Online monitoring method for thermal load of spiral water-cooled wall hearth under supercritical working condition

Abstract

The invention provides an on-line monitoring method for the thermal load of a spiral water-cooled wall hearth under a supercritical working condition. The on-line monitoring method comprises the steps that a spiral water-cooled wall is divided into a plurality of sections, and a plurality of wall temperature measuring points are arranged on the back fire side of the spiral water-cooled wall; constructing a relational database between different boundary conditions of the spiral water wall and the back fire side wall temperature on the basis of analog calculation; updating the wall surface heat load, the working medium flow and the water cooling wall inlet and outlet pressure difference of each section for multiple times until the pressure drop of each section meets the convergence condition; in each updating process, the heat load of each wall temperature measuring point is obtained according to the wall surface heat load of each section, the working medium flow, the initial value of the pressure difference between the inlet and the outlet of the water cooling wall, the measured value of each wall temperature measuring point and the relational database; and updating the wall surface heat load, the working medium flow and the water cooling wall inlet and outlet pressure difference of each section according to the heat load of each wall temperature measuring point. According to the method, the thermal load distribution of the spiral water-cooled wall hearth in the height direction and the width direction can be monitored more accurately and comprehensively.

Description

Technical Field

[0001] The present application belongs to the technical field of boilers, and in particular, relates to an online monitoring method for the heat load of a spiral water-cooled fireplace hearth under supercritical conditions. Background Art

[0002] The furnace heat load can directly reflect the heat entering the boiler and its distribution, which has important guiding significance for operation adjustment. At the same time, as the boundary condition for the water-cooled wall hydrodynamic calculation, the furnace heat load is the key to accurately calculate the flow distribution in the parallel tubes under actual operating conditions and judge the safety of the water-cooled wall tube temperature and hydrodynamic stability. Due to the spiral rising structural characteristics of the spiral water-cooled wall, the furnace heat load cannot be simply calculated from the inlet and outlet wall temperatures of each water-cooled wall tube. New methods need to be studied to monitor the furnace heat load of the spiral water-cooled furnace.

[0003] At present, the direct measurement of the heat load on the furnace wall in the spiral water-cooled wall area mainly relies on heat flux meters. This method is costly, has limited measurement locations, and is difficult to achieve large-scale online monitoring. The method of adding temperature points on the fire-facing and back-facing side walls of the water-cooled wall can obtain the furnace heat load by calculation, but the fire-facing side wall temperature points are easy to burn out and cannot meet the long-term monitoring requirements, and fin holes need to be opened, affecting the safety of the water-cooled wall. There is also a spiral water-cooled wall heat load monitoring method that relies on the back-facing side temperature points. The temperature rise along the characteristic tube is used to calculate the heat absorption to reflect the water-cooled hearth heat load. This method can only be used to monitor the heat load along the height direction of the furnace, and cannot reflect the furnace heat load in the width direction. Summary of the invention

[0004] The technical problem solved by the present application is: how to more accurately and comprehensively obtain the heat load of the furnace wall in the spiral water-cooled wall area.

[0005] The present application provides an online monitoring method for the heat load of a spiral water-cooled fireplace hearth under supercritical conditions, the online monitoring method comprising:

[0006] The spiral water-cooled wall is divided into several sections and multiple wall temperature measuring points are arranged on the back-fire side of the spiral water-cooled wall;

[0007] Based on simulation calculation, a database of the relationship between different boundary conditions of spiral water-cooled wall and the back-fired side wall temperature was established;

[0008] Update the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section multiple times until the pressure drop of each section meets the convergence condition;

[0009] Among them, in each updating process, the heat load of each wall temperature measuring point is obtained according to the initial values ​​of the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section, the measured values ​​of each wall temperature measuring point, and the said relational database. The wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section are updated according to the heat load of each wall temperature measuring point, and it is determined whether the pressure drop of each section meets the convergence condition according to the updated wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference.

[0010] Optionally, the method of dividing the spiral water-cooled wall into several sections includes:

[0011] The spiral water-cooled wall is divided into a number of sections according to the structural information of the spiral water-cooled wall, and the pipe length, outer diameter, inner diameter and radiation projection area of ​​each section are obtained.

[0012] Optionally, the method of arranging a plurality of wall temperature measuring points on the back-fire side of the spiral water-cooled wall comprises:

[0013] According to the structure of the spiral water-cooled wall, the burner, the wind box arrangement, the water-cooled wall intermediate mixing header, and the arrangement information of the upper water-cooled wall outlet header measuring points, multiple wall temperature measuring points are arranged on the back-fire side in the height direction and the length direction of the spiral water-cooled wall.

[0014] Optionally, the method for constructing a database of relationships between different boundary conditions of the spiral water-cooled wall and the back-fired side wall temperature based on simulation calculation includes:

[0015] According to the material specifications of the spiral water-cooled wall, numerical calculation methods are used to simulate the installation positions of the back-fire side wall temperature measuring points of the spiral water-cooled wall under supercritical conditions with different working fluid thermal parameters, different working fluid flow rates, and different heat loads on the fire-facing side wall. A database of the relationship between different boundary conditions and the back-fire side wall temperature is established.

[0016] Optionally, when numerical calculation is used, a three-dimensional physical model of the spiral water-cooled wall is established, and the temperature field of the spiral water-cooled wall is calculated using numerical calculation methods. The boundary conditions include the furnace heat load on the flue gas side and the thermal physical parameters on the working fluid side. According to the range of the boundary conditions during operation and at certain change intervals, the wall temperature of the back-fire side distribution points is calculated for all permutations and combinations, and a database of the relationship between different boundary conditions and the back-fire side wall temperature is established.

[0017] Optionally, during the first update, the initial values ​​of the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section are calculated based on the inlet working fluid flow rate, temperature and partition number of each section of the spiral water-cooled wall; when it is not the first update, the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section after the last update are used as the initial values ​​of the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section during this update.

[0018] Optionally, after updating the wall heat load, a systematic correction is performed according to the heat balance.

[0019] The present application provides an online monitoring method for the heat load of a spiral water-cooled fireplace hearth under supercritical conditions, which has the following technical effects:

[0020] This method can more accurately and comprehensively monitor the heat load distribution of the spiral water-cooled fireplace in the height and width directions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1a is an overall flow chart of an online monitoring method for heat load of a spiral water-cooled fireplace hearth under supercritical conditions according to one or more embodiments;

[0022] Figure 1b is a detailed flow chart of an online monitoring method for heat load of a spiral water-cooled fireplace hearth under supercritical conditions according to one or more embodiments;

[0023] Figure 2a A schematic diagram of segment division of a spiral water-cooled wall according to one or more embodiments;

[0024] Figure 2b is a schematic diagram of an expanded spiral water-cooled wall according to one or more embodiments;

[0025] Figure 3 A schematic diagram of wall temperature distribution of a spiral water-cooled wall tube cross section according to one or more embodiments;

[0026] Figure 4a A furnace heat load distribution diagram of each wall temperature measurement point in the width direction according to one or more embodiments;

[0027] Figure 4b A furnace heat load distribution diagram of each wall temperature measurement point in the height direction according to one or more embodiments;

[0028] Figure 5 The figure is a heat load distribution diagram of the entire furnace wall of the spiral water-cooled wall according to one or more embodiments. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0030] Before describing in detail the various embodiments of the present application, the technical concept of the present application is first briefly described: the current calculation method for the furnace wall heat load in the spiral water-cooled wall area is difficult to accurately obtain a comprehensive furnace heat load situation. To this end, the online monitoring method of the spiral water-cooled hearth heat load under supercritical conditions provided by the present application divides the spiral water-cooled wall into several sections and sets multiple wall temperature measurement points, constructs a database of the relationship between different boundary conditions and the back-fire side wall temperature, and updates the values ​​of the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section multiple times until the pressure drop of each section meets the convergence conditions, so as to obtain a more accurate and comprehensive spiral water-cooled hearth heat load. The specific principles of the online monitoring method of the spiral water-cooled hearth heat load under supercritical conditions of the present application are described below in combination with more embodiments.

[0031] Specifically, Figure 1a and Figure 1b As shown, the online monitoring method of the heat load of the spiral water-cooled fireplace hearth under supercritical conditions in this embodiment includes the following steps:

[0032] Step S10, dividing the spiral water-cooled wall into several sections and arranging a plurality of wall temperature measuring points on the back-fire side of the spiral water-cooled wall;

[0033] Step S20, constructing a database of the relationship between different boundary conditions of the spiral water-cooled wall and the back-fired side wall temperature based on simulation calculation;

[0034] Step S30, repeatedly updating the wall heat load, working fluid flow rate, and water wall inlet and outlet pressure difference of each section until the pressure drop of each section meets the convergence condition. In each updating process, the heat load of each wall temperature measuring point is obtained according to the initial values ​​of the wall heat load, working fluid flow rate, and water wall inlet and outlet pressure difference of each section and the measured values ​​of each wall temperature measuring point and the relational database, and the wall heat load, working fluid flow rate, and water wall inlet and outlet pressure difference of each section are updated according to the heat load of each wall temperature measuring point, and it is determined whether the pressure drop of each section meets the convergence condition according to the updated wall heat load, working fluid flow rate, and water wall inlet and outlet pressure difference.

[0035] In one or more embodiments, in step S10, the spiral water-cooled wall is divided into several sections according to the structural information of the spiral water-cooled wall, such as Figure 2a As shown, the spiral water-cooled wall is divided into n zones with a roots as one zone, and each zone is divided into m sections along the way, totaling n*m sections, and the tube length l and outer diameter d of each section are obtained. r , inner diameter d n and radiation projection area, and calculate the friction coefficient ξ of the pipe section m , local resistance coefficient ξ jb . Figure 2bThe unfolded structure of the spiral water-cooled wall and the arrangement of two spiral water-cooled tubes are shown. According to the structure of the spiral water-cooled wall, the burner, the wind box arrangement, the water-cooled wall intermediate mixing header, and the arrangement information of the upper water-cooled wall outlet header measurement points, multiple wall temperature measurement points are arranged on the back-fire side in the height direction and length direction of the spiral water-cooled wall.

[0036] Exemplarily, in the height direction, the measuring points are mainly arranged on the left and right side walls, from the lower cold ash hopper area to below the middle mixing header, and suitable positions are selected for arrangement based on factors such as the burner position, furnace coking, and high-temperature corrosion. In the width direction, they are mainly arranged above the ember wind, and within the furnace soot blowing and purge range on the corresponding fire side. They are arranged on the front, back, left and right walls, and multiple points are arranged at a single selected position.

[0037] In one or more embodiments, the method of constructing a database of relationships between different boundary conditions of the spiral water-cooled wall and the back-fired side wall temperature based on simulation calculation in step S20 includes: according to the material specifications of the spiral water-cooled wall, using numerical calculation means, simulating and calculating the installation positions of the back-fired side wall temperature measuring points of the spiral water-cooled wall under supercritical conditions, different working fluid thermal parameters in the tube, different working fluid flow rates, and different heat loads on the fire-facing side wall surface, Figure 3 The wall temperature distribution of the spiral water-cooled wall tube section under typical working conditions is shown, and a database of the relationship between different boundary conditions and the back-fire side wall temperature is established.

[0038] For example, in order to improve the accuracy of numerical calculation results, it is necessary to establish a three-dimensional physical model of the water-cooled wall tubes and use numerical calculation methods to calculate the water-cooled wall temperature field; the boundary conditions in the calculation mainly include the furnace heat load on the flue gas side and the thermal physical parameters on the working fluid side. According to the possible range of boundary conditions during operation, the wall temperature of the back-fire side distribution points is calculated at a certain change interval under all permutations and combinations, and a database of the relationship between different boundary conditions and the back-fire side wall temperature is established.

[0039] Furthermore, during the first update, the initial values ​​of the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section are calculated based on the inlet working fluid flow rate, temperature, and partition number of each section of the spiral water-cooled wall; when it is not the first update, the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section after the last update are used as the initial values ​​of the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section during this update.

[0040] For example, at the first update, according to the inlet working fluid flow rate G of the spiral water-cooled wall in , temperature T in , pressure P in According to the inlet working fluid flow rate and the number of water-cooled wall partitions i, the initial working fluid flow rate of each section is calculated. Assuming the outlet pressure P out0 According to the measured spiral water wall inlet and outlet temperatures T out n , calculate the total heat absorption Q of the water-cooled wall 0 , according to the total area of ​​the spiral water-cooled wall, initialize the heat load of each section of the water-cooled wall Lower water wall inlet and outlet pressure difference

[0041] For example, when calculating the heat load of each wall temperature measuring point, according to the working fluid flow rate G of each section of the water-cooled wall i , heat load of each section of the water wall q ij , calculate the resistance loss of the pipe section from the water-cooled wall inlet to the measuring point installation location of the wall temperature measuring point circuit, including the friction resistance ΔP mk , local resistance ΔP jbk , gravity pressure difference ΔP zwk and enthalpy increase ΔH k , calculate the working fluid pressure P at the backfire side wall temperature measurement point k =P in -(ΔP mk +ΔP jbk +ΔP zwk ), according to the wall temperature measuring point location temperature T k , combined with the circuit flow G k And measure the wall temperature at multiple points on the back-fire side, and update the water-cooled fireplace heat load q at the back-fire side wall temperature measurement point location according to the relational database k , and update the furnace heat load q of each section ij . Figure 4a The heat load distribution of the furnace at each wall temperature measuring point in the width direction is shown. Figure 4b The furnace heat load distribution at each wall temperature measurement point in the height direction is shown.

[0042] For example, after obtaining the furnace heat load at each wall temperature measurement point, the interpolation algorithm is used to calculate the furnace wall heat load of the entire spiral water-cooled wall. Considering the influence of the back-fire side wall temperature measurement error and the complexity of the heat load distribution in the furnace, the lower furnace heat load distribution obtained based on the limited back-fire side measurement points still has a certain error from the actual situation, so it needs to be systematically corrected according to the heat balance. Figure 5 The heat load distribution of the furnace wall in the entire area of ​​the spiral water-cooled wall is shown.

[0043] Furthermore, when determining the pressure drop of each section, since the pressure balance pipe is used to connect the middle mixing headers, the pressure of the mixing headers in the front, back, left and right walls is consistent, and the static pressure effect of the header width is ignored, the pressure difference between the inlet and outlet of the water-cooled wall in each partition should be the same. According to this principle, when the inlet pressure of the water-cooled wall and the total feedwater flow are known, the iterative calculation of the lower water-cooled wall flow distribution is performed to determine the pressure drop of each section. Specifically, the working fluid flow resistance of each section is calculated, including the friction resistance ΔP mij , local resistance ΔP jbij , gravity pressure difference ΔP zwij , obtain the total pressure drop from the water wall inlet to the outlet of each section Update the water wall inlet and outlet pressure difference ΔP; where the convergence condition is:

[0044]

[0045] If converged, the current furnace heat load q of each section of the spiral water-cooled wall is output ij , working fluid flow G i , water wall inlet and outlet pressure difference. If it does not converge, repeat the above step S30 until the convergence condition is met.

[0046] The specific implementation methods of the present application are described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that these embodiments can be modified and improved without departing from the principles and spirit of the present application whose scope is defined by the claims and their equivalents. These modifications and improvements should also be within the scope of protection of the present application.

Claims

1. An online monitoring method for the heat load of a spiral water-cooled hearth under supercritical conditions, characterized in that: The online monitoring method comprises: The spiral water-cooled wall is divided into several sections and multiple wall temperature measuring points are arranged on the back-fire side of the spiral water-cooled wall; Based on simulation calculation, a database of the relationship between different boundary conditions of spiral water-cooled wall and the back-fired side wall temperature was established; Update the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section multiple times until the pressure drop of each section meets the convergence condition; Among them, in each updating process, the heat load of each wall temperature measuring point is obtained according to the initial values ​​of the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section, the measured values ​​of each wall temperature measuring point, and the said relational database. The wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section are updated according to the heat load of each wall temperature measuring point, and it is determined whether the pressure drop of each section meets the convergence condition according to the updated wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference.

2. The method for online monitoring of heat load of a spiral water-cooled hearth under supercritical conditions according to claim 1 is characterized in that: The method for dividing the spiral water-cooled wall into a plurality of sections comprises: The spiral water-cooled wall is divided into several sections according to the structural information of the spiral water-cooled wall, and the pipe length, outer diameter, inner diameter, radiation projection area, pipe section friction resistance coefficient and local resistance coefficient of each section are obtained.

3. The method for online monitoring heat load of a spiral water-cooled fireplace hearth under supercritical conditions according to claim 1, characterized in that: The method of arranging a plurality of wall temperature measuring points on the back-fire side of the spiral water-cooled wall comprises: According to the structure of the spiral water-cooled wall, the burner, the wind box arrangement, the water-cooled wall intermediate mixing header, and the arrangement information of the upper water-cooled wall outlet header measuring points, multiple wall temperature measuring points are arranged on the back-fire side in the height direction and the length direction of the spiral water-cooled wall.

4. The method for online monitoring heat load of a spiral water-cooled hearth under supercritical conditions according to claim 1, characterized in that: The method for constructing a database of relationships between different boundary conditions of the spiral water-cooled wall and the back-fired side wall temperature based on simulation calculation includes: According to the material specifications of the spiral water-cooled wall, numerical calculation methods are used to simulate the installation positions of the back-fire side wall temperature measuring points of the spiral water-cooled wall under supercritical conditions with different working fluid thermal parameters, different working fluid flow rates, and different heat loads on the fire-facing side wall. A database of the relationship between different boundary conditions and the back-fire side wall temperature is established.

5. The method for online monitoring of heat load of a spiral water-cooled hearth under supercritical conditions according to claim 4, characterized in that: When numerical calculation is used, a three-dimensional physical model of the spiral water-cooled wall is established, and the temperature field of the spiral water-cooled wall is calculated using numerical calculation methods. The boundary conditions include the furnace heat load on the flue gas side and the thermal physical parameters on the working fluid side. According to the range of the boundary conditions during operation and at a certain change interval, the wall temperature of the back-fire side distribution points is calculated under all permutations and combinations, and a database of the relationship between different boundary conditions and the back-fire side wall temperature is established.

6. The method for online monitoring heat load of a spiral water-cooled hearth under supercritical conditions according to claim 1, characterized in that: During the first update, the initial values ​​of the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section are calculated based on the inlet working fluid flow rate, temperature and partition number of each section of the spiral water-cooled wall; when it is not the first update, the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section after the last update are used as the initial values ​​of the wall heat load, working fluid flow rate, and water-cooled wall inlet and outlet pressure difference of each section during this update.

7. The method for online monitoring heat load of a spiral water-cooled hearth under supercritical conditions according to claim 1, characterized in that: After updating the wall heat load, a systematic correction is made according to the heat balance.

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