Biomass Co-Combustion With Coal

Abstract

Dairy Biomass (DB) or dairy manure ,Feedlot biomass (FB) or Beef cattle manure, mesquite and juniper were evaluated as a possible co-firing fuel with coal. Torrefaction has been considered to be one of the thermal pretreatment options to improve the chemical (e.g., heat content) and physical (e.g. grindability) properties of raw biomass. Cofiring of DB offers a technique of utilizing dairy manure for power/steam generation, reducing greenhouse gas concerns, and increasing financial returns to dairy operators. The effects of cofiring coal and DB/Mesquite/Juniper have been studied in a 30kW (100,000 BTU/h) burner boiler facility. Two forms of partially composted DB fuels were investigated: low ash separated solids and high ash soil surface. Two types of coal were investigated: Texas Lignite (TXL), and Wyoming powder river basin coal (WYO/PRB). For the case of mesquite and juniper, both raw and torrefied biomass (TB) were cofired with coal to study the emission characteristics.The NOx emissions for equivalence ratio (Φ) varying from 0.9 to 1.2 ranged from 0.34 to 0.90kg/GJ (0.79–0.16lb/mmBTU) for pure TXL. They ranged from 0.35 to 0.7kg/GJ (0.82–0.16lb/mmBTU) for a 90:10 TXL: low ash partially composted dairy biomass (LA-PC-DB-SepS) blend and from 0.32 to 0.5kg/GJ (0.74–0.12lb/mmBTU) for a 80:20 TXL:LA-PC-DB-SepS blend over the same range of Φ. In a rich environment, DB:coal cofiring produced less NOx and CO than pure coal. This result is probably due to the fuel bound nitrogen in DB is mostly in the form of urea which reduces NOx to non-polluting gases such as nitrogen (N2).Co-firing 10% by mass of raw mesquite with coal reduced the NOx emission from 420ppm to 280ppm for an Equivalence ratio (ER) of 0.9. Further cofiring TB with coal reduced the NOx emission by 10% when compared to base case NOx emission from combustion of pure PRB coal. NOx emission decreased with increase in equivalence ratio. In addition, a term used in the biological literature, respiratory quotient (RQ), is applied to fossil and biomass fuels to rank the potential of fuels to produce carbon dioxide during oxidation process. Lesser the value of ‘RQ’ of a fuel, lower the global warming potential.