Calculation method for improvement effect of peak regulation capacity and heat supply capacity of cogeneration unit based on zero output of low-pressure cylinder

Abstract

The invention discloses a method for calculating the peak load regulation capacity and heat supply capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder, and the method comprises the steps: strengthening the coal mixing or blending work, enabling the quality of coal entering a furnace to be uniform as much as possible, improving or solving the problem through coal blending, processing and mixing different types of coal with different properties into mixed coal according to a certain proportion, and calculating the peak load regulation capacity and heat supply capacity improvement effect of the cogeneration unit. A primary air folded edge type sandwich air burner is adopted for burning mixed coal, improvement is conducted on distribution of pulverized coal concentration in primary air flow, secondary air is divided into two coaxial annular air flows, namely, inner-layer secondary air and outer-layer secondary air, and the rotational flow strength of the two air flows is adjusted through an adjustable axial blade type swirler; and double-channel double-air-regulation is realized. According to the calculation method for the peak regulation capacity and heat supply capacity improvement effect of the cogeneration unit based on zero output of the low-pressure cylinder, ignition and combustion stability is improved, generation and emission of NOx in combustion are controlled, the concentration of pulverized coal at an outlet of a combustor is basically uniform, and a pulverized coal pipeline is prevented from being blocked or accumulated.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal power generation energy conservation, and in particular to a method for calculating the peak regulation capacity and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder. Background Art

[0002] The power plant not only produces electricity, but also uses the steam from the turbine generator to provide heat to users. It refers to the process of producing electricity and heat at the same time, which saves fuel compared to producing electricity and heat separately. A thermal power plant that operates in a cogeneration mode is called a thermal power plant, and the unit is also called a cogeneration unit.

[0003] In recent years, due to the outstanding advantages of cogeneration in improving people's livelihood, saving energy, and protecting the environment, it has been strongly supported by national policies and local governments, and the installed capacity of cogeneration in the power grid has developed rapidly. At the same time, the peak-to-valley difference of the power load of the power grid continues to increase, the proportion of installed capacity of new energy sources continues to rise, the problem of wind and solar power abandonment begins to emerge, and there is also great pressure on hydropower consumption. However, for a long time, cogeneration units have been restricted by their own safety and heating safety, and rarely participate in the peak load regulation of the power grid. These situations have brought great difficulties to the arrangement of the operation mode of the power grid during the heating period, and the dispatching agencies and thermal power companies have an urgent demand for approving the peak load regulation capacity of thermal power units.

[0004] In order to respond to the national policy requirements for thermal power flexibility transformation, improve the deep peak-shaving capability and heating capacity of the units during the heating period, and enhance the competitiveness and profitability of the units in the electricity market, many cogeneration units have carried out low-pressure cylinder zero-output transformation to improve the flexibility of the heating units.

[0005] In order to meet the heating demand in winter, there is a prominent contradiction between the operation of wind turbines and cogeneration units. In order to meet the heating needs of residents, cogeneration units need to be operated first, which increases the heating load while also increasing the power generation. In addition, the wind power load has an anti-peaking characteristic, which causes a sharp increase in peak-shaving pressure and cannot meet the peak-shaving requirements of the power grid. Moreover, different types of coal have different burnout performance after combustion and different calorific values, resulting in different peak values ​​of thermal power plants.

[0006] The ash in the fuel not only cannot release heat during the combustion process, but also absorbs heat. Therefore, the greater the ash content, the lower the calorific value, which easily leads to ignition difficulties and delayed ignition; at the same time, the furnace combustion temperature is significantly reduced, the coal burnout degree becomes worse, resulting in high fly ash combustibles. As the ash content increases, the carbon particles may be wrapped by the ash layer, the surface combustion rate of the carbon particles decreases, and the flame propagation speed decreases, resulting in poor combustion; in addition, the higher the fly ash concentration, the more severe the wear on the boiler heating surface, especially the economizer and low-temperature superheater heating surface at the tail. The increase in ash discharge increases the dust removal cost and plant electricity consumption, and the thermal physical loss of fly ash and slag increases, thereby reducing the efficiency of the boiler. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides a method for calculating the peak-shaving capacity and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder, to solve the problems raised in the background technology.

[0008] To achieve the above object, the present invention provides the following technical solutions: A method for calculating the peak load regulation capability and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder comprises the following steps: S1: Strengthen coal blending or coal blending to make the coal quality entering the furnace as uniform as possible. Coal blending can be used to improve or solve the problem. Different types and properties of coal can be mixed into mixed coal in a certain proportion under the condition of ensuring the safe operation of the unit. S2: Use a primary air folded-edge sandwich burner to burn the mixed coal, focus on improving the distribution of coal powder concentration inside the primary air flow, achieve dense and thin combustion of the primary air flow at an optimal coal powder concentration at a certain position of the burner outlet, improve ignition and combustion stability, and control the generation and emission of NOx during combustion; S3: The secondary air is divided into two coaxial annular airflows, the inner secondary airflow and the outer secondary airflow, and the swirl intensity of the two airflows is adjusted by the adjustable axial blade swirlers to achieve dual-channel dual-adjustment airflow; S4: When the cogeneration unit is not operating at zero output of the low-pressure cylinder, the unit is tested for heating peak-shaving capacity. The heating steam extraction flow rate of the unit is used as the benchmark, the rated heating steam extraction parameters are maintained, and the unit load is changed by changing the evaporation rate of the boiler, so that the unit meets the upper and lower operating boundary conditions of the power generation load. The heating peak-shaving capacity test is performed when the cogeneration unit is not operating at zero output of the low-pressure cylinder; S5: When the cogeneration unit is in low-pressure cylinder zero-output operation, the unit is tested for heating peak-shaving capacity. The heating extraction steam flow rate of the unit is used as the benchmark, the rated heating extraction steam parameters are maintained, and the unit load is changed by changing the evaporation volume of the boiler to make the unit meet the low-pressure cylinder zero-output operation boundary conditions. The heating peak-shaving capacity test is performed when the cogeneration unit is not in low-pressure cylinder zero-output operation; S6: By comparing the heating capacity and minimum power generation load of the unit under the two test conditions, the peak-shaving capacity and heating capacity improvement effect of the cogeneration unit when the low-pressure cylinder is running at zero output are obtained.

[0009] Preferably, when dual-channel air adjustment is performed in S3, the primary wind speed and the secondary wind speed are controlled, the adjustment method of the powder feeding amount is optimized, the powder feeding amount in the same layer should be kept consistent, the coal powder concentration at the burner outlet is basically uniform, and the coal powder pipeline is prevented from being blocked or accumulated.

[0010] Preferably, when it is found in S3 that the primary wind speed of the coal pipe decreases and the coal powder concentration increases, the speed of the powder feeder should be reduced immediately, and the burner and powder feeder should be checked on site. If any abnormality is found, the powder feeder should be stopped, the primary wind speed should be increased, and other powder feeders should be added to maintain normal operation.

[0011] Preferably, the operating boundary conditions satisfying the upper limit of power generation load in S4 are: the main steam and reheat steam parameters are rated values, the steam quality meets the specified requirements, the unit operates in a unit mode, and all heat recovery systems operate normally.

[0012] Preferably, the operating boundary conditions satisfying the lower limit of power generation load in S5 are: the main steam and reheat steam parameters are rated values, the steam quality meets the specified requirements, the unit operates in a unit mode, and all heat recovery systems operate normally.

[0013] Preferably, the boundary conditions for the low-pressure cylinder zero-output operation in S5 are: the main steam and reheat steam parameters are rated values, the steam quality meets the specified requirements, the unit is operated in a unit mode, and all heat recovery systems are operated normally.

[0014] Preferably, the mixed coal consists of anthracite, bituminous coal and high-moisture lignite, and the ratio of the three is 1.5:1.2:1.

[0015] Preferably, the optional types of steam turbines supporting the combined cycle unit include back-pressure steam turbines, extraction-back steam turbines and extraction-condensing steam turbines.

[0016] Preferably, when two extraction condensing units are selected for operation, they can serve as backup for each other. When one steam turbine fails, the maximum extraction capacity of the other steam turbine can be used to provide as much heat as possible.

[0017] Preferably, the burner includes one of a primary air folded-edge sandwich air burner, a blunt body burner, a "boat-type" burner, a large speed difference burner, and a flat jet burner.

[0018] Compared with the prior art, the present invention provides a method for calculating the peak load regulation capacity and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder, which has the following beneficial effects: 1. The calculation method for improving the peak-shaving capacity and heating capacity of the cogeneration unit based on the zero output of the low-pressure cylinder adopts a primary air folded-edge sandwich air burner to burn the mixed coal, and focuses on improving the distribution of coal powder concentration inside the primary air flow, so as to achieve the primary air flow at a certain position of the burner outlet at the optimal coal powder concentration. The burner can be rich and thin, improve the ignition and combustion stability, and control the generation and emission of NOx during combustion.

[0019] 2. The calculation method for improving the peak-shaving capacity and heating capacity of the cogeneration unit based on the zero output of the low-pressure cylinder divides the secondary air into two coaxial annular airflows, the inner secondary air and the outer secondary air, and adjusts the swirl intensity of the two airflows through adjustable axial blade swirlers to achieve dual-channel dual-adjustment air. The coal powder concentration at the burner outlet is basically uniform, preventing the coal powder pipeline from being blocked or accumulated.

[0020] 3. The calculation method of the peak-shaving capacity and heating capacity improvement effect of the cogeneration unit based on the zero output of the low-pressure cylinder is to make the coal quality entering the furnace as uniform as possible by strengthening the work of mixing or blending coal, and to improve or solve it by blending coal. Different types and properties of coal are mixed into mixed coal in a certain proportion under the condition of ensuring the safe operation of the unit. The mixed coal is composed of anthracite, bituminous coal and high-moisture lignite, so that the price of the mixed coal is the lowest, which can effectively reduce the cost of power generation. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] A method for calculating the peak load regulation capability and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder comprises the following steps: S1: Strengthen coal blending or coal blending to make the coal quality entering the furnace as uniform as possible. Coal blending can be used to improve or solve the problem. Different types and properties of coal can be mixed into mixed coal in a certain proportion under the condition of ensuring the safe operation of the unit. The mixed coal consists of anthracite, bituminous coal and high-moisture lignite, with the ratio of the three being 1.5:1.2:1.

[0023] The weight loss curve of lignite tends to low temperature, indicating that it is the easiest to burn and has the strongest reaction ability, followed by bituminous coal, and anthracite is the weakest. The higher the volatile matter level of the coal, the better the combustion performance; the length of the late combustion time, the steeper the burnout performance, the better, indicating that the shorter the late combustion time, lignite has the steepest burnout section and the best burnout performance, followed by bituminous coal, and inferior bituminous coal and anthracite are the worst.

[0024] The lowest calorific value corresponding to stable combustion in the boiler without adding oil to assist combustion is lignite. After being dried by the pulverizing system, the calorific value of lignite with high moisture content almost doubles, while the calorific value of bituminous coal and anthracite with low moisture content does not change much after drying on a dry ash-free basis.

[0025] S2: Use a primary air folded-edge sandwich burner to burn the mixed coal, focus on improving the distribution of coal powder concentration inside the primary air flow, achieve dense and thin combustion of the primary air flow at an optimal coal powder concentration at a certain position of the burner outlet, improve ignition and combustion stability, and control the generation and emission of NOx during combustion; S3: The secondary air is divided into two coaxial annular airflows, the inner secondary airflow and the outer secondary airflow, and the swirl intensity of the two airflows is adjusted by the adjustable axial blade swirlers to achieve dual-channel dual-adjustment airflow; When performing dual-channel air adjustment, control the primary and secondary air speeds, optimize the adjustment method of the powder feeding amount, the powder feeding amount in the same layer should be kept consistent, the coal powder concentration at the burner outlet should be basically uniform, and prevent the coal powder pipeline from being blocked or accumulated.

[0026] When it is found that the primary wind speed of the coal pipe decreases and the coal powder concentration increases, the speed of the powder feeder should be reduced immediately, and the burner and powder feeder should be checked on site. If any abnormality is found, the powder feeder should be stopped, the primary wind speed should be increased, and other powder feeders should be added to maintain normal operation.

[0027] S4: When the cogeneration unit is not operating at zero output of the low-pressure cylinder, the unit is tested for heating peak-shaving capacity. The heating steam extraction flow rate of the unit is used as the benchmark, the rated heating steam extraction parameters are maintained, and the unit load is changed by changing the evaporation rate of the boiler, so that the unit meets the upper and lower operating boundary conditions of the power generation load. The heating peak-shaving capacity test is performed when the cogeneration unit is not operating at zero output of the low-pressure cylinder; The operating boundary conditions for meeting the upper limit of power generation load are: the main steam and reheat steam parameters are rated values, the steam quality meets the specified requirements, the unit operates in a unit system, all heat recovery systems operate normally, the heating steam extraction parameter requirements are guaranteed, and the middle exhaust temperature does not exceed the temperature; the steam turbine maintains the rated operating steam intake of the unit.

[0028] S5: When the cogeneration unit is in low-pressure cylinder zero-output operation, the unit is tested for heating peak-shaving capacity. The heating extraction steam flow rate of the unit is used as the benchmark, the rated heating extraction steam parameters are maintained, and the unit load is changed by changing the evaporation volume of the boiler to make the unit meet the low-pressure cylinder zero-output operation boundary conditions. The heating peak-shaving capacity test is performed when the cogeneration unit is not in low-pressure cylinder zero-output operation; The operating boundary conditions that meet the lower limit of power generation load are: the main steam and reheat steam parameters are rated values, the steam quality meets the specified requirements, the unit operates in a unit system, all heat recovery systems operate normally, and the minimum steam inlet flow to the low-pressure cylinder is guaranteed, that is, the CV valve opening is guaranteed to be at the minimum value, and the low-pressure cylinder steam inlet pressure is higher than the safe operation design value.

[0029] The boundary conditions for meeting the zero-output operation of the low-pressure cylinder are: the main steam and reheat steam parameters are rated values, the steam quality meets the specified requirements, the unit operates in a unit system, all heat recovery systems operate normally, the heating steam extraction parameter requirements are guaranteed, the middle row temperature does not exceed the temperature, the bypass pipeline cooling steam flow is kept above the safe value, and the remaining middle row steam is all used for heating.

[0030] S6: By comparing the heating capacity and minimum power generation load of the unit under the two test conditions, the peak-shaving capacity and heating capacity improvement effect of the cogeneration unit when the low-pressure cylinder is running at zero output are obtained.

[0031] The optional types of steam turbines for combined cycle units include back-pressure steam turbines, extraction-back steam turbines and extraction-condensing steam turbines.

[0032] Back-pressure steam turbines are not equipped with conventional condensers, and exhaust steam is all used for external heat supply, which can achieve the maximum heating capacity of the unit and the maximum utilization of waste heat. Its advantages are high thermal energy utilization efficiency, simple structure, no cold source loss, and investment savings. Its disadvantages are that the exhaust pressure is generally determined according to the requirements of process heat and heating. If the operation deviates from the design conditions, the efficiency of the whole machine will be greatly reduced; the thermal and electrical outputs are strongly coupled, and there is no room for independent adjustment.

[0033] The extraction steam turbine is a back pressure steam turbine with an additional extraction port, which makes it easier to adapt to the needs of different heating parameters and can utilize the heat of all low-grade steam. Of course, it also has the disadvantages of the back pressure steam turbine.

[0034] The heat and electricity loads of the extraction condensing unit can be adjusted independently within a certain range, which is equivalent to the superposition of the back pressure machine and the condensing machine, and the operation is flexible. The extraction condensing steam turbine has a minimum condensing steam flow requirement to ensure that the low-pressure cylinder has ventilation cooling steam. The maximum extraction steam volume is generally about 80% of the main steam volume.

[0035] Since the extraction condensing steam turbine has its own independent condensing system, it is less restricted by the heat load and can even provide dual-parameter heat extraction steam. Its application range is much larger than that of the back pressure unit. When two extraction condensing units are selected for operation, they can serve as backup for each other. When one steam turbine fails, the maximum extraction capacity of the other steam turbine can be used to provide as much heat as possible. At the same time, it can be considered to set up a standby temperature and pressure reduction device for the reheating hot section of each unit to meet the demand for heat load supply and ensure the reliability of heat supply.

[0036] Generally, heat-using enterprises are mainly processing and manufacturing enterprises, which are easily affected by changes in market conditions and economic situations. Therefore, from the perspective of ensuring heat supply reliability, adapting to changes in heat load, and reducing investment risks, new projects should give priority to the use of extraction condensing steam turbines.

[0037] Therefore, due to the limitations of heating radius and heat load, back pressure units can usually only be used in large industrial parks or areas with long-term sufficient and stable heat load, and it is necessary to use them in combination with condensing units. The back pressure unit carries the basic heat load, and the condensing unit operates according to the changes in heat load, that is, heating is provided by the combined operation of the condensing unit + back pressure unit.

[0038] The combustion is unstable at low load, and the main contradiction is to solve the problem of stable combustion, improving efficiency and taking environmental protection into consideration. Over the years, in the pulverized coal combustion technology of coal-fired boilers, in order to improve the ignition and combustion stability of the pulverized coal airflow, various technical measures have been taken in the boiler combustion equipment, with the aim of establishing a stable ignition heat source, enhancing the heating capacity of the pulverized coal airflow and reducing the ignition heat of the primary air pulverized coal airflow. Peak-shaving boilers must be equipped with a combustion system that is highly efficient at high load and can operate stably and reliably at low load. Maintaining stable combustion at low load is a necessary condition for safe operation.

[0039] The structure of the burner is mainly focused on the improvement and development of the primary air inlet structure. It improves the airflow conditions, promotes the improvement of ignition and combustion stability, and achieves high-efficiency combustion. Representative ones include primary air folded-edge sandwich air burners, blunt body burners, "ship-type" burners, large speed difference burners, flat jet burners, etc. The main focus is on the distribution of coal powder concentration inside the primary air flow for improvement and development. The primary air flow is realized at a certain position of the burner outlet at the optimal coal powder concentration. It not only improves the ignition and combustion stability, but also effectively controls the generation and emission of NOx during combustion. Representative ones include horizontal thick and thin burners, and foreign ones include PM type and WR type burners. In terms of swirl burners, in order to improve the adaptability of swirl burners to coal types and loads, and effectively control NOx emissions, the main method is to combine graded air supply with thick and thin combustion. It is generally suitable for burning high-volatile coal types.

[0040] The specific structural features are as follows: the secondary air is divided into two coaxial annular airflows: the inner secondary air (also known as the secondary air) and the outer secondary air (also known as the tertiary air abroad). The swirl intensity of the two airflows is adjusted by the adjustable axial blade swirler to achieve double-channel double-adjustment air. The size and position of the recirculation zone can be effectively controlled; single-tooth or double-tooth flame stabilizing rings, flame isolation rings, etc. are set at the burner outlet according to the characteristics of the coal type to further improve the ignition and combustion stability; burnout air is set above the main burner. After using these combustion technologies, the minimum stable combustion load capacity of the boiler has been effectively improved. The 100MW and 200MW unit boilers can reach 60%~45%BMCR (maximum continuous evaporation capacity of the boiler) from the original 70%~60%. To achieve the goals of high efficiency, low-load stable combustion of the boiler, ensure reliable operation of the water-cooled wall and reduce thermal deviation of the heating surface.

[0041] Cogeneration units refer to units that produce both electricity and thermal products (steam, hot water). Cogeneration units include back-pressure steam turbines, extraction-condensing steam turbines, condensing-extraction dual-purpose steam turbines, and gas-steam combined cycle heating units. Cogeneration has comprehensive benefits such as saving energy, improving the environment, improving heating quality, and increasing power supply. The construction of thermal power plants is an important measure to control air pollution and improve energy utilization. With the increase in the country's efforts to save energy and reduce emissions, many pure condensing units around cities have been transformed for heating, and the proportion of heating units has increased year by year. In order to meet the peak-shaving needs of the power grid, deep peak-shaving is carried out for pure condensing units that are completely used for power generation, and at the same time, "heat determines electricity" is implemented for cogeneration units, that is, while meeting the thermal load of heat users, the electrical load is reduced to a minimum to make room to meet the requirements of deep peak-shaving.

[0042] There are two forms of shaft configuration for gas combined cycle units: one is multi-shaft configuration, that is, the gas turbine and steam turbine drive the generator separately; the other is single-shaft configuration, each single-shaft combined cycle generator set is composed of a gas turbine, a steam turbine, a waste heat boiler and a generator, and the gas turbine and steam turbine drive the generator coaxially or by clutch connection. Multi-shaft configuration can be divided into: "1+1" mode, that is, the exhaust gas of a gas turbine generator set is sent to a waste heat boiler, and the steam generated drives a steam turbine generator set; In the "2+1" mode, the exhaust gas of two or more gas turbine generator sets is sent to their respective matching waste heat boilers, and the steam generated jointly drives a steam turbine generator set.

[0043] Taking the F-class improved combined cycle unit as an example, for the heating unit, if a single-shaft configuration is adopted, the change in the steam extraction volume of the steam turbine for heating will induce increased vibration of the shaft system, which is not conducive to the stability and safety of the shaft system.

[0044] In the F-class (F-class improved) units of about 390~460MW, according to the heat load characteristics of various user industries, the unit heating extraction steam parameters should consider the pressure loss and temperature drop within the heating radius. In typical cases, the extraction steam pressure is 1.8MPa and the temperature is 250℃; the extraction steam flow rate is 230th, so that the rated heat-to-electricity ratio reaches 50%; the possible maximum extraction steam is temporarily set at 300th. The calculation conditions use the atmospheric parameters under the rated heating performance guarantee conditions of the unit (pressure 100kPa; temperature 28℃; relative humidity 82%); the unit back pressure is 7.8kPa; the plant power consumption rate is 2.5%; the natural gas is temporarily based on the relevant natural gas quality data of the West-East Gas Transmission Line 2.

[0045] The gas turbine supply contract states that the NO emission should not exceed 50mg / m3 at 75%-100% load. 3The requirements of the gas turbine are met, and the operating efficiency of the gas turbine drops a lot at low load, so the operating condition of the gas turbine reducing the load to below 75% is no longer considered. The calculation range of the unit variable operating condition is based on the gas turbine reducing the load from 100% to 75%, and the calculation is performed at different steam extraction volumes to obtain the relationship between the combined cycle power supply output, power generation heat consumption and heat supply.

[0046] For the same heating steam extraction capacity, the heat consumption under 100% total output condition is lower than that under 75% total output condition, that is, the efficiency is high and the operation economy is relatively better. For the same output condition, as the heating steam extraction capacity increases, the unit output will decrease and the heat consumption will increase, that is, the efficiency will decrease; conversely, as the heating steam extraction capacity decreases, the unit output will increase and the efficiency will improve.

[0047] When the heating demand increases from the rated steam extraction to the maximum steam extraction, the only adjustment method is to reduce the electric load. When the heating demand decreases from the rated steam extraction, the adjustment methods are available to increase and decrease the electric load. That is, within the two curves of 100% total output and 75% total output, the cogeneration unit can achieve independent adjustment of heat and electricity loads. Corresponding to a certain heating load, whether the gas turbine can continue to operate at reduced load depends on whether the heating parameters (pressure, temperature, flow) can be guaranteed to remain unchanged, and on whether the environmental protection emissions will exceed the standard.

[0048] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for calculating the peak load regulation capacity and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder, characterized in that: The following steps are involved: S1: Strengthen coal blending or coal blending to make the coal quality entering the furnace as uniform as possible. Coal blending can be used to improve or solve the problem. Different types and properties of coal can be mixed into mixed coal in a certain proportion under the condition of ensuring the safe operation of the unit. S2: Use a primary air folded-edge sandwich burner to burn the mixed coal, focus on improving the distribution of coal powder concentration inside the primary air flow, achieve dense and thin combustion of the primary air flow at an optimal coal powder concentration at a certain position of the burner outlet, improve ignition and combustion stability, and control the generation and emission of NOx during combustion; S3: The secondary air is divided into two coaxial annular airflows, the inner secondary airflow and the outer secondary airflow, and the swirl intensity of the two airflows is adjusted by the adjustable axial blade swirlers to achieve dual-channel dual-adjustment airflow; S4: When the cogeneration unit is not operating at zero output of the low-pressure cylinder, the unit is tested for heating peak-shaving capacity. The heating steam extraction flow rate of the unit is used as the benchmark, the rated heating steam extraction parameters are maintained, and the unit load is changed by changing the evaporation rate of the boiler, so that the unit meets the upper and lower operating boundary conditions of the power generation load. The heating peak-shaving capacity test is performed when the cogeneration unit is not operating at zero output of the low-pressure cylinder; S5: When the cogeneration unit is in low-pressure cylinder zero-output operation, the unit is tested for heating peak-shaving capacity. The heating extraction steam flow rate of the unit is used as the benchmark, the rated heating extraction steam parameters are maintained, and the unit load is changed by changing the evaporation volume of the boiler to make the unit meet the low-pressure cylinder zero-output operation boundary conditions. The heating peak-shaving capacity test is performed when the cogeneration unit is not in low-pressure cylinder zero-output operation; S6: By comparing the heating capacity and minimum power generation load of the unit under the two test conditions, the peak-shaving capacity and heating capacity improvement effect of the cogeneration unit when the low-pressure cylinder is running at zero output are obtained.

2. According to claim 1, a method for calculating the peak load regulation capacity and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder, characterized in that: When dual-channel air adjustment is performed in S3, the primary and secondary air velocities are controlled, and the adjustment method of the powder feeding amount is optimized. The powder feeding amount in the same layer should be kept consistent, and the coal powder concentration at the burner outlet should be basically uniform to prevent the coal powder pipeline from being blocked or accumulated.

3. The method for calculating the peak load regulation capability and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder according to claim 1 is characterized in that: When it is found in S3 that the primary wind speed of the coal pipe decreases and the coal powder concentration increases, the speed of the powder feeder should be reduced immediately, and the burner and powder feeder should be checked on site. If any abnormality is found, the powder feeder should be stopped, the primary wind speed should be increased, and other powder feeders should be added to maintain normal operation.

4. The method for calculating the peak load regulation capability and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder according to claim 1 is characterized in that: The operating boundary conditions that meet the upper limit of power generation load in S4 are: the main steam and reheat steam parameters are rated values, the steam quality meets the specified requirements, the unit operates in a unit system, and all heat recovery systems operate normally.

5. The method for calculating the peak load regulation capability and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder according to claim 1 is characterized in that: The operating boundary conditions that meet the lower limit of power generation load in S5 are: the main steam and reheat steam parameters are rated values, the steam quality meets the specified requirements, the unit operates in a unit system, and all heat recovery systems operate normally.

6. The method for calculating the peak load regulation capability and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder according to claim 1 is characterized in that: The boundary conditions for the low-pressure cylinder zero-output operation in S5 are: the main steam and reheat steam parameters are rated values, the steam quality meets the specified requirements, the unit operates in a unit system, and all heat recovery systems operate normally.

7. The method for calculating the peak load regulation capability and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder according to claim 1 is characterized in that: The mixed coal consists of anthracite, bituminous coal and high-moisture lignite, and the ratio of the three is 1.5:1.2:

1.

8. The method for calculating the peak load regulation capability and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder according to claim 1 is characterized in that: The optional types of steam turbines supporting the combined cycle unit include back-pressure steam turbines, extraction-back steam turbines and extraction-condensing steam turbines.

9. The method for calculating the peak load regulation capability and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder according to claim 8, characterized in that: When two extraction condensing units are selected for operation, they can serve as backup for each other. When one steam turbine fails, the maximum extraction capacity of the other steam turbine can be used to provide as much heat as possible.

10. The method for calculating the peak load regulation capability and heating capacity improvement effect of a cogeneration unit based on zero output of a low-pressure cylinder according to claim 1, characterized in that: The burner includes one of a primary air folded-edge sandwich burner, a blunt body burner, a "boat-type" burner, a large speed difference burner, and a flat jet burner.