A method for operating and regulating a low-temperature backwater combined heat and power system
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NORTH CHINA POWER ENG
- Filing Date
- 2026-03-25
- Publication Date
- 2026-07-03
Smart Images
Figure CN122328802A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of heating technology, specifically relating to a method for operating and regulating a low-temperature return water cogeneration heating system. Background Technology
[0002] Conventional cogeneration heating systems are typically designed with supply and return water temperatures of 130℃ / 70℃, while low-temperature return water cogeneration systems are typically designed with supply and return water temperatures of 130℃ / 30℃. At the power plant side, exhaust steam from the turbine directly heats the circulating water in the heating network, and then extracted steam is used for peak heating. At the city heating station, absorption heat exchangers are used to lower the primary network return water temperature to around 30℃. In 2016, the Shanxi Gujiao-Taiyuan long-distance heating project, the first to apply this technology, was officially put into operation. The project employs a multi-stage high back-pressure heating method, utilizing six thermal power units at the Gujiao Power Plant, and transmitting heat through a 37.8km long-distance pipeline, successfully supplying 76 million cubic meters of heating water to Taiyuan City with a design supply and return water temperature of 130℃ / 30℃. 2 Users implementing centralized heating account for 30% of the centralized heating area in Taiyuan City. Low-temperature return water cogeneration heating systems are large-scale, complex, and subject to many operational influencing factors. Operating parameters and adjustment methods have a significant impact on system energy efficiency.
[0003] With changes in outdoor temperature and heating load, conventional heating systems employ regulation methods such as quality regulation (changing the supply water temperature) and quantity regulation (changing the circulating water flow rate). The main considerations are changes in heat load, power consumption of the water pumps, and the stability of the hydraulic system. In low-temperature return water heating systems, the circulating water volume and temperature have a significant impact on system energy consumption, and different operating regulation methods result in substantial differences in heating energy consumption. Furthermore, power plant units employ multi-stage exhaust steam + extraction steam heating, and the matching of the unit's heating steam under different heat loads also greatly affects energy consumption. Therefore, there is an urgent need to propose an operating regulation method suitable for low-temperature return water cogeneration heating systems. Summary of the Invention
[0004] The technical problem to be solved by this invention is to provide a method for regulating the operation of a low-temperature return water cogeneration heating system, which solves the problem of high energy consumption in existing regulation methods, reduces the equivalent electricity of power plant heating, and reduces annual operating costs.
[0005] According to the technical solution of the present invention, the present invention provides a method for operation and regulation of a low-temperature return water cogeneration heating system, comprising the following steps: Step S1: Determine the minimum water supply temperature t0 of the system; Step S2: When the heating load is greater than the load threshold Q0, the system operates at maximum circulating water volume, and the water supply temperature gradually decreases from the design temperature to the minimum water supply temperature t0. When the heating load is less than or equal to the load threshold Q0, the system operates at a variable circulating water volume within a set range to maintain the water supply temperature at the minimum water supply temperature t0. Here, the load threshold Q0 is the heating load of the system under the conditions of maximum circulating water volume and minimum water supply temperature t0. Step S3: Calculate the equivalent electricity for heating of each stage of steam and each operating condition using the following formula; The equivalent electricity from exhaust steam for heating of the i-th unit is w c,i The calculation formula is as follows: , Among them, h c,i h is the enthalpy of the exhaust steam of the i-th unit. cs,i h is the enthalpy of the exhaust steam condensate of the i-th unit. co,i The exhaust steam enthalpy value under THA conditions of the unit. The utilization rate of exhaust steam for heating of the i-th unit; The equivalent electricity for steam extraction heating from the i-th unit is w e,i The calculation formula is as follows: , Among them, h e,i h represents the enthalpy of the extracted steam from the i-th unit, expressed in kJ / kg. es,i Here is the enthalpy of the extraction steam condensate from the i-th unit, expressed in kJ / kg. The formula for calculating the weighted average power equivalent to electricity (w) from a power plant for heating is as follows: , Where n is the number of units, q c,i For the exhaust steam heating power of the i-th unit, q e,i Let q be the extraction steam heating power of the i-th unit, and q be the total heating power of the power plant. Step S4: Using the lowest weighted equivalent power w for heating from the power plant as the sorting principle, determine the steam extraction sequence and steam volume of each unit during the heating load change process.
[0006] In some implementations, in step S4, the equivalent power reduction value per unit extraction steam reduction of each unit is calculated using the following formula: Equivalent power reduction value per unit extraction steam reduction = Reduced extraction steam heating capacity × Equivalent power of extraction steam heating capacity + Exhaust steam heating capacity × Equivalent power reduction value of exhaust steam heating capacity; the larger the equivalent power reduction value per unit extraction steam reduction, the better the energy-saving effect; the priority order for extraction steam withdrawal of each unit is determined according to the energy-saving effect from best to worst.
[0007] In some implementations, step S5 is also included, in which the power plant's heating during the initial and final stages of heating is entirely provided by the exhaust steam. Under the quantity regulation mode, the exhaust steam heating capacity of each unit changes accordingly with the change in circulating water volume.
[0008] In some implementations, in step S5, the back pressure of each unit gradually decreases as the heating load decreases.
[0009] In some implementations, in step S5, as the heating load gradually decreases at the end of the heating season, the back pressure of the units that have withdrawn from steam extraction is kept constant, and the back pressure of the units that are still participating in exhaust steam heating is finely adjusted. The reduction in equivalent electricity for heating corresponding to a unit back pressure reduction is calculated. The larger the reduction in equivalent electricity for heating corresponding to a unit back pressure reduction, the higher the unit's equivalent electricity sensitivity. The priority order of regulation is determined according to the unit's equivalent electricity sensitivity from high to low, and regulation is carried out in the order of decreasing unit equivalent electricity sensitivity.
[0010] Compared with the prior art, the beneficial technical effects of the present invention are as follows: 1. The low-temperature return water cogeneration heating system operation and regulation method of the present invention can realize the fine-grained regulation of power plant heating. Based on the traditional simple quality and quantity regulation, the method incorporates the power plant circulating water volume, water supply temperature, heating steam matching, and unit back pressure into the heating regulation range, which can systematically optimize the power plant heating energy consumption.
[0011] 2. The operation and regulation method of the low-temperature return water cogeneration heating system of the present invention is particularly suitable for the operation and regulation of complex low-temperature return water cogeneration heating systems with two or more heating units and multi-stage exhaust steam + extraction steam combined heating.
[0012] 3. The adjustment method of this invention can reduce heating energy consumption by about 10% compared with conventional heating adjustment methods. Attached Figure Description
[0013] Figure 1 This is a flowchart of the method provided by the present invention.
[0014] Figure 2 This is a structural diagram of a low-temperature return water cogeneration heating system according to an embodiment of the present invention.
[0015] Figure 3 This is a graph showing the relationship between heating load and equivalent electricity for heating at three minimum water supply temperatures.
[0016] Figure 4 This is a graph showing the relationship between heating load and equivalent electricity under three different regulation methods.
[0017] Figure 5 This is a graph showing the relationship between heating load and equivalent electricity for heating under conditions of using and not using heating steam matching.
[0018] Figure 6 This is a graph showing the relationship between heating load and heating exhaust steam volume and heating extraction steam volume in a preferred economic operation scheme of this invention. Detailed Implementation
[0019] This invention provides a method for regulating the operation of a low-temperature return water cogeneration heating system, addressing the problems of high heating energy consumption in existing methods and reducing the equivalent electricity generated by power plant heating, thereby lowering annual operating costs. This invention primarily involves regulating the power plant's circulating water volume, supply water temperature, and the extraction steam, exhaust steam, and back pressure of each unit during changes in heat load. Key aspects include determining the minimum supply water temperature, employing staged quality regulation, calculating the equivalent electricity generated by steam at each stage and under each operating condition, determining the extraction steam sequence based on the principle of minimizing the weighted equivalent electricity generated by the power plant, and optimizing the turbine exhaust back pressure at the beginning and end of the heating season. Based on this method, and considering different heating loads during the heating season, a comprehensive economic operation method for a low-temperature return water cogeneration heating system is proposed, encompassing circulating water volume, supply and return water temperatures, heating steam matching, and unit back pressure regulation. This method effectively reduces the heating energy consumption of power plants and improves their heating economy.
[0020] Please see Figure 1 The operation and regulation method of the low-temperature return water cogeneration heating system of the present invention includes the following steps.
[0021] Step S1: Determine the minimum supply water temperature t0 of the system. Specifically, based on the performance of the absorption heat exchanger unit of the urban heating station, determine the minimum supply water temperature t0 of the system (e.g., 90℃) to ensure that the heating system is at a lower return water temperature (e.g., 30℃). The minimum supply water temperature t0 is jointly determined by the system design and equipment safety.
[0022] Step S2 involves phased qualitative and quantitative regulation. Specifically, when the heating load exceeds the load threshold Q0, qualitative regulation is used, with the system operating at maximum circulating water volume, and the supply water temperature gradually decreasing from the design temperature (e.g., 130℃) to the minimum supply water temperature t0. When the heating load is less than or equal to the load threshold Q0, quantitative regulation is used, with the circulating water volume variable within a set range to maintain the supply water temperature at the minimum supply water temperature t0. Here, the load threshold Q0 is the heating load of the system under the conditions of maximum circulating water volume and minimum supply water temperature t0.
[0023] Step S3: Calculate the equivalent electricity for heating at each steam level and under each operating condition. Each steam level refers to steam at different pressures and temperatures, and each operating condition refers to different conditions such as heating or shutdown. In the following formula, 'i' represents the steam level and operating condition. The equivalent electricity for heating represents the ratio of the reduced power generation due to extraction or exhaust steam heating to the reduced heat supply. It is related to the enthalpy of extraction steam, exhaust steam, condensate enthalpy under THA operating conditions, condensate enthalpy, unit back pressure, and exhaust steam heating utilization rate. The equivalent electricity for exhaust steam heating of the i-th unit is w.c,i (Unit: kWh / GJ) The calculation formula is as follows: , Among them, h c,i h represents the enthalpy of the exhaust steam from the i-th unit, expressed in kJ / kg. cs,i h represents the enthalpy of the exhaust steam condensate from the i-th unit, expressed in kJ / kg. co,i The enthalpy of exhaust steam under THA conditions is expressed in kJ / kg. Let be the exhaust steam heating utilization rate of the i-th unit.
[0024] The equivalent electricity for steam extraction heating from the i-th unit is w e,i (Unit: kWh / GJ) The calculation formula is as follows: , Among them, h e,i h represents the enthalpy of the extracted steam from the i-th unit, expressed in kJ / kg. es,i Let enthalpy be the enthalpy of the extraction steam condensate of the i-th unit, expressed in kJ / kg.
[0025] The formula for calculating the weighted average heating equivalent power w of a power plant (or the total heating equivalent power of a power plant, in kWh / GJ) is as follows: , Where n is the number of units; q c,i q represents the exhaust steam heating capacity of the i-th unit, in MW; e,i q represents the extraction steam heating power of the i-th unit, in MW; q represents the total heating power of the power plant, in MW.
[0026] Step S4: Determine the heating steam extraction sequence based on the principle of minimizing the weighted equivalent power of the power plant's heating supply (determine the optimal heating steam matching strategy). The equivalent power of extraction steam and exhaust steam for heating differs among units; when the turbine's heating extraction steam volume decreases and the low-pressure cylinder flow increases, the exhaust steam enthalpy, exhaust steam heating utilization rate, and exhaust steam equivalent power will also change. Therefore, the principle of minimizing the power plant's weighted equivalent power of heating supply should be used to determine the extraction steam input sequence and volume for each unit during changes in heating load.
[0027] One specific approach involves step S4, where the reduction value of the equivalent electricity generated per unit reduction in extracted steam is introduced as a core evaluation indicator. This is defined as the reduction in the equivalent electricity generated by the unit's overall heating capacity when the extracted steam heating capacity of a single unit is reduced (the reduction is represented by subtracting the reduced extracted steam heating capacity from the initial weighted equivalent electricity generated by the power plant, reflecting the magnitude of the reduction). The reduction value of the equivalent electricity generated per unit reduction in extracted steam is calculated using the following formula: Reduction value of equivalent electricity generated per unit reduction in extracted steam = Reduction in extracted steam heating capacity × Equivalent electricity generated by extracted steam + Exhaust steam heating capacity × Reduction value of equivalent electricity generated by exhaust steam heating. Here, the reduction value of equivalent electricity generated by exhaust steam heating refers to the change in equivalent electricity generated by exhaust steam heating due to the reduction in extracted steam heating capacity (equivalent electricity generated by exhaust steam heating before the change minus the changed equivalent electricity generated by exhaust steam heating, reflecting the magnitude of the reduction). The greater the reduction in equivalent electricity per unit of reduced steam extraction, the lower the overall equivalent electricity for heating and the better the energy-saving effect after the corresponding unit reduces steam extraction for heating. The priority order for removing steam extraction from each unit is determined according to the order of energy-saving effect from best to worst, and the steam extraction volume of the units is adjusted according to this order when reducing the heating load.
[0028] Step S5: Optimization of turbine exhaust steam back pressure during the initial and final stages of heating. During the initial and final stages of heating, the power plant's heating supply is entirely provided by exhaust steam. Under the flow regulation mode, the exhaust steam heat supply of each unit changes accordingly with the change in circulating water volume. Preferably, the back pressure of each unit gradually decreases as the heating load decreases, resulting in better energy efficiency.
[0029] One specific approach involves using the lowest weighted equivalent power generation for heating from the power plant as the sorting principle in step S5. As the heating load gradually decreases towards the end of the heating season, the back pressure of units that have ceased steam extraction is maintained constant. For units still participating in exhaust steam heating, the back pressure is fine-tuned. The reduction in equivalent power generation for heating per unit back pressure is calculated. The larger the reduction in equivalent power generation per unit back pressure, the higher the unit's equivalent power sensitivity, and consequently, the lower the overall equivalent power generation of the system after the corresponding unit's back pressure is lowered. The priority order of regulation is determined by sorting the units from highest to lowest equivalent power sensitivity, and regulation is carried out in descending order of equivalent power sensitivity.
[0030] Please see Figure 2The low-temperature return water cogeneration system mainly includes a cogeneration turbine and a heating network circulating water pipeline 2. A condenser, a peak heater, and a relay energy station 5 are installed on the heating network circulating water pipeline 2. Return water (low-temperature water) is output from the relay energy station 5 and enters the heating network circulating water pipeline 2, where it is heated by the condenser and peak heater to become supply water (high-temperature water) at the design temperature before entering the relay energy station 5 again. On the heating network circulating water pipeline 2, the peak heater is located downstream of the condenser. The exhaust pipe of the cogeneration turbine is connected to the exhaust gas input end of the condenser, thereby using the exhaust steam (specifically, low-pressure cylinder exhaust steam; the exhaust steam source can be selected according to the design) to heat the heating network circulating water. The extraction steam pipeline of the cogeneration steam turbine is connected to the heating steam input end of the peak heater, thereby using the steam extracted from the steam turbine (specifically, steam extracted from the high-pressure cylinder, intermediate-pressure cylinder and / or low-pressure cylinder, the source of steam extraction can be designed and selected according to the situation) to further heat the circulating water of the heating network, so that the circulating water of the heating network reaches the required supply water temperature.
[0031] More specifically, there are generally multiple cogeneration turbines (or simply units) (in this article, "multiple" means two or more, including two), and there are also multiple condensers. The condensers are connected to the cogeneration turbines one by one. Figure 2 In the illustrated embodiment, the cogeneration turbine includes Unit 1 101, Unit 2 102, Unit 3 103, Unit 4 104, Unit 5 105, and Unit 6 106; the condenser includes Unit 1 condenser 301, Unit 2 condenser 302, Unit 3 condenser 303, Unit 4 condenser 304, Unit 5 condenser 305, and Unit 6 condenser 306; and the peak heater includes Unit 1 peak heater 401 and Unit 2 peak heater 402.
[0032] Optionally, on the circulating water pipeline 2 of the heating network, all condensers are connected in series, or some condensers 3 are connected in series while others are connected in parallel; in other words, the process of heating the circulating water of the heating network with exhaust steam from multiple cogeneration turbines can be achieved through series heating of exhaust steam from multiple cogeneration turbines, or through a combination of parallel and series connections, thereby fully utilizing the waste heat from the high back pressure exhaust steam. The combination of parallel and series connections refers to, for example... Figure 2 In the embodiment shown, condenser No. 5 305 and condenser No. 6 306 are connected in parallel (there may also be other condensers connected in parallel), while all condensers are connected in series (individual condensers and condensers connected in parallel are connected in series).
[0033] Similarly, the process of heating the circulating water of the heating network with extracted steam from a cogeneration turbine can be achieved through series heating of extracted steam from multiple cogeneration turbines, or through a combination of parallel and series connections. Specifically, there are multiple cogeneration turbines and one or more peak-load heaters. In the case of multiple peak-load heaters, all peak-load heaters can be connected in series, all peak-load heaters can be connected in parallel, or some peak-load heaters can be connected in series while others are connected in parallel on the circulating water pipeline 2. For example... Figure 2 In the illustrated embodiment, peak heater 401 and peak heater 402 are connected in parallel. If other peak heaters are connected in series before or after the parallel connection of peak heater 401 and peak heater 402, a partially parallel and partially series structure is formed. Furthermore, in all cogeneration turbines, some cogeneration turbines have extraction steam lines connected to the same peak heater 4, while others have extraction steam lines connected to different peak heaters 4. Multiple connection relationships are available between the extraction steam lines, thus forming specific structures, i.e., specific extraction steam heating methods, thereby utilizing extraction steam heat more effectively. For example... Figure 2 In the embodiment shown, the extraction steam from turbine No. 5 105 and turbine No. 6 106 is connected to peak heater No. 2 402, and the extraction steam from turbine No. 3 103 and turbine No. 4 104 is connected to peak heater No. 1 401.
[0034] One of the key innovations of this scheme lies in the optimization of turbine exhaust steam back pressure during the initial and final stages of the heating season. During these periods, the power plant's heating supply is entirely provided by exhaust steam. Under the current regulation mode, the exhaust steam heat supply of each unit changes accordingly with variations in circulating water volume. At this time, the back pressure of each unit gradually decreases as the heating load decreases, resulting in better energy efficiency.
[0035] The following example, a thermal power plant in Shanxi Province, further illustrates the technical solution and effects of the present invention.
[0036] like Figure 2 As shown, the thermal power plant has six direct air-cooled thermal power units (2×300MW, 2×600MW, and 2×660MW, n=6). The units employ a six-stage exhaust steam + four-stage extraction steam heating system. Units 5 and 6 are connected in parallel with exhaust steam from other units, and are supplied with heat via a high back-pressure system. Units 1 and 2 are supplied with heat via a back-pressure system. The power plant's heating process and main parameters are detailed below. Figure 2 .
[0037] The distance between the power plant and the relay energy station (pressure reducing station) is 37.8 km, and the pipeline diameter is 4×DN1400, with two supply and two return lines. In the heating area, 381 heating stations are equipped with absorption heat exchange units, accounting for 60% of the heating area. Simultaneously, a 750MW gas-fired boiler room is configured for peak shaving of the heating system.
[0038] Urban heating pipelines typically use polyurethane foam as the insulation layer. The maximum allowable temperature for polyurethane material during 30 years of continuous operation is 140℃. Therefore, 130℃ is generally taken as the design water supply temperature for the heating system.
[0039] The temperature difference between the turbine heating condenser terminals is approximately 3°C. With a fixed circulating water volume and unit back pressure, a higher return water temperature results in a smaller proportion of exhaust steam heating and higher energy consumption for the heating system. Furthermore, the reduced temperature difference between the supply and return circulating water in the heating network will decrease the power plant's heating capacity.
[0040] The circulating water volume of the heating network is determined by calculations based on the heating capacity and the supply and return water temperatures. The circulating water volume directly impacts the power plant's heating energy consumption and the power consumption of the pipeline pumps. Under rated heating load, when the return water temperature is constant, the relationship between the circulating water volume and the supply water temperature is constant. As the circulating water volume gradually increases, the proportion of power plant exhaust steam used for heating gradually increases, while the equivalent electricity generated by heating continuously decreases. The design flow rate of the circulating water pumps (transfer pumps) in the thermal power plant and long-distance pipeline network is 34,400 t / h, and the circulating water volume of the power plant can be further increased from the base of 30,000 t / h.
[0041] During the initial and final stages of the heating season, there are significant differences in heating energy consumption between operating with a fixed circulating water volume (20,000 t / h) and operating with a variable circulating water volume (constant supply water temperature of 90℃, circulating water volume ranging from 20,943 t / h to 27,214 t / h). After comprehensively considering the changes in the power consumption of the circulating water pump (transfer pump), the equivalent electricity consumption for heating can be reduced by approximately 6.8 kWh / GJ when using a system operating with a variable circulating water volume.
[0042] According to the power plant's data, the design flow rate of the circulating water pumps in the long-distance pipeline network is 34,400 t / h, and the design total head is 530 mH2O. Each stage of the circulating water pumps uses frequency converter speed regulation and DCS centralized control. Taking into account factors such as pump configuration, pipeline resistance, and system operating pressure, the power plant's circulating water volume can be further increased to 31,500 t / h.
[0043] In the heating system, the maximum exhaust back pressure of Unit 1 determines the proportion of power plant exhaust steam used for heating under different operating conditions. The maximum allowable operating back pressure for direct air-cooled turbines is generally 40 kPa to 50 kPa. Operating above this back pressure can cause safety issues such as flutter due to insufficient volumetric flow rate of the last-stage blades, necessitating high back pressure retrofitting of the turbine rotor. Different exhaust back pressures of Unit 1 correspond to different maximum exhaust water temperatures. As the back pressure of Unit 1 increases from 35 kPa to 160 kPa, the maximum exhaust water temperature can increase from 70°C to 110°C, and the proportion of exhaust steam used for heating under rated operating conditions can increase from 40% to 80%. While the proportion of power plant exhaust steam used for heating increases with the increase in the maximum back pressure of Unit 1, the enthalpy of exhaust steam from high-back-pressure units also increases, leading to an increase in the equivalent electricity generated by exhaust steam heating. When the maximum back pressure of Unit 1 is 120 kPa, the power plant's average annual equivalent electricity generated for heating is at its lowest. At this time, the back pressures of units 1 through 6 of the power plant were 120 kPa, 70 kPa, 56 kPa, 23 kPa, 10.5 kPa, and 10.5 kPa, respectively. Units 1, 2, and 3 all required low-pressure cylinder rotor modifications, which increased the difficulty of heating system modifications and unit operation. Therefore, considering both system energy consumption and modification operating conditions, the maximum back pressure of the units was set at 70 kPa, and rotor modifications were only performed on Unit 1. During the heating season, the low-pressure cylinder of Unit 1 uses a 2×4-stage blade heating rotor, operating at a back pressure of 70 kPa; during the non-heating season, the low-pressure cylinder uses a 2×5-stage blade pure condensing rotor, operating at a back pressure of 20 kPa pure condensing.
[0044] The system's minimum supply water temperature refers to the minimum circulating water supply temperature that must be guaranteed during the initial and final stages of heating to meet the normal operating requirements of the absorption heat exchanger units in the heating station. Figure 3 It can be seen that during the initial and final stages of the heating season, the lower the minimum water supply temperature, the significantly less the equivalent electricity for heating. The equivalent electricity for heating is reduced by an average of approximately 1.8 kWh / GJ and 4 kWh / GJ compared to 90℃ water supply, with water supply temperatures of 85℃ and 80℃ respectively.
[0045] The minimum supply water temperature is determined by the performance of the absorption heat exchanger unit in the secondary station. Under ideal conditions, the average temperature of the hot fluid (primary network water) in an absorption heat pump should be equal to the average temperature of the cold fluid (secondary network water), as shown in the following equation: , in, This is the limit temperature of the primary network return water. For the primary water supply temperature, For the secondary network water supply temperature, This refers to the secondary network return water temperature. When the primary network supply water temperature is 90℃ and 85℃, the corresponding primary network return water limit temperatures are 5℃ and 8℃, respectively. In practice, the performance of absorption heat pumps does not reach the ideal state; the minimum supply water temperature needs to be determined based on the manufacturer's equipment performance specifications. In the example, the absorption heat exchanger unit used in the heating station can operate at a supply water temperature of 85℃.
[0046] Regarding the preferred adjustment method mentioned in step S2, the following is a comparative explanation with two other operation adjustment schemes.
[0047] Comparative Example 1: A two-stage quantity regulation scheme, i.e., the heating system adopts a quantity regulation method. When the heating load is between 3500MW and 2052MW, the supply and return water temperatures are guaranteed to be 130℃ / 30℃, and the circulating water volume is between 30000t / h and 29300t / h; when the heating load is between 1905MW and 1466MW, the supply and return water temperatures are guaranteed to be 90℃ / 30℃, and the circulating water volume is between 27214t / h and 20943t / h.
[0048] Comparative Example 2: Two-stage quality regulation (power plant design and operation scheme), i.e., the heating system adopts quality regulation. When the heating load is between 3500MW and 2052MW, the circulating water flow rate is 30000t / h, the return water temperature is 30℃ and remains constant, and the supply water temperature operates between 130℃ and 90℃; when the heating load is between 1905MW and 1466MW, the circulating water flow rate is 20000t / h, the return water temperature is 30℃ and remains constant, and the supply water temperature operates between 111.7℃ and 92.8℃.
[0049] Embodiment of the present invention: A phased quality regulation scheme. When the heating load is between 3500MW and 2052MW, the heating system adopts a quality regulation method: the circulating water volume is kept constant at 30000t / h and the return water temperature is kept constant at 30℃, while the supply water temperature operates between 130℃ and 90℃. When the heating load is between 1905MW and 1466MW, the heating system adopts a quantity regulation method: the supply and return water temperatures are kept constant at 90℃ / 30℃, while the circulating water volume operates between 27214t / h and 20943t / h.
[0050] from Figure 4 It can be seen that the phased quality regulation scheme has the lowest equivalent electricity for heating. This is because when the heating load is greater than 2052MW, the system circulating water volume is relatively large and the supply water temperature is relatively low when the quality regulation method is used; when the heating load is less than 2052MW, in order to ensure the minimum supply water temperature, the system circulating water volume is relatively large when the quantity regulation method is used.
[0051] The table below shows the range of changes in the extraction steam, exhaust steam parameters, and equivalent electricity for heating of each unit during the heating season.
[0052]
[0053] It is generally believed that when the heating load gradually decreases from the rated heating condition, the heating steam extraction should be sorted by pressure and should be withdrawn from heating in the order of Unit 3, Unit 4, Unit 5 / 6 (traditional heating steam matching scheme). This scheme does not take into account the difference in equivalent electrical loss of the units to carry out global energy consumption optimization, which is prone to causing the overall heating energy consumption to be too high under low load conditions.
[0054] According to the method of the present invention (step S4), the optimal heating steam matching strategy is determined. Each unit is sorted from largest to smallest according to the equivalent power reduction value per unit extraction steam reduction, and the extraction steam withdrawal priority is determined based on this. To ensure uniformity of the comparison conditions, a fixed comparison condition is set where the extraction steam rate of each unit is reduced by 200 t / h from the rated value. This 200 t / h is the minimum safe and stable operating threshold for heating steam extraction of Units 5 and 6. After reducing steam extraction by 200 t / h from each unit, the changes in the equivalent electricity generated by exhaust steam for heating varied significantly. Unit 4 showed a reduction of approximately 5 kWh / GJ in equivalent electricity generated by exhaust steam for heating, demonstrating significant energy-saving potential. Unit 3 showed an increase of approximately 1.5 kWh / GJ in equivalent electricity generated by exhaust steam for heating, indicating that reducing steam extraction would exacerbate system energy consumption. The surplus exhaust steam from Units 5 and 6 was entirely incorporated into the air-cooled system, reducing its equivalent electricity generated by exhaust steam for heating to zero. Based on the change in equivalent electricity generated per unit reduction in steam extraction, from best to worst, the priority for steam extraction withdrawal was: Unit 4 extraction > Units 5 / 6 extraction within the 200 t / h threshold > Unit 3 extraction > Units 5 / 6 remaining extraction outside the 200 t / h threshold.
[0055] In summary, to reduce the overall heating energy consumption of the power plant, as the heating load gradually decreases from 3500MW to 2052MW, the optimized heating steam matching scheme should be determined according to the principle of minimizing the equivalent electricity of the system heating: first reduce the extraction steam of Unit 4 to 0, then reduce the extraction steam of Unit 5 by about 200t / h, then reduce the extraction steam of Unit 6 by about 200t / h, then reduce the extraction steam of Unit 3 to 0, then reduce the extraction steam of Unit 5 to 0, and finally reduce the extraction steam of Unit 6 to 0.
[0056] Using the calculation model, the equivalent electrical loads for heating under different heat loads can be obtained for both the traditional heating steam matching scheme and the optimized heating steam matching scheme of this invention. (See...) Figure 5 .from Figure 5 It can be seen that by adopting the optimized heating steam matching scheme of the present invention, the average heating equivalent electricity can be reduced by about 1 kWh / GJ between 2491MW and 3371MW of power plant heat load.
[0057] For step S5, the optimization process of turbine exhaust steam back pressure during the initial and final stages of heating, when the power plant's heating load is between 1905MW and 1466MW, all heating for the units is provided by exhaust steam, operating in a quantity regulation mode, with the supply and return water temperatures maintained at 90℃ / 30℃. It is generally believed that the back pressure of each unit should remain constant at this time, and the amount of exhaust steam supplied by each unit should be adjusted accordingly when the heat load changes.
[0058] Research has found that: (1) At low load, the equivalent electricity for exhaust steam heating of Units 4, 5 and 6 is 0; the equivalent electricity for heating of Units 1 and 2 (both back pressure units) changes little with the amount of exhaust steam; the equivalent electricity for exhaust steam heating of Unit 3 increases as the amount of exhaust steam for heating decreases (due to the increase in the amount of exhaust steam on the air-cooled platform).
[0059] (2) The equivalent electricity from exhaust steam for heating from Unit 1 and Unit 2 (both back-pressure units) is less than that from Unit 3. Under low load conditions, the exhaust steam supply from Unit 1 and Unit 2 can be kept constant while reducing the exhaust steam supply from Unit 3. At this time, the back pressure of Unit 3 can be adjusted within the range of 35kPa to 25kPa, and the back pressure of Unit 2 can be adjusted within the range of 54kPa to 46kPa.
[0060] With this variable back pressure operation mode, the equivalent heating level can be reduced by about 1.3 kWh / GJ within the heat load range of 1759MW to 1466MW.
[0061] Based on the above considerations and calculations, the preferred specific operation in this embodiment is as follows: (1) The heating system adopts phased quality regulation. When the heating load is greater than 2052MW, the quality regulation method is adopted, and the system operates at the maximum circulating water volume. As the heating load decreases, the water supply temperature gradually decreases from 130℃. When the heating load is less than 2052MW, the quantity regulation method is adopted to ensure the minimum water supply temperature of the system.
[0062] (2) Based on the circulating water pump (water transfer pump) and the absorption heat exchanger unit of the heat station, it is recommended that the maximum circulating water volume of the heating system be 31,500 t / h and the minimum water supply temperature be 85℃.
[0063] (3) During the process of gradually reducing the heating load from 3500MW to 2052MW, in accordance with the principle of minimizing the equivalent electricity for heating: first reduce the steam extraction of Unit 4 to 0, then reduce the steam extraction of Unit 5 by about 200t / h, then reduce the steam extraction of Unit 6 by about 200t / h, then reduce the steam extraction of Unit 3 to 0, then reduce the steam extraction of Unit 5 to 0, and finally reduce the steam extraction of Unit 6 to 0. Quality regulation is adopted throughout this stage to maintain the maximum circulating water volume unchanged.
[0064] (4) During the transition process of the heating load gradually decreasing from 2052MW to 1905MW, after the system switches to the quantity regulation mode, it continuously locks the minimum water supply temperature of 85℃, keeps the circulating water volume slightly adapted to the load, and at the same time maintains the existing back pressure parameters of each unit and the 504t / h exhaust steam of Unit 1 and Unit 2.
[0065] (5) During the process of gradually reducing the heating load from 1905MW to 1466MW, the back pressure of the units that have withdrawn from steam extraction (Unit 4, Unit 5, and Unit 6) is kept constant, and the exhaust steam supply of Unit 1 and Unit 2 remains unchanged at 504t / h. Only the back pressure of the back pressure / extraction condensing units (Unit 1, Unit 2, and Unit 3) that are still participating in exhaust steam heating is adjusted. The priority of the adjustment is ranked according to the criterion of "the reduction of the equivalent electricity of heating corresponding to the unit back pressure reduction is the largest". The units with the highest sensitivity of equivalent electricity are adjusted first, and then the units with decreasing sensitivity are adjusted in turn. Therefore, the back pressure of Unit 3 is gradually reduced from 35kPa to 23Pa first, the back pressure of Unit 2 is gradually reduced from 54kPa to 40kPa second, and the back pressure of Unit 3 is gradually reduced from 70kPa to 65kPa last.
[0066] The above-mentioned economic operation method in this plan, including the distribution of heating steam extraction and exhaust steam for each unit during the heating season, is detailed in [the relevant section]. Figure 6 Simultaneously, calculations show that, using the economic operation method of this scheme, the average equivalent electricity generated during the heating season can be reduced by 2.50 kWh / GJ compared to the two-stage quality regulation scheme (power plant design and operation scheme) and the simple phased quality regulation scheme, respectively. With the unit heating operation cost during the heating season calculated at 13.06 yuan / GJ, the economic operation method reduces costs by 1.04 yuan / GJ, 0.6 yuan / GJ, and 0.38 yuan / GJ compared to the two-stage quantity regulation, two-stage quality regulation (power plant design and operation scheme), and conventional phased quality regulation, respectively, resulting in annual operating cost reductions of 37.24 million yuan, 21.53 million yuan, and 13.52 million yuan, respectively.
[0067] In summary, the low-temperature return water cogeneration heating system operation and regulation method of the present invention enables refined regulation of power plant heating. Building upon traditional simple quality and quantity regulation, it incorporates factors such as power plant circulating water volume, supply water temperature, heating steam matching, and unit back pressure into the heating regulation scope, thus systematically optimizing power plant heating energy consumption. The regulation method of the present invention is particularly suitable for the operation and regulation of complex low-temperature return water cogeneration heating systems with two or more heating units and multi-stage exhaust steam + extraction steam combined heating. Using the regulation method of the present invention, heating energy consumption can be reduced by approximately 10% compared to conventional heating regulation methods.
[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; obviously, the described embodiments are some embodiments of the present invention, but not all embodiments; based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention; in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other; modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions for some of the technical features, do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for operation and regulation of a low-temperature return water cogeneration heating system, characterized in that, Includes the following steps: Step S1: Determine the minimum water supply temperature t0 of the system; Step S2: When the heating load is greater than the load threshold Q0, the system operates at maximum circulating water volume, and the water supply temperature gradually decreases from the design temperature to the minimum water supply temperature t0. When the heating load is less than or equal to the load threshold Q0, the system operates at a variable circulating water volume within a set range to maintain the water supply temperature at the minimum water supply temperature t0. Here, the load threshold Q0 is the heating load of the system under the conditions of maximum circulating water volume and minimum water supply temperature t0. Step S3: Calculate the equivalent electricity for heating of each stage of steam and each operating condition using the following formula; Equivalent electric w of the i th unit exhausted steam heat supply c,i The calculation formula is as follows: ， Among them, h c,i h is the enthalpy of the exhaust steam of the i-th unit. cs,i h is the enthalpy of the exhaust steam condensate of the i-th unit. co,i The exhaust steam enthalpy value under THA conditions of the unit. The utilization rate of exhaust steam for heating of the i-th unit; Equivalent electric w of steam extraction of the ith unit for heating e,i The calculation formula is as follows: ， Among them, h e,i h represents the enthalpy of the extracted steam from the i-th unit, expressed in kJ / kg. es,i Here is the enthalpy of the extraction steam condensate from the i-th unit, expressed in kJ / kg. The formula for calculating the weighted average power equivalent to electricity (w) from a power plant for heating is as follows: ， Where n is the number of units, q c,i For the exhaust steam heating power of the i-th unit, q e,i Let q be the extraction steam heating power of the i-th unit, and q be the total heating power of the power plant. Step S4: Using the lowest weighted equivalent power w for heating from the power plant as the sorting principle, determine the steam extraction sequence and steam volume of each unit during the heating load change process.
2. The operation and regulation method for a low-temperature return water cogeneration heating system according to claim 1, characterized in that, In step S4, the equivalent power reduction value per unit extraction steam reduction of each unit is calculated using the following formula: Equivalent power reduction value per unit extraction steam reduction = Reduced extraction steam heating capacity × Equivalent power of extraction steam heating capacity + Exhaust steam heating capacity × Equivalent power reduction value of exhaust steam heating capacity; The larger the equivalent power reduction value per unit extraction steam reduction, the better the energy-saving effect; The priority order for extraction steam withdrawal of each unit is determined according to the energy-saving effect from best to worst.
3. The operation and regulation method for a low-temperature return water cogeneration heating system according to claim 1, characterized in that, It also includes step S5, in which the power plant's heating during the initial and final stages of heating is entirely provided by the exhaust steam. Under the quantity regulation mode, the exhaust steam heating of each unit changes accordingly with the change in circulating water volume.
4. The operation and regulation method for a low-temperature return water cogeneration heating system according to claim 3, characterized in that, In step S5, the back pressure of each unit gradually decreases as the heating load decreases.
5. The operation and regulation method for a low-temperature return water cogeneration heating system according to claim 3, characterized in that, In step S5, as the heating load gradually decreases at the end of the heating season, the back pressure of the units that have stopped extracting steam is kept constant. For the units that are still participating in exhaust steam heating, the back pressure is finely adjusted. The reduction in equivalent electricity for heating corresponding to a unit back pressure reduction is calculated. The larger the reduction in equivalent electricity for heating corresponding to a unit back pressure reduction, the higher the unit's equivalent electricity sensitivity. The priority order of regulation is determined according to the unit's equivalent electricity sensitivity from high to low, and regulation is carried out in the order of decreasing unit equivalent electricity sensitivity.