Economical structural design of natural gas processing plants
Case study of a butane treatment unit illustrates effective structural designprocedures andhighlights construction challenges encountered innewandexpansionprojects
OSAMA BEDAIR Consultant
N atural gas processing sepa- rates hydrocarbons and flu - ids from pure natural gas to produce dry gas suitable for pipe- line transportation. Raw natural gas is first collected from oil wells then processed at collection points using separator vessels to remove fluids and other impurities. Gas process- ing plants convert natural gas to other products such as gasoline, ethane, butane, and propane. In some cases, hydrocarbon materials such as ethane, propane, and butane must be extracted from natural gas prior to pipeline transportation. Fractionation converts raw material into refined products transported using pipelines to various process- ing units for further processing. Liquefied petroleum gas (LPG) refers to propane or butane (either separate or in a mix), maintained in a liquid state under specific pres - sure/temperature within a vessel. LPG is a valuable energy source and is widely used as a chemical feedstock for the petrochemical and agriculture industries. Butane is a hydrocarbon gas (C 4 H 10 ) that is colourless, odourless, flammable, and can be easily liquefied. Butane is used as fuel for portable stoves/ barbecues, a propellant in aero- sols, refrigerants, and a feedstock to manufacture ethylene and buta- diene, a key ingredient of synthetic rubber. Butane extractions occur in a closed-loop extraction system. These units are closed, devoid of atmosphere, and recover the gas to its original vessel. Design cycles of natural gas pro- cessing plants are complicated and require close interaction between
time optimisation models in the gas processing industry. The con- cept enables operating facilities to respond efficiently and effectively to changing feed rates and compo- sition, equipment condition, and dynamic processing economics. Liu, et al 6 presented modelling and optimisation tools for the petro- leum refinery process. Bulasara, et al 7 presented a study to revamp heat exchangers in process plants to evaluate various commercial aspects. Lulianelli and Drioli 8 pre- sented a review of recent develop- ments of gas separation technology used in the petrochemical indus- try and refineries. The review also highlighted the importance of mem- brane reactors for fuel processing and membrane-based pretreatments and integrated membrane gas sepa- ration systems. Other aspects deal- ing with process design or butane process plants are presented by Gallagher 9 and Meyers 10 . Bedair 11-15 addressed various design aspects of structural members used in heavy industry. Not much information is available on the structural design improve- ments of natural gas process- ing plants. Most effort is directed towards process or chemical design aspects. Investigators and plants owners have given barely any atten - tion to improving structural design aspects of hydrocarbon facilities. Minimal literature has addressed structural engineering requirements of natural gas processing plants. Furthermore, most of the design provisions available in the North American codes of practice 16-22 deal with residential structures.
process, mechanical, and structural engineering disciplines. The engi- neering design is normally staged into several gates that require the owner’s approval for funding. Delays in construction projects due to engineering ambiguities may result in substantial losses in the form of interest on construction loans, management/staff time, and an increase in commodities prices as a result of the continuous inflation of material prices. Significant work has dealt with chemical and mechanical design improvements compared to structural aspects. Patience and Bockrath 1 presented a butane oxi- dation technique used in circulating a fluidised bed reactor to produce anhydride from n-butane Wu, et al 2 presented a study to enhance catalytic performance for butane oxidation. Sáez, et al 3 performed experimental tests employing a diesel oil burner to study the com- bustion process of liquid butane. A dual pumping and injection system was designed to operate with pres- sures varying from 0.8 to 2.0 MPa. They also performed a feasibility study to modify the combustion technology of diesel oil burners to use liquid butane as an alternative fuel. Yang, et al 4 presented a pro- cess model that utilises n-butane compounds to extract organic pol- lutants from contaminated water. Removal efficiencies for hydropho - bic pollutants were greater than 90%. Removal of residual butane in treated effluent was achieved by depressurisation, air stripping, and elevating operating temperature. Mokhatab and Poe 5 introduced real-
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