Until recently, little was known about US company Solena Fuels. But the announcement of its latest project in partnership with British Airways, called GreenSky London, has placed it firmly on the aviation industry’s radar. Solena is set to build Europe’s first plant to convert low-carbon urban waste into sustainable jet fuel. The facility will combine the proven Fischer-Tropsch (FT) process, first introduced in the 1920s, with Solena’s proprietary plasma gasification technology, to convert syngas created from urban waste into clean-burning, drop-in liquid jet fuel.
The chosen site for the GreenSky plant is part of the former Coryton oil refinery in Thurrock, Essex, with building due to be completed by 2017. Solena says it will convert 575,000 tonnes of post-recycled waste, normally destined for landfill or incineration, into 120,000 tonnes of clean-burning liquid fuel a year, of which 50,000 tonnes will be jet fuel and the remaining 70,000 tonnes will be diesel and naphtha.
BA has made a long-term commitment of £300 million to purchase the 50,000 tonnes of jet fuel the facility will produce each year. Jonathan Counsell, head of environment for BA, says the company aims to have carbon-neutral growth by 2020 and to reduce its net carbon emissions by 50% by 2050. BA hopes that Solena’s solution will move the company closer to achieving these ambitious targets.
Counsell says: “We chose the landfill waste FT route provided by Solena as we firmly believe it’s the most sustainable pathway that also happily avoids food-versus-fuel issues associated with other sustainable fuel options.”
Dr Robert Do, founder of Solena, says that the quantities of waste required for the GreenSky plant will be sourced from waste-management companies. Normally, they would send municipal solid waste to be sorted at their recycling facilities. However, Dr Do explains that a significant amount of the waste isn’t recycled, making the process far from green. “Traditionally,” he says, “this post-processed fraction of the waste is sent to landfills where it decomposes producing carbon dioxide and methane, both powerful greenhouse gases. But by diverting the waste away from landfills and on to the Solena facility, landfill gases are avoided and virtually all of the post-processed waste is recycled into renewable fuels.”
The Solena Integrated Biomass Gas-to-Liquid process doesn’t only use feedstock from municipal waste, but from agricultural, forestry, industrial and commercial sources too. As long as the waste feedstock is partly composed of carbon it can be used in the Solena gasification process. That covers anything from paper, cardboard and wood waste to food and plastics. As the feedstock is so cheap and widely available, Dr Do says Solena can avoid problems commonly associated with other fuel feedstock such as wood chips, corn and sugarcane, which are geographically limited, more expensive, and often viewed unfavourably by end users concerned about sustainability and land-use issues.
But if using landfill waste is such an attractive option, why has no one else been using this cheap resource to create sustainable fuel? Dr Do explains that it’s all down to one thing – heat. Incredibly high temperatures are needed to process such a wide range of feedstock, but Solena is able to succeed where others have failed because of its proprietary high-temperature plasma gasification technology.
Dr Do has been working with this technology for more than two decades. In the 1990s, he collaborated with the then Nasa scientist Dr Salvador Camacho who was developing plasma torches to recreate the temperatures that the space shuttle experienced upon re-entry to the earth’s atmosphere. The plasma torch works by creating and maintaining an electric arc between two hollow cylindrical electrodes. As gas is fed through the electrodes at high pressure it interacts with the electric arc and becomes ionised, forming high-temperature plasma – the fourth state of matter after solid, liquid and gaseous. “In essence, the plasma torch is a tool that enables the conversion of electricity directly into heat very efficiently and instantaneously,” says Dr Do.
The GreenSky plant’s 13m-high gasification reactor vessels will each contain four plasma torches that can generate 3,500°C. This intense heat breaks down the solid feedstock at molecular level – without burning it – thereby extracting the elemental components, carbon, hydrogen, oxygen, nitrogen and so on.
Dr Do explains that the high temperatures are especially important when dealing with feedstock that has relatively low carbon content compared with coal or other fossil fuels. He adds: “In lower-temperature applications, only the volatile carbon is extracted, leaving the fixed carbon behind as ash or particulate matter. However, the high temperatures also break down the fixed carbon, enabling the extraction of virtually all of the carbon in the feedstock.”
The shape of the gasification vessel is vital to the process, allowing the gas to cool and form into bio-synthetic gas, or BioSynGas, that will later be converted to liquid fuel. The key to this is the conical plenum area on the top that’s designed to slow down the flow of gas as it rises. This allows for sufficient time for the elemental gases to recombine and form the BioSynGas (CO, H2, N2). However, at 1,200°C, the raw BioSynGas that leaves the gasification vessel must be rapidly cooled and conditioned in a conditioning island before it can enter the Fischer-Tropsch system.
The gas is cooled in a heat exchanger, which enables the recovery of the heat in the form of steam. Dr Do says that at this stage it’s vital that the BioSynGas, made up mainly of carbon monoxide and hydrogen, is also cleaned to remove water vapour and small amounts of sulphur and chlorine compounds that could negatively affect the FT processing island. Finally, the clean BioSynGas is passed through a series of filters and moisture separators to condition it before being sent to the FT processing island where the gas will be transformed into liquid form.
When the conditioned BioSynGas reaches the FT island it passes through a micro-channel reactor, where the gas is converted – via an exothermic chemical synthesis reaction – into long-chain hydrocarbons such as wax and light FT liquids. Dr Do explains that the FT catalyst drives H2 and CO – the compounds that form the SynGas – to react with each other to form water and larger molecules of hydrogen and carbon. This is the long-chain hydrocarbon wax or ‘bio-crude’ needed for the final stage of the process – hydrocracking.
A standard refinery process, hydrocracking uses hydrogen at high partial pressure as well as a catalyst to drive reactions that rearrange and break down the long-chain hydrocarbon wax into the desired jet fuel, diesel and naphtha.
As a result of using such established technology – the FT process is a tried-and-trusted industry method that’s been used to create synthetic diesel fuel for decades – the synthetic fuel created by Solena can be used in jet engines without the need for airlines to invest in system modifications. While the clean-burning fuel is proven to reduce harmful particulate matter by 50-90%, sulphur dioxides by virtually 100% and with 1% less fuel burn, it seems the advantages of the Solena process speak for themselves.
However, with the project still in its infancy, the impact it will have on the fuel industry remains to be seen, although it seems little can shake either BA or Solena’s confidence in the technology. Plans are already being made to find UK locations for future GreenSky facilities. Counsell believes the future is bright. “Now that the process is under way, the plan is that this will be the first of many similar biofuel plants. We hope the government gives a level playing field to aviation fuels in relation to road transport to enable more of these plants to be built in the UK.”
Testing the process: Fischer-Tropsch reactor at the Velocys pilot plant in Ohio