| Application of biomass-energy technologies |
|VI. Conversion of biomass into electricity|
Although this paper is involved in the analysis of established bioenergy projects, it is also of value to examine the potential for electricity production in the north-east region of Brazil, as assessed by Carpentieri et al, (1992), since this has implications for other developing countries. The north-east region has a low population density, an economy heavily dependent on agriculture, and an energy consumption about half the national average. Over 90 per cent of all electricity produced in Brazil, and virtually all that is produced in the north-east is hydroelectric. To meet projected growth rates for electricity consumption in the north-east up to 2015 would require a capital investment in new power plants (all hydroelectric) in excess of £40 billion. It is planned to develop essentially all remaining hydroelectric potential in the Northeast by 2005, and costs will rise as less favourable sites are developed. However, the hydroelectric potential will inevitably be exhausted and alternative electricity sources must be found. One option under consideration is importing electricity from new hydroelectric projects to be located in the Amazon river basin. But this would be expensive, environmentally controversial and would involve little direct long-term investment or job creation in the north-east.
In 1982, the Division of Alternative Energy Sources of the Hydroelectric Company of Sao Francisco (CHESF), responsible for production and transmission of bulk energy in the north-east, initiated studies on alternative advanced technologies for converting biomass into electricity. There are three potential biomass resources in the north-east that could be utilized for electricity production: sugarcane residues, plantations. and the residues of other agricultural products. Of these, the first two show most promise for large-scale use as plantations are well established. In fact, both plantation industries in Brazil are recognized as world leaders.
In this region practically all woodfuel comes from natural forests with devastating environmental effects. Efforts to establish plantation have been quite successful in Brazil as a whole with over 40 per cent of all charcoal now being derived from this source (Abracave, 1992), and plantations are estimated to cover 4 to 6 million ha (mostly used by steel and paper and pulp producers). Large investments have been made in plantation technology and techniques resulting in a great improvement over the last 15 to 20 years. CHESF carried out a biogeoclimatic assessment to evaluate the potential for wood-plantation energy, considering only land area judged to be sub-optimal for agriculture (CHESF, 1990). It estimated that 50 million ha (a third of the land area of the north-east) was available for plantations with productivities ranging from 6 to 44 m³/ha/yr of wood, and that the total plantation production potential is about 1340 million m³/yr of wood which could produce 12.6 EJ/yr. This compares with a total energy use in the north-east of about I. I EJ. Cost estimates range from 7.3 c/kWh for condensing steam turbine technology (CST) down to 4.3 c/kWh for gas turbine/steam turbine combined cycle technology (GTCC). Over 86 per cent of the wood production would be at an average cost less than $1.35/GJ (Carpentieri et al, 1992).
Sugarcane, on the other hand, is already widely grown in Brazil and some sugarcane processing facilities are already selling small quantities of electricity produced from bagasse to utilities. The present biomass energy production potential in the north-east from the area of cane planted in 1989 is estimated to be 174 PJ/yr. Looking at a future scenario, the average cost of producing the electricity with STIG technology is around 4.04.4 c/kWh. This would be competitive with marginal costs of anticipated new hydroelectric supply. If tops and leaves are also used, the bioenergy available could be increased by up to 75 per cent, and off-season jobs baling and transporting the barbojo would be created (Carpentieri et al, 1992).
Carpentieri et al, (1992) constructed two alternative scenarios for the production of electricity in the Northeast to the year 2015, these are summarized in table 17. The "Hydro" scenario is based on CHESF plans for continued expansion of the hydroelectric system; while the "Biomass" scenario is "intended to be a plausible scenario of how biomass could be incorporated into the utility system." Both proposals include the initial installation of 4100 MW of hydroelectric power at a single site, Xingo 1. The Biomass scenario then assumes sugarcane CEST systems (including barbojo) begin to make a contribution in 1987 such that half of the total potential is installed by 2000 at 320 MW/yr. From 200O, STIG systems come on line at the rate of 280 MW/yr until 2010 when the full electricity-generating potential of sugarcane is realized. Plantation activity is assumed to begin in 1994 with stand-alone power stations first coming on line in 2000 based on GTCC technology with an installed capacity of 250 MW, and annual additions will increase up to 1000 MW of new supply in 2015 (this is supplied by only 4 per cent of CHESF's assumed potential fuelwood in the north-east).
Total new land required by the Biomass scenario would represent only 1.6 per cent of the total land area of the north-east. Since the biomass facilities are smaller and greater in quantity they offer more security and can follow demand more closely. The Hydro scenario would contribute 25 GW between 1990 and 2015 compared with 15 GW in the Biomass scenario. Average unit investment costs would be 25 per cent higher for the HYDRO case, the total required capital investment would be twice as much, average electricity production costs will be higher, and marginal production costs will be substantially higher. This scenario assumes "a reasonable commitment from government, utilities, industry and relevant R&D organizations, and the support of the population in general." (Carpentieri et al, 1992).
The energy potentially available from other agricultural residues in the north-east is estimated to be about 145 PJ/yr, which is equivalent to about 10 per cent of primary energy consumption in this region. Since these sources are widely dispersed and lack any infrastructure for energy use, they are of more importance for use locally, in a decentralized manner (Carpentieri et al, 1992). The Brazilian Government is promising to introduce a new policy across Brazil that will mandate the State-controlled electricity utilities to enter into long-term contracts to buy cogenerated power. This will encourage further the growth of biomass electricity production from residues.