Converter valve waste heat recovery equipment model and method

Abstract

The invention relates to a converter valve waste heat recovery equipment model and method, which can effectively reduce the influence of waste heat generated by operation of a converter valve on the environment, improve the utilization efficiency of heat energy and realize energy conservation and environmental protection. The model mainly comprises a waste heat recovery device formed by connecting a heat pump system and a lithium bromide absorption refrigeration system in series. According to the system, the refrigerating and heating functions of the converter valve hall can be realized through five reasonably designed circulation processes, and a technical scheme for efficiently utilizing heat energy resources is formed. The application of the method not only can improve the operation efficiency of the converter valve and reduce the operation cost, but also can remarkably reduce the consumption of water resources and respond to the national water-saving policy while heating in winter and refrigerating in summer, and has good economic benefits and environmental protection values.

Description

Technical Field

[0001] The present invention belongs to the field of waste heat recovery in green converter stations, and more specifically relates to a waste heat recovery equipment model and method for converter valves. Background Art

[0002] Currently, in power equipment such as substations and converter stations, due to the requirements of high current and high voltage for equipment operation, a large amount of waste heat is generated during the operation of the equipment. Most of this generated high-temperature heat energy is cooled by air or directly discharged into the atmosphere, resulting in a large waste of heat energy resources. In order to change this situation, some existing technologies have proposed to reduce the direct discharge and loss of heat energy by adding equipment such as heat pumps, but these equipment generally have problems such as large investment, high operating costs, and low heating efficiency. As one of the key equipment in the power grid system, the converter valve generates a relatively large amount of waste heat during its operation, but there is currently no effective technical invention to efficiently recover and utilize this part of waste heat.

[0003] In addition, large-scale power facilities such as substations and converter stations generally have a large indoor space that needs to be temperature-controlled. The traditional adjustment method is to use air conditioners and heating equipment for adjustment, but such a method has high energy consumption and certain environmental pollution. To solve this problem, some technical personnel have proposed to utilize the waste heat generated during the operation of these power equipment, recover the heat energy through waste heat recovery equipment, and then use this as an energy source for temperature control. However, such equipment usually cannot absorb heat energy well for various types of equipment, and the recovery rate and conversion efficiency are not very high, and there is still room for improvement.

[0004] Moreover, the existing heat energy recovery technologies generally have problems such as low recovery efficiency, complex equipment, large cost investment, and difficult operation and maintenance. Therefore, how to design an equipment model and method that can effectively improve the waste heat utilization rate of converter valves, have less investment, and low operating costs has become a scientific and technological problem that needs to be solved urgently at present. Summary of the Invention

[0005] The present invention not only effectively solves the cooling problem of the converter valve, but also can realize the dual functions of heating and cooling in the converter valve hall. Through the system design, by making full use of the waste heat generated during the operation of the converter valve, reasonable distribution and conversion are carried out to achieve combined heat and power supply. On the basis of meeting the heating and cooling requirements of the converter station in winter and summer, the system can significantly reduce the consumption of water resources.

[0006] To achieve the above object, the present invention is implemented by adopting the following technical solutions: The model includes:

[0007] A waste heat recovery device composed of a heat pump system and a lithium bromide absorption refrigeration system connected in series;

[0008] The heat pump system is configured with a regenerator. The working medium of the lithium bromide absorption refrigeration system is a water-lithium bromide combination, which includes a generator, a condenser, an evaporator, and an absorber, as well as two expansion valves and a solution heat exchanger. The high-temperature hot water output by the heat pump system enters the generator of the lithium bromide absorption refrigeration system through a small hot water circulation system, heating the lithium bromide solution, causing water to evaporate and enter the condenser and condense into a liquid state. The remaining high-concentration lithium bromide solution flows back to the absorber after passing through the solution heat exchanger. The cold water system sequentially passes through the absorber and the condenser in series to complete the cooling task. The entire system realizes the efficient utilization of the waste heat of the commutation valve through five circulation processes, providing heating and refrigeration functions for the commutation valve hall.

[0009] In one solution, for the waste heat recovery equipment model, there are the following five circulation processes:

[0010] (1) The circulation of the heat pump working medium in the heat pump system;

[0011] (2) The circulation of the commutation valve cooling water;

[0012] (3) The circulation of the hot water output by the heat pump between the heat pump condenser and the generator of the lithium bromide absorption system;

[0013] (4) The circulation of water (steam) in the lithium bromide absorption system;

[0014] (5) The circulation of the lithium bromide solution in the absorption system;

[0015] Through this multi-level circulation design, the system can efficiently integrate heat energy resources and achieve the dual goals of heating and refrigeration.

[0016] In one solution, when establishing the analysis model of the heat pump system, the following assumptions are made:

[0017] (1) The system is in a stable circulation state;

[0018] (2) The heat dissipation loss between the equipment and the environment is ignored;

[0019] (3) The flow resistance and heat loss in the pipeline are not considered;

[0020] (4) The flow rate of the system working medium is measured in unit flow rate.

[0021] In one solution, the waste heat recovery equipment model includes:

[0022] Evaporator model:

[0023] t 1H =t 6H =t e

[0024] p 1H= p 6H = p e

[0025] Heat exchanger model:

[0026] t 2H = t 1H + Δt

[0027] p 2H = p e

[0028] p 5H = p c

[0029] t sH = f(h sH , p sH )

[0030] Condenser model:

[0031] p 3H = p 4H = p c

[0032] t 3H = f(h 3H , p 3H )

[0033] t 4H = t c

[0034] Evaporator heat load:

[0035] q e = h 1H - h 6H

[0036] Compressor power consumption:

[0037] w = w s / η is

[0038] Where w s is the isentropic compression work consumption, w s = h 3sH - h 2H η is is the compressor isentropic efficiency, ranging from 0.5 to 0.8;

[0039] Heat exchanger H heat load:

[0040] q hx = h 2H - h 1H = h 4H - h 5H

[0041] Throttle valve model:

[0042] h 5H = h 6H

[0043] q h = h 3H - h 4H

[0044] Coefficient of performance of heat pump:

[0045]

[0046] In this model, given the evaporation temperature t e , condensation temperature t c , suction superheat temperature Δt, the thermodynamic calculation of the system can be completed, that is, the input matrix is

[0047] I = [t e , t c , Δt].

[0048] In a scheme, for the analysis and calculation of a lithium bromide absorption refrigeration system, the following assumptions are set:

[0049] (1) The system is in a steady-state operating condition.

[0050] (2) The pressure drop and heat loss in the system pipeline are ignored.

[0051] (3) The lithium bromide solution at the outlet of each component is in a saturated state.

[0052] (4) The influence of the recirculation ratio of the dilute solution in the absorber on the system is ignored, and it is assumed that the recirculation ratio f = 0.

[0053] In a scheme, the physical property model of lithium bromide working medium for the lithium bromide absorption refrigeration system described

[0054] t LiBr = f1(P, w)

[0055] w = f2(P, t)

[0056] h LiBr = f3(w, t)

[0057] Solution heat exchanger model:

[0058] h w = f4(t)

[0059] h vap = f s (P, t)

[0060] Q E = mw (h1 - h3) = m w C p (t WEi -t WEo )

[0061] Q A = m r h8 + m w h1 - m a h2 = m WA C p (t WAo -t WAi )

[0062] Q C = m w (h 4' -h3) = m WC C p (t WCo -t WCi )

[0063] Q G = m r h4 + m w h4. - m a h7 = m WG C p (t WGi -t WGo )

[0064] Q H = m r (h8 - h4) = m a (h2 - h7)

[0065] Coefficient of performance:

[0066]

[0067] Blowdown range:

[0068] Δw = w r -w a

[0069] Circulation ratio:

[0070]

[0071] In the above formulas, m w 、m r and m a are the refrigerant water flow rate, strong solution flow rate, and weak solution flow rate respectively, with the unit of kg / s. w r 、w a are the concentrations of the lithium bromide strong solution and weak solution respectively; Q is the heat load of the equipment, with the unit of k W; P is the pressure, in kPa; t is the temperature, in °C; h is the enthalpy of the fluid, in kJ / kg.

[0072] In one aspect, a method for modeling a waste heat recovery device of a converter valve, the method being applicable to the model. The cold-end temperature difference in industry is generally 15 - 25 °C. Taking 15 °C, the following formula can be obtained

[0073]

[0074] The temperature t of the dilute solution leaving the heat exchanger 3A , assuming the solution circulation ratio is a, That is

[0075]

[0076] Then the outlet temperature of the dilute solution:

[0077] t 3A = f(h 3A , w a )

[0078] The calculation method of the generator heat load is as follows:

[0079] Q g = m a · [h 9A + (a - 1) · h 5A - a · h 3A )]

[0080] The calculation method of the absorber heat load is as follows:

[0081] Q a = m a · [h 12A + (a - 1) · h 6A - a · h 1A )]

[0082] The calculation method of the evaporator heat load is as follows:

[0083] Q ae = m a · (h 12A - h 11A )

[0084] The calculation method of the condenser heat load is as follows:

[0085] Q ak = m a · (h 9A - h 10A )

[0086] The calculation method of the solution heat exchanger heat load is as follows:

[0087] Q a-a = m a ·(a - 1)·(h 5A - h 6A )

[0088] The coefficient of performance of the system is:

[0089]

[0090] COP T = COP A ·COP H (3 - 50).

[0091] Advantages of the present invention:

[0092] By designing a waste heat recovery device composed of a series connection of a heat pump system and a lithium bromide absorption refrigeration system, the present invention realizes the efficient utilization of the waste heat generated during the operation of the converter valve, and improves the energy utilization efficiency.

[0093] By using the recovered heat energy for the refrigeration and heating of the converter valve hall, the present invention meets the requirements of the converter station in different seasons and improves the energy utilization efficiency.

[0094] The traditional cooling method of the converter valve mainly uses external water supply, resulting in a large amount of water resource waste. The method of the present invention effectively reduces the consumption of water resources and responds to the national water-saving policy requirements. At the same time, it reduces the waste heat and greenhouse gases discharged into the environment and reduces environmental pollution.

[0095] The present invention integrates a variety of waste heat recovery and utilization technologies, and the designed system process flow is simple, and the equipment and operation costs are low, having good economic benefits. Brief description of the drawings

[0096] Figure 1 is the overall scheme of the converter valve waste heat recovery of the present invention;

[0097] Figure 2 is the system thermal cycle process of the present invention;

[0098] Figure 3 is the pressure-enthalpy diagram of the heat pump cycle of the present invention;

[0099] Figure 4 Relationship diagram between the system COP and the evaporation temperature under different condensation pressures;

[0100] Figure 5 Variation of COP with the condensation temperature;

[0101] Figure 6 is the enthalpy-concentration of the lithium bromide second-class absorption heat pump cycle process;

[0102] Figure 7 The influence of circulating cooling water on system parameters;

[0103] Figure 8 It is the influence of the outlet water temperature of the absorber on the system performance parameters. Specific embodiments

[0104] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Typical embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0105] The present invention discloses a converter valve waste heat recovery equipment model and method. The present invention not only effectively solves the cooling problem of the converter valve, but also can realize the dual functions of heating and cooling in the converter valve hall. The system design makes full use of the waste heat generated during the operation of the converter valve, and through reasonable distribution and conversion, realizes combined heat and power supply. On the basis of meeting the heating demand in winter and cooling demand in summer of the converter station, the system can significantly reduce the consumption of water resources.

[0106] As Figure 1 shown, the overall design of the present invention: This system combines a heat pump system and a lithium bromide absorption refrigeration system in series to achieve efficient utilization of waste heat. The heat pump system is equipped with a recuperator, and the selection of specific working fluids will be described in detail later due to the involved calculations. The working fluid of the lithium bromide absorption refrigeration system is selected as a water-lithium bromide combination, and a single-effect unit can meet the requirements of this design. In addition to the four main heat exchangers, the system also includes two expansion valves and a heat exchanger for lithium bromide solution. The chilled water system flows through the absorber and condenser in series in turn to complete the cooling task.

[0107] The two systems are connected by a small hot water circulation system. The high-temperature hot water output by the heat pump system enters the generator of the lithium bromide absorption system. The high-temperature hot water heats the lithium bromide solution, causing the water to evaporate and enter the condenser and condense into a liquid state. The remaining high-concentration lithium bromide solution then returns to the absorber after passing through the solution heat exchanger. The hot water after cooling returns to the condenser of the heat pump system and enters the next cycle.

[0108] In the whole system, there are the following five circulation processes:

[0109] 1. The circulation of the heat pump working fluid in the heat pump system;

[0110] 2. The circulation of the converter valve cooling water;

[0111] 3. The circulation of the hot water output by the heat pump between the condenser of the heat pump and the generator of the lithium bromide absorption system;

[0112] 4. Circulation of water (steam) in the lithium bromide absorption system;

[0113] 5. Circulation of lithium bromide solution in the absorption system.

[0114] Through this multi-level circulation design, the system can efficiently integrate thermal energy resources and achieve the dual goals of heating and cooling.

[0115] Performance analysis of waste heat recovery invention: According to the research results of the previous visit to the Jinguan Converter Station, the invention is based on the cooling load of 280 kW of the valve hall air conditioner in the converter station as the basis for system performance design. The heat pump working fluids are initially selected as R134a and CO2. The two are alternative working fluids because of their excellent thermodynamic properties, good heat transfer and flow performance, and wide application in engineering practice. In addition, these two working fluids have high safety, chemical stability and thermal stability, and can meet the system operation requirements.

[0116] 1) Mathematical model of heat pump system

[0117] According to the driving method, heat pumps are mainly divided into vapor compression heat pumps and absorption heat pumps. Absorption heat pumps can be further divided into the first type of absorption heat pump (heat-increasing type) and the second type of absorption heat pump (temperature-raising type). Combining the actual needs of waste heat utilization in the converter station, the invention has studied and analyzed R134a, CO2 vapor compression heat pumps and lithium bromide absorption heat pumps.

[0118] When establishing the analysis model of the heat pump system, the following assumptions are made in the invention:

[0119] 1. The system is in a stable circulation state.

[0120] 2. The heat dissipation loss between the equipment and the environment is ignored.

[0121] 3. The flow resistance and heat loss in the pipeline are not considered.

[0122] 4. The flow rate of the system working fluid is measured in unit flow rate.

[0123] A conventional R134a compression heat pump system generally consists of a compressor, a condenser, a heat exchanger, an evaporator and a throttle valve. The system flow and the system thermodynamic cycle process are as Figure 2 Figure 3 shown.

[0124] Evaporator model

[0125] t 1H = t 6H = t e

[0126] p 1H = p 6H = pe

[0127] Heat exchanger model

[0128] t 2H = t 1H + Δt

[0129] p 2H = p e

[0130] p 5H = p c

[0131] t sH = f(h sH , p sH )

[0132] Condenser model

[0133] p 3H = p 4H = p c

[0134] t 3H = f(h 3H , p 3H )

[0135] t 4H = t c

[0136] Evaporator heat load

[0137] q e = h 1H - h 6H

[0138] Compressor power consumption

[0139] w = w s / η is

[0140] Where w s is the isentropic compression work consumption, w s = h 3sH - h 2H η is is the compressor isentropic efficiency, generally between 0.5 and 0.8. Heat exchanger H heat load

[0141] q hx = h 2H - h 1H = h 4H - h 5H

[0142] Throttle valve model

[0143] h5H = h 6H

[0144] q h = h 3H -h 4H

[0145] Heat pump heating coefficient

[0146]

[0147] In this model, given the evaporation temperature t e , the condensation temperature t c , and the suction superheat temperature Δt, the thermodynamic calculation of the system can be completed, that is, the input matrix is

[0148] I = [t e , t c , Δt]

[0149] For a CO2 heat pump system, the outlet temperature t of the gas cooler needs to be introduced co . That is, the input matrix is

[0150] I = [t e , t c , Δt, t co

[0151] Below Figure 4 and Figure 5 show the variation law of the COP of the CO2 heat pump with the evaporation temperature under different condensation pressures. It can be seen from the figure that the decrease in the condensation pressure increases the COP, and it can also be seen that the increase in the evaporation temperature also increases the COP. The subsequent heat pump design parameters need to increase the evaporation temperature as much as possible while reducing the condensation pressure.

[0152] By comparing the above results, under the same condensation pressure and temperature conditions, the coefficient of performance (COP) of CO2 is higher than that of R134a. However, it should be noted that the critical temperature of R134a is 101.1 °C (4.07 MPa), while the critical temperature of CO2 is only 31.2 °C (7.38 MPa). In this system, the waste heat temperature of the commutation valve is about 40 - 50 °C. Therefore, the maximum evaporation temperature of the heat pump system can only reach about 25 °C, which makes CO2 more advantageous under low-temperature heat source conditions. The evaporation temperature of R134a can reach 35 °C or higher, thereby increasing the COP.

[0153] ​As the heat source of the absorption refrigeration system, the present invention requires that the heat exchange temperature range of the working fluid reach above 85°C. Under the specified evaporation temperature, the variation relationship of the COP of two working fluids with the condensation temperature. Since there is no phase change heat transfer of CO2 in the gas cooler, the traditional calculation method based on the condensation temperature is no longer applicable, and the present invention uses the equivalent condensation temperature method for analysis. It can be seen from the figure that under the same evaporation temperature and condensation temperature conditions, the COP of CO2 is lower than that of R134a. In addition, the high operating pressure of the transcritical CO2 heat pump system requires higher material strength, sealing performance and pipeline connection of the system, increasing the cost and reducing the economic efficiency of the system.

[0154] Based on the above analysis, the present invention finally selects R134a as the heat pump working fluid for subsequent calculation and analysis.

[0155] The second type of lithium bromide absorption heat pump cycle is driven by medium and low temperature waste heat, where a part of the heat is released to a lower temperature low-temperature heat source, and the other part is provided to a high-temperature heat source. The following figure shows the representation of the second type of lithium bromide absorption heat pump cycle process in the enthalpy-concentration (h-w) Figure 6 representation.

[0156] Figure 6 In it, 5-4 is the process of dilute solution generation; 4-8 is the heat exchange process of concentrated solution in the solution heat exchanger; 8-6 is the heat exchange process of concentrated solution in the absorber; 6-2 is the absorption process of the absorber; 2-7 is the heat exchange process of dilute solution in the solution exchanger; 7-5 is the process of heating the dilute solution to boiling in the generator.

[0157] Lithium bromide working fluid physical property model

[0158] t LiBr = f1(P, w)

[0159] w = f2(P, t)

[0160] h LiBr = f3(w, t)

[0161] Solution heat exchanger model

[0162] h w = f4(t)

[0163] h vap = f s (P, t)

[0164] Q E = m w (h1 - h3) = m w C p (t WEi - t WEo )

[0165] Q A = m r h8 + m w h1 - m a h2 = m WA C p (t WAo - t WAi )

[0166] Q C = m w (h 4' - h3) = m WC C p (t WCo - t WCi )

[0167] Q G = m r h4 + m w h4. - m a h7 = m WG C p (t WGi - t WGo )

[0168] Q H = m r (h8 - h4) = m a (h2 - h7)

[0169] Coefficient of performance

[0170]

[0171] Air release range

[0172] Δw = w r - w a

[0173] Circulation ratio

[0174]

[0175] In the above equations, mw, mr, and ma are the refrigerant water flow rate, strong solution flow rate, and weak solution flow rate respectively, with the unit of kg / s. wr and wa are the concentrations of the lithium bromide strong solution and weak solution; Q is the heat load of the equipment, with the unit of kW; P is the pressure, with the unit of kPa; t is the temperature, with the unit of °C; h is the enthalpy value of the fluid, with the unit of kJ / kg.

[0176] Regarding the problem of waste heat recovery from low-temperature converter valves, the waste heat water discharged from the system is used as the driving heat source for a second-generation absorption heat pump. Here, the outlet temperature of the hot water from the evaporator WEo t, the outlet temperature of the hot water from the generator WGo t, the inlet and outlet temperatures of the cooling water in the condenser WCo t, and the outlet temperature of the circulating hot water from the absorber WAo t are taken as known variables to determine the operating state of the lithium bromide second-generation absorption heat pump system.

[0177] As Figure 7 and Figure 8 shown, under the condition that other conditions remain unchanged, the influence of the cooling water outlet temperature on the COP and the blowdown coefficient is as follows: as the cooling water outlet temperature increases, the condensation temperature increases accordingly, and Δw (solution concentration difference) shows a linear decreasing trend, resulting in a gradual decrease in the COP. This is because the increase in the condensation temperature increases the generator pressure, thereby reducing the concentration of the outlet concentrated solution. Although a lower condensation temperature helps to improve the performance of the heat pump system, it will also lead to an increase in the concentration of the concentrated solution, increasing the risk of crystallization of the lithium bromide solution. Therefore, in the system design, it is necessary to improve the performance by reducing the cooling water outlet temperature, and at the same time control the concentration of the concentrated solution within a reasonable range to avoid crystallization.

[0178] The circulating water at the outlet of the absorber is the hot water that meets the demand output by the second-generation absorption heat pump. To drive the lithium bromide absorption refrigerator, the temperature of this hot water needs to be not lower than 85°C. As can be seen from the figure, as the water temperature at the outlet of the absorber increases, the heating coefficient of the system gradually decreases, and Δw shows a linear decreasing trend. This indicates that the increase in the absorption temperature will weaken the absorption effect of the absorber, thereby reducing the performance coefficient of the system.

[0179] Combined with the current situation of the waste heat of the converter valve, the second-generation absorption heat pump requires cooling water at a lower temperature to operate. However, limited by the layout conditions of the converter valve hall, it is difficult to meet this requirement. In addition, when the required hot water temperature is relatively high, the heat pump performance coefficient of the system decreases significantly.

[0180] Considering the above factors, the R134a vapor compression heat pump is selected as the preferred invention. Through analysis, it can be seen that appropriately increasing the evaporation temperature and reducing the condensation temperature helps to improve the overall performance of the system. Based on the waste heat water temperature of 45°C and the hot water heating demand of 85°C, the evaporation temperature of the system is determined to be 35°C, and the condensation temperature is 90°C.

[0181] In this invention, the compressor efficiency is set to 0.8, while the efficiency of the compressor of an actual vapor compression heat pump is usually between 0.5 and 0.8. The state parameters and calculation results of each cycle point of the heat pump system are as follows.

[0182] State parameters of each cycle point of the heat pump

[0183]

[0184]

[0185] 2) Absorption refrigeration system

[0186] To simplify the analysis and calculation of a single-effect lithium bromide absorption refrigeration system, the following assumptions are set:

[0187] 1. The system is operating under steady-state conditions.

[0188] 2. The pressure drop and heat loss in the system pipeline are ignored.

[0189] 3. The lithium bromide solution at the outlet of each component is in a saturated state.

[0190] 4. The influence of the recirculation ratio of the dilute solution in the absorber on the system is ignored, and it is assumed that the recirculation ratio f = 0.

[0191] The condensation temperature of the absorption system is set as t ak , and the system condensation pressure is set as P ak , Generally, the set condensation temperature is about 2 - 7 °C higher than the temperature at the outlet of the condenser. In this invention, 3 °C is taken. It can be calculated from the following formula

[0192]

[0193] P ak = f(t ak )

[0194] The evaporation temperature is set as t ae and the evaporation pressure is set as P ae , Generally, the evaporation temperature is about 2 - 4 °C lower than the temperature of the refrigerant outlet. In this invention, 2 °C is taken here, then there is

[0195]

[0196] P ae = f(t ae )

[0197] The outlet temperature t of the dilute solution in the absorber 1A is generally 3 - 5 °C higher than the cooling water temperature at the outlet of the absorber. Taking a smaller value is beneficial to the absorption effect

[0198]

[0199] The pressure P in the absorber a is generally slightly lower than the evaporation pressure, and the difference is about 10 - 70 Pa. Its ratio relative to the evaporation pressure is 1% - 4%. If this pressure drop is ignored, it may have a certain impact on the accuracy. Therefore, this invention considers this pressure drop. Then it can be calculated from the following formula

[0200] Pa = P ae -10 Pa

[0201] The concentration of the strong lithium bromide solution is set as w r , and the concentration of the strong solution is set as w a , and the concentrations of the strong and weak solutions are taken

[0202] The difference is 0.056. The concentration difference is the air release range, and this value is generally taken as a certain design value between 0.025 and 0.07 in industry. In engineering applications, the concentration of the strong lithium bromide solution generally ranges from 0.55 to 0.60, and the concentration of the weak solution ranges from 0.50 to 0.55. It is verified that the concentrations of the two solutions taken in this article are within this range. The generation pressure p s is usually taken to be equal to the condensation pressure P ak , and according to the industrial design requirements, the temperature t of the strong lithium bromide solution when it flows out of the heat exchanger 6A must exceed the crystallization temperature corresponding to the strong lithium bromide solution by more than 10°C. The cold-end temperature difference in industry is generally 15 - 25°C. In this article, 15°C is taken. Then, from the following formula, we can get

[0203]

[0204] The temperature t of the weak solution when it flows out of the heat exchanger 3A , and the solution circulation ratio is set as a That is

[0205]

[0206] Then the outlet temperature of the weak solution is

[0207] t 3A = f(h 3A , w a )

[0208] The calculation method of the generator heat load is as follows

[0209] Q g = m a ·[h 9A +(a - 1)·h 5A - a·h 3A )] The calculation method of the absorber heat load is as follows

[0210] Q a = m a ·[h 12A +(a - 1)·h 6A - a·h 1A )] The calculation method of the evaporator heat load is as follows

[0211] Q ae = m a ·(h12A -h 11A )

[0212] The calculation method of the condenser heat load is as follows:

[0213] Q ak = m a ·(h 9A -h 10A )

[0214] The calculation method of the solution heat exchanger heat load is as follows:

[0215] Q a-a = m a ·(a - 1)·(h 5A -h 6A )

[0216] The coefficient of performance of the system is:

[0217]

[0218] COP T = COP A ·COP H (3 - 50)

[0219] Energy analysis results of the lithium bromide absorption system

[0220]

[0221]

[0222] The calculation results show that while the converter valve waste heat system provides 280 kW of cooling capacity for the valve hall, it utilizes 255.25 kW of waste heat and consumes 112.75 kW of mechanical work. The overall coefficient of performance (COP) of the system is 2.48. The cooling capacity of the system can be adjusted according to actual needs, and the required waste heat is only a part of the available heat.

[0223] The coefficient of performance of this system is comparable to that of traditional mechanical refrigeration methods. It can be used as an auxiliary invention for valve hall refrigeration or an alternative invention when the mechanical refrigeration method fails, ensuring the stability and reliability of the system operation.

[0224] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above methods. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM), etc.

[0225] It should be understood that the detailed description of the technical solutions of the present invention by means of the preferred embodiments above is illustrative rather than restrictive. Those of ordinary skill in the art can modify the technical solutions recorded in each embodiment on the basis of reading the specification of the present invention, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims

1. A model of a converter valve waste heat recovery device, characterized in that: The described model includes: a waste heat recovery device composed of a heat pump system and a lithium bromide absorption refrigeration system connected in series; The heat pump system is equipped with a recuperator. The working medium of the lithium bromide absorption refrigeration system is a water-lithium bromide combination, which includes a generator, a condenser, an evaporator, and an absorber, as well as two expansion valves and a solution heat exchanger. The high-temperature hot water output by the heat pump system enters the generator of the lithium bromide absorption refrigeration system through a small hot water circulation system, heating the lithium bromide solution to evaporate water into the condenser and condense it into a liquid state. The remaining high-concentration lithium bromide solution flows back to the absorber after passing through the solution heat exchanger. The cold water system sequentially passes through the absorber and the condenser to complete the cooling task. The entire system realizes the efficient utilization of the waste heat of the commutation valve through five circulation processes, providing heating and refrigeration functions for the commutation valve hall.

2. The model of a converter valve waste heat recovery device according to claim 1, characterized in that: The described waste heat recovery equipment model has the following five circulation processes: (1) The circulation of the heat pump working medium in the heat pump system; (2) The circulation of the commutation valve cooling water; (3) The circulation of the hot water output by the heat pump between the heat pump condenser and the generator of the lithium bromide absorption system; (4) The circulation of water (steam) in the lithium bromide absorption system; (5) The circulation of the lithium bromide solution in the absorption system; Through this multi-level circulation design, the system can efficiently integrate thermal energy resources and achieve the dual goals of heating and refrigeration.

3. The model of a converter valve waste heat recovery device according to claim 1, wherein: When establishing the analysis model of the heat pump system, the following assumptions are made: (1) The system is in a stable circulation state; (2) The heat dissipation loss between the equipment and the environment is ignored; (3) The flow resistance and heat loss in the pipeline are not considered; (4) The flow rate of the system working medium is measured in unit flow rate.

4. A commutation valve waste heat recovery equipment model according to claim 1, characterized in that: The described waste heat recovery equipment model includes: Evaporator model: t 1H = t 6H = t e p 1H = p 6H = p e Heat exchanger model: t 2H = t 1H + Δt p 2H = p e p 5H = p c t sH = f(h sH , p sH ) Condenser model: p 3H = p 4H = p c t 3H = f(h 3H , p 3H ) t 4H = t c Evaporator heat load: q e = h 1H -h 6H Compressor power consumption: w = w s / η is where w s is the work consumed in isentropic compression, and w s = h 3sH - h 2H η is is the isentropic efficiency of the compressor, ranging from 0.5 to 0.8; Heat exchanger H heat load: q hx = h 2H -h 1H = h 4H -h 5H Throttle valve model: h5H = h6H q h = h 3H -h 4H Heat pump heating coefficient: In this model, given the evaporation temperature t e , the condensation temperature t c , and the suction superheat temperature Δt, the thermodynamic calculation of the system can be completed, that is, the input matrix is I = [t e , t c , Δt].

5. The model of a converter valve waste heat recovery device according to claim 1, characterized in that: For the analysis and calculation of the lithium bromide absorption refrigeration system, the following assumed conditions are set: (1) The system is in a steady-state operating condition; (2) The pressure drop and heat loss in the system pipeline are ignored; (3) The lithium bromide solution at the outlet of each component is in a saturated state; (4) The influence of the recirculation ratio of the dilute solution in the absorber on the system is ignored, and it is assumed that the recirculation ratio f = 0.

6. The model of a converter valve waste heat recovery device according to claim 5, wherein: The lithium bromide working medium property model of the described lithium bromide absorption refrigeration system t LiBr = f1(P, w) w = f2(P, t) h LiBr = f3(w, t) Solution heat exchanger model: h w = f4(t) h vap = f s (P, t) Q E = m w (h1 - h3) = m w C p (t WEi - t WEo ) Q A = m r h8 + m w h1 - m a h2 = m WA C p (t WAo - t WAi ) Q C = m w (h 4' - h3) = m WC C p (t WCo - t WCi ) Q G = m r h4 + m w h4 - m a h7 = m WG C p (t WGi - t WGo ) Q H = m r (h8 - h4)= m a (h2 - h7) Coefficient of performance: Gas release range: Δw = w r -w a Circulation ratio: In the above equations, m w , m r and m a are the refrigerant water flow rate, strong solution flow rate, and weak solution flow rate respectively, with the unit of kg / s. w r , w a are the lithium bromide strong solution and weak solution concentrations respectively; Q is the heat load of the equipment, with the unit of k W ; P is the pressure, with the unit of kPa; t is the temperature, with the unit of °C; h is the fluid enthalpy value, with the unit of kJ / kg.

7. A method for a model of a waste heat recovery device of a converter valve, the method being applicable to the model described in any one of claims 1-6, characterized in that: The cold end temperature difference in industry is generally 15 - 25 °C. Taking 15 °C, the following formula can be obtained The temperature t of the dilute solution exiting the heat exchanger 3A , assuming the solution circulation ratio is a, That is Then the outlet temperature of the dilute solution: t 3A = f(h 3A , w a ) The calculation method of the generator heat load is as follows: Q g = m a · [h 9A + (a - 1)·h 5A - a·h 3A )] The calculation method of the absorber heat load is as follows: Q a = m a · [h 12A + (a - 1)·h 6A - a·h 1A )] The calculation method of the evaporator heat load is as follows: Q ae = m a ·(h 12A - h 11A ) The calculation method of the condenser heat load is as follows: Q ak = m a ·(h 9A - h 10A ) The calculation method of the solution heat exchanger heat load is as follows: Q a-a = m a ·(a - 1)·(h 5A - h 6A ) The system refrigeration coefficient is: COP T = COP A ·COP H (3 - 50).

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