Economic factors in cryogenic gas processing
Publication Date: 2009-May-05
The IP.com Prior Art Database
Economic factors • In
Comparison of natural-gas-processing methods
Pure Methane and LNG
o 10 20 30 40 50 60 70 80 90 100
Typical component recovery %
D. B. CRAWFORD,
J. O. CRONK, and
J. C. NORE:'-IBVRG
M. W. Kellogg Co.
WHAT can cryogenic gas processing of
natural gas accomplish that can't be done as economically by other proc- esses? The answer is, "Recover heli- um. reject nitrogen, produce pure methane or L:'-IG, and recover ethane."
Furthermore such a plant can easily and economically be designed to re- cover propane and heavier hydrocar- bons. Propane recovery will ordinarily exceed 95% if the plant is designed for optimum recovery of ethane.
Fig. 1 is a bar graph which com- pares the typical economic recoveries for refrigerated-lean-oil plants to cryo- genic plants.
The refrigerated-lean-oil p I ant, which is the standard of the industry for the recovery of propane and heav- ier hydrocarbons. is represented on the graph by unshaded blocks. The cryo- genic plant 15 illustrated b\ lined blocks.
Obviously the cryogenic plants' re- covery exceeds that achievable b) lean oil.
The general scheme of a cryogenic plant for the recovery of hydrocar- bon liquids from natural gas is shown in Fig. 2.
Fig. 3 shows the percentage of each
Paper presented at ",GPA annual meeting, Dallas. 1969.
Cryogenic naturaI-gas-liquids extraction plant
removall Ethane •
Butane Butane $plltter
component in a natural gas that has condensed as the temperature is low- ered from ambient to just about total conuensation. Eighty percent propane or ethane recovery is achieved by processing condensate created at _90 c
F. or 125" F. respectively.
Helium extraction is accomplished
by first condensing 80 to 90~i (cool- ing to approximately 150') of the fceu: the 10 to 20'7c uncondensed va- pors are further cooled to approxi- mately -300 c F. where all compo- nents except helium are condensed.
Ethane. The separation of methane- ethane mixtures at SOO psia has been studied to evaluate the optimum eth- ane-recovery level. Fig. 4 presents the results of the study, but it does not include costs associated with hy- drocarbon fractionation, feed-gas dry- ing. CO~ removal, or product storage.
The lowest cost of ethane occurs at a recovery between 50-70OC.
Actual optimum recovery for a given facility is dependent upon feeu- gas composition and the requireu tail- gas composition or heating value.
It will also depend on plant location and whether the ethane plant is an independent economic unit or whether it is combined \\ ith a large ethylene complex: in the latter case, higher recovery levels may provide an attrac- tive return on investment.
It may be necessary to go beyond minimum-cost etha...