FUNDAMENTAL STUDIES OF DRYING, COMBUSTION, AND ASH PROPERTIES OF BIOMASS AND IMPACTS ON BOILER AND PULP AND PAPER MILL OPERATIONS
PROJECT 1: COMBUSTION AND ASH BEHAVIOURS
A biomass boiler in pulp and paper mills typically converts about 75% of the combustion heat of its feedstock into steam and power. The thermal conversion efficiency of the boiler depends greatly on the moisture content, ash content and ash properties of the biomass, and on the design and operating conditions of the boiler. Modern bubbling fluidized bed (BFB) boilers are generally more efficient and less susceptible to moisture variations than older stoker grate (SG) boilers. For a given boiler, the boiler efficiency is dictated mainly by the moisture content and the combustion behaviour of the feedstock, and the amount and thermal properties of the ash. Understanding the combustion and ash behaviours of the feedstock is of vital importance for predicting the combustion efficiency and for evaluating the impact of ash on biomass boiler operations.
- To characterize feedstock, ash, and deposits from biomass boilers
- To determine factors affecting bed agglomeration in bubbling fluidized bed boilers
- To determine factors affecting clinker formation in stoker grate boilers
- To characterize in-situ real-time fly ash particles
- To determine the effects of feedstock size, size distribution, and moisture content on combustion
PROJECT 2: DEWATERING AND DRYING BEHAVIOURS OF BIOSLUDGE
Most kraft pulp mills use aerobic treatment systems such as the activated sludge process to treat their final mill effluent. Although such systems are highly effective at reducing biochemical oxygen demand in downstream effluent decomposition, they also generate between 10 to 70 kg dry weight of biosolids (biosludge) per air dried tonne of pulp that require disposal. While landfilling has been a common method of disposal, there are increasing incentives to reduce landfill costs and greenhouse gas emissions and to recover energy from the biosludge by co-firing it with hog-fuel in biomass boilers. Effective removal of water from biosludge prior to incineration is key to improving biomass boiler performance. The overall goal of this project is to enhance our understanding of the biosludge dewatering process in the context of biomass combustion and examine strategies to improve the economics of biosludge combustion.
- To determine the effects of primary sludge addition on biosludge dewatering
- To determine methods of biosludge pretreatment for improved dewaterining
- To investigate anaerobic digestion for improved dewatering
PROJECT 3: DEPOSIT FORMATION AND REMOVAL
The thermal efficiency of biomass boilers is influenced greatly by the amount of fly ash that builds up on boiler wall tubes, superheater tubes and generating bank tubes where high flue gas temperatures prevail. Understanding how fly ash particles may deposit on tube surfaces and how such deposits may withstand the bombardment of high pressure sootblower jets to keep building up is important for devising viable deposit control strategies.
- To investigate the sticky temperature of fly ash
- To investigate deposit strength and tenacity
- To investigate the interaction between sootblower jets and boiler tube geometrics
- To conduct experiments and modeling of deposit breakup
- To investigate the electrical resistivity of fly ash
- To determine the fates of Zn Compounds in biomass boilers
- To determine the effects of burning non-condensable gases on ash chemistry
PROJECT 4: ASH UTILIZATION AND DISPOSAL
The solubility of important nutrients and potentially deleterious metals and salts is key to predicting ash behaviour in the environment or to intentionally modifying ash prior to use or disposal. Although the vast majority of biomass boiler ashes are presently landfilled in Canada, there is substantial potential to utilize ash waste from wood biomass boilers to improve the fertility of managed forest soils, while simultaneously diverting a costly waste stream from landfills, and herein lies the partners’ economic and environmental rationale for supporting this portion of the research program. However, key questions remain unanswered related to ash chemical and physical properties as influenced by feedstock and industrial operations and their subsequent dynamics across different forest soil/ecosystem types.
- To characterize ash constituents and ash leachability
- To investigate the utilization of ash as a soil amendment