In the last few decades, increasing emission of greenhouse gases worldwide hasbecome a major concern. With a growing world population and with increasing energyconsumption coupled with higher living standards, there is a huge challenge in limiting theemissions of pollution and greenhouse gases. Moreover, the available fossil fuels are limited;consequently, with increasing prices we need alternative energy sources to replace the fossilfuels. The European Commission has set the goal that by 2020, 20% of the energy consumedshould come from renewable energy sources, as well as 10% of the energy consumed withinthe transport sector [EC, 2011]. The commercially renewable vehicle fuels available today areethanol, biogas, biodiesel, and electricity produced from renewable energy sources.
Biogas is a renewable, high-quality fuel, which can be produced from a lot of different organic raw materials and used for various energy services. Biogas technology has been developed and widely used over the world, because it has a lot of advantages, including reduce of the dependence on non-renewable resources, high energy-efficiency, environmental benefits, available and cheap resources to feedstock, relatively easy and cheap technology for production, extra values of digestate as a fertilizer, etc. But the current status of biogas production and utilization largely varies among the different continents.
Biogas is produced when microorganisms degrade organic materials in the absence of oxygen. This process is also named anaerobic digestion (AD). The feedstock can derive from the agricultural, industrial or municipal sources. To date, in order to obtain a higher biogas yield, a lot of agricultural biogas plants digest manure with some additional co-substrates for increasing the content of organic materials. Besides input materials, biogas yield and AD process are affected by several other factors. There are a lot of different types of biogas plants over the world, and they are accepted and widely used by different countries. For example, floating drum and fixed dome biogas plants are two major types of small to medium scale biogas digesters used in African countries.
The implementation of biogas technology provides benefits in terms of positiveenvironmental impacts and additional values of digestate used as fertilizer if consideringcurrent energy consumption, waste handling and agricultural production practices. Inaddition, biogas itself can be used in several ways: either raw or upgraded, such asproduction of heat or steam (the lowest value chain utilization), electricity production withcombined heat and power production (CHP), upgraded and utilization as vehicle fuel,upgrading and injection in the natural gas grid. There are big differences of biogas utilizationamong various countries, in particular between developing countries and developed countries.In spite of the multiple benefits of biogas systems, present biogas production only uses asmall part of the potential.
1.2 AIM AND OBJECTIVES
Therefore, this seminar report is aimed to review the production and application of biogas, based on the following objectives:- 1) To review the study various aspects of biogas technology, including its production,feedstock, different types of digesters, etc
2) To review the benefits of biogas technology, including the energy value (biogas utilization), environmental benefits, and the values of digestate; its installation costs and economic performance.
2.0 LITERATURE REVIEW
The global energy demand is increasing rapidly, and about 88% of this demand reliesupon fossil fuels to date (Weiland, 2010). The energy demand will continue to grow during thiscentury. However, GHGs emissions have become one of the most severe environmentalproblems. Use of fossil fuels is one of the main reasons for these emissions. According to thereport of Intergovernmental Panel on Climate Change (IPCC), GHG emissions must be reducedto less than half of global emission levels of 1990 in order to minimize climate changeimpacts and global warming. Besides, the energy supply is another important global challenge,because some continents such as Africa are already faced with an energy crisis but most ofthe known conventional oil and gas resources are concentrated in politically unstable regions.
Today, there is a lot of research focusing on renewable energy resources. Thedevelopment of renewable energy technology can help to reduce the dependence on the non-renewable resources and the problems of environmental degradation related to fossilfuels (Parawira, 2009). Biogas which is a renewable energy resource from wastes, residues,and energy crops will play an important role in future. The production of biogas fromanaerobic digesters has significant advantages compared with other forms of bio-energyproduction. Firstly, biogas production has been considered as one of the mostenergy-efficient and environmentally beneficial ways to produce renewable energy. Secondly, itcan use locally available and cheap resources to produce biogas, and it drastically reducesGHGs emissions compared to fossil fuels. Thirdly, the digestate associated with the biogasproduction is considered as an improved fertilizer that could partly substitute for mineralfertilizers.
2.1 Biogas Technology Status in Africa
The African continent has already encountered an energy crisis, including bothcommercial (petroleum products, natural gas, coal, and electricity) and traditional energysources (wood and other biomass) (Parawira, 2009). However, the energy consumption anddemand of the African continent is estimated to grow continuously, at rates even faster thandeveloped countries. The factors contribute to this increase include the growth in population,energy demands from various domestic sectors and the demand for improving quality of life.In order to meet the Millennium Development Goals (MDGs), especially MDG1—reducing by halfthe percentage of people living in poverty by 2015, it is required to improve the quality and magnitude of energy services in developing countries (Parawira, 2009). In eastern andsouthern Africa it is estimated that energy use significantly relies on traditional biomassenergy technologies but hardly takes modern, sustainable energy technologies. Due to thecurrent economic situation in most African countries and the shortage of commercialmodern energy, it is almost unlikely that the fossil fuels substitute for biomass (Parawira,2009). The fossil energy resources distribute on the African continent unevenly, which leads70% of countries in Africa rely on imported energy resources (Parawira, 2009). Certainly,biomass is an inexpensive and abundant resource, but if used in an inappropriate andunplanned way it will limit regenerative utilization and cause significantly environmentalconsequences. So it may be helpful to change the energy situation in Africa in ways ofupgrading the biomass to higher-quality energy carriers.
The problems of traditional biomass fuels and non-sustainable fossil fuels havecaused widespread research on the production and application of new and renewable energyresources, such as biogas, bio-fuels, and biodiesel. It is necessary to develop the renewableenergy technologies, in particular biogas technology, because it helps to reduce thedependence on non-sustainable resources and the environmental degradation problemscaused by the fossil fuel. Compared with other renewable energy production systems such asbiodiesel and bio-ethanol, biogas production systems are not complicated and can be builtand operated at both small and large scales in urban and rural areas. Moreover, the biogastechnology does not compete with food production but biodiesel and bio-ethanol technologies do (Parawira, 2009). According to global experience, biogas technology is a relatively simpletechnology in term of the requirements of construction and management. It has beenconsidered as a appropriate, adaptable and locally acceptable technology in Africa(Parawira, 2009).
Various international organizations and foreign aid agencies have made a lot ofefforts through their publications, meetings and visits to promote the biogas technology andstimulate the interest of biogas technology in Africa. To date, some digesters have beenconstructed in several sub-Saharan countries. Various wastes are used as feedstock forbiogas production, such as wasters from slaughterhouses, agricultural wastes, industrialwastes, animal dung and human excreta. The exact number of plants installed in Africa isunknown but most plants were installed in Tanzania and Kenya. In other African countriesonly a few up to hundreds biogas plants have been installed (Van Nes and Nhete, 2007).However, most of biogas plants installed in the African continent are small-scale plants, andthe development of large-scale AD technology in Africa is still embryonic. Unfortunately, it isestimated that 60% of plants installed in Africa failed to stay in operation, although otherplants show the success in providing benefits to the users over a number of years and theevidence on the reliability of the technology if properly operated (Van Nes and Nhete, 2007). Inmost cases, in order to promote the biogas technology some demonstration projects wereintroduced usually free of cost by governmental structures. It is assumed that thedemonstrated benefits of running the biogas plants would stimulate people to adopt this technology automatically. However, it seems that this approach has not caused widespread promotion and the market of biogas technology failed to develop. Moreover, most of the installed plants are abandoned eventually.
Generally speaking, the government expects to disseminate the biogas technology overAfrica based on a market-oriented approach, but it has not achieved to date. An onlyexception may be Tanzania, where most of the plants have been installed on asemi-commercial basis, but a large-scale dissemination is still not achieved (Van Nes andNhete, 2007).
There are a number of constraints that affect the implementation of the biogas technology on large scale in Africa, including (Parawira, 2009):
1. Inexperienced contractors and consultants leading to poor-quality biogas plants andpoor choice of materials;
2. Lack of reliable information on the potential benefits of the biogas technology;
3. Lack of academic, legislation and commercial infrastructure in the region;
4. Lack of knowledge on the biogas system in practice; - 5. Poor ownership responsibility by users;
6. Lack of pilot studies and full-scale experience;
7. Lack of properly educated operators and technical knowledge on maintenance andrepair;
8. Poorly informed authorities and policy makers;
9. Failure to support biogas technology through the energy policy by government;
10. Research at universities is sometimes considered to be too academic in practice.
2.2 Types of Biogas Plant in Africa
There are numerous types of biogas plants over the world, categorized according tothe type of digested substrates, according to the technology applied or according to the plantscale, etc. Briefly, a biogas plant has to consist of two components: a digester (orfermentation tank) and a gas holder. Usually the digester is a cube shaped or cylindricalwaterproof container including an inlet which introduces the fermentable mixture in the formof slurry into the digester. And the gas holder is an air tight steel container which cuts off airfrom the digester and collects the gas produced and it normally floats like a ball on thefermentable mixture.
There are different types of small to medium scale biogas digesters which have beendeveloped in African countries, including the floating drum, fixed dome, and plastic bag design.The former two have been applied widely in Africa. The fixed dome digester and the floatingdrum digester are shown in Figure1. The major differences between the two digesters are thegas collection method, which the gas holder of the fixed dome type is equipped with a gasoutlet and its digester has an overflow pipe to lead the sludge out into drainage, but the digestion processes of the both two digesters are the same (Amigun and Blottnitz, 2007).
Table 1 shows the comparison of constructed material, capital investment, output, lifetime and advantages/disadvantages between these two types of biogas plants.Depending on the text, any type of biogas plant may be used. Nevertheless, most of the plantsinstalled so far are the fixed dome type in Africa because of its advantages. There are nomoving parts designed for the fixed dome type and also no rusting steel parts existing so along life of the plant, 20 years or more, can be expected (Amigun and Blottnitz, 2010). Thebiogas plant is constructed underground which can protect it from physical damage and savespace.
- Quote paper
- Adeyemi Phillips (Author), 2017, Resource requirements and multiple values of biogas technology for rural households in developing countries, Munich, GRIN Verlag, https://www.grin.com/document/444170