Gas boiler environmental protection standard fast start control method

Abstract

The present application relates to the technical field of boiler control. A kind of gas boiler environmental protection reaches standard fast start control method, comprising the following steps: about 30min before the whole point time, the boiler is purged;About 10min before the whole point time, complete the preparation work of boiler ignition, and the boiler is ignited;Before the whole point time, each drain valve of the boiler is opened, LDG fuel is switched and input at the left side input port and right side input port of the boiler in time, and the furnace top diffuser valve is opened or closed small in stages, until the boiler is grid-connected and started.The beneficial effects of the present application are: shorten the start time, reduce the oxygen content during start, ensure that the boiler is heated evenly during temperature and pressure rising, and achieve the purpose of non-exceeding standard of boiler start-up flue gas emission.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of boiler control, in particular to a rapid start-up control method for a gas-fired boiler meeting environmental protection standards. BACKGROUND

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

[0003] Currently, although the gas-fired boiler meets the environmental emission standards during normal operation, the gas-fired boiler starts in the conventional manner, and during the start-up process of the gas-fired boiler, the environmental protection standards are exceeded. The specific reasons for the environmental protection standards being exceeded include the following:

[0004] First, during the safety stage of using coke oven gas (COG) for ignition during the start-up of the gas-fired boiler, the flow rate of the coke oven gas (COG) and the air volume of the fan are not adjusted to adapt to each other. For example, the flow rate of the coke oven gas (COG) is adjusted too small (the flow rate of the coke oven gas under the full open valve condition is about 200 m 3 / h), and the air volume of the fan is adjusted too large (the air volume corresponding to a fan damper opening of 10% is about 6000 m 3 / h), which cannot meet the parameter control requirements of the boiler for rapid heating and pressure rise, resulting in a long time of about 2.5 hours required for the conventional boiler to start up in a hot state;

[0005] Second, when a certain amount of converter gas (LDG) main fuel is put in, the start-up opening of the diffuser valve is adjusted too small, the boiler pressure is not controlled, only rises, the boiler temperature rise rate is also greater than the specified rate;

[0006] Third, in the gas boiler starting process, due to the high oxygen content, close to the atmospheric oxygen content (value close to 21%), when the actual emission of the two gas boilers is very small, it will cause the environmental protection emission conversion value to be too large. SUMMARY

[0007] The purpose of the present application is to provide a kind of gas boiler environmental protection standard fast start control method, can shorten the boiler start time, reduce the oxygen content of boiler start, ensure that the boiler is heated evenly in the process of temperature and pressure rise, reach the purpose of flue gas emission not overproof in the process of boiler start.

[0008] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0009] A kind of gas boiler environmental protection standard fast start control method, comprising the following steps:

[0010] Step S1: about 30min before the whole point time, the boiler is purged;

[0011] Step S2: after the completion of the boiler purging, the preparation work of the boiler ignition is carried out, about 10min before the whole point time, the preparation work of the boiler ignition is completed, and the boiler is ignited, wherein the preparation work flow of the boiler ignition is as follows:

[0012] Step S2.1: start induced draft fan and air supply fan, ventilate the boiler, and the air volume is controlled at 5000-7000Nm 3 / h;

[0013] Step S2.2: open the gas regulating valve, and input COG fuel to the boiler, and the hearth negative pressure of the boiler is controlled at-50 to-90Pa, wherein the input flow of the COG fuel is set to 180Nm 3 / h;

[0014] Step S2.3: the opening degree of each drain valve of the boiler is set to 3-7%;

[0015] Step S3: before entering the whole point time, input LDG fuel at the left side input port of the boiler, the opening degree of the furnace top diffuser valve is set to 100%, the opening degree of each drain valve of the boiler is set to 100%, after 5min of LDG fuel input, stop the input of LDG fuel, the opening degree of the furnace top diffuser valve is set to 3-7%, wherein the input flow of the LDG fuel is set to 2500-3000Nm 3 / h;

[0016] Step S4: After timing 3-6 minutes, LDG fuel is input at the right side input port of the boiler, the opening degree of the boiler top diffusion valve is set to 100%, after 5 minutes of LDG fuel input, the LDG fuel input is stopped, and the opening degree of the boiler top diffusion valve is set to 3-7%, wherein the input flow of the LDG fuel is set to 2500-3000 Nm 3 / h.

[0017] Step S5: After timing 5 minutes, LDG fuel is input at the left side input port of the boiler, the opening degree of the boiler top diffusion valve is set to 100%, and the starting control of the boiler is completed, wherein the input flow of the LDG fuel is set to 2500-3000 Nm 3 / h.

[0018] Wherein, when the input time of the COG fuel reaches 10 minutes, the opening degree of the gas regulating valve is set to 0%.

[0019] Further, in the step S1, the operation process of the boiler purging is as follows:

[0020] Step S1.1: Start the induced draft fan first, and start the forced draft fan after the current is stable;

[0021] Step S1.2: The damper opening degree of the induced draft fan and the forced draft fan is set to 30%, and the furnace negative pressure of the boiler is controlled at -180 Pa, after purging the boiler for 5 minutes, the damper opening degree of the induced draft fan and the forced draft fan is set to 0%;

[0022] Step S1.3: COG fuel and LDG fuel are input into the boiler respectively, and gas burst tests are performed on the COG fuel and the LDG fuel respectively, if the gas burst tests of the COG fuel and the LDG fuel are both qualified, the boiler purging is completed, the induced draft fan and the forced draft fan are stopped and reset, otherwise return to step S1.2.

[0023] Further, in the step S2.1, the damper opening degree of the induced draft fan is set to 10-15%, and the damper opening degree of the forced draft fan is set to 4-6%.

[0024] Further, in the step S2.2, the opening degree of the gas regulating valve is set to more than 50%.

[0025] Further, in the step S2, an ignition lance for ignition is arranged in the boiler, and the ignition lance is provided with an ignition regulating valve.

[0026] Further, in the step S5, when the steam drum pressure is 0.05 MPa lower than the cylinder pressure and the main steam temperature reaches 245-287°C, the boiler is started in parallel.

[0027] Further, during the duration of the boiler grid connection, if the boiler is to be stopped, all fuel input is stopped within 5 minutes after the hour.

[0028] Advantages of the present application:

[0029] 1. The method as a whole takes the time axis as the constraint main line, and the starting of the gas-fired boiler is strategically optimized and operationally controlled. The combustion mode is changed during the starting of the gas-fired boiler, which can shorten the starting time of the boiler, reduce the oxygen content during the starting of the boiler, achieve the purpose that the flue gas emission does not exceed the standard during the starting of the boiler, and realize energy saving and emission reduction.

[0030] 2. The method advances the input time point of the LDG fuel, and the LDG fuel is input by switching at the left side and the right side of the gas-fired boiler, and the stage switching input parameters of the LDG fuel are controlled, so that the actual temperature rising rate is controlled within the maximum allowed temperature rising rate during the hot state starting of the boiler, and then the left half and the right half of the gas-fired boiler are balanced with each other, and the gas-fired boiler is also balanced in heating during the temperature rising and pressure rising process, so as to avoid the stress caused by uneven heating and reduce the service life of the equipment, and the gas-fired boiler can also be quickly heated and pressurized, so as to quickly meet the starting requirements of the boiler grid connection. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is the boiler starting control process diagram based on the time axis provided by the embodiment of the present application.

[0032] Figure 2 is the temperature rising and pressure rising test data statistical graph of the gas-fired boiler after starting optimization provided by the embodiment of the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described below with reference to the drawings.

[0034] As shown in Figure 1 A gas-fired boiler environmental protection standard rapid starting control method comprises the following steps:

[0035] Step S1: about 30 minutes before the hour, the boiler is purged, and the operation process of the boiler purge is as follows:

[0036] Step S1.1: first start the induced draft fan, and then start the supply fan after the current is stable;

[0037] Step S1.2: the damper opening of the induced draft fan and the supply fan is set to 30%, and the furnace negative pressure of the boiler is controlled at-180Pa. After purging the boiler for 5 minutes, the damper opening of the induced draft fan and the supply fan is set to 0%;

[0038] Step S1.3: respectively input COG fuel and LDG fuel into the boiler, and respectively perform coal gas explosion test on the COG fuel and the LDG fuel, if the coal gas explosion test of the COG fuel and the LDG fuel are both qualified, then the boiler purging is completed, the induced draft fan and the forced draft fan are stopped and reset, otherwise return to step S1.2;

[0039] Step S2: after the boiler purging is completed, perform the preparation work of the boiler ignition, complete the preparation work of the boiler ignition about 10 minutes before the whole point, and ignite the boiler, wherein the preparation work flow of the boiler ignition is as follows:

[0040] Step S2.1: start the induced draft fan and the forced draft fan, the baffle opening of the induced draft fan is set to 10-15%, the baffle opening of the forced draft fan is set to 4-6%, ventilate the boiler, and control the air volume to 5000-7000 Nm 3 / h;

[0041] Step S2.2: open the gas regulating valve, the opening of the gas regulating valve is set to more than 50%, input COG fuel into the boiler, and control the hearth negative pressure of the boiler to-50--90Pa, wherein the input flow of the COG fuel is 180 Nm 3 / h;

[0042] Step S2.3: set the opening of each drain valve of the boiler to 3-7%;

[0043] Step S3: before entering the whole point, input LDG fuel at the left input port of the boiler, set the opening of the furnace top diffuser valve to 100%, set the opening of each drain valve of the boiler to 100%, stop the input of the LDG fuel after 5 minutes of the LDG fuel input, set the opening of the furnace top diffuser valve to 3-7%, wherein the input flow of the LDG fuel is set to 2500-3000 Nm 3 / h;

[0044] Step S4: after timing for 3-6 minutes, input LDG fuel at the right input port of the boiler, set the opening of the furnace top diffuser valve to 100%, stop the input of the LDG fuel after 5 minutes of the LDG fuel input, set the opening of the furnace top diffuser valve to 3-7%, wherein the input flow of the LDG fuel is set to 2500-3000 Nm 3 / h;

[0045] Step S5: after timing for 5 minutes, input LDG fuel at the left input port of the boiler, set the opening of the furnace top diffuser valve to 100%, complete the start-up control of the boiler, wherein the input flow of the LDG fuel is set to 2500-3000 Nm 3 / h;

[0046] Wherein, when the COG fuel input time reaches 10 min, the opening degree of the coal gas regulating valve is set to 0%.

[0047] It should be noted that the main purpose of the boiler purge based on the step S1 of the method is to prevent deflagration, ensure the safe operation of the gas boiler, and ensure the personal safety of the operator. Before the start of the gas boiler, the inside of the furnace and the pipeline may accumulate unburned coal powder or flammable gas. Purging these combustible substances inside the boiler can avoid deflagration and equipment damage caused by deflagration when the temperature and concentration reach a certain level. Boiler purge can also remove the ash on the heating surface, reduce the thermal resistance, and improve the boiler efficiency.

[0048] Secondly, the coal gas explosion test is the existing conventional detection means. The specific operation method is as follows: the test cylinder is used to collect the coal gas sample from the pipeline port of the boiler, and then the sample is ignited and burned to observe the burning situation of the coal gas sample in the test cylinder, so as to judge whether the coal gas sample is pure and whether the inside of the boiler is clean. If the coal gas sample burns stably in the cylinder and is extinguished only when it burns to the bottom of the cylinder, it means that the coal gas sample in the boiler is pure, and the coal gas explosion test is qualified. If the coal gas sample in the test cylinder produces an explosion sound after ignition and burns out quickly, or the coal gas sample burns unstably, it means that there are still flammable substances in the equipment, and the coal gas explosion test is unqualified.

[0049] It should be noted that the steps S2 to S5 based on the method are implemented in the whole starting control process of the gas boiler, which takes the time axis as the main constraint line, executes the targeted strategy optimization and operation control, and selects the best time for boiler starting ignition as 10 min before the whole point according to the preset control before and after the whole point. The LDG fuel is input before the whole point, and the LDG fuel is switched to the input port on the left and right sides of the boiler. The input time point, input time and input amount of the LDG fuel in each input stage can control the actual temperature rising rate of the boiler within the maximum allowed temperature rising rate in the hot state starting, so as to balance the pressure of the left half and the right half of the gas boiler, make the heating of the gas boiler uniform, avoid the stress caused by uneven heating, reduce the service life of the equipment, and make the gas boiler quickly rise in temperature and pressure, so as to quickly reach the starting requirement of the boiler grid connection. The specific implementation can realize the starting of the boiler grid connection within 1 hour of the whole point and not less than 45 minutes.

[0050] Secondly, the drain valve is used to control the water inflow of the boiler, so that the quantitative water can be stably heated to form steam.

[0051] 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 avoid the boiler's pressure or temperature rising too quickly.

[0052] In step S2, the boiler is equipped with an ignition gun for ignition, and the flame spray end of the ignition gun is provided with an ignition regulating valve. The ignition gun can continuously ignite the boiler until ignition is successful. During the boiler ignition process, if the furnace flame is observed to be abnormal during observation in the control room, the ignition regulating valve can be closed on-site through the control room to stop ignition in a timely manner to ensure the safety of the boiler and personnel.

[0053] In step S5, the boiler is connected to the grid and started when the drum pressure is 0.05 MPa lower than the cylinder pressure and the main steam temperature reaches 245-287°C. These requirements are met for boiler grid connection startup. By completing boiler startup control using this method, these requirements can be quickly met, meeting the steam needs of the entire steel plant.

[0054] If the boiler needs to be shut down during the grid connection process, all fuel input should be stopped within 5 minutes after the hour. This allows for rapid completion of the boiler shutdown process, facilitating the elimination of abnormal data during the shutdown period and facilitating the normal collection and statistics of data from a single gas-fired boiler during ignition startup, temperature and pressure increase, grid connection startup, continuous steam supply, and shutdown.

[0055] The following will provide further technical explanation of this method in combination with detailed relevant experimental data.

[0056] 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 pressure increase rate is 0.012MPa / min; the temperature increases from 157℃ to 266℃, and the average temperature increase rate 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, and the average pressure increase rate is 0.011MPa / min; the temperature increases from 152℃ to 287℃, and the average temperature increase rate is 2.14℃ / min;

[0057] Based on the test data of the two gas-fired boilers, the optimized gas-fired boiler start-up control can meet the speed requirement of temperature and pressure rise during the whole process from boiler ignition to grid connection in hot start-up. The method is based on the current operation mode of gas-fired boilers, and optimizes the start-up strategy and operation control of gas-fired boilers. Under the premise of ensuring the safe operation of boilers and related equipment, the main fuel is put into use in advance, the main fuel is switched on both sides of the boiler, the temperature and pressure rise of the gas-fired boiler is accelerated, the start-up time of the gas-fired boiler is shortened, and the oxygen content during start-up is reduced.

[0058] In combination Figure 1 and Figure 2 , based on the gas-fired boiler start-up optimization method, the two fuel-fired boilers take about 20 minutes from start-up preparation to boiler ignition, and about 40-60 minutes from boiler ignition to boiler grid connection. The start-up time of the gas-fired boiler can be stably controlled within 1 hour, and the environmental protection emission during the start-up process of the gas-fired boiler is guaranteed to be within the standard;

[0059] During the start-up process of the 1# gas-fired boiler, the average environmental protection emission concentration of the 1# gas-fired boiler is: SO2=3.27mg / Nm 3 , NO x =129.46mg / Nm 3 , particulate matter=7.72mg / Nm 3 ;

[0060] During the start-up process of the 2# gas-fired boiler, the average environmental protection emission concentration of the 2# gas-fired boiler is: SO2=12.75mg / Nm 3 , NO x =96.66mg / Nm 3 , particulate matter=7.66mg / Nm 3 ;

[0061] The technical optimization of the fast start-up control strategy of the gas-fired boiler is based on the combination of the process, equipment characteristics and start-up environmental protection emission test application practice of the gas-fired boiler. The total time from hot start-up to grid connection of the gas-fired boiler is reduced from 2.5 hours to within 1 hour, energy saving and emission reduction are achieved, and the environment is protected.

Claims

1. A method for quickly starting a gas boiler to meet environmental standards, 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, preparations for ignition of the boiler are carried out. About 10 minutes before the hour, preparations for ignition of the boiler are completed and the boiler is ignited. The preparation process for ignition of the boiler 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 inlet 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 LDG fuel addition is stopped, and the opening of the furnace top relief valve is set to 3-7%. The input flow rate of the LDG fuel is set to 2500-3000 Nm 3 / h; Step S4: After timing for 3 to 6 minutes, add LDG fuel to the right inlet of the boiler, and set the opening of the top relief valve to 100%. After 5 minutes of LDG fuel addition, stop adding LDG fuel, and set the opening of the top relief valve 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, 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 added 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, characterized in that: In step S1, the operation process of the boiler purge 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 openings of the induced draft fan and the forced draft fan are set to 30%, the furnace negative pressure of the boiler is controlled at -180 Pa, and after the boiler is purged for 5 minutes, the damper openings of the induced draft fan and the forced draft fan are 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.

3. The method for controlling the rapid startup of a gas boiler meeting environmental standards according to claim 1, 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 forced draft fan 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 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.

6. The method for controlling the rapid startup of a gas boiler meeting environmental standards according to claim 1, 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, 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.

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