A load control system and method for a supercritical heat supply unit

Abstract

The present invention discloses a load control system and method for a supercritical heat supply unit, including a high and intermediate pressure cylinder, a extraction steam pressure regulating valve, a heat network heat exchanger, a low pressure cylinder of a steam turbine, and a connecting pipe pressure regulating valve. Since the requirements for the steam parameters of the extraction steam for heating are not high, the steam source is usually extracted from the exhaust of the intermediate pressure cylinder of the steam turbine. This extraction steam enters the heat supply heat exchanger, exchanges heat with the cold working medium of the heat network users, and then enters the condenser through the drain pipe, and re-enters the thermal cycle through the condensate pump. To ensure the extraction steam pressure, a connecting pipe pressure regulating valve is provided on the connecting pipe from the exhaust of the intermediate pressure cylinder to the inlet of the low pressure cylinder to regulate the extraction steam pressure. A pressure regulating valve is provided on the side of the heating extraction steam pipeline, which is used to regulate the steam flow rate of the working medium of the heat network heat exchanger when the heat user demand changes.

Description

Technical Field

[0001] The present invention belongs to the technical field of automatic control of thermal power plants, and particularly relates to a load control system and method for a supercritical heating unit. Background Art

[0002] In recent years, the proportion of heating units in the installed capacity has gradually increased, and more and more large-scale supercritical units are used as heating units for heating. Super (ultra) critical units have a large capacity, high parameters, and high overall thermal efficiency, and can play a more important role in energy conservation, environmental protection, and emission reduction compared with conventional cogeneration units.

[0003] Compared with the industrial extraction steam system, the heating extraction steam system has its own characteristics. Its purpose is to provide heating for residents and urban public utilities, so the requirements for extraction steam parameters are not high. Usually, the exhaust steam from the intermediate pressure cylinder of the steam turbine is used as the steam source. It has obvious seasonality, with large annual variations and small daily variations.

[0004] Since the requirements for the steam parameters of the heating extraction steam are not high, the steam source is usually extracted from the exhaust steam of the intermediate pressure cylinder of the steam turbine. This extraction steam enters the heating heat exchanger, exchanges heat with the cold working medium of the heat network users, and then enters the condenser through the drain pipe and re-enters the thermal cycle through the condensate pump. To ensure the extraction steam pressure, a connecting pipe pressure regulating valve is set on the connecting pipe from the exhaust of the intermediate pressure cylinder to the inlet of the low pressure cylinder to regulate the extraction steam pressure.

[0005] When it is necessary to reduce the extraction steam pressure, the opening of the connecting pipe pressure regulating valve is increased to allow more exhaust steam from the intermediate pressure cylinder to enter the low pressure cylinder for work. When it is necessary to increase the extraction steam pressure, the opening of the connecting pipe pressure regulating valve is reduced to allow more exhaust steam from the intermediate pressure cylinder to enter the extraction steam system to heat the heat network users. At the same time, to ensure the minimum steam flow of the low pressure cylinder, when the inlet pressure of the low pressure cylinder is low, the closing of this regulating valve is blocked to ensure the safety of the low pressure cylinder blades. A pressure regulating valve is set on the heating extraction steam pipeline side to regulate the steam flow of the working medium of the heat network heat exchanger when the heat user demand changes.

[0006] Since the extraction of some steam from the exhaust of the intermediate pressure cylinder for heating in the heating unit will affect the entry of this part of the steam into the low pressure cylinder for work, resulting in a mismatch between the electrical load and the heating load of the unit; if the electrical load of the unit is still used as the reference for unit coordinated control at this time, it will inevitably cause an imbalance between the energy of the boiler and the demand of the steam turbine, leading to the imbalance of important parameters such as load, temperature, and pressure, and further affecting the safe and stable operation of the unit, and it is even more impossible to meet the rapid response requirements of the grid AGC for the unit load. Summary of the Invention

[0007] The object of the present invention is to solve the problems in the prior art and provide a load control system and method for a supercritical heat supply unit. The present invention can accurately calculate the heating extraction steam heat load and effectively add it to the unit coordinated control system to improve the regulation quality of the load control of the supercritical heat supply unit.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A load control system for a supercritical heat supply unit includes:

[0010] A boiler, the exhaust steam of the boiler enters the high-pressure and intermediate-pressure cylinders to do work, and the exhaust steam after doing work enters the low-pressure cylinder for exhaust;

[0011] A low-pressure cylinder, the exhaust steam of the low-pressure cylinder sequentially passes through a condenser, a condensate pump, a low-pressure heater, a deaerator, a feed water pump and a high-pressure heater and then returns to the boiler;

[0012] A heat network heat exchanger, the heat source of the heat network heat exchanger comes from a part of the exhaust steam of the high-pressure and intermediate-pressure cylinders, and after heat exchange, it is transported to the inlet of the condensate pump.

[0013] A further improvement of the present invention lies in:

[0014] A part of the exhaust steam of the high-pressure and intermediate-pressure cylinders enters the low-pressure cylinder through a connecting pipe pressure regulating valve, and another part enters the heat network heat exchanger through an extraction steam pressure regulating valve in sequence.

[0015] A heating extraction steam check valve is arranged at the inlet of the extraction steam pressure regulating valve.

[0016] A load control method for a supercritical heat supply unit includes the following steps:

[0017] Step 1, calculate the heat quantity of the extraction steam parameters;

[0018] Step 2, when the unit load changes or the heat network user demand changes, calculate the heating heat quantity using the steam parameters;

[0019] Step 3, when the extraction steam flow or the drainage flow measurement is inaccurate, calculate the heat quantity using the inlet and outlet water temperatures and the flow rate on the heat network user side;

[0020] Step 4, convert the calculated extraction steam heat quantity into heat power;

[0021] Step 5, convert the heat power into electric power;

[0022] Step 6, when the heating extraction steam check valve is closed or the extraction steam pressure regulating valve command is less than 5%, delay for 20 s; when the calculated heating electric load has bad quality, lock the calculated load;

[0023] Step 7: When the calculated change in thermoelectric load is less than the set value, maintain the current value; when the change in the calculated load value is greater than the set value, output the value that tracks the actual calculation; then add speed limit, inertia, and high and low amplitude limiting links, and finally obtain the heating and electric loads required for coordinated control.

[0024] Step 8: According to the calculated heating and electric loads, add them to the coordinated control to make the heat of the boiler match the demand of the steam turbine and the electric load of the generator match the thermal load of the steam turbine.

[0025] A further improvement of the method of the present invention is as follows:

[0026] In step 1, the heat of the extraction steam parameters is calculated according to the following formula:

[0027] q r =(T s -T0)C ps +r+(T0-T w )C pw Q m

[0028] Wherein, q r is the calculated extraction steam heat, T s is the extraction steam temperature, T0 is the saturation temperature at the extraction steam pressure, C ps is the specific heat capacity at constant pressure of the steam at the extraction steam pressure, r is the latent heat of vaporization of water vapor, T w is the drain temperature, C pw is the specific heat capacity of water, and Q m is the extraction steam mass flow rate.

[0029] In step 2, the steam parameters include the heating extraction steam flow rate, pressure, and temperature.

[0030] In step 3, when the measurement of the extraction steam flow rate or the drain water flow rate is inaccurate, the heat is calculated according to the following formula:

[0031] q r =(T1-T2)C pw Q m

[0032] Wherein, q r is the calculated extraction steam heat, T1 is the outlet water temperature on the heat network user side, T2 is the inlet water temperature on the heat network user side, C pw is the specific heat capacity of water, and Q m is the mass flow rate of water on the heat network user side.

[0033] In step 4, the method of converting the calculated extraction steam heat into thermal power is as follows:

[0034] P rl =1000q r / 3600 = 0.278q r

[0035] Among them, P rl is the calculated thermal power, in MW.

[0036] In the said step 5, the method for converting thermal power into electric power is as follows:

[0037] P r = K × η LP × P rl

[0038] Among them, P rl is the calculated thermal power; P r is the calculated extraction thermoelectric power; η LP is the low-pressure cylinder efficiency; K is the correction coefficient.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention considers aspects such as the calculation of heating extraction steam heat, the calculation of heating electric load, and the optimization of unit load control (boiler master control loop, main steam pressure generation loop, fuel correction loop) for supercritical heating units. On the premise of ensuring accurate calculation of the heating load, the load control loop is modified accordingly to meet the requirements of the unit coordinated system to respond in a timely manner when the extraction steam changes. According to the actual operation situation, a reasonable calculation method for the heating extraction steam load is selected to accurately calculate the magnitude of the heating load and ensure the stable operation of the unit coordinated control. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0042] Figure 1 Heating extraction steam system diagram.

[0043] Figure 2 Logic diagram of heating electric load generation loop.

[0044] Figure 3 Logic diagram of heating unit load control optimization.

[0045] Wherein: 1 - boiler, 2 - high and medium pressure cylinder, 3 - low pressure cylinder, 4 - condenser, 5 - condensate pump, 6 - low pressure heater, 7 - deaerator, 8 - feed water pump, 9 - high pressure heater, 10 - heat exchanger for heat supply network, 11 - connecting pipe pressure regulating valve, 12 - check valve for extraction steam for heat supply, 13 - extraction steam pressure regulating valve. Specific implementation manners

[0046] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0048] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0049] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship in which the product of the invention is usually placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention. In addition, terms such as "first", "second", etc. are only used for distinguishing descriptions and cannot be construed as indicating or implying relative importance.

[0050] In addition, if the term "horizontal" appears, it does not mean that the component is required to be absolutely horizontal, but it can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but it can be slightly inclined.

[0051] In the description of the embodiments of the present invention, it should also be noted that unless otherwise clearly specified and limited, if the terms "set", "installed", "connected", and "connected" are used, they should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0052] The following further describes the present invention in detail with reference to the accompanying drawings:

[0053] See Figure 1 , an embodiment of the present invention discloses a load control system for a supercritical heating unit, including a high-pressure and intermediate-pressure cylinder 2, an extraction steam pressure regulating valve 13, a heat network heat exchanger 10, a low-pressure cylinder 3 of a steam turbine, and a connecting pipe pressure regulating valve 11. Since the steam parameters required for heating extraction steam are not high, the steam source is usually extracted from the exhaust of the intermediate-pressure cylinder of the steam turbine. The extracted steam enters the heating heat exchanger, exchanges heat with the cold working medium of the heat network user, and then enters the condenser 4 through the drain pipe, and re-enters the thermal cycle through the condensate pump 5. To ensure the extraction steam pressure, a connecting pipe pressure regulating valve 11 is provided on the connecting pipe from the exhaust of the intermediate-pressure cylinder to the inlet of the low-pressure cylinder 3 to regulate the extraction steam pressure. A pressure regulating valve is provided on the side of the heating extraction steam pipeline to regulate the steam flow of the working medium of the heat network heat exchanger 10 when the heat user demand changes.

[0054] In the present invention, the steam parameters of the heating extraction steam are calculated. Usually, a flow nozzle is provided behind the extraction steam regulating valve of the unit to measure the flow, temperature, and pressure of the heating extraction steam. Therefore, the extraction steam heat can be calculated through the steam parameters of the heating extraction steam. When the unit load changes or the heat network user demand changes, the flow, pressure, and temperature of the heating extraction steam all change rapidly. Using the above steam parameters for heating heat calculation can timely and accurately reflect the change of the extraction steam heat load, ensure that the sub-circuits such as water, coal, and air of the boiler 1 make timely responses, and ensure the stable operation of the unit. When the extraction steam pressure measurement is inaccurate or there is no measuring point, the drainage volume of the heat network heater can be used for calculation.

[0055] After calculating the heating extraction steam heat, it is necessary to convert it into the unit of electric load and add the corresponding judgment and switching logic to ensure the authenticity and effectiveness of the calculated heat.

[0056] The calculated heating electric load is added to the coordinated control to ensure that the heat of the boiler 1 matches the demand of the steam turbine, and the electric load of the generator is consistent with the heat load of the steam turbine.

[0057] For a supercritical coal-fired unit with a heat extraction function for heating, the heating load changes relatively slowly. On the premise of ensuring accurate calculation of the heating load, corresponding modifications to the load control loop can meet the requirements of the coordinated control system of the unit to respond promptly to the changes in extraction steam. According to the actual operating conditions, reasonably selecting the calculation method of the heating extraction steam load to accurately calculate the magnitude of the heating load is the key to ensuring the stable operation of the unit's coordinated control.

[0058] In the present invention, the steam parameters of the heating extraction steam are used for calculation. Usually, a flow nozzle is provided behind the extraction steam regulating valve of the unit to measure the flow rate, temperature, and pressure of the heating extraction steam. Therefore, the extraction steam heat can be calculated through the steam parameters of the heating extraction steam. The heat calculation formula for the extraction steam parameters is as follows:

[0059] q r =(T s -T0)C ps +r+(T0-T w )C pw Q m

[0060] Wherein, q r is the calculated extraction steam heat, T s is the extraction steam temperature, T0 is the saturation temperature at the extraction steam pressure, C ps is the specific heat capacity at constant pressure of the steam at the extraction steam pressure, r is the latent heat of vaporization of water vapor, T w is the drain temperature, C pw is the specific heat capacity of water, Q m is the extraction steam mass flow rate.

[0061] When the unit load changes or the demand of the heat network users changes, the flow rate, pressure, and temperature of the heating extraction steam all change rapidly. Using the above steam parameters for calculating the heating heat can timely and accurately reflect the change of the extraction steam heat load, ensuring that the sub-loops such as water, coal, and air in Boiler 1 make timely responses and ensuring the stable operation of the unit. When the extraction steam pressure measurement is inaccurate or there is no measurement point, the heat can be calculated using the drain water volume of the heat network heater. When calculating with the cold working medium parameters of the heat network and the heat network system is in a stable state, the heat consumed by the heat network extraction steam is equal to the heat absorbed by the cold working medium on the user side. Therefore, when the extraction steam flow rate or the drain water volume measurement is inaccurate, the heat can be calculated using the inlet and outlet water temperatures and the flow rate on the user side of the heat network. The calculation formula is as follows:

[0062] q r =(T1-T2)C pw Q m

[0063] Wherein, q r is the calculated extraction steam heat, T1 is the outlet water temperature on the user side of the heat network, T2 is the inlet water temperature on the user side of the heat network, C pw is the specific heat capacity of water, Q mis the water mass flow rate on the user side of the heat network.

[0064] The extracted steam heat calculated by the above formula is in energy unit, and it needs to be converted to power unit first. The conversion formula is as follows:

[0065] P rl = 1000q r / 3600 = 0.278q r

[0066] where q r is the calculated extracted steam heat, GJ / h; P rl is the calculated heat power, MW.

[0067] Since the heating extracted steam is extracted from the exhaust of the intermediate pressure cylinder and this part of the steam does not enter the low pressure cylinder 3 to do work, the calculated heat power in the above formula needs to be converted to electric power. The conversion formula is as follows:

[0068] P r = K × η LP × P rl .

[0069] where P rl is the calculated heat power, MW; P r is the calculated extracted steam thermoelectric power, MW; η LP is the efficiency of the low pressure cylinder 3, which can be obtained from the steam turbine instruction manual; K is the correction coefficient, which can be calculated by comparing the non-heating and heating operating conditions of the on-site unit.

[0070] The heating electric load is calculated from the measured points such as the working medium flow rate, temperature, and pressure. There are many influencing factors, and the water side flow rate fluctuates relatively frequently. Therefore, corresponding logical judgments are required to ensure the authenticity and effectiveness of the heating load calculation. The specific logic is shown in Figure 2 .

[0071] When the heating extracted steam check valve 12 is closed or the command of the extracted steam pressure regulating valve 13 is less than 5%, a 20s delay is applied, and it is considered that the heating extracted steam circuit has been cut off at this time, and its heating electric load is switched from the calculated value to 0. When there is bad quality in the calculated heating electric load, the calculated load is locked to avoid load fluctuations caused by inaccurate measured points.

[0072] Since this control scheme is for the heating thermal load and its daily variation range is small, in order to avoid large fluctuations in the calculated electric load caused by measured point disturbances, a load calculation locking function is added. When the calculated thermoelectric load changes relatively little, the current value is maintained to keep the system stable. When the calculated load value changes greatly, the output tracks the actual calculated value to ensure the accuracy of the calculation result. To avoid large fluctuations in the calculated measured points and measurement errors, speed limit, inertia, and high and low amplitude limiting links are added later to finally obtain the heating electric load required for coordinated control.

[0073] According to the calculated heat and power loads, add them to the coordinated control to ensure that the heat output of Boiler 1 matches the demand of the steam turbine, and the electrical load of the generator is consistent with the thermal load of the steam turbine. The specific logic is shown in Figure 3 .

[0074] (1) Master control loop of Boiler 1. When the heat extraction electrical load changes, it directly requires a change in the energy of Boiler 1. Therefore, this calculated load is superimposed on the feedforward of the master control command of Boiler 1 to ensure corresponding increases and decreases in sub-loops such as air, coal, and water, thus ensuring the timely response of Boiler 1 when the heat supply load changes.

[0075] (2) Main steam pressure generation loop. Due to the generation of heat extraction steam, the steam inlet volume of the steam turbine increases, resulting in a deviation from the actual electrical load. If the original sliding pressure curve is still used for operation at this time, it will lead to too low main steam pressure, too large throttle opening, reducing the unit's economy and affecting safety. Therefore, the heat extraction electrical load superimposed value needs to be added to the steam turbine sliding pressure curve generation loop to ensure normal main steam pressure of the unit.

[0076] (3) Fuel correction loop (BTU). The fuel correction loop adjusts the fuel correction coefficient through the difference between the designed coal quantity and the actual coal quantity at the current load, thereby realizing the adaptive function of coordinated control when the coal type changes. Therefore, the heat extraction electrical load needs to be superimposed on the designed coal quantity calculation loop to ensure the accuracy of the adjustment of the fuel correction loop.

[0077] For a supercritical coal-fired unit with heat extraction steam function, the change of its heat supply load is relatively slow. On the premise of ensuring accurate calculation of the heat supply load, corresponding modifications to the load control loop can meet the requirements of the unit's coordinated system for timely response when the steam extraction changes. According to the actual operation situation, reasonably select the calculation method of the heat extraction steam load, so as to accurately calculate the size of the heat supply load, which is the key to ensuring the stable operation of the unit's coordinated control.

[0078] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A load control method for a supercritical heat supply unit, the method being based on a load control system for a supercritical heat supply unit, the control system comprising a boiler (1), a low-pressure cylinder (3), and a heat network heat exchanger (10); The exhaust steam of the boiler (1) enters the high and intermediate pressure cylinder (2) to do work, and the exhaust steam after doing work enters the low pressure cylinder (3) for exhaust; a part of the exhaust steam of the high and intermediate pressure cylinder (2) enters the low pressure cylinder (3) through the connecting pipe pressure regulating valve (11), and another part enters the heat network heat exchanger (10) successively through the extraction steam pressure regulating valve (13); a heat supply extraction steam check valve (12) is arranged at the inlet of the extraction steam pressure regulating valve (13); the exhaust steam of the low pressure cylinder (3) successively passes through the condenser (4), condensate pump (5), low pressure heater (6), deaerator (7), feed water pump (8) and high pressure heater (9), and then returns to the boiler (1); the heat source of the heat network heat exchanger (10) comes from a part of the exhaust steam of the high and intermediate pressure cylinder (2), and after heat exchange, it is transported to the inlet of the condensate pump (5); it is characterized in that, The control method comprises the following steps: Step 1, calculate the extraction steam heat; Step 2, when the unit load changes or the heat network user demand changes, calculate the heating extraction steam heat using steam parameters; the steam parameters include the heating extraction steam flow rate, pressure, and temperature; Step 3, when the extraction steam flow rate or the drain water volume measurement is inaccurate, calculate the extraction steam heat using the inlet and outlet water temperatures and flow rate on the heat network user side; Step 4, convert the calculated extraction steam heat into thermal power; Step 5, convert the thermal power into electric power; Step 6, when the heating extraction steam check valve (12) is closed or the command of the extraction steam pressure regulating valve (13) is less than 5%, delay for 20 s; when the calculated heating electric load has bad quality, lock the calculated load; Step 7, when the change in the calculated thermal and electric load is less than the set value, maintain the current value; when the change in the calculated load value is greater than the set value, output and track the actual calculated value; add speed limit, inertia, and high and low amplitude limiting links thereafter, and finally obtain the heating electric load required for coordinated control; Step 8, according to the calculated heating electric load, add it to the coordinated control to make the heat of the boiler (1) match the demand of the steam turbine and the electric load of the generator match the thermal load of the steam turbine.

2. The load control method for a supercritical heat supply unit according to claim 1, wherein In the said Step 3, when the extraction steam flow rate or the drain water volume measurement is inaccurate, the heat is calculated according to the following formula: Among them, For calculating the extraction steam heat, is the outlet water temperature on the heat network user side, is the inlet water temperature on the heat network user side, is the specific heat capacity of water, is the water mass flow rate on the heat network user side.

3. The supercritical heat supply unit load control method according to claim 1, characterized in that, In the said Step 4, the method for converting the calculated extraction steam heat into thermal power is as follows: Among them, is for calculating the thermal power, in MW.

4. The load control method for a supercritical heat supply unit according to claim 1, wherein In the said Step 5, the method for converting the thermal power into electric power is as follows: wherein, is for calculating the thermal power; is for calculating the extraction thermoelectric power; is the low-pressure cylinder efficiency; is the correction factor.

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