Combustion of Corn Stover Bales in a Small 146-kW Boiler

Abstract

Spring harvested corn stover was used for direct combustion in a 146 kW dual chamber boiler designed for wood logs. Stover had a very low moisture content (6.83 ± 0.17%), a gross calorific value (GCV) of 18.57 MJ/kg of dry matter (±0.32 MJ/kg DM) and an ash content of 5.88% (±1.15%). Small stover bales (8.83 ± 0.90 kg) were placed manually in the upper combustion chamber at a rate of 10.5 to 12.8 kg/h over a 24-h period, with three replications, and compared to a control wood combustion trial (12.1 kg/h during 24 h). The overall heat transfer efficiency for stover was lower than for wood (57% vs. 77%). Stover bales produced on average 7.5% ash which included about 2% of unburned residues while wood produced 1.7% ash. CO gas emissions averaged 1324 mg/m³ for stover (118 mg/m³ for wood). The corn stover showed a good calorific potential, but it would have to be densified and the boiler should be modified to improve airflow, completeness of combustion and handling of the large amount of ash formed.

Impact of Harvest Equipment on Ash Variability of Baled Corn Stover Biomass for Bioenergy

“…The lowest measured ash value for each of the treatments (5.8 %±0.6 %; mean±1 standard deviation) is in agreement with the average of 5.6 % for "clean" whole plant corn stover reported by others [9][10][11]18], evidence that the elevated ash content of the majority of core samples is due to soil contamination. Several important trends relating to the influence of equipment combination on bale ash content can be interpreted from the grouped datasets for each treatment.…”

“…This suggests that the removal of a raking step by shredding reduced ground contact and soil entrainment into the windrowed material, similar in principal to the reduced ash content of single and two-pass bales reported by Shinners et al [20]. Morissette et al [18] showed small square bales created from a shred flail windrower in the spring to have an average ash content of only 5.9 % with an upper range of 9.3 %, suggesting that further improvement may be possible if delayed collection time and reduced yield are viable tradeoffs for improving quality. To this affect, it should be noted that the shred flail field resulted in the lowest yield of the three tested, potentially aiding its increased performance insofar as soil contamination is concerned (Table 1).…”

“…The ash content of biomass has been documented for a number of crop types, with hand-harvested whole plant corn stover typically in the range of 5-7 % [4, [8][9][10][11] and singlepass corn stover (usually lacking lower stalk) as low as 2-4 % [12,13]. Although the intrinsic ash content of different crops can vary widely (from less than 1 % in pine chips to over 15 % for rice hulls [14]), elevated ash levels are commonly attributed to soil contamination during harvest and collection [11,[15][16][17][18]. Traditional multipass collection of corn stover involves several steps where the material comes into contact with soil.…”

Corn Stover and Wheat Straw Combustion in a 176-kW Boiler Adapted for Round Bales

“…CS ash content after the 12-bale combustion trial averaged 9.17% d.b., which was lower than the TGA value (11.70% d.b.). Various ash levels for CS are reported in the literature: 4% for standing stalk, unwashed [20] and 5.9% for small stover bales harvested in the spring six months after grain harvest [21]. Higher values and variations observed for ash content of CS are probably linked to the harvesting method and soil contamination.…”

Biomass Fuel and Combustion Conditions Selection in a Fixed Bed Combustor

“…Due to this fact, and to reduce logistic costs, most operations occur in small-scale plants [11]. Of all the biomass low-output boiler combustion methods, fixed bed boilers are most desirable because of their simplicity, reduced costs, higher automation, and batch control, which, in turn, enable the feeding of heterogeneous biofuels [12].…”