• Energy Research

Abstract Oxygen enriched combustion of coal under different oxidant concentrations and staging levels has been performed in a 20 kW down fired pilot scale combustion test facility. The introduction of oxygen resulted in additional reduction of NO emissions as compared to simple air staged configuration. In comparison to air staged combustion, oxygen enriched air staged combustion at the 31% level of staging resulted in approximately 7%, 20% and 35% NO reduction for 28%, 30% and 35% overall oxygen concentration, respectively. Experimental evidence has also indicated that oxygen enrichment does appear to reduce NO levels along with improvement of carbon burnouts. The provision of oxygen has also resulted in operation of the test facility under lowered stoichiometric ratios. The advantages attributable to oxygen enriched combustion also included enrichment of CO2 concentration in the flue gas to reduce the cost of CO2 scrubbing and capture. The present work provides data associated to oxygen enriched combustion technology, which can be considered a compromise between conventional air-firing combustion and the emerging oxy-fuel combustion systems.

Abstract Oxygen enriched combustion of coal under different oxidant concentrations and staging levels has been performed in a 20 kW down fired pilot scale combustion test facility. The introduction of oxygen resulted in additional reduction of NO emissions as compared to simple air staged configuration. In comparison to air staged combustion, oxygen enriched air staged combustion at the 31% level of staging resulted in approximately 7%, 20% and 35% NO reduction for 28%, 30% and 35% overall oxygen concentration, respectively. Experimental evidence has also indicated that oxygen enrichment does appear to reduce NO levels along with improvement of carbon burnouts. The provision of oxygen has also resulted in operation of the test facility under lowered stoichiometric ratios. The advantages attributable to oxygen enriched combustion also included enrichment of CO2 concentration in the flue gas to reduce the cost of CO2 scrubbing and capture. The present work provides data associated to oxygen enriched combustion technology, which can be considered a compromise between conventional air-firing combustion and the emerging oxy-fuel combustion systems.

Bubbling fluidized bed combustion of biomass has benefits of fuel flexibility, high combustion efficiency, and lower emissions. Bed agglomeration is where bed particles adhere together with alkali silicate melts and can lead to unscheduled plant shutdown. This pilot-scale study investigates performance and agglomeration when varying fuel (white wood, oat hull waste, miscanthus, wheat straw), bed height, bed material, and includes a novel spatial analysis of agglomerates from different bed locations. White wood was the best performing fuel and did not undergo bed defluidization due to its low ash content (0.5% mass as received), whereas wheat straw (6.67% mass as received ash) performed worst (defluidization times <25 min). Olivine was a superior bed material to silica sand, with 25%+ longer defluidization times with the worst performing fuel (wheat straw). Calcium-rich layers formed at olivine particle surfaces within wheat straw ash melts, and capillary action drew potassium silicate melt fractions into olivine particle fractures. An analysis of agglomerate samples from different bed spatial locations following tests with oat hull waste showed that ash layers on agglomerates retrieved further from the landing point of fuel onto the bed had reduced potassium and elevated calcium, likely due to reduced availability of fresh fuel ash for reaction with bed material.

Bubbling fluidized bed combustion of biomass has benefits of fuel flexibility, high combustion efficiency, and lower emissions. Bed agglomeration is where bed particles adhere together with alkali silicate melts and can lead to unscheduled plant shutdown. This pilot-scale study investigates performance and agglomeration when varying fuel (white wood, oat hull waste, miscanthus, wheat straw), bed height, bed material, and includes a novel spatial analysis of agglomerates from different bed locations. White wood was the best performing fuel and did not undergo bed defluidization due to its low ash content (0.5% mass as received), whereas wheat straw (6.67% mass as received ash) performed worst (defluidization times <25 min). Olivine was a superior bed material to silica sand, with 25%+ longer defluidization times with the worst performing fuel (wheat straw). Calcium-rich layers formed at olivine particle surfaces within wheat straw ash melts, and capillary action drew potassium silicate melt fractions into olivine particle fractures. An analysis of agglomerate samples from different bed spatial locations following tests with oat hull waste showed that ash layers on agglomerates retrieved further from the landing point of fuel onto the bed had reduced potassium and elevated calcium, likely due to reduced availability of fresh fuel ash for reaction with bed material.

The influence of iron-, aluminum-, and silicon-based oxides (fuel improver) toward coal combustion was investigated in a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrophotometer, temperature-controlled two-stage bench reactor (TSBR), and 100 kWth combustion test facility (CTF). The metallic oxides, 5, 15, and 33% by weight, to prepare overall 20 mg of sample blends were mixed with pulverized coal for the TGA–FTIR study. The individual unblended samples of fuel improver and coal were also analyzed separately. The analysis of fuel improver samples revealed no evidence of hydrocarbon release or weight change; however, substantial changes in the weight as well as the release of hydrocarbons (HCs) and CO were observed for coal. More importantly, the study of the combustion data shows a distinct change in the peak intensities for CO and HCs, especially when the coal sample was blended with 5, 15, and 33% (by weight) of fuel improvers. This suggests enhanced cracking of...

The influence of iron-, aluminum-, and silicon-based oxides (fuel improver) toward coal combustion was investigated in a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrophotometer, temperature-controlled two-stage bench reactor (TSBR), and 100 kWth combustion test facility (CTF). The metallic oxides, 5, 15, and 33% by weight, to prepare overall 20 mg of sample blends were mixed with pulverized coal for the TGA–FTIR study. The individual unblended samples of fuel improver and coal were also analyzed separately. The analysis of fuel improver samples revealed no evidence of hydrocarbon release or weight change; however, substantial changes in the weight as well as the release of hydrocarbons (HCs) and CO were observed for coal. More importantly, the study of the combustion data shows a distinct change in the peak intensities for CO and HCs, especially when the coal sample was blended with 5, 15, and 33% (by weight) of fuel improvers. This suggests enhanced cracking of...

Fe-based additives can be used to improve coal combustion and reduce NOx emissions; further to this, iron oxide (Fe2O3) has been found to interact with ammonia. Therefore, it is critically imperative to understand and assess the impact of the Fe-based additive on the use of ammonia based selective non-catalytic reduction (SNCR) and to evaluate the economic feasibility of such a combination for full-scale use. Experiments were performed using a 100 kWth down fired-combustion test facility burning pulverised coal over three Fe-based additive concentrations, while the ammonia input was varied between normalised stoichiometric ratios 0-3. This study finds evidence of an interaction between the Fe-based additive and SNCR. The interaction leads to greater ammonia utilisation and an increased NOx reduction due to the SNCR of >10%. The interaction is theorised to be pseudo-catalytic with the fuel additive providing an active site for ammonia to reduce NO. Using Carnegie Mellon University’s ‘Integrated Environmental Control Model’ (IECM), this has been shown to create an economically viable opportunity to increase SNCR effectiveness.

Fe-based additives can be used to improve coal combustion and reduce NOx emissions; further to this, iron oxide (Fe2O3) has been found to interact with ammonia. Therefore, it is critically imperative to understand and assess the impact of the Fe-based additive on the use of ammonia based selective non-catalytic reduction (SNCR) and to evaluate the economic feasibility of such a combination for full-scale use. Experiments were performed using a 100 kWth down fired-combustion test facility burning pulverised coal over three Fe-based additive concentrations, while the ammonia input was varied between normalised stoichiometric ratios 0-3. This study finds evidence of an interaction between the Fe-based additive and SNCR. The interaction leads to greater ammonia utilisation and an increased NOx reduction due to the SNCR of >10%. The interaction is theorised to be pseudo-catalytic with the fuel additive providing an active site for ammonia to reduce NO. Using Carnegie Mellon University’s ‘Integrated Environmental Control Model’ (IECM), this has been shown to create an economically viable opportunity to increase SNCR effectiveness.

A new inclined plates extractor-separator is developed for operation with immiscible liquids in which extraction and separation is achieved in one unit contrary to mixer settlers. The inclined plates extractor-separator combines turbulent jets for contacting, and an inclined plate for separation of the two phases. The inclined plates extractor-separator does not have any moving part inside the vessel. This feature makes it free from the mechanical problems associated with conventional apparatus. The proposed inclined plates extractor-separator was operated in batch mode under various operating conditions to evaluate its performance on the basis of extraction efficiency. Water (light phase) was used as solvent to extract ethyl acetate from a heavy phase pool of tetrachloroethylene and ethyl acetate. The ethyl acetate content was analysed using chromatography. A hydrodynamic study was carried out using high speed photography to understand the mechanisms occurring during mass transfer across the two phases. Furthermore, it was found that the proposed inclined plate extractor-separator reduces the overall operating time by 67% and consumes only 13% of the power in comparison to a mixer-settler. A hydraulic power consumption comparison with a mixer settler and a gullwing extractor-separator is also presented.