The concept of co-firing is quite simple. It consists in the use of two or more fuels inside the same combustion device. It is applicable to all kind of combustion systems traditionally used for power generation (pulverized fuel, fluidized bed and combustion on grate). Co-firing in cement kilns is already a quite widespread solution for valorization of waste materials mostly, as well as for biomass. Iron industry and domestic sector (coal stoves) are also sectors where co-firing could be implemented, though those are minority in Spain.
The use of biomass replacing coal in the so different combustion technologies may vary from very trivial solutions (involving few modifications) to complex implementations requiring, like in diverse systems for coal power stations, important reforms and costs to retrofit the units. Modifications and cost impact depend on fuel characteristics, original combustion technology, secondary devices and degree of coal substitution. Those aspects are object of Work-package 3 (WP3)More info on co-firing (pdf-Spanish)
Use of biomass in co-firing incorporate additional environmental, socio-economic and strategy advantages respect the use of biomass in dedicated biomass plants. Next a summary of them:
Currently the consumption of solid fossil fuels (coal and petroleum coke) in Spain accounts for more than 16% share in the consumed primary energy. Associated emissions are over 20% of GHG stemming from the high carbon content of those fuels respect to other fossil fuels like gasolines, gasoils and gas. The 20% of GHG emissions are comparable to the emissions from domestic sector or road transport in Spain.
Spanish Plan for Renewable Energies established objectives on biomass energy generation to be accomplished on 2010. The progress of biomass use, specially for power generatio, are on worrying retard. Main reasons are the important barriers still existing for the developement of biomass initiatives. Low cost in investment, high efficiency and low uncertainty respect to biomass procurement are important features required currently by a project to reduce risk. Co-firing is a technology solution with all those advantages and thus able to break with the up-to-date immobilism of the sector.
High expectations have been placed on the potential of co-firing technologies in Spain. Still few data and no holistic analysis have been carried out. However potentials are expected to be large according to the size of the coal power generation and cement sectors, as well as regarding the a priori high potential of biomass resources in Spain. Industry. Therefore the possibilities of co-firing as a key technology for reducing the GHG emissions may be of great interest and mak a new line of environmentally friendly practices in the industry.
An example of co-firing in Spain is the project “Co-firing in Escucha power station” managed by the Natural Resources Division of CIRCE between 1999 and 2002. This project tested co-firing full scale tests where up to 8% of the coal power station electricity was produced by co-firing biomass. Reduction in CO2, SO2x and NOx were proved to be reduced under co-firing black lignite with forestry residues.
Images of burners with adapted biomass entry, and coal power station from project “Co-firing at Escucha power station” (1999- 2002)