JRA's Patent Application

Patent Application

Biomass Charcoal Fuel for Gas Turbines

ABSTRACT

The U.S. government and industry are developing technologies to expand the use of biomass (agricultural residues, or crops grown specifically for energy production) to produce electric power. The U.S. Department of Energy, Biomass Power Program supports the development of three technologies: direct combustion, pyrolysis, and gasification. In direct combustion, conventional boilers burn bulk biomass to generate steam to drive electric generators. Pyrolysis processes produce oils from biomass that can be burned like petroleum to generate electricity. Biomass gasification generates a low or medium heating value fuel gas for use in high-efficiency gas turbine-generators.

The object of the present invention is to convert biomass to charcoal and use the charcoal in a solid fuel gas turbine combustion system. Biomass charcoal would be used as feedstock for either a topped or non-topped Pressurized Fluid Bed Combustion (PFBC) combined cycle process to generate steam and electricity. Producing charcoal from biomass and using the charcoal as a solid fuel for a gas turbine is an improved process for the use of biomass for steam and electric power production.

REFERENCES:

U.S PATENT DOCUMENTS:

5,551,958 Antal, Jr. Sept. 3, 1996, Process for charcoal production from woody and herbaceous plant material.

5,584,970 Schmalfeld, et. al. Dec. 17, 1996, Process of producing wood charcoal in a moving bed.

5,255,506 Wilkes, et. al. Oct. 26, 1993, Solid fuel combustion system for gas turbine engine.

OTHER PUBLICATIONS:

Antal, Jr., et al., "High Yield Biomass Charcoal", Energy & Fuels, Volume 10, Number 3, 652-658 (1996) month unavailable

BACKGROUND OF THE INVENTION

The U.S. Department of Energy, Biomass Power Program supports the development of biomass gasification to produce a fuel gas suitable for high-efficiency combustion turbine-generators used in the electric power industry.

Gasification of biomass normally occurs in two steps: pyrolysis to drive off volatile matter and leave behind chars and ash, followed by gasification of the char to produce a low or medium heating value fuel gas. The gasifier operating temperatures must be high enough (typically above 850 degrees C) to gasify the tars produced as pyrolytic byproducts. Gasifiers are pressurized, sometimes to 325 psig and higher, to increase the biomass processing rates (throughput) and to provide the desired inlet pressure to the gas turbine. For biomass, these higher pressure operating conditions complicate the gasifer feeding operations.

Operating conditions for a biomass charcoal reactor are less severe. Antal discloses that when pyrolysis of biomass is performed in a charcoal reactor operating at lower temperatures (approximately 350 degrees C.) and pressures (between 15 to 150 psig), in a stagnant gas environment, the charcoal yield reaches 45% or more and few tars are produced. Equipment and construction costs, and operation and maintenance costs, for a charcoal reactor would probably be less than comparable costs for a high-pressure gasifier with the same biomass throughput capacity.

Pressurized Fluid Bed Combustion (PFBC) was developed in the U.S. Department of Energy, Clean Coal Technology Program that began in 1986 with a mandate to improve the efficiency of coal-fired electric power generation systems. Commercial scale demonstration PFBC systems are capable of achieving efficiencies up to 42 percent. The PFBC burns char from coal to produce steam, and combustion gases for the gas turbine. The object of the present invention is to transfer this technology to biomass by using charcoal from biomass (rather than char from coal) as a feedstock for either a topped or non-topped Pressurized Fluid Bed Combustion (PFBC) combined cycle system to generate steam and electricity.

SUMMARY OF THE INVENTION

The present invention is a new and improved process for biomass energy recovery based on the production and use of charcoal from biomass as a solid fuel for a combustion turbine combined cycle power generation system.

BIOMASS CHARCOAL

Biomass Charcoal would be produced using the following processes or improved version of same:

In Antal, U.S. Patent 5,551,958, an improved batch process for the pyrolytic conversion of biomass (woody and herbaceous plant material) is provided which yields charcoal, on a dry weight basis, in yields ranging from about 35% to about 50%, having volatile matter content of about 25% or less, and fuel value of 13,000 Btu per pound.

In Schmalfeld, U.S. Patent 5,584,970 biomass, particularly lump wood, is supplied to a shaft reactor at its top and is initially preheated to temperatures of about 150 to 280 degrees. C. and dried by a counter-flowing hot gas. This is followed by a treatment in an underlying carbonizing zone, the upper portion of which is supplied with hot purging gas at a temperature of 250 to 600 degrees C. The hot purging gas flows downward through the carbonizing zone cocurrently with the wood.

Using charcoal, rather than biomass as a renewable energy source, would have the following advantages:

	The same charcoal production process can be used for a variety of agricultural and forestry residues and dedicated energy crops. This would lead to cost savings via standardization of processes and equipment. Also, if there are sufficient biomass resources available, e.g. wood chips when bagasse is not available as a feedstock, plant downtime can be reduced and charcoal can be produced year round.
	The supply of biomass fuels from agricultural residues is usually seasonal. Year round operation of a biomass gasification plant based power plant would require storage of large quantities of biomass. Charcoal from biomass would be more economical to handle and store than raw biomass.
	Crop residues are generally low density, adding to transportation costs and limiting the throughput capacity rating of biomass gasification plants. Charcoal with a heating value of 13,000 Btu per pound compared to perhaps 4,800 for raw biomass, would be more economical to transport.
	Drying of biomass for a charcoal reactor is not required, where as, biomass used in direct heated gasifiers is typically dried from 45 or 50% to approximately 20% moisture content.

Table 1. Presents a theoretical analysis of the overall energy effectiveness of production of high yield charcoal compared to biomass gasification. The apparent energy effectiveness, based on the energy content of the product gas or charcoal divided by the energy content of the input bagasse, is approximately 70% for both cases. The values used are only estimates obtained from the literature. However, it does appear that the parasitic losses for the direct heated, high pressure, fluidized bed gasification process are higher than the high yield charcoal process. Savings in transportation of charcoal vs. biomass could provide additional energy credits for biomass charcoal.

Concerning electric power production, based on information presented in the references, the overall thermal efficiency of firing biomass charcoal in a solid fuel combustion system for a gas turbine should be equal or better than that for firing of biomass gasifier product gas in a gas turbine.

Table 1. ENERGY EFFICIENCY ANALYSIS

Plant Capacity: Bagasse (Bone Dry)	100	TPD
% H2O if Feed	20	%
Bagasse (20%)	125	TPD
Bagasse HHV	6600	Btu per lb.

BIOMASS CHARCOAL PLANT (1)
Charcoal Yield	45	% per lb. Dry Bagasse
Charcoal Produced	45	TPD
Charcoal HHV	13,000	Btu per lb.
Energy in Bagasse	1,650	MM Btu
Energy in Charcoal	1,170	MM Btu
Energy Recovered in Charcoal %	70.9	%
Energy Used to Pre-Dry Biomass (1a)	0.0	MM Btu
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
Overall Energy Efficiency	67	%

BIOMASS GASIFICATION PLANT (2)
Gasifier Operating Pressure	340.7	psia
Fuel Gas Yield	34.3	SCF per lb. wet bagasse
Fuel Gas HV, Btu per Std Cu. Ft.	136.6	Fuel Gas HV, Btu per Std Cu. Ft.
Energy in Bagasse	1,650	MM Btu
Energy in Fuel Gas	1,171	MM Btu
Energy Recovered in Fuel Gas	71.0	%
Energy Used in Biomass Drying (2a)	125	MM Btu
Energy Input to Gasifier (2b)	102	MM Btu
Steam, 0.15 lb. per lb. (20%) feed (2c)	51	MM Btu
Net Energy Recovered	893	MM Btu
Overall Energy Efficiency	54	%

Notes:
(1) Based on "Antal" High Yield Biomass Charcoal Process
(1a) Dry Biomass Feed from 40% to 14% MC using Charcoal Reactor Off Gas
(2) Based on Air Blown IGT RENUGAS Process:
(2a) Dry Biomass Feed from 40% to 20% MC using propane.
(2b) Air Compressors for Fluid Bed Gasifier : 1250 BHP
(2c) Steam at 350 psig and 700 degrees F.

Pressurized Fluid Bed Combustion (PFBC)

Biomass charcoal would be used as feedstock for either a topped or non-topped Pressurized Fluid Bed Combustion (PFBC) combined cycle process to generate electric power and steam. A first generation system will be as demonstrated using coal at the U.S. Department of Energy, Morgantown Energy Technology Center, is described in Figure 1. An advanced system, shown in figure 2., would include a topping combustor to increase the turbine inlet temperature with fuel generated in a carbonizer in which charcoal is partially combusted to produce a combustible fuel gas.

Figure 1. Biomass Charcoal Power Plant Schematic

Figure 2. Advanced Biomass Charcoal Power Plant Schematic

BRIEF DESCRIPTION OF FIGURE 1.

A biomass charcoal reactor is shown with a non-topped pressurized fluidized bed combustion system for a gas turbine engine to generate electric power in a combined cycle operation.

BRIEF DESCRIPTION OF FIGURE 2.

A biomass charcoal carbonizer and topping combustor are shown with a pressurized fluidized bed combustion system for a gas turbine engine to generate electric power in a combined cycle operation.

DETAILED DESCRIPTION

The process of the present invention will be described hereinafter in conjunction with the biomass charcoal power plant schematic, Figure 1. .

	Biomass is defined as organic matter available on a renewable basis. Biomass includes forest and mill residues, agricultural crops and wastes, wood and wood wastes, animal wastes, livestock operation residues, aquatic plants, fast-growing trees and plants, and municipal and industrial wastes.
	Charcoal Reactor: The charcoal reactor will produce charcoal using the Antal process, U.S. Patent 5,551,958, Schmalfeld, U.S. Patent 5,584,970, or other suitable process. The present patent does not limit the methods to be used to produce biomass charcoal. The Antal method 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 fuel gas stream from the Antal charcoal reactor will contain combustible gases, entrained tar vapors and water. The fuel gas could be used for pre-drying the raw biomass. Schmalfeld is a continuous process using a moving bed in a shaft reactor that incorporates preheating, carbonizing and cooling zones. The Schmalfeld reactor fuel gas can be combusted, at least in part, outside the reactor to produce hot purging gas.
	PFBC: The PFBC will burn the charcoal in an oxygen rich atmosphere. The temperature of the bed is controlled by using heat transfer surfaces inside the fluidized bed to generate steam for the steam cycle. The PFBC flue gas is sent to the Hot Gas Filters and unburned solids are collected, cooled, and stored for disposal.
	The Hot Gas Filters will remove solids from the flue gas from the Pressurized Fluidized Bed Combustor. The Hot Gas Filters operate at high temperatures to 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. The exhaust temperature is dependent upon the specific gas turbine, but the temperature is usually greater than 800degrees F.
	The Heat Recovery Steam Generator will transfer the heat remaining in the Gas Turbine Exhaust Gas to the Steam Cycle. The temperature of the Gas Turbine Exhaust Gas varies with the specific gas turbine, but it is usually greater than 800F for larger gas turbines. This hot exhaust is usually cooled to about 280F before being sent to the stack.
	Steam Turbine: The steam cycle uses high pressure and 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 and a 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 process of the present invention will be described hereinafter in conjunction with the biomass charcoal power plant schematic, Figure 2.

	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.

CLAIMS

What is claimed is:

A new and improved process for biomass energy recovery based on the production and use of charcoal from biomass as a solid fuel for a combustion turbine combined cycle power generation system.
Charcoal will be produced from biomass sources using the Antal process, U.S. Patent 5,551,958 ; Schmalfeld, U.S. Patent 5,584,970 ; or other selected process.
Charcoal produced from biomass will be used as feedstock for either a topped or non-topped Pressurized Fluid Bed Combustion (PFBC) combustion turbine combined cycle power generation system.