A method for online calculation of condenser pressure under variable operating conditions

Abstract

The present invention discloses an online calculation method for condenser pressure under variable working conditions, including: step 1, calculating the steam energy entering the turbine; step 2, calculating the steam energy discharged from the turbine; step 3, calculating the heat load entering the condenser; step 4, calculating the condenser cooling water volume based on the measured condenser inlet and outlet cooling water temperatures; step 5, fitting the relationship between the circulating pump running speed and the condenser cooling water volume under different circulating pump running numbers; step 6, calculating the condenser cleanliness coefficient under variable working conditions; step 7, fitting the relationship between different condenser heat loads and condenser cleanliness coefficients; step 8, calculating the condenser heat load and cooling water volume based on steps 1-4, and calculating the condenser pressure under variable working conditions based on the relationship obtained in steps 5-7. The condenser pressure under variable working conditions calculated by the present invention can be used as the condenser pressure required value for condenser thermal performance analysis, online performance monitoring, etc.

Description

Technical Field

[0001] The present invention belongs to the field of gas-steam combined cycle units, and specifically relates to a method for calculating the condenser pressure of a combined cycle unit under variable operating conditions. Specifically, the method is based on operating parameters and can accurately calculate the condenser pressure under variable operating conditions. The method can be used for variable operating condition thermal performance analysis of the condenser, online performance monitoring, etc. Background Art

[0002] In the combined cycle unit, the condenser plays a very important role. It uses circulating water to condense the steam exhausted by the steam turbine, establishes and maintains the required vacuum in the exhaust space of the steam turbine, and recovers pure condensate to supply feed water for the waste heat boiler.

[0003] Due to the changes in the combined cycle unit load and environmental meteorological conditions, the steam turbine is often in a variable operating state, so the heat load entering the condenser will often change, and for the combined cycle unit of cogeneration, the change in heat supply will also cause the heat load of the condenser to change; the condenser inlet water temperature is also affected by the heat exchange performance of the cooling tower. With the change of environmental meteorological conditions, the condenser inlet water temperature (i.e., the cooling tower outlet water temperature) will also change frequently; in addition, if the operating mode of the circulating water pump changes, it will also directly affect the cooling water volume in the condenser. The above factors all cause the condenser to often be in a variable operating state. Therefore, studying the calculation method of the condenser pressure under variable conditions is crucial for predicting and analyzing the thermal performance of the condenser or even the combined cycle unit under variable conditions.

[0004] Condenser equipment suppliers will provide the condenser design cleanliness factor, but do not provide the changing law of the condenser cleanliness factor under variable conditions. Therefore, in the traditional condenser pressure calculation method, if the condenser design cleanliness factor is used to calculate the condenser pressure under variable conditions, the result will have a large deviation from the actual operation result of the condenser. In addition, during the operation of the condenser, the power plant is not equipped with a measurement point for the condenser cooling water flow, so it is impossible to directly measure the cooling water flow in the condenser. Based on the above considerations, the present invention proposes an online calculation method for condenser pressure under variable conditions. The method reversely infers the condenser cleanliness factor under variable conditions of the condenser through the measured operation data of the condenser, and calculates the condenser pressure under variable conditions based on the changing law of the condenser cleanliness factor; in addition, in order to reverse the condenser cooling water flow, the present invention is also based on the principle of heat balance, and the condenser heat load is obtained from the turbine side, and then the condenser cooling water flow is calculated. The present invention can calculate the condenser pressure under variable working conditions more accurately, avoiding the problem that the traditional method cannot accurately calculate the condenser pressure under variable working conditions by using the condenser design cleanliness coefficient. The condenser pressure under variable working conditions calculated by the present invention can be used as the condenser pressure target value for condenser thermal performance analysis, online performance monitoring, etc. Summary of the invention

[0005] The technical problem to be solved by the present invention is: in view of the problem that in the traditional condenser pressure calculation method, the condenser pressure under variable working conditions is calculated by using the condenser design cleanliness coefficient, and the result will have a large deviation from the actual operation result of the condenser. The present invention proposes an online calculation method for condenser pressure under variable working conditions, which can calculate the condenser pressure under variable working conditions more accurately. The condenser pressure under variable working conditions calculated by the present invention can be used as the condenser pressure required value for condenser thermal performance analysis, online performance monitoring, etc.

[0006] The present invention is achieved by adopting the following technical solutions:

[0007] A method for online calculation of condenser pressure under variable working conditions comprises the following steps:

[0008] Step 1, calculating the steam energy entering the steam turbine based on the measured steam enthalpy and flow rate at the inlet of the steam turbine;

[0009] Step 2, based on the measured exhaust enthalpy and flow rate of the steam turbine entering the waste heat boiler, and the enthalpy and flow rate of the heating steam, calculate the steam energy discharged from the steam turbine excluding the heat load of the condenser;

[0010] Step 3, calculating the heat load entering the condenser based on the principle of steam turbine energy balance by using the steam energy entering the steam turbine calculated in step 1, the steam energy discharged from the steam turbine excluding the heat load of the condenser calculated in step 2, and the measured steam turbine output power;

[0011] Step 4, calculating the condenser cooling water volume based on the condenser heat load calculated in step 3 and the measured condenser inlet and outlet cooling water temperatures;

[0012] Step 5, under different condenser operating boundary conditions, based on the condenser cooling water volume calculated in step 4 and the circulating water pump operating mode, fit the relationship between the circulating pump operating speed and the condenser cooling water volume under different numbers of circulating pumps in operation;

[0013] Step 6, under different condenser operating boundary conditions, based on the condenser heat load calculated in step 3, the condenser cooling water volume calculated in step 4, and the measured condenser inlet and outlet water temperatures, condenser pressure, and condenser area, solve the condenser cleanliness coefficient under variable operating conditions;

[0014] Step 7, based on the heat load entering the condenser calculated in step 3 and the condenser cleanliness factor under the variable working condition calculated in step 6, fitting a relationship between different condenser heat loads and condenser cleanliness factors;

[0015] Step 8, calculate the condenser pressure under variable operating conditions: calculate the condenser cooling water volume based on the actual number of circulating pumps in operation, the circulating pump operating speed, and the relationship between the circulating pump operating speed and the condenser cooling water volume under different numbers of circulating pumps in operation obtained in step 5; calculate the condenser heat load based on the condenser cooling water volume and the measured condenser inlet and outlet water temperatures; calculate the condenser cleanliness coefficient based on the condenser heat load and the relationship between the condenser heat load and the condenser cleanliness coefficient under variable operating conditions obtained in step 7; calculate the condenser pressure under variable operating conditions based on the condenser cooling water volume, the condenser inlet and outlet water temperatures, the condenser cleanliness coefficient and the condenser area.

[0016] A further improvement of the present invention is that in step 1, the specific calculation formula is as follows:

[0017]

[0018] Where: E st,in is the steam energy entering the turbine, kW; H st,i is the enthalpy of the i-th steam entering the turbine, kJ / kg; W st,i is the flow rate of the i-th steam entering the turbine, kg / s.

[0019] A further improvement of the present invention is that in step 2, the specific calculation formula is as follows:

[0020]

[0021] Where: E st,out1 is the steam energy entering the turbine, kW; H st,i is the enthalpy of the i-th steam flowing out of the steam turbine, excluding the exhaust steam entering the condenser, in kJ / kg; W st,i is the flow rate of the i-th steam flowing out of the turbine excluding the exhaust steam entering the condenser, kg / s.

[0022] A further improvement of the present invention is that in step 3, the heat load entering the condenser is calculated as follows:

[0023] E con =E st,in -E st,out1 -P st

[0024] Where: E con is the condenser heat load, kW; P st is the turbine output power, kW.

[0025] A further improvement of the present invention is that in step 4, the amount of cooling water for the condenser is calculated as follows:

[0026]

[0027] Where: Wcon is the cooling water volume of the condenser, kg / s; T conout,w is the cooling water temperature at the condenser outlet, °C; T conout,w is the cooling water temperature at the condenser inlet, ℃; c p,w is the specific heat of cooling water, J / kg.℃.

[0028] A further improvement of the present invention is that in step 5, the relationship between the operating speed of the circulating pump and the amount of cooling water for the condenser is as follows:

[0029] W con =f(N cwp ,n cwp )

[0030] Where: N cwp is the number of circulating pumps in operation; n cwp is the operating speed of the circulating pump, rpm.

[0031] A further improvement of the present invention is that in step 6, under different condenser operating boundary conditions, based on the condenser pressure, the saturated water vapor temperature corresponding to the condenser pressure is solved:

[0032]

[0033] Where: p con,k is the condenser pressure, kPa; t con,s is the saturated water vapor temperature corresponding to the condenser pressure, °C;

[0034] Based on the calculated saturated steam temperature corresponding to the condenser pressure and the condenser inlet and outlet cooling water temperatures, the condenser heat transfer end difference is solved:

[0035] δt con =t con,s -T conout,w

[0036] Where: σt con is the heat transfer end difference of the condenser, °C;

[0037] The overall heat transfer coefficient of the condenser is calculated based on the calculated condenser heat transfer end difference, condenser cooling water volume, condenser inlet and outlet cooling water temperature, and condenser area as follows:

[0038]

[0039] Where: K con is the overall heat transfer coefficient of the condenser, W / (m 2 ℃); A con is the condenser area, m 2 ;

[0040] The condenser cleanliness factor under variable operating conditions is calculated according to the empirical formula of the American Heat Transfer Society, namely:

[0041]

[0042] Where: K c is the condenser cleanliness coefficient under variable conditions; K1 is the modified heat transfer coefficient, W / (m 2 ℃); K w K is the correction coefficient of the condenser inlet water temperature; m is the pipe correction factor.

[0043] A further improvement of the present invention is that in step 7, the specific calculation formula is as follows:

[0044] K c =f(E con ).

[0045] A further improvement of the present invention is that, in step 5, the operating mode of the circulating water pump includes the number of circulating pumps in operation and the operating speed.

[0046] The present invention has at least the following beneficial technical effects:

[0047] During the operation of the condenser, since the condenser cooling water flow cannot be directly and accurately measured, the power plant is not equipped with a condenser cooling water flow measurement point. Considering the need to provide accurate condenser cooling water flow for condenser pressure calculation, especially the condenser cooling water flow at different circulating pump speeds, the present invention proposes a method based on the principle of thermal balance to obtain the condenser heat load from the turbine side, and then to calculate the condenser cooling water flow, thereby solving the problem that the condenser cooling water flow cannot be measured in the processes of condenser thermal performance analysis and online performance monitoring. In addition, when the condenser design cleanliness coefficient based on the traditional method cannot accurately calculate the condenser pressure under variable conditions, the calculated condenser pressure is compared with the condenser pressure monitored by the unit, and the deviation between the two can reach more than 10%, and the calculation accuracy is poor. To solve this problem, the present invention proposes to reversely infer the condenser cleanliness coefficient under variable operating conditions through the measured operating data of the condenser, and calculate the condenser pressure under variable operating conditions based on the changing law of the condenser cleanliness coefficient. The condenser pressure calculated by this method is compared with the condenser pressure monitored by the unit, and the deviation between the two is within 3%, which has good accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The present invention is a flow chart of a method for calculating the condenser cooling water flow rate based on the steam turbine heat balance.

[0049] Figure 2 The present invention is a flow chart of a method for calculating the cleanliness factor of a condenser under variable operating conditions based on operating parameters.

[0050] Figure 3 This is a flow chart of the condenser pressure calculation method under variable operating conditions.

[0051] Figure 4 This is a comparison chart of the condenser pressure calculated by the method of the present invention and the condenser pressure monitored by the unit. DETAILED DESCRIPTION

[0052] The following is a detailed introduction to the patent of this invention in conjunction with the accompanying drawings:

[0053] like Figure 1 As shown in Figure 2, the steam energy entering the steam turbine is calculated based on the measured steam enthalpy and flow rate at the inlet of the steam turbine:

[0054]

[0055] Where: E st,in is the steam energy entering the turbine, kW; H st,i is the enthalpy of the i-th steam entering the turbine, kJ / kg; W st,i is the flow rate of the i-th steam entering the turbine, kg / s.

[0056] like Figure 1 As shown in Figure 1, based on the measured exhaust enthalpy and flow rate, heating enthalpy and flow rate of the steam turbine entering the waste heat boiler, the steam energy discharged from the steam turbine excluding the condenser heat load is calculated:

[0057]

[0058] Where: E st,out1 is the steam energy entering the turbine, kW; H st,i is the enthalpy of the i-th steam flowing out of the steam turbine, excluding the exhaust steam entering the condenser, in kJ / kg; W st,i is the flow rate of the i-th steam flowing out of the turbine excluding the exhaust steam entering the condenser, kg / s.

[0059] like Figure 1 As shown in the figure, the heat load entering the condenser is calculated based on the principle of steam turbine energy balance by calculating the steam energy entering the turbine, the steam energy discharged from the turbine excluding the heat load of the condenser, and the measured output power of the steam turbine:

[0060] E con =E st,in -E st,out1 -P st

[0061] Where: E con is the condenser heat load, kW; P st is the turbine output power, kW.

[0062] like Figure 1 As shown in the figure, based on the calculated condenser heat load and the measured condenser inlet and outlet cooling water temperatures, the condenser cooling water volume is calculated:

[0063]

[0064] Where: Wcon is the cooling water volume of the condenser, kg / s; T conout,w is the cooling water temperature at the condenser outlet, °C; T conout,w is the cooling water temperature at the condenser inlet, ℃; c p,w is the specific heat of cooling water, J / kg.℃.

[0065] Under different condenser operating boundary conditions, based on the calculated condenser cooling water volume and the circulating water pump operating mode (number of circulating pumps in operation, operating speed), the relationship between the circulating pump operating speed and the condenser cooling water volume under different numbers of circulating pumps in operation is fitted as follows:

[0066] W con =f(N cwp ,n cwp )

[0067] Where: N cwp is the number of circulating pumps in operation; n cwp is the operating speed of the circulating pump, rpm.

[0068] like Figure 2 As shown in the figure, under different condenser operating boundary conditions, based on the condenser pressure, the saturated water vapor temperature corresponding to the condenser pressure is solved:

[0069]

[0070] Where: p con,k is the condenser pressure, kPa; t con,s is the saturated water vapor temperature corresponding to the condenser pressure, ℃.

[0071] like Figure 2 As shown in the figure, based on the calculated saturated water vapor temperature corresponding to the condenser pressure and the condenser inlet and outlet cooling water temperatures, the condenser heat transfer end difference is solved:

[0072] δt con =t con,s -T conout,w

[0073] Where: σt con is the heat transfer end difference of the condenser, ℃.

[0074] like Figure 2As shown in the figure, the overall heat transfer coefficient of the condenser is calculated based on the calculated condenser heat transfer end difference, condenser cooling water volume, condenser inlet and outlet cooling water temperature and condenser area.

[0075]

[0076] Where: K con is the overall heat transfer coefficient of the condenser, W / (m 2 ℃); A con is the condenser area, m 2 .

[0077] The condenser cleanliness factor under variable operating conditions can be calculated according to the empirical formula of the American Heat Transfer Society, namely:

[0078]

[0079] Where: K c is the condenser cleanliness coefficient under variable conditions; K1 is the modified heat transfer coefficient, W / (m 2 ℃); K w K is the correction coefficient of the condenser inlet water temperature; m is the pipe correction factor.

[0080] Based on the calculated heat load of the condenser and the calculated cleanliness factor of the condenser under variable working conditions, the relationship between different heat loads of the condenser and the cleanliness factor of the condenser is fitted, that is:

[0081] K c =f(E con )

[0082] like Figure 3 As shown, the calculation of condenser pressure under variable operating conditions is carried out: the condenser cooling water volume is calculated based on the actual number of circulating pumps in operation, the circulating pump operating speed, and the relationship between the circulating pump operating speed and the condenser cooling water volume under different numbers of circulating pumps in operation; the condenser heat load is calculated based on the condenser cooling water volume and the measured condenser inlet and outlet water temperatures; the condenser cleanliness coefficient under variable operating conditions is calculated based on the condenser heat load and the relationship between the condenser heat load and the condenser cleanliness coefficient; the condenser pressure under variable operating conditions is calculated based on the condenser cooling water volume, the condenser inlet and outlet water temperatures, the condenser cleanliness coefficient and the condenser area.

[0083] The application effects of the present invention are as follows:

[0084] According to the historical operation data of the steam turbine and condenser of a combined cycle unit, the relationship between the operating speed of the circulating pump and the cooling water volume of the condenser, the relationship between the heat load of the condenser and the cleanliness factor of the condenser under different numbers of circulating pumps are calculated by the method proposed by the present invention, and the condenser pressure of the combined cycle unit on a certain day is calculated and compared with the condenser pressure monitored by the unit. The deviation between the two is within 3%. Figure 4 Therefore, the calculation method of the condenser pressure proposed in the present invention can be used for condenser thermal performance analysis and online performance monitoring.

Claims

1. A method for online calculation of condenser pressure under variable working conditions, characterized in that: The following steps are involved: Step 1, calculating the steam energy entering the steam turbine based on the measured steam enthalpy and flow rate at the inlet of the steam turbine; Step 2, based on the measured exhaust enthalpy and flow rate of the steam turbine entering the waste heat boiler, and the enthalpy and flow rate of the heating steam, calculate the steam energy discharged from the steam turbine excluding the heat load of the condenser; Step 3, calculating the heat load entering the condenser based on the principle of steam turbine energy balance by using the steam energy entering the steam turbine calculated in step 1, the steam energy discharged from the steam turbine excluding the heat load of the condenser calculated in step 2, and the measured steam turbine output power; Step 4, calculating the condenser cooling water volume based on the condenser heat load calculated in step 3 and the measured condenser inlet and outlet cooling water temperatures; Step 5, under different condenser operating boundary conditions, based on the condenser cooling water volume calculated in step 4 and the circulating water pump operating mode, fit the relationship between the circulating pump operating speed and the condenser cooling water volume under different numbers of circulating pumps in operation; Step 6, under different condenser operating boundary conditions, based on the condenser heat load calculated in step 3, the condenser cooling water volume calculated in step 4, and the measured condenser inlet and outlet water temperatures, condenser pressure, and condenser area, solve the condenser cleanliness coefficient under variable operating conditions; Step 7, based on the heat load entering the condenser calculated in step 3 and the condenser cleanliness factor under the variable working condition calculated in step 6, fitting a relationship between different condenser heat loads and condenser cleanliness factors; Step 8, calculate the condenser pressure under variable operating conditions: calculate the condenser cooling water volume based on the actual number of circulating pumps in operation, the circulating pump operating speed, and the relationship between the circulating pump operating speed and the condenser cooling water volume under different numbers of circulating pumps in operation obtained in step 5; calculate the condenser heat load based on the condenser cooling water volume and the measured condenser inlet and outlet water temperatures; calculate the condenser cleanliness coefficient based on the condenser heat load and the relationship between the condenser heat load and the condenser cleanliness coefficient under variable operating conditions obtained in step 7; calculate the condenser pressure under variable operating conditions based on the condenser cooling water volume, the condenser inlet and outlet water temperatures, the condenser cleanliness coefficient and the condenser area.

2. The method for online calculation of condenser pressure under variable working conditions according to claim 1, characterized in that: In step 1, the specific calculation formula is as follows: Where: E st,in is the steam energy entering the turbine, kW; H st,i is the enthalpy of the i-th steam entering the turbine, kJ / kg; W st,i is the flow rate of the i-th steam entering the turbine, kg / s.

3. The method for online calculation of condenser pressure under variable working conditions according to claim 2, characterized in that: In step 2, the specific calculation formula is as follows: Where: E st,out1 is the steam energy entering the turbine, kW; H st,i is the enthalpy of the i-th steam flowing out of the steam turbine, excluding the exhaust steam entering the condenser, in kJ / kg; W st,i is the flow rate of the i-th steam flowing out of the turbine excluding the exhaust steam entering the condenser, kg / s.

4. The method for online calculation of condenser pressure under variable working conditions according to claim 3 is characterized in that: In step 3, the heat load entering the condenser is calculated as follows: AND con =And st,in -AND st,out1 -P st Where: E con is the condenser heat load, kW; P st is the turbine output power, kW.

5. The method for online calculation of condenser pressure under variable working conditions according to claim 4, characterized in that: In step 4, the condenser cooling water volume is calculated as follows: Where: Wcon is the cooling water volume of the condenser, kg / s; T conout,w is the cooling water temperature at the condenser outlet, °C; T conout，w is the cooling water temperature at the condenser inlet, °C; c p，w is the specific heat of cooling water, J / kg.℃.

6. The method for online calculation of condenser pressure under variable working conditions according to claim 5, characterized in that: In step 5, the relationship between the circulating pump speed and the condenser cooling water volume is as follows: W con =f(N cwp ,n cwp ) Where: N cwp is the number of circulating pumps in operation; n cwp is the operating speed of the circulating pump, rpm.

7. The method for online calculation of condenser pressure under variable working conditions according to claim 6, characterized in that: In step 6, under different condenser operating boundary conditions, based on the condenser pressure, the saturated water vapor temperature corresponding to the condenser pressure is solved: Where: p con，k is the condenser pressure, kPa; t con，s is the saturated water vapor temperature corresponding to the condenser pressure, °C; Based on the calculated saturated steam temperature corresponding to the condenser pressure and the condenser inlet and outlet cooling water temperatures, the condenser heat transfer end difference is solved: δt con =t con，s -T conout，w Where: σt con is the heat transfer end difference of the condenser, °C; The overall heat transfer coefficient of the condenser is calculated based on the calculated condenser heat transfer end difference, condenser cooling water volume, condenser inlet and outlet cooling water temperature, and condenser area as follows: Where: K con is the overall heat transfer coefficient of the condenser, W / (m 2 ℃); A con is the condenser area, m 2 ; The condenser cleanliness factor under variable operating conditions is calculated according to the empirical formula of the American Heat Transfer Society, namely: Where: K c is the condenser cleanliness coefficient under variable conditions; K1 is the modified heat transfer coefficient, W / (m 2 ℃); K w K is the correction coefficient of the condenser inlet water temperature; m is the pipe correction factor.

8. The method for online calculation of condenser pressure under variable working conditions according to claim 7, characterized in that: In step 7, the specific calculation formula is as follows: K c =f(E con )。 9. The method for online calculation of condenser pressure under variable working conditions according to claim 1, characterized in that: In step 5, the operating mode of the circulating water pump includes the number of circulating pumps in operation and the operating speed.

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