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Thermochemical conversion technologies convert biomass and its residues to fuels, chemicals, and power using gasification and pyrolysis technologies. Gasification—heating biomass with about one-third of the oxygen necessary for complete combustion—produces a mixture of carbon monoxide and hydrogen, known as syngas. Pyrolysis—heating biomass in the absence of oxygen—produces a liquid pyrolysis oil. Both syngas and pyrolysis oil can be used as fuels that are cleaner and more efficient than the solid biomass. Both can also be chemically converted to other valuable fuels and chemicals.
Researchers are working to improve the efficiency and economics of the thermochemical
conversion process technologies by focusing their efforts on the most challenging steps in the
process. The major thrust of the advanced R&D on thermochemical conversion technologies is
on syngas production and utilization.
Researchers are also working to demonstrate thermochemical conversion processes
in real-world applications. Integration and production activities involve industrial partners
and focus on gasifier system development and rural energy systems.
Activities in this area investigate advanced concepts for thermochemical conversion of biomass
or address barriers that apply to a wide range of potential applications and thus are not yet sufficiently
developed for integration into a large system, nor good candidates for partnering with a single industrial
entity or sector.
Syngas Production
The objective of this project area is to identify and develop advanced technologies that will
improve the efficiency or reduce the cost of producing liquid fuel, chemicals and utilities (steam and
electricity) in the context of the biorefinery. The principal goal will be to create a syngas that meets the
cleanliness specifications of existing synthesis and utility generation processes from widely available biomass.
The current focus of the syngas production R&D is on gas cleanup and conditioning.
Gas Cleanup
A major challenge in development and commercialization of biomass gasification is the integration
of the gasifier with downstream processing applications. Each end use application—syngas to fuels, chemicals,
and combined heat and power—has specific requirements for gas cleanup and gas conditioning. The objective
of this project is to develop and evaluate gas cleanup and conditioning systems, including tar steam reforming
and hot gas particulate removal, required for the production of fuels and chemicals from syngas derived from
biomass gasification. In 2003, NREL will purchase and install an on-line particle size analyzer in NREL's
TCPDU to continuously measure particulate removal efficiencies of existing and novel gas filtration processes
for comparison to existing particulate specifications for gas turbines and synthesis operations; design and
install a steam reforming catalytic tar-conditioning reactor in NREL's thermochemical pilot development unit
(TCPDU) to test tar-cracking catalysts needed to reduce the concentration of condensable organics to a level
acceptable for fuels and chemicals synthesis; and screen at least five commercially available catalysts or novel
catalyst formulations at three temperatures for maximum tar destruction activity, long lifetime and
regenerability.
Syngas Utilization
The objective of this project area is to examine end-use applications for clean syngas including
the direct production of fuels or products and use for generation of heat and electricity for biorefinery use.
R&D efforts are currently focused on:
- Fuel Synthesis Chemistry
- Biorefinery Utilities
Fuel Synthesis Chemistry
The petroleum and petrochemical industries have developed a number of first generation commercial
catalytic processes for conversion of synthesis gas-to fuels and chemicals, including the Mobil Methanol-to-Gasoline
process, methanol synthesis, hydrocarbon fuels synthesis, and hydrogen synthesis, among others. The objectives of the
fuels synthesis chemistry project are to provide additional insights about gas cleaning process configurations, to
provide supporting experimental results about commercial synthesis processes, and to investigate catalyst modifications
with the potential to improve yield and selectivity to desired products.
Specifically, NREL will examine conventional synthesis routes and catalysts employing a micro
catalytic reactor system operating on a slipstream of syngas produced in the NREL Thermochemical Process Development Unit
(TCPDU). The syngas slipstream will be cleaned to remove contaminants specific to a given catalytic conversion process.
Products from the syngas catalytic reactor system will be characterized to determine yield and selectivity. The initial
set of evaluations will include ethanol (mixed alcohols) and F-T liquids production. A key result will also be verification
of the required cleanliness of the synthesis gas.
Biorefinery Utilities
As with petrochemical refineries, biorefineries will require electric power and heat for operation.
Regardless of a given biorefinery core technology (biological or thermochemical) residue streams will be generated, e.g.,
bark, hog-fuel, and lignin. For optimum material, energy, economic, and environmental efficiency, these residues must be
utilized. While some residues may be suitable as co-products, others will be better suited for conversion to on-site power
and heat. Thermochemical gasification of biomass residues to syngas is the preferred conversion route to combined heat and
power generation because it is a fast, high yield process that is potentially omnivorous. In addition, syngas has been
demonstrated in reciprocating internal combustion engines (ICEs) and gas turbines, with little modification from natural
gas-based units. Furthermore, the potential exists for effective use of the product gas as fuel for high temperature fuel
cells, such as the solid oxide type.
The overall objective is to develop a knowledge base of technology options and a database of their performance
as systems, to enable the integration of biomass gasifiers with a variety of end uses, ranging from power generation to
fuels/chemicals synthesis. The research focus for 2003 is on gas turbine performance and emissions as functions of syngas
composition (especially hydrogen concentration) and electric power load. A second subtask will develop research plans and
industrial partnerships for testing solid oxide fuel cells (SOFC) with a biomass gasifier in 2004.
Activities in this area focus largely on specific systems that have developed to the point that large-scale
or advanced prototype demonstrations are taking place. Since this involves industrial partners and significant cost share,
NREL's role is a supporting one in the form of technical consultation to the DOE contracting office and to the projects in
the form of engineering advice or analytic support using specialized techniques developed at NREL. Thermochemical Integration
and Production Projects include:
- Gasifier System Development
- Rural Energy Systems
Gasifier System Development
The objective of this task is to enlist NREL's expertise and experience in the field of biomass gasification to
provide technical support, consultation and review of the major gasification projects underway in DOE's Biomass Program, specifically
the Vermont Gasifier Demonstration Project.
Vermont Gasifier Support
The Vermont gasifier project is a partnership between DOE, NREL, Battelle, Burlington Electric Department, and
the Future Energy Resources Corporation (FERCO). The goal of the project is to demonstrate low-pressure, indirect gasification of wood
chips in the 300+ tons of biomass per day gasifier. Gasifier start-up and shake-down testing, which began in 1998, verified process
performance projections and have demonstrated the flexibility of the process to efficiently convert biomass with widely varying physical
characteristics; i.e., the product gas heating value remains constant at 450-500 BTU/scf regardless in changes in the moisture content
of the wood chips, which ranges from 10%-50%. Gasifier throughput has been demonstrated to be 150% of design. At the end of 2001, the
gasifier produced enough fuel to generate more than 200 MWh of electricity per day.
Throughout the development of this demonstration project, NREL has provided engineering and technical support to the
project. This has included extensive data analysis, reduction and reporting throughout the extensive testing periods in the last two
years as well as participation in HAZOPs reviews and solution of engineering and operational issues. As the plant continues in its
demonstration phase and evolves into a demonstration platform, NREL will continue to provide engineering and data collection/analysis
as needed by the project.
Rural Energy Systems
Agricultural residues will be a key element in the bioeconomy as will a variety of energy and other crops. Rural development
is both a significant benefit and necessary component of a mature and integrated bioeconomy. The rural energy systems projects arise from
on-going work that relates directly to improving the economies of rural farm and forest areas of the nation and include:
- Small Modular Biomass Power
- Chariton Valley Project
Small Modular Biomass Power
In 1998 the U.S. Department of Energy began a multi-phase Small Modular Biopower (SMB) Initiative for developing biomass-based
electricity generating systems less than 5 megawatts that are efficient and clean. Partners in the initiative include the U.S. Forest Service,
Community Power Corp., Carbona Corporation, the European Commission, and the Government of Denmark. Feasibility studies, prototype demonstrations,
and ultimately, demonstration of an integrated small-scale biopower system with the operation and performance required for commercial success
are conducted as part of the initiative. NREL provides the subcontract management and technical support for development of small modular biomass
systems.
Specific objectives for 2003 include: design, construction, start-up, and testing of a prototype biomass gasifier-gas engine power
plant with a capacity of 9-MJ/s district heat and 5-MW electric power generation (collaboration with Carbona Corporation); and fabrication and testing
of seven prototype 15-25 kW SMBs (downdraft gasifier feeding producer gas to a spark ignition engine coupled to a generator) to establish operating
and maintenance costs, and to identify remaining design issues before developing a commercial prototype (collaboration with U.S. Forest Service
and Community Power Corporation).
Chariton Valley
In 1996, the U.S. Department of Energy and Chariton Valley Resource Conservation and Development, Inc. in Centerville, Iowa,
began a study to look at the feasibility of using biomass to generate electricity in Southeastern Iowa. The project includes studies of agronomic,
economic and technical issues, such as developing a fuel supply plan, optimizing the yields of energy crops on Iowa farmland, and examining the
effects of co-firing switchgrass in existing coal boilers.
In support of the Chariton Valley Biomass Project NREL will: 1) participate in the design of the first commercial cofire feed system
for the Alliant Energy, Ottumwa Generating Station, 2) participate in the development, review and implementation of operation maintenance, and safety
specifications; 3) develop and review project test and evaluation procedures, including participation in a technical advisory committee; 4) review start-up
and check-out procedures and participate in project start-ups and shakedowns, as requested; and 5) participate in project reviews, HAZOPS reviews, and
perform on-site reviews and detailed inspections.
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