Chapter 1 Introduction
1.1 Motivation and Background:
Global warming and energy shortage crisis are serious problems for human beings now. Therefore, controlling the emissions of greenhouse gases and finding alternative energy become international issues.
Recently, people pay a lot of attention to renewable energy, including hydropower, solar thermal energy, wind energy, geothermal energy and biomass energy. Renewable energy, which has a great potential substitution of fossil fuel, is an important part of carbon offset, it not only can avoid the carbon dioxide produced from the fossil fuel (see Fig. 1.1), but also has renewability to handle energy shortage crisis.
Biomass energy, a kind of renewable energy, becomes more popular due to its contribution to energy supply and environmental protection in the same time. It comprises about two thirds of total renewable energy. The source of biomass energy can be derived from plant or animal organic matter, such as waste, wood, gas, etc.
Biogas is one of the biomass energy resources, it can be generated from many places, including landfill, farm biogas plant and sewage digester.
Different sources of biogas contain different components, which is illustrated in Table 1.1. Concerning with the reduction of carbon dioxide emission and high dependence on import energy, which was 98.2% in 1998, 99.0% in 2003, and 99.3% in 2008 [1], in Taiwan, biogas appears to be an attractive energy resource.
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Table1.1 Biogas Contents from Different Biogas Producing Plants [2]
Animal manure of the farm can produce biogas after anaerobic treatment. The main components of the biogas are methane (CH4) and carbon dioxide (CO2) with relatively little amounts of nitrogen (N2), hydrogen (H2), ammonia (NH3), hydrogen sulfide (H2S) and organic compounds. Methane inside the biogas is a flammable fuel, therefore, such biogas can be used as renewable fuel, provided that methane content is sufficient enough.
The main greenhouse gases in atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, ozone and chlorofluorocarbons. When the earth is radiated by the sun light, part of radiation is reflected to the outer space, another part of radiation is absorbed by the earth’s surface. These greenhouse gases can absorb the heat energy emitted by the earth surface, leading to the increasing temperature of atmosphere. There are many benefits using the farm biogas. First of all, untreated manure contains nitrous oxide (NOx), carbon dioxide (CO2) and methane (CH4) gases. The greenhouse potential of methane is 23 times of the carbon dioxide. If those gases emit into the surroundings, the impact to the environment is huge. Furthermore, the biogas is a carbon neutral energy resource. Unlike fossil fuels that releases carbon dioxide which is captured by billion years ago, carbon dioxide released by the biogas which is captured recently. The carbon in the biogas comes from the photosynthesis through plants, and after burning it, the carbon dioxide goes back to the
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surroundings, so the net of carbon amount in this cycle is zero (see Fig. 1.2 for the illustration). However, the carbon of fossil fuels is out of the carbon cycle because they are captured long time ago, and its combustion leads more carbon dioxide content in environment. For this reason, biogas can make balance of greenhouse gas emissions in earth. In other words, biogas is an environmentally friendly fuel. Second, animal manure has lots of organic matters, which lead the river quality to become deteriorated, and wastewater treatment can avoid the further pollution. Third, biogas can generate power that has great potential to reduce the amount of import energy by this way in Taiwan.
Last, biogas is a renewable energy resource. The carbon of the biogas comes from photosynthesis through plants. As long as the sun continues emitting light, the energy supply will not stop. Beside, according to the survey of Tsai and Lin [4], with a practical basis of the total swine population from the farm scale of over 1000 heads, the usage of bio-energy from swine manure management showed following benefits: emissions of methane reduce 21.5 Gg, total electricity is generated of 7.2 × 107kW-h per year, equivalent to electricity charge saving of USD 7.2 × 106, and carbon dioxide mitigation is of 500 Gg per year. To sum up, biogas is a renewable and green alternative energy fuel.
This laboratory has been awarded a three-year research project by National Science and Technology Program for Energy from 2010 to 2012. The project is named as Development the technology of agricultural waste bioconversion to biogas for electricity generation and carbon dioxide elimination by microalgae.
Constructing a pilot biogas plant is the ultimate goal of this project. The project is divided into four subprojects. The subproject 1 is to upgrade the utilization efficiency of biogas by removing H2S and CO2 to improve the biogas generation rate. In the subproject 2, the desulfurized biogas of subproject 1 will
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be utilized to operate the biogas engine to produce electricity under different monitoring parameters. The subproject 3 is to produce biodiesel from high lipid-content algae utilizing waste CO2 either from the engine flue gas or the biogas itself. The purpose of subproject 4 is to research the operating conditions which will affect biogas production rates and methane concentrations emission during the anaerobic processes.
This study is originated from the subproject 2 mentioned above. In the first year, the subproject uses a 30kW generator as a vehicle to build a waste heat recovery system and to analyze the power supply and efficiency for the system in a small scale. In the second year, based on the achievements and experience from the first year, a pilot plant is constructed for biogas and power plant in Taiwan Sugar swine farm. In the meantime, a fuzzy control system is also installed to enhance the performance. In the third year, a completely self-operated biogas plant with CHP system is constructed. By 2010, this subproject is capable to generate 90,000kW-h electricity per year, equivalent to electricity charge saving of 270 thousand NT dollars, in an order of 2000 pigs.
In the first year, Lin [3] tested different air-fuel ratio for 30kW generator with 60% methane concentration of biogas in a small swine farm in Miaoli. The oxygen-enriched combustion and heat recovery were also applied to his research. The results showed that the efficiency of the generator is improved by using oxygen-enriched combustion and heat recovery system. For the following years, the biogas plant is enlarged in Taiwan Sugar swine farm in Taichung.
This study mainly will test the scale-up effect based on Lin’s research [3].
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