Bioenergy

last updated 04/99

Introduction

Biomass makes up the thin, living skin of the Earth – the plants and animals that populate its surface. When primitive human beings first discovered fire, they became the first users of bioenergy (energy derived from the combustion of biomass). For many thousands of years wood was humanity's primary fuel source. However, in the eighteenth and nineteenth centuries, technological advances and an increasingly urban population led to an increasing reliance on fossil fuels. In the twentieth century these fossil fuels were augmented by nuclear energy and, in the developed world at least, the benefits of bioenergy (see below) have been largely forgotten. Indeed, a graph of GDP versus percentage of energy obtained from biomass shows a negative relationship. Nevertheless, in the last few years there has been an upsurge of developed-world interest in the use of biomass as a sustainable and environmentally friendly fuel.

In Europe, there are now real efforts being made to increase the percentage of energy obtained from biomass, efforts which will help the continent to in reaching its goal of increasing renewable energy from 6 to 12 % of total generation. An indication of the importance with which biomass is viewed is the increasing importance of the European Conference on Biomass for Energy and Industry (held every two years). The conference has become more and more well-attended over the last ten years and by 1998 was hosting more than 1000 delegates from 40 countries. (This report later focuses on some of the issues raised in the eighth, ninth and tenth conferences)

Types of biomass energy and biofuels

Biomass energy comes from both primary and secondary sources. Primary sources are those that have energy production as their sole purpose – widely called ‘energy crops’ Such crops include woody plants (planted in short-rotation sustainable forests), sugar beet (used to generate ethanol), and rape-seed oil (a major source of biodiesel). Secondary sources of biomass energy are those where fuel for energy production is a by-product of another process. Examples of secondary sources of biomass energy include sugar cane fiber, rice husks, and wood waste from horticulture, waste liquors from the pulp and paper industry, and manure from animal farming.

These then, are the main sources of biofuels, which are utilized in many different ways. If the water content of the fuel is low enough, the fuel can be burnt directly to release energy. Examples of biofuels suitable for direct combustion include chicken litter (burnt in a 12.5 MW power plant which opened in Suffolk, England in 1992), straw (the UK produces 7 million surplus tonnes every year), and forestry waste. Such fuels can also be treated by pyrolisis to increase their energy density.

Fuels with a higher water content can be gasified (reacted with hot air and steam to produce a gaseous fuel) or anaerobically digested. This latter technique is particularly useful for sewage sludge and similar animal wastes.

Potential for biomass energy in developed nations

Although the world population is growing, the amount of land required for food production continues to drop (a result of more efficient farming practices and increasing yields). As a result, it is estimated that there is a global area of 800 million hectares available for the growing of energy crops. Even in an area as densely populated as Europe, there is a land surplus of some fifty million hectares which could (in theory) supply 30-40% of the continent's total energy demand, reducing total energy imports from 50% to 10-20% of total demand.

Indeed, the EU considers that biomass energy is the most important renewable resource on the continent. Since 1979, it has supported 261 projects as part of the "Energy and Biomass from waste" program (total funding of 160.5 million ECUs). By 1995 it had set 1nearly 1 000 000 ha of land aside for growing of rapeseed for fuel. Following the Kyoto protocol, it has further pledged to significantly increase the percentage of total energy produced from biomass (from 3.3 to 8.5%). This would mean an increase bioenergy production from the current 20 million Mtoe (million tonnes oil equivalent) to 50 Mtoe by 2005, and an increase in electricity production from biofuels from 1.4 Mtoe to 4.4 Mtoe over the same period.

Key Benefits

The single most important benefit of using short-rotation biomass as a fuel, is that it produces no net increase in atmospheric carbon dioxide. (The carbon given off in combustion is compensated for by that sequestered in growing biomass.) Biomass is also a very-low sulfur fuel. Weight for weight, it contains just 0.1% as much sulfur as it does carbon (by comparison, natural gas contains as much as 15% sulfur, oils have 0.3-3.5%, and levels in coal are between 0.5 and 8%). Low sulfur levels should result in better air-quality in cities and reduction of production of acid rain.

In addition to its environmental-friendliness as a fuel, biomass also has a number of other benefits, one of the most important being job-creation. Production, harvesting and transportation of biomass are all labor-intensive processes. It has been estimated that compared to mining and burning fossil-fuel - biomass use and production can involve 4 or 5 times as many people. In the German state of Bavaria alone, use of biomass as a major energy source has resulted in creation of some 18 000 jobs.

The EU also believes that the increased use of biomass will have agricultural benefits. A change in emphasis from food-producing to energy-producing crops will provide a more varied agricultural landscape, which will in turn provide a greater range of habitats for wildlife and will increase the biodiversity of farmland.

Examples of Bioenergy I - Biomass in Denmark

The Danish Government is committed to reducing the country’s total CO2 emissions 20% by the year 2005. It sees increased biofuel use as an important part in reaching of that goal and is actively promoting their use. As a result, by 1998, biofuels accounted for 6% of Denmark’s energy consumption. By the Year 2000, it is expected that powerplants across Denmark will be burning a total of 19PJ of biomass. The majority of this (17PJ) will comprise straw, with the remainder being wood.

The success of increased biomass use in Denmark has been largely due to the will of the Government and its commitment to the introduction of green taxes. By charging no energy tax on biofuels (but taxing fossil fuels heavily) the Government has successfully made biofuels economically attractive and encourage their use at all levels throughout the country. The policy has probably had some influence in the increase of on-farm straw-burning heating systems to more than 8000 over the past few years.



In addition to the burning of straw, the Danish Government is also committed to the use of Municipal Solid Waste (MSW) in energy production. Organic and non-organic MSW are separated at source by householders; the organic waste is then sent to biogas digester plants, By the Year 2000 all combustible waste will be used for energy production. Furthermore, to ensure the efficiency of energy production from the burning of waste, all furnaces of more than 1MW will be required to be converted into co-generation units (producing heat and electricity) by the Year 2000.

Examples of Bioenergy II - Biomass in Finland

Finland is currently the largest user of bioenergy in the industrialized world, generating some 19% of its total energy requirements from biomass (ca. 330 PJ/yr). However, the country is aggressively extending its use of bioenergy, believing that the properties of biofuels will help it meet its Year 2000 targets of reducing sulphur dioxide emissions by 80 % (from 1980 levels), nitrogen oxides by 30 % (from 1980 levels), and stopping any further rise in carbon dioxide emissions.

Switching to bioenergy in Finland is feasible because forestry is the country’s largest industry. Pulp, paper and other wood products provide more than 35% of the nation’s total export revenue. Although some wood is being grown specifically for energy production, it is the waste products from mainstream forestry (waste wood and liquors from the pulping process etc) that are increasingly being exploited as biofuels. Indeed, pulp waste liquors are now the largest single source of bioenergy in the country (45% of total). As early as 1990, electricity production from biofuels was 630MW (93% of it within the forestry industry); by 1996 biofuels were already responsible for 14% of the country’s total energy production.

The rapid increase is use of biofuels has been due to a number of technical factors including:

• The increased use of fluidized bed boilers which allow the use of different types of fuel, and efficient combustion of material with a high moisture content.
• The introduction of techniques which allowed black liquor (waste liquids from the pulping process) to be evaporated to 75-80% dry solids, resulting in more stable combustion, lower SO2 emissions and a relative increase in boiler capacity.
• Increased availability of larger-sized bark boilers, recovery boilers, lime kilns and steam turbines.

However, a further reason for the rapid increase in the use of biofuels in Finland is purely economic – a trend towards partnerships between forestry companies and municipalities. The concept is based around a waste-burning co-generation powerplant, which produces electricity, process heat (used in the factory), and also provides district heat to the houses of the municipality. Plants as small as 5MW of electricity have been found to be economic, with the specific investment cost as low as 100-1500 ECU/kWe. As a result the biofuel industry is becoming an increasingly important employer in the country – wood fuel production employed 450 people by 1994, and heat and power plants another 11 000 persons.

Future increase in the use of biofuels will probably be helped by the introduction of more advanced IGCC (Integration Gasification Combined Cycle) powerplants within the forestry industry. These new powerplants reached small-scale demonstration in 1996 and a Swedish prototype system (fuelled by forest waste woodchips) has now produced 6MW electricity and 9MW of heat for over 1300 hours. Production IGCC powerplants are expected to double the power-to-heat ratios achieved by current technologies and to have a total efficiency of 85% (compared to 43% for an efficient coal-fired powerplant). They emit no net CO2 and no SO2 whatsoever. Nitrogen Oxides are emitted, but at about 20% lower levels than coal-fired power stations.

In addition to more advanced gasification technology, there isles rapidly-advancing research in the field of solid-fuel combustion, which would enable sawmills and mechanical-pulping plants to economically produce energy in powerplants rated under 10MW. Promising alternatives include atmospheric gasification of fuel, direct combustion, and conversion of wood waste to high-grade oil products.

Examples of Bioenergy III - Industrial Research

The advantages of biomass as a source of energy are becoming more and more widely recognized, and even major petrochemical companies are becoming involved.
Shell Oil is already trialing energy production from biomass in Chile and in Uruguay. In order to maximize profitability, the company is researching ways to increase the growth potential of certain tree species and reduce operating costs through new (and cost effective) methods of harvesting, transporting, drying and chipping the biomass.

In parallel, the company is also examining new technologies for conversion of biomass to energy. Shell believes that conversion efficiencies can be increased if the biomass is first gasified and then (depending on the process) the resulting biofuel is used to fuel a gas turbine (with waste heat recovery).

Conclusions

The European studies have shown that biomass can be a renewable and sustainable source of energy, and that powerplants can be designed which can burn the fuel with efficiencies more than double those of conventional coal-fired powerplants. In many cases these powerplants are burning waste from the forestry industry (such as waste liquors), which would otherwise enter the environment, polluting streams and rivers.

There is both the technological ability and the political to develop a new generation of turbines and boilers to turn waste (and short-rotation crops) into energy even more efficiently, and partnerships between municipalities and forestry companies which make the installation of such equipment economically attractive. The lesson could be learnt by other developed countries, particularly in Asia, where the projected percentage of energy generation from biomass is extremely low, even over the medium to long term.

Sources

G. Boyle (ed.), Renewable Energy: Power for a Sustainable Future, Oxford University Press, 1996

European Biomass Conference 1994 : Vienna, Austria Biomass for energy, environment, agriculture and industry : proceedings of the 8th European Biomass Conference, Vienna, Austria, 3-5 October 1994, 1995

International Energy Agency, Biomass energy: data, analysis and trends : Paris, France, 23th-24th March 1998 : conference proceedings ,1998.

‘Bioenergy in Finland’ http://www.finbioenergy.fi/bioweben/index.html

‘Biomass Energy in ASEAN Member Countries’ http://www.rwedp.org/

‘Bioenergy is forever’ http://www.energywise.co.nz/59sep98/59bio.htm

‘www.shell.com — About the Shell group’ http://investor.shell.com/about/content/0,1369,1506-3090,00.html

 

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