5.6 Gas

The gaseous fuels available are natural, manufactured, water, and oil gas and by-product gases such as coke-oven, blast-furnace, and refinery gas. Natural gas is widely distributed by means of high-pressure pipeline systems. Nevertheless, cost and availability of natural gas vary widely and depend on the exploration and drilling costs, as well as the distance the gas must be transported. In some instances, natural gas at a reduced cost is available for steam generation during periods when primary customer demand is low. By-product gas usually is used in the same plant in which it is produced or in a neighboring plant.

Natural gas from high-pressure pipelines is reduced in pressure and distributed to local customers through a low-pressure network of piping. When the pressure in the supply mains is above that required by the burners, pressure-regulator valves are used to maintain constant pressure at the burners. However, when the supply main pressure is less than that required at the burners, it becomes necessary to install booster compressors. These boosters are either multistage centrifugal blowers or constant-volume units similar in principle to a gear pump. The outlet pressure of constant-volume units must be controlled by spring-loaded bypass valves. In some instances it is necessary to install coolers in these bypass lines to remove the heat developed in the compressor. Gas burners are designed and regulated for a given pressure, and this pressure must be maintained for efficient and satisfactory operation. In like manner, provision must be made to supply by-product...