Circulating fluidised bed co-combustion of coal and biomass

Abstract

Circulating fluidised bed combustion (CFBC) is receiving wide research attention in view its potential as an economic and environmentally acceptable technology for burning low-grade coals, biomass and organic wastes, and thereby mixtures of them. Designs of the existing fluidised bed boilers for biomass combustion are mainly based on experience from coal combustion because the mechanism of combustion of biomass in fluidised beds is still not well understood. A good understanding of the combustion and pollutant formation processes and the modelling of the combustor can greatly avoid costly upsets of the plants. In this paper the performance of CFBC burning coal and biomass mixtures was analysed. Experimental results were obtained from the combustion of two kind of coals with a 2 forest residue (Pine bark) in two CFB pilot plants (0.1 and 0.3MW th). The effect of the main operating conditions on carbon combustion efficiency was analysed. Moreover, a mathematical model to predict the behaviour of the co-combustion of coal and biomass wastes in CFB boilers has been developed and validated. The developed model can predict the different gas concentrations along the riser (O 2 , CO, CH 4 , etc.), and the carbon combustion efficiency. The experimental results of carbon combustion efficiencies were compared with those predicted by the model and a good correlation was found for all the conditions used.

Model Research of Gas Emissions From Lignite and Biomass Co-Combustion in a Large Scale CFB Boiler

“…Similar to the results presented in (Abelha et al, 2008;Armesto et al, 2003;Hein and Bemtgen, 1998;Leckner et al, 2004;Nussbaumer, 2003;Sami et al, 2001) the emissions of NO x also decreased with a biomass fraction in the fuel blends, even though nitrogen content in biomass was about 3-6 times higher than that in coal. The decrease could be attributed to a higher char content in biomass than that in lignite (Gayan et al, 2004) as char has a capability to reduce NO content. Another explanation could be the DeNO x mechanism, favoured by the presence of H and OH radicals from volatiles (Hupa, 2005;Sami et al, 2001).…”

“…Different from coal chemical constitution of biomass affects co-combustion processes and makes them more complex. There are many papers dealing with coal and biomass cocombustion: Abelha et al (2002), Armesto et al (2003), Armesto et al (2008), Bahillo et al (2003), Hein and Bemtgen (1998), Hupa (2005), Gayan et al (2004), Jenkins et al (1998), Knobig et al (1998), Leckner (2004), Leckner (2007), Leckner (2008), Liu and Gibbs (2002), Lyngfelt and Leckner (1999), McIlveen-Wright et al (2006), Nussbaumer (2003), Sami et al (2001), Skreiberg et al (2004), Thunman et al (2002), Werther (2009), Yu et al (2009). Co-firing tests in a CFB boiler of olive cake, straw pellets, meat and bone meal and wood pellets mixed with bituminous Colombian coal in the proportions of 5, 15 and 25% of biomass by weight were presented by Abelha et al (2008).…”

“…The particle was divided into four regions: moist, dry and devolatilising fuel, char residue and ash. A model of coal and wood co-firing, validated on a pilot-scale 0.1 and 0.3 MWth test-rigs was presented by Gayan et al (2004). The existence of three zones in the riser: bottom, splash and transport zone were taken into account by the model.…”

Release Profile of Volatiles in Fluidised Bed Combustion of Biomass

“…There are two ways to utilize this biomass resource. It can be co-combusted in a large boiler plant using coal as the main fuel [3][4][5][6]. The other option is to burn the fuel in smaller plants producing electric energy.…”

“…Fluidised bed combustion technology is advantageous for various fuels [3][4][5][6][7][8] since it is not always necessary to process the waste to more refined fuels but it can usually be burned directly. However, processing the fuel for example by pelletizing before combustion could be beneficial [9].…”