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type     June, 2005

Vol 1 Chapter 18: Design, scale up and cost assessment of a membrane shift reactor

Ted R. Ohrn et al SOFCo-EFS Alliance, USA

Abstract: The objective of the design, scale up and cost assessment of membrane shift reactor project was to produce a detailed design and cost estimate of a commercial scale membrane water gas shift (MWGS) reactor. The requirements for the reactor were:

  • retentate dry CO2 molar content - 90%;
  • permeate LHV - 150 Btu/SCF;
  • hydrogen extraction >90%;
  • feed/retentate pressure drop <2.76 bar (40 psid);
  • sweep/permeate pressure drop <0.34 bar (5 psid)

The flux of hydrogen through the membrane was approximately 234 MMSCFD.

Two feasible MWGS reactor designs have been developed, which use either a planar or a tubular hydrogen separation membrane. The planar membrane is composed of a curved membrane supported by a corrugated Type 430 stainless steel sheet. Finite element analysis which considered the pressure, gravity, and differential thermal expansion loadings indicates that it is structurally adequate for 41.1 bar (600 psid) pressure loading at 450°C (842°F). A second MWGS reactor concept is based on a tubular membrane sized appropriately to contain the high pressure inside the tubes.

An analysis tool to permit examination of different arrangements for the MWGS reactor was developed and bench-marked against the model developed in Phase I. This analysis tool determined the membrane area required for each reactor concept. The planar membrane reactor has the following characteristics:

  • a multi-pass cross flow arrangement;
  • forty stacks of 159 membrane wafer panels, 2 m (6.55 ft) long by 3.05 m (10 ft) tall by 0.305 m (1 ft) wide;
  • total active membrane surface area of 5357 m² (57,662 ft²);
  • catalyst placement between membrane stacks, catalyst gap of 0.15 m (6 in.);
  • length is approximately 26.8 m (88 ft).

The tubular membrane reactor concept has the high-pressure feed gas inside the tubes and the sweep gas flowing across the tube bank. The tube length was varied to meet the feed-side pressure drop constraint for a given tube diameter, and the tube pitch and baffle arrangement were varied to meet the sweep-side pressure drop constraint. The characteristics of the tubular reactor include:

  • four separate membrane reactors interstaged with catalyst reactors;
  • each membrane reactor has 9730 U-tubes, 1.07 cm (0.424 in.) ID, 4.2 m (13.8 ft) long;
  • total active membrane surface area of 5685 m² (61,193 ft²);
  • each membrane reactor is about 7.6 m (25 ft) long and 3.2 m (10.5 ft) diameter.

The baseline planar design places the membrane internals inside of a conventional pressure vessel. The tubular membrane reactor concept, which was not designed as rigorously as the planar options, was based on standard shell and tube construction. The vessels are designed according to Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code, for an internal pressure of 41.4 bar (600 psig) at a vessel metal temperature of 454°C (850°F). The estimated order-of-magnitude cost to fabricate the baseline planar reactor is approximately $19 million. The estimate is based on input from various suppliers of materials and services, as well as manufacturers specializing in the fabrication of components specified for the reactor. In many cases, where detailed information is not yet developed, rough cost estimates were provided by vendors based on similar work and standard cost models. The alternative tubular concept was estimated at approximately $12 million.

Carbon Dioxide Capture for Storage in Deep Geologic Formations – Results from the CO2 Capture Project Capture and Separation of Carbon Dioxide from Combustion Sources - Volume 1
Edited by:
David C. Thomas, Senior Technical Advisor, Advanced Resources International Inc, USA

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