Gas lines

Figure A2.5.1. Schematic phase diagram (pressure p versus temperature 7) for a typical one-component substance. The full lines mark the transitions from one phase to another (g, gas liquid s, solid). The liquid-gas line (the vapour pressure curve) ends at a critical point (c). The dotted line is a constant pressure line. The dashed lines represent metastable extensions of the stable phases.

The presence of ethane in Hquefied petroleum gas must be avoided because of the inabiHty of this lighter hydrocarbon to Hquefy under pressure at ambient temperature and its tendency to register abnormally high pressures in the LPG containers. On the other hand, the presence of pentane in Hquefied petroleum gas must also be avoided because this particular hydrocarbon, a Hquid at ambient temperatures and pressures, can separate in the Hquid state in the gas lines. 

Schemes to control the outlet temperature of a process furnace by adjusting the fuel gas flow are shown in Figure 13. In the scheme without cascade control (Fig. 13a), if a disturbance has occurred in the fuel gas supply pressure, a disturbance occurs in the fuel gas flow rate, hence, in the energy transferred to the process fluid and eventually to the process fluid furnace outlet temperature. At that point, the outlet temperature controller senses the deviation from setpoint and adjusts the valve in the fuel gas line. In the meantime, other disturbances may have occurred in the fuel gas pressure, etc. In the cascade control strategy (Fig. 13b), when the fuel gas pressure is disturbed, it causes the fuel gas flow rate to be disturbed. The secondary controller, ie, the fuel gas flow controller, immediately senses the deviation and adjusts the valve in the fuel gas line to maintain the set fuel gas rate. If the fuel gas flow controller is well tuned, the furnace outlet temperature experiences only a small disturbance owing to a fuel gas supply pressure disturbance.

Cases (e), (g), and (h) are of interest in the cathodic protection of warm objects (e.g., district heating schemes [89] and high-pressure gas lines downstream from compressor stations [82]) because the media of concern can arise as products of cathodic polarization. The use of cathodic protection can be limited according to the temperature and the level of the mechanical stressing. The media in cases (a) and (f) are constituents of fertilizer salts in soil. Cathodic protection for group I is very effective [80]. 

Flue gas line hydraulics to the expander, including the regenerator pressure control valve... 

Examples. Find the fuel values equivalent to 5.00/ MM BTU natural gas. Connect 5.00/MM BTU on the natural gas line with the left-hand focal point. Read the following values along the connecting line, for example ... 

Valves in the inlet, seal water and pilot gas lines should be located according to permissible radiant heat densities for personnel (refer to the last section of this chapter for specific guidelines). Piping to the burning pit should be suitably protected against flame impingement (e.g., by installation below grade). 

The required pipe internal diameter can be calculated based on the volumetric flow rate and a maximum velocity. The maximum velocity may be the erosional velocity or a limiting value based on noise or inability to use corrosion inhibitors. In gas lines it is recommended that the maximum... 

The inlet gas line should have taps for gas sampling, temperature measurement, pressure measurement, and for an injection nozzle for... 

Gas dehydration is the process of removing water vapor from a gas stream to lower the temperature at which water will condense from the stream. This temperature is called the dew point of the gas. Most gas sales contracts specify a maximum value for the amount of water vapor allowable in the gas. Typical values are 7 Ib/MMscf in the Southern U.S., 4 Ib/MMscf in the Northern U.S. and 2 to 4 Ib/MMscf in Canada. These values correspond to dew points of approximately 32°F for 7 lb/ MMscf, 20°F for 4 lb MMscf, and 0°F for 2 Ib/MMscf in a 1,000 psi gas line. 

It is possible to inject glycol in a gas line and have it absorb the water vapor in co-current flow. Such a process is not as efficient as countercurrent flow, since the best that can occur is that the gas reaches near equilibrium with the rich glycol as opposed to reaching near equilibrium with... 

As pointed out in Volume 1, Chapter 3, a compressor may have any number of stages. Each stage normally contains a suction scrubber to separate any liquids that carry over or condense in the gas line prior to the compressor cylinder (or case for centrifugal compressors). When gas... 

Water hammer (also known as hydraulic shock) occurs in two distinct ways when the flow of liquid in a pipeline is suddenly stopped, for example, by quickly closing a valve [13], and when slugs of liquid in a gas line are set into motion by movement of gas or condensation of vapor. The latter occurs when condensate is allowed to accumulate in a steam main, because the traps are too few or out of order or in the wrong place. High-pressure mains have been ruptured, as in the following incident. 

A boiler had been shut down for the repair of a forced draft fan. A blind was not installed in the fuel gas line, nor apparently was a double block and bleed in the fuel line utilized. Gas leaked into the firebox during the repair period and was not removed. A severe explosion occurred during the attempt to light of. 

Fires of tliis origin are most coimnonly caused by sparks and hot metal from cutting and welding operations, by defective gauges, or deteriorated gas lines on welding equipment. 

Parker, R. E, Programmable Galculators Speed Gas-Line Calcu-iations, Oil and Gas Journal, May 7, 1979, p. 67. 

Chemical (and Water) Tank and Pump. The pump injects water, liquid foamers and chemical corrosion inhibitors into the high-pressure air (or gas) line after compression of the air and prior to the standpipe. 

Safety valve venting is noisy. It should only happen infrequently and therefore may be acceptable. If the location is near to offices or housing, it may be advisable to fit silencer heads. Noise levels from gas lines and meters should not normally prove a problem on industrial premises. 

Polarisation resistance This technique, sometimes referred to as linear polarisation resistance (LPR), has been applied widely in industrial monitoring because of its ability to react instantaneously to a corrosion situation or change in corrosion rate " " . The limitation of the technique arises from the necessity to have a defined electrolyte as the corrosive (the author has seen an LPR probe installed in a dry gas-line in an oil refinery). 

Solids formed under pressure from liquid water and natural gas (even if the temperature is higher than 0 °C). These deposits may plug gas lines and, therefore the gas must first be dehydrated to remove them. 

When the equipment is turned off, close the fuel gas cylinder valve tightly and bleed the gas line to the atmosphere via the exhaust system. 

Bonney Forge, Allentown, Pa. Mean pressure in a gas line [57]. 

Nozzles and orifices, 82, 83 Vapors and gases, 54 Flow, long natural gas lines, 120... 

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