Refuse-Derived Fuel Processing Operations
This integrated RDF power plant sits on a 28-acre plot designated for MSW handling by the Malaysian government. Local authorities in the Kajang municipality have contracted to deliver 700 tons of unsegregated MSW daily and are charged a tipping fee currently at RM 46 per ton (US$13). The waste consists of a large percentage of organics (putriciables) with a high moisture content, about 15% mixed plastics, and other items. The RDF plant is tailored to process this waste for extraction of recyclable plastics and metals present in it and for maximum production of RDF for energy recovery.
“The pre-processing of waste enables recovery of recyclables like plastics, metals, etc. and segregation of wet organics, enabling the further digestion process to release methane-rich biogas for firing in the boiler to enhance power generation, thus maximizing the extraction of energy from the waste,” according to K.S. Sivaprasad, director and technical advisor at the facility.
Commingled waste is brought by trucks, weighed, and received in a waste-receiving pit. The pit is sized to hold one and half days’ stock and needs to be increased to three days’ stock, according to Sivaprasad. The whole receiving area is canopied and sprayed with an enzyme to deodorize the air. Additionally, the air over the pit is constantly evacuated, allowing the ingress of fresh air. Grab cranes over the pit are used to mix waste coming from different areas to get a measure of uniform composition before feeding the waste to the plant. Bulky items are removed at this stage.
Each of four identical processing lines has the capacity to process 12 tons per hour. The RDF plant operates for 16 hours a day, producing enough fuel for 24-hour operation of the power plant. The remaining eight hours are used for a thorough cleanup, which is essential to ensure reliable operation of the plant. Leachate from the receiving pit and wash water from the process plant are treated by the in-house effluent treatment plant, and the water is recycled for use in the plant (Figure 1).
|1. Leachate treatment. Leachate from the receiving pit and wash water from the process plant are treated by the in-house effluent treatment plant, and the water is recycled for use in the plant. Courtesy: Core Competencies Sdn Bhd |
Waste generated in this part of the world is characterized by high moisture and organics contents and low calorific value, which is increased by eliminating noncombustibles and reducing moisture in the RDF process. Waste size is controlled to form a homogenous fuel to achieve uniform combustion on the boiler grate.
The calorific value of raw MSW averages around 1,200 to 1,400 kCal/kg (2,160 to 2,520 Btu/lb). Moisture content is reduced from 52% to 60% in the raw MSW to 25% in RDF. As a result of the various pretreatments, the calorific value of RDF is around 4,000 to 4,500 kCal/kg, and roughly 28% to 32% of the original MSW ends up as fuel. This fuel is suitable for controlled combustion rather than MSW incineration, thus enabling strict pollution control. The ash content of RDF is around 10%.
The wet organics segregated in the first stage of processing have power-generating potential as well. In the next phase of the project, power generation will be enhanced by burning biogas derived from anaerobic digestion.