Biomass Cofiring for Emissions Management

Abstract

Biomass cofiring in coal‐fired utility boilers has been demonstrated as an effective means to trim certain gaseous products of combustion including sulfur dioxide ( SO 2 ), fossil‐based carbon dioxide ( CO 2 ), and, for the most part, oxides of nitrogen (NO x ). In some projects, it has also been shown to reduce mercury (Hg) emissions. As this article elucidates, the mechanisms by which biomass cofiring achieves these results include fuel composition—biomass is deficient in sulfur and its carbon is within the global carbon inventory available for recycling through the photosynthetic process. These mechanisms, when applied to NO x emissions reduction, capitalize on the high reactivity of the biomass fuel and the ability of reactive solid fuels to impart that reactivity to less reactive coals. The biomass fuels used in the United States are largely woody and herbaceous materials. Processed biomass in the form of pellets and/or torrefied wood has not been used extensively in the United States because of the high costs associated with double handling of the material and the processing itself. Animal manure has been tried but largely unsuccessfully. There have been numerous demonstrations and tests of cofiring; several such case studies are summarized in this article. These case studies document how the fuel properties of biomass are used in cofiring applications to achieve environmental benefits.

Advances in Biomass Co-Combustion with Fossil Fuels in the European Context: A Review

“…Experience from these facilities confirmed the conclusions of Hein and Bemtgen (1998) [17] in terms of NO x emissions reduction exhibiting positive synergistic effect and a manageable decrease in boiler thermal efficiency of up to 2% in the co-combustion mode. The reported NO x trend was further corroborated in a publication by Tillman (2015) [34] stating that the observed NO x emission reduction was higher than what resulted from simple linear dependence assumption with varying biomass share in 65% of examined full scale systems. Moreover, a decrease of CO 2 emissions of 2.7 to 3.15 ton per ton of combusted biomass was reported.…”

“…For the latter one, a complete independent biomass preparation and feeding system has to be constructed; however, the biomass co-combustion ratio can reach up to 20% wt. [31,34].…”

“…Pilot and full scale systems studies conducted several decades ago [17][18][19] continue to be published [20,21], but they are more recently accompanied by laboratory experiments employing drop tube furnaces [22][23][24], thermogravimetric analyses (TGA) [25][26][27], and other laboratory equipment [28,29]. Experience with co-combustion systems operation are reported in the USA [30,31], Europe [32], as well as other parts of the world [33], generally claiming reduction in CO 2 and other greenhouse gases emissions [34] with only minor changes in co-fired power plants and utility boilers thermal efficiencies [35]. Operational issues including the propensity for boiler slagging [36], fouling, and corrosion [15] are still not tackled sufficiently, though.…”