Fuel Gas Firing – Fuel Gas Pressure
The operating pressure for a fuel gas mix drum should be chosen so that its pressure controller can hold it constant in spite of swings in the various supply pressures.
Frequently, butane is vaporized to maintain the mix drum pressure as the availability of gas from other sources varies. This should be done within the dewpoint constraint discussed above, as well as within the limitations of the burners. Therefore, the operator should balance the overall fuel supply to limit the swings in the butane content of the mixed fuel gas. This balance may need auxiliary firing of fuel oil.
Fuel gas pressure should be further reduced at the using plant’s plot limit. Controlling the on-plot pressure so that it cannot blow out the burners adds substantially to flame reliability. This controller also stabilizes gas pressure to the firing control valves of furnaces fired in parallel from the same on-plot supply; load changes on one furnace will not upset the other furnaces if the on-plot header is big enough.