Very few new innovations have been introduced and accepted without controversy and liquid biofuels are no exception. Tony Wheatley explores biofuels across the globe further, a controversial resource in any language.

Although there is little consensus over when, it is generally accepted that global production volumes of oil and natural gas must ‘peak’ at some point in time. Undeveloped reserves, new discoveries and new extraction techniques will continue to provide growing volumes in the future, but recent price trends reflect global fears of its eventual depletion.

Liquid biofuels, derived from food crops promised an early solution to the challenge of reducing the developed world’s dependence on fossil fuels for transportation. In Europe, targets for biofuel substitution were carefully calculated to support the overall objective of limiting global warming to 2°C above the pre-industrial average temperature.

Stavros Dimas, the EU’s Environment Commissioner, admitted recently that its goal of sourcing 10% of Europe’s transportation fuel from biofuel resources by 2020 overlooked some sustainability issues. In his 2007 State of the Union address, ex-president George Bush announced his ‘Twenty in Ten’ plan for the US that is similarly flawed.

Controversy over land use and food price inflation has exposed these plans to be somewhat short sighted and accelerated the development of a new generation of biofuels.

This word has gained popularity in recent times and in reports and treaties associated with the Kyoto Protocol, or the UN Framework Convention on Climate Change, ‘sustainability’ usually means long-term viability.

In the developing countries of Asia, Africa and South America, where unemployment exceeding 40% is common, populations of vast informal townships suffer without effective sanitation or paved roads and millions exist on less than $2 per day, the word ‘sustainability’ is likely to be associated with more immediate consequences. To a farm worker in Indonesia for example, the word sustainability probably means finding work next season so that his family won’t starve.

It is interesting to note that maize farmers in the US have demonstrated no greater insight or commitment to long-term sustainability, than palm oil producers in Indonesia, or sugar and soy growers in Brazil and Argentina. Profit has always been the prime motive for economic activity because human needs are unlimited, but resources are finite.

The effectiveness of policy decisions in Europe and North America, in achieving the intended effect on global warming, is compromised because the demand created for certain food crops is already large enough to distort world markets.

Gaseous biofuels
Flammable biogas is believed to have been used in ancient Persia but the first known sewerage plant built to capture this energy-rich gas was in Mumbai, India in 1859. In 1895 the UK city of Exeter adopted similar technology to provide street lighting. Estimates put the number of small digesters producing biogas for household heating and cooking in China at seven and a half million and in India at three million.

The anaerobic digestion process operates at temperatures above 95°C and is very effective in warmer climates to convert animal, plant or human waste into clean burning fuel gas and liquid fertilizer. Usually constructed below ground of either brick or concrete, biogas digesters are inexpensive and simple to build and operate reliably for 20 to 30 years.

Biogas generated this way consists of a mixture of methane (50-75%) and carbon dioxide (25-50%) with small amounts of nitrogen, hydrogen, hydrogen sulphide, oxygen and water vapour. This is very similar to landfill gas and by removing the carbon dioxide and other impurities can be upgraded to match the properties of natural gas, may be called Synthetic Natural Gas (SNG) and substituted in most applications. This so-called green natural gas is generated by small biogas plants of less than 1MW output capacity in many European countries.

Injection of SNG sourced from landfills into the natural gas grid, was first tested in the Netherlands as early as the late 1990s. Since then this technology has been established in Switzerland, Sweden, Austria and Germany with nearly 30 biogas plants connected to the grid by 2007. Distributing bio-SNG through the existing grid doubles the potential energy efficiency to almost 90%, by avoiding the waste heat loss of peripheral Combined Heat and Power (CHP) facilities.

Since 2000 micro CHP units have rapidly gained popularity in several countries driven by tax credits, feed-in tariffs and other incentives; Japan leads this initiative with 90,000 units in use. SNG can also power fuel cells for direct conversion into electricity where heat is not required.

It is expected that after 2015 plants greater than 100MW will provide bio-SNG to substitute for significant proportions of natural gas across the EU. Second generation bio-SNG technology under development now, will use dry biomass feedstock like waste wood, which is first gasified to produce a stream containing about 11% methane, 32% hydrogen and 21% carbon monoxide with 30% carbon dioxide and other contaminants. Catalytic methanation and removal of carbon dioxide and contaminants will produce bio-SNG.

Compressed Natural Gas (CNG) is widely used to fuel the efficient operation of city busses and an estimated 10 million vehicles worldwide have been converted to use CNG. The availability of public facilities for refuelling cars is still patchy except in Germany, California and several major cities like Paris and Barcelona. Some gas companies like Gaz de France allow domestic consumers to install a compressor for overnight refuelling at home.

A study commissioned by the German Green Party in 2006, by two leading German environmental science organisations, concluded that biogas and bio-SNG could replace the EU’s total requirements for natural gas by 2020. This may have been optimistic, but achievements to date have demonstrated the enormous potential of biogas and several other countries including the UK plan to investigate the technology over the next few years.

Avoiding the controversy
The feedstock for biogas generation can include wastewater, animal manure, crop residues, forestry waste, scrap paper, food waste and virtually any organic waste material and need not rely solely on cultivated energy crops.

The controversial issues of competing land use and potential inflation of basic food prices are avoided.

Maximising bio-SNG
Biogas and bio-SNG, being derived from renewable resources, can boast carbon neutrality even if the carbon dioxide removed during upgrading is released.

If carbon dioxide is collected and sequestered, biogas and bio-SNG they could even have a negative impact on greenhouse gas levels.

The EU’s goal of maximising the substitution of bio-SNG will require the importation of significant volumes of biomass.

Vehicles fuelled with CNG have limited range because of the size of tanks required. A limited range of new vehicles is now available equipped for duel-fuel operation. Standards for grid injection of bio-SNG need to be harmonised across Europe.