V. P. Tormala, Senior Advisor to BMP Ltd.,Fortum Engineering, Finland
In the Thai province of Chai Nat, a dense network of irrigation channels cut the plains which give a generous three and a half harvests per year. Amid this rich rice-producing region, a rice husk-burning power plant is in its commissioning phase.
The power plant project was originally started in late 1996 but stalled when the Asian financial crisis hit. After standing idle for over two years, work has once again begun to complete the project, which is located around 200 km north of Bangkok.
The power plant is one of the first private small scale base load power plants with a firm 25-year electric power supply contract with the Electricity Generating Authority of Thailand (EGAT). The power purchase agreement (PPA) was signed on 22 October 1996, and originally the company was to commence the sale of 5 MW of electricity at 22 kV in February 1998.
The owner of the power plant is the BioMass Power Company Limited (BMP), a Thai-owned company which is aiming to build several comparable biomass fuelled power plants in Thailand. It was founded by a small group of people with considerable experience in the petrochemical and power industries.
Signs of recovery
BMP started to build the power plant in October 1996 with equipment mainly of Chinese manufacturing, but the construction was halted one year later when the plant was 75 per cent complete, when the funding problems arose due to the Asian economic crisis and the sharp decline in the Thai Baht.
Using the rice husks will help to keep carbon dioxide emissions low and reduce emissions of methane, a powerful greenhouse gas
The project has been moving slowly for the last two and a half years, but a contract for completing remaining installation and erection activities of the biomass power plant was signed on 17 April 2000, signalling a recovery in Thailand’s economy. The contract was awarded to S.T. Fortum Engineering, Thailand, which then signed Fortum Engineering of Finland for support and project expertise. The contract includes commissioning and test runs of the power plant, and the start of
commercial operation within the planned scheduleby the end of September 2000 is essential due to financial reimbursement for the contract.
BMP and the operating personnel service company Epcom will together continue the project implementation.
Since the project is in line with the target of decentralized power production, the promotion of prosperity in rural areas and the exploitation of renewable resources, it clearly is in harmony with the principle of sustainable development.
Renewables and SPPs
Today renewable energy accounts for an estimated 26 per cent of Thailand’s total energy consumption. The vast majority of this demand comes from the use of wood for domestic uses such as cooking. About Baht6 billion ($153.5 million) of the country’s newly approved Baht30 billion national conservation programme is appointed for the promotion of renewable energy. The government’s goal is to triple the production of renewable energy from one per cent to three per cent of total power production within the next five years. Total electric generating capacity was 17 500 MWe 1998.
The BMP biomass project was rendered possible under Thailand’s Small Power Producer (SPP) programme. BMP has obtained a promotional certificate from the Board of Investment (BOI), the government’s investment arm, that gives meaningful benefits in taxation, depreciation and deductibles to the company. EGAT will buy from a SPP under the established standard term either in the form of a ‘firm’ or ‘non-firm’ basis.
A ‘firm’ contract has contract terms between five and 25 years with a specified capacity and is eligible for both energy payment and capacity payment. A ‘non-firm’ contract has contract terms not exceeding five years with unspecified capacity and is only eligible for energy payment.
In the regulation of the purchase of power from SPPs, the National Energy Policy Council emphasises that using renewable energy fuels reduces the financial burden on the public sector with respect to investment in electricity generation and distribution. It is interesting to note that at the moment, new SPPs can only be proposed if they are based on renewable energy sources.
Recently, the National Energy Policy Office (NEPO) gave advanced notification of its intention to recruit bids for 300 MW of power from SPPs using renewable energy. NEPO will select technically and commercially sound projects for support in the form of incentive payments from the Energy Conservation Promotion Fund (Encon Fund). Successful bidders under the competition will be offered subsidy contracts with an incentive payment for a period of approximately five years. The incentive payment will be in the form of a pricing subsidy per unit of electricity (kWh) sold to EGAT.
All renewable energy technologies in compliance with SPP regulations are eligible: non-conventional energy; waste or residues from agricultural activities or waste from production of agricultural products; products derived from waste or residues from agricultural products and industrial production processes; garbage (i.e. municipal waste); and dendrothermal fuels (i.e. tree plantations). Renewable technologies that operate in a cogeneration mode are also eligible for support.
Thailand is a signatory to the Kyoto Protocol. Of total carbon emissions in Thailand (43 million tonnes in 1998) the industrial sector was responsible for emitting 19 million tonnes of carbon. The transportation sector released an equal amount, 18 million tonnes of carbon. Thailand’s share of total carbon emissions in the world is 0.7 per cent.
The boiler design enables various fuels to be burned, but the chosen fuel in this project is 100 per cent rice husk
Given the generous harvests in the region where the BMP power plant is being built, large amounts of rice husk residue is left unexploited every year. Currently, part of the rice husk waste is disposed of by burning and part is dumped and left to decompose in the open air. Burning rice husks in the power boiler will add to Thailand’s potential to preserve indigenous fossil fuels, namely natural gas, lignite and oil reserves, and reduce reliance on imports. In addition, the use of the rice husks will help Thailand to keep carbon dioxide emissions low, and reducing the amount left to decompose will also reduce emissions of methane, a powerful greenhouse gas.
From a distance, the lone power plant in the middle of the vast rice fields, surrounded by the silhouettes of mountain ridges, has an almost august appearance. The stack reaches a modest 30 m high, only 6 m higher than the rain roof of the boiler. The turbine plant and control room is a closed structure of cast in-situ concrete. A 60 000 m3 raw water pond has been excavated next to the power plant yard to store water for cooling during the dry seasons. The cooling of the condensing power plant is arranged with three 50 per cent motorized cooling towers.
The boiler is a rectangular bottom fluidized bed boiler with a semi-circular shape. Two-stage superheaters hang from the roof of the 13 m high furnace. These components have a cross-sectional dimension of 4.5 m x 4.1 m and divide the combustion gas into two cyclones. From the cyclones the gases are led to the second draw, which holds tube bank type economizers in two stages, and a tube type air preheater, also in two stages. After passing the air preheater, the flue gas rushes to a ceramic 160 per cent multi-cyclone fly ash separator. A single impeller vane-controlled radial type induced draft fan gives the necessary velocity.
When rice husks are burned, the boiler gives 35 t/h of steam at 450°C and 39 bar[g]. Electrically driven feedwater pumps (2 x 100 per cent) are rated at 60 bar outlet pressure at 105°C.
Burning air is supplied by two forced draft fans. One fan runs the burning air through the air preheater, after which the 145°C air is divided into primary air and tertiary air. Primary air is blown to an evaporator water cooled wind box, which also serves as a combustion chamber for two heavy oil start-up burners. Recirculating flue gas can be mixed with the primary air. The tertiary air is led through eight air openings in the front and rear walls, over the fuel inlets. The second forced draft fan acts as a combined secondary air and fuel carrier air fan.
This boiler enables various fuels to be burned, but the chosen fuel for this project is 100 per cent rice husk. The rice husk will be blown into the furnace through four openings without any pretreatment. Thanks to the physical surface properties of rice husk, it does not get adherent or sticky even when it is wet. The low specific weight, around 150 kg/m3, makes it possible to blow the rice husks into the furnace in a similar way as is common with pulverized fuels. A second bunker is equipped with four fuel feed screw conveyors, enabling the use of other, less ‘blowable’, fuels.
Rice husks are purchased from several rice mills located within 40 km of the power plant. Due to the low weight of the husks, and its high volume per calorific value, transportation costs play a significant role in fuel acquisition. Large truck-trailer combinations for lightweight transport are not common in Thailand.
The turbine-generator is a 6 MVA unit, amply dimensioned for the contracted firm electricity sales of 5 MW. The power is supplied to a 22 kV transmission line owned by PEA (the Provincial Electricity Authority). PEA buys the power from EGAT, the holder of the PPA.
The steam turbine is a single case impulse condensing turbine. The direct-coupled generator is an air-cooled 6.3 kV unit operating at 3000 r/min. The closed-cycle coolant air is water cooled.
The automation system of the power plant is fairly sophisticated. Modern PLCs from GE are used: one PLC for the demineralized water plant control, one PLC for closed-loop controls and two PLCs form a redundant interlocking control system. The control room is on the same level as the turbine-generator, from which there is straight access to the main boiler platforms. The operation room as well as the maintenance staff is, at least in the beginning, going to be manned by Epcom.
The rice husks contain about 17-18 per cent ash on a dry basis. The ash of rice husks has very high silica content, typically 93 per cent (dry basis). Part of the ash will be sold abroad, where there is a market for its high silica content, and part of it will be sold to construction materials companies for use in concrete prefabricates.
Participation in the final constructing works of what was originally a Thai-Chinese power plant is perhaps not in line with the usual core objectives of Fortum Engineering, or its Thai subsidiary STFE. Both companies see themselves as turnkey deliverers of power plants, power plant reconstruction projects or partial projects such as flue gas cleaning plants.
However, Fortum considers this kind of activity as an essential step in building confidence among potential Thai clients. It is also considered to be an advantageous if not highly profitable way to learn about the market expectations and economic bottom-line of SPPs.
The waste from the paddy fields of Thailand will provide the people with power
Earlier this year Fortum Engineering signed an agreement with the Energy Conservation Center of Thailand (ECCT) to survey and to make a conceptual design for 12 different types of industrial biomass burning CHP plants, of which four will be subject to a more accurate basic design and feasibility calculations.
While the company’s own fluidized bed boilers range is 5 MWe to 20 MWe, it has now decided to upgrade a boiler concept, called FEBio10, and to test its compatibility and competitiveness in the Thai power market.
Fortum’s O&M sector, which also operates in Thailand, is looking forward to serving the growing SPP market.