Gas-fired boiler environment-friendly up-to-standard quick start control method

Abstract

The invention relates to the technical field of boiler control. An environment-friendly and standard-reaching quick start control method for a gas-fired boiler comprises the following steps that the boiler is purged about 30 min before the hourly moment; the preparation work of boiler ignition is completed about 10 min before the hourly moment, and the boiler is ignited; before the hourly moment, all drain valves of the boiler are opened, LDG fuel is put into a left input port and a right input port of the boiler in a mutual switching mode in good time, and a furnace top blow-off valve is opened or closed in stages till the boiler is started in a grid-connected mode. The method has the beneficial effects that the starting time is shortened, the starting oxygen content is reduced, it is guaranteed that the boiler is heated in a balanced mode in the temperature and pressure rising process, and the purpose that boiler starting flue gas emission does not exceed the standard is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of boiler control, and in particular to a method for quickly starting a gas boiler to meet environmental protection standards. Background Art

[0002] At present, the gas boiler currently under construction by the applicant is a double-drum natural water circulation boiler with a rated steam supply evaporation capacity of 50t / h. It is mainly responsible for balancing the low-pressure steam system of the entire steel plant and meeting the early start-up steam demand of the steel plant. Specifically, the recovered coal gas is burned to generate superheated steam, which is sent to the steam network to meet the steam demand of the steel plant. The two gas boilers use converter gas (LDG) as the main fuel and coke oven gas (COG) as the safety fuel. The safety fuel is the minimum fuel required to ensure personal safety and equipment safety, and is generally used for boiler ignition and startup; under normal operating conditions, after the boiler is connected to the grid and started, the average concentration of environmental protection emissions is: SO2=1.46mg / Nm 3 、NO x =77.79mg / Nm 3 , particulate matter = 2.42 mg / Nm 3 The flue gas emissions of the two gas-fired boilers that burn converter gas (LDG) meet the environmental protection requirements of GB-13271-2014 "Boiler Air Pollutant Emission Standards".

[0003] At present, although the gas boiler meets the environmental standards in normal operation, when the gas boiler is started in the conventional way, the environmental standards may be exceeded during the startup process. The specific reasons for the environmental standards exceeding are as follows: First, during the safety stage of using coke oven gas (COG) to ignite the gas boiler during startup, the flow rate of coke oven gas (COG) and the air volume of the fan were not adjusted. For example, the flow rate of coke oven gas (COG) was adjusted too small (the flow rate of coke oven gas in the fully open valve state was about 200m 3 / h), the fan air volume is adjusted too large (the fan damper opening is 10%, corresponding to an air volume of about 6000m 3 / h), which cannot meet the parameter control requirements of rapid temperature and pressure rise of the boiler, resulting in a long time required for hot start of conventional boilers, about 2.5 hours; Second, when a certain amount of converter gas (LDG) is added as the main fuel, the boiler pressure is out of control and only rises but does not fall, because the opening of the relief valve is adjusted too small, and the boiler temperature rise rate is also greater than the specified rate; Third, during the startup of the gas boiler, due to the high oxygen content, which is close to the atmospheric oxygen content (the value is close to 21%), when the actual emissions detected by the two gas boilers are very small, the environmental emission conversion value will be too large. Summary of the invention

[0004] The purpose of the present invention is to provide a gas boiler environmental protection standard fast startup control method, which can shorten the boiler startup time, reduce the boiler startup oxygen content, ensure that the boiler is heated evenly during the temperature and pressure increase process, and achieve the purpose of not exceeding the flue gas emission standard during the boiler startup process.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: A method for quickly starting a gas boiler to meet environmental standards comprises the following steps: Step S1: About 30 minutes before the hour, purge the boiler; Step S2: After the boiler is purged, the preparation for boiler ignition is carried out. The preparation for boiler ignition is completed about 10 minutes before the hour, and the boiler is ignited. The preparation process for boiler ignition is as follows: Step S2.1: Start the induced draft fan and the forced draft fan to ventilate the boiler, and control the air volume at 5000-7000Nm 3 / h; Step S2.2: Open the gas regulating valve and feed COG fuel into the boiler. The negative pressure of the boiler furnace is controlled at -50 to -90 Pa. The input flow rate of the COG fuel is set to 180 Nm 3 / h; Step S2.3: The opening of each steam trap of the boiler is set to 3-7%; Step S3: Before entering the hour, LDG fuel is added to the left input port of the boiler, the opening of the furnace top relief valve is set to 100%, and the opening of each steam trap of the boiler is set to 100%. After 5 minutes of LDG fuel addition, the addition of LDG fuel is stopped, and the opening of the furnace top relief valve is set to 3-7%, wherein the input flow rate of the LDG fuel is set to 2500-3000Nm 3 / h; Step S4: After timing for 3 to 6 minutes, LDG fuel is added to the right inlet of the boiler, and the opening of the furnace top relief valve is set to 100%. After 5 minutes of LDG fuel addition, the LDG fuel addition is stopped, and the opening of the furnace top relief valve is set to 3 to 7%. The input flow rate of the LDG fuel is set to 2500 to 3000 Nm 3 / h; Step S5: After 5 minutes of timing, LDG fuel is added to the left inlet of the boiler, and the opening of the top relief valve is set to 100%, completing the start-up control of the boiler. The input flow rate of the LDG fuel is set to 2500-3000 Nm 3 / h; When the COG fuel is put into the tank for 10 minutes, the opening of the gas regulating valve is set to 0%.

[0006] Furthermore, in step S1, the operation process of the boiler purging is as follows: Step S1.1: Start the induced draft fan first, and then start the supply fan after the current stabilizes; Step S1.2: The damper opening of the induced draft fan and the forced draft fan is set to 30%, the furnace negative pressure of the boiler is controlled at -180Pa, and after the boiler is purged for 5 minutes, the damper opening of the induced draft fan and the forced draft fan is set to 0%; Step S1.3: Add COG fuel and LDG fuel to the boiler respectively, and perform gas explosion tests on COG fuel and LDG fuel respectively. If the gas explosion tests of COG fuel and LDG fuel are both qualified, the boiler purge is completed, and the induced draft fan and the forced draft fan are shut down and reset, otherwise return to step S1.2.

[0007] Furthermore, in the step S2.1, the damper opening of the induced draft fan is set to 10-15%, and the damper opening of the blower is set to 4-6%.

[0008] Furthermore, in the step S2.2, the opening of the gas regulating valve is set to be above 50%.

[0009] Furthermore, in the step S2, an ignition gun for ignition is provided in the boiler, and an ignition regulating valve is provided at the flame spraying end of the ignition gun.

[0010] Furthermore, in the step S5, when the drum pressure is 0.05 MPa lower than the cylinder pressure and the main steam temperature reaches 245-287°C, the boiler is connected to the grid and started.

[0011] Furthermore, during the process of the boiler being connected to the grid, if the boiler is to be shut down, all fuel inputs shall be stopped within 5 minutes after the hour.

[0012] Beneficial effects of the present invention: 1. This method takes the time axis as the main constraint line, optimizes the strategy and controls the operation of the gas boiler startup, and changes the combustion mode during the startup of the gas boiler, which can shorten the boiler startup time and reduce the oxygen content of the boiler startup, so as to achieve the purpose of not exceeding the flue gas emission standard during the boiler startup process, and realize energy saving and emission reduction.

[0013] 2. This method advances the time point of LDG fuel input, switches the LDG fuel input between the left and right sides of the gas boiler, and controls the phased switching input parameters of the LDG fuel, so that the actual heating rate is controlled within the maximum allowable heating rate when the boiler is hot started, thereby making the pressure of the left and right halves of the gas boiler balanced with each other, and making the gas boiler heated evenly during the process of heating and pressure increase, avoiding the stress caused by uneven heating that leads to a reduction in equipment life, and can also make the gas boiler quickly heat up and increase pressure, so as to quickly meet the startup requirements of boiler grid connection. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of a boiler startup control process based on a timeline provided in an embodiment of the present invention.

[0015] Figure 2 It is a statistical chart of temperature and pressure increase test data after the gas boiler startup optimization provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present invention will be described below with reference to the accompanying drawings.

[0017] like Figure 1 As shown, a gas boiler environmental protection standard quick start control method includes the following steps: Step S1: About 30 minutes before the hour, the boiler is purged. The operation process of the boiler purging is as follows: Step S1.1: Start the induced draft fan first, and then start the supply fan after the current stabilizes; Step S1.2: The damper opening of the induced draft fan and the forced draft fan is set to 30%, the furnace negative pressure of the boiler is controlled at -180Pa, and after the boiler is purged for 5 minutes, the damper opening of the induced draft fan and the forced draft fan is set to 0%; Step S1.3: COG fuel and LDG fuel are added to the boiler respectively, and gas explosion tests are performed on the COG fuel and LDG fuel respectively. If the gas explosion tests of the COG fuel and LDG fuel are both qualified, the boiler purge is completed, and the induced draft fan and the forced draft fan are shut down and reset, otherwise, return to step S1.2; Step S2: After the boiler is purged, the preparation for boiler ignition is carried out. The preparation for boiler ignition is completed about 10 minutes before the hour, and the boiler is ignited. The preparation process for boiler ignition is as follows: Step S2.1: Start the induced draft fan and the forced draft fan, set the damper opening of the induced draft fan to 10-15%, and the damper opening of the forced draft fan to 4-6%, ventilate the boiler, and control the air volume to 5000-7000Nm 3 / h; Step S2.2: Open the gas regulating valve, the opening of the gas regulating valve is set to more than 50%, COG fuel is added to the boiler, and the negative pressure of the boiler furnace is controlled at -50 to -90Pa, wherein the input flow rate of the COG fuel is 180Nm 3 / h; Step S2.3: The opening of each steam trap of the boiler is set to 3-7%; Step S3: Before entering the hour, LDG fuel is added to the left input port of the boiler, the opening of the furnace top relief valve is set to 100%, and the opening of each steam trap of the boiler is set to 100%. After 5 minutes of LDG fuel addition, the addition of LDG fuel is stopped, and the opening of the furnace top relief valve is set to 3-7%, wherein the input flow rate of the LDG fuel is set to 2500-3000Nm 3 / h; Step S4: After timing for 3 to 6 minutes, LDG fuel is added to the right inlet of the boiler, and the opening of the furnace top relief valve is set to 100%. After 5 minutes of LDG fuel addition, the LDG fuel addition is stopped, and the opening of the furnace top relief valve is set to 3 to 7%. The input flow rate of the LDG fuel is set to 2500 to 3000 Nm 3 / h; Step S5: After 5 minutes of timing, LDG fuel is added to the left inlet of the boiler, and the opening of the top relief valve is set to 100%, completing the start-up control of the boiler. The input flow rate of the LDG fuel is set to 2500-3000 Nm 3 / h; When the COG fuel is put into the tank for 10 minutes, the opening of the gas regulating valve is set to 0%.

[0018] It should be noted that, based on the implementation of step S1 described in the present method, the main purpose of boiler purging is to prevent deflagration, ensure the safe operation of the gas boiler, and ensure the personal safety of the operator. Before the gas boiler is started, incompletely burned coal powder or combustible gas may accumulate inside the furnace and pipeline. Purging these combustible substances accumulated inside the boiler can avoid the possible deflagration caused by these combustible substances when they reach a certain temperature and concentration, as well as equipment damage caused by the deflagration. Boiler purging can also remove ash accumulation on the heating surface, reduce thermal resistance, and improve boiler efficiency. Secondly, the gas explosion test is an existing conventional detection method. The specific operation method is: use a test tube to collect a gas sample from the pipe port of the boiler, then ignite it and burn it, and observe the combustion of the gas sample in the test tube to determine whether the gas sample is pure, and then determine whether the inside of the boiler has been purged clean. If the gas sample burns stably in the tube and burns to the bottom of the tube before going out, it means that the gas sample in the boiler is pure and the gas explosion test is qualified. If the gas sample in the test tube produces a popping sound after ignition and burns out quickly, or the gas sample burns unstably, it means that there are still combustible substances mixed in the equipment and the gas explosion test fails.

[0019] It should be noted that, based on the targeted implementation of steps S2 to S5 described in the present method, in the entire gas boiler startup control process, the time axis is used as the main constraint line to perform targeted strategy optimization and operation control. According to the preset control before and after the hour, the best time for boiler startup ignition is selected as 10 minutes before the hour. LDG fuel is added before entering the hour, and the LDG fuel is switched to be added at the input ports on the left and right sides of the boiler. The time point, time and amount of LDG fuel added in each stage of addition are controlled, so that the actual heating rate of the boiler can be controlled within the maximum allowable heating rate during hot start, thereby making the pressure of the left and right halves of the gas boiler balanced with each other, and making the gas boiler evenly heated during the heating and pressure increase process, avoiding the stress caused by uneven heating that leads to a reduction in equipment life, and making the gas boiler quickly heat up and pressure increase, so as to quickly meet the startup requirements of boiler grid connection, specifically, the boiler grid connection startup can be achieved within 1 hour and not less than 45 minutes after the hour. Secondly, the steam trap is used to control the water inlet of the boiler, so that a certain amount of water is stably heated to form steam; Third, in view of the control requirements of the boiler's heating rate and pressure increase rate, in order to keep the pressure and temperature inside the boiler in a steady and uniform upward trend, the LDG fuel input will be stopped in time at each LDG fuel input stage, and the opening of the furnace top relief valve will be reduced to prevent the boiler's pressure or temperature from rising too quickly.

[0020] In step S2, an ignition gun for ignition is provided in the boiler, and an ignition regulating valve is provided at the flame spraying end of the ignition gun. The ignition gun can realize continuous ignition of the boiler until the ignition is successful. During the ignition of the boiler, if the furnace flame is found to be abnormal through observation in the control room, the ignition regulating valve can be closed on site through operation in the control room, and the ignition can be stopped in time to ensure the safety of the boiler and personnel.

[0021] In the step S5, when the drum pressure is 0.05 MPa lower than the cylinder pressure and the main steam temperature reaches 245-287°C, the boiler is connected to the grid and started. The drum pressure is 0.05 MPa lower than the cylinder pressure and the main steam temperature reaches 245-287°C as the start-up requirements for the boiler to be connected to the grid. After the start-up control of the boiler is completed by this method, the start-up requirements for the boiler to be connected to the grid can be quickly met to meet the steam demand of the entire steel plant.

[0022] During the continuous process of the boiler being connected to the grid, if the boiler is to be shut down, all fuel inputs shall be stopped within 5 minutes after the hour. The boiler shutdown and flameout work can be completed quickly, which is convenient for eliminating abnormal data during the shutdown period, and further facilitates the normal collection and statistics of the working process data of a single gas boiler during ignition start-up, temperature and pressure increase, grid connection start-up, continuous steam supply, and shutdown and flameout.

[0023] The following will provide a further technical description of this method in combination with detailed relevant test data.

[0024] like Figure 2 As shown in the figure, the hot start of the 1# gas boiler, from boiler ignition to boiler grid connection, takes about 50 minutes, the pressure increases from 0.51MPa to 1.09MPa, and the average rate of pressure increase is 0.012MPa / min; the temperature increases from 157℃ to 266℃, and the average rate of temperature increase is 2.18℃ / min; the hot start of the 2# gas boiler, from boiler ignition to boiler grid connection, takes about 63 minutes, the pressure increases from 0.42MPa to 1.1MPa, the average rate of pressure increase is 0.011MPa / min, the temperature increases from 152℃ to 287℃, and the average rate of temperature increase is 2.14℃ / min; Based on the test data of the above two gas boilers, the gas boiler startup control optimized by this method, during the whole process from boiler ignition to boiler grid connection, the average values ​​of temperature and pressure rise can meet the speed requirements of temperature and pressure rise allowed during hot startup; based on the current operation mode of the gas boiler, this method optimizes the strategy and controls the operation of the gas boiler startup, and on the premise of ensuring the safe operation of the boiler and related equipment, accelerates the temperature and pressure rise of the gas boiler, shortens the startup time of the gas boiler, and reduces the oxygen content of the boiler startup by adding the main fuel in advance and switching the main fuel on the left and right sides of the boiler.

[0025] Combination Figure 1 and Figure 2 Based on the gas boiler startup optimization of this method, the two fuel boilers only take about 20 minutes from startup preparation to boiler ignition, and only take about 40 to 60 minutes from boiler ignition to boiler grid connection. The gas boiler startup time can be stably controlled within 1 hour. At the same time, during the gas boiler startup process, the flue gas emission is guaranteed not to exceed the environmental protection standard. During the startup of the 1# gas boiler, the average concentration of environmental emission conversion of the 1# gas boiler is: SO2=3.27mg / Nm 3 、NO x =129.46mg / Nm 3 , particulate matter = 7.72mg / Nm 3 ; During the startup of the 2# gas boiler, the average concentration of environmental emission conversion of the 2# gas boiler is: SO2=12.75mg / Nm 3 、 NO x =96.66mg / Nm 3 、 Particles = 7.66mg / Nm 3 ; This method is aimed at the technical optimization of the gas boiler quick start control strategy. It is based on the combination of gas boiler process, equipment characteristics and application practice of startup environmental protection emission test. The total time from hot start to grid-connected start of the gas boiler is reduced from the original 2.5 hours to less than 1 hour, achieving energy conservation and emission reduction and protecting the environment.

Claims

1. A gas boiler environmental protection standard quick start control method, characterized by: The following steps are involved: Step S1: About 30 minutes before the hour, purge the boiler; Step S2: After the boiler is purged, the preparation for boiler ignition is carried out. The preparation for boiler ignition is completed about 10 minutes before the hour, and the boiler is ignited. The preparation process for boiler ignition is as follows: Step S2.1: Start the induced draft fan and the forced draft fan to ventilate the boiler, and control the air volume at 5000-7000Nm 3 / h; Step S2.2: Open the gas regulating valve and feed COG fuel into the boiler. The negative pressure of the boiler furnace is controlled at -50 to -90 Pa. The input flow rate of the COG fuel is set to 180 Nm 3 / h; Step S2.3: The opening of each steam trap of the boiler is set to 3-7%; Step S3: Before entering the hour, LDG fuel is added to the left input port of the boiler, the opening of the furnace top relief valve is set to 100%, and the opening of each steam trap of the boiler is set to 100%. After 5 minutes of LDG fuel addition, the addition of LDG fuel is stopped, and the opening of the furnace top relief valve is set to 3-7%, wherein the input flow rate of the LDG fuel is set to 2500-3000Nm 3 / h; Step S4: After timing for 3 to 6 minutes, LDG fuel is added to the right inlet of the boiler, and the opening of the furnace top relief valve is set to 100%. After 5 minutes of LDG fuel addition, the LDG fuel addition is stopped, and the opening of the furnace top relief valve is set to 3 to 7%. The input flow rate of the LDG fuel is set to 2500 to 3000 Nm 3 / h; Step S5: After 5 minutes of timing, LDG fuel is added to the left inlet of the boiler, and the opening of the top relief valve is set to 100%, completing the start-up control of the boiler. The input flow rate of the LDG fuel is set to 2500-3000 Nm 3 / h; When the COG fuel is put into the tank for 10 minutes, the opening of the gas regulating valve is set to 0%.

2. The method for controlling the rapid startup of a gas boiler meeting environmental standards according to claim 1 is characterized in that: In step S1, the operation process of the boiler purging is as follows: Step S1.1: Start the induced draft fan first, and then start the supply fan after the current stabilizes; Step S1.2: The damper opening of the induced draft fan and the forced draft fan is set to 30%, the furnace negative pressure of the boiler is controlled at -180Pa, and after the boiler is purged for 5 minutes, the damper opening of the induced draft fan and the forced draft fan is set to 0%; Step S1.3: Add COG fuel and LDG fuel to the boiler respectively, and perform gas explosion tests on COG fuel and LDG fuel respectively. If the gas explosion tests of COG fuel and LDG fuel are both qualified, the boiler purge is completed, and the induced draft fan and the forced draft fan are shut down and reset, otherwise return to step S1.

2.

3. The method for controlling the rapid startup of a gas boiler meeting environmental standards according to claim 1 is characterized in that: In the step S2.1, the damper opening of the induced draft fan is set to 10-15%, and the damper opening of the blower is set to 4-6%.

4. The method for controlling the rapid startup of a gas boiler meeting environmental standards according to claim 1 is characterized in that: In the step S2.2, the opening of the gas regulating valve is set to be above 50%.

5. The method for controlling the rapid startup of a gas boiler meeting environmental standards according to claim 1, 3 or 4, characterized in that: In the step S2, an ignition gun for ignition is arranged in the boiler, and an ignition regulating valve is arranged at the flame spraying end of the ignition gun.

6. The method for controlling the rapid startup of a gas boiler meeting environmental standards according to claim 1 is characterized in that: In step S5, when the drum pressure is 0.05 MPa lower than the cylinder pressure and the main steam temperature reaches 245-287°C, the boiler is connected to the grid and started.

7. The method for controlling the rapid startup of a gas boiler meeting environmental standards according to claim 6 is characterized in that: During the process of the boiler being connected to the grid, if the boiler is to be shut down, all fuel input shall be stopped within 5 minutes after the hour.

Images