On the Rice Track

Assessments conducted by COGEN Asian Institute of Technology show that the aggregate power generation potential from biomass fuels in Thailand is around 3000 MW. Private company A.T. Biopower is one company developing biomass plants under Thailand’s SPP programme.

The environmental benefits of using biomass fuels for power generation include neutrality in greenhouse gas emissions, reduction of NOx and SOx emissions, and elimination of unwanted solid wastes.

Like many countries in Asia, Thailand has many agricultural and forest resources which provide potential sources for biomass fuel. The government, through its National Energy Policy Office (NEPO) acknowledges the importance of promoting the use of renewable energy. Accordingly, NEPO has earmarked Baht2 billion ($45.5 million) to support private investments of up to 300 MW of power purchase from small power producers (SPPs) using renewable energy. So far, 59 SPP projects with a combined capacity of 2283 MW have signed contracts with the Electricity Generating Authority of Thailand (Egat). Nearly half of these, with a generating capacity of 220 MW, will be renewable energy projects (see Table 1).

Thailand has many agricultural and forest resources
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A.T. Biopower, a private Thai power producer, is developing four rice husk-fuelled power plants under Thailand’s SPP programme to supply Egat with power under a 25-year power purchase agreement. The aggregate generating capacity of the four plants will roughly be 90 MW. These four power plants will be located in provinces within central Thailand, roughly 80 km away from each other near rice mills at Pichit, Nakhon Sawan, Singburi, and Nakhon Pathom.

The reason behind the plants’ location and size has a lot to do with transport facilities. Jackrit Watanatada, assistant to the CEO at A.T., Thailand said: “Central Thailand, also known as the Central Plains or the ‘Rice Bowl’, is a relatively large area. Large enough to make transport distances an important consideration with regards to the projects’ economics, and the security of its fuel supply. The plants are strategically sited in the area to keep transport distances short and their supply reliable.” He adds: “In terms of the projects’ overall economics, a ‘portfolio concept’ of multiple, identical plants takes advantage of economies of scale for plant equipment to improve competitiveness.” The plants will also produce saleable rice husk ash for the construction industry.

The sub profits gained will aid the overall financing of the project as well as lessen the burden of having an additional disposable problem, which will involve a mixture of cash and bank loans. Dr. Thawat Watanatada, CEO of A.T. Biopower, said: “The whole project will cost around $30 million and will be financed through a mixture of equity and debt.” Although Watanatada would not specify financial details of the deal due to its sensitivity, he hinted that a debt to equity ratio of around 50-50 would not be unreasonable with the three to four Thai banks that are likely to be involved in the ten-year tenor.

Low sulphur

The four steam cycle thermal power plants will use a stoker-fired or suspension-fired boiler to produce steam at around 65 bar and 440-485à‚°C which is fed into a steam turbine generator to generate approximately 22 MW each in gross capacity. Rice husk will be stored inside a storage house on a short-term basis or outdoors for longer. Suitable equipment will transfer rice husk from the house to a one-hour service silo. It will then be delivered to the boiler combustion chamber.

One major characteristic of rice husk is its very low sulphur content. Therefore, emissions of SO2 will be very low, well below standard emissions for fossil fuel fired power plants. In order to meet the emission standard for particulates, the flue gas will be purified by a bag house or an electrostatic precipitator (ESP) before being sent to the stack. The fly ash which travels with the flue gas is collected at the electrostatic precipitator or a bag house and fed into fly ash silo. The bottom ash will be dissipated using a screw conveyor and fed into a bottom ash silo. The ash will be conditioned for sale.

Flow diagram of rice husk and ash handling system for stoker-fired boiler
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A closed cooling water system will be used for steam condenser and heat will be dissipated via a cooling tower, supplied from a local reservoir. The flue gas emissions from the stack will be monitored by a continious emission monitoring system. For solid and liquid wastes, rice husk ash will be stored in the silo before packing. The cooling water will be treated to secure a zero waste water discharge.

Plentiful fuel

A.T. Biopower has already signed a long-term take-or-pay rice husk supply contract with the local rice millers. More than 100 rice millers are involved in the fuel supply contracts. Transport agreements with trucking companies are also arranged. Each power plant requires approximately 21 t/h of rice husk.

The cost of rice husk, including transportation, can be estimated at Baht300-500/t. Jackrit said: “Rice husk is a fuel that is in plentiful supply in Thailand. Rice husk, a high volume and low density biomass fuel, is produced in large quantities by the rice milling process. Much of it goes unused, largely dumped and burned in the open.” He adds, “What A.T. Biopower aims to do is to put a large amount of the rice husk to good use, harness the technology’s maturity, and find a way to put it all together economically and competitively. Indeed, at the moment, the electricity generated from a biomass plant is not the cheapest around, but it’s important to show that this situation will change.”

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SPP regulations allow the use of commercial fuels such as oil, natural gas and coal as supplementary fuels, if thermal energy produced by such supplementary fuels each year does not exceed 25 per cent of the total thermal energy used in generation in that year.

Professional sponsors

Flagship Asia Corporation, a project development and finance company, is a principal sponsor of the project along with E&Co, a US-based non-profit energy investment service, and Al Tayyar Energy, a sustainable energy project development and investment company based in Abu Dhabi. The company has been working closely with A.T. Biopower on all management and technical aspects of the project, especially power plant conceptual design, technical specifications, and EPC and operation and management (O&M) bid evaluation.

The project participants consist of many professional and experienced organizations covering all power aspects. Energy House Capital Corporation serves as lead financial advisor. Egat’s Engineering Business Unit is responsible for basic engineering, drafting EPC and O&M tender documents, and preparing applications for power sale permits with Egat. COGEN Asian Institute of Technology is a consultant reviewing the feasibility study report and power plant conceptual design, potential contractors and suppliers. Clean Technology, a Thai environmental engineering and construction company, is carrying out environmental impact assessments for each plant.

Emission mitigation

The socio-economic benefits of the project include contribution to the income of local communities and creation of local job opportunities. A paddy drying service to local rice farmers will enable them to receive a better price for their crop. Without the implementation of the project, the power would come from the Thai grid, where electricity generation has a given fuel mix and certain power plant technology, which changes from year to year. The rice husk supposed to be used in the plants would either be dumped or burned in the open. This would result in CO, CO2, CH4 and other emissions. The greenhouse gas (GHG) emissions of 80 MW from the Thai grid mix, plus the estimated GHG emissions from open burning of rice husks, equivalent to four power plants during 2003-2011. Therefore, the A.T. Biopower plants have a total

GHG emission mitigation potential of approximately 448 000 t of CO2 annually.

Most of the rice husk is currently disposed of through burning, either in rice mills using old incinerators or boilers, or out in the open space, resulting in high emissions, especially particulates. This is much greater than burning rice husk in the power plants, where electrostatic precipitators/bag houses and carefully designed combustion will result in a minimum of particulate and other emissions. A monitoring programme will check air quality for SO2 on an annual and quarterly basis, and water quality on a semi-annual basis. Waste water, including water blowdown, is prohibited from leaving the the plant. Rather waste water will first be treated to national standards as required and then either used for plant watering or evaporated in a pond.

For every used ton of rice husk ash as a partial substitute or additive to Portland cement, a further ton of CO2 will be prevented from being released into the atmosphere. The concrete also lasts significantly longer, reducing the need to manufacture new concrete. The World Bank’s Worldwide Environmental Facility estimates that two per cent of global CO2 emissions arise from the manufacture of cement.

Byproduct sale

Thailand offers a huge potential to implement power plants using biomass as fuel. The aggregate power generation potential from biomass residues in Thailand is around 3000 MW.

The design of the four 22 MW rice husk-fuelled power plants will integrate features to produce saleable rice husk ash for the cement and steel industries and, possibly, steam for paddy drying services. The benefits from the implementation are, among others, a contribution to a higher income of the local communities, the reduction of dependence on increasingly expensive imported fossil fuels, and the implementation of further biomass power generation in Thailand.


“Thailand SPP programme case study: A. T. Biopower’s rice husk fuelled power plant” by Ludovic Lacrosse, Alan Dale Gonzales, Komkrit Chuawittayawuth; COGEN, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand, presented at POWER-GEN Asia, Kuala Lumpur, Malaysia, 2001.

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