Biofuels
Introduction
Biofuels are considered an energy source with high potential to address problems in several areas, such as the crisis of climate change, environmental degradation, energy supply and security. The use of biofuels largely depends on the availablity of different feedstocks. However, biofuels have some common features that they are all non-toxic and biodegradable, and they can reduce greenhouse gas(GHG) emissions. Recent studies from Soil and Tillage Research show that replacing fossil energy with renewable energy like biofuels is an important way of reaching climate policy goalsTypes of biofuels
The figure below shows that there are various opportunities for the production of biofuels. The features between biofuels and fossil fuels are quite similar. For instance, biodiesel is similar to fossil diesel, and bioethanol is similar to petrol. This is a great advantage since the existing infrastructure does not necessarily to be intensively change.First-generation biofuels
PPO, biodiesel, ETBE and bioehthanol are the first-generation biofuels. They are generally produced by the action of microorganisms and enzymes through the fermentation of any biological feedstock. Bioethanol, the most common biofuel feedstock, offers the greatest short-term bioful potential today since the conversion is widely developed and approved in practice . Although the first-generation biofuels are different in properties, technical requirements, economical aspects and potential usages, they can all contribute to guarantee long-term sustainability.
Second-generation biofuels
Second-generation biofuels are derived from feedstocks, which are not traditionally used for human consumption. They include BTL fuels and ethanol from lingo-cellulose. These products are not yet commercial available since their conversion technologies are not improved enough as products of first-generation biofuels. However, second-generation biofuels are considered to be more environmental healthy and produce less GHGs than first generation biofuels. The reason is that they can make use of the vast majority of feedstock in the process of production and avoid the waste inherent in the production of first generation biofuels. Second-generation biofuels can not only help solve this waste problem, but also can supply a larger proportion of our fuel supply sustainably, affordably, and with greater environmental benefits.
The figure below focuses on the pathways of biofuel production. It shows that feedstocks sources can be divided into animal fats, oil crops, sugar plants, starchy plants, cellulosic biomass and wet biomass. During the different processes, such as refining, extraction, hydrolysis and fermentation etc., they can be transformed into liquid or gaseous biofuels.
Current biofuel promotion policies
A turning point for biofuels policies occurred in 2005–06, when several countries dramatically stepped up targets and mandates for biofuels to make a great promotion of their use. The promotion of biofuels is attractive for many governments, especially for the ones who want to take action to fight against global warming, diminish environmental pollutions, and to set up a sustainable policy of future gobal energy requirements.The result of recent policy activity is that biofuels mandates now exist at the national level. "In the United States, a renewable fuel standard was enacted in 2005 that requires fuel distributors to increase the annual volume of biofuels blended up to 7.5 billion gallons (28 billion liters) by 2012 (although this target was expected to be met anyway through tax incentives). The federal government also extended a 43 cents/gallon (12 cents/liter) biodiesel tax credit for blenders through 2008"t is clear that policy has played an important role in influencing on the promotion of biofue
Environmental benefits and problems
By the way of reducing GHGs and local pollution, biofuels can provide many benefits to the environment. For example, bioethanol is water soluble, non-toxic and biodegradable. In addition, bioethanol is not as flammable as petrol, which means that it can reduce the incidence of severe vehicle fires and other daily transportation accidents. Compared to the carbon dioxide-based fuels, it is an environmentally friendly option to use hydrocarbon-based fuels.It is important to remember that, as Abdersib and Fergusson(2006) argue, "none of the fuels derived from biomass energy can be considered truly carbon-neutral when one bears in mind that stages of production, transportation and processing required non-renewable energy. Attention also need to be paid to crop types, especially since it is clear that some first-generation feedstocks are more applicable to biofuel production than others. " Furthermore, attention should also paid to the application of fertilizers, pesticides and herbicides and the production of biofuels itself to guarantee they are not harmful to the environment in the long term.
Socio-economic benefits of biofuels
Generally, biofuels are expected to have a positive impacts in socio-economic, especially for local areas. Biofuel production is a new market for agriculture products and as a result, it offers new income options for farmers. For example, under the generous subsidies provided by the Common Agricultural policy(CPA), members of powerful European farming lobbies are guaranteed sufficient incomes in a truly competitive agricultural market. It shows that the increased feedstock production will have a significant contribution in the agriculture sector. Therefore, agriculture not only plays a role in food production, but also in energy provision in the future.Case Study—Biofuels in China
Biofuel usage has become a broad debate in many countries' energy policies since it covers many areas, such as energy security, food security, climate change mitigation, and international biofuel development. With 20 percent of the world's population and 10 percent of its arable land, China's debate on biofuel production is about the conflict between food security and energy crops. Now, the Chinese central government has taken ambitious moves to reduce petroleum products by adopting renewable energy sources.In January 2007, China’s State Forestry Administration (SFA) and the oil company PetroChina signed an agreement of developing diversity of potential energy crops, such as an oil-bearing plant, Jatropha. Jatropha curcas is considered as a high potential biodiesel feedstock in China since it grows on marginal land in Southwest China and avoids the compeltition with the food system. Southwest China, including Guizhou Province, Sichuan Province, and Yunnan Province, is the official target area for Jatropha production in China(see table below). Especially for Yunnan Province, it has significantly more land available for Jatropha production than neither Guizhou nor Sichuan Province. Therefore, Yunnan may be the province capable of achieving the National Development and Reform Commission (NDRC)'s goal: to expand Jatropha plantations to 10 million mu in each Southwest province in China.
Guizhou, Sichuan, and Yunnan Provinces are the poorest regions in China. Although the southwest is one of the most ecologically important regions in China, the individuals' incomes and provincial goverment revenue per person are below the national averages. Planting Jatropha could offer rural income generation and employment opportunities to improve the living standard of the local farming lobbies.
The Process of transferring Jatropha into biofuel
Biodiesel was probably the first of the alternative fuels to really become known to the public. The great advantage of biodiesel is that it can be used in existing vehicles with little or no adaptation necessary. Biodiesel is, naturally, a compromise for this reason, but still balances positively on the energy scales. There are energy plants available that will produce a higher yield in kWh per area, but the simplicity of having a fuel that is fully compatible with present fuel and engine technology makes it very attractive.
Cars running on BioEthanol, which is produced from agricultural crops, sugar cane or bio-mass, are governed by the same law of physics as those using gasoline. That means both emit CO2, as an inevitable consequence of the combustion process. But there is a crucial difference: burning ethanol, in effect, recycles the CO2 because it has already been removed from the atmosphere by photosynthesis during the natural growth process. In contrast, the use of gasoline or diesel injects into the atmosphere additional new quantities of CO2 which have lain fixed underground in oil deposits for millions of years.
Biogas
Biogas is becoming increasingly interesting as an alternative to natural gas. It is especially useful that the composition is practically identical, so the same burners can be used for both fuels. Biogas can be produced from plant or animal waste, or a combination of both. There are many different methods used dependent on the starting material and quantity involved. A mixtrue of both has proven to be the best method. The animal waste produces the nitrogen needed for growth of the bacteria and the vegetable waste supplies most ofthe carbon and hydrogen necessary.
Biomass
Biomass can be a practicable alternative for small district heating schemes in rural areas. Traditional biomass is wood residue and excess straw from agriculture being burned to provide heat or power. There are also gasification plants that produce a gas composed mainly of carbon monoxide and hydrogen from plant material. This has the advantage of being capable of transportation by pipeline or being filled into cylinders for distribution. Pyrolyis, as it is known, is being investigated in many countries presently.
Pyrolysis of Biomass
Pyrolysis of biomass is used to produce a mixture of three combustible products from biomass: tar, gas and coke are formed in varying proportions. After cleaning the gas can be used to drive turbines or gas motors. The tar is also suitable for the plastics industry and the coke can also be burned in the conventional way.
Landfill gas analyzer
The landfill gas analyzer is similar to a standard flue gas analyser, but capable of measuring methane and carbon dioxide directly. There are many landfill sites in use still, which all produce gas naturally. More advanced models of landfill gas analyzer will also be capable of measuring the products of combustion.
Landfill sites
Landfill sites are now being used for the commercial production of methane in many areas instead of simply flaring the gas for safety reasons. Methane is produced in commercially viable quantities for many years after a landfill site has been closed. Nevertheless, there are still many landfill sites where the gas is being wasted. This source will dry up in time to come, since many countires are now finally emphasising the separation of waste and recycling, but there is gas for the next twenty years in the landfill sites presently existing.
Measurements in biogas
Measurement of the concentrations of carbon dioxide and methane in biogas has produced interesting errors, probably due to the difference in size of the molecules. These factors require consideration when biogas is measured before combustion. Commercial use of biogas makes knowledge of the composition and heating value essential.
Methane digester
Although not a detailed description of how to build a methane digester, this is a good explanation of the working principle. The methane digester is a plant to produce methane in the form of biogas from plant and animal waste. Such systems are common in certain countries, such as India, but sorely neglected in others, although the raw material is available everywhere.
