A soft measurement method for real-time water consumption rate of wet-cooled thermal power units

Abstract

The present invention discloses a soft measurement method for the real-time water consumption rate of a wet-cooled thermal power unit. The method takes the unit as a unit and indirectly converts the power generation water consumption rate according to the changes in main parameters, thereby meeting the real-time water consumption rate calculation under different ambient temperatures and different power generation load rates, solving the problems existing in the prior art and improving the accuracy of the calculation.

Description

Technical Field

[0001] The invention belongs to a wet-cooling type thermal power unit in a thermal power plant, and in particular relates to a method for measuring the power generation water consumption rate of the wet-cooling type thermal power unit. Background Art

[0002] Wet-cooled thermal power units are the main cooling method for thermal power units. Except for thermal power units located on the coast, wet-cooled units in inland areas of my country are mainly closed-cycle wet-cooling systems. The wet-cooling method is to use a hyperbolic cooling tower to draw ambient air from the bottom to the top to exchange heat with the circulating water that flows naturally from the top to the bottom, so as to ensure that a certain vacuum environment is formed in the condenser, the equipment on the heat absorption side of the circulating water, to ensure the stability of the back pressure of the thermal power unit, to complete the cold source of the thermal power cycle, so that the reheating and heat recovery Rankine cycle of the power plant with water vapor as the working fluid can be carried out continuously, so as to achieve the purpose of the energy conversion process in which the steam turbine unit continuously outputs kinetic energy to drive the generator unit to output electricity.

[0003] Although the power generation water consumption rate is one of the main technical and economic indicators of power plants, the water source itself is priced relatively low and has little impact on the power generation cost. Therefore, the main power generation units currently conduct monthly statistical analysis of the power generation water consumption rate based on the amount of water taken from the outside world by the power plant. In recent years, with the development of the power market and the continuous advancement of the real-time bidding mechanism, the changes in power generation costs caused by different power generation water consumption rates must be further paid attention to. Summary of the invention

[0004] The purpose of the present invention is to provide a soft measurement method for the real-time water consumption rate of a wet-cooled thermal power unit. Taking the unit as a unit, the power generation water consumption rate is indirectly converted according to the changes in the main parameters, which satisfies the real-time water consumption rate calculation under different ambient temperatures and different power generation load rates, and solves the problems existing in the prior art. The main points include the following:

[0005] 1. The actual water consumption is unmeasurable: Generally, the amount of fresh water or other water (such as recycled water) introduced into thermal power plants only has an inlet meter, but no sub-unit meter;

[0006] 2. Wind loss cannot be calculated: According to industry standards, wind loss of cooling towers can be converted as a percentage of circulating water volume, which can meet the needs of daily industrial monitoring, but under normal circumstances, there is no direct measurement meter for circulating water volume;

[0007] 3. The calculation deviation of circulating water volume is large: According to industry standards, in the absence of direct metering, the real-time flow rate can be inferred by calculating the working characteristics of the water pump. However, the circulating water pumps in thermal power plants generally operate in single-pump, two-pump parallel or three-pump parallel modes, resulting in large changes in pump characteristics, complex conversion and reduced accuracy.

[0008] The technical solution of the present invention is a soft measurement method for real-time water consumption rate of a wet-cooled thermal power unit, which is characterized by comprising the following steps:

[0009] 1. Define the water consumption rate of the unit

[0010] Water consumption rate of unit power generation = water consumption of generator (G) / generator export power (P), unit: kg / kWh;

[0011] The generator export power P is the measured value, taken from the generator power meter, in MWh;

[0012] 2. Calculation of water consumption of generator

[0013] G=G0+k bs ×G bs +G xhs +G fc

[0014] Where G0 is the hourly allocation of fresh water such as domestic water, industrial water, fire water, etc. that is not related to the load rate to this unit; G bs k is the hourly water replenishment of the unit’s desalted water, measured from the condenser water replenishment flow meter. bs G is the desalted water production rate, which refers to the amount of fresh water consumed by the desalted water system to produce 1 ton of desalted water; xhs G is the amount of water evaporated per hour by the cooling tower; fc It is the wind loss of circulating water in cooling tower;

[0015] 3. Calculation of actual circulating water volume

[0016] Circulating water system Figure 1 As shown, the condenser 1 is a surface heat exchanger, which serves as a cold source for the wet-cooled steam turbine generator set. It uses circulating water for surface heat exchange, absorbs the heat of the exhaust steam of the steam turbine 2, and maintains the continuous thermodynamic cycle. The circulating water used for cooling in the condenser 1 is powered by three circulating water pumps 3 running in parallel. It flows from bottom to top in the condenser, and then enters the spray layer of the cooling water tower after being collected by the inlet and outlet valves V9\V10. After passing through the splash device and the filler, it falls freely and exchanges heat with the air in the tower. The density of the heated air decreases, and under the action of the difference in air density inside and outside the tower body, it flows upward naturally. The circulating water flowing downward is cooled and merged into the water pool at the bottom of the tower, and then flows to the inlet of the circulating pump through the circulating water pipe, forming a closed circulation of circulating water. The part of the circulating water consumed by evaporation is directly supplemented into the tower pool at the bottom of the cooling water tower by the fresh water from the water intake pipe outside the factory.

[0017] According to the principle of the same flow rate of series fluids, the water flow rate flowing through the condenser, the cooling water tower and the circulating pump group is consistent.

[0018] Assuming that the environment inside condenser 1 remains unchanged and the pipeline is smooth, according to the throttling flow measurement principle,

[0019]

[0020] Among them G v is the circulating water flow rate, unit: m 3 / h; Δp is the differential pressure between the inlet and outlet of the throttling device, in kPa; ρ is the water density, which is converted from the standard state according to the real-time temperature t and pressure p; k is the flow coefficient, a dimensionless quantity, which is calibrated according to the shape of the throttling device and the outlet flow coefficient based on the actual field measurement value.

[0021] Reuse formula Convert to mass flow rate, unit t / h.

[0022] 4. Calculation of evaporation circulation water volume

[0023] According to the heat balance calculation formula in the cooling tower, Q fr =Q xr ,

[0024] The circulating water releases heat Q fr =G m *C*(t r -t c ), circulating water evaporation heat absorption

[0025] Q xr =G xhs *(h s -h w )

[0026] Then G xhs =G m ×C×(t r -t c ) / (h s -h w )

[0027] Where C is the specific heat capacity of water at the corresponding pressure and temperature; t r is the temperature of hot water entering the water tower, t c is the cold water temperature of the outlet tower, h s is the enthalpy of saturated water vapor at ambient temperature, h w is the saturated enthalpy of water at ambient temperature.

[0028] 5. Calculation of water loss due to wind

[0029] According to the relevant standards for thermal calculation of cooling towers, G fc =α×G m , where α is taken according to the standard value, generally calculated as 5%.

[0030] The present invention has the following characteristics

[0031] (1) The present invention proposes an accurate calculation method for real-time water consumption rate analysis based on a unit.

[0032] (2) The present invention divides the main water consumption of the unit into stable water consumption G0, fresh water consumption for supplementing demineralized water k×G bs , cooling tower evaporation G xhs , Wind loss circulating water volume G fc .

[0033] (3) The present invention determines the stable water consumption G0 and the fresh water consumption k×G bs , Evaporation of cooling tower G xhs , Wind loss circulating water volume G fc The actual acquisition method of etc.

[0034] (4) The present invention is to obtain a stable water consumption G0 and replenish the desalted water with fresh water consumption k×G bs , Evaporation of cooling tower G xhs , Wind loss circulating water volume G fc The condenser inlet pressure measuring points p1, p2 and the condenser outlet pressure measuring points p3, p4 were added to the original system based on the data.

[0035] (5) The present invention is to obtain a stable water consumption G0 and replenish the desalted water with fresh water consumption k×G bs , Evaporation of cooling tower G xhs , Wind loss circulating water volume G fc The uncertainty analysis of the newly installed condenser inlet pressure measuring points p1, p2 and condenser outlet pressure measuring points p3, p4 was carried out based on the data, and the accuracy of these four measuring points was required to reach level 0.1.

[0036] (6) In order to improve the calculation accuracy of the present invention, it is necessary to install an online table of ambient temperature t0 and an online table of ambient atmospheric pressure p0. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the circulating water system and newly added measuring points. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0040] like Figure 1 As shown in the figure, the soft measurement calculation formula for the real-time water consumption rate of the generator set is:

[0041]

[0042] The actual acquisition process is as follows:

[0043] 1. Fixed apportioned water consumption G0 is calculated by averaging the industrial water consumption obtained from periodic water consumption analysis to the value of a single unit;

[0044] 2. Unit desalination water supply G bs Calculated based on the online measurement value of the water supply flow from the desalted water tank to the unit condenser;

[0045] 3. Desalted water production coefficient k bs Calculation based on desalinated water system test measurements;

[0046] 4. The flow measurement coefficient k is calculated based on the flow test value of the actual unit.

[0047]

[0048] 5. Throttling differential pressure Δp = average ((p1-p3), (p2-p4));

[0049] 6. Specific heat capacity of circulating water C = f(p0, t0), calculated according to the water vapor function ratio;

[0050] 7. Circulating water density ρ = f(p0, t0), calculated according to the water vapor function ratio;

[0051] 8. Saturated water vapor enthalpy at ambient temperature h s 、Saturated water enthalpy at ambient temperature h w They are all functions of ambient pressure and ambient temperature, calculated according to the water vapor function table;

[0052] 9. The wind loss coefficient α is selected based on the unit water balance test results or relevant national standards.

[0053] The above is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a technician familiar with the field within the technical scope disclosed in the present invention should be covered by the protection scope of the present invention.

Claims

1. A soft measurement method for real-time water consumption rate of a wet-cooled thermal power unit, characterized in that the generator The water consumption calculation formula is G = G0 + k bs ×G bs +G xhs +G fc Where G0 is the fixed apportioned water consumption per hour of the unit for domestic water, industrial water, and fire water that is not related to the load rate; k bs G is the desalted water production coefficient, which refers to the amount of fresh water consumed by the desalted water system to produce 1 ton of desalted water; bs The hourly water replenishment volume of desalted water for this unit; G xhs G is the amount of water evaporated per hour by the cooling tower; fc The wind loss of circulating water in the cooling tower; The actual acquisition process is as follows: The fixed apportioned water consumption G0 is calculated by averaging the industrial water consumption obtained from the periodic water consumption analysis to the value of a single unit; Unit desalination water supply G bs Calculated based on the online measurement value from the condenser feed water flow meter; Desalinated water production coefficient k bs Calculated based on the test values ​​of the desalted water system; Cooling tower water evaporation volume per hour G xhs =G m ×C×(t r -t c ) / (h s -h w ) Where C is the specific heat capacity of circulating water at the corresponding pressure and temperature, and the specific heat capacity of circulating water C = f(p0, t0), which is calculated according to the water vapor function ratio; t r is the temperature of hot water entering the water tower, t c is the cold water temperature of the outlet tower; h s is the enthalpy of saturated water vapor at ambient temperature, h w is the saturated water enthalpy at ambient temperature, calculated according to the water vapor function table; The circulating water mass flow rate Unit: t / h; Δp is the differential pressure between the inlet and outlet of the throttling device, unit is kPa, Δp=average((p1-p3),(p2-p4)); circulating water density ρ=f(p0,t0), calculated according to the water vapor function ratio; Among them, p1 and p2 are the condenser inlet pressure measurement point values, p3 and p4 are the condenser outlet pressure measurement point values, t0 is the ambient temperature online meter measurement value, and p0 is the ambient atmospheric pressure online meter measurement value; The flow coefficient k is based on the flow test value G of the actual unit shiyan Conversion, Cooling tower circulating water wind loss G fc =α×G m , where the circulating water mass flow rate is Unit: t / h; α is taken as 5% of the standard; So the final generator water consumption calculation formula is:

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