ERIP

NIST Energy-Related Inventions Program (ERIP)
"Biomass Charcoal Fuel for Gas Turbines"
Request for Evaluation # 33512 submitted for evaluation on May 27, 1997.

Executive Summary

1.0 Technical Description
2.0 Technical Advantages
3.0 Energy Impact
4.0 Cost and Economic Considerations
5.0 Commercial Potential and Market Considerations
6.0 Development and/or Commercialization Requirements

Executive Summary

Renewable resources (solar, wind, geothermal, hydro-electric, biomass, and waste) currently provide nearly 12 percent of the U.S. electricity supply. Hydroelectric resources provide almost 10 of this 12 percent. Biomass and municipal solid waste (MSW) together contribute more than 1 percent. The production of electricity from wood has been highly successful in moderate-scale cogeneration facilities. However, restructuring in the electric power industry is causing a shakeout of the least profitable power producers.

The characteristics and quality of biomass feedstocks greatly influences the design, choice, and performance of conversion technologies as well as the requirements for feedstock storage, fuel handling, and ash disposal. Biomass feedstocks that are variably sized and high in moisture or ash content can reduce boiler efficiencies, increase O&M costs, and lower capacity factors. The technical advantages of using charcoal rather than biomass for power generation include:

The low density and high moisture of agricultural residues increase costs for transportation and limit the practical capacity of biomass processing systems. Charcoal has an energy content and material handling properties similar to coal and could be economically transported from regional production sites to central power plants.

	Year round operation of a biomass power plant requires storage of large quantities of raw biomass. Storage is expensive and often problematic.
	Charcoal from biomass would be easier to store than raw biomass and could utilize equipment proven in coal handling service. Also, if alternative biomass resources are available, charcoal can be produced year round to minimize fuel storage requirements.

Biomass resources have different physical properties and special equipment is required for different conversion processes. In contrast, the same charcoal production process could be used for a variety of agricultural and forestry residues and dedicated energy crops.

The DOE presents potential paths for energy conversion improvements to enhance the competitiveness of biomass power: improvements in direct combustion systems, and development of biomass gasification and liquefaction processes for producing clean fuels for gas turbines. The present invention proposes another viable option: convert biomass to charcoal for use as a solid fuel in a Pressurized Fluid Bed Combustion (PFBC) combined cycle process to generate steam and electricity.

Biomass Charcoal Power Plant Schematic

Biomass charcoal could be produced using the high yield charcoal process developed by Dr. Michael J. Antal, at the University of Hawaii, Hawaii Natural Energy Institute. The process has charcoal yields of about 35% to 50%, volatile matter content of about 25% or less, and fuel value of approximately 13,000 Btu per pound. The University of Hawaii, Office of Technology Transfer and Economic Development is granting an exclusive license for large scale energy and industrial applications of Dr. Antal’s charcoal process; to Select University Technologies, Inc., Newport Beach, CA.

Estimated capital and O&M costs for a commercial-scale, high yield charcoal plant were not available to the author. A charcoal plant located at or near the source of biomass feedstock would reduce the cost of biomass fuel delivered to a power generation site. Annual transportation costs savings for a 25-mile haul of 65,000 tons of charcoal vs. the equivalent 200,000 tons of green wood is approximately $ 800,000. A simple payback analysis for 20 years would justify a $16 MM expenditure.

The DOE is encouraging co-firing of wood with coal as a cost-effective near term opportunity with lower initial capital requirements. How much wood is available for energy use and charcoal production? The DOE estimates that wood use for electrical power generation will be approximately 0.5 quad in 2000 and about 3 quads in 2030. Co-firing coal with charcoal produced from wood would represent a large market, as coal is the principal energy source for U.S. electric utilities.

Pressurized Fluidized Bed Combustion (PFBC) is one of several approaches for improving the efficiency of coal-fired power systems. The present invention will transfer this proven technology to biomass power generation by using charcoal from biomass (rather than char from coal) as a feedstock for a PFBC combined cycle to generate steam and electricity. Using charcoal in a PFBC could increase system performance and reduce O&M costs because of charcoal’s lower ash content and the reduced requirements for sulfur removal using limestone.

A DOE, METC study investigated the feasibility of co-firing a pressurized fluidized-bed combustor (PFBC) with coal and refuse-derived fuel (RDF) for the production of electricity. The study concluded there are no technology barriers to the co-firing of waste materials with coal in a PFBC power plant. However, as part of technology development, there remained several design and operational areas requiring data and verification before this concept could realize commercial acceptance. Fuel handling and feed systems for the waste materials were a concern to be addressed by PFBC facility designers. Power plant designers, owners and operators may consider biomass charcoal with properties similar to coal more acceptable than RDF and other biomass fuels.

The Biomass Charcoal Power Program could be developed cooperatively by a joint effort between industry and the DOE's Offices of: Fossil Energy, Energy Efficiency and Renewable Energy, and Feedstock Supply Development Program.

Initial production of biomass charcoal and test firing in a PFBC could be performed at the Wilsonville Power Systems Development Facility. A potential site for co-firing biomass charcoal with coal is the DOE, Clean Coal Technology, Lakeland (FL) Pressurized Circulating Fluidized Bed Clean Coal Technology Project. The plant will be designed to generate 157 megawatts of electricity, using the advanced "pressurized circulating fluidized bed" combustor. Plans are to later add a topping cycle to boost efficiencies to as high as 46% and increase power output by 12 megawatts.

Successful demonstration of the high yield charcoal technology and co-firing with coal in a PFBC would prove the stabilizing effect of a reliable bioenergy fuel supply and assist in the transition to dedicated feedstock supply system biomass power facilities.

1. Technical Description:

The U.S. Department of Energy (DOE) and industry are developing technologies to expand the use of biomass (e.g., wood and wood wastes; agricultural crops and their waste byproducts; municipal solid waste; and crops grown specifically for energy production) to produce electric power. Currently, residue sources account for 100% of the fuel used for biomass power production. About 90% of the residues are wood waste. To increase use of biomass resources and realize the full potential of biomass power;

	more efficient methods must be developed to transport biofuels,
	energy system efficiencies must be improved, and
	the cost of biomass energy must be cost-competitive with fossil fuels.

The present invention addresses these objectives by converting biomass to charcoal for use in a Pressurized Fluid Bed Combustion (PFBC) combined cycle process to generate steam and electricity.

The technical advantages of using charcoal rather than biomass for power generation include:

	Year round operation of a biomass power plant requires storage of large quantities of raw biomass. Storage is expensive and often problematic.
	Charcoal from biomass would be easier to store than raw biomass and could utilize equipment proven in coal handling service. Also, if alternative biomass resources are available, charcoal can be produced year round to minimize fuel storage requirements.

Biomass resources have different physical properties and special equipment is required for different conversion processes. In comparison, the same charcoal production process could be used for a variety of agricultural and forestry residues and dedicated energy crops.

Table 1. presents a theoretical mass and energy balance for high yield charcoal production using the Antal process.

Table 1. MASS & ENERGY BALANCE FOR HIGH YIELD CHARCOAL
Description	Btu per Btu in Charcoal Produced
MASS AND ENERGY BALANCE
Energy in Charcoal Reactor Feed	1.50
Energy Input to Charcoal Reactor	0.06
TOTAL INPUTS	1.56
Energy in Charcoal	1.00
Energy in Off Gases Plus Losses	0.56
TOTAL OUTPUTS	1.56

Wood Supply (DryBasis)	100	Tons
Wood HHV (Dry)	8750	Btu per lb.
Charcoal Yield	0.45	Lb. per lb. Dry Wood
Charcoal Produced	45	TPD
Charcoal HHV	13,000	Btu per lb.
Energy in Wood Feed	1,750	MM Btu
Energy in Charcoal	1,170	MM Btu
Energy Recovered in Charcoal	67%
Energy Used to Pre-Dry Wood	0.0	Use Reactor Off Gas
Energy Input to Charcoal Reactor	0.06	Btu per Btu in Charcoal Produced
Energy Input to Reactor	70	MM Btu
Net Energy Recovered	1100	MM Btu
Energy Recovery Efficiency	63%

The present invention will be described hereinafter in conjunction with Figure 1. Biomass Charcoal Power Plant Schematic.

Biomass is defined as organic matter available on a renewable basis and includes forest and mill residues, agricultural crops and wastes, wood and wood wastes, and fast-growing trees and plants.

Charcoal Reactor: The present patent does not limit the methods to be used to produce biomass charcoal. The high yield charcoal process developed by Dr. Michael J. Antal, at the University of Hawaii, Hawaii Natural Energy Institute, is a batch process with charcoal yields of about 35% to 50%, volatile matter content of about 25% or less, and fuel value of approximately 13,000 Btu per pound. The fuel gas stream from the Antal charcoal reactor will contain combustible gases, entrained tar vapors and water and could be used for pre-drying the raw biomass.

PFBC: The PFBC will burn the charcoal in an oxygen rich atmosphere. The temperature of the PFBC bed will be controlled using heat transfer surfaces inside the fluidized bed to generate steam for the steam turbine. The PFBC flue gas is sent to the Hot Gas Filters where unburned solids are collected, cooled, and stored for disposal.

Hot Gas Filters: The hot gas filters will remove solids from the flue gas from the PFBC. The filters will operate at high temperatures and maintain the thermal efficiency of the system.

Gas Turbine Compressor: The gas turbine compressor provides compressed air to the pressurized fluidized bed combustor.

Gas Turbine Expander: The gas turbine expander accepts the high-temperature, high-pressure gas from the pressurized fluidized bed combustor and converts the pressure and thermal energy to electricity.

Heat Recovery Steam Generator (HRSG): The heat recovery steam generator transfers the heat in the gas turbine exhaust to the steam cycle. The exhaust temperature is usually greater than 800 degrees F. The exhaust gas is normally cooled to about 280 degrees F. before being sent to the stack.

Steam Turbine: The steam turbine uses high pressure, high temperature steam from the PFBC and the HRSG to produce electricity. Typical steam conditions for a PFBC system are 1800 psig and 1000 degrees F. at the throttle with reheat to 1000 degrees F. Other configurations are possible depending on how the Pressurized Fluidized Bed Combustor is designed and the specific gas turbine used in the system.

The present invention will be described hereinafter in conjunction with Figure 2. Advanced Biomass Charcoal Power Plant Schematic.

	Charcoal is fed to a carbonizer (partial gasifier) that creates a fuel gas and a solid char.
	The char is the solid fuel to the PFBC and is burned to completion as in Figure 1.
	The fuel gas from the carbonizer and the flue gas from the PFBC are fed to the topping combustor where the fuel gas is burned to create the desired gas turbine inlet temperature.
	The rest of the system is the same as Figure 1.

Figure 1. Biomass Charcoal Power Plant Schematic

Figure 2. Advanced Biomass Charcoal Power Plant Schematic

2. Technical Advantages

Antal discloses that pyrolysis of biomass can be performed in a charcoal reactor with charcoal yields of 45% or more and reaction times of 15 min to 2 hours depending on the moisture content of the feed. The charcoal reactor operates at approximately 350 degrees C. and pressures between 15 to 150 psig. These conditions offer advantages over some biomass gasifiers with an operating temperature over 850 degrees C. and pressure of 325 psig and higher. The lower operating pressure for the charcoal reactor would simplify the biomass feeding system requirements. There would also be less production of condensible oils and tars, and a substantial decrease in the production of alkali species, compared to biomass gasification.

Biomass gasifierers are usually close coupled to the gas turbine and for continuous operations biomass is reclaimed from storage facilities. Biomass typically has a low density and high moisture content and generally unfavorable material handling characteristics. Charcoal storage and feeding systems could use proven coal handling technology and avoid many of the "bridging and plugging" and other material handling difficulties encountered in biomass processing systems.

PFBC plants burn char from coal to produce steam, and combustion gases for a gas turbine. The present invention will transfer this proven technology to biomass power generation by using charcoal from biomass (rather than char from coal) as a feedstock for a PFBC combined cycle system to generate steam and electricity. Using charcoal in a PFBC could increase plant performance and reduce O&M costs because of charcoal’s lower ash content and the reduced requirements for sulfur removal using limestone.

3. Energy Impacts

Current, grid-connected biomass electrical generating capacity in the U.S. employs relatively inefficient direct-fired steam generating technology. Average efficiencies for existing systems are often less than 25%. Co-firing biomass with coal in existing utility boilers could convert biomass into electricity at higher efficiencies (>35%). Higher conversion efficiencies appear possible based on current commercial-scale demonstration of coal fired PFBC systems achieving efficiencies up to 42 percent. Anticipated technology improvements point to realistic goals achievable by 2015 that advanced FBC commercial units will operate at efficiencies in excess of 50 percent and cost 25 percent less than today's units.

Development efforts for biomass power include the evaluation of advanced technologies such as biomass gasification. The report "Cost and Performance Analysis of Three Integrated Biomass Gasification Combined Cycle (IGCC) Power Systems" examined the efficiency and cost of electricity for systems incorporating biomass gasification technology. Three biomass IGCC systems were studied:

	a direct-fired pressurized fluidized bed gasifier of the type under development by the Institute of Gas Technology ,
	the Battelle Columbus Laboratory low pressure indirect-heated biomass gasifier, and
	an air-blown low-pressure gasifier similar to that developed by Thermiska Processor AB (TPS).

System performance for the direct-fired pressurized fluidized bed gasifier and the low-pressure indirect-heated biomass gasifier, are summarized in Table 2. A biomass charcoal PFBC application using the same feedstock as the direct-fired gasifier is shown for comparison.

The energy savings in transport, handling and storage of charcoal vs. biomass were not considered in the analysis but could be significant. Biomass charcoal with a heating value of 13,000 Btu per pound compared to perhaps 4,800 for raw biomass, would require less energy to transport. A sample calculation of energy savings in transportation is presented in Table 3.

Table 2: Process Data Summary and System Performance Results
	High pressure Direct heated gasifier	Low-pressure indirectly- heated gasifier	Biomass Charcoal PFBC*

Wood Feedstock	Maple	Hybrid Poplar	Maple
Feed, dry tons/day	1620	1486	1620
Moisture as received, %	38	50	38
HHV, Btu/lb., dry basis	8,476	8,722	8,476
Wood flow rate, lb./hr	151,361	136,494	151,361
Wood MW	376	349	376
Fuel Gas flow rate, lb./hr	378,360	114,734	-
Fuel Gas LHV, Btu/SCF	115	354	-
Fuel Gas MW	271	251	-
Cold Gas Efficiency (estim.)	72%	72%
Charcoal flow rate, lb./hr	-	-	68,112
Charcoal HHV, Btu/lb.	-	-	13,000
Charcoal MW	-	-	259
Charcoal Energy Recovery	-	-	69%
Gas turbine output, MWe	93	82	49
Steam turbine, MWe	47	55	71
Internal Use, MWe	8	15	6
Net system output, MWe	132	122	114
Power Plant Efficiency	49%	49%	44%
Net Plant Efficiency	35%	35%	30%

* Note: Data was obtained by reference to PFBC data in "PFBC Concepts Analysis for Improved Cycle Efficiency and Cost".

Table 3. Energy Savings for Trucking Charcoal vs. Green Wood
Load Difference TPD *	One Way Haul Distance (miles)	Ton-miles saved per day	Energy Consumption kWh / ton-mile	Energy Savings kWh

2,000	25	50,000	0.34	17,000
2,000	30	60,000	0.34	20,400
2,000	40	80,000	0.34	27,200
2,000	50	100,000	0.34	34,000

* Note: Based on green wood at 50% MC. 1,500 dry tons of wood at 8,500 Btu per lb. equivalent to approx. 1,000 tons of charcoal at 13,000 Btu per lb. Additional energy savings via fewer empty back-hauls for charcoal were not considered.

4. Cost and Economic Considerations

BIOMASS FEEDSTOCKS: A number of different biomass feeds could be used to produce biomass charcoal, e.g., crops specifically grown for bioenergy, and various agricultural residues, wood residues and waste streams. Their costs and availability would vary widely. Waste streams are often inexpensive to obtain as in many instances they have a high disposal costs. A principal waste stream to be considered is wood waste from municipal and commercial collection sources.

Biomass Charcoal Production: The Antal charcoal reactor is a batch process for the pyrolytic conversion of biomass with charcoal yields of about 35% to 50%, having volatile matter content of about 25% or less, and fuel value of 13,000 Btu per pound. The process would have to be developed from the current pilot plant scale to the prototype commercial scale.

Pressurized Fluid Bed Combustion (PFBC): Co-firing biomass with coal is a route to biomass capacity growth at lower unit costs. However, in regions where biomass resources are abundant and co-firing opportunities do not exist, dedicated biomass power facilities can be developed. A preferred arrangement for stand-alone biomass charcoal power systems would be a PFBC cycle with a topping combustion, referred to as a load following PFBC cycle. An oil or gas external fuel source would be controlled to quickly follow load. The thermal efficiency of load following coal PFBC plants is expected to be about 41% (HHV).

Figure 3. Load Following PFBC System Schematic

Biomass power projects are relatively capital intensive and to be cost effective need to be operated as base-load stations. In general, biomass power plants in the 100 MWe range have not been considered feasible because of the requirement for receiving and storing large quantities of biomass feedstock. Converting biomass to charcoal for use in a PFBC power plant would reduce fuel storage requirements to manageable levels and makes large utility scale power plants possible.

The total capital costs provided in the literature for combustion turbine systems utilizing biomass fuels range from approximately 1,000 to 1,500 $ per kW depending on the turbine category (industrial or advanced) and the system specifications (low or high technology). ABB Carbon articles price coal PFBC plants of 100, 200 and 425 MW net output at 1200, 1100 and 1400 $ per kW respectively.

The cost-of-electricity (COE) is often used to compare generation alternatives. The COE for a high-pressure gasifier, advanced utility gas turbine power plant is stated as approximately 7 �/kWh. The COE for a large coal fired PFBC power plants is approximately 4.5 �/kWh according to literature from ABB Carbon.

Estimated capital and O&M costs for a commercial-scale, high yield charcoal plant were not available to the author. A charcoal plant located at or near the source of biomass feedstock would reduce the cost of biomass fuel delivered to a power generation site. The estimated potential savings in transportation costs for charcoal vs. green wood are shown in Table 4. A 25-mile haul of 65,000 tons of charcoal vs. 200,000 tons of green wood would save $ 800,000. A simple payback analysis for 20 years would justify a $16 MM expenditure.

Table 4. Estimated Trucking Cost Savings for Charcoal vs. Green Wood
Load Difference TPD	One Way Haul Distance (miles)	Trucking Cost $ per ton	Trucking Cost Savings $

2,000	15	$ 5.00	$ 10,000
2,000	25	$ 6.00	$ 12,000
2,000	50	$ 8.50	$ 17,000
2,000	75	$ 10.50	$ 21,000
2,000	100	$ 13.00	$ 26,000

* Note: Based on 3,000 tons of green wood vs. 1,000 tons of charcoal. Additional cost savings via fewer empty back-hauls for charcoal were not considered.

5. Commercial Potential and Market Considerations

The DOE estimates that wood use for electrical power generation will be approximately 0.5 quad in 2000 and about 3 quads in 2030, assuming that wood comprises more than half the energy derived from forest and agricultural residues and municipal solid waste. The DOE also projects that energy crops will contribute less than 0.5 quad in 2000 but will eventually overtake agricultural and forest residues as a source of electricity before 2020.

Co-firing wood charcoal with coal in PFBC power plants would be a possible market entry point for development of the current invention. IPPs that build or own coal-fired stations may also be interested. Advantages of co-firing charcoal with coal from the utility perspective would include:

	Lower-risk and costs compared to stand-alone bioenergy production.
	More favorable acceptance by permitting authorities by introducing a new biomass derived fuel on a supplemental basis at existing permitted facilities.

Direct environmental benefits of reduced air emissions (lower SOx, NOx, and CO2 emissions) and reduced solid waste streams.

Possible economic benefits accruing to SO2 allowances and avoidance of potential carbon taxes.

A DOE, METC study investigated the feasibility of co-firing a pressurized fluidized-bed combustor (PFBC) with coal and refuse-derived fuel (RDF) for the production of electricity. The study concluded there are no technology barriers to the co-firing of waste materials with coal in a PFBC power plant. However, as part of technology development, there remained several design and operational areas requiring data and verification before this concept can realize commercial acceptance. Fuel handling and feed systems for the waste materials were a concern to be addressed by PFBC facility designers, e.g., fuel delivery, handling and stocking concerns; on-site fuel storage area required for low density fuel; fuel pile emissions, fire hazards and decomposition; separate on-site fuel processing equipment needs; fuel feed and boiler interconnections; fuel processing and handling safety and systems reliability.

Power plant designers, owners and operators are likely to consider wood charcoal produced off-site, and delivered with properties similar to coal, a more desirable fuel than RDF and other biomass fuels.

Non-utilities are also expected to supply a significant portion of the generating capacity needed to meet the future energy requirements of electric utilities. Non-utility power producers project that mostly gas and renewable energy will fuel non-utility capacity sources.

6. Development and/or Commercialization Requirements

The Biomass Charcoal Power Program could be developed cooperatively by a joint effort between industry and the DOE's Offices of:

	Fossil Energy,
	Energy Efficiency and Renewable Energy, and
	Feedstock Supply Development Program.

The University of Hawaii, Office of Technology Transfer and Economic Development is granting an exclusive license for large scale energy and industrial applications of Dr. Michael J. Antal’s charcoal production process; to Select University Technologies, Inc. located in Newport Beach, CA.

A biomass charcoal program could be developed in parallel with the Department of Energy, Clean Coal Technology, Lakeland (FL) Pressurized Circulating Fluidized Bed Clean Coal Technology Project. The new plant initially will be designed to generate 157 megawatts of electricity, using the advanced "pressurized circulating fluidized bed" combustor. Test operations are scheduled to begin in mid-2000. Plans are to later outfit the coal-burning process with a "carbonizer." to process coal into a fuel gas and char. The char will be fed to the pressurized fluidized bed combustor, along with fresh coal, while the gas will be cleaned and routed to a topping combustor to drive the gas turbine. This configuration referred to as a "topped PCFB," will boost efficiencies perhaps as high as 46% and add another 12 megawatts of power output. The "topped PCFB" could be operational in 2002.

References

	U.S PATENT 5,551,958 Antal, Jr. Sept. 3, 1996. Process for charcoal production from woody and herbaceous plant material.
	Dr. Michael J. Antal, Jr., "High Yield Biomass Charcoal", Energy & Fuels, Volume 10, Number 3, 652-658 (1996) month unavailable.

Erik Olsson, Chairman Fluid Bed Conversion, Gothenburg, Sweden, "Pressurized Fluid Bed Combustion Technology" February 1996

Executive Summary

Table 1. MASS & ENERGY BALANCE FOR HIGH YIELD CHARCOAL

Figure 1. Biomass Charcoal Power Plant Schematic