Calculation method for direct contact heat exchange of steam and water in temperature and pressure reduction tank

Abstract

The invention discloses a heat exchange calculation method for direct contact of steam and water in a temperature and pressure reduction tank, which comprises the following steps: spraying atomized cooling water and pretreating high-temperature steam, accurately calculating the liquid drop speed and the steam mass flow rate, and further calculating to obtain a convective heat exchange coefficient; and the pressure value is preset, quasi-steady-state heat exchange calculation is conducted in combination with the convective heat exchange coefficient and the conservation equation, the outlet steam mass flow and the outlet steam density of the heat exchange section are obtained, the actual pressure of the heat exchange section is obtained through calculation on the basis of the outlet steam mass flow and the outlet steam density, and the actual pressure and the preset pressure are compared and continuously adjusted till matching is achieved. According to the method, the temperature and pressure reduction box model is simplified, the calculation efficiency and accuracy are improved, parameters can be simulated and output in real time, and convenience is provided for optimization of a secondary circuit simulation structure model.

Description

Technical Field

[0001] The invention belongs to the field of simulation technology, and in particular relates to a method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box. Background Art

[0002] In the steam exhaust system, the temperature and pressure reduction box is a very important component structure, and the working state of the temperature and pressure reduction box is closely related to the economy and safety of the steam exhaust system. In normal working state, after the high-pressure steam in the steam system is generated by the steam generator, it enters the steam turbine through the steam pipe to perform work and is finally discharged into the condenser. However, when the external output power changes or when encountering special circumstances that require the steam turbine to be separated from the steam system, the excess high-temperature and high-pressure steam cannot be directly discharged into the condenser. For safety reasons, the high-temperature and high-pressure steam needs to pass through the steam exhaust system first, and after the temperature and pressure reduction treatment of the temperature and pressure reduction box, it can be safely discharged into the condenser and return to the secondary circuit circulation.

[0003] The direct contact heat exchange between steam and water inside the desuperheating and decompression box is complicated. Usually, the relevant thermal calculations assume that the sprayed cooling water and high-temperature steam are completely mixed, and only simple mass conservation and energy conservation calculations are performed. The direct contact heat exchange between steam and water inside the desuperheating and decompression box has the characteristics of large heat exchange area and intense turbidity, so it takes a lot of time to actually rely on CFD methods for simulation calculations. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box to solve the above problems in the prior art.

[0005] To achieve the above object, the present invention provides a method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box, comprising:

[0006] Atomize the cooling water spray of the heat exchange section of the temperature reduction and pressure reduction box and calculate the droplet velocity of the cooling water droplets; pre-treat the high-temperature steam in the non-heat exchange section and calculate the mass flow rate of the high-temperature steam in the non-heat exchange section; average the preset cooling water mass flow rate;

[0007] The pressure value of the heat exchange section of the temperature reduction and pressure reduction box is preset, and the heat exchange coefficient between the high-temperature steam and the cooling water droplets is calculated based on the mass flow rate of the high-temperature steam and the droplet velocity of the cooling water droplets; the mass conservation equation and the energy conservation equation are obtained based on the convection heat transfer coefficient, the cooling water mass flow rate and the high-temperature steam mass flow rate; based on the mass conservation equation and the energy conservation equation, the quasi-steady-state heat exchange process is calculated to obtain the outlet steam mass flow rate and outlet steam density of the heat exchange section;

[0008] The actual heat exchange section pressure is calculated based on the outlet steam mass flow rate and the outlet steam density. The actual heat exchange section pressure is compared with the preset pressure value. If they are consistent, the next stage of calculation is carried out. If they are inconsistent, the preset pressure value is corrected and the actual heat exchange section pressure is calculated again until they are consistent.

[0009] Optionally, the method further includes: simplifying the cooling and decompression box according to the connection mode to obtain a simplified structure of the cooling and decompression box; and performing direct contact heat exchange calculation of steam and water inside the cooling and decompression box based on the simplified structure.

[0010] Optionally, the process of calculating the droplet velocity of the cooling water droplet includes:

[0011] The droplet diameter of the cooling water droplets is obtained based on the pressure difference before and after the nozzle and the steam specific volume; the number of droplets and the droplet heat exchange area are calculated based on the cooling water mass flow rate and the droplet diameter; the droplet velocity of the cooling water is obtained based on the number of droplets and the droplet heat exchange area.

[0012] Optionally, the process of calculating the high-temperature steam mass flow rate of the non-heat exchange section includes: calculating the high-temperature steam mass flow rate of the non-heat exchange section based on a preset pressure value of the heat exchange section, a box pressure of the non-heat exchange section, and a steam density at an outlet of the non-heat exchange section, and the formula is as follows:

[0013]

[0014] Where P 前 Indicates the pressure of the non-heat exchange section box, MPa; P 后 represents the heat exchange section pressure, MPa; Kr represents the pressure loss coefficient, which is determined according to the outlet steam physical parameters; G g,出 Indicates the steam mass flow rate from the non-heat exchange section to the heat exchange section, kg / s; ρ g Indicates the steam density at the outlet of the non-heat exchange section, kg / m 3 .

[0015] Optionally, the process of obtaining the heat transfer coefficient between the high-temperature steam and the cooling water droplets includes:

[0016] Based on the high-temperature steam mass flow rate and the droplet velocity, a relative motion velocity is calculated;

[0017] Calculate the Reynolds number based on high-temperature steam and cooling water droplets;

[0018] The convective heat transfer coefficient between high-temperature steam and cooling water droplets is calculated based on the Reynolds number and the empirical formula for calculating convective heat transfer on the surface of a sphere, and the convective heat transfer coefficient is corrected by the Reynolds number of the high-temperature steam to obtain the final convective heat transfer coefficient.

[0019] Optional, quasi-steady-state heat transfer process calculation:

[0020] The heat exchange time is estimated based on the geometric structure of the desuperheating and decompression box and the high-temperature steam flow rate;

[0021] After each step of heat exchange, it is determined whether the cooling water droplets have reached the saturation temperature under the pressure of the heat exchange section. If the saturation temperature is reached, the droplets start the evaporation heat exchange process; if the evaporation heat exchange process has been started, it is determined whether the droplets are completely evaporated. If they are completely evaporated, the quasi-steady-state calculation process is terminated. If they are not completely evaporated, the outlet steam mass flow rate and outlet steam density of the heat exchange section are output until the heat exchange time ends.

[0022] Optionally, the mass conservation equation is expressed as follows:

[0023]

[0024] In the formula, δm represents the mass of direct contact heat transfer phase change between steam and water, kg; G l Indicates the mass flow rate of cooling water in the heat exchange section, kg / s; G g Indicates the mass flow rate of high-temperature steam in the heat exchange section, kg / s;

[0025] The energy conservation equation is expressed as follows:

[0026]

[0027] In the formula, τ represents time, A m represents the steam-water contact heat exchange area, ΔT represents the temperature difference between high-temperature steam and cooling water droplets, K·h represents the corrected convective heat transfer coefficient, h g Indicates the enthalpy of high-temperature steam, kJ / kg; h l Indicates the cooling water droplet enthalpy, kJ / kg.

[0028] Optionally, the process of calculating the heat exchange section pressure includes:

[0029] The condenser pressure is obtained as the pressure outlet boundary, and the heat exchange section pressure is calculated based on the pressure outlet boundary, the average mass flow rate and the average density of the high-temperature steam at the heat exchange section outlet.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] This method simplifies the cooling and decompression box model, takes into account the input parameters such as high-temperature steam and cooling water and the condenser pressure as the model boundary conditions, fully considers the direct contact and mixing heat exchange between high-temperature steam and cooling water droplets, and combines the droplet phase change to finally obtain the real-time simulation output parameters of the cooling and decompression box, including the steam or steam and droplet mixture discharged to the condenser in the case of insufficient heat exchange. At the same time, the calculation efficiency is high and the accuracy is good, which provides convenience for the future optimization of the secondary circuit simulation structure model. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0033] Figure 1 This is a schematic diagram of the structure of a temperature and pressure reduction box according to an embodiment of the present invention;

[0034] Figure 2 It is a simplified schematic diagram of the structure of a temperature and pressure reduction box according to an embodiment of the present invention;

[0035] Figure 3 This is a flow chart of the calculation process of the pressure and flow heat exchange in the heat exchange section of the desuperheating and decompression box according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0037] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0038] Embodiment 1

[0039] like Figure 3 As shown, this embodiment provides a method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box, including:

[0040] During the calculation process, the physical parameters of water and steam need to be called multiple times according to the water vapor physical property library. The time is discretized during processing, which corresponds to the discrete time of the system. At the same time, each step needs to start with the pressure assumption of the temperature reduction and pressure reduction heat exchange section, and then perform preprocessing and heat exchange calculation.

[0041] Step 1: Simplify the simulation object structure;

[0042] The spray heat exchange section of the desuperheating and decompression box is the main calculation object. The structural diagram of the desuperheating and decompression box is shown in the attached figure. Figure 1 As shown in the figure, the entire temperature and pressure reduction box is simplified according to the connection method. Figure 2 shown.

[0043] Step 2: Cooling water spray atomization treatment method for the heat exchange section of the temperature reduction and pressure reduction box;

[0044] The cooling water input parameters in the system are: cooling water temperature, pressure before spraying and cooling water mass flow rate. When the cooling water spray enters the temperature reduction and pressure reduction section, it is atomized into droplets according to the nozzle. The heat transfer calculation requires the flow velocity of the droplets to calculate the heat transfer coefficient. The flow velocity of the cooling water sprayed from the nozzle is calculated as follows:

[0045] Atomizing nozzle flow rate:

[0046] Where, μ is the velocity coefficient. If there is no experimental data, μ=0.64 can be used. ΔP represents the pressure difference before and after the nozzle, MPa; υ l represents the specific volume of water, m 3 / kg.

[0047] Calculation method of droplet diameter after cooling water atomization treatment:

[0048] d max =1000×4×συ g / ζ 2 (mm)

[0049] Where, σ is the water surface tension coefficient, N / M; ζ is the medium resistance coefficient, which can be taken as 0.5; υ g Indicates the steam specific volume, m 3 / kg.

[0050] When the droplet diameter is well atomized, the average droplet diameter can be taken as: d m =0.8-1.2mm

[0051] The number of droplets and the total surface area of ​​droplets can be calculated based on the cooling water mass flow rate and droplet diameter;

[0052] Number of drops:

[0053]

[0054] Where n is the number of droplets; G l Indicates the cooling water mass flow rate, kg / s; ρ l Indicates cooling water density, kg / m 3 ;

[0055] Total droplet surface area:

[0056] In the formula, A m is the total surface area of ​​the droplet, m 2 ;d m represents the average droplet diameter, m 2 .

[0057] Step 3: High temperature and high pressure steam treatment before the heat exchange section of the temperature reduction and pressure reduction box;

[0058] The volumetric effect of mixing and diffusion of high-temperature and high-pressure steam is mainly considered to be mixed in the non-heat exchange volume. The inlet steam mass flow rate is the input condition of the temperature reduction and pressure reduction box, and the outlet steam quality is calculated by the pressure difference of the heat exchange section connected to the back.

[0059]

[0060] Where P 前 Indicates the pressure of the non-heat exchange section box, MPa; P 后 Indicates the heat exchange section pressure, MPa; Kr indicates the pressure loss coefficient, which is related to the outlet steam physical parameters; G g,出 represents the steam flow rate at the outlet of the non-heat exchange section, i.e. the steam flow rate at the inlet of the heat exchange section, kg / s; ρ g Indicates the steam density at the outlet of the non-heat exchange section, kg / m 3 .

[0061] In the non-heat exchange section, the mass change of high-temperature steam always follows the mass conservation equation:

[0062]

[0063] Where V' represents the internal volume of the non-heat exchange section, m 3 ; G g,进 Indicates the steam mass flow rate at the inlet of the non-heat exchange volume, kg / s; G g,出 is the steam flow rate at the outlet of the non-heat exchange section, i.e. the steam flow rate at the inlet of the heat exchange section, kg / s;

[0064] While considering the volumetric effect, the non-heat exchange section of the temperature and pressure reduction box is simplified by energy conservation.

[0065] Step 4: Simplify the volume effect of cooling water spray in the heat exchange section of the temperature and pressure reduction box;

[0066] The cooling water spray inside the desuperheating and decompression box is averaged within the time step, and the quasi-steady-state heat exchange stage of the desuperheating and decompression box is carried out after the cooling water mass flow is averaged. The conservation equation of the spray cooling water in the heat exchange section, which is averaged and simplified within the unit time step considering the volume effect, is as follows:

[0067] The mass conservation equation:

[0068]

[0069] In the formula, τ represents time, M l Indicates the total mass of coolant mist in the desuperheating and decompression box, G l,in ,G l,out Indicates the mass flow rate of cooling water input and output in the desuperheating and decompression box;

[0070] Energy conservation equation:

[0071]

[0072] In the formula, Q l Indicates the total energy of the cooling water spray liquid mist inside the desuperheating and decompression box, h l,in Indicates the enthalpy value of the cooling water sprayed into the desuperheating and decompression box. Indicates the enthalpy value of cooling water discharged from the desuperheating and decompression tank.

[0073] Step 5: Assumption of the pressure in the heat exchange section of the temperature and pressure reduction box;

[0074] At the beginning of the calculation, the pressure of the heat exchange section of the cooling and decompression box is assumed. Only after the pressure is assumed can the cooling water spray droplets and the high-temperature steam in the non-heat exchange section be processed. To verify whether the assumed pressure of the heat exchange section of the cooling and decompression box is correct, the flow heat transfer calculation and pressure coupling analysis of the heat exchange section of the cooling and decompression box in the following sixth to ninth steps are needed to make a judgment.

[0075] According to the conservation of mass and energy, the water vapor physical property library is called to obtain the physical property parameters of cooling water droplets and high-temperature steam when they enter the heat exchange section, and then the next step is to perform quasi-steady-state flow heat transfer calculation in the heat exchange section.

[0076] Step 6: Calculation of heat transfer coefficient of heat exchange section of desuperheating and decompression box;

[0077] After obtaining the assumed pressure in the previous step, the heat exchange section of the desuperheating and decompression box is made zero-dimensional, and its internal details are ignored. At the same time, for the sake of fine calculation of the heat exchange process, a quasi-steady-state process is used to calculate the direct contact heat exchange between the internal high-temperature steam and the cooling water droplets.

[0078] The high-temperature steam and spray droplet results obtained by the third and fourth steps are used as the input of the quasi-steady-state heat exchange calculation of the heat exchange section of the cooling and decompression box. The output of the quasi-steady-state heat exchange calculation is the zero-dimensional simplified output of the heat exchange section of the cooling and decompression box.

[0079] First, the relative motion speed is calculated based on the high-temperature steam mass flow calculated in the third step and the droplet velocity calculated by the spray cooling droplet atomization process in the second step.

[0080] Then the Reynolds number is calculated by combining the physical properties of high-temperature steam and cooling water droplets:

[0081] Re=d m u l / v l

[0082] Where Re is the Reynolds number of the droplet, u l Indicates the outlet flow rate of the droplet nozzle, m / s; v l represents the droplet kinematic viscosity, m 2 / s.

[0083] The convective heat transfer coefficient between the two is further calculated using the Reynolds number and the empirical formula for convective heat transfer on the spherical surface:

[0084] h=λ(2+0.6Pr 0.33 Re 0.5 ) / d m

[0085] Where h represents the direct contact convection heat transfer coefficient of steam and water, W / (m 2 ·℃); λ represents the thermal conductivity of cooling water, W / (m 2 ℃); d m represents the average droplet diameter, Pr represents the cooling water Prandtl number;

[0086] Considering the enhancement effect of high-temperature steam flow on heat transfer, the Reynolds number correction of high-temperature steam is introduced here. The correction coefficient K is:

[0087]

[0088] In the formula, α and β represent the parameters of heat transfer coefficient affected by high temperature steam, Re g Reynolds number for high temperature steam flow.

[0089] Step 7: Calculation of quasi-steady-state heat exchange process in the heat exchange section of the temperature and pressure reduction box;

[0090] Estimation of quasi-steady-state heat exchange time: Assuming that the heat exchange section is a short pipe box, the quasi-steady-state heat exchange time of the high-temperature steam in the box from inlet to discharge is approximately calculated as:

[0091] t m =Lρ g S / G g

[0092] In the formula, t m It represents the upper limit of steam heat exchange time at this steam mass flow rate, L represents the length of the heat exchange section, and S represents the flow cross-sectional area of ​​the heat exchange section;

[0093] In the direct contact heat exchange process between steam and water, the mass conservation equation and energy conservation equation are as follows:

[0094] According to the mass conservation equation:

[0095]

[0096] In the formula, δm represents the mass of direct contact heat transfer phase change between steam and water, kg; G l Indicates the mass flow rate of cooling water in the heat exchange section, kg / s; G g Indicates the mass flow rate of high-temperature steam in the heat exchange section, kg / s.

[0097] According to the energy conservation equation:

[0098]

[0099] In the formula, A m represents the steam-water contact heat transfer area, ΔT represents the temperature difference between high-temperature steam and cooling water droplets, K·h represents the corrected steam-water direct contact convection heat transfer coefficient, h g Indicates the enthalpy of high-temperature steam, kJ / kg; h l Indicates the cooling water droplet enthalpy, kJ / kg.

[0100] During the quasi-steady-state calculation process, at the end of each heat exchange step, it is necessary to determine whether the droplet has reached the saturation temperature under the pressure of the heat exchange section. If the saturation temperature is reached, the droplet will begin the evaporation heat exchange process. Furthermore, at each step, it is necessary to determine whether the droplet has evaporated completely. If the evaporation is complete, the quasi-steady-state process iterative calculation can be ended in advance. Otherwise, until the quasi-steady-state heat exchange time is over, the final result is returned to the outlet result of the heat exchange section of the desuperheating and decompression box to calculate the next pressure.

[0101] Step 8: Calculation of heat exchange section pressure;

[0102] The condenser pressure is the pressure outlet boundary. The heat exchange section pressure is affected by the condenser pressure. At the same time, the local resistance between the two is related to the high-temperature steam after spraying and cooling. The local resistance loss is considered to be directly related to the average mass flow rate and average density at the heat exchange volume outlet, that is:

[0103]

[0104] Where P 1 Indicates the heat exchange section pressure, P out represents the condenser pressure, Kr represents the pressure loss coefficient, which is related to the outlet steam physical parameters, G g represents the outlet steam mass flow rate, ρ g Indicates the outlet steam density.

[0105] The pressure in the heat exchange volume is mainly affected by the condenser and the local resistance structure, and is highly correlated with the steam flow rate. The pressure loss coefficient Kr in the local pressure drop calculation can be obtained from experimental data.

[0106] The outlet steam parameters of the desuperheating and decompression box at the end of the discretized time step are used to calculate the pressure in the heat exchange section while taking into account the condenser pressure and the pressure drop caused by some resistance structures.

[0107] Step 9: De-temperature and de-pressure box heat exchange and pressure coupling judgment process;

[0108] Compare the heat exchange section pressure calculated in the eighth step with the heat exchange section pressure assumed at the beginning of the time step to see if they are consistent. If they are consistent, proceed to the next time step calculation. If they are inconsistent, return to the fifth step, correct the assumed pressure, iterate until they are consistent, and then proceed to the next step of calculation.

[0109] In this way, the temperature, quality, flow rate and other parameters of the steam at the outlet of the desuperheating and decompression box can be obtained, and at the same time, whether there is any cooling water left and the relevant temperature, mass flow rate and other parameters of the remaining cooling water can be calculated.

[0110] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box, characterized in that: The following steps are involved: Atomize the cooling water spray of the heat exchange section of the temperature reduction and pressure reduction box and calculate the droplet velocity of the cooling water droplets; pre-treat the high-temperature steam in the non-heat exchange section and calculate the mass flow rate of the high-temperature steam in the non-heat exchange section; average the preset cooling water mass flow rate; The pressure value of the heat exchange section of the temperature reduction and pressure reduction box is preset, and the heat exchange coefficient between the high-temperature steam and the cooling water droplets is calculated based on the mass flow rate of the high-temperature steam and the droplet velocity of the cooling water droplets; the mass conservation equation and the energy conservation equation are obtained based on the convection heat transfer coefficient, the cooling water mass flow rate and the high-temperature steam mass flow rate; based on the mass conservation equation and the energy conservation equation, the quasi-steady-state heat exchange process is calculated to obtain the outlet steam mass flow rate and outlet steam density of the heat exchange section; The actual heat exchange section pressure is calculated based on the outlet steam mass flow rate and the outlet steam density. The actual heat exchange section pressure is compared with the preset pressure value. If they are consistent, the next stage of calculation is carried out. If they are inconsistent, the preset pressure value is corrected and the actual heat exchange section pressure is calculated again until they are consistent.

2. The method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box according to claim 1, characterized in that: The method further includes: simplifying the temperature reduction and pressure reduction box according to the connection mode to obtain a simplified structure of the temperature reduction and pressure reduction box; and performing steam-water direct contact heat exchange calculation inside the temperature reduction and pressure reduction box based on the simplified structure.

3. The method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box according to claim 1, characterized in that: The process of calculating the droplet velocity of cooling water droplets includes: The droplet diameter of the cooling water droplets is obtained based on the pressure difference before and after the nozzle and the steam specific volume; the number of droplets and the droplet heat exchange area are calculated based on the cooling water mass flow rate and the droplet diameter; the droplet velocity of the cooling water is obtained based on the number of droplets and the droplet heat exchange area.

4. The method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box according to claim 1, characterized in that: The process of calculating the high-temperature steam mass flow rate of the non-heat exchange section includes: based on the preset pressure value of the heat exchange section, the box pressure of the non-heat exchange section and the steam density at the outlet of the non-heat exchange section, the high-temperature steam mass flow rate of the non-heat exchange section is calculated, and the formula is as follows: Where P 前 Indicates the pressure of the non-heat exchange section box, MPa; P 后 represents the heat exchange section pressure, MPa; Kr represents the pressure loss coefficient, which is determined according to the outlet steam physical parameters; G g,出 Indicates the steam mass flow rate from the non-heat exchange section to the heat exchange section, kg / s; ρ g Indicates the steam density at the outlet of the non-heat exchange section, kg / m 3 .

5. The method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box according to claim 1, characterized in that: The process of obtaining the heat transfer coefficient between high-temperature steam and cooling water droplets includes: Based on the high-temperature steam mass flow rate and the droplet velocity, a relative motion velocity is calculated; Calculate the Reynolds number based on high-temperature steam and cooling water droplets; The convective heat transfer coefficient between high-temperature steam and cooling water droplets is calculated based on the Reynolds number and the empirical formula for calculating convective heat transfer on the surface of a sphere, and the convective heat transfer coefficient is corrected by the Reynolds number of the high-temperature steam to obtain the final convective heat transfer coefficient.

6. The method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box according to claim 1, characterized in that: Quasi-steady-state heat transfer process calculation: The heat exchange time is estimated based on the geometric structure of the desuperheating and decompression box and the high-temperature steam flow rate; After each step of heat exchange, it is determined whether the cooling water droplets have reached the saturation temperature under the pressure of the heat exchange section. If the saturation temperature is reached, the droplets start the evaporation heat exchange process; if the evaporation heat exchange process has been started, it is determined whether the droplets are completely evaporated. If they are completely evaporated, the quasi-steady-state calculation process is terminated. If they are not completely evaporated, the outlet steam mass flow rate and outlet steam density of the heat exchange section are output until the heat exchange time ends.

7. The method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box according to claim 1, characterized in that: The mass conservation equation is expressed as follows: In the formula, δm represents the mass of direct contact heat transfer phase change between steam and water, kg; G l Indicates the mass flow rate of cooling water in the heat exchange section, kg / s; G g Indicates the mass flow rate of high-temperature steam in the heat exchange section, kg / s; The energy conservation equation is expressed as follows: In the formula, τ represents time, A m represents the steam-water contact heat exchange area, ΔT represents the temperature difference between high-temperature steam and cooling water droplets, K·h represents the corrected convective heat transfer coefficient, h g Indicates the enthalpy of high-temperature steam, kJ / kg; h l Indicates the cooling water droplet enthalpy, kJ / kg.

8. The method for calculating direct contact heat exchange between steam and water inside a temperature and pressure reduction box according to claim 1, characterized in that: The process of calculating the heat exchange section pressure includes: The condenser pressure is obtained as the pressure outlet boundary, and the heat exchange section pressure is calculated based on the pressure outlet boundary, the average mass flow rate and the average density of the high-temperature steam at the heat exchange section outlet.

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