Owner/operator: Core Competencies Sdn Bhd/Recycle Energy Sdn Bhd
At Malaysia’s first waste-to-energy plant, municipal solid waste (MSW) is converted into refuse-derived fuel for use in an integrated steam power plant. This facility was designed to achieve the twin objectives of environmentally friendly MSW disposal and generating renewable power.
Malaysia is a multicultural smorgasbord of Malay, Chinese, Indian, and British influences. This fusion of different cultures has helped to promote an entrepreneurial economy that embraces modern development. To meet the electrical needs of this dynamic country, the private sector is turning to new generation technologies. Commissioned in 2009, Kajang Waste-to-Energy Plant, which is located approximately 13 miles from the national capital Kuala Lumpur, is an example of such innovation.
The waste-to-energy (WTE) facility consists of the refuse-derived fuel (RDF) plant, which prepares the fuel, and the steam power plant. The facility has the capacity to process approximately 1,100 U.S. tons of municipal solid waste (MSW) per day into RDF in fluff form and then use that fuel to produce approximately 8 MW of electricity daily. Electricity produced powers the RDF plant, and the remainder is sold to the national power grid.
Malaysian Electric Power Industry
Malaysia has a population of 25,715,819 (July 2010 estimates) and is considered to be a middle-income country. Since the 1970s, it has transformed itself from a producer of raw materials into an emerging multi-sector economy, which includes high technology industries, medical technology, and pharmaceutical manufacturing, according to the U.S. Central Intelligence Agency’s (CIA) World Factbook. According to the CIA’s research, estimates of 2007 electrical production and consumption in Malaysia were approximately 103.2 billion kWh and 99.25 billion kWh. Recent statistics also show that Malaysia annually exports approximately 2.268 billion kWh (2007 estimates).
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.
Overview of the Power Plant
The power plant consists of a single 8.9-MW extraction condensing turbine generator set and a steam generator of 55 tons maximum continuous rating, designed to combust the RDF. The turbine is equipped with a water-cooled condenser and a fan-mounted induced draft cooling tower.
The boiler is equipped with rotary feeders and pneumatic spreaders for feeding the RDF into the furnace. Fuel is partially burned in suspension and then on the chain grate stocker. The furnace has a single-pass radiation heat transfer zone with gooseneck arches at the secondary combustion zone and the inlet to the superheater.
Fuel on the grate with 70% volatiles burning with primary air in a reduction zone at a temperature of less than 650C (1,200F) releases the volatiles, which move up to the secondary combustion zone for complete combustion with minimum formation of nitrogen oxides. The solids burn on the grate. The wind box supplying primary air is compartmentalized along the length of the grate with individual dampers to enable effective control of fuel combustion on the grate.
In the secondary combustion zone, the volatiles and lighter elements of fuel that float when injected by the spreaders are subjected to the turbulent secondary air jets, and combustion takes place. With 30% excess air in this oxidizing zone, complete combustion is ensured.
The flue gas passes through a mechanical dust collector for removing fly ash and a wet scrubber for neutralizing acid gases. An activated carbon injection system is used for adsorbing remnant contaminants such as heavy metals and dioxins, which are trapped in a bag filter and then sent to a government-approved hazardous waste treatment plant.
The boiler operates at around 46 tons per hour (tph) load, delivers 38 tons of steam to the turbine and 8 tons to the process plant at medium pressure (338 pounds per square inch absolute pressure) through a pressure-reducing valve for hot air generation in the waste-drying system by secondary heat exchanger. The turbine operates at 8 MW load and 8 tph extraction. After meeting the captive power demand of 3 MW for the process plant and power plant auxiliaries, 5 MW are exported to the national utility grid. The extraction steam meets the demand of the deaerator and the process plant’s primary heat exchanger for hot air generation in the waste-drying system. The condensate of both heaters is returned to the power plant and joins the water loop.
“Good combustion has been achieved, resulting in very low unburned carbon in bottom ash and fly ash,” Sivaprasad said. “Emission levels achieved for all contaminants, including heavy metals and dioxin, have met internationally prescribed standards, which indicates that the pollution abatement system is functioning well.”
Redundant capacity has been built into each segment of the unit: the fuel preparation plant, the steam generation plant, and the power generation plant. Once the whole unit attains steady state operation, efforts will be made to increase the export of power from 5 MW to about 6 MW, according to Sivaprasad.
The facility’s twin goals of environmentally friendly disposal of MSW and maximum extraction of energy have been achieved to a large extent. Currently, 77% of dormant energy in the waste is recovered in the fuel. By adding the use of biogas released from wet organics, recovery will increase to 83%, because only 17% of the energy will be used in the conversion of waste into fuel.
Malaysia generates about 17,000 tons of MSW per day, which has a net power potential of 150 MW if RDF and biogas firing in boilers are used. The Core Competencies management hopes this new WTE facility will be the forerunner for large-scale adoption of this technology. The Malaysian government has already awarded one more project to handle 1,000 tons per day of MSW; that project is located in Johar province in the southern tip of peninsular Malaysia.
This $50 million venture was set up by private initiative. The three revenue streams from this operation are:
- Tipping fees charged at the beginning of the process.
- The sale of by-products such as plastics, metals, and organics for composting at the intermediate stage.
- The sale of electricity at the end of the process.
These different revenue sources ensure the viability of the operations.
“Encouraged by the successful operation of this venture, the national government here is actively considering adopting this technology on a large scale,” Sivaprasad said. “This is one way of meeting the commitments that national governments have made for mitigation in the realm of climate change”
— Angela Neville, JD, is senior editor of POWER.