refrigerant, and may be a general shell and tube type, or may be a plate type or a falling film evaporator to improve heat exchange efficiency, but is not limited thereto.

[0050] The refrigerant evaporator EV can receive a low-temperature, low-pressure liquid refrigerant, for example, a refrigerant having a pressure of 0.5 to 40 bar or 1 to 20 bar and a temperature of 10 to 60° C. or 15 to 50° C. When heated refrigerant streams that flow out of the heat exchangers HE1, HE2, HE3, ... and are integrated in the integrated pipe 10 flow into the refrigerant evaporator EV through which such low-temperature, low-pressure refrigerant flows, the refrigerant is vaporized by heat exchange.

[0051] That is, when a coolant mixed stream heated to a temperature in the range of 13 to 60°C flows into the refrigerant evaporator EV, the refrigerant absorbs heat through mutual heat exchange and is converted into a relatively high-temperature vapor stream. Meanwhile, the heated coolant is cooled to a temperature in the range of 10 to 50°C by heat supply in the refrigerant evaporator, and then circulates to each of the heat exchangers HE1, HE2, HE3, ... through a plurality of branch pipes connected to pipe 20.

[0052] If necessary, a pump for effective circulation of the cooling water can be installed at the rear end of the refrigerant evaporator EV, into which the heated cooling water flows.

[0053] In one embodiment of the present invention, the total flow rate of the refrigerant flowing into the refrigerant evaporator EV through the integrated pipe 10 may be 10 to 1,000 ton / hr, for example, 20 to 500 ton / hr or 30 to 400 ton / hr, and the flow rate of the heated cooling water mixed stream flowing into the refrigerant evaporator EV may be 0.1 to 100,000 ton / hr, for example, 0.5 to 50,000 ton / hr or 1 to 40,000 ton / hr, but is not limited thereto.

[0054] The refrigerant stream vaporized in the refrigerant evaporator EV then flows into the refrigerant compressor CP, where electrical energy is supplied to compress the refrigerant stream and increase its pressure. Here, the temperature of the vapor refrigerant stream can also increase in proportion to the amount of electrical energy supplied.

[0055] The refrigerant compressor CP may be any device known in the art that can compress a gas phase flow, such as a turbo compressor capable of high-capacity compression. The refrigerant compressor CP may be a single device or multiple devices connected in series, depending on the volume of the incoming refrigerant stream.

[0056] The refrigerant compressor CP can increase the pressure of the gaseous refrigerant stream flowing in through the refrigerant evaporator EV by 1.2 to 5 times or 1.4 to 4.5 times. For example, the pressure of the refrigerant stream passing through the compressor CP can be 0.5 to 50 bar or 1 to 40 bar. When the gaseous refrigerant stream is compressed within this range, the compressor type can be easily selected, designed, and manufactured.

[0057] In addition, the temperature of the refrigerant stream compressed through the compressor CP can be adjusted within a range of 90 to 200° C. or 105 to 180° C. If the temperature of the compressed refrigerant stream is less than 90° C., a problem of a rapid decrease in the heat exchange efficiency with water in the downstream refrigerant condenser may occur, and if the temperature of the compressed refrigerant stream is more than 200° C., carbonization of the refrigerant or compressor lubricant oil may occur, or an excessive increase in refrigerant vapor pressure may make it impossible to manufacture the equipment or cause it to operate imperfectly.

[0058] Thereafter, the high-temperature / high-pressure refrigerant stream flowing out of the compressor flows into a refrigerant condenser CD, where heat exchange occurs between the high-temperature / high-pressure refrigerant stream that has been compressed in the refrigerant condenser CD and water replenished from the outside, thereby condensing the refrigerant stream and generating steam or hot water.

[0059] The refrigerant condenser CD applicable to the present invention may be a general shell and tube type, or may be a plate type or a falling film type to improve heat exchange efficiency, but is not limited thereto. Also, the refrigerant condenser CD may be one or multiple refrigerant condensers connected in series depending on the volume of the incoming refrigerant stream.

[0060] In the refrigerant condenser CD, the refrigerant releases heat through heat exchange with water, condensing from a high-temperature / high-pressure vapor stream into a low-temperature liquid stream, and water supplied from the outside absorbs the heat generated as the refrigerant condenses and can be converted into high-temperature hot water or steam.

[0061] More specifically, in the present invention, a gaseous refrigerant stream obtained by recovering waste heat from cooling water heated by a heat pump device is compressed by supplying electricity, and the compressed refrigerant stream is then circulated through a refrigerant condenser CD to exchange heat with water. By changing the discharge pressure of the water passing through the refrigerant condenser CD, hot water or steam can be selectively generated.

[0062] For example, after water receives heat from the refrigerant condenser CD, if the outlet pressure of the pipe from which the water is discharged is adjusted to a value equal to or greater than the vapor pressure using a valve, hot water in a liquid phase state of approximately 85 to 180°C, specifically 100 to 150°C, can be produced by heat exchange between the compressed refrigerant stream and the water. Here, when the outlet pressure of the water passing through the refrigerant condenser is adjusted based on the vapor pressure, the vapor pressure can be determined according to the temperature of the discharged water. Therefore, if the temperature of the water discharged from the condenser is 90°C, the outlet pressure of the pipe can be adjusted to 0.7 bar or more; if the temperature of the discharged water is 100°C, the outlet pressure of the pipe can be adjusted to 1 bar or more; and if the temperature of the discharged water is 150°C, the outlet pressure of the pipe can be adjusted to 4.8 bar or more.

[0063] The hot water discharged from the refrigerant condenser CD can be used as high-temperature process water in a petrochemical process (for example, boiler feed water or heat source water for emulsion polymerization). The production of such hot water uses waste heat and electricity, and is much more efficient in terms of energy consumption than existing methods of producing hot water by mixing steam with industrial water.

[0064] On the other hand, when the outlet pressure of the pipe through which the water that has received heat through the refrigerant condenser CD is discharged is adjusted to be less than the vapor pressure, the hydrogen bonds of the water molecules are broken by heat exchange between the compressed refrigerant stream and the water, and vapor-phase steam can be generated. As described above, the vapor pressure, which is the basis of the outlet pressure of the pipe, can be determined according to the temperature of the discharged water.

[0065] During the process, hot water and steam can flow out of the refrigerant condenser CD in a mixed state.

[0066] In one embodiment of the present invention, the refrigerant stream condensed by heat exchange with water in the refrigerant condenser CD preferably maintains a saturation temperature of 85 to 170°C at a high pressure of 3 to 50 bar or 6 to 40 bar. If the temperature of the condensed refrigerant stream is below 85°C, the water pressure in the refrigerant condenser CD may become lower than atmospheric pressure, which may contaminate the steam or hot water generated by heat exchange and make it unusable in the process. If the temperature of the condensed refrigerant stream exceeds 170°C, carbonization of the refrigerant or compressor lubricant oil may occur, or an excessive increase in refrigerant vapor pressure may cause the equipment to be unable to be constructed or to operate imperfectly.

[0067] To ensure that the temperature of the condensed refrigerant stream is 85°C or higher, it is advantageous to adjust the critical temperature of the refrigerant to 100°C or higher. The critical temperature of a refrigerant is a thermodynamic property unique to each substance and refers to the maximum temperature at which the gas phase and liquid phase can be physically separated. When the difference between the critical temperature and the temperature of the condensed refrigerant stream is 15°C or more, the heat exchange potential of the refrigerant can be maintained. If the heat exchange potential in the refrigerant condenser decreases and the temperature of the condensed refrigerant stream falls below 85°C, the temperature lift when generating steam or hot water is insufficient, which can lead to malfunctions such as compressor surge.

[0068] As long as the refrigerant meets the above-mentioned critical temperature conditions, the refrigerant can be selected from various types known in the art without particular limitation and used. For example, one or more refrigerants selected from HFC (hydrofluorocarbon)-based refrigerants R245fa, R134a, R1234ze, and R1234yf, and HFO (hydrofluoroolefin)-based refrigerants R1234ze(E), R1234ze(Z), and R1233zd(E) can be used.

[0069] The pressure of the condensed refrigerant stream can be maintained at a high pressure of 3 to 50 bar or 6 to 40 bar, but is not limited thereto.

[0070] Meanwhile, the water supplied to the refrigerant condenser CD must be in a pure state with ions and oxygen removed, and may be supplied at a temperature of 10 to 100°C or 20 to 95°C and a pressure of 1 to 20 bar or 1.5 to 10 bar. The flow rate of the water supplied to the refrigerant condenser CD may be, but is not limited to, 1 to 100 Ton / hr, for example, 2 to 80 Ton / hr or 3 to 50 Ton / hr.

[0071] The steam or the mixture of steam and hot water generated by heat exchange with the high-temperature / high-pressure gas phase refrigerant stream in the refrigerant condenser CD can have a temperature of 95 to 200°C or 100 to 180°C and a pressure of 0.5 to 16 bar or 1 to 10 bar.

[0072] Then, the liquid refrigerant stream flowing out of the refrigerant condenser CD passes through a refrigerant expansion valve (EP valve) to reduce its pressure, and the refrigerant stream that has passed through the refrigerant expansion valve can be circulated to a refrigerant evaporator EV.

[0073] The refrigerant expansion valve (EP valve) is a device that controls the flow rate of a refrigerant stream by lowering its pressure and temperature so that the refrigerant stream liquefied in the condenser can easily evaporate in the evaporator. That is, the liquid refrigerant stream that passes through the expansion valve has a lower pressure and boiling point, so it can evaporate at a relatively low temperature when it flows back into the refrigerant evaporator.

[0074] For example, the refrigerant stream passing through the expansion valve may be in the form of a low temperature / low pressure liquid phase exhibiting a pressure of 0.5 to 30 bar or 1 to 20 bar and a temperature of 10 to 60°C or 20 to 50°C, respectively.

[0075] The expansion valve (EP valve) applicable to the present invention can have various structures such as an electronic expansion valve, a thermostatic expansion valve, an automatic expansion valve, etc. Also, one expansion valve or multiple expansion valves connected in series can be used depending on the volume of the incoming refrigerant stream.

[0076] On the other hand, since the steam flowing out from the refrigerant condenser CD exhibits a low pressure of 0.5 to 16 bar, it may be difficult to immediately use it in the process, so it is preferable to convert it into high-pressure steam by additional compression.

[0077] As shown in FIG. 4, a steam compressor S-CP is connected to a refrigerant condenser CD of the heat pump device 300, and the steam flowing out from the refrigerant condenser CD is introduced into the steam compressor S-CP, thereby increasing the final steam pressure to a range of 2 to 60 bar or 3 to 30 bar.

[0078] Similar to the above-mentioned refrigerant compressor CP, the steam compressor S-CP may be a turbo compressor capable of handling a large capacity, and electrical energy is supplied to compress water molecules, and the temperature of the steam can be increased in proportion to the amount of electrical energy supplied.

[0079] Here, when superheated steam is introduced into a heat exchanger in the process, the heat exchange efficiency decreases, so make-up water can be supplied to form saturated steam. The make-up water supplied to the steam compressor S-CP must be in a pure state with ions and oxygen removed, and can be added to the saturated steam while reducing the degree of superheat of the steam and then introduced into the process. The flow rate of the make-up water can be, but is not limited to, 0.1 to 30 ton / hr or 1 to 20 ton / hr.

[0080] The high-pressure steam flowing out to the steam compressor S-CP can finally exhibit a temperature of 140 to 280°C or 150 to 240°C.

[0081] In this way, in the present invention, after heat exchange between each of a plurality of waste heat sources and cooling water, the heated cooling water flows into a heat pump device through an integrated pipe, and the waste heat of the heated cooling water is recovered by heat exchange with the refrigerant flow circulating in the heat pump device. The refrigerant flow is vaporized using the waste heat of the cooling water, and then compressed using electricity and heat exchanged with water to generate hot water or steam. The steam is further compressed to generate a large amount of saturated steam that can be finally introduced into a process. For example, the amount of final steam generated by the present invention can be 1 to 120 ton / hr or 6 to 100 ton / hr.

[0082] The heat of steam generation according to the present invention can be defined by the following Equation 1, and the coefficient of performance (COP) of a system applied to the method for generating steam or hot water according to the present invention can be expressed by the following Equation 2.

[0083] [Formula 1] Heat of steam generation = Waste heat + Power supply (power used to compress the refrigerant and steam)

[0084] [Formula 2] COP = Steam generation heat / power supply

[0085] The coefficient of performance (COP) according to Equation 2 is defined as the heat of steam generation (amount of heat absorbed by water) relative to the electrical energy input to the refrigerant compressor and the steam compressor. For example, a COP value of 1.5 means that 1.5 times the amount of heat of the input electrical energy is obtained.

[0086] The steam generated by the method according to the present invention has a COP value calculated by the above-mentioned formula 2 of 1.3 or more, specifically 1.5 or more, and can ensure economic efficiency with respect to the input electrical energy.

[0087] The steam generated by waste heat recovery in accordance with the present invention, which couples multiple waste heat sources into a single heat pump system, can be stored and then distributed to supply local uses throughout the process.

[0088] The present invention will be described in more detail with reference to the following examples. However, the following examples are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present invention, and the scope of the present invention is not limited to these examples.

[0089] Example 1 As illustrated in Figure 3, a system of three waste heat sources 100 and heat exchangers 200 connected to a single heat pump unit 300 via integrated piping 10 was used to recover waste heat and generate steam / hot water.

[0090] (Step 1) First, gaseous (75°C and 5 bar) process waste heat fluids WH1, WH2, and WH3 were supplied to each of the three waste heat sources 100 at a flow rate of 52 tons / hr, and the process waste heat fluids were then flowed into heat exchangers HE1, HE2, and HE3, respectively, in which cooling water at 30°C circulated at a pressure of 5 bar, to perform heat exchange. After the heat exchange, the process waste heat fluids WH1, WH2, and WH3 dissipated heat and flowed out of the heat exchangers HE1, HE2, and HE3 in a liquid state at 65°C and 4 bar, and cooling water (40°C and 5 bar) that had been heated by heat absorption flowed out.

[0091] (Step 2) The cooling water (40°C, 5 bar) streams heated in the three heat exchangers HE1, HE2, and HE3 were combined in a combined pipe 10 (straight length 50 m, flow rate 1 m / s) and then supplied to the refrigerant evaporator EV of the heat pump device 300.

[0092] The heat pump device 300 includes a refrigerant evaporator EV, a refrigerant compressor CP, a refrigerant condenser CD, and a refrigerant expansion valve (EP valve). A liquid refrigerant (trans-1-chloro-3,3,3-trifluoropropene, R1233zd(E)) (25°C, 1.3 bar) is circulated through the refrigerant evaporator EV at a flow rate of 310 ton / hr, and heat is exchanged with a mixed stream (40°C) of heated cooling water supplied via the integrated pipe 10.

[0093] After the heat exchange, the cooling water mixed stream is cooled to 30°C in the refrigerant evaporator EV, and then circulated to the respective heat exchangers HE1, HE2, and HE3 through multiple branch pipes connected to pipe 20, where the refrigerant is vaporized by absorbing heat and flows out in a gaseous state at 25°C and 1.3 bar.

[0094] (Step 3) The gas phase refrigerant stream was allowed to flow into a refrigerant compressor CP, which then compressed the refrigerant stream under an electric power of 9.9 Gcal / h to obtain a refrigerant stream compressed to a gas state at 128°C and 16 bar.

[0095] (Step 4) The compressed refrigerant stream (128°C and 16 bar) flowed into a refrigerant condenser CD, and water (20°C and 5 bar) was supplied to the refrigerant condenser CD at a flow rate of 38 ton / hr to perform heat exchange. Here, the outlet pressure of the pipe through which the water passed after passing through the refrigerant condenser CD, i.e., the discharge pressure of the water, was adjusted to 2 bar using a pressure control valve attached to the pipe so that the pressure was maintained below the vapor pressure (2.3 bar) at the temperature of the heat-exchanged water (124°C). As a result, the heat-exchanged water was produced at 38 ton / hr of steam at 124°C and 2 bar, and the refrigerant stream was condensed and discharged in a liquid state at 120°C and 16 bar.

[0096] (Step 5) The condensed refrigerant stream (120°C and 16 bar) was passed through an expansion valve (EP valve) to obtain a liquid refrigerant stream at 25°C and 1.3 bar, which was then circulated through the refrigerant evaporator EV.

[0097] Example 2 The same process as in Example 1 was carried out, but in step 4, water (20°C and 5 bar) was supplied to the refrigerant condenser CD at a flow rate of 240 ton / hr, and the outlet pressure of the supply water piping was adjusted to 2.5 bar so that it was maintained at or above the vapor pressure (2.3 bar) at the temperature of the heat-exchanged water (124°C), and 240 ton / hr of hot water at 124°C and 2.5 bar was generated from the heat exchange between the compressed refrigerant and water (20°C and 1 bar).

[0098] Example 3 The same process as in Example 1 was carried out, but the steam generated in the refrigerant condenser CD was further transferred to the steam compressor S-CP for compression.

[0099] The compression was carried out under a power of 4.0 Gcal / h by supplying water (20°C and 5 bar) at a flow rate of 38 ton / hr, resulting in the final production of steam at 200°C and 13 bar at a rate of 45 ton / hr. The amount of steam finally produced was greater than the amount of water initially supplied because additional water was supplied to cool the superheated steam in the steam compressor.

[0100] The heat of steam generation for the final steam generated was calculated according to the following equation 1, and the coefficient of performance (COP) was calculated according to the following equation 2.

[0101] [Formula 1] Heat of steam (or hot water) generation = waste heat + power supply (power used for refrigerant compression and steam compression)

[0102] [Formula 2] COP = Steam (or hot water) generation heat / power supply

[0103] Example 4 The same process as in Example 1 was carried out, except that a gas phase refrigerant stream was compressed in a refrigerant compressor CP under an electric power of 6.9 Gcal / h to obtain a refrigerant stream compressed to a gas state of 98°C and 7.8 bar. The compressed refrigerant stream was then heat exchanged with water (20°C and 1 bar) at 27 ton / hr in a refrigerant condenser CD to generate steam at 78°C and 0.4 bar, while a condensed refrigerant stream at 87°C and 7.8 bar was discharged and transferred to an expansion valve (EP valve).

[0104] The steam produced in the refrigerant condenser CD was transferred to the steam compressor S-CP, where water (20°C and 1 bar) was supplied at a flow rate of 30 ton / hr under an electric power of 3.5 Gcal / h and compressed, thereby finally producing steam at 149°C and 3.9 bar at a rate of 35 ton / hr.

[0105] Example 5 The same process as in Example 1 was carried out, except that the flow velocity in the integrated piping was changed to 0.3 m / s, the steam generated in the refrigerant condenser CD was transferred to the steam compressor S-CP, and water (20°C and 5 bar) was supplied at a flow rate of 38 ton / hr under an electric power of 4.0 Gcal / h and compressed therein.

[0106] Example 6 The same process as in Example 1 was carried out, except that the flow velocity of the integrated piping was changed to 6 m / s, the steam generated in the refrigerant condenser CD was transferred to the steam compressor S-CP, and water (20°C and 5 bar) was supplied at a flow rate of 38 ton / hr under an electric power of 4.0 Gcal / h and compressed therein.

[0107] Comparative Example 1 According to the process illustrated in FIG. 5, the process waste heat fluids WH1, WH2, and WH3 from the three waste heat sources 100 were supplied to heat exchangers HE1, HE2, and HE3, respectively, and heat exchanged with cooling water under the same conditions as in Example 1. After that, the mixed streams of heated cooling water (40° C., 5 bar) flowing out of the heat exchangers were supplied to a cooling tower (CT) for cooling.

[0108] Specifically, the cooling tower was an open, forced-draft, counterflow type commonly used in the art, and the heated cooling water mixture was supplied to the filler through a spray nozzle installed at the top. Air flowing in from the cooling tower's upper fan came into contact with the cooling water in a counterflow manner at the filler, picking up moisture equivalent to the saturated vapor amount and dissipating it into the atmosphere. During this process, the cooling water's temperature decreased by the amount of latent heat of vaporization, collected in the lower water tank, and then circulated to each of the heat exchangers HE1, HE2, and HE3.

[0109] That is, the mixed stream of cooling water heated in the cooling tower was forced to lose heat upon contact with air, making it impossible to recover.

[0110] The results of waste heat recovery from the cooling water heated in the above examples and comparative examples are shown in Table 1 below.

[0111] [Table 1]

[0112] As shown in Table 1, in Comparative Example 1, the cooling water heated by heat exchange with multiple waste heat sources was forced to dissipate heat through contact with air in the cooling tower CT, making it impossible to recover the heat. In contrast, in Examples 1 to 6, after heat exchange with multiple waste heat sources, the heated cooling water was introduced into a heat pump device through an integrated pipe, and the waste heat of the heated cooling water was recovered by heat exchange with the flow of refrigerant circulating in the heat pump device, and the recovered waste heat was used to generate steam or hot water.

[0113] In particular, in Example 3, the flow velocity of the integrated piping was in the range of 0.5 to 5 m / s, the heated cooling water stream was maintained uniformly mixed, the temperature of the refrigerant condensed in the refrigerant compressor was controlled to 85°C or higher, the temperature of the steam generated in the refrigerant condenser was maintained at 85°C or higher, and additional steam compression was performed, resulting in the highest temperature lift, i.e., the difference between the initial waste heat temperature and the final steam temperature.

[0114] On the other hand, in Example 4, the flow velocity of the integrated piping was within the range of 0.5 to 5 m / s, but the temperature of the condensed refrigerant after compression was low at 75°C, resulting in a low steam temperature of 78°C. As a result, the temperature increase after steam compression was insufficient. In addition, the low steam pressure caused air leakage, which resulted in steam contamination and corrosion and erosion of the piping. As a result, the temperature and pressure of the final steam generated were lower than in Example 3.

[0115] In Example 5, the flow velocity of the integrated piping was low at 0.3 m / s, which reduced the thermal mixing efficiency of the vaporized refrigerant at the front end of the refrigerant compressor, resulting in large fluctuations in the refrigerant temperature and pressure. This caused surges and cavitation in the refrigerant compressor and steam compressor, which in turn caused changes in the amount of steam at the rear end of the steam compressor, resulting in changes in pressure. As a result, the temperature, pressure, and coefficient of performance (COP) of the final steam generated were lower than those in Example 3.

[0116] In Example 6, the high flow velocity of the integrated piping of 6 m / s caused erosion and vibration in the refrigerant piping at the front end of the refrigerant compressor. This made long-term operation of the refrigerant piping difficult, requiring maintenance or piping replacement. Furthermore, the eroded foreign matter damaged the rotating components in the compressor and caused noise due to vibration. As a result, the temperature, pressure, and coefficient of performance (COP) of the final steam generated were lower than in Example 3. [Explanation of symbols]

[0117] 100 Multiple waste heat sources including process waste heat fluids (WH1, WH2, WH3, . . . ). 200 Multiple heat exchangers (HE1, HE2, HE3, etc.) 300 Heat pump equipment EV refrigerant evaporator CP refrigerant compressor CD Refrigerant Condenser EP valve refrigerant expansion valve 10, 20 Integrated piping S-CP Steam Compressor

Claims

1. (S1) a step of flowing process waste heat fluid supplied from a plurality of waste heat sources into heat exchangers configured in a number corresponding to the plurality of waste heat sources, and exchanging heat with cooling water; (S2) flowing the cooling water, whose temperature has been increased by heat exchange with the process waste heat fluid in each of the heat exchangers, into a refrigerant evaporator through an integrated pipe, and vaporizing the refrigerant by heat exchange with the refrigerant; (S3) compressing the vaporized refrigerant stream in a refrigerant compressor; (S4) exchanging heat between the compressed refrigerant stream and water in a refrigerant condenser to produce a condensed refrigerant stream and steam or hot water; (S5) passing the condensed refrigerant stream through a refrigerant expansion valve to reduce its pressure, and then circulating the condensed refrigerant stream to the refrigerant evaporator.

2. 2. The method according to claim 1, wherein the heated cooling water is cooled by heat exchange in a refrigerant evaporator, and then branched and circulated to each heat exchanger used in step (S1).

3. 2. The method according to claim 1, wherein the temperature of the cooling water flowing into each heat exchanger in step (S1) is in the range of 10 to 50°C, and the cooling water is heated to a temperature in the range of 13 to 60°C by heat exchange.

4. 10. The method of claim 1, wherein the integrated piping has a straight length of 5 to 5,000 m and is controlled to maintain a flow velocity of 0.5 to 5 m / s.

5. 2. The method of claim 1, wherein the pressure and temperature of the refrigerant entering the refrigerant evaporator range from 0.5 to 40 bar and from 10 to 60°C, respectively.

6. 10. The method of claim 1, wherein the refrigerant compressor uses electrical energy to increase the pressure of the refrigerant stream entering the refrigerant compressor by 1.2 to 5 times.

7. 10. The method of claim 1, wherein the temperature of the compressed refrigerant stream is between 90 and 200°C.

8. 2. The method of claim 1, wherein the refrigerant stream condensed by heat exchange with water in the refrigerant condenser has a temperature of 85 to 170°C.

9. 2. The method of claim 1, wherein the temperature of the hot water produced by heat exchange between the refrigerant stream and water in the refrigerant condenser is between 85 and 180°C.

10. 10. The method of claim 1, wherein the hot water is produced by adjusting the discharge pressure of water passing through a refrigerant condenser above its vapor pressure.

11. 2. The method of claim 1, wherein the pressure of the steam produced by heat exchange between the refrigerant stream and water in the refrigerant condenser is between 0.5 and 16 bar.

12. 10. The method of claim 1, wherein the steam is generated by adjusting the discharge pressure of water passing through a refrigerant condenser to less than the vapor pressure.

13. 10. The method of claim 1, wherein the steam exiting the refrigerant condenser is further compressed and converted to high pressure steam before being used as a process heat source.

14. The heat pump device includes a plurality of waste heat sources, a heat exchanger configured in a number corresponding to the plurality of waste heat sources, and a heat pump device connected to the heat exchanger via an integrated pipe and a branch pipe, the heat pump device includes a refrigerant evaporator, a refrigerant compressor, a refrigerant condenser, and a refrigerant expansion valve, which are connected via piping; The heated cooling water flowing out of each heat exchanger is integrated through an integrated pipe and flows into a refrigerant evaporator of the heat pump device, where the refrigerant is vaporized through heat exchange, and then circulated to each heat exchanger again through branch pipes.

15. 15. The system of claim 14, wherein the refrigerant condenser of the heat pump unit is coupled to an additional steam compressor.

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