Co-combustion of biomass fuels with coal in a fluidised bed combustor.

Co-combustion of biomass with coal has been investigated in a 0.15 m diameter and 2.3 m high fluidised bed combustor under various fluidisation and operating conditions. Biomass materials investigated were chicken waste, rice husk, palm kernel shells and fibres, refuse derived fuel and wood wastes. These were selected because they are produced in large quantities particularly in the Far East. The carbon combustion efficiency was profoundly influenced by the operating and fluidising parameters in the decreased following order: fuel properties (particle size and density), coal mass fraction, fluidising velocity, excess air and bed temperature. The smaller particle size and lower particle density of the fuels (i.e. coal/chicken waste, coal/rice husk and coal/wood powder), the higher carbon combustion efficiency obtained in the range of 86-90%, 83-88%, 87-92%, respectively. The carbon combustion efficiency increases in the range of 3% to 20% as the coal fraction increased from 0% to 70%, under various fluidisation and operating conditions. Also, the carbon combustion efficiency increases with increasing excess air from 30- 50% in the range of 5 - 12 % at 50% coal mass fraction in the biomass mixture. However, further increased of excess air to 70% will reduced the carbon combustion efficiency. Relatively, increasing fluidising velocity contributed to a greater particle elutriation rate than the carbon to CO conversion rate and hence increased the unburned carbon. Furthermore, the bed temperature had insignificant influence of carbon combustion efficiency among the biomass fuels. Depending upon excess air ranges, fluctuations of CO emissions between 200 - 1500 ppm were observed when coal added to almost all biomass mixtures. In ash analyses, the percentages of unburned carbon were found to have increased in the range 3 to 30% of the ash content with the increases of coal fraction in the coal! biomass mixture. Furthermore, no fouling, ash deposition and bed agglomeration was observed during the combustion runs for all tests due to lower operating bed temperature applied. Lastly, a simple model was developed to predict the amount of combustion in the freeboard. This study demonstrated the capability of co-firing biomass with coal and also demonstrated the capability to be burnt efficiently in existing coal-fired boilers with minimum modification

Coal bottom ash for palm oil mill effluent (POME) decolourization

The utilization of coal bottom ash (CBA) from thermal power plant for palm oil mill effluent (POME) decolourization was studied. CBA is prepared using chemical activation with hydrochloric acid (HCl) to increase adsorption performance. Physico-chemical characterizations of CBA-HCl was analysed using BET for surface area, FTIR for its surface chemistry, SEM for morphology and EDX for elemental analysis. The effectiveness of CBA-HCl for colour adsorption of POME was investigated as a function of pH, initial concentration, adsorbent dosage and contact time by batch experiments. Adsorption increased with increasing contact time and the equilibrium states could be achieved in range of 18 to 24 hr. Results showed that CBA-HCl perform with maximum colour removal of 93% at pH 6 with 10% (w/v) adsorbent dosage in 24 hr. It was shown that the isotherm for adsorption of colour from POME on CBA-HCl was well fitted by Freundlich equation (correlation coefficient, R2 = 0.9636). Based on the results, CBA showed potential adsorbent candidate for POME decolourization

Physico-chemical characterizations of sawdust-derived biochar as potential solid fuels

Characterization Malaysian rubber-wood sawdust derived biochar (MRWSB) produced in the fixed bed pyrolysis under different temperatures (450 to 850°C) were studied for its applicability as a solid fuel. A range of analyses were carried out, including biochar oxidation reactivity , inorganic species, oxygen and hydrogen contents in the biochars, release of heteroatoms in biochar as the gaseous product, and biochar structural evolution during pyrolysis process. The results show that the optimum temperature for carbonization to obtain a char having moderately high yield was found as 450 °C. Thermogravimetric analyses (TG) shows that temperatures induces a progressively more ordered carbonaceous structure and leads to a significant changes in the biochar reactivity. The process is coupled with the loss of heteroatoms, released as dominantly carbon dioxide (C02) and carbon dioxide (CO). In addition, the elemental study of wood-derived biochar shows the higher carbon content but with low H/C and 0/C ratio suggested this material was dominated by highly aromatic structures and this were revealed in the Fourier transform infra-red (FTIR). More importantly, insignificant amount of inorganic species is evidenced in the samples

Co-combustion of refuse derived fuel with coal in a fluidised bed combustor

Power generation from biomass is an attractive technology which utilizes municipal solid waste-based refused derived fuel. In order to explain the behavior of biomass-fired fluidized bed incinerator, biomass sources from refuse derived fuel was co-fired with coal in a 0.15 m diameter and 2.3 m high fluidized bed combustor. The combustion efficiency and carbon monoxide emissions were studied and compared with those from pure coal combustion. This study proved that the blending effect had increased the carbon combustion efficiency up to 12% as compared to single MSW-based RDF. Carbon monoxide levels fluctuated between 200-1600 ppm were observed when coal is added. It is evident from this research that efficient co-firing of biomass with coal can be achieved with minimum modification of existing coal-fired boilers

The effect of ultrasonic energy on the enhancement of the biodegradability of food waste

In this study, the effect of ultrasonic pretreatment on the physicochemical property changes and methane production potential of anaerobic digestion of food waste was investigated. The study, involving a laboratory experimentation by sonicating 200 mL of food waste sample, was investigated at different sonication times (2, 4, 6, 8, 10 min), and the specific energy input ranged from 5,396 to 25,997 kJ/kg total solid. The experimental results found that the mean particle size diameter (d50) of the ultrasonically treated food waste decreased from 59 to 21.9 μm with the specific surface area increasing from 0.523 to 1.2 μm2/g. This is evidenced in the food waste morphological structure changes from particles or granules varying in size and shape from small to large and round to oval or unsymmetrical shaped when the food waste samples were sonicated in the range of 2–10 min as shown by scanning electron microscopy. The value of soluble chemical oxygen demand was increased about 34–40% while the degree of disintegration was recorded as 57.15, 61.10, 71.08, 68.94, and 68.68%, respectively. The CODsolubilization was achieved around 11.4, 11.8, 13.4, 12.7, and 13.2%, when the food waste sample was sonicated at 2, 4, 6, 8, and 10 min, respectively. This CODsolubilization correlated well with DD when the linear relationship was shown by R2 = 0.945. The result shows that the use of sonicated food waste in the anaerobic digestion process has increased about 45.9, 40.3, 46.6, 64.4, and 70.5% of cumulative CH4 production rates in the food waste sample sonicated at 2, 4, 6, 8, and 10 min, respectively, when compared to the non-sonicated food waste sample

Co-combustion of agricultural residues with coal in a fluidised bed combustor

Power generation from biomass is an attractive technology that utilizes agricultural residual waste. In order to explain the behavior of biomass-fired fluidised bed incinerator, biomass sources from agricultural residues (rice husk and palm kernel) were co-fired with coal in a 0.15 m diameter and 2.3 m high fluidised bed combustor. The combustion efficiency and carbon monoxide emissions were studied and compared with those for pure coal combustion. Co-combustion of a mixture of biomass with coal in a fluidised bed combustor designed for coal combustion increased combustion efficiency up to 20% depending upon excess air levels. Observed carbon monoxide levels fluctuated between 200 and 900 ppm with the addition of coal. It is evident from this research that efficient co-firing of biomass with coal can be achieved with minimal modifications to existing coal-fired boilers

Anaerobic batch digestion of cattle manure under various oscillatory flow mixing

The feasibility of an anaerobic digestion of cattle manure for biogas production is studied in this paper. A batch thermophilic oscillatory flow anaerobic bioreactor (OFBR) operated in thermophilic (55oC) condition was used. Within the experimental conditions set in this study, the effect of mixing intensity on volatile solids removal was found out to be significant. Results demonstrated that increasing the level of mixing decreased the digester performance. Low intensity mixing at oscillatory Reynolds number (Reo) of 100 achieved an increase of 37% in biogas yields compared to high mixing intensity, Reo of 500. It was observed that the mixing intensity effect interacts with the methane composition in the biogas. The benefit of decreasing mixing intensity emerges to significantly increase the methane composition in the biogas. These experiments established that high intensity mixing was not essential for good performance of oscillatory flow anaerobic bioreactor. In addition, the effect of mixing intensity might be reduced through the use of a slightly lower total solid concentration, hence, lowering the operational cost of the process. Although the study was lab scale a pilot-scale system where mixing retention times are longer would be useful