Method and system for calculating efficiency of booster pump in steam feed pump set

Abstract

The invention discloses a method and a system for calculating the efficiency of a booster pump in a steam feed pump set, belongs to the technical field of auxiliary equipment of thermal generator sets, and solves the problems of large error and low precision of the efficiency calculation result of the booster pump in the existing steam feed pump set. The total shaft power output to the combined pump by the small steam turbine is derived according to the effective power of the combined pump, then the effective power of the feed pump in the combined pump and the shaft power output to the feed pump by the small steam turbine are separated, and then the shaft power output to the booster pump by the small steam turbine can be obtained. The booster pump efficiency is calculated according to the ratio of the effective power of the booster pump to the shaft power transmitted to the booster pump by the small steam turbine through the transmission shaft, the booster pump efficiency can be prevented from being measured directly depending on the temperature difference, the problems that the error of booster pump efficiency calculation based on a thermodynamic method is too large, and engineering application is difficult are solved, the number of measuring points is reduced, and the cost is reduced. The system complexity is simplified, and the design cost is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of auxiliary equipment of thermal power generating sets, and relates to a method and system for calculating the efficiency of a pre-pump in a steam-driven water feed pump set. Background Art

[0002] Steam-driven feedwater pump systems are a key auxiliary equipment component of large thermal power plants. These systems consist of a pre-pump, feedwater pump, and small steam turbine. Their power consumption accounts for a significant proportion of the unit's total output power, and therefore their efficiency significantly impacts the efficiency of the entire power plant. Currently, most newly built 600MW / 1000MW coal-fired power units utilize a coaxial arrangement of the pre-pump and feedwater pump. However, determining the efficiency of the pre-pump within a steam-driven feedwater pump system presents significant challenges.

[0003] Currently, the efficiency of steam-driven water supply pumps is primarily determined using thermodynamic methods. This method, also known as the micro-temperature difference method, is based on the first and second laws of thermodynamics. Based on the steady-state flow energy equation established by the first law of thermodynamics, it is known that pump efficiency can be calculated by simply measuring the pump inlet and outlet temperatures and pressures. The temperature difference stems from two factors: first, the fluid undergoes an isentropic compression process from the pump inlet to the outlet; second, the work done on the fluid by the rotation of the pump impeller not only generates useful power for the fluid but also generates heat energy converted from losses such as friction in the bearings and shaft seals, and heat dissipation from the pump casing.

[0004] Prior art, such as the invention patent with application publication number CN108019344A, discloses a method for testing the efficiency of an electric water supply pump group. The method uses a pressure gauge, a thermometer, a differential pressure transmitter, and a power measuring device to detect the inlet pressure and temperature, outlet pressure and temperature of the front pump, the inlet fluid flow, outlet pressure and temperature of the water supply pump, the pressure, temperature and flow of the intermediate tap, as well as the power and power factor of the motor. According to the law of conservation of energy, the power is converted into the effective power of the electric water supply pump group, thereby calculating the efficiency of the tested electric water supply pump group.

[0005] In fact, since the output and capacity of the pre-pump are much smaller than those of the feed water pump, the temperature rise of the water side at the inlet and outlet of the pump is very small, and it is difficult to accurately measure the inlet and outlet temperature difference of the pre-pump. For example, the design operating temperature rise of the pre-pump of the steam-driven feed water pump group of a 1000MW coal-fired power unit is only 0.2℃, while the measurement error of the commonly used industrial-grade Pt100 thermal resistor is about 1℃. This leads to a large error in measuring the efficiency of the pre-pump if the thermodynamic method is still used. In actual experiments and engineering applications, it is difficult to use the above method to determine the efficiency of the pre-pump in the steam-driven feed water pump group. Summary of the Invention

[0006] The technical solution of the present invention is used to solve the problem of large error and low precision in the calculation result of the efficiency of the pre-pump in the existing pneumatic water supply pump group.

[0007] The present invention solves the above technical problems through the following technical solutions:

[0008] A method for calculating the efficiency of a pre-pump in a steam-driven water supply pump group comprises the following steps:

[0009] S1. A combined pump model is established based on the coaxial arrangement of the pre-pump and the feed water pump, and the combined pump efficiency is calculated based on the combined pump inlet water parameters and the combined pump outlet water parameters;

[0010] S2. Calculate the effective power of the combined pump and the total output shaft power of the small steam turbine based on the transmission efficiency of the coupling;

[0011] S3. Calculate the effective power of the water feed pump based on the water parameters of the water feed pump, and calculate the shaft power of the water feed pump based on the transmission efficiency of the coupling;

[0012] S4. Based on the difference between the total output shaft power of the small steam turbine and the shaft power of the feed water pump, combined with the effective power of the pre-pump, deduce the efficiency of the pre-pump.

[0013] Furthermore, the combined pump inlet water parameters in S1 include the pre-pump inlet pressure p1 and the pre-pump inlet temperature t1, and the combined pump outlet water parameters include the feed water pump outlet pressure p3 and the feed water pump outlet temperature t3.

[0014] Furthermore, the calculation of the combined pump efficiency described in S1 is specifically as follows: based on the pressure difference, flow rate difference and fluid density between the pre-pump inlet and the feed pump outlet, combined with the gravity acceleration parameter, the ratio of the combined pump head to the enthalpy increment is calculated, and the combined pump efficiency is obtained after adjustment by the correction coefficient, which is expressed using the following logic:

[0015]

[0016] Among them, η 联 is the combined pump efficiency, g is the acceleration of gravity, c is the correction coefficient, H 13 is the combined pump head, in m; h1 is the water enthalpy value obtained from the combined pump inlet water parameters, in kJ / kg; h3 is the water enthalpy value obtained from the combined pump outlet water parameters, in kJ / kg;

[0017] Use the following logic to calculate the combined pump head H 13 :

[0018]

[0019] Where ρ2 is the average density of the combined pump inlet and outlet, in kg / m 3 ; v1 and v3 are the inlet and outlet flow rates of the combined pump, respectively, in m / s; ΔZ 13It is the height difference between the inlet and outlet center lines of the combined pump, in meters.

[0020] Furthermore, the calculation of the total shaft power output of the small steam turbine in S2 is specifically as follows: based on the combined pump flow, combined pump head and gravity acceleration parameters, the effective power of the combined pump is calculated, and the total shaft power is obtained after considering the coupling transmission efficiency, which is expressed by the following logic:

[0021]

[0022] P 总轴 =P3 / η 联轴器

[0023] Among them, P3 is the effective power of the combined pump, in kW; Q is the flow rate, in t / h; P 总轴 is the total shaft power output of the small steam turbine, η 联轴器 is the transmission efficiency of the coupling.

[0024] Furthermore, one end of the transmission shaft of the small steam turbine is connected to the rotor of the pre-pump through a coupling, and the other end of the transmission shaft of the small steam turbine is connected to the rotor of the feed water pump through a coupling. The pre-pump and the feed water pump are coaxially arranged at both ends of the small steam turbine.

[0025] Furthermore, the feed water pump inlet water parameters in S3 include the feed water pump inlet pressure p2 and the feed water pump inlet temperature t2.

[0026] Furthermore, the step S3 includes the following steps:

[0027] S31. Based on the pressure difference, flow rate difference and fluid density of the feed water pump inlet and outlet, combined with the gravity acceleration parameter, calculate the ratio of the feed water pump head to the enthalpy value increment, and adjust it with the correction coefficient to obtain the feed water pump efficiency, which is expressed using the following logic:

[0028]

[0029] Among them, η 给水泵 is the efficiency of the water pump, H 23 is the head of the water pump, in m; h2 is the enthalpy of water obtained from the water inlet parameters of the water pump, in kJ / kg;

[0030] Use the following logic to calculate the feed pump head H 23 :

[0031]

[0032] Among them, p2 and p3 are the inlet and outlet pressures of the water pump, respectively, in Pa; v2 and v3 are the inlet and outlet flow rates of the water pump, respectively, in m / s; ρ3 is the average density of the inlet and outlet of the water pump, in kg / m3 ; ΔZ 23 The height difference between the inlet and outlet center lines of the water pump, in meters;

[0033] S32. Calculate the effective power of the water feed pump based on the flow rate, head, and gravity acceleration parameters of the water feed pump. Calculate the shaft power of the water feed pump in combination with the transmission efficiency of the coupling. Use the following logic to express:

[0034]

[0035] P water pump shaft = (P2 / η 给水泵 ) / η 联轴器

[0036] Among them, P2 is the effective power of the water pump, P 给水泵轴 is the shaft power of the water feed pump.

[0037] Furthermore, the S4 includes the following steps:

[0038] S41. Calculate the effective power of the pre-pump based on the pre-pump flow rate, pre-pump head, and gravity acceleration parameters, using the following logic:

[0039]

[0040] Among them, P1 is the effective power of the front pump, H 12 is the head of the pre-pump, in m;

[0041] Use the following logic to calculate the head H of the pre-pump 12 :

[0042]

[0043] Among them, p1 and p2 are the inlet pressures of the fore pump and the feed pump, respectively, in Pa; v1 and v2 are the inlet flow rates of the fore pump and the feed pump, respectively, in m / s; ρ1 is the average density of the inlet and outlet of the fore pump, in kg / m 3 ; ΔZ 12 The height difference between the inlet and outlet center lines of the front pump, in meters;

[0044] S42. The difference between the total shaft power output of the small steam turbine and the shaft power of the feedwater pump is used as the shaft power of the pre-pump. Combined with the effective power of the pre-pump, the efficiency of the pre-pump is calculated using the following logic:

[0045]

[0046] Among them, η 前置泵 is the efficiency of the pre-pump.

[0047] The present invention also provides a system for calculating the efficiency of a pre-pump in a steam-driven water supply pump group, comprising:

[0048] Combined pump construction module, used to establish a combined pump model based on the coaxially arranged pre-pump and feed water pump, and calculate the combined pump efficiency based on the combined pump inlet water parameters and combined pump outlet water parameters;

[0049] The total shaft power calculation module is used to calculate the effective power of the combined pump and the output total shaft power of the small steam turbine in combination with the transmission efficiency of the coupling;

[0050] The water pump shaft power calculation module is used to calculate the effective power of the water pump based on the water parameters of the water pump inlet and the shaft power of the water pump in combination with the transmission efficiency of the coupling;

[0051] The fore pump efficiency calculation module is used to derive the fore pump efficiency based on the difference between the output total shaft power of the small steam turbine and the shaft power of the feed water pump, combined with the effective power of the fore pump.

[0052] The advantages of the present invention are:

[0053] The present invention provides a method for indirectly deriving the efficiency of a pre-pump by distributing and calculating shaft power. First, the overall efficiency of the pre-pump and the feed water pump is calculated by a combined pump model. The total shaft power output by a small steam turbine to the combined pump is derived based on the effective power of the combined pump. Then, the effective power of the feed water pump in the combined pump and the shaft power output by the small steam turbine to the feed water pump are separated. Thus, the shaft power output by the small steam turbine to the pre-pump can be obtained. The efficiency of the pre-pump is derived based on the ratio of the effective power of the pre-pump to the shaft power transmitted by the small steam turbine to the pre-pump through the transmission shaft.

[0054] The present invention can avoid directly relying on temperature difference to measure the efficiency of the fore pump, and overcome the problem that the error of calculating the efficiency of the fore pump based on thermodynamic methods is too large and difficult to apply in engineering; the present invention does not require a high-precision temperature sensor and can also realize the efficiency calculation of the fore pump and the steam-driven feed water pump group, and does not need to be based on the relevant equipment parameters of the small steam turbine (such as exhaust enthalpy, etc.) to directly obtain the output total shaft power of the small steam turbine, thereby reducing the influence of parameter measurement errors on the calculation results, reducing the number of measuring points, simplifying the system complexity, and greatly reducing the design cost.

[0055] The present invention simplifies the system complexity by establishing a combined pump model and avoids directly measuring the small temperature rise of the pre-pump; in the process of indirect calculation, the present invention also takes into account the energy loss of the coupling during the energy transmission from the small turbine to the combined pump, and improves the calculation accuracy of the pre-pump efficiency by correcting the coupling efficiency; in addition, the present invention takes into account the fluid compressibility and other losses in the process of calculating the combined pump efficiency, introduces a correction coefficient to correct the efficiency calculation result, and reduces the influence of parameter errors on the calculation result. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a flow chart of a method for calculating the efficiency of a pre-pump in a steam-driven water supply pump group according to the first embodiment of the present invention;

[0057] Figure 2 This is a schematic diagram of the shaft connection of a steam-driven water supply pump group in which a pre-pump and a water supply pump are coaxially arranged according to the first embodiment of the present invention;

[0058] Figure 3 Schematic diagram of the arrangement of test points for the combined pump model according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0060] The technical solution of the present invention is further described below with reference to the accompanying drawings and specific embodiments:

[0061] Example 1

[0062] like Figure 1 Specifically, a method for calculating the efficiency of a pre-pump in a steam-driven water supply pump group is disclosed, comprising the following steps:

[0063] S1. A combined pump model is established based on the coaxial arrangement of the pre-pump and the feed water pump, and the combined pump efficiency is calculated based on the combined pump inlet water parameters and the combined pump outlet water parameters;

[0064] like Figure 3 As shown, the coaxially arranged pre-pump and feed water pump are regarded as a combined pump, and a combined pump model is established. In this embodiment, the pre-pump inlet pressure p1 and pre-pump inlet temperature t1 are collected by a measuring point set at the pre-pump inlet as the inlet water parameters of the combined pump, and the feed water pump outlet pressure p3 and feed water pump outlet temperature t3 are collected by a measuring point set at the feed water pump outlet as the outlet water parameters of the combined pump. The combined pump efficiency η is calculated using the following logic 联 :

[0065]

[0066] Where g is the acceleration due to gravity, which is 9.81 m / s 2 ;H 13is the combined pump head, in m; c is the correction coefficient, which is taken as 0.01 in this implementation; h1 is the enthalpy of water obtained from the pre-pump inlet pressure p1 and temperature t1 (combined pump inlet water parameters), in kJ / kg; h3 is the enthalpy of water obtained from the water supply pump outlet pressure p3 and temperature t3 (combined pump outlet water parameters), in kJ / kg.

[0067] In this embodiment, the enthalpy value is determined by looking up the thermodynamic property table or model calculation based on the corresponding pressure and temperature parameters.

[0068] The combined pump head H is expressed using the following logic: 13 :

[0069]

[0070] Among them, p1 and p3 are the inlet pressure p1 of the fore pump and the outlet pressure p3 of the water pump (i.e. the inlet and outlet pressures of the combined pump), respectively, in Pa; ρ3 is the average density of the inlet and outlet of the combined pump, in kg / m 3 v1 and v3 are the inlet and outlet flow rates of the combined pump, respectively. The flow rate is obtained by dividing the fluid volume by the cross-sectional area of ​​the pipe, and the unit is m / s. ΔZ 13 It is the height difference between the inlet and outlet center lines of the combined pump, in meters.

[0071] This embodiment reflects the energy conversion efficiency of the combined pump group through the ratio of the head to the enthalpy difference. Specifically, this embodiment uses the product of the combined pump head and the gravitational acceleration to represent the total mechanical energy of the fluid lifted by the combined pump, uses the enthalpy difference of the fluid to represent the total energy added by the fluid when flowing through the combined pump (including heat energy, pressure energy and kinetic energy), and uses the ratio of the mechanical output work (energy corresponding to the head) to the total energy input (enthalpy difference) of the fluid to represent the efficiency of the combined pump. At the same time, the influence of fluid loss on the efficiency calculation of the pump group is also considered, and a correction coefficient (1+c) is introduced to correct the efficiency of the combined pump. At this time, the efficiency of the combined pump η 联 Indicates the efficiency of the fore pump and feed pump as a whole.

[0072] S2. Calculate the effective power P3 of the combined pump and calculate the total output shaft power P of the small steam turbine based on the transmission efficiency of the coupling. 总轴 ;

[0073] The existing steam-driven feedwater pump group includes a small steam turbine, coupling, feedwater pump, pre-pump, condenser and other equipment. The small steam turbine is the prime mover, which drives the small steam turbine to rotate through steam work. The transmission shaft of the small steam turbine is connected to the pump rotor through a coupling. Figure 2 As shown, the two ends of the small steam turbine are connected to the pre-pump and the feed water pump respectively, so the pre-pump and the feed water pump can be arranged coaxially.

[0074] In this embodiment, the effective power P3 of the combined pump is calculated based on the combined pump flow, combined pump head and gravity acceleration parameters, and the total shaft power P is obtained after correction by the coupling transmission efficiency. 总轴 , using the following logic:

[0075]

[0076] P 总轴 =P3 / η 联轴器

[0077] Where P3 is the effective power of the combined pump, in kW; Q is the flow rate, in t / h. The feed water flows through the pre-pump and the feed water pump in sequence. Specifically, the feed water first passes through the pre-pump, the pressure is increased once, and then passes through the feed water pump, the pressure is increased again; η 联轴器 is the transmission efficiency of the coupling, in this embodiment, η is taken 联轴器 is 0.98.

[0078] In this embodiment, the rotors of the feed water pump and the pre-pump are connected to the two ends of the transmission shaft of the small steam turbine through couplings, respectively. 联轴器 It is a kind of transfer efficiency, which indicates the smaller loss in the process of energy transfer. In this embodiment, η is calibrated by preset empirical values ​​or measured data. 联轴器 The value of .

[0079] This embodiment directly calculates the effective power P3 of the combined pump based on the flow rate and head of the combined pump, and inversely deduces the total shaft power P of the small steam turbine according to the connection relationship between the combined pump and the small steam turbine. 总轴 This embodiment also considers the energy loss of the coupling during the energy transmission from the small steam turbine to the combined pump, by calculating the coupling efficiency η 联轴器 Correction, improve the calculation accuracy of the pre-pump efficiency, without the need to rely on the relevant equipment parameters of the small steam turbine (such as exhaust enthalpy, etc.) to directly obtain the output total shaft power P of the small steam turbine 总轴 .

[0080] S3. Calculating the efficiency of the water feed pump according to the water feed pump inlet parameters, calculating the effective power of the water feed pump, and calculating the shaft power of the water feed pump in combination with the transmission efficiency of the coupling, including the following steps:

[0081] S31. Calculate the efficiency of the water supply pump based on the water supply pump inlet water parameters.

[0082] like Figure 3 As shown, in this embodiment, the feed water pump inlet pressure p2 and feed water pump inlet temperature t2 are collected as feed water pump inlet water parameters by setting a measuring point at the feed water pump inlet, and the feed water pump efficiency η is calculated using the following logic 给水泵 :

[0083]

[0084] Among them, H 23 is the head of the water pump, in m; h2 is the enthalpy of water obtained from the inlet pressure p2 and temperature t2 of the water pump (the inlet water parameters of the water pump), in kJ / kg.

[0085] Use the following logic to calculate the feed pump head H 23 :

[0086]

[0087] Among them, p2 and p3 are the inlet and outlet pressures of the water pump, respectively, in Pa; v2 and v3 are the inlet and outlet flow rates of the water pump, respectively, in m / s; ρ3 is the average density of the inlet and outlet of the water pump, in kg / m 3 ; ΔZ 23 It is the height difference between the inlet and outlet center lines of the water pump, in meters.

[0088] S32. Calculate the effective power of the water supply pump and calculate the shaft power of the water supply pump in combination with the transmission efficiency of the coupling.

[0089] Use the following logic to calculate the effective power P2 of the water supply pump:

[0090]

[0091] Use the following logic to calculate the shaft power P of the water supply pump 给水泵轴 :

[0092] P water pump shaft = (P2 / η 给水泵 ) / η 联轴器

[0093] In this embodiment, the shaft power P of the water pump is 给水泵轴 Refers to the shaft power output from one end of the small steam turbine to the feed water pump. For the feed water pump efficiency η calculated in step S31 给水泵 , can be directly calculated based on existing thermodynamic methods by measuring the temperature (t2, t3) and pressure (p2, p3) at the inlet and outlet of the feed water pump. However, the temperature change of the flow through the pre-pump is smaller than that of the feed water pump. The accuracy of the temperature sensors installed at the inlet and outlet of the pre-pump is limited. If the efficiency of the pre-pump is calculated based on thermodynamic methods, the calculation result will be obviously unreasonable and there will be a large error. Therefore, this embodiment is based on the effective power P2 of the combined pump and the efficiency η of the feed water pump. 给水泵 Derived feedwater pump shaft power P 给水泵轴 , used to represent the shaft power output from one end of the small steam turbine to the feed water pump, and the total output shaft power P of the small steam turbine 总轴 Only the feed water pump shaft power P 给水泵轴and the pre-pump shaft power, so the present invention can deduce the pre-pump shaft power based on the combined pump model combined with the output total shaft power of the small turbine.

[0094] S4. Based on the difference between the total shaft power output of the small steam turbine and the shaft power of the feedwater pump, combined with the effective power of the fore pump, the efficiency of the fore pump is derived, which includes the following steps:

[0095] S41. Calculate the effective power P1 of the pre-pump using the following logic:

[0096]

[0097] Among them, H 12 is the head of the pre-pump, in m, and the following logic is used to calculate the head of the pre-pump H 12 :

[0098]

[0099] Among them, p1 and p2 are the inlet pressures of the fore pump and the feed pump, respectively, in Pa; v1 and v2 are the inlet flow rates of the fore pump and the feed pump, respectively, in m / s; ρ1 is the average density of the inlet and outlet of the fore pump, in kg / m 3 ; ΔZ 12 It is the height difference between the inlet and outlet center lines of the front pump, in meters.

[0100] S42. Based on the difference between the total shaft power output of the small steam turbine and the shaft power of the feedwater pump, use the following logic to derive the pre-pump efficiency η 前置泵 :

[0101]

[0102] In this embodiment, based on the characteristics that the pre-pump and the feed water pump are coaxially arranged at both ends of the small steam turbine, the difference P between the total shaft power output of the small steam turbine and the shaft power of the feed water pump is used. 总轴 -P 给水泵轴 Indicates the shaft power of the pre-pump and is expressed by the coupling efficiency η 联轴器 Correct the shaft power transmitted by the small steam turbine to the pre-pump, and the effective power P1 of the pre-pump can be directly calculated according to the pre-pump flow, pre-pump head and gravity acceleration parameters. The pre-pump efficiency is equal to the effective power P1 of the pre-pump, which is equal to the shaft power (P 总轴 -P 给水泵轴 )η 联轴器 This embodiment can calculate the efficiency of the pre-pump and the steam-driven water supply pump group without the need for a high-precision temperature sensor, greatly reducing the design cost.

[0103] The present invention also provides a system for calculating the efficiency of a pre-pump in a steam-driven water supply pump group, comprising:

[0104] Combined pump construction module, used to establish a combined pump model based on the coaxially arranged pre-pump and feed water pump, and calculate the combined pump efficiency based on the combined pump inlet water parameters and combined pump outlet water parameters;

[0105] The total shaft power calculation module is used to calculate the effective power of the combined pump and the output total shaft power of the small steam turbine in combination with the transmission efficiency of the coupling;

[0106] The water pump shaft power calculation module is used to calculate the effective power of the water pump based on the water parameters of the water pump inlet and the shaft power of the water pump in combination with the transmission efficiency of the coupling;

[0107] The fore pump efficiency calculation module is used to derive the fore pump efficiency based on the difference between the output total shaft power of the small steam turbine and the shaft power of the feed water pump, combined with the effective power of the fore pump.

[0108] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for calculating the efficiency of the pre-pump in a steam-driven water supply pump group, characterized in that: The following steps are involved: S1. A combined pump model is established based on the coaxial arrangement of the pre-pump and the feed water pump, and the combined pump efficiency is calculated based on the combined pump inlet water parameters and the combined pump outlet water parameters; S2. Calculate the effective power of the combined pump and the total output shaft power of the small steam turbine based on the transmission efficiency of the coupling; S3. Calculate the effective power of the water feed pump based on the water parameters of the water feed pump, and calculate the shaft power of the water feed pump based on the transmission efficiency of the coupling; S4. Based on the difference between the total output shaft power of the small steam turbine and the shaft power of the feed water pump, combined with the effective power of the pre-pump, deduce the efficiency of the pre-pump.

2. The method for calculating the efficiency of the pre-pump in a steam-driven water supply pump group according to claim 1 is characterized in that: The combined pump inlet water parameters in S1 include the pre-pump inlet pressure p1 and the pre-pump inlet temperature t1, and the combined pump outlet water parameters include the feed water pump outlet pressure p3 and the feed water pump outlet temperature t3.

3. The method for calculating the efficiency of the pre-pump in a steam-driven water supply pump group according to claim 2, characterized in that: The calculation of the combined pump efficiency described in S1 is specifically as follows: based on the pressure difference, flow rate difference and fluid density between the pre-pump inlet and the feed pump outlet, combined with the gravity acceleration parameter, the ratio of the combined pump head to the enthalpy increment is calculated, and the combined pump efficiency is obtained after adjustment by the correction coefficient, which is expressed using the following logic: Among them, η 联 is the combined pump efficiency, g is the acceleration of gravity, c is the correction coefficient, H 13 is the combined pump head, in m; h1 is the water enthalpy value obtained from the combined pump inlet water parameters, in kJ / kg; h3 is the water enthalpy value obtained from the combined pump outlet water parameters, in kJ / kg; Use the following logic to calculate the combined pump head H 13 : Where ρ2 is the average density of the combined pump inlet and outlet, in kg / m 3 ; v1 and v3 are the inlet and outlet flow rates of the combined pump, respectively, in m / s; ΔZ 13 It is the height difference between the inlet and outlet center lines of the combined pump, in meters.

4. The method for calculating the efficiency of the pre-pump in a steam-driven water supply pump group according to claim 1, characterized in that: The calculation of the total shaft power output of the small steam turbine described in S2 is specifically as follows: based on the combined pump flow, combined pump head and gravity acceleration parameters, the effective power of the combined pump is calculated, and the total shaft power is obtained after considering the coupling transmission efficiency, which is expressed using the following logic: P 总轴 =P3 / h 联轴器 Among them, P3 is the effective power of the combined pump, in kW; Q is the flow rate, in t / h; P 总轴 is the total shaft power output of the small steam turbine, η 联轴器 is the transmission efficiency of the coupling.

5. The method for calculating the efficiency of the pre-pump in a steam-driven water supply pump group according to claim 4 is characterized in that: One end of the transmission shaft of the small steam turbine is connected to the rotor of the pre-pump through a coupling, and the other end of the transmission shaft of the small steam turbine is connected to the rotor of the feed water pump through a coupling. The pre-pump and the feed water pump are coaxially arranged at both ends of the small steam turbine.

6. The method for calculating the efficiency of the pre-pump in a steam-driven water supply pump group according to claim 4, characterized in that: The feed water pump inlet water parameters in S3 include the feed water pump inlet pressure p2 and the feed water pump inlet temperature t2.

7. The method for calculating the efficiency of the pre-pump in a steam-driven water supply pump group according to claim 6, characterized in that: The S3 includes the following steps: S31. Based on the pressure difference, flow rate difference and fluid density of the feed water pump inlet and outlet, combined with the gravity acceleration parameter, calculate the ratio of the feed water pump head to the enthalpy value increment, and adjust it with the correction coefficient to obtain the feed water pump efficiency, which is expressed using the following logic: Among them, η 给水泵 is the efficiency of the water pump, H 23 is the head of the water pump, in m; h2 is the enthalpy of water obtained from the water inlet parameters of the water pump, in kJ / kg; Use the following logic to calculate the feed pump head H 23 : Among them, p2 and p3 are the inlet and outlet pressures of the water pump, respectively, in Pa; v2 and v3 are the inlet and outlet flow rates of the water pump, respectively, in m / s; ρ3 is the average density of the inlet and outlet of the water pump, in kg / m 3 ; ΔZ 23 The height difference between the inlet and outlet center lines of the water pump, in meters; S32. Calculate the effective power of the water feed pump based on the flow rate, head, and gravity acceleration parameters of the water feed pump. Calculate the shaft power of the water feed pump in combination with the transmission efficiency of the coupling. Use the following logic to express: P water pump shaft = (P2 / η 给水泵 ) / η 联轴器 Among them, P2 is the effective power of the water pump, P 给水泵轴 is the shaft power of the water feed pump.

8. The method for calculating the efficiency of the pre-pump in a steam-driven water supply pump group according to claim 7, characterized in that: The S4 comprises the following steps: S41. Calculate the effective power of the pre-pump based on the pre-pump flow rate, pre-pump head, and gravity acceleration parameters, using the following logic: Among them, P1 is the effective power of the front pump, H 12 is the head of the pre-pump, in m; Use the following logic to calculate the head H of the pre-pump 12 : Among them, p1 and p2 are the inlet pressures of the fore pump and the feed pump, respectively, in Pa; v1 and v2 are the inlet flow rates of the fore pump and the feed pump, respectively, in m / s; ρ1 is the average density of the inlet and outlet of the fore pump, in kg / m 3 ; ΔZ 12 The height difference between the inlet and outlet center lines of the front pump, in meters; S42. The difference between the total shaft power output of the small steam turbine and the shaft power of the feedwater pump is used as the shaft power of the pre-pump. Combined with the effective power of the pre-pump, the efficiency of the pre-pump is calculated using the following logic: Among them, η 前置泵 is the efficiency of the pre-pump.

9. A system for calculating the efficiency of the pre-pump in a steam-driven water supply pump group, characterized in that: include: Combined pump construction module, used to establish a combined pump model based on the coaxially arranged pre-pump and feed water pump, and calculate the combined pump efficiency based on the combined pump inlet water parameters and combined pump outlet water parameters; The total shaft power calculation module is used to calculate the effective power of the combined pump and the output total shaft power of the small steam turbine in combination with the transmission efficiency of the coupling; The water pump shaft power calculation module is used to calculate the effective power of the water pump based on the water parameters of the water pump inlet and the shaft power of the water pump in combination with the transmission efficiency of the coupling; The fore pump efficiency calculation module is used to derive the fore pump efficiency based on the difference between the output total shaft power of the small steam turbine and the shaft power of the feed water pump, combined with the effective power of the fore pump.

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