Flash gas compressor

Compressors are used whenever it is necessary to flow gas from a lower pressure to a higher pressure system. Flash gas from low-pressure vessels used for multistage stabilization of liquids, oil treating, water treating, etc., often exists at too low a pressure to flow into the gas sales pipeline. Sometimes this gas is used as fuel and the remainder flared or vented. Often it is more economical or it is necessary for environmental reasons to compress the gas for sales. In a gas field, a compressor used in this service is normally called a flash gas compressor. Flash gas compressors are normally characterized by low throughput rate and high differential pressure. 

Flash gas compressors typically have an overall compressor ratio in the range of 5 to 20. 

The use of large compressors is probably more prevalent in oil field facilities than in gas field facilities. Oil wells often require 1 Tee pressure and the gas that flashes off the oil in the separator must be compressed in a flash gas compressor. Often a g i lift system is nei help lift the oil to the surface. As described in Volume 1, a gas li pressor must compress not only the formation gas that is produce. . .. v,. r oil, but also the gas-lift gas that is recirculated down the well. Gas lift i npressors are chaiacterized by both high overall compressor ratios and 1 atively high throughputs. 

I ween the tubing and the casing. When it is economical to recover this j >, or when the gas must be recovered for environmental reasons, a . asinghead gas compressor will be installed. These are somei called casing vapor recovery (CVR) units or just vapor recovery (VRU). Casinghead compressors are typically characterized by low tion pressure (0 to 25 psig). They often discharge at low pressure (50 to 300 a booster or flash gas compressor or into a... 

There are some low horsepower (140 to 360) integrals that are nonnaf ly skid mounted as shown in Figure 10-6 and used extensively in small oil fields for flash gas or gas-lift compressor service. In these units the power cylinders and compressor cylinders are both mounted horizontally... 

Most gas lift, flash gas, and vapor recovery compressors require a recycle valve because of the unsteady and sometimes unpredictable nature of the flow rate. Indeed there may be periods of time when there is no flow at all to the compressor. 

The flare valve also allows production to continue momentarily if a compressor shuts down automatically. Even in booster service it may be beneficial to allow an operator to assess the cause of the compressor shutdown before shutting in the wells. In flash gas or gas-lift service, it is almost always beneficial to continue to produce the liquids while the... 

On June 22, 1997, an explosion and fire destroyed an olefin plant at the Shell Deer Park, Texas chemical complex. Thirty workers received minor injuries and extensive damage resulted to both the plant and adjacent community. The incident was caused by the sudden failure of a pneumatic check valve in a 300-psig gas compressor discharge line that led to a large release of propylene vapor. A few minutes after the release, the gas ignited causing a vapor cloud explosion and flash fire. 

Methanator m) C02 removal solvent boiler n) Process condensate separator o) C02 absorber p) Synthesis gas compressor q) Process air compressor r) Ammonia converter s) High-pressure ammonia separator 1) Ammonia and hydrogen recovery from purge and flash gas... 

Both the vacuum section and moving parts of vacuum pumps may be lubricated by the same lubricants as those used for gas compressors. This only applies to industrial equipment producing low or medium vacuum. For high vacuum, lubricants must have better properties, particularly vapour pressure and sealing of the vacuum section, therefore more viscous lubricants are used. The best petroleum-based vacuum pump lubricants are narrow oil fractions of sufficiently high viscosity. These oils have high flash points and do not contain low-boiling components which will affect the flnal vacuum achieved, produce oil mist and lead to condensate formation in adjacent areas. 

An example of an estimate of the total capital investment for a processing plant is given in Tables 16.14 and 16.15 for an ammonia plant producing 1 billion Ib/yr. The costs are for the year 2000 at a U.S. Midwest location. The plant is part of an integrated complex. The process involves a variety of equipment, including gas compressors, pumps, heat exchangers, a catalytic reactor, a distillation column, an absorber, a flash drum, a gas adsorber, and gas permeation membrane separators. The material of construction is almost exclusively carbon steel. 

Methane / CO2 Recovery Recover lost gas from venting, flaring, or fugitive sources Flash gas recovery LDAR Compressor wet seal vent recovery... 

Also End flash gas used for diyer bed regeneration is currently at higher temperature due to design deficiencies in the EFG compressor after cooler. This is impacting final cooling temperature of the molecular sieve beds. 

The liquid ammonia from the separator contains a small amount of dissolved gases. These are partly released by pressure reduction in a let-down vessel normally to about 20 bar. The gases released are normally used as fuel. Recycle to the synthesis gas compressor has been proposed [635]. Flashing at an intermediate pressure with recycle of the released gas to the process feed has been used, e.g. in revamp projects [452]. 

The overhead vapor from the main fractionation column enters the wet gas compressor train. The vapor leaving the compressor train then enters a high-pressure flash system. The vapor from the high-pressure flash enters the primary absorber. The C5 components leave with the bottom product from the primary absorber. This bottom product re-enters the high-pressure flash. The overhead vapor product enters a sponge oil absorber where it is contacted with LCO drawn... 

For gas turbines, especially the more advanced high-temperature gas turbines, the oil of choice should be synthetic oil, since synthetic oils have a high flash point. Gas turbine lubrication systems should be run for about 20 minutes after shutdown since maximum temperatures are reached after 10 minutes of shutdown especially in the bearing area. Most gas turbines are also on turning gear to avoid sagging in the shaft. Mineral oils can be used for the compressor. It is not uncommon to have two types of oil in a petrochemical plant. Mineral oil costs much less than the synthetic oil. 

Sidestream compressors are used in refrigeration processes where, for economy, the refrigerant is flashed off at different pressure levels. Ideally, separate compressors could be used to successively compress the gas back up to the condensing pressure level. The pressure ratio for each stage is low enough to enable this to be done with only one or two impellers in each section. Because of this, compressors can be made with all sections in one casing so that mixing of the streams takes place intern.ll I v. 

Depending on the number of stages, the gas that flashes in the lowci pressure separators can be compres.sed and then recombined with the gas from the high-pressure separator. Both reciprocating and centrifugal compressors are commonly used. In low-horsepower installations, especially lor compressing gas from stock tanks (vapor recovery), rotary aiuf vane type compressors are common. 

Figure 1-1. The Selexol process for acid gas removal (1) absorber, (2) flash drum, (3) compressor, (4) low-pressure drum, (5) stripper, (6) cooler.

In a two-stage system, the vapors from the compressor s first stage discharge are partially condensed and flashed in an interstage drum. The liquid hydrocarbon is pumped forward to the gas plant, either to the high pressure separator (HPS) or directly to the stripper. 

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