Thailand’s first coconut power plant commences commercial operations
In Thailand, a new tropical biomass fuel milestone has been reached as the 9.5 MWe Mahachai Green Power plant enters into commercial operations. A “first-of-a-kind” facility it is specifically designed for the simultaneous combustion of all forms of coconut waste as well as conventional biomass.
Mahachai Green Power Lo., Ltd is a Thai-German joint venture majority owned by TPC Power Holding PCL and CarbonBW Thailand Co., Ltd. At the beginning of April 2016, its Mahachai biomass power plant in Samut Sakhorn Province passed its 24 hours full-load test thus obtaining the necessary Provincial Electricity Authority (PEA) permit to feed electricity into the national power grid. In doing so it has become one of the world’s first biomass power plants to utilise all types of coconut waste as fuel.
According to China-headed DP Cleantech, the combustion technology developers and suppliers selected in 2013 as full turnkey EPC contractors for the project, the facility is specifically designed to use all types of coconut waste; husk, shell, bunch, fronds, leaves, trunk along with conventional biomass such as wood and rice husk. The unique boiler island design enables all parts of the coconut plant to be used by allowing different types and sizes of coconut waste to be simultaneously combusted.
The scope of supply included the supply and installation of all components, such as the boiler, steam turbine, cooling tower, water treatment plant, fuel- and ash handling, electromechanical and control systems, 22kV transformer station and switchgears. The plant was designed on an end-to-end basis to ensure optimal integration of different components, and maximum efficiency and performance.
High temperature and pressure
The fuel is stored in outdoor and indoor storage areas, and transported to the pusher feeder via an automatic moving floor, screw and belt conveyors, all supplied as redundant systems. The screw conveyor system is equipped with weight cells to ensure the proper mixing of the fuel and fuel consumption data management. Belt conveyors transport the fuel to the inlet hopper of the pusher feeder.
There is also an alternative fuel inlet via a ground hopper directly on to the belt conveyors. The pusher feeder solution allows the combustion of pre-processed coconut shell, feeding the fuel into the boiler combustion chamber.
The coconut waste is combusted on a water-cooled vibrating grate under carefully controlled conditions. The vibrating movements regulate the stages of combustion and occur in cycles that alternate between 1.5–3 minutes for a period of 3–5 seconds at a time. Part of the combustion air is fed to the furnace from beneath the grate and additional combustion air is led to the furnace through nozzles situated above the grate.
The steam boiler is a water tube boiler with hanging super-heaters that produce 40 tonnes of steam per hour at 92 bar and 537°C. Specially selected materials and advanced temperature control counteract the fouling and corrosive effects of the fuel. The steam produced is used in a conventional steam cycle turbine. The generator set was also delivered by DP Cleantech and manufactured under supervision in China. The generator and gearbox are German manufactured and designed to produce up to 9.9MWe gross.
The flue gas, having been cooled in the boiler, is passed through an electrostatic precipitator (ESP) filter for removal of particulate matter (PM) before stack discharge. The fly ash is collected in a storage silo via a dense phase pneumatic transport system. The fly ash can be discharged from the silo into trucks for redistribution as fertiliser or used as construction filler. The plant is equipped with a CEMS (Continuous Emission Monitoring System) for online monitoring of emissions.
There were many preconceived ideas about what was and wasn’t possible with coconut waste residue as a feedstock, but our vision to use not just a part, but all the waste residue of this most abundant natural resource has now been realised. We hope that we have shown the way towards creating a sustainable economic cycle for the coconut producing industry and that this is only the first of many similar plants in the region, ended Khun Cherdsak Wattanavijitkul President Executive Committee of TPC Power Holding PCL
This article was first published in Bioenergy International no. 4-2016. Note that as a magazine subscriber you get access to the e-magazine and articles like this before the print edition reaches your desk!
Coconut (Cocos nucifera) is a large palm found throughout the humid tropics and is tolerant of saline and other conditions considered to be marginal for many other crops. According to Food and Agriculture of the United Nations (FAO), over 12.3 million ha (2012) is under coconut cultivation. Global coconut production (2014) was just over 51 million tonnes with the world’s top three producers; Indonesia, Philippines and India together accounting for just over 89 percent.
Thailand has around 216 000 ha under cultivation and is the ninth largest producer with 1.01 million tonnes coconut or about 2 percent of global production. Whole nuts, copra (dried coconut flesh), desiccated coconut, coconut oil, coconut milk and coir (coconut fibre) are internationally traded products whereas other products such as shell charcoal, coconut water and palm sugar are traded locally or regionally.