Foot on gas to alternative fuels01 August 2006
Whereas there has been much recent publicity about running motor vehicles on biologically-derived liquid fuels, an increasing number of enterprises, from very large to very small, are turning to gas as a feedstock, presently mostly derived from fossil sources, but also from biological wastes.
Everything from cow dung to waste wood and general domestic rubbish may go into the front end of processes to produce fuels that are usually mainly methane, but in some cases are producer gas: carbon monoxide, plus hydrogen and nitrogen. Also, researchers in various countries have demonstrated how it is possible to turn plastics, waste oils and other waste products into hydrogen and hydrides.
Hundreds of thousands of biogas plants are already in operation in Third World and not so Third World countries. More than a million motor vehicles are running on compressed natural gas in India and Pakistan, and the US Air Force has begun trials with jet fuel derived from natural gas by the 'Syntroleum' version of the Fischer-Tropsch process.
According to biogas expert Govinda Devkota, there are in Nepal alone some 140,000 family-sized biogas plants, mostly of 4 to 10 cubic metre capacity, fed on animal and vegetable waste and producing a mixture of methane (50% to 65%), carbon dioxide (30% to 40%), hydrogen sulphide (less than 1%), plus traces of nitrogen, hydrogen and carbon monoxide. Put organic rubbish in a closed space, exclude air and keep it warm, and you obtain biogas. In Europe, landfill is said to have the potential to generate as much as 94 billion cubic metres of methane each year. The European Natural Gas Vehicle Association website comments: "Landfill gas composition is such that the primary processing consists of removing carbon dioxide (40% to 60%) and moisture. Other contaminates are removed in the liquefaction processes. The processing may be configured to produce both LNG and a gas product that can be used for heating or for power generation. This is particularly advantageous, if the refuse hauliers and landfill equipment utilise LNG as a vehicle fuel." According to the Environmental Services Association, the UK has 22 plants that generate energy from the treatment of almost four million tonnes of waste per year, but it extracts energy from less than three million tonnes (less than 10%) of municipal solid waste, as compared with 50% in Denmark and 45% in the Netherlands. However while methane-based gas can be expected to be produced by landfills over 50 to 100 years, usable gas production can be expected for only 10 to 15 years. The domestic-sized production units in Nepal and other Third World countries, on the other hand, are managed so as to continue to produce usable gas from waste throughout their working lives.
Use in Nepal is mainly for cooking and lighting as an alternative to wood, which, if it were to continue to be used as the main fuel source, would lead to the loss of all forest in the country in less than 25 years. While many countries, including the UK, have substantial fleets of LNG-powered vehicles, the lead towards mass conversion to gas powering is being taken by countries in South America and South Asia.
Tesla Technologies in Pakistan says that 300 of its new CNG dispenser digital units have been installed in forecourts in Pakistan in the last 18 months and that there are now a million cars converted from petrol to gas power. The gas dispensing units use a touch screen interface and have built-in gas detectors that freeze all functions if a leak is detected. The units automatically come back on-line when the gas leak ceases.
According to the International Association for Natural Gas Vehicles, there are also 1.5 million gas-powered vehicles in Argentina, 1.1 million in Brazil, 400,000 in Italy and 250,000 in India, while the UK has just 543. In the US, however, there has been much interest in reviving a version of the German Fischer-Tropsch process which was first disclosed in 1923 and widely used during World War II to produce motor and aircraft fuels from coal, but can also be adapted to use methane as a feedstock.
The Syntroleum Corporation, headquartered in Tulsa, Oklahoma, has a version of the process that starts with natural gas, steam and air to form producer gas, which is then catalytically converted to hydrocarbons and water. The water and gases are removed and the remainder cracked to produce a mixture of useful hydrocarbon-based fuels. Details of the Syntroleum version of the process are sketchy, but the catalysts most commonly used in the past were based on iron, nickel and cobalt. This September, the US Air Force is to conduct tests in which a B52, based at the Edwards Air Force Base in California, will run two of its eight engines on a blend of conventional JP-8 jet fuel and jet fuel produced by the Syntroleum process. The other six engines will be run on conventional jet fuel. Syntroleum can produce 43 US gallons of synthetic fuel from 10,000 cubic feet of natural gas. The raw materials cost about $70. The US Air Force consumed 3.2 billion US gallons of aviation fuel in the fiscal year 2005, amounting to 52.5% of all fossil fuel used by the government. The total bill topped $4.7 billion.
"The cost of using Fischer-Tropsch has been cost-prohibitive until now," says Major Timothy Schulteis, Air Force propulsion programme element monitor. "Today's petroleum prices are making liquid fuels derived from the process more cost-competitive. The recent rise in cost of fuel has brought us to where many think we are now at the break-even point."
Almost anything carbonaceous can be turned into producer gas and India has started to pursue a strategy based on the use of producer gas made from waste wood. According to Aseem Narain, senior programme officer with the National Mission on Bamboo Applications in New Delhi, the Indian Institute of Science in Bangalore has developed a gasification plant that is being installed at a rate of one plant per five villages to produce fuel to power small, local electric generating plants.
The calorific value of dry, waste bamboo is 16MJ/kg. Every kg of dry bamboo generates 2.8 cubic metres of producer gas with a calorific value of 4.5 to 5 MJ/cubic metre. The composition of the gas is carbon monoxide 20%, hydrogen 18%, methane 2% and carbon dioxide 12%. The other end product is 5% to 15% active charcoal. Each plant is of down-draft design, with open top, twin air entry. Throughput is 1kg/hour. Tar and particulates are less than 10 parts per million. Price is 775,000 rupees (£9,091) for a complete plant of which 500,000 (£5,865) is for the gasifier, 250,000 (£2,933) for the generator and 25,000 (£293) for the engine. Electric power output is 25kW.
There are also a large number of processes that convert various waste materials to hydrogen. One is the Luxotherm 1 (Luxemburg) process that takes in waste oils, refrigerants, paint, glues, plastics, rubber and bituminous residues, and feeds them into an alkali hydroxide molten salt bath at 800ºC. This induces a cracking process to produce a gas stream that is 90% hydrogen and some methane, plus sodium and sodium hydride, which are condensed out. It has so far reached the stage of a pilot plant that has been tested on model substances and also wastes from McDonald's, Goodyear, DuPont de Nemours, Cegedel and Superdreckskescht.
Various researchers - particularly, but not exclusively, in the US - have been using microorganisms to convert waste to hydrogen. The problem is to avoid the conversion by other bacteria to methane, but this difficulty may have been overcome by the discovery of hydrogen-producing bacteria that are spore forming. Application of heat kills the methane-producing bacteria, while turning the hydrogen-producing bacteria into spores that revive when the temperature goes down. Suitable bacteria are found in ordinary garden soil.
Hydrogen is being promoted as a fuel in the UK by the United Kingdom Hydrogen Association, which elected its first board of directors and subsequently held its first board meeting on 16 May 2006 at the NEC in conjunction with the National Energy Management Exhibition. In the chair is John Carolin of BOC and the vice chairs are Ian Williamson of Air Products and Alastair Rennie of Amec. Treasurer is Graham Hillier of the Centre for Process Innovation and secretary is Karen Hall of the Technology Transition Corporation.
? Everything from cow dung to waste wood and general domestic rubbish may be used in producing biofuels.
? Hundreds of thousands of biogas plants are already in operation in the Third World and beyond.
? More than a million motor vehicles are running on compressed natural gas in India and Pakistan.
? The UK extracts energy from less than three million tonnes (less than 10%) of municipal solid waste, compared with 50% in Denmark and 45% in the Netherlands.
? At the International Association for Natural Gas Vehicles' last count, there were 1.5 million gas-powered vehicles in Argentina, 1.1 million in Brazil, 400,000 in Italy and 250,000 in India. The UK had 543.
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