JPH0124971B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a flare stack.

Flare stacks are designed to deal with situations where flammable or toxic gases are suddenly released from safety valves in plants. In an emergency, the safety valve is opened and the process gas is combusted in the flare stack, but the gas remaining in the process gas conduit after the safety valve is closed flows into the flare stack until it reaches atmospheric pressure. Moreover, the safety valves may not close completely, and process gas often flows into the flare stack throughout the year. In such a situation, the main burner of the flare stack is designed to discharge the maximum amount from the safety valve, so when the processing gas is small, it burns inside the main burner due to wind entrainment, often resulting in burnout of the main burner. This will cause an accident. It is customary to inject steam into the main burner to prevent this internal combustion. In addition, after the safety valve is closed, if the processing gas density is lower than the atmospheric density, the remaining processing gas will be rapidly exhausted by the draft generated inside the flare stack barrel.
There is a vacuum inside the cylinder. This draws air from the main burner, forming an explosive gas mixture inside the cylinder, and when the gas mixture is ignited by the always-on pilot burner, the flame advances toward the plant side. This backfire is completely prevented by the water seal drum and does not affect the plant side. However, since the water seal drum backfires, a loud explosion sound is generated within the water seal drum. To suppress this explosion noise, purge gas is constantly supplied to the downstream side of the water seal drum to prevent air from being drawn in from the main burner. Incidentally, the running costs of these steam and purge gas become enormous throughout the year, and this often becomes a problem as it runs counter to recent energy saving efforts.

The present invention provides a method for operating a flare stack that can solve the above problems.

That is, the present invention provides a method for operating a flare stack, which also includes a sub-burner that burns when the amount of processing gas is small, and in which when processing gas exceeding the capacity of the sub-burner is released, the excess amount is introduced into the main burner. The sub-burner excess is detected in advance, and steam to prevent combustion inside the main burner and purge to prevent backfire are automatically supplied to the main burner line.
Furthermore, the present invention provides a method of operating a flare stack that detects when the amount of gas to be processed in a subburner decreases and automatically supplies purge gas for preventing subburner backfire to the line of the subburner.
According to this method, a pressure detector installed in the processing gas pipe detects in advance that the processing gas exceeds the capacity of the sub-burner, and supplies steam for preventing combustion inside the main burner and purge gas for preventing main burner backfire. detects a drop in the amount of processed gas in the sub-burner, closes the automatic valve in that line, and supplies purge gas to subsequent conduits, which can significantly reduce the amount of steam and purge gas, thereby saving energy. can be measured.

An embodiment of the present invention will be described below based on the drawings. 1 is a main burner, and 2 is a sub-burner. Processing gas is introduced into these burners 1 and 2 through separately attached water seal drums 3 and 4, respectively.
That is, both water seal drums 3 and 4 have drums 3A and 4A filled with water inside, and a certain depth L,
It consists of inlet pipes 3B, 4B, etc. inserted into l.
These inlet pipes 3B and 4B are branched from a common processing gas conduit 5 extending from safety valves of plants, etc., and the constant depths L and l are set in the relationship [L>l], and the pressure detector 7A , 7B is as follows.

When the process gas is released L>P>p>l When the process gas decreases L>P>l>p Therefore, the process gas that has passed through the process gas conduit 5 first breaks the water seal of the sub-burner water seal drum 4 and then enters the sub burner. When the pressure in the sub-burner line 4C reaches a specified pressure, the automatic valve 8 opens in response to a signal from the pressure detector 7A, and the processing gas flows through the processing gas introduction pipe 4D and is burned in the sub-burner 2. Ru. This processing gas amount further increases,
When the capacity of the sub-burner 2 is exceeded, the water seal of the main burner water seal drum 3 is broken, and the excess amount of the process gas in the sub-burner 2 flows to the main burner 1. Here, the capacity of the sub-burner 2 is set to correspond to the amount that constantly leaks from the safety valve, and depending on the amount, multiple units are installed around the main burner 1, and a pilot burner 11 that is also used as the main burner 1 is installed in the sub-burner 2. be done. Note that the pilot burner 11 is always kept in the ignition state.

In the above, when processing gas exceeding the capacity of the sub-burner 2 flows through the processing gas conduit 5, the excess breaks the water seal of the water seal drum 3 and flows into the main burner 1 from the main burner line 3C as described above. The main burner 1 is ignited by a pilot burner 11 installed around the main burner 1, and the main burner 1 causes combustion. In this case, the pressure detector 7B installed in the process gas conduit 5 detects that the sub-burner 2 exceeds the limit before breaking the water seal of the water seal drum 3, and prevents internal combustion of the main burner 1. The steam valve 10 and the flashback prevention purge gas valve 9B are automatically opened to supply steam and purge gas. Incidentally, the water seal depth L of the water seal drum 3 and the operating pressure P of the pressure detector 7B are naturally set to have a relationship of [L>P].
In addition, the pressure detector 7B installed in the processing gas conduit 5 detects that the processing gas amount has decreased and processing gas no longer flows to the main burner 1, and the internal combustion prevention steam valve 10 of the main burner 1 is automatically activated. Close to. However, the purge gas valve 9B for preventing backfire continues to open.
For about 10 minutes, the process gas remaining in the main burner line 3C, cylinder body 6, and main burner 1 after the main burner water seal drum 3 is completely purged, and the purge gas valve 9B for preventing backfire is automatically closed. . Furthermore, the pressure detector 7A detects that the amount of processing gas flowing through the processing gas conduit 5 has decreased, and the pressure in the processing gas introduction pipe 4D after the sub-burner water seal drum 4 has decreased, and the automatic valve 8 is closed. Fire prevention purge gas valve 9
A automatically opens and purges the process gas inlet pipe 4D after automatic valve 8 and the sub-burner 2 for about 10 minutes,
This backfire prevention purge gas valve 9A is automatically closed, and the purging of the sub-burner 2 is completed. 12 in the diagram
13 is a pilot gas introduction pipe, 13 is a purge gas introduction pipe, and 14 is a steam introduction pipe.

According to the flare stack operating method of the present invention described above, it is detected in advance that the processing gas exceeds the capacity of the sub-burner by a pressure detector installed in the processing gas pipe, and the main burner internal combustion prevention steam and main burner backfire are detected. By supplying preventive purge gas, detecting a drop in the amount of processing gas in the sub-burner, closing the automatic valve of that line, and supplying purge gas to subsequent conduits, the amount of steam and purge gas can be greatly increased. This can lead to energy savings.

[Brief explanation of drawings]

The drawing is a system diagram showing one embodiment of the present invention. 1...Main burner, 2...Sub burner, 3, 4...
... Water seal drum, 3A, 4A ... Drum, 3B, 4
B...Inlet pipe, 3C...Main burner line, 4C...
...Subburner line, 4D...processing gas introduction pipe,
5...Processing gas conduit, 6...Cylinder body, 7A, 7B...
...Pressure detector, 8...Automatic valve, 9A, 9B...Purge gas valve for flashback prevention, 10...Internal combustion prevention steam valve, 11...Pilot burner, 12...Pilot gas introduction pipe, 13...Purge gas introduction tube,
14...Steam introduction pipe.

Claims (1)

[Claims] 1. A method of operating a flare stack that also includes a sub-burner that burns when the amount of processed gas is small, and in which when the amount of processed gas that exceeds the capacity of this sub-burner is released, the excess amount is introduced into the main burner,
Detects the sub-burner excess in advance, automatically supplies main burner internal combustion prevention steam and flashback prevention purge to the main burner line, and also detects when the amount of processed gas decreases in the sub-burner,
A flare stack operating method characterized by automatically supplying purge gas for subburner backfire prevention to a subburner line.