PES received a design, supply, supervise and startup contract in 2016 for a complete biomass energy system incorporating its Fluid Bed Combustion System. It designed the system to supply the necessary energy in the form of hot gas to dry the 60 per cent + MC wet basis sludge to 40 per cent MC wet basis with the majority of the energy produced from the sludge used to generate process steam. The combined energy is produced from a single PES system without the use of natural gas. Natural gas is only used for startup of the system to obtain the required temperature for sludge feeding.
Producing process steam from the sludge-waste residuals, or biomass, promotes the plant’s green energy independence and the company’s green recycling plan by reducing the volume of waste sent to landfills.
PES designed the complete system and supplied all system equipment, including: the wet and dry sludge storage bins, the wet sludge feed system to the dryer, a single pass rotary drum dryer, the dry sludge collection and storage bin, the dry sludge fuel metering and conveyance system, the PES Fluidized Bed Combustion System with automatic ash cleaning system, a 35,000 PPH, 250 psig waste heat boiler specially designed by PES to allow removal of the high ash quantities generated from the fuel, the boiler economizer and air heater, gas cleaning system and ash collection and storage silo.
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The majority of the system was designed to fit into the plant’s existing infrastructure, allowing the majority of the equipment — including the boiler system — to be inside the existing building with only the dryer, baghouse and ash silo outside of the building. A small portion of the building roof was removed to install the boiler system, although the height of equipment required a penthouse to be installed over the boiler.
The PES system receives and processes the incoming sludge, and combusts the sludge leaving only an ash that is white in colour with no carbon residual. This ash, according to PES, is collected from nine points throughout the boiler, economizer, air heater, multiclones and baghouse and is conveyed pneumatically to an ash silo. The ash system was designed and supplied by PES to have no rotary valves, which are a constant maintenance issue on biomass boilers. The sealed ash system conveys all of the fly ash to a sealed ash silo for unloading into sealed trailers, which PES says will help ensure the complete boiler system is sealed from the point the fuel is pneumatically conveyed into the fluid bed combustor.
The ash is held in the ash silo for pick up by a nearby cement plant where it is utilized as an admixture to the concrete manufactured by the plant. The beneficial utilization of the ash from the sludge is a major advantage to the plant as there is not a requirement for ash landfilling, says PES.
Specifically, the ash produced by the boiler system has very similar properties to Kaolin clay, a feedstock which accounts for approximately 40 per cent of cement’s composition. The sludge ash can be added (substituted) at approximately 5 per cent by weight, and actually, improves the final concrete performance. If the ash were to be used in a Ready-Mix plant, it could be used to directly substitute cement, but the sludge ash would require grinding to a consistent, fine particle size. PES has successfully designed and implemented ash-grinding equipment in other energy systems to increase the marketability of the ash.
In 2011, PES supplied the sludge-to-energy system to Atlantic Packaging’s 111 Progress Ave, Toronto, Ont., location, which replaced a combustion technology that was unable to reliably burn the wet paper mill sludge.
“We are excited to announce that our client’s second sludge-to-energy plant was completed in early 2017. Our client will see a sufficient reduction in the plant’s overall waste disposal cost as well as a major reduction of their energy cost by the savings obtained in burning the biomass fuel to produce steam, offsetting the use of natural gas,” said Mike Oswald, president of PES.
Atlantic Packaging owns and operates three paper facilities in the greater Toronto area.