By the end of 2015, all British Airways flights from London City Airport will be littered with fuel.
Fischer-Tropsch reactor built by Velocys
By the end of 2015, all British Airways flights from London City Airport will be littered with waste (paper, food scraps, grass under garden trimmings, and organic debris discarded by other urban residents).
But before these wastes become fuel, they will be processed in the "London Green Sky." This is a biofuel plant located in the east of London and is currently under construction. Each year, the plant will receive about 500,000 tons of municipal waste and convert its organic content into 60,000 tons of jet fuel.
This level of output is hard to notice in traditional refineries. In traditional refineries, raw materials can produce equal amounts of products within a week. Nathanael Greene, director of renewable energy policy at the New York City Department of Natural Resources Conservation, said: “It's almost impossible to imagine collecting enough biomass to run a refinery.†As a second-generation biofuel plant, materials used in the “London Green Sky†It can be corn stalks, sawdust, other forms of agricultural waste, and municipal waste, but it is still insufficient in quantity. The hope now lies in the fact that factories can drastically cut transportation costs—relocating factories to places where biomass is rich, rather than the current opposite.
Proponents believe that the new catalytic technology and the compact design will enable the second-generation biofuel factories not only to protect the ecological environment, but also to be profitable without subsidies, and to compete with petroleum fuels. The question now is whether such an idea can become a reality. But at least some customers are giving factories a chance to try; related business units have sprung up in Finland, Mississippi, and Alaska.
Greene said that if the second-generation plants succeed, compared to their “predecessorsâ€, they will bring a major advantage: the production of fuel suitable for existing vehicles in a low-carbon way.
Limited compatibility is a major issue that limits the development of first-generation biofuel plants. The first-generation factory used technology that has been developed for more than a thousand years to produce beer, wine, and spirits. These machines grind foods such as corn, sugar cane, and add water and yeast. This process can produce large quantities of ethanol, which is the perfect fuel for blending with gasoline.
However, the growing population and limited arable land have made the use of food to produce fuels very limited. Therefore, for more than a decade, the biofuel industry has been working on more economical methods, such as using corn stalks, sawdust, and other by-products that have been wasted. This poses a challenge to the fermentation process because these materials contain strong long-chain molecules (eg, cellulose, lignin), and it is difficult for yeast to break them down. In the past 5 to 10 years, advances in the use of acid and enzyme pretreatment methods have overcome this problem to some extent. Commercial plants that plan to produce cellulosic ethanol are currently being built in locations such as Iowa and Kansas.
Mixed wall puzzle
However, these plants are currently unable to completely overcome the biggest problem in the fermentation process: "Mixed walls" - the maximum amount of ethanol that can be mixed with gasoline without causing fuel pipe and engine corrosion. The current model has a "mixed wall" ratio of about 10% to 15% - the first generation of fermentation equipment has produced "more than enough" ethanol to meet this demand. In fact, some ethanol refineries established in the United States in the past 10 years have been idle. They are victims of drought-induced price increases and market saturation.
In the past nine years, the price of oil has remained high - about 100 US dollars per barrel, making a large number of research turned to the field of thermochemistry. Thermochemical plants can directly convert biomass into fuel.
The most common thermochemical method is gasification, which is the heating of carbon-rich materials (such as coal, wood chips, municipal waste) to produce syngas (referring to a mixture of carbon monoxide and hydrogen, especially flammable gases produced by low-grade coal). At the Green Sky plant in London, the gasifier unit built by Solena Fuels (a renewable energy company in Washington, DC) will complete this step—using sprayed ionized plasma to evaporate the waste and heat it to 3,500 degrees Celsius. These devices consume more energy than other gasification methods. The reason why the London Green Sky Factory does this is that the municipal waste is varied and the composition of the syngas is kept consistent by adjusting the temperature of the plant.
The second step in the process is to send syngas to a chemical reactor (built by Velocys, Ohio Plains), where consistency is very important. In this step, the synthesis gas will undergo Fischer-Tropsch synthesis reaction—hydrogen and carbon monoxide are fused to form long-chain hydrocarbons. By controlling the amount of cobalt-containing catalyst powder and placing it next to a series of microchannels, Velocys was able to design an extremely compact system and control the flow of syngas.
The Fischer-Tropsch synthesis unit has also been designed to be as modular as possible so that the plant can handle the material more conveniently. Neville Hargreaves, Velocys' business development manager, said: "Profits are not speculative on scale, but need to improve your production methods."
Another system
Another compact system, the BioMax gasifier, was developed by the Community Power Company in Englewood, Colorado. The company said that the modular device has the advantage of small size, each standard container can be put into four, and applies to any kind of chopped biological material, whether it is food debris, cardboard or wood chips. The resulting syngas can replace natural gas and can function as heating, cooling, or power generation. A typical unit can generate 150 kilowatts of electricity, support the power needs of 25 to 50 homes or three supermarkets, and even maintain the normal operation of major hospital equipment. In the near future, the BioMax device will be able to be used in Fischer-Tropsch synthesis reactors and also to produce biodiesel.
In 2011, the community power company was acquired by Afognak. Afognak is located on Afognak Island, Alaska. They want to sell the device in Alaska and northern Canada, because in these areas, electricity and transportation fuels are very expensive.
Clean combustion
The biggest selling point of the two-step gasification process is that all the syngas is converted to hydrocarbons that do not have double bonds or ring structures so that the produced fuel can be burned cleanly and thoroughly. But this advantage has not hindered researchers from finding a single step alternative approach. During the pyrolysis process, biomaterials are heated to 500 degrees Celsius in an oxygen-free environment and then converted directly into organic liquids. Through standard techniques, these liquids can be refined into fuel. Mark Nimlos, chief scientist at the National Renewable Energy Laboratory in Boulder, Colo., said that pyrolysis is a relatively immature technology compared to gasification. But this can be seen as an advantage. "This technology has a lot of room for improvement."
Some companies have begun to test the commercial feasibility of the technology. For example, UOP, Des Plaines, Ill., a subsidiary of Honeywell International of New Jersey, is working with Ensyn Technologies of Ottawa to promote Ensyn's Rapid Thermal Processing (RTP) unit. These companies foresee that the RTP unit can be installed next to the lumber mill so that everyone can convert the waste wood into 76 million liters of pyrolysis oil per year. This amount of energy is enough to “warm†31,000 families if they are used directly as civilian fuel oil; they can also be refined into gasoline, which can fuel the United States’ 35,000 cars.
Green Fuel Nordic (a biorefinery company in Kuopio, Finland) is planning to build at least one RTP unit next to the town of Isarmi. Here, the company handles rubbish from the Finnish forest industry. The company is also working with the European Commission to develop a set of quality standards for pyrolysis fuels. Tar is an ingredient that is more difficult to handle. It is a sticky residue of long-chain molecules and is difficult to extract. The other is oxygen. Many biological materials are rich in oxygen. It reacts easily with pyrolysis oil to form organic acids that can seriously corrode oil refining equipment. Finding a better way to deal with these two pollutants is the main goal of the study. At present, the easiest way to remove oxygen is to add hydrogen molecules from natural gas, but this will have a negative impact on the environment and increase costs.
For London Green Sky, economic viability is still an open question. But its partners - Velocys, Solena, British Airways - are full of hope. They did not disclose the cost of the facilities, but none of the three companies considered the cost as a core issue. British Airways hopes that this approach will help it achieve the EU's mandatory carbon emissions targets while ensuring a stable supply of jet fuel (not subject to price fluctuations). Solena and Velocys wanted the London Green Sky company to be the first company in the world to apply the facility to the airport.
Hargreaves said that every field, forest, and landfill are potential sources of fuel for these facilities. The demand for liquid fuel will never disappear. He said: "Five decades later, we may achieve complete electrification of land transportation." But the aircraft needs the capacity density is far beyond the battery can provide. "Liquid fuel is hard to replace."
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