Electricity production with the use of a renewable energy source on a sustainable basis is clearly the most important contribution of the cofiring alternatives discussed here. Additionally, natural gas could be used in a more rational manner, allowing gradual changes within the energy matrix and reduction of environmental impacts. In fact, a transition into biomass for power generation can be interesting for natural gas distribution companies. These companies could maximize their take-off in the beginning of the cash flow project and further extend their supply of natural gas at a very low cost (or even no cost) as the consumer market is further developed. This transition into biomass could also be considered for countries where the market of natural gas is already well developed. Another interesting point to be considered concerns the required investment to find new reserves at high marginal costs.

One of the main conclusions of a detailed study of the cofired option presented in Case В was that cofiring could be instrumental for the market development of the BIG-CC technology in its early stages. In fact, besides the possibility of overcoming technical constraints for the very first BIG-CC units, the enlargement of the fuel heating value due to the natural gas contribution boosts the plant efficiency and, consequently, contributes to the reduction of the cost of electricity generated from biomass. The cost reduction is, to a large extent, due to economies of scale. Small biomass-fueled gasification plants can benefit from the high efficiency and low capital costs of large combined cycles without scaling up the biomass parts. However, in the medium — to long-term, as the BIG-CC is further developed and gas turbines for biomass-derived gas are redesigned, cofired combined cycles would probably be less justifiable (Souza, 2001). In the case of Brazil, successful experiences with cofiring natural gas and biomass could not only help foster BIG-CC market expansion, but also could allow a more efficient use of sugarcane residues for electricity generation.

Measures

kPa= 103N/m2

LHV = Lower heating value

MMBTU = Million of British Thermal Units

Mol = Molecular weight

MPa=106N/m2