Flare System Design

The flaring of natural gas (mostly methane , CH 4 ) is a way to get rid of the residual gas used in industrial plants as oil refineries , chemical plants or plants natural gas processing , as well as in areas where this gas is produced, including  oil wells , gas fields and garbage dumps.

In industrial plants, torches are mainly used to burn flammable gas released by pressure relief devices during unplanned overpressures of plant equipment. during starts or stops -partials or total - also often used for combustion gases expected for relatively short periods.

Flare system design

Torch burning protects the equipment of many gas and oil extraction facilities from the dangers of overpressure. When oil is extracted from marine or inland deposits, the natural gas associated with this oil is also brought to the surface . Especially in areas of the world where there are no  gas pipelines or other infrastructure for the transport of gas - for example , liquefaction plants , or conversion of gas to liquid hydrocarbons ( gas-to-liquid processes , GTL for its acronym in English) 7- The vast quantities of this associated gas are generally burned as waste or unusable gas. The burning of said gas can be carried out at the top of a tower (as in the first photo) or, at ground level, in a specific burning pit.

This practice is considered "a waste of valuable resources, as well as a significant source of greenhouse gases." 8 It is considered preferable to re-inject the associated gas into the reservoir, saving it for future use, and keeping the well pressure high. , which facilitates the extraction of oil (reducibility).

Torch burning system in industrial plants

When the equipment of an industrial plant is subjected to overpressures (pressures greater than those that by design can withstand), the pressure relief valve is an essential safety device. If the pressure exceeds the limit, the valve opens automatically (purge), almost always releasing gas and sometimes liquids. These pressure relief valves are required by industrial design regulations and applicable standards, as well as by law.

The gases and liquids released are conducted by piping systems called flare headers to a vertical raised torch. The gases burn when they go outside (there is a pilot flame permanently in the device). The size and brightness of the resulting flare depends on the flow of flammable material in joules per hour.

Most plant torches have a steam separator (also known as an extraction drum, knockout drum) upstream of the flame to extract any large amount of liquid that may accompany these pressure relief gases.

Very often water vapor is injected into the flame to reduce the formation of black smoke. If too much steam is added, what is known as "over evaporation" (over steaming) is produced, with less combustion efficiency and higher emissions.

In order to keep the entire system functional, it is necessary to permanently burn a small amount of gas to feed the pilot flame, so that the system is always ready for its primary purpose: to avoid the dangers of overpressures.

Schematic flow diagram of a vertical torch

The adjacent flowchart shows the typical components of an industrial overpressure gas torch burn system:

An extraction drums to remove any oil or water from the relief gas stream.

A sealing drum to prevent the flame from the top of the torch from spreading to lower elements of the assembly.

An alternative gas recovery system for use during partial starts and stops of the plants, as well as at other times when required. The recovered gas is taken to the fuel system of the plant.

A steam injection system to provide an amount of movement that effectively mixes the air in the atmosphere with the relieved gas, so that combustion occurs without smoke.

A pilot flame (with its ignition system) that is burning all the time, so that, when there is a relief gas flow, it becomes a flare, and thus prevents it from going outside as combustible gas, which could cause fires or poisonings.

The torch itself, including in its upper part a section to prevent the spread of the flame.

Ways to reduce burned gas to relieve overpressures

Use efficient torch tips, and optimize the size and number of combustion nozzles.

Maximize the combustion efficiency of the torch, controlling and optimizing the flow of fuel / air / steam to ensure a correct ratio between the main and auxiliary streams of the torch.

Minimize, without compromising safety, the gas intended for the torch, with measures such as the installation of purge gas reduction devices, gas recovery units, inert purge gases, elastomer seat valves or installation of protection pilots.