Effect of secondary gas injection on the peanut shell combustion and its pollutant emissions in a vortexing fluidized bed combustor.

Peanut shell is a common agricultural waste in Asia, and its high calorific value is suitable to be used as a fuel. In this study, a vortexing fluidized bed combustor (VFBC) with silica sand as the bed material was used for peanut shell combustion. There was no indication of bed agglomeration during combustions for as long as 12h. The temperatures and gas concentrations were measured along the axial direction at various operating conditions, including excess oxygen ratio and secondary gas flow rate. Results show that CO emission decreases with rising excess oxygen ratio and secondary gas flow rate, while NOx emissions show a reverse trend. To meet the minimum CO and NOx emission standards of Taiwan EPA, excess oxygen ratio ranging from 40% to 55% and secondary gas flow rate ranging from 1.56 to 2 Nm(3)/min are found optimal for crushed peanut shell combustion in a VFBC.

Pollutant emission characteristics of rice husk combustion in a vortexing fluidized bed incinerator.

Rice husk with high volatile content was burned in a pilot scale vortexing fluidized bed incinerator. The fluidized bed incinerator was constructed of 6 mm stainless steel with 0.45 m in diameter and 5 m in height. The emission characteristics of CO, NO, and SO2 were studied. The effects of operating parameters, such as primary air flow rate, secondary air flow rate, and excess air ratio on the pollutant emissions were also investigated. The results show that a large proportion of combustion occurs at the bed surface and the freeboard zone. The SO2 concentration in the flue gas decreases with increasing excess air ratio, while the NOx concentration shows reverse trend. The flow rate of secondary air has a significant impact on the CO emission. For a fixed primary air flowrate, CO emission decreases with the secondary air flowrate. For a fixed excess air ratio, CO emission decreases with the ratio of secondary to primary air flow. The minimum CO emission of 72 ppm is attained at the operating condition of 40% excess air ratio and 0.6 partition air ratio. The NOx and SO2 concentrations in the flue gas at this condition are 159 and 36 ppm, which conform to the EPA regulation of Taiwan.

Experimental study on rice husk combustion in a vortexing fluidized-bed with flue gas recirculation (FGR).

Vortexing fluidized-bed combustor (VFBC) has been proven to be an effective equipment in converting biomass wastes into clean energy. This study conducted experiments on rice husk combustion in a VFBC with FGR. The effect of FGR on combustion characteristics is investigated. In addition, the effect of operating variables such as excess oxygen ratio, and in-bed stoichiometric oxygen ratio on the temperature distributions, pollutants emissions, and combustion efficiency are also studied. The results show that the combustion efficiency of rice husk can reach 99% at optimal operation condition. CO emission increases with the in-bed stoichiometric oxygen ratio, but decreases with excess oxygen ratio. NOx emissions show inverse trend, and it can be effectively reduced by using FGR in the VFBC.

Incineration of kitchen waste with high nitrogen in vortexing fluidized-bed incinerator and its NO emission characteristics.

Some municipal solid waste (MSW) can be used as the fuel. Combustion of MSW with high nitrogen content is successfully conducted in a lab-scale vortexing fluidized-bed incinerator (VFBI). Pigskin with 16.5 wt.% nitrogen content was used to simulate the high nitrogen content kitchen waste, and silica sand was used as the bed material. The effects of operating conditions, such as the bed temperature, freeboard temperature, excess oxygen ratio, and static bed height on the CO and NO concentrations at the exit of combustor and cyclone were investigated. The experimental results show that the freeboard temperature is the most important factor for CO emission. The order of operating conditions impact on the NO emission is: (1) excess oxygen ratio; (2) bed temperature; (3) freeboard temperature; and (4) static bed height. Utilizing cyclone can significantly reduce the CO emission concentration when the CO concentration released from the freeboard is higher than 50 ppm. On the other hand, the cyclone has no significant effect on the NO emission. Despite having high nitrogen content, a low conversion from fuel-N to NO was attained. Compared with other types of combustors, VFBI reduces the CO and NO emission concentrations much better when burning MSW with high nitrogen content.

A study on fluidized bed combustion characteristics of corncob in three different combustion modes.

This paper presents results obtained from corncob combustion in a pilot scale vortexing fluidized bed combustor (VFBC). Three combustion modes including direct combustion, staged combustion and flue gas recirculation (FGR) combustion were employed, and their combustion and pollutant emission characteristics were studied. In addition, the effects of combustion fraction and bed temperature on pollutant emission characteristics were investigated. The experimental results show that the combustion fractions vary with different combustion modes, resulting in different CO and NO emission characteristics. Staged and FGR combustions can reduce the NO emission concentration. Under similar working condition, NO concentration decreases by 30% in FGR mode, while 15% in staged mode compared with direct mode.

Combustion and NO emission of high nitrogen content biomass in a pilot-scale vortexing fluidized bed combustor.

The combustion of biomass of various nitrogen contents and its NO emission were investigated experimentally in this study. All the experiments were conducted in an I.D. 0.45 m pilot-scale vortexing fluidized bed combustor (VFBC). Rice husk, corn, and soybean were used as feeding materials. Urea was added into the feeding materials for the purpose of adjusting nitrogen content. The effects of various operating parameters on NO emission, such as bed temperature, excess air ratio, and flow rate of secondary air, were investigated. The effects of nitrogen content of fuels on NO emissions were also investigated by using the mixtures of rice husk/soybean, rice husk/urea, corn/soybean, and corn/urea in various weight ratios. The NO concentrations at various positions in the combustor were sampled and recorded. The experimental results show that most nitric oxide is formed at just above the bed surface. Temperature and excess air ratio are the major operating parameters for NO emission. For biomass with high nitrogen content, NO emission decreases with excess air, and increases with bed temperature. Compared with char-N, volatile-N is the more dominant reactant source for NO emission.