JP2001065863A - Method for preventing gas explosion accident of boiler or incinerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent self explosion of gas at the time of restart by closing an exhaust gas damper at the outlet of the flue temporarily and supplying inert gas to the combustion chamber when a large volume of unburnt gas is generated in the combustion chamber and the flue and standing therein. SOLUTION: Combustion state in the combustion chamber is detected by means of a flame monitor, visual monitoring or a gas analyzer provided at the outlet of the flue. When abnormal combustion state is detected and the risk of gas explosion is expected because of a large volume of unburnt gas standing in the combustion chamber and the flue, fuel and combustion air supply to the combustion chamber is interrupted. At the same time, inert gas, e.g. nitrogen gas, is supplied from a gas cylinder to the combustion chamber by a volume equal to or larger than the total volume of the combustion chamber and the flue. The ratio of concentration between the large volume of standing unburnt gas and the supplied inert gas is kept higher than the range of gas explosion and ventilation is performed by a volume equal to or larger than the total volume of the combustion chamber and the flue while supplying inert gas gradually thus discharging the remaining unburnt gas until the concentration thereof drops below the range of explosion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION Many gas explosion accidents in boilers and incinerators are caused by repeated ignition failures or delayed detection of abnormal combustion, resulting in a large amount of unburned gas remaining in the combustion chamber or flue. To prevent gas explosion accidents in such cases.

[0002]

2. Description of the Related Art In a conventional boiler / incinerator, the combustion state of a combustion chamber is monitored by a flame monitoring device or an operator's eyes, and repeated ignition failures, poor fuel spraying, combustion chamber temperature during combustion, and the like. If incomplete combustion occurs due to a decrease in fuel consumption or lack of combustion air, and an abnormal combustion state is detected, the system is stopped immediately and the supply of fuel and combustion air to the combustion chamber is immediately stopped. The exhaust gas damper at the outlet of the flue is opened to provide ventilation, and the ignition and restart are performed after discharging the unburned gas in the combustion chamber and flue. Insufficient cooling has caused a gas explosion accident.

When an abnormal combustion state in the combustion chamber is detected, ventilation is gradually performed over a sufficient period of time after an emergency stop of the combustion state, and ignition / restart is performed after cooling the combustion chamber. Although it is thought that most gas explosion accidents can be prevented, the larger the scale of the equipment, the more difficult it is for the on-site situation to continue operation shutdown for a long time, and the on-site operators also need to perform restart operations. In many cases, misoperations become easy in a hurry, and gas explosion accidents often occur.

[0004] In such a case, as a method for preventing a gas explosion accident, there is no proposal to supply an inert gas to a combustion chamber, and no method has been practiced in an actual apparatus.

[0005] References dealing with the explosion range of combustible gas include, in 1967, published by Nikkan Kogyo Shimbun, written by Tetsuzo Kitagawa,
There is chemical safety engineering, and there is a commentary on pages 81-83, 4.4, "Explosion range diagram of combustible gas". It is a theoretical explanation and does not mention how to prevent gas explosion.

[0006] Regarding the use of the inert gas of claim 1,
Japanese Patent Application Laid-Open No. 6-229546 discloses a case in which high-pressure compressed air is used for operating a control valve in a boiler facility, and a control valve using nitrogen gas from a nitrogen gas supply device is used instead of an abnormal decrease in air pressure for operation. There are proposals to back up operations and keep the device safe. In that case, it is stated that by supplying nitrogen gas from the pressure regulating valve into the boiler body, the remaining unburned carbon content will not burn, but it does not mention prevention of gas explosion .

[0007] Japanese Patent Application Laid-Open No. Hei 10 (1998) discloses a method for controlling the combustion of a boiler by providing a gas analyzer at the outlet of a flue.
No. 26346 proposes a method for detecting the oxygen concentration in exhaust gas as a boiler combustion control device. The patent focuses on the function of the oximeter, and according to the method, the accuracy and reliability of the oximeter can be improved,
It is said that the accuracy and reliability of combustion air amount control can be improved. The use of an oximeter for boiler combustion control is described, but no mention is made of its use for gas explosion prevention.

[0008]

In the case of a boiler or an incinerator, if a large amount of unburned gas remains in the combustion chamber or the flue due to incomplete combustion, ventilation in the combustion chamber or the flue is conventionally performed. Thus, a method of igniting and restarting after sufficiently discharging the retained unburned gas is adopted, but this method does not provide a reliable accident prevention measure. Prevention of gas explosion accident at such restart.

Conventionally, the cause of the gas explosion accident upon restart is that an ignition source is installed in the combustion chamber in a state where the ventilation in the combustion chamber / flue is insufficient and the concentration of unburned gas is within the gas explosion range. Often it occurs because it entered. Prevention of gas explosion accident at such restart.

[0010] Further, even though the ignition source is not supplied to the combustion chamber, the ventilation of the combustion chamber / flue is started and new air is supplied to the combustion chamber. As a result, a gas explosion accident has occurred, with some high-temperature portions in the combustion chamber serving as ignition sources. Prevention of gas explosion accident at such restart.

[0011]

Means for Solving the Problems The present invention is intended for use in a case where a large amount of unburned gas is generated or accumulated in a combustion chamber or a flue of a boiler, an incinerator or the like, and a dangerous state of generating a gas explosion occurs.
Emergency shut down of the system to stop the supply of fuel and combustion air to the combustion chamber, minimize the generation of unburned gas, and temporarily close the flue gas exhaust damper. At the same time, an inert gas such as nitrogen gas is supplied to the combustion chamber, and the concentration of the unburned gas and the inert gas in the combustion chamber and the flue is maintained at a ratio exceeding the gas explosion range.

While continuing to supply the inert gas little by little, the flue gas damper at the outlet of the flue is gradually opened to sufficiently ventilate the combustion chamber and the flue, and the accumulated unburned gas is discharged together with the inert gas. Then, after the concentration of the unburned gas is lower than the gas explosion range, the ignition and restart operations are performed to more reliably prevent the occurrence of a gas explosion accident upon restart.

When an abnormal combustion state is found in the combustion chamber, the combustion state is urgently stopped, and then the ventilation is performed gradually for a sufficient period of time, and after the combustion chamber is cooled, the ignition and restart are performed. It is thought that most gas explosion accidents can be prevented by doing this.However, as the scale of the equipment increases, it is often difficult to keep the operation stopped for a long time, and the operator also needs to perform the restart operation. There are many cases where a gas explosion accident occurs due to erroneous operation in a hurry. The occurrence of a gas explosion accident is prevented by preventing erroneous operation even in such an abnormal situation.

Therefore, when abnormal combustion is detected by a combustion monitoring method such as a flame monitoring device of a combustion chamber or a flue gas analyzer provided at a flue gas outlet and emergency stop of the combustion state is performed, First, supply a large amount of inert gas into the combustion chamber to maintain the concentration of unburned gas and inert gas within the gas explosion range, and then perform ignition and restart to ensure Prevent gas explosion accidents.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In a boiler, an incinerator or the like, an abnormality in the combustion state is detected by a combustion monitoring method such as a flame monitoring device or a flue gas analyzer provided at a flue gas outlet or a flue gas outlet. If a large amount of unburned gas is retained in the combustion chamber or flue and a danger of gas explosion is expected, the emergency stop of the device is automatically or manually stopped immediately, and the fuel and combustion in the combustion chamber are stopped. The supply of service air is stopped to minimize the generation of unburned gas.

At the same time as the emergency stop of the device, an inert gas such as nitrogen gas is automatically or automatically supplied from a permanent gas supply device such as a gas cylinder to the combustion chamber based on an amount equal to or greater than the total volume of the combustion chamber and the flue. The concentration of unburned gas that has been supplied by hand and accumulated in large amounts and the concentration of inert gas that has been supplied is in a state where the concentration of the gas is in excess of the gas explosion range (the state in which the amount of unburned gas and inert gas is excessive and the amount of oxygen is insufficient). Hold.

Further, while the inert gas supply valve is opened and the inert gas is gradually supplied, the exhaust gas damper at the flue outlet is gradually opened, and the amount of the combustion gas is increased to a level not less than the total volume of the combustion chamber and the flue. After sufficient ventilation, remove the remaining unburned gas concentration to a small percentage below the explosion range (unburned gas is insufficient), then stop the supply of inert gas, Perform the restart operation.

In case of emergency stop due to failure of ignition operation or occurrence of abnormal combustion, first, supplying inert gas to the combustion chamber is a basic measure for preventing gas explosion accident.

When an inert gas is supplied from an inert gas supply device such as a gas cylinder, the inert gas supply valve is automatically opened in conjunction with a combustion state monitoring device or the like, but the monitoring device always operates reliably. Since it is not possible to determine that, we will try to visually monitor the combustion state of the combustion chamber, and in the event of abnormal combustion, allow the control room to manually open the inert gas supply valve by remote control, Further, even at the site, the supply valve of the inert gas is manually opened so that the gas can be supplied smoothly.

The supply pipes and the respective opening valves from the inert gas supply device described in the preceding paragraph are provided with a number and amount capable of supplying a required amount of the inert gas into the combustion chamber and the flue in a short time. Predict the number and time to open the release valve in advance according to the required amount according to the equipment, and automatically supply the required number and time in advance and supply it smoothly even by manual operation. To be able to do. For ventilation before restarting, predict the opening degree and time of the damper necessary to vent the combustion gas for each device, and also notify the site operators in advance,
Do not mistake opening and closing operations.

When supplying inert gas, in order to prevent personal injury due to lack of oxygen in workers in and around the equipment, make sure that no workers are in the equipment such as the combustion chamber and flue. I do. In addition, an alarm is sounded to notify a worker on site of an emergency.

The method for preventing gas explosion of the present invention is not limited to the size and type of boiler, incinerator and the like.

[0023]

The present invention is the most reliable and reliable method for preventing gas explosion when igniting and restarting when ignition operation fails repeatedly or abnormal combustion occurs. Particularly in the past, large gas explosion accidents have occurred in soda recovery boilers in pulp mills and CO boilers in steelworks, and such dangers are expected in incinerators. By implementing the gas explosion prevention method of the present invention, it is possible to effectively prevent a large and dangerous gas explosion accident that is likely to be accompanied by personal injury effectively without incurring a large cost.

Claims (3)

[Claims] 1. The present invention relates to a boiler, an incinerator, etc., in which repeated ignition failures, misfires during combustion, abnormal combustion occur, and a large amount of unburned gas in the combustion chamber / flue. In the case of stagnation, after an emergency stop of the device, at the same time as supplying inert gas to the combustion chamber and maintaining the concentration of unburned gas and inert gas in an excessive ratio exceeding the gas explosion range, While continuing to supply inert gas gradually, open the flue gas exhaust dumper and gradually ventilate the combustion chamber and flue to discharge unburned gas, and the unburned gas concentration is below the gas explosion range. A method to prevent a gas explosion accident at the time of restart by performing an ignition and restart operation after setting the ratio to an appropriate level. 2. The method according to claim 1, wherein the inert gas is supplied from the inert gas supply device by automatically or manually opening the inert gas supply valve after an emergency stop of the device. Since it is not necessary to supply the inert gas more than the required amount, the release amount or release time corresponding to the required supply amount of the inert gas is predicted in advance for each device,
After supplying the required amount, once shut off the inert gas supply valve, open the inert gas supply valve, and gradually supply the inert gas, open the flue gas exhaust gas damper, and burn. This method is to gradually ventilate the inside of the room / flue and exhaust the unburned gas before closing the inert gas supply valve and flue gas exhaust damper. 3. A flue gas gas analyzer is attached to a flue outlet of a boiler, an incinerator, or the like. When it is detected that the concentration of the fuel gas or the residual oxygen has become abnormally high, it is determined that abnormal combustion has occurred, and the boiler / incinerator or the like is automatically or manually emergency stopped.
A method for preventing a gas explosion accident at the time of restarting by supplying an inert gas to the combustion chamber by the method described in claim 2 and ventilating the combustion chamber / flue and then performing ignition / restart operation. .