Biomass Energy Technology

Wood Energy Data

Thermo-Chemical Process

Thermo-chemical processes convert biomass into higher-value or more convenient products. The process releases a gas, an oil-like liquid and/or a char, and depending on the technology one of these is the final product. Charcoal production is the most common form of thermo-chemical processes. For other processes (e.g. gasification, bio-diesel), extensive research is being carried out, and applications of the technologies can be found in a number of countries (mainly small scale applications).

Pyrolysis - Charcoal production - Gasification

Pyrolysis

Pyrolysis is the breakdown of biomass in the absence of oxygen at temperatures above 250C. The process produces a solid (char or charcoal), a liquid (bio-oil) and a mixture of gases. The ratio of the products varies with the chemical composition of the biomass and the operating conditions. For example the pyrolysis of 1 tonne european hardwood, gives about 350kg charcoal, 450kg bio-oil, 75kg tar and 60m3 gas. Fast or flash pyrolysis is used to maximise either gas or liquid products according to the temperature employed. Much of the present interest in pyrolysis focuses on its liquid output (bio-oil) due to its high energy density (energy per unit of volume) and potential for liquid fuel substitution, but as of yet this technology remains in its development stage. There has been little research and development for small scale applications.

Charcoal production

Charcoal is produced in kilns via a form of pyrolysis. Efficiencies are generally low, but charcoal has advantages over fuelwood like easier distribution, high heat to weight ratio and more convenient. The oldest and probably still most widely used method for charcoal production is the earth kiln (earth pit kiln, earth mound kiln). Several other types of charcoal kilns have been developed, which generally have higher efficiencies but also require higher investments. Two often-used types are the fixed kilns made of mud, clay, bricks, and portable steel kilns.

Charcoal Production
Country	Year	Type	Capacity	Eff.	Yield	Op.costs	Note/Source
			(m3)	(%)	(%)	(US$/kg)
Malaysia	1989	Transportable metal kiln		19-23			fuel input: rubberwood, carbonization time: 24-61 hr; WET, 1996
Malaysia	1989	Transportable metal kiln		20-25			fuel input: coconut shells, carbonization time: 12-36 hr; WET, 1996
Malaysia	1989	Transportable metal kiln		17-22			fuel input: sawmill rejects, carbonization time: 21-166 hr; WET, 1996
Thailand	1983	Brick beehive kiln	50.5		36.6	0.14	yield includes firewood used, carbonization time: 222 hr, construction costs: 2,284$; RWEDP, 1992
Thailand	1983	Brick beehive kiln	43.5		35.6		yield includes firewood used, carbonization time: 246 hr; RWEDP, 1992
Thailand	1984	Brazilian modified	5-8			0.06	ESCAP, 1991
Thailand	1984	Brick beehive kiln	2-8		40	0.05-0.07	ESCAP, 1991
Thailand	1984	Mud beehive kiln	2-8		38	0.07	ESCAP, 1991
Thailand	1984	Mark V	2-8			0.08	ESCAP, 1991
Thailand	1984	Tonga	< 1			0.28	ESCAP, 1991
Thailand	1984	Single drum	< 1			0.17	ESCAP, 1991
Thailand	1984	Sawdust mound	< 1			0.1	ESCAP, 1991
Thailand	1984	Earth mound kiln	< 1		30	0.12	ESCAP, 1991
Thailand	1984	Rice husk mound kiln	< 1		32	0.1	ESCAP, 1991
Vietnam	1993	Brick beehive kiln		21.5-24.7		0.08	Construction costs $453.6, process takes 27-37 days; RWEDP, 1993d
Notes: eff.=energy efficiency, yield=yield on a weight basis, op.costs=operation costs

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Gasification

Gasification is a form of pyrolyses and is the complete thermal breakdown of biomass into a combustible gas, volatiles and ash in an enclosed reactor or gasifier. The gas produced can be used either for heat generation or for power generation.

Biomass gasification is normally practised at a relatively small scale, but systems exist up to 50 MWe. High system efficiencies (up to 50%) are achievable using combined cycle gas turbine systems. A wide range of biomass materials (wood, charcoal, coconut shells, rice husk) can be used to fuel gasifiers. Typically 1kg of air dried biomass gives 3-3.6kWh heat, or 0.7-0.9kWh electricity plus 1.4kWh heat.

Commercial gasifiers are available in a range of size and types. The Indian Government had a large programme providing small (5-100kW) locally manufactured gasifier units for irrigation. Locally manufactured gasifiers were also made in Thailand and Indonesia.

Biomass Gasifier Systems
Country	Year	Type	Inst.Cap.	Cap./unit	Investm.	#units	Note/Source
			(MW)	(kW/unit)	(US$)
China	1990	Gasifier				100	APDC, 1993
China	1990	Gasification power generator		160	100,000 /set		fuel input: husk; APDC, 1993
China	1990	Gasifier (downdraft, fixed-bed)		420			efficiency 62-79%, fuel input:loose residues; RWEDP, 1998
India	1990	Gasifier engine			387-775 /kW		APDC, 1993
India	1990	Gasifier engine pumpset		3.8	1.162 /unit		100% locally made; APDC, 1993
India	1993	Gasifier			6,200		wood gasifier serving 40 households, operation costs 3,880 $/yr; APDC, 1993
India	1992	Gasifier	6.5	3.7-100		800	most of systems installed have capacity < 10 kW; Hall, 1995
India	1993	Gasifier	15.5				TIDE, 1995
India	1995	Gasifier	32			1,604	TEDDY, 1995
Indonesia	1990	Gasifier			720 /kWe	27	gasifier locally made; APDC, 1993
Thailand	1989	Gasifier		7-30	150 /kW		typical figures; ESCAP, 1991
Thailand	1989	Gasifier (fixed-bed)		30-500	300-800 /kW		typical figures; ESCAP, 1991
Thailand	1989	Gasifier (fluidised-bed)		>500	1,000 /kW		typical figures; ESCAP, 1991
Notes: Inst.Cap.= total installed capacity up to reference year; Cap./unit= Capacity per unit; Investm.= Investment; #units= number of units installed up to reference year

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