Bioenergy is considered as the resource with the highest environmental impact amongst the renewable energy sources and this does not refer to incineration or waste treatment only, but it even applies to wood combustion. This is due to the fact that there are always residues (such as ash and liquid effluents) to be disposed off and practically in all applications there is a stack or a chimney. This may induce the general public to relate bioenergy plants to coal fired plants, incinerators and in general emission of gaseous pollutants. It is therefore mandatory that all Bioenergy technologies must carefully and convincingly address the problem of emissions if they are ever going to be accepted by the general public, the political establishment and subsequently the industry.

Practically in all Bioenergy applications at the end the energy carrier (biogas, fuel gas, bio-oil, ethanol, solid fuel or hydrogen) will be used in a combustionprocess to release the chemical energy of the carrier. It is therefore of critical importance that emissions from the combustion of all energy carriers are minimised to whatever possible extend. It is preferable whenever possible to try to reduce the concentration of the pollutants in the energy carrier before it's combustion so as to minimise or eliminate emissions of sulphur oxides, heavy metals, halogenated compounds and other pollutants. This can (be achieved in gasification or pyrolysis processes, however, it is not possible for combustion unless extensive feedstock pretreatment takes place which is always relative expensive. In the medium term future this can prove an advantage for gasification and pyrolysis processes for contaminated biomass or waste recovered fuels in relation to combustion. Although there has been significant progress in the reduction of emissions for all the above pollutants, this is a field where the R&D work should be intensified. This is becoming even more critical as waste recovered fuels and contaminated biomass such as demolition wood are becoming an important cheap resource in countries where there is scarcity of other biomass feedstocks.

 

ETHANOL FUEL PROGRAM EVOLUTION

The fuel ethanol program in Brazil was formally established in 1975, aiming at reducing oil imports. Other important considerations were: the existing know-how in fuel ethanol production/utilization; land and labor availability; and low sugar prices in the world market. After 1980, with the ethanol-dedicate engines, local environmental benefits became evident (elimination of Pb in gasoline blends; lower CO emissions; less aggressive HC and NO_x). The global environmental benefits, with a substantial reduction in CO₂ net emissions, was well quantified in 1990. [1]

The program was established within the context of a strong government intervention in the sugar cane sector; before 1975 sugar was produced and commercialized within "production quotas", and all exports were made by the government. In the 90's all the production/commercialization of sugar and ethanol were totally de-regulated as follows:

From 1975 - 80's

Ethanol:

-   Level of guaranteed purchase, at controlled prices

-   "Fixed" ratio of ethanol/gasoline selling prices:

0.59 (1975) ® 0.75 (1989)

-   Low interest rate in loans for investment (1980-1985)

Sugar: Government issued "production quotas"

Exports: by the Government

*    1990    Sugar Exports Privatized

*    1994    Ethanol: 22% ethanol in gasoline blends

*    1995    Sugar: de-regulation (end of quotas)

*    1997    Anhydrous ethanol (blends) de-regulation (end of quotas and controlled prices)

*    Ethanol: 24% ethanol in gasoline blends

*    Hydrated ethanol (E 1 00): de-regulation

Those policies and the world market positions for sugar and oil resulted in productions as are summarized in Figure 1. It is important to see the sugar cane availability, its causes and consequences, to understand the possibilities today.

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Figure 1: Production - Brazil [2]

Internal sugar consumption in Brazil grew in the expected way, somewhat above population growth in some periods. Sugar cane growth from 120 M ton to 240 Mt (from 1979 to 85) was almost entirely driven by the E-l00 (dedicated ethanol car) in the period. In the following years production stabilized; the government policy of paying the producer according to officially audited production costs was gradually abandoned (if not officially), and the "fixed" ratio of pump price ethanol/gasoline increased from 0.59 to 0.75. Sugar exports were privatized in 1990, and a shortage of ethanol (1989-90) led to consumer mistrust and very rapid decline in sales of ethanol dedicated vehicles.

In the 90's, the export privatization and the very competitive production costs led to an extraordinary increase in sugar exports (from 1.5 to 11 M ton sugar) pushing sugar cane production to the 300 MT level; this was stabilized again by the drop in sugar prices and the over supply of ethanol in the 97-2000 period.