Biomass

What is Biomass?

Biomass is the name given to any recent organic matter from living organisms as a result of the photosynthetic conversion process. Biomass energy is mostly derived from plant and animal material, such as wood from forests, residues from agricultural and forestry processes, and industrial, human or animal wastes.

The energy value of biomass from plant matter originally comes from solar energy through the process known as photosynthesis. The chemical energy that is stored in plants and animals, or in the wastes that they produce, is called bioenergy. During conversion processes, such as combustion (burning), biomass releases its energy (often in the form of heat), and the carbon in the biomass is re-oxidised to carbon dioxide. This carbon, which was absorbed by the organism when growing, is returned to the environment to be reused by other organisms in the natural carbon cycle. Essentially, the use of biomass for energy is the reversal of photosynthesis (see Figure 1).

Figure 1 The equation for photosynthesis in reverse can represent the use of biomass to generate heat.

The Need for Biomass in a Sustainable Energy system

In nature, all biomass ultimately decomposes to its elementary molecules with the release of heat. The release of energy from the conversion of biomass into useful energy imitates natural processes, except at a faster rate. Therefore, the energy obtained from biomass is a form of renewable energy. Utilising this energy recycles the carbon and does not add extra carbon dioxide to the environment over time, in contrast to fossil fuels (Twidell 1998). Of all the renewable sources of energy, biomass is unique in that it is effectively stored solar energy. Furthermore, it is the only renewable source of carbon, and is able to be processed into convenient solid, liquid and gaseous fuels (World Energy Council 1994).

Biomass can be used directly (e.g. burning wood for heating and cooking) or indirectly, by converting it into a liquid or gaseous fuel (e.g. ethanol from sugar crops, or biogas from animal waste). The net energy available in combustion of the biomass ranges from about 8 MJ/kg for green wood, to 20 MJ/kg for oven-dry plant matter, to 55 MJ/kg for methane; compared with about 23 – 30 MJ/kg for coal (Twidell 1998). The efficiency of the conversion process determines how much of the actual energy can be practically utilised. The incredible flexibility of biomass fuel allows it to displace or supplement all of our existing fuels with a sustainable one that is carbon neutral. The amount of biomass available worldwide is enormous. With sustainable harvesting and a utilisation of many biomass waste products, this resource can play a major role in obtaining a sustainable energy system.

Biomass Resources

Biomass resources that can be used for energy production cover a wide range of materials. The use of biomass energy can be separated into two categories, namely modern biomass and traditional biomass. Modern biomass usually involves large-scale use, and aims to be a substitute for conventional fossil fuel energy sources. It includes: forest wood, agricultural residues, urban wastes, biogas and energy crops. Traditional biomass is generally confined to developing countries and small-scale uses. It includes fuel wood and charcoal for domestic use, rice husks, other plant residues and animal dung.

Agricultural Crops

There are many agricultural crops that can be grown specifically as energy sources, including sugar cane, corn (maize), wheat, sorghum, and vegetable oil-bearing crops such as sunflowers, canola (rapeseed), and soya beans. The majority of these crops are grown as liquid fuel sources, that is, they are harvested and processed, into fuels such as ethanol (a petrol substitute) or biodiesel. The most widely grown energy crops are sugar cane (a special type known as 'energy cane') and corn (maize). In Brazil over 4 million vehicles have been run on pure ethanol produced by energy crops. There has been a large increase in the production and use of ethanol in many countries (see Figure 2 and Table 1), especially the US, where the production of liquid biofuels is subsidised.

Figure 2 World Ethanol Production 1975 – 2005.

Table 1 World Ethanol Production by Country in 2005.

The Australian government has supported ethanol since 2000 with a range of tax exemptions and production subsidies, with an aim to produce 92 million gallons of biofuel by 2010. This figure would be enough to replace around one percent of the domestic fuel supply. Currently in Australia agricultural crops are not grown specifically as energy sources because it is uneconomic to do so, but there is some use of crop wastes as fuel sources. The feedstock used for ethanol production in Australia is currently waste from growing sugarcane, sweet sorghum, wheat and other assorted grains.

Biodiesel can be produced from seed crops that contain a high proportion of oil, which are crushed to extract the oil. This can be used directly or after esterification, to replace diesel (derived from fossil fuels) or can also be used as a heating oil. There are a wide range of crops that can be used for biodiesel production, but the most common used is canola (rapeseed). Other raw materials used are palm-oil, sunflower-oil, soya bean-oil, tallow (animal fat) and recycled frying oils. For a comparison of the energy contents of different oil crops, see Table 2. However, the most important factor affecting the overall cost of production is the cost of producing the raw material. There are currently a large number of existing biodiesel production plants globally, and a large number under construction or planned to supply the growing global demand (see Figure 3 and Table 3).

Oil Crop	Energy Content
Canola	40.4 GJ/t
Safflower	39.7 GJ/t
Sunflower	39.7 GJ/t
Diesel	38.5 GJ/t

Table 2 Vegetable oils and diesel calorific values
Source: Todd, J. 1998, Environment Technology unit, University of Tasmania.

Figure 3 World Biodiesel Production 1991 – 2005.

Table 3 World Biodiesel Production by Country in 2005.

There are a number of benefits associated with biodiesel, including a reduction in greenhouse gases of at least 3.2kg of carbon dioxide-equivalent per kilogram of biodiesel, a 99% reduction of sulphur oxide emissions, a 39% reduction in particulate matter, a high biodegradability, and energy supply security (Korbitz 1998).

Agricultural Residues

Large quantities of crop residues (waste matter) are produced annually worldwide, and are vastly under-utilised. A common agricultural residue is the rice husk, which makes up 25% of rice by mass. Other plant residues include sugar cane fibre (known as bagasse), coconut husks and shells, palm oil fibre, groundnut shells, and cereal straw.

In Australia, the major residues produced are those from winter cereals, sugar cane and sorghum. Current farming practice is usually to plough these residues back into the soil, or they are burnt, left to decompose, or grazed by stock. A number of agricultural and biomass studies, however, have concluded that it may be appropriate to remove and utilise a portion of crop residue for energy production, providing large volumes of low cost material (ERDC, 1994). These residues can be processed into liquid fuels or combusted/gasified, to produce electricity and heat. Currently there are 33 bagasse cogeneration projects in Australia representing a total of 481.12 MW of installed capacity. In Western Australia there is one operating 6 MW power plant that runs on bagasse in Kununurra that uses a steam turbine.

Figure 4 Bagasse (courtesy of Murdoch University)

Animal Waste

There are a wide range of animal wastes that can be used as sources of biomass energy. The most common sources are manures from pigs, chickens and cattle (in feed lots). This is because these animals are reared in confined areas, generating a large amount of waste in a small area. In the past this waste has been recovered and sold as a fertilizer or simply spread onto agricultural land, but the introduction of tighter environmental controls on odour and water pollution means that some form of waste management is now required, which provides further incentives for waste-to-energy conversion.

A common method of converting these waste materials is via anaerobic digestion, described in a later section of this information page. The product from anaerobic digestion is a 'biogas' that can be used as a fuel for internal combustion engines, to generate electricity from small gas turbines, burnt directly for cooking, or for space and water heating. Food processing and abattoir wastes are also a potential anaerobic digestion feedstock. In Australia, Berrybank Farm is home to 15,000 pigs that are fed in an intensive feedlot farm. The large number of pigs at Berrybank farm produce the same quantity of effluent as a city of 40,000 people - almost two-thirds as much as the City of Ballarat. To address the disposal issue, the operators installed an anaerobic digester (see Figure 5). Berrybank’s recycling system cost approximately $2 million to install, which was repaid in five years through sales of the products and efficiency savings (Victoria Museum, 1999). Products of the recycling system are; 7 tonnes of fertiliser, large amounts of mineralised and recycled water, and 1,700 cubic metres of biogas per day that is used in a cogeneration plant to generate 2900 kW of electricity daily (The University of Ballarat, 2004). The electricity is used on the farm and fed into the electricity grid, the mineralised water to irrigate crops, and the remaining solids are used as potting mix, fertiliser, compost and worm food (Victoria Museum, 1999).

Figure 5 A component of the biogas installation at Berrybank farm (© Museum Victoria Australia 1999).

Black Liquor

Black liquor is a waste product generated by the paper and pulp making industry. Black liquor can be pyrolysed or gasified as a biomass energy source. The University of Melbourne has developed a fluidised bed fast pyrolysis process that can convert black liquor into a "bio-oil" (see Figure 6). The bio-oil can be processed into transport fuel substitutes such as biodiesel.

Figure 6 Black liquor waste (courtesy of Keith Weller).

Sugar Industry Wastes

The sugar cane industry produces large volumes of bagasse (sugar cane fibre) each year (see Figure 7). Bagasse is potentially a major source of biomass energy as it can be used as boiler feedstock to generate steam for process heat and electricity production. Most sugar cane mills utilise bagasse to produce electricity for their own needs, but recently a few of these plants have been expanded and upgraded to allow the exportation of large quantities of electricity to the grid. In Australia in 2003, biomass installed generating capacity (that mostly use sugar wastes) had a combined capacity of 578 MW and our sugar industry estimates that bagasse has the potential to produce more than 4000 MW of electricity annually.

Figure 7 Sugar cane harvesting (courtesy of the Australian Greenhouse Office).

Forestry Crops

Wood is a major energy source in many parts of the world including Asia, Africa and South America, and the potential exists for it to become a significant renewable source all over the world. The best type of trees for these wood crops are those which are fast growing and suitable for coppicing. Coppicing involves harvesting the tree after a few years and then allowing the tree to sprout again from the stump, followed by subsequent harvesting on a 2 - 5 year period. The wood can be burnt for water and space heating, the production of steam for electricity generation, for cooking, or used to manufacture charcoal.

Growing energy forestry crops in large-scale plantations has received renewed interest in Australia and other parts of the developed world (see Figure 8). There is over 1 million hectares of marginal intensive agricultural land in Australia that could be used for this purpose. It has the potential to improve agricultural productivity, conserve land, and diversify farm income, but the financial viability for farmers is currently unproven (ERDC, 1994).

Figure 8 Spotted Gum plantation near access roads (courtesy of Association of Societies for Growing Australian Plants).

Forestry Residues

Forestry residues are generated by operations such as thinning of plantations, clearing for logging roads, extracting stemwood for pulp and timber, and natural attrition in accessible woodlands (see Figure 9). Wood processing also generates significant volumes of residues, usually in the form of sawdust, off-cuts, bark and woodchip rejects. This waste material is often not utilised and is left to rot on site. However it can be collected and used as a fuel source, in the same way that traditional wood or forestry crops can.

Figure 9 Forests in the southwest of Western Australia (courtesy of Webshots.com).

Industrial Waste

The food industry produces a large number of residues and by-products that can be used as biomass energy sources. These waste materials are generated from all sectors of the food industry, with everything from meat production to confectionery producing waste that can be utilised as an energy source. Solid wastes include: peelings and scraps from fruit and vegetables, food that does not meet quality control standards, pulp and fibre from sugar and starch extraction, filter sludges and coffee grounds. These wastes are usually disposed of in landfill dumps with the food company paying for their disposal.

Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruit and vegetables, pre-cooking meats, poultry and fish, cleaning and processing operations, as well as in wine making (see Figure 10). This wastewater contains sugars, starches and other dissolved and solid organic matter, but in a fairly dilute form (ERDC, 1994). The potential exists for these industrial wastes to be anaerobically digested to produce biogas, or fermented to produce ethanol, and several commercial examples of waste-to-energy conversion already exist.

Figure 10 Feedstock for biofuel production can be derived from meat production (courtesy of Lurgi Pacific - Biofuels Made Easy).

Municipal Solid Waste (MSW)

Millions of tonnes of household waste are collected each year, with the vast majority disposed of in landfill dumps. The composition of MSW varies according to the location and type of the collection service. In 1994, the average composition of Australian MSW was found to be 46% putrecibles (decaying organic matter), 24% paper, 26% plastic, glass and metal, and 4% "other" (ERDC, 1994). The biomass resource in this MSW comprises the putrecibles, paper and plastic and averages 80% of the total MSW collected.

Municipal solid waste can be converted into energy by direct combustion, or by natural anaerobic digestion in the landfill. In Australia there are a number of landfill gas plants. At these landfill sites the gas produced by the natural decomposition of MSW (approximately 50% methane and 50% carbon dioxide) is collected from the stored material and scrubbed and cleaned before feeding into internal combustion engines or gas turbines to generate heat and power. There are 9 landfill gas plants currently in operation or under construction (see Table 4).

Table 4 Western Australia’s Landfill gas production (courtesy of the Australian Business Council for Sustainable Energy).

Sewage

Sewage is a source of biomass energy that is very similar to the other animal wastes previously mentioned, the only difference being that it has been treated in developed countries for many years. Energy can be extracted from sewage using anaerobic digestion to produce biogas. The sewage sludge that remains can then be incinerated or undergo pyrolysis to produce more biogas and 'bio-oil'. In Western Australia the Water Corporation’s Woodman Point has three 600 kW turbines that run on biogas produced from Perth’s wastewater, giving a total rated capacity of 1.8 MW (see Figure 11).

Figure 11 The 38 meter high anaerobic digester at Woodman Point South of Perth produces around 14 000m³ of biogas per day (courtesy of the Water Corporation).

Biomass Use

Modern biomass now represents only 3% of primary energy consumption in industrialised countries (Ramage & Scurlock 1996), and this value has remained steady over recent years. However, much of the rural population in developing countries, which represents about 50% of the world’s population are reliant on traditional biomass, mainly in the form of wood for fuel. Traditional biomass accounts for 35% of primary energy consumption in developing countries, raising the world total to 14% of primary energy consumption (Ramage & Scurlock 1996).

The Earth's natural biomass replacement represents an energy supply of around 3 Zettajoules (3 x 10²¹ J) a year, of which just under 2% is currently (1998) used as fuel. It is not possible, however, to use all of the annual production of biomass in a sustainable manner. One analysis carried out by the United Nations Conference on Environment and Development (UNCED) estimates that biomass could potentially supply about half of the present world primary energy consumption by the year 2050 (Ramage & Scurlock 1996).

The Future for Biomass

In the future, biomass has the potential to provide a cost-effective and sustainable supply of energy, while at the same time aiding countries to meet their greenhouse gas reduction targets under international agreements. By the year 2050, it is estimated that 90% of the world population will live in developing countries (Ramage & Scurlock 1996). It is critical therefore that the biomass processes used in these countries are sustainable. The modernisation of biomass technologies, leading to more efficient biomass production and conversion, is one possible direction for biomass use in these countries.

In industrialised countries, the main biomass processes utilised in the future are expected to be the direct combustion of residues and wastes for electricity generation, bio-ethanol and biodiesel as liquid fuels, and combined heat and power production from energy crops. In the short to medium term, biomass waste and residues are expected to dominate biomass supply, to be substituted by energy crops in the longer term. The future of biomass electricity generation lies in biomass integrated gasification/gas turbine technology, which offers high-energy conversion efficiencies and will be further developed to run on biomass produced fuels.

Further Information

RISE Resources - Information regarding available renewable energy resources.

RISE Technologies - An extensive collection of information regarding renewable energy technologies.

RISE Applications & System Design - Renewable energy application information and system designs.

RISE System Displays - Case studies and information on installed renewable energy systems & performance data.

Biomass Energy Conversion Technology - RISE Information Portal

Business Council for Sustainable Energy

IEA Bioenergy

US Bioenergy Information Network

U.S. Department of Energy’s Biomass Power Program

National BioEnergy Industries Association

The Earth Policy Institute

CADDET Technical Brochures

Wood Energy Development Programme in Asia

Biomass Energy in ASEAN Member Countries

Turning sawdust in charcoal in Malaysia

Cookstoves for the developing world

Food Waste Disposal Using Anaerobic Digestion, Korea

Biomass Energy Development in Yunnan Province, China

Biomass cogeneration in Indonesia

References

ERDC (Energy Research and Development Corporation), 1994. “Biomass in the Energy Cycle Study” ERDC, Canberra.

Korbitz, W., 1998. "From the field to the fast lane- biodiesel", Renewable Energy World, vol.1, no.3, pp.32-37.

Ramage, J. & Scurlock, J., 1996. "Biomass", in Renewable energy- power for a sustainable future, ed. G. Boyle, Oxford University Press, Oxford.

REN21 Renewable Energy Policy Network, 2005. “Energy for Development: The Potential Role of Renewable Energy in Meeting the Millennium Development Goals.” Washington, DC:Worldwatch Institute.

Twidell, J., 1998. "Biomass energy", Renewable Energy World, vol.1, no.3, pp.38-39.

University of Ballarat, 2004. “Berrybank Piggery”, (Online) http://www.ballarat.edu.au/projects/ensus/case_studies/piggery/ (Accessed 16 February 2007).

Victoria Museum, 1999. “Pig Power”, (Online) http://www.museum.vic.gov.au/FutureHarvest/case1.html (Accessed 16 February 2007).

World Energy Council, 1994. New renewable energy resources, Kogan Page, London.

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