Method for generating steam using waste heat

Abstract

The present invention provides a steam generation method and a waste heat recovery system for performing the method, the method comprising: (S1) introducing process waste heat fluid supplied from a plurality of waste heat sources into refrigerant evaporators, the number of which corresponds to the plurality of waste heat sources, to vaporize the refrigerant through heat exchange; (S2) combining the refrigerant streams vaporized in the respective refrigerant evaporators into a single integrated pipe; (S3) compressing the refrigerant stream combined into the integrated pipe using a refrigerant compressor; (S4) exchanging heat between the compressed refrigerant stream and water in a refrigerant condenser to generate a condensed refrigerant stream and steam; and (S5) reducing the pressure of the condensed refrigerant stream by passing it through a refrigerant expansion valve, branching it, and circulating it to each of the plurality of refrigerant evaporators, the method further comprising transferring the steam flowing out of the refrigerant condenser to a steam compressor and compressing it.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0007494 filed on January 18, 2023, and Korean Patent Application No. 10-2023-0183502 filed on December 15, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a method for generating steam using waste heat, and more particularly to a method for generating high-temperature / high-pressure steam required in a process by connecting multiple waste heat sources to a single heat pump system. [Background technology]

[0003] Petrochemical processes use a lot of energy to produce products, and the energy used is then either discarded or reused.

[0004] Generally, petrochemical products are manufactured through processes including reaction, separation, and purification. The lower part of the column where these processes are carried out is heated with steam, and the resulting high-temperature fluid at the upper part of the column is cooled by heat exchange with cooling water, resulting in a large amount of heat being wasted. The heated cooling water is then flowed into a cooling tower and cooled while dissipating heat. All heat dissipated during this cooling process can be referred to as waste heat within the process.

[0005] On the other hand, steam used as an energy source in petrochemical processes is generally generated from the heat of combustion produced by burning hydrocarbons, which is a costly process and causes global warming due to the carbon dioxide produced during the steam generation.

[0006] Therefore, there is a growing need to reduce the amount of steam used in petrochemical processes in order to lower production costs and reduce carbon emissions. As part of this, there has been an increasing attempt to recover waste heat in petrochemical processes and reuse it to generate steam.

[0007] FIG. 1 illustrates a process in which waste heat (WH) from a petrochemical process is recovered using a heat pump device including an evaporator (EV), a compressor (CP), a condenser (CD), and an expansion valve.

[0008] The heat pump is a device that performs a cycle of transferring a low-temperature heat source to a high temperature or a high-temperature heat source to a low temperature using the heat of evaporation or condensation of the refrigerant. In the evaporator EV, a low-temperature, low-pressure liquid refrigerant vaporizes through heat exchange with waste heat WH. The vaporized low-temperature, low-pressure refrigerant gas is compressed into a high-temperature, high-pressure gas in the compressor CP. The compressed refrigerant gas releases heat to the outside and condenses into a low-temperature, high-pressure liquid in the condenser CD. The condensed high-pressure refrigerant expands due to a pressure drop in the narrowed section as it passes through the expansion valve (EP valve), again becoming a low-temperature, low-pressure liquid. During this cycle of recovering waste heat, make-up water flowing into the condenser CD absorbs the latent heat generated by the condensation of the refrigerant and vaporizes, generating steam.

[0009] However, in existing methods, waste heat energy is recovered by connecting only one waste heat source to a heat pump device, and if multiple waste heat sources are to be applied, the number of heat pump devices must be increased, which results in an increase in the size of the steam generation equipment and an associated increase in production costs.

[0010] Furthermore, with existing heat pump technologies, when generating steam from recovered waste heat, the temperature rise (temperature lift) is low, making it difficult to meet the energy levels required for petrochemical processes, such as temperatures of 100 to 250°C.

[0011] Therefore, there is a need for a technology that can increase the economic and thermodynamic efficiency of waste heat recovery to generate steam, and that can generate the high-temperature / high-pressure steam required in petrochemical processes. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention is intended to solve the problems mentioned in the Background of the Invention section above, and provides a method for generating large amounts of high-temperature / high-pressure steam required in a process using a simple and economical design that can connect multiple waste heat sources to a single heat pump device. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, the present invention provides a method for generating steam, comprising the steps of: (S1) introducing process waste heat fluid supplied from a plurality of waste heat sources into refrigerant evaporators, the number of which corresponds to the plurality of waste heat sources, and vaporizing the refrigerant through heat exchange; (S2) combining the vaporized refrigerant streams from each of the refrigerant evaporators into a single integrated pipe; (S3) compressing the refrigerant stream combined into the integrated pipe using a refrigerant compressor; (S4) exchanging heat between the compressed refrigerant stream and water in a refrigerant condenser to generate a condensed refrigerant stream and steam; and (S5) reducing the pressure of the condensed refrigerant stream through a refrigerant expansion valve, branching the condensed refrigerant stream, and circulating it to each of the plurality of refrigerant evaporators, and further comprising transferring the steam discharged from the refrigerant condenser to a steam compressor for compression.

[0014] In the present invention, the temperature of the compressed refrigerant stream may be 100 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.

[0015] The present invention also provides a steam generation system for performing the above method, comprising a plurality of waste heat sources and a heat pump device connected thereto, the heat pump device including a refrigerant evaporator, a refrigerant compressor, a refrigerant condenser, and a refrigerant expansion valve connected via piping, the refrigerant evaporator being configured in plurality to communicate with each of the process waste heat fluids supplied from the plurality of waste heat sources, refrigerant streams flowing out from the piping connected to the plurality of refrigerant evaporators being integrated via an integration piping and transferred to the refrigerant compressor, the refrigerant stream passing through the refrigerant expansion valve being circulated to the plurality of refrigerant evaporators via branch piping, and the refrigerant condenser being connected to an additional steam compressor. [Effects of the Invention]

[0016] According to the present invention, a plurality of waste heat sources are connected to a heat pump device including a corresponding number of evaporators, and waste heat is recovered by performing heat exchange between each of the plurality of waste heat sources and branched refrigerant streams. The refrigerant streams vaporized in the plurality of evaporators are combined and compressed, and then heat exchanged with water to generate a large amount of steam required in the process.

[0017] In addition, when generating steam from the waste heat 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 reducing the manufacturing cost of petrochemical products and carbon emissions.

[0018] Furthermore, by applying one heat pump device to multiple waste heat sources, it is possible to simplify the steam generation equipment, reduce costs by improving operational efficiency, minimize maintenance, and stabilize operation. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram illustrating a waste heat recovery process of a heat pump device according to the prior art. [Figure 2] 1 is a diagram illustrating a steam generating system connected to a heat pump device including a plurality of waste heat sources and a corresponding number of evaporators according to the present invention; [Figure 3] 10 is a diagram illustrating a configuration in which an additional steam compressor is connected to a refrigerant condenser of a heat pump device in a steam generating system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] 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.

[0021] 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.

[0022] 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. The fluid can contain one or more components of gas, liquid, and solid.

[0023] One embodiment of the present invention relates to a method for recovering waste heat by connecting multiple waste heat sources to a single heat pump device and generating steam, specifically including a step (S1) of evaporating a refrigerant by heat exchange between multiple process waste heat fluids and a refrigerant, a step (S2) of combining the evaporated refrigerant streams, a step (S3) of compressing the combined refrigerant streams, a step (S4) of generating a condensed refrigerant stream and steam by heat exchange between the compressed refrigerant stream and water, and a step (S5) of reducing the pressure of the condensed refrigerant stream and branching it, and may further include compressing the steam.

[0024] Hereinafter, the steam generating method will be described in detail step by step with reference to the accompanying drawings.

[0025] Referring to FIG. 2, the method for generating steam by waste heat recovery according to the present invention can be performed using a steam generating system including a plurality of waste heat sources 100 and heat pump devices 200 connected thereto.

[0026] The plurality of waste heat sources 100 are components that supply various process fluids containing waste heat, i.e., a plurality of process waste heat fluids WH1, WH2, WH3, ..., using cooling water in a petrochemical process. In the present invention, in order to increase the economic and thermodynamic efficiency of steam generation using waste heat, at least one or more waste heat sources 100, for example, 2 to 10 waste heat sources 100, are configured and connected to one heat pump device 200 via piping so that the fluids communicate with each other.

[0027] In one embodiment of the present invention, the temperature of the process waste heat fluids WH1, WH2, WH3, ... supplied from the plurality of waste heat sources 100 may be in the range of 30 to 140°C, specifically 60 to 100°C. If the temperature of the process waste heat fluid is less than 30°C, the refrigerant compression ratio increases during waste heat recovery in the heat pump device 200, resulting in increased energy consumption. If the temperature is more than 140°C, an excessive increase in refrigerant vapor pressure may make it difficult to fabricate the equipment, or the latent heat per unit mass may decrease, making it difficult to select the capacity of the refrigerant condenser.

[0028] The heat pump device 200 performs a cycle of transferring a low-temperature heat source to a high temperature or transferring a high-temperature heat source to a low temperature using the heat of evaporation or condensation of the refrigerant, and includes a refrigerant evaporator EV, a refrigerant compressor CP, a refrigerant condenser CD, and a refrigerant expansion valve (EP valve), and each of these components is connected via piping so that the refrigerant can circulate.

[0029] In the heat pump apparatus 200, the refrigerant evaporator EV is a component connected to the plurality of waste heat sources 100 via pipes and performs heat exchange between the refrigerant and process waste heat fluids WH1, WH2, WH3, ..., and may be configured with a plurality of refrigerant evaporators (EV1, EV2, EV3, ...). Refrigerant streams flowing from respective pipes 11, 12, 13, ... connected to the plurality of refrigerant evaporators are combined via an integrated pipe 10, and the combined refrigerant stream passes through a refrigerant compressor CP, a refrigerant condenser CD, and a refrigerant expansion valve (EP valve) in this order. Thereafter, the refrigerant stream passing through the refrigerant expansion valve may circulate to the plurality of refrigerant evaporators via pipes 41, 42, 43, ... branching from an integrated pipe 40.

[0030] More specifically, the refrigerant evaporators EV included in the heat pump apparatus 200 may be configured in a number (EV1, EV2, EV3, ...) corresponding to the plurality of waste heat sources 100 so as to be in communication with the respective process waste heat fluids WH1, WH2, WH3, ... supplied from the plurality of waste heat sources 100. For example, when the plurality of waste heat sources 100 is configured as 2 to 10 units, the refrigerant evaporators EV may also be configured as 2 to 10 units.

[0031] Each refrigerant evaporator applicable to the present invention may be a general shell and tube type, or may be a plate type or a falling film evaporator type to improve heat exchange efficiency, but is not limited thereto.

[0032] A low-temperature, low-pressure liquid refrigerant, for example, a refrigerant having a pressure of 1 to 30 bar or 3 to 20 bar and a temperature of 10 to 120°C or 40 to 80°C, can flow into each of these refrigerant evaporators EV1, EV2, EV3, ... via piping, and high-temperature process waste heat fluids WH1, WH2, WH3, ... supplied from multiple waste heat sources 100 are respectively flowed into each of the refrigerant evaporators through which the low-temperature, low-pressure refrigerant flows, and the refrigerant is vaporized by heat exchange.

[0033] That is, when a process waste heat fluid of 30 to 140°C flows into each refrigerant evaporator, the refrigerant absorbs heat from the process waste heat fluid through mutual heat exchange and can be converted into a relatively high temperature vapor stream.

[0034] In one embodiment of the present invention, the total flow rate of the refrigerant flowing into each of the refrigerant evaporators EV1, EV2, EV3, ... through piping 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 each of the process waste heat fluids flowing into each of the refrigerant evaporators EV1, EV2, EV3, ... may be 5 to 10,000 Ton / hr, for example, 10 to 5,000 Ton / hr or 15 to 4,000 Ton / hr, but is not limited thereto.

[0035] The refrigerant stream vaporized in the refrigerant evaporator is rich in gas components among all components, for example, the molar fraction of the gas components among all components of the refrigerant stream may be 1.0.

[0036] In one embodiment of the present invention, the temperature of the refrigerant stream evaporated in each of the refrigerant evaporators can satisfy the following formula 1, thereby allowing high-temperature steam to be generated using waste heat of 30 to 140°C.

[0037] [Formula 1] 1℃≦T WH -T G ≦20℃

[0038] In the above formula, T WH is the final temperature of the process waste heat fluid entering each of the refrigerant evaporators; T G is the temperature of the vaporized refrigerant stream in each of the refrigerant evaporators.

[0039] Meanwhile, the process waste heat fluid that has exchanged heat with the refrigerant in each of the refrigerant evaporators EV1, EV2, EV3, ... may flow out from each of the refrigerant evaporators at a temperature lower than the initial temperature, for example, 25 to 135°C or 55 to 95°C.

[0040] Then, the refrigerant streams vaporized in the refrigerant evaporators EV1, EV2, EV3, . . . flow out through pipes 11, 12, 13, .

[0041] In the present invention, refrigerant streams vaporized through heat exchange in multiple refrigerant evaporators EV1, EV2, EV3, ..., which receive multiple process waste heat fluids WH1, WH2, WH3, ..., are combined in integrated piping 10, and the combined refrigerant stream passes sequentially through a refrigerant compressor CP, a refrigerant condenser CD, and a refrigerant expansion valve (EP valve). If the refrigerant streams flowing out of the multiple refrigerant evaporators were to flow directly into the refrigerant compressor CP without passing through integrated piping 10, the physical properties of the refrigerant streams, such as flow rate, temperature, and pressure, would become uneven, making it difficult for the refrigerant compressor CP to operate normally. That is, when multiple waste heat sources are used, the refrigerant streams vaporized from the multiple refrigerant evaporators must flow into the refrigerant compressor via integrated piping to operate normally.

[0042] In one embodiment of the present invention, the linear length of the integrated pipe 10 may 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 surging 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.

[0043] The flow velocity of the integrated pipe 10 may be in the range of more than 5 m / s to 50 m / s, specifically 10 to 40 m / s. If the flow velocity of the integrated pipe is less than 5 m / s, the thermal mixing efficiency of the evaporated refrigerant may decrease, and if it is more than 50 m / s, erosion and vibration may occur within the pipe.

[0044] By applying the integrated piping 10 as described above, it is possible to simplify the steam generating equipment, reduce costs by improving the efficiency of operation, minimize maintenance, and stabilize operation.

[0045] More specifically, the prior art recovers waste heat energy by connecting only one waste heat source to a heat pump device, which requires multiple heat pumps for multiple waste heat sources, resulting in the inconvenience of having to manage multiple pieces of equipment and the associated increase in personnel and costs.In contrast, the present invention combines the refrigerant streams that have exchanged heat with multiple waste heat sources in an integrated pipe before flowing into the compressor, thereby simplifying control and operation, reducing the number of abnormal operations, and increasing the replacement cycle.

[0046] In addition, when a single waste heat source is connected to a single heat pump, there are waste heat sources that cannot be recovered due to the limitations of small-capacity equipment. However, the introduction of a heat pump that uses a compressor after passing through integrated piping as in the present invention makes it possible to recover even very small amounts of waste heat.

[0047] Furthermore, when multiple heat pumps are used to generate steam individually, there is the inconvenience of having to adjust the material balance of all the equipment. However, by introducing a heat pump using a compressor via integrated piping as in the present invention, it is possible to reduce the number of maintenance operations and achieve more efficient material balance adjustment, thereby stabilizing operation.

[0048] The gas phase refrigerant streams joined in the integrated pipe 10 flow into one refrigerant compressor CP, where the pressure of the gas phase refrigerant stream increases due to compression using electrical energy, and the temperature of the gas phase refrigerant stream can also increase in proportion to the amount of electrical energy supplied.

[0049] 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.

[0050] This refrigerant compressor CP can increase the pressure of the gaseous refrigerant stream that flows in through the refrigerant evaporator EV by 1.2 to 5 times. For example, the pressure of the refrigerant stream passing through the compressor CP can be 3 to 50 bar or 6 to 40 bar. When the gaseous refrigerant stream is compressed within this range, the compressor type can be easily selected, designed, and manufactured.

[0051] 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 a 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.

[0052] 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 generating a condensed refrigerant stream and steam.

[0053] 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.

[0054] In the refrigerant condenser CD, the refrigerant is condensed by releasing heat through heat exchange with water, and the water replenished from the outside absorbs the heat generated by the condensation of the refrigerant and turns into steam.

[0055] The refrigerant stream condensed by heat exchange with water in the refrigerant condenser CD is preferably maintained at a temperature of 85 to 170°C, more specifically 100 to 170°C, under 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 result in air leakage and contamination of the steam generated by heat exchange, making it difficult to use in the process or causing corrosion and erosion of the piping. 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 make it impossible to construct the equipment or cause imperfect operation.

[0056] To ensure that the temperature of the condensed refrigerant stream is above 85°C, it is advantageous to adjust the critical temperature of the refrigerant to above 100°C. The critical temperature of a refrigerant is a thermodynamic property inherent to each substance and refers to the maximum temperature at which the gas and liquid phases 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 of the refrigerant condenser decreases, it becomes difficult to produce the required steam within the process, and malfunctions such as compressor surge may occur.

[0057] 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 R245fa, R134a, R1234ze, and R1234yf, and HFO (hydrofluoroolefin)-based R1234ze(E), R1234ze(Z), and R1233zd(E) can be used.

[0058] 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.

[0059] Meanwhile, the water replenished to the refrigerant condenser CD must be in a pure state with ions and oxygen removed, and may be introduced 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 replenished 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.

[0060] In the refrigerant condenser CD, the steam generated by heat exchange with the high temperature / high pressure gas phase refrigerant stream can exhibit a temperature of 100 to 200°C or 101 to 180°C and a pressure of 1 to 16 bar or 1 to 10 bar.

[0061] Thereafter, the liquid phase refrigerant stream flowing out from the refrigerant condenser CD is decompressed by passing through a refrigerant expansion valve (EP valve), and the refrigerant stream that has passed through the refrigerant expansion valve can be circulated to each of the plurality of evaporators via pipes 41, 42, 43, ... branched from the integrated pipe 40.

[0062] 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.

[0063] 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 3 to 20 bar and a temperature of 10 to 120°C or 40 to 80°C, respectively.

[0064] 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.

[0065] The refrigerant stream that has passed through the expansion valve can be circulated to the plurality of evaporators EV1, EV2, EV3, . . . via pipes 41, 42, 43, .

[0066] On the other hand, the steam generated in the refrigerant condenser CD exhibits a low pressure of 1 to 16 bar, making it difficult to immediately use in the process. Considering the lower limit of the effective pressure that can be used in petrochemical processes, the steam used in the process requires a pressure of 4 to 60 bar or 5 to 30 bar.

[0067] Therefore, in the present invention, as shown in FIG. 3, a steam compressor S-CP is connected to the refrigerant condenser CD of the heat pump device 200, and the steam flowing out from the refrigerant condenser CD is introduced into the steam compressor S-CP, thereby increasing the pressure of the final steam to a range of 4 to 60 bar or 5 to 30 bar.

[0068] 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.

[0069] Here, when superheated steam is introduced into a heat exchanger in the process, the heat exchange efficiency decreases, so water is supplied to form saturated steam. The water supplied to the steam compressor S-CP must be pure, with ions and oxygen removed, and can be introduced into the process by joining with the saturated steam while reducing the degree of superheat of the steam. The flow rate of the supplied water can be, but is not limited to, 0.1 to 30 Ton / hr or 1 to 20 Ton / hr.

[0070] The saturated steam flowing out from the steam compressor S-CP can finally exhibit a temperature of 140 to 280°C or 150 to 240°C, which can satisfy the energy level required in petrochemistry.

[0071] In this way, in the present invention, a plurality of waste heat sources are connected to a heat pump device including a corresponding number of evaporators, and the waste heat is recovered by performing heat exchange between each of the plurality of waste heat sources and the branched refrigerant streams, and the refrigerant streams vaporized in the plurality of evaporators are combined and compressed, and then heat exchanged with water to generate a large amount of steam required in the process. For example, the final amount of steam generated by the present invention can be 1 to 120 tons / hr or 2 to 100 tons / hr.

[0072] The heat of steam generation according to the present invention can be defined by the following Equation 2, and the coefficient of performance (COP) of the system applied to the steam generation method of the present invention can be expressed by the following Equation 3.

[0073] [Formula 2] Heat of steam generation = Waste heat + Power supply (power used to compress the refrigerant and steam)

[0074] [Formula 3] COP = Steam generation heat / power supply

[0075] The coefficient of performance (COP) according to Equation 3 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 2 means that twice the amount of heat is obtained as the input electrical energy.

[0076] The steam generated by the method according to the present invention has a COP value calculated by the above formula 3 of 2 or more, and can ensure economic efficiency with respect to the input electrical energy.

[0077] 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.

[0078] 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.

[0079] Example 1: As illustrated in FIG. 3, a system in which three waste heat sources 100 are connected to one heat pump device 200 was used to recover waste heat and generate steam.

[0080] Specifically, the heat pump device 200 includes three refrigerant evaporators EV1, EV2, and EV3, a refrigerant compressor CP, a refrigerant condenser CD, and a refrigerant expansion valve (EP valve), which are connected via pipes to circulate the refrigerant. A liquid state (60°C, 3.9 bar) refrigerant (trans-1-chloro-3,3,3-trifluoropropene, R1233zd(E)) is introduced into each of the three refrigerant evaporators EV1, EV2, and EV3 at a flow rate of 310 ton / hr to circulate the refrigerant.

[0081] Gas-state (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 ton / hr and flowed into the three refrigerant evaporators EV1, EV2, and EV3 to perform heat exchange. After the heat exchange, the process waste heat fluids WH1, WH2, and WH3 released heat from the three refrigerant evaporators EV1, EV2, and EV3, respectively, and flowed out in a liquid state at 65°C and 4 bar, while the refrigerant vaporized by heat absorption and flowed out in a gas state at 60°C and 3.9 bar.

[0082] The refrigerant streams discharged after vaporization from the respective refrigerant evaporators EV1, EV2, and EV3 were merged into one integrated pipe 10 (straight length: 50 m, flow rate: 10 m / s) to mix the refrigerant streams.

[0083] The mixed refrigerant stream was flowed into the refrigerant compressor CP through the integrated pipe, and then compressed under a power of 4.4 Gcal / h to obtain a refrigerant stream in a gas state at 128°C and 16 bar.

[0084] The compressed refrigerant stream (128°C and 16 bar) was flown into a refrigerant condenser CD, and water (20°C and 1 bar) was supplied to the refrigerant condenser CD at a flow rate of 27 ton / hr to perform heat exchange. After the heat exchange, the water was produced into 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.

[0085] The condensed refrigerant stream (120°C and 16 bar) was passed through an expansion valve (EP valve) to obtain a liquid refrigerant stream at 60°C and 3.9 bar, which was then circulated to the multiple evaporators EV1, EV2, EV3, ... via pipes 41, 42, 43, ... branching from the integrated pipe 40.

[0086] Furthermore, 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 27 ton / hr and compressed under an electric power of 3.5 Gcal / h, thereby finally producing steam at 200°C and 13 bar at a rate of 34 ton / hr.

[0087] The heat of steam generation for the final steam generated was calculated by the following equation 2, and the coefficient of performance (COP) was calculated by the following equation 3.

[0088] [Formula 2] Heat of steam generation = Waste heat + Power supply (power used for refrigerant compression and steam compression)

[0089] [Formula 3] COP = Steam generation heat / power supply

[0090] Example 2: The vaporization of the refrigerant by heat exchange between the process waste heat fluid (75°C and 5 bar) and the refrigerant (60°C, 3.9 bar) in three refrigerant evaporators EV1, EV2, and EV3, and the mixing of the vaporized refrigerant in the integrated pipe 10 were carried out under the same conditions as in Example 1.

[0091] The mixed refrigerant stream was compressed in a refrigerant compressor CP under a power of 1.5 Gcal / h to obtain a gaseous refrigerant stream at 88°C and 7.8 bar, which then flowed into a refrigerant condenser CD, where water (20°C and 1 bar) was supplied at a flow rate of 27 ton / hr to perform heat exchange. Steam at 78°C and 0.4 bar was generated by the heat exchange, while a condensed refrigerant stream at 75°C and 7.8 bar was discharged and sent to an expansion valve (EP valve).

[0092] 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 27 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 32 ton / hr.

[0093] The subsequent steps were the same as in Example 1.

[0094] Example 3: The same process as in Example 1 was carried out, except that the flow velocity of the integrated piping was changed to 40 m / s.

[0095] Example 4: The same process as in Example 1 was carried out, except that the flow velocity in the integrated piping was changed to 5 m / s.

[0096] Example 5: The same process as in Example 1 was carried out, except that the flow velocity of the integrated piping was changed to 60 m / s.

[0097] Comparative Example 1 The same process as in Example 1 was performed in the heat pump device 200, except that the integrated piping 10 was not provided, i.e., the refrigerant streams vaporized in the multiple refrigerant evaporators EV1, EV2, and EV3 and then discharged were not integrated, but instead flowed directly into the refrigerant compressor CP, and no additional steam compression process was performed on the steam generated in the refrigerant condenser CD.

[0098] The results of steam generation in the examples and comparative examples are shown in Table 1 below.

[0099] [Table 1]

[0100] As shown in Table 1, in Examples 1 to 5, waste heat was recovered by heat exchange between the process waste heat fluid and the refrigerant in each of a plurality of refrigerant evaporators, and the refrigerant was vaporized. The vaporized refrigerant was mixed and compressed through an integrated pipe, and then steam was generated by heat exchange with water in a condenser. The steam was further compressed to finally generate high-temperature and high-pressure steam.

[0101] In particular, in Examples 1 and 3, the flow velocity of the integrated piping is in the range of more than 5 m / s to 50 m / s, and the temperature of the condensed refrigerant after compression is controlled to 85°C or higher, thereby maintaining the temperature of the generated steam at 85°C or higher. Thereafter, it can be confirmed that the difference between the initial waste heat temperature and the final generated steam temperature due to steam compression, i.e., the temperature lift, is high.

[0102] In the case of Example 2, the flow velocity of the integrated piping was in the range of over 5 m / s to 50 m / s, but the temperature of the condensed refrigerant after compression was low at 75°C, so the generated steam was low at 78°C, and therefore the temperature increase after steam compression was insufficient.In addition, the low steam pressure caused air leakage, which contaminated the steam and led to corrosion and erosion of the piping, making it impossible to produce the high-temperature / high-pressure steam required in petrochemical processes.

[0103] In Example 4, the flow velocity of the integrated piping was low at 5 m / s, which reduced the thermal mixing efficiency of the vaporized refrigerant upstream of the refrigerant compressor, resulting in large fluctuations in the temperature and pressure of the refrigerant. This caused surging and cavitation in the refrigerant compressor and steam compressor, and changes in the amount of steam downstream of the steam compressor, causing pressure changes. As a result, the temperature, pressure, and coefficient of performance (COP) of the final steam generated were lower than those in Example 1.

[0104] In Example 5, the high flow velocity of the integrated piping of 60 m / s caused erosion and vibration in the refrigerant piping upstream of the refrigerant compressor. This made long-term operation of the refrigerant piping difficult, necessitating 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 reduced compared to Example 1.

[0105] On the other hand, in Comparative Example 1, because integrated piping was not used, the physical properties of the inlet fluid, such as the flow rate, temperature, and pressure of the refrigerant stream, were non-uniform at the inlet of the refrigerant compressor CP, and changes in the performance of the refrigerant compressor CP caused the refrigerant compressor CP to operate abnormally, resulting in non-uniform steam production or steam production failure. Furthermore, continuous compressor surging and cavitation phenomena caused damage to the equipment, making long-term operation difficult and leading to problems with maintenance and equipment replacement. Furthermore, the lack of steam compression made it impossible to produce the high-temperature / high-pressure steam required in petrochemical processes. [Explanation of symbols]

[0106] 100 Process waste heat fluids WH1, WH2, WH3, ... multiple waste heat sources 200 Heat pump equipment EV1, EV2, EV3 Refrigerant evaporators CP refrigerant compressor CD Refrigerant Condenser EP valve Refrigerant expansion valve 10, 40 Integrated piping 11, 12, 13, 41, 42, 43 Branch piping S-CP Steam Compressor

Claims

1. (S1) a step of causing process waste heat fluid supplied from a plurality of waste heat sources to flow into refrigerant evaporators configured in a number corresponding to the plurality of waste heat sources, and vaporizing the refrigerant by heat exchange; (S2) combining the refrigerant streams vaporized in each of the refrigerant evaporators into one integrated pipe; (S3) compressing the refrigerant stream joined to the integrated pipe with a refrigerant compressor; (S4) exchanging heat with water in a refrigerant condenser to produce a condensed refrigerant stream and steam; (S5) passing the condensed refrigerant stream through a refrigerant expansion valve to reduce the pressure, and then branching the refrigerant stream to circulate to each of the plurality of refrigerant evaporators; The method for generating steam further comprises the step of transferring the steam discharged from the refrigerant condenser to a steam compressor and compressing it.

2. The steam generating method according to claim 1 , wherein the plurality of waste heat sources and the plurality of refrigerant evaporators each comprise 2 to 10 units.

3. 2. The method for generating steam according to claim 1, wherein the initial temperature of the process waste heat fluid entering each of the refrigerant evaporators is between 30 and 140°C.

4. 2. The method for generating steam according to claim 1, wherein the pressure and temperature of the refrigerant flowing through each of the refrigerant evaporators are in the ranges of 1 to 30 bar and 10 to 120°C, respectively.

5. 2. The method for generating steam according to claim 1, wherein the temperature of the refrigerant stream vaporized in each of the refrigerant evaporators satisfies the following formula 1: [Formula 1] 1℃≦T ＷＨ -T Ｇ ≦20℃ In the above formula, T ＷＨ is the final temperature of the process waste heat fluid entering each of the refrigerant evaporators; T Ｇ is the temperature of the vaporized refrigerant stream in each of the refrigerant evaporators.

6. 2. The method for generating steam according to claim 1, wherein the integrated piping has a linear length of 5 to 5,000 m and is controlled to maintain a flow velocity of more than 5 m / s to 50 m / s.

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

8. 2. The method for generating steam according to claim 1, wherein the temperature of the compressed refrigerant stream is between 90 and 200°C.

9. 2. The method for generating steam according to claim 1, wherein the temperature of the refrigerant stream condensed by heat exchange with water in the refrigerant condenser is 85 to 170°C.

10. 2. The method for generating steam according to claim 1, wherein the pressure of the refrigerant stream passing through the refrigerant expansion valve is between 0.5 and 30 bar.

11. 2. The method for generating steam according to claim 1, wherein the pressure of the steam generated by heat exchange between the refrigerant stream and water in the refrigerant condenser is 1 to 16 bar.

12. 2. The method for generating steam according to claim 1, wherein the steam discharged from the refrigerant condenser is compressed at 4 to 60 bar by supplying electrical energy in a steam compressor, and water is supplied to the compressed steam to convert it into saturated steam, which is then used as a process heat source.

13. a plurality of waste heat sources and heat pump devices coupled thereto; 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 refrigerant evaporator is configured in a plurality of units so as to be in communication with the process waste heat fluids supplied from the plurality of waste heat sources, Refrigerant streams flowing from pipes connected to the plurality of refrigerant evaporators are combined through a combined pipe and transferred to the refrigerant compressor; The refrigerant stream passing through the refrigerant expansion valve is circulated to the plurality of refrigerant evaporators via branch pipes, The steam generating system, wherein the refrigerant condenser is coupled to an additional steam compressor.

14. 14. The steam generating system according to claim 13, wherein the steam compressor compresses the steam generated by heat exchange between the refrigerant stream compressed in the refrigerant condenser and water, and converts the steam into saturated steam.

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