Novel Method for Gas Separation By: Chris Wilson For: Senior Capstone 2008

Overview Current process New process Economic comparison

Natural Gas Processing The Way it is Done Current process Remove excess water Remove acid gas Dehydrate Remove mercury Remove nitrogen Separate NGL (ethane, and heavier hydrocarbons)

Natural Gas Processing Everything Together

Water removal Removes free liquid water and condensate gas Sends the gas to a refinery The water goes to waste

Natural Gas Processing Everything Together

Natural Gas Processing Acid Gas Removal Hydrogen sulfide Mercaptans Carbon dioxide Acid gas removal processes Amine treating Benfield process Sulfinol process others

Natural Gas Processing Amine Treatment Most common used amines Monoethanolamine Diethanolamine Diisopropylyamine Methylethanolamine Hydrogen sulfide goes through a Claus process 64,000,000 metric tons of sulfur are produced from this process

Natural Gas Processing Amine Treating

Natural Gas Processing Sulfinol Process Used to reduce H2S, CO2, and mercaptans from gases Great for treating large quantities of gas Solvent absorbs the sour gas Sulfolane is used Sulfolane, a clear colerless liquid, developed by shell in the 1960’s

Natural Gas Processing Sulfinol Process

Natural Gas Processing Everything Together

Natural Gas Processing Glycol Dehydration Method for removing the water vapor from the gas Usable glycols Triethylene glycol – most commonly used Diethylene glycol Ethylene glycol Tetraethylene glycol Works by having the glycol adsorb the water

Natural Gas Processing Glycol Dehydration Wet gas enters a contacting tower at the bottom. Dry glycol flows down the tower from the top, from tray to tray, or through packing material. A bubble cap configuration maximizes gas/glycol contact, removing water to levels below 5 lbs/MMscf. Systems can be designed to achieve levels down to 1lb/MMscf. The dehydrated gas leaves the tower at the top and returns to the pipeline or goes to other processing units. The water rich glycol leaves the tower at the bottom, and goes to the reconcentration system. In the reconcentration system, the wet glycol is filtered of impurities and heated to 400°F. Water escapes as steam, and the purified glycol returns to the tower where it contacts wet gas again.

Pressure Swing Adsorption Adsorbent material is used Gas and material go under high pressure Material adsorbs the gas ( H2S, mercaptans, CO2) Disadvantages Requires high pressures Slow cycle times

Natural Gas Processing

Mercury removal Current Processes Activated carbon – through chemisorption. Activated has extremely high surface area Mercury can damages aluminum heat exchangers Those used in cryogenic processing plants Those use in liquefaction plants

Natural Gas Processing

Nitrogen Rejection Processes that can reject nitrogen Cryogenic process Absorption process (using lean oil or solvent) Membrane separation Adsorption process (activated carbon)

Natural Gas Processing Cryogenic Process Common refrigerants used Most common method for removal of impurities such as nitrogen Disadvantages Must reach extremely low temperatures Only useful for large scale production

Natural Gas Processing Lean Oil Removal Lean oil is fed countercurrent with the wet gas Temperature and pressure are set to allow for the greatest absorption of unwanted gases In the ambient lean oil absorption process the natural gas is contacted with the lean oil (molecular weight of about 150) in an absorber column at the ambient temperature of about 100°F. The rich oil exiting the bottom of the absorber flows into a rich oil depropanizer (ROD) which separates the propane and lighter components and returns them to the gas stream. The rich oil is then fractionated in a still, where the NGL's (C4+) are recovered as an overhead product and the lean oil is recycled to the absorber column. Typically, 75 percent of butanes and 85-90 percent of pentanes and heavier components are recovered. In the refrigerated lean oil absorption process, the lean oil is chilled against propane refrigerant to improve the recovery of propane to the 90 percent level, and depending upon the gas composition, up to 40 percent of ethane may be recovered (Elliot, 1997). Since reducing the molecular weight of lean oil enhances the lighter component absorption and an external refrigerant is used to chill the lean oil, 100 to 110 molecular weight lean oils are generally used in this process.

Natural Gas Processing Membranes Driving force Partial pressure Type of material determine permeability D = diffusion coefficient (cm2/s) k = Henry’s law sorption coefficient (cm3/cm3cmHg) P1 = Permeability of component 1 P2 = Permeability of component 2

Natural Gas Processing Economics

Demethanizer

Demethanizer The next step is to recover the NGL’s Process Cryogenics using a turbo-expander can be used This is the most common Lean oil adsorption can be used here

Natural Gas Processing Cryogenic Process

NGL recovery

NGL recovery Now the rest of the liquid is fed to three units Process Deethanizer Debutanizer Depropanizer Process Each sent to a distillation column

Sweetening NGL’s

Merox Processes Mercaptan oxidation Removes mercaptans from Propane Butane Larger hydrocarbons

Natural Gas Processing Another Process

Novel Method Technical information momentarily not available due to IP issues However economics will be compared If you want the access to this, then talk to OTD

Novel Method Advantage More cost effective than any previous methods Less environmental impacts than previous methods Separates all contaminants Separates each component Everything is done using one process If you want the access to this, then talk to OTD

Novel Method

Current Method

Economics - Amine Treating

Amine Treating - Simulation

Economics - Demethanizer

Demthanizer - Simulation

Economics - Dethanizer

Deethanizer - Simulation

Economics

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