Energy from biomass and waste

Abstract

Biomass, a broad term for all organic matter of plants, trees and crops, is currently regarded as a renewable energy source which can contribute substantially to the world's energy supply in the future. Various scenarios for the development of energy supply and demand, such as compiled by the World Energy Council (WEC), the Intergovernmental Panel on Climate Change (IPCC), Shell and the Stockholm Environmental Institute (SEI), indicate that biomass has the potential to make a large contribution to the world's energy supply. Estimates of this potential in the year 2050 vary from 14% to 50% of the total supply, or from 100 to about 300 EJ/yr. It is estimated that currently biomass contributes 10-14% of the energy supply, which is equivalent to about 40-55 EJ/yr. The use of firewood in developing countries makes up a large part of this 40-55 EJ, but there it is for a large part non-commercial and non-sustainable use of biomass.

In recent years there has been renewed interest in biomass as a commercial and sustainable source of energy. There are three main reasons for this: 1. Technological developments, in the field of crop production and conversion technology permit the more efficient and cleaner utilisation of biomass at lower costs. These developments make bioenergy more competitive with energy produced from fossil fuels. 2. The agricultural systems of especially the European Union and the United States are producing food surpluses. This situation has led to policies whereby agricultural land is 'set-aside', resulting in depopulation of rural areas. The continuously increasing productivity in agriculture might strengthen these trends. There is therefore a desire to develop alternative crops. Energy crops could be a suitable alternative since there is virtually an infinite market for this, provided the costs are competitive with those of fossil fuels. 3. There is a threat of global climate change due to the rapid increase in the concentration of greenhouse gases, especially CO2 in the atmosphere, resulting mainly from the large scale use of fossil fuels. If produced sustainably, biomass can be a carbon neutral alternative for fossil energy carriers.

If biomass is to make a substantial contribution to the world's energy supply it will have to include not only biomass residues - such as from commercial forestry (e.g. thinnings) and agriculture (e.g. straw) - and organic wastes, but also energy crops. Perennial crops seem to be a particularly promising energy source. Crops like Short Rotation Coppice (e.g. Willow and Eucalyptus) and grasses (e.g. Miscanthus) give a relatively high net energy yield per hectare, have a low environmental impact and produce relatively cheap energy. The use of such crops in a Biomass Integrated Gasifier/Combined Cycle (BIG/CC) plant to produce electricity or combined heat and power, and the gasification of these crops to produce fuels like methanol and hydrogen appear to be promising routes for achieving high energy conversion efficiency at relatively low cost.

However, despite the promising outlook, various barriers are hampering the large scale development and implementation of commercial biomass energy systems. Currently, the commercial use of biomass to generate electricity is limited mainly to the utilization of zero- or low-cost biomass waste or residues. At the moment specially cultivated biomass is too expensive an option. However, biomass is able to compete on a significant scale in countries, like Sweden, Denmark and Brazil, where government policies support its use financially or have actively discouraged the use of fossil fuels (such as by the introduction of a carbon tax). The complexity of large scale bioenergy systems is also a barrier. Furthermore, biomass has a relatively low energy density. The production of biomass is bound up with seasons and makes high demands on organization and logistics. Furthermore, it involves many different actors involved in the production and utilisation of energy crops: farmers, utilities, industries, governments, etc. Difficulties concerning public acceptability and uncertainties concerning the ecological effects of the large scale production of use of biomass be form another problem. Last but not least, the availability of land may be a major problem if the large scale production of energy crops is being considered. If agriculture is not modernizing, especially in developing countries, there might be very little room left for alternative crops. Energy farming may then conflict with food production, a situation which is highly undesirable.

This thesis focuses on a number of aspects relating to the utilization of biomass and waste for energy purposes. The general objective of this work is as follows: "To analyse the possibilities for biomass (both crops and wastes) as a modern energy carrier in the Dutch energy system." Therefore this thesis has the following specific objectives: 1. To analyze of the technical, economic and environmental characteristics of Biomass Integrated Gasifier/Combined Cycle technology for the conversion of biomass and waste streams. 2. To examine the potential energy supply of energy farming, biomass residues, organic waste streams and waste in the Netherlands. 3. To analyze of the potential costs and benefits of different biomass energy systems (including waste treatment) in the Netherlands.