Mark S. Bohn

Dish/Stirling hybrid-heat-pipe-receiver design and test results

A 75-kW/sub t/ hybrid receiver, intended for dish/Stirling application, has been designed, fabricated, and tested. The receiver is a 6-x scale-up of our earlier successful bench-scale hybrid concept. It is a major extension of the bench-scale concept to a compact package comprising a fully-integrated solar absorber, gas-fired surface, heat pipe, combustor, and recuperator. The device is built around a sodium heat pipe having a spherical-dome solar absorber and a pin-fin-studded, cylindrical-sidewall, gas-fired surface. The combustion system uses a metal-matrix burner, with premixed air and natural gas. The recuperator is a folded-membrane design. The receiver is designed for simultaneous solar and gas-fired heating, with a nominal throughput of 75 kW/sub t/. The nominal operating (sodium vapor) temperature is 750 C. The receiver has been ground tested (gas only) at throughput power levels from 18 to 75 kW/sub t/and output temperatures up to 750 C. It was tested in four different orientations, corresponding to sun elevations of 12, 22, 45 and 80 degrees. The tests have established several landmarks at the 75 kW/sub t/ power level, including: (1) preheat of fuel/air mixtures above 600 C without preignition, (2) internal wall temperatures over 800 C with minimal warping, particularly at critical internal seals, and (3) 68% thermal efficiency including parasitics. We believe the efficiency could be boosted to 75% by the addition of an external insulation package. Our tests also verified smooth ignition, as well as the absence thermocouples, differential pressure gauges on all major flow elements, and calorimetry. Some nonfatal problems occurred during the tests, including occasional transient leakage at an internal seal, and warping of the burner matrix. Late in the scheduled tests, a hot spot developed on the heat-pipe gas-fired surface. This behavior is believed to be the result of a wick flaw; it has been seen in other heat pipes, and has been the subject of an ongoing separate effort. Design details and rationale will be presented, along with test data illustrating the behavior of the receiver, and demonstrating its efficiency.

Integrated solar receiver/biomass gasifier research

Processes for producing liquid fuels from olefin-rich pyrolysis gases obtained from fast pyrolysis of biomass are being developed by J. Kuester at Arizona State University and J. Diebold at the Naval Weapons Center, China Lake, Calif. In the Diebold process the biomass, carried by steam, is blown through an entrained bed gasifier. The olefins are then separated from the rest of the reaction products and polymerized thermally to gasoline; the other gases are used as fuel for the process. The Kuester process uses a fluidized bed gasifier and a catalytic Fischer-Tropsch reactor which converts the olefins, hydrogen, and carbon monoxide into n-propanol and paraffinic hydrocarbons. The advantages over the Diebold process are shorter residence time and elimination of the gas separation requirement. One disadvantage is the low octane rating of the fuel. As part of the solar thermal program at the Solar Energy Research Institute (SERI), an entrained bed reactor/receiver for fast pyrolysis of biomass is being developed for use with either the Diebold or Kuester process. This system is discussed.

EARLY ENTRANCE COPRODUCTION PLANT

The 1999 U. S. Department of Energy (DOE) award to Texaco Energy Systems Inc. (presently Texaco Energy Systems LLC, a subsidiary of ChevronTexaco) was made to provide a Preliminary Engineering Design of an Early Entrance Coproduction Plant (EECP). Since the award presentation, work has been undertaken to achieve an economical concept design that makes strides toward the DOE Vision 21 goal. The objective of the EECP is to convert coal and/or petroleum coke to electric power plus transportation fuels, chemicals and useful utilities such as steam. The use of petroleum coke was added as a fuel to reduce the cost of feedstock and also to increase the probability of commercial implementation of the EECP concept. This objective has been pursued in a three phase effort through the partnership of the DOE with prime contractor Texaco Energy Systems LLC and subcontractors General Electric (GE), Praxair, and Kellogg Brown and Root (KBR). ChevronTexaco is providing gasification technology and Rentechs Fischer-Tropsch technology that has been developed for non-natural gas feed sources. GE is providing gas turbine technology for the combustion of low energy content gas. Praxair is providing air separation technology, and KBR is providing engineering to integrate the facility. The objective of Phase I was to determine the feasibility and define the concept for the EECP located at a specific site; develop a Research, Development, and Testing (RDT and prepare a Preliminary Project Financing Plan. The objective of Phase II is to implement the work as outlined in the Phase I RD&T Plan to enhance the development and commercial acceptance of coproduction technology. The objective of Phase III is to develop an engineering design package and a financing and testing plan for an EECP located at a specific site. Phase I Preliminary Concept Report was completed in 2000. The Phase I Preliminary Concept Report was prepared based on making assumptions for the basis of design for various technologies that are part of the EECP concept. The Phase I Preliminary Concept Report was approved by the DOE in May 2001. The Phase I work identified technical and economic risks and critical research, development, and testing that would improve the probability of the technical and economic success of the EECP. The Project Management Plan (Task 1) for Phase II was approved by the DOE in 2001. The results of RD&T efforts for Phase II are expected to improve the quality of assumptions made in Phase I for basis of design for the EECP concept. The RD&T work plan (Task 2 and 3) for Phase II has been completed. As the RD&T work conducted during Phase II concluded, it became evident that sufficient, but not necessarily complete, technical information and data would be available to begin Phase III - Basic Engineering Design. Also due to the merger of Chevron and Texaco, the proposed refinery site for the EECP was not available. It became apparent that some additional technical development work would be needed to correctly apply the technology at a specific site. The objective of Task 4 of Phase II is to update the concept basis of design produced during Phase I. As part of this task, items that will require design basis changes and are not site dependent have been identified. The team has qualitatively identified the efforts to incorporate the impacts of changes on EECP concept. The design basis has been modified to incorporate those changes. The design basis changes for those components of EECP that are site and feedstock dependent will be done as part of Phase III, once the site has been selected.