One-Step Air Separation, Syngas Generation R&D Moving Ahead On Two Fronts With DOE Funding
11/20/1999
Gas-to-Liquids News
(c) 1999 Phillips Business Information, Inc.
Cincinnati -- U.S. Department of Energy (DOE) is funding two separate research & development (R&D) teams that are aiming to combine air separation and syngas generation processes into a single ceramic membrane reactor.
If either project is successful, then the estimated 60% share of gas-to-liquids process costs borne by air separation/ syngas generation might be cut in half, according to researchers who provided project overviews to DOE's "Energy Products for the 21st Century" conference here (see related stories, October 1999, Gas To Liquids News). That could speed GTL commercial development by making GTL project costs much closer to those of crude oil refining.
One R&D team, headed up by Air Products & Chemicals, is developing a "non-porous, multi-component metallic oxides" ceramic membrane technology that operates at high temperatures (typically over 700oC) with exceptionally high oxygen flux and selectivity.
This oxygen "Ionic Transport Membrane" (ITM) concept combines air separation and high-temperature, nitrogen-free syngas generation into a single, compact ceramic membrane reactor.
DOE is putting up $30 million for the eight-year, $85 million ITM syngas R&D project, with partners including Air Products, Chevron, Norsk Hydro, Arco, Eltron Research, Pacific Northwest National Laboratory, Ceramatec, McDermott Technology Inc., and three U.S. universities (Penn State, University of Pennsylvania, and University of Alaska).
While GTL is a major focus of the ITM syngas project, a second goal is studying creation of hydrogen for fuel-cell vehicles, aiming to reduce the cost of delivered hydrogen by 25%. ("This also could aid hydrogen production for oil refiners for desulfurization," DOE gas processing program manager expert Ralph Avallenet added.)
"We're now in phase one of the project -- ceramic membrane and process development," Air Products engineering manager Chris Chen told the DOE conference attendees. This phase includes process designs and economic studies, for both offshore and land-based GTL, as well as hydrogen production evaluation.
Also included in phase one is ITM material selection to achieve "acceptable oxygen flux, stability, strength and fabricability" as well as "stable membrane/seal assemblies."
"It is essential that the development and selection of the ITM material [be] thoroughly integrated with the process design and engineering, ceramic fabrication and membrane reactor design tasks to optimize the necessary combination of performance and fabrication properties," according to a related ITM paper by Air Products research manager Paul Dyer.
"We're very pleased with our progress on materials development. We've taken a deeper look at the economics of the ITM syngas process, and our forecasts are holding up," Chen said.
Reactor design must address seals, differential expansion and safety, as the membrane system "must be able to tolerate the pressure differentials, reasonable ramp-up and ramp-down rates and emergency shutdown transients," Dyer said. Combining syngas and air separation in a single unit presents safety risk and "imposes severe demands on ITM materials and catalysts," but proper R&D aims to resolve those issues. "We're looking at reliability, strength, and reactor design to mitigate any potential leaks or safety issues," Chen explained. "Our laboratory reactors incorporate a number of design and operational safety features to achieve a safe operation. This includes, for instance, operating above the auto-ignition temperature. The laboratory systems will establish the basis for safe commercial design and operation."
Meantime, "we've made good progress" in high-pressure laboratory-scale tests on the reactor concept so far, he said. "We have test reactors up and running at Eltron, and we're producing syngas at high pressure. It's proven to be leak-tight for more than 500 hours at 250 psig," he said.
On a related R&D front for the ITM syngas project, ceramic process development aims to ensure raw material purity, proper powder preparation, contamination prevention, proper part forming, firing and assembly, he said.
Verification and scale-up R&D will include tests "at a variety of scale sizes so that models developed for flux, conversion and stability can be understood with confidence," Dyer said. Following that, manufacturing scale-up will involve not only evaluation of reactors and process equipment, but also the manufacturing process "necessary for the fabrication of commercial quantities of ceramic components at economic yields," he said.
In "phase two" of the R&D, to ensure that scale-up can be demonstrated at a "reasonable scale," an engineering "Process Development Unit" (PDU) will "test sub-scale membranes under full operating conditions at 12,000 standard cubic feet/day rates," Dyer said.
"The next scale for development in the second phase of the program is a 500,000 SCFD Sub-scale Engineering Prototype (SEP). This large facility will be integrated into the alternate fuels development unit facility operated by Air Products at DOE's LaPorte, Texas, site," which will demonstrate suitability of ITM syngas for further scale-up.
In phase three, the "the final stage" of development, a "15 million SCFD pre-commercial technology demonstration unit using the ITM syngas process will be designed, constructed and tested," in order to show that ITM syngas is suitable for world-scale GTL application, he said.
That demonstration aims to spur GTL plants of 60,000 barrels/day scale, tapping deepwater gas near the U.S. Gulf Coast, or the trillions of feet of stranded gas on the Alaska North Slope, conveniently near the existing Trans-Alaska Pipeline.
BP Amoco, UAF Work on 'Electropox' R&D
In a separate development, BP Amoco and University of Alaska- Fairbanks (UAF) are working on development of another one-step air separation/ syngas preparation technology called "Electropox." This two-year, $3.15 million project includes a $2.5 million contribution from DOE.
"Electropox uses novel and proprietary solid metal oxide ceramic oxygen transport membranes, which selectively conduct both oxide ions and electrons through their lattice structure at elevated temperatures," UAF professor Sukumar Bandopadhyay and BP researcher Terry Mazanec explained. "Under the influence of an oxygen partial pressure gradient, oxygen ions move through the dense, non-porous membrane lattice at high rates with 100% selectivity. Transported oxygen reacts with natural gas on the fuel side of the ceramic membrane in the presence of a catalyst to produce syngas ," they said.
Six main R&D areas are included in the Electropox project, including oxygen diffusion kinetics, grain structure and atomic segregation, phase stability and stress development, mechanical property evaluation in thermal and chemical stress fields, graded ceramic/metal seals, and oxygen defect ordering. All of this R&D aims to find keys to optimal membrane performance, reliability, structure and design.
"Since the reactors utilize ceramic membranes -- brittle materials -- traditional design and engineering methodologies are not applicable and new strategies have to be developed," Bandopadhyay and Mazanec explained. "Thus there is a real need for the generation of fundamental information on the chemical and mechanical properties of the ceramic oxygen transport membranes and for the development of reliable techniques for sealing the brittle membrane materials into conventional reactor housings."
While there are some subtle differences between Electropox and ITM concepts, some differences that seem to be readily apparent include Electropox's temperature/pressure range (1,100oC and 40 bar pressure) and ITM's usage of a coating "that will allow faster passage of molecules," Bandopadhyay explained to Gas-To-Liquids News. However, the proprietary nature of the research means that some of the key differences aren't apparent to anyone outside the two research teams.
Meantime, related research sponsored by BP Amoco and partners Praxair, Sasol and Statoil aims to develop a continuous extrusion process for ceramic membrane fabrication. Major technical challenges include materials performance, fabrication process/reliability, ceramics reactor design/seal, process integration, engineering/scale- up, and cost, Bandopadhyay said.
Materials performance understanding is farther along than fabrication, design and integration. Scale-up is least-understood among the major issues.
At UAF, the "Electropox" R&D will focus on mechanical property evaluation in thermal and chemical stress fields.
These research tasks include: completion of a high-temperature test facility and a methodology for sample preparation/testing; completion of "strength maps" for two materials in a synthetic gas environment at 1,000oC; strength and modulus-of-elasticity tests with high-temperature air or nitrogen; strength maps as a function of oxygen partial pressure at 1,000oC; strength determining mechanism at 1,000o and 1,100oC in two different atmospheres; correlation of mechanical properties with microstructural changes; and recommendation of strength models to predict long-term strength of oxygen transport membrane materials.
Tests such as these aim to find answers to issues including thermal shock, mechanical strength and fracture tendencies of the membranes, he said.
-- Jack Peckham |
