Collaboration between two Canadian firms will see the launch of a cogeneration plant fuelled by wood waste converted into bio oil. It produces power using a specially modified industrial gas turbine package.
In February this year the West Lorne BioOil Cogeneration Project, near London, Ontario, achieved a significant milestone in the field of biomass energy production when the first five tonnes of bio oil was produced from seven tonnes of wood waste. Plant owner DynaMotive Energy Systems Corporation (DynaMotive), expects to commence commercial production of bio oil at the rate of 100 t per day. The biofuel will be used to drive a 2.5 MW gas turbine engine in a system that has undergone extensive testing in which the fuel has performed to similar standards as natural gas.
Bio oil is produced using a fast pyrolysis process developed and patented by DynaMotive called BioTherm. Pyrolysis is the transformation of a substance through exposure to high temperatures. In this case, forest and agricultural wastes such as bark, sawdust and sugar cane bagasse are converted into a liquid fuel having been heated at 500˚C with almost no oxygen. The resulting dark brown, free-flowing liquid is carbon dioxide neutral and emits virtually no sulphur oxides (SOx) and low levels of nitrogen oxides (NOx) when burned.
Figure 1: GT2500 with on line hot section cleaning system.
The benefits of utilizing renewable source by-products to produce a bio oil deemed to be a greenhouse gas neutral fuel are numerous. The raw materials are readily available, cost-effective and clean and have the potential to revolutionize how isolated communities produce energy. However, before this project commenced it had to be demonstrated that this alternative fuel could be effectively used in an industrial gas turbine.
In 1994, Canadian-based Orenda Aerospace Corporation, a division of Magellan Aerospace Corporation, started a development programme to utilize bio-gas fuel in an industrial gas turbine engine. This programme was stepped up in December 2003 with a programme to investigate the technical feasibility of utilizing alternative fuels such as bio oil, ethanol, bio diesel and bituminous crude oil in a 2.5 MW GT2500 gas turbine. The gas turbine engine was designed and manufactured by Zorya-Mashproekt in the Ukraine and further modified for the alternative fuels application through a joint development programme between Zorya-Mashproekt and Orenda. A test rig equipped with a 3 MW load bank was designed and built to test the modified GT2500 engine on different fuels.
Operation of a gas turbine on alternative fuels presents several challenges. Some bio oils and heavy oils are very viscous and require preheating for satisfactory atomisation. In this programme, preheating as well as external compressed air were used to achieve the required droplet sizes for satisfactory combustion. Bio oils also tend to be acidic so corrosion resistant materials must be used in the handling system and fuel lines – a particular problem in the case of pumps that are required to pressurize the fuel prior to atomization.
Particulate matter in biofuels presents a problem that must be addressed through filtering, grinding or homogenisation, if fuel nozzles are not to be blocked. Alternative fuels also tend to produce deposits on hot section hardware that can produce hot corrosion and severely reduce efficiency. Methods are required to dislodge and clean such harmful deposits. Attention also needs to be given to ease of maintenance so that blade and vane replacement can be accomplished onsite, rather than requiring the costly and time-consuming removal of the gas turbine from the package.
Figure 2: Fuel treatment module interior.
Fuel nozzle design is extremely important. The fuel nozzles designed under this programme operate in a dual fuel mode, allowing startup on diesel and gradual switch over to alternative fuels. In addition, they allow for enhanced atomisation using an external compressed air supply. The addition of a comprehensive fuel handling system and logistic of operation on such alternative fuels requires a very complex control system and associated hardware development. As well as controlling the normal aspects of operation the system must also control several emergency procedures which are complicated by the inherent properties of these fuels and the need for flushing fuel lines with ethanol in an emergency situation.
Emission control is another significant challenge. Bio oil produces virtually no SOx emissions but NOx and CO emissions need to be kept within allowable limits. Heavy oil, on the other hand, has a high sulphur content and produces high levels of SOx emissions.
In order to address the challenges presented by using alternative fuel in the GT2500, Zorya-Mashproekt and Orenda made a number of modifications to the package. The combustion system was modified to incorporate fuel nozzles capable of duel fuel operation using diesel or alternative fuels, with external compressed air supply to improve fuel atomisation. Combustion liners were modified for better alternative fuels burning as well as to reduce emissions.
The GT2500 gas turbine engine hot section was modified in such a way as to make it possible to replace all hot section vanes and blades on site without gas turbine removal. After manufacturing, the GT2500 was tested with two sets of hot section components. A unique on-line hot section cleaning system using crushed nut shells was designed and developed to clean the hot gas path of the gas turbine engine from possible accumulation of deposits while operating on alternative fuels. Again, this was successfully tested at the Orenda test rig with the GT2500 gas turbine operating from idling to full power
The fuel treatment part of the package contains both a diesel and bio oil tank. The bio oil tank is equipped with a heater and mixer. Upstream of the high pressure pumps both fuels are preheated by hot glycol, which in turn is preheated by steam. Ethanol is used to wash the fuel system internal path after operation on biofuels.
Specially developed control algorithms for the gas turbine and fuel treatment system logic and closed-loop controls were utilized by a PLC-based control system.
Testing of the modified gas turbine engine, fuel treatment module and control system using a variety of fuels proved that the package was capable of operating to the standards achieved by natural gas and was ready for commercial operation. The test results are shown in Table 1. Following the success of the tests, which were concluded in May 2004, a power generation package with engine and fuel handling module was assembled for commercial operation at the West Lorne cogeneration plant.
The West Lorne bio oil plant is located 50 km southwest of London, Ontario on the shore of Lake Erie and is the largest biomass to bio oil cogeneration facility in the world. It is a showcase for DynaMotive’s pyrolysis and Orenda’s industrial generation technologies. The bio oil project consortium, headed by DynaMotive and Orenda, is supported by the Government of Canada through technology and sustainable development programmes. The plant cost $13.5 million to build, plus $1.8 million for commissioning and research and development.
The plant is expected to process 100 t of wood waste, supplied by the nearby Erie Flooring and Wood Products firm, and to produce 70 t of fuel per day. The fuel will be used to drive the GT2500 gas turbine with the resulting 2.5 MW of electricity being used to meet the power demands of the Erie Flooring plant and to export energy to the Ontario grid. Surplus heat generated by the turbine will be used to generate 12 000 pounds of steam per hour for Erie Flooring’s industrial operations. DynaMotive has entered into a three-year fixed price contract with an Ontario third party for the sale of excess bio oil, char and electricity. Based on contracts entered into and terms agreed upon, it is projected that annual revenues from plant operations will be approximately $2 million.
“Once we have been running for three to six months, there will be many other opportunities, because so many people are watching us,” says Frank Button, vice-president of Orenda. “There are opportunities across North America and throughout the underdeveloped world, especially in places where you could take crop waste that so far has just been thrown away.”
The Pikangikum First Nation, an Ojibway community in Northwestern Ontario, has signed a memorandum of understanding with DynaMotive to set up a bio oil plant through the Whitefeather Forest Initiative. “Our community runs on fuel oil generators, so we have to fly in fuel, which is very expensive. But we have all these trees we can get the bio oil out of,” says Alex Peters, President of Whitefeather Forest Management Corporation. The Pikangikum project, still in the planning stages, will not be operational for about five more years.
As for other avenues, DynaMotive and its partners are also engaged in research and development on a range of derivative products that, if successful, would further enhance the market and value for bio oil as an alternative fuel and product source.
Nigel Blackaby, Features Editor