1 Overview:
Due to the characteristics of the gas itself, it is flammable, explosive and easy to spread. The gas boiler is more dangerous than the coal-fired boiler, and the quality and safety performance of the control system are strict. This paper only discusses the safety of small and medium-sized gas boilers.
2. Safety devices "Safety is the life of the gas industry." Without safety, there is no benefit and no development.
2.1 Automatic alarm device When the gas boiler is running, the temperature and pressure of water and steam in the boiler and the water level in the steam boiler are the monitoring parameters to ensure its safe operation. When these parameters are abnormal, the automatic alarm device should emit sound and light signals. .
(1) Over-temperature alarm "Procedure" stipulates: If the rated hot water temperature of the hot water boiler is higher than or equal to 120 °C and the rated outlet hot water temperature is lower than 120 °C but the rated power is greater than or equal to 4.2 MW, an over-temperature alarm device shall be provided. And interlock protection, for small and medium-sized gas boilers, the standard signal is generally output from the temperature transmitter on the hot water outlet to the programmable logic controller (PLC), the standard value is compared with the given value, once over temperature The PLC immediately performs an emergency shutdown.
(2) When the rated evaporation of the overpressure alarm steam boiler is greater than or equal to 6t/h, it shall be equipped with a steam overpressure alarm, and an interlock protection overpressure alarm shall be simultaneously closed to close the solenoid valve, the gas source is cut off, the induced draft fan is still running, the boiler steam The pressure is generally controlled automatically by the pressure controller.
(3) Water level alarm steam boiler rated evaporation is greater than or equal to 2t / h, should be installed high and low water level alarm, high and low water level alarm signal should be able to distinguish, when the low water level alarm occurs, close the solenoid valve, cut off the gas source, the blower stops after 30s The induced draft fan is still running.
(4) Flow alarm The DC boiler shall be equipped with an alarm device when the feed water flow rate is lower than the start flow rate.
2.1.2 Cutting device The gas boiler shall be equipped with an interlocking device. When the conditions described in (1) to (5) occur in the operation of the boiler, the gas supply can be automatically cut off; for the boiler equipped with the blast burner, the supply of the air supply can be automatically cut off.
(1) The pressure of the hot water boiler is reduced until vaporization occurs or the water temperature rises above the specified value;
(2) The steam boiler pressure exceeds the specified value or the water level is low to the low value of zui;
(3) When the gas pressure is too high, there will be a phenomenon of fire, even if an explosion occurs in the furnace. Therefore, the burner must be operated under the designed gas pressure. The cutting device should be activated when the pressure is too high or too low. At present, domestic and gas-fired boilers are imported burners with high degree of automation, not only equipped with gas high and low pressure controllers, but also equipped with automatic leak detection controllers (in the process of ignition, furnace purge, leak detection control) Automatically check the gas valve system for leak detection);
(4) When the circulating water pump of the blower, the induced draft fan, and the hot water boiler suddenly loses power or stops running or a fault such as a frequency conversion fault or a contact point fault occurs, the cutting device is activated;
(5) Start of the smoke temperature protection device: The temperature of the smoke also reflects the normal operation of the boiler. Once the smoke temperature exceeds the set value, the cutting device should be activated.
2.1.3 Sprinklers When the steam boiler is equipped with a reheater, an automatic sprinkler should be installed. When the reheater outlet steam temperature reaches the allowable value of zui, it can automatically be put into accidental water spray to cool down.
2.1.4 Ignition control system and flameout protection device Gas boilers are relatively high in explosion-proof requirements compared with coal-fired boilers, especially natural gas. The explosion limit of natural gas is 5% 15%. If a leak occurs, it is easy to produce an explosion. When exploding in a closed volume, the pressure generated is approximately 0.75 MPa to 1.65 MPa for different gases. Therefore, before the gas boiler is ignited, the furnace and the flue must be carefully purged to remove the combustible gas that may accumulate in the furnace. Reliable ignition control and flameout protection are indispensable safety protection devices for gas boilers.
A reasonable ignition program control system that automatically controls the ignition process. Only when the fan completes the cleaning task can the ignition be performed; only when the ignition flame has been established (as confirmed by the flame detector) and after a predetermined time has elapsed, The control valve of the main burner can be opened; the ignition flame can be automatically extinguished after a predetermined time; when the main flame fails to be ignited within a predetermined time, the main burner can automatically close quickly while the ignition flame is extinguished, the gas boiler The ignition procedure is typically monitored and controlled by the program controller.
In the ignition program control, the total ventilation before ignition should be not less than 3 times the total volume from the furnace to the chimney population, and the ventilation time is not less than the value specified in Table 1.
Table 1
Boiler type zui small ventilation time (seconds)
Shell boiler 20
Water tube boiler 60
In order to prevent the flameout caused by excessive air volume during low-load operation, the gas-fired boiler should be equipped with an automatic combustion regulating device on each boiler to control the air intake and gas supply of the gas boiler. The flameout protection device is composed of a flame detector and a solenoid valve. When the solenoid valve (not explosion-proof) is not suitable for direct contact with the gas, the flameout protection device should also include a pneumatic valve controlled by a solenoid valve, and the flame monitor is a flameout protection device. The key equipment, its working principle is: when the boiler furnace is turned off, the change of flame intensity will change the radiation frequency of light and heat. By using the monitoring component installed on the furnace, the frequency change of the optical radiation can be converted into electric energy and passed. The electrical circuit controls the supply of gas. The flame monitor detects whether the burner is burning. Once the flameout occurs, the solenoid valve is cut off to prevent the gas from leaking into the furnace. Therefore, it is required to be sensitive. The response speed must meet the specified requirements, and the operation is stable and reliable, and can be adapted to the boiler burner. Characteristics and send out relevant signals.
At present, there are two main types of flame monitors: one is to monitor ultraviolet rays in the flame, such as ultraviolet photosensitive tubes; the other is to monitor the flame by the conductivity of the flame, such as ion monitoring needles.
2.2 Safety devices for mitigating damage Explosion accidents of gas boilers often occur during the ignition process. The gas source valve of the gas boiler is not sealed and leaks, so that the mixed gas in the furnace or flue reaches the explosion limit, and the furnace is not effectively purged during ignition. Explosion; there is also a gas boiler in front of the burner due to too much fluctuation of gas pressure or wind pressure caused by fire or tempering, causing explosion to cause explosion; sometimes, because the burner does not match the gas type or boiler, during ignition Or an explosion occurred during operation. In order to reduce the damage degree of the furnace and flue in the explosion of mixed gas, the explosion-proof door must be installed after the coal-fired boiler is changed to burn gas. The area of ​​the explosion-proof door is selected according to the volume of the furnace and the flue and should meet the relevant regulations, generally taking 0.025m2/ M3, the explosion-proof door should be installed in a place where it is easy to vent, and the furnace, the flue, especially the dead zone, the turning place, the boring roof, etc., which are difficult to avoid in the flue, are susceptible areas where the flammable gas is easily accumulated, so The explosion-proof door is usually installed in the furnace and flue of the gas boiler and other parts that are vulnerable to the pressure wave generated by the explosion of the boiler. Once the explosion of the combustible gas occurs in these parts, the explosion of the explosion-proof door is prevented, and the boiler body is prevented from being damaged. Collapse to prevent casualties.
3. It is recommended that we can take various measures to ensure the safe operation of gas boilers. For example, in the use of advanced computer control systems on gas-fired boilers, in view of the uneven management level and the quality of personnel in the society, more than 10,000 gas boilers are scattered in urban areas, and there are many potential safety hazards. Therefore, we should learn from the lessons of small coal kiln, fireworks factory decentralized management, frequent accidents, and heavy casualties in recent years, paying enough attention to the safe operation of gas boilers, preventing accidents, and maintaining social economic development and social stability.
Due to the characteristics of the gas itself, it is flammable, explosive and easy to spread. The gas boiler is more dangerous than the coal-fired boiler, and the quality and safety performance of the control system are strict. This paper only discusses the safety of small and medium-sized gas boilers.
2. Safety devices "Safety is the life of the gas industry." Without safety, there is no benefit and no development.
2.1 Automatic alarm device When the gas boiler is running, the temperature and pressure of water and steam in the boiler and the water level in the steam boiler are the monitoring parameters to ensure its safe operation. When these parameters are abnormal, the automatic alarm device should emit sound and light signals. .
(1) Over-temperature alarm "Procedure" stipulates: If the rated hot water temperature of the hot water boiler is higher than or equal to 120 °C and the rated outlet hot water temperature is lower than 120 °C but the rated power is greater than or equal to 4.2 MW, an over-temperature alarm device shall be provided. And interlock protection, for small and medium-sized gas boilers, the standard signal is generally output from the temperature transmitter on the hot water outlet to the programmable logic controller (PLC), the standard value is compared with the given value, once over temperature The PLC immediately performs an emergency shutdown.
(2) When the rated evaporation of the overpressure alarm steam boiler is greater than or equal to 6t/h, it shall be equipped with a steam overpressure alarm, and an interlock protection overpressure alarm shall be simultaneously closed to close the solenoid valve, the gas source is cut off, the induced draft fan is still running, the boiler steam The pressure is generally controlled automatically by the pressure controller.
(3) Water level alarm steam boiler rated evaporation is greater than or equal to 2t / h, should be installed high and low water level alarm, high and low water level alarm signal should be able to distinguish, when the low water level alarm occurs, close the solenoid valve, cut off the gas source, the blower stops after 30s The induced draft fan is still running.
(4) Flow alarm The DC boiler shall be equipped with an alarm device when the feed water flow rate is lower than the start flow rate.
2.1.2 Cutting device The gas boiler shall be equipped with an interlocking device. When the conditions described in (1) to (5) occur in the operation of the boiler, the gas supply can be automatically cut off; for the boiler equipped with the blast burner, the supply of the air supply can be automatically cut off.
(1) The pressure of the hot water boiler is reduced until vaporization occurs or the water temperature rises above the specified value;
(2) The steam boiler pressure exceeds the specified value or the water level is low to the low value of zui;
(3) When the gas pressure is too high, there will be a phenomenon of fire, even if an explosion occurs in the furnace. Therefore, the burner must be operated under the designed gas pressure. The cutting device should be activated when the pressure is too high or too low. At present, domestic and gas-fired boilers are imported burners with high degree of automation, not only equipped with gas high and low pressure controllers, but also equipped with automatic leak detection controllers (in the process of ignition, furnace purge, leak detection control) Automatically check the gas valve system for leak detection);
(4) When the circulating water pump of the blower, the induced draft fan, and the hot water boiler suddenly loses power or stops running or a fault such as a frequency conversion fault or a contact point fault occurs, the cutting device is activated;
(5) Start of the smoke temperature protection device: The temperature of the smoke also reflects the normal operation of the boiler. Once the smoke temperature exceeds the set value, the cutting device should be activated.
2.1.3 Sprinklers When the steam boiler is equipped with a reheater, an automatic sprinkler should be installed. When the reheater outlet steam temperature reaches the allowable value of zui, it can automatically be put into accidental water spray to cool down.
2.1.4 Ignition control system and flameout protection device Gas boilers are relatively high in explosion-proof requirements compared with coal-fired boilers, especially natural gas. The explosion limit of natural gas is 5% 15%. If a leak occurs, it is easy to produce an explosion. When exploding in a closed volume, the pressure generated is approximately 0.75 MPa to 1.65 MPa for different gases. Therefore, before the gas boiler is ignited, the furnace and the flue must be carefully purged to remove the combustible gas that may accumulate in the furnace. Reliable ignition control and flameout protection are indispensable safety protection devices for gas boilers.
A reasonable ignition program control system that automatically controls the ignition process. Only when the fan completes the cleaning task can the ignition be performed; only when the ignition flame has been established (as confirmed by the flame detector) and after a predetermined time has elapsed, The control valve of the main burner can be opened; the ignition flame can be automatically extinguished after a predetermined time; when the main flame fails to be ignited within a predetermined time, the main burner can automatically close quickly while the ignition flame is extinguished, the gas boiler The ignition procedure is typically monitored and controlled by the program controller.
In the ignition program control, the total ventilation before ignition should be not less than 3 times the total volume from the furnace to the chimney population, and the ventilation time is not less than the value specified in Table 1.
Table 1
Boiler type zui small ventilation time (seconds)
Shell boiler 20
Water tube boiler 60
In order to prevent the flameout caused by excessive air volume during low-load operation, the gas-fired boiler should be equipped with an automatic combustion regulating device on each boiler to control the air intake and gas supply of the gas boiler. The flameout protection device is composed of a flame detector and a solenoid valve. When the solenoid valve (not explosion-proof) is not suitable for direct contact with the gas, the flameout protection device should also include a pneumatic valve controlled by a solenoid valve, and the flame monitor is a flameout protection device. The key equipment, its working principle is: when the boiler furnace is turned off, the change of flame intensity will change the radiation frequency of light and heat. By using the monitoring component installed on the furnace, the frequency change of the optical radiation can be converted into electric energy and passed. The electrical circuit controls the supply of gas. The flame monitor detects whether the burner is burning. Once the flameout occurs, the solenoid valve is cut off to prevent the gas from leaking into the furnace. Therefore, it is required to be sensitive. The response speed must meet the specified requirements, and the operation is stable and reliable, and can be adapted to the boiler burner. Characteristics and send out relevant signals.
At present, there are two main types of flame monitors: one is to monitor ultraviolet rays in the flame, such as ultraviolet photosensitive tubes; the other is to monitor the flame by the conductivity of the flame, such as ion monitoring needles.
2.2 Safety devices for mitigating damage Explosion accidents of gas boilers often occur during the ignition process. The gas source valve of the gas boiler is not sealed and leaks, so that the mixed gas in the furnace or flue reaches the explosion limit, and the furnace is not effectively purged during ignition. Explosion; there is also a gas boiler in front of the burner due to too much fluctuation of gas pressure or wind pressure caused by fire or tempering, causing explosion to cause explosion; sometimes, because the burner does not match the gas type or boiler, during ignition Or an explosion occurred during operation. In order to reduce the damage degree of the furnace and flue in the explosion of mixed gas, the explosion-proof door must be installed after the coal-fired boiler is changed to burn gas. The area of ​​the explosion-proof door is selected according to the volume of the furnace and the flue and should meet the relevant regulations, generally taking 0.025m2/ M3, the explosion-proof door should be installed in a place where it is easy to vent, and the furnace, the flue, especially the dead zone, the turning place, the boring roof, etc., which are difficult to avoid in the flue, are susceptible areas where the flammable gas is easily accumulated, so The explosion-proof door is usually installed in the furnace and flue of the gas boiler and other parts that are vulnerable to the pressure wave generated by the explosion of the boiler. Once the explosion of the combustible gas occurs in these parts, the explosion of the explosion-proof door is prevented, and the boiler body is prevented from being damaged. Collapse to prevent casualties.
3. It is recommended that we can take various measures to ensure the safe operation of gas boilers. For example, in the use of advanced computer control systems on gas-fired boilers, in view of the uneven management level and the quality of personnel in the society, more than 10,000 gas boilers are scattered in urban areas, and there are many potential safety hazards. Therefore, we should learn from the lessons of small coal kiln, fireworks factory decentralized management, frequent accidents, and heavy casualties in recent years, paying enough attention to the safe operation of gas boilers, preventing accidents, and maintaining social economic development and social stability.
Cooling Patch(Gel series)
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