Chemical Processing - September 2007 - (Page 58)

>> MAKING IT WORK Membrane boasts material benefits simulation eases the design of innovative module to remove carbon dioxide By Paul J. Rubas and Kevin R. Geurts, ExxonMobil Upstream Research Co. Economical sEparation of contaminants (e.g., co2 and H2s) from natural gas is becoming increasingly important as companies look to commercialize lower quality gas fields. co2 separation can be accomplished using one of several different methods, including cryogenic distillation, recirculating solvent systems or selectively permeable gas-separation membranes. membranes offer potential advantages over other methods in compactness, simplicity and reduced cost. recently, membranes based on inorganic or ceramic materials have been developed. these new membrane materials promise to provide better performance and a wider operating-temperature range than available polymer membranes. at the wellhead, temperatures up to 300°f have been measured, yet conventional polymer membranes can handle a maximum operating temperature of about 150°f. another issue is that co2 used for enhanced gas recovery must be re-injected into ground at high pressure, which makes it beneficial to perform the separation at higher pressures than polymer membranes can withstand. inorganic membranes have the potential to overcome these problems. such membranes typically can handle temperatures up to 500°f or 600°f, which is considerably higher than any temperatures reached by producing wells. in addition, they can withstand much higher pressures than polymer membranes — so they can be operated at a substantially higher mass flow rate per unit of surface area. inorganic membranes are thin films that generally are synthesized on a porous structural support. the membrane and its support structure are mounted in a module that can be easily connected to the feed and outlet streams. in a typical application, the feed stream contains a mixture of gases such as cH4 and co2. the membrane usually is designed to allow the co2 to rapidly pass through while effectively blocking the cH4. relatively constant flow and chemical species distribution over the full surface area of the membrane is required to obtain high separation performance. researchers at Exxonmobil have made significant improvements in laboratory-scale inorganic membranes by modeling gas flow across the membrane surface using compu58 • september 2007 tational fluid Dynamics (cfD). such simulations have provided insights into improving distribution and effectively using surface area. Membrane module design challenges the goal of module design is to fully use all of the available membrane surface area to maximize throughput. there are several design objectives involved in this effort — all revolve around the idea of keeping the gases well >> Original module design Feed inlet Feed inlet Annular gap Housing tube Membrane tube Permeate outlet Seal Seal Retentate (residue) outlet Retentate (residue) outlet Figure 1. A single radial inlet leads to flow maldistribution. www.chemicalprocessing.com F http://www.chemicalprocessing.com

Table of Contents Feed for the Digital Edition of Chemical Processing - September 2007

Contents From the Editor Field Notes In Process Energy Saver Compliance Advisor Succeed at Simulation Rethink Your Approach to Process Safety Avoid Blending Blunders Get the Right Cartridge or Bag Filter Wireless Proponents Take HART Membrane Boasts Material Benefits Process Puzzler Plant InSites Chem Show Product Preview ISA Product Preview Equipment & Services Product Spotlight/Classifieds Ad Index End Point

Chemical Processing - September 2007

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