Biomethane (biogas) is an alternative and renewable energy source produced ... Figure 2: Biogas plant for biomas and animal manure (Austria, 2004) [7].
BIOGAS, A MODERN RENEWABLE ENERGY IN THE EUROPEAN CONTEXT DILEA Mirela, PARASCHIV Gigel, UNGUREANU Nicoleta, VOICU Gheorghe, BIRIS Sorin-Ştefan, IONESCU Mariana University POLITEHNICA of Bucharest, Department of BIOTECHNICAL SYSTEMS
ABSTRACT
One of the main environmental problems of today’s society is the continuously increasing production of organic waste. Biogas technology is widely used in Europe since several decades and is a highly developed technology. Biogas installations processing agricultural substrates are some of the most important applications of anaerobic digestation today. In the present paper there are presented examples of biogas plants, anaerobic digesters and biogas storage tanks widely used in Europe. 1. INTRODUCTION
In Europe and worldwide production and use of biogas has increased considerably as a result of increasing demand for renewable energy as a substitute for fossil energy. Most agricultural and industrial biogas plants in Europe use biogas to produce electricity in cogeneration plants (CHP – Combined Heat and Power). Today there are over 8,500 biogas plants in Europe. The interest in biogas has further increased today due to global efforts of displacing the fossil fuels used for energy production and the necessity of finding environmentally sustainable solutions for the treatment and recycling of animal manure and organic wastes. To date, biogas is the only technologically fully established renewable energy source that is capable of producing heat, steam, electricity and vehicle fuel. It is, in the true sense of the word, a versatile energy source [1]. Production of biogas through anaerobic digestion of animal manure as well as of a wide range of digestible organic wastes, converts these substrates into renewable energy and offers a natural fertilizer for agriculture [2, 3]. Biomethane (biogas) is an alternative and renewable energy source produced through the anaerobic (oxygen free) digestion of organic matter whereby the organic matter is converted into a combustible biogas rich in methane (CH4) and a liquid effluent. Anaerobic digesters have been used successfully in municipal and industrial wastewater treatment plants and on a number of livestock farms for many years [4]. The composition of the biogas is an important characteristic affecting the biogas combustion in the cogeneration unit and, therefore, the composition and temperature of the flue gas evacuated. This affects the quantity and quality of heat which can be used in a concept of thermal energy. Furthermore, the concept of the biogas plant is characterized by the temperature in digesters, which are usually heated to a part of the heat from the cogeneration unit in order to allow the bacteria a rapid decomposition of material [5].
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In line with the other biofuels, biogas from anaerobic digestion is an important priority of the European transport and energy policy, as a cheap and CO2-neutral source of renewable energy, which offers the possibility of treating and recycling a wide range of agricultural residues and byproducts, in a sustainable and environmentally friendly way. A wide range of biomass types can be used as substrates (feedstock) for the production of biogas from anaerobic digestion. The most common biomass categories used in European biogas production are: • Animal manure and slurry • Agricultural residues and by-products • Digestible organic wastes from food and agro industries (vegetable and animal origin) • Organic fraction of municipal waste and from catering (vegetable and animal origin) • Sewage sludge • Dedicated energy crops (e.g. maize, miscanthus, sorghum, clover). In the present paper there are presented the construction, operation and main components of biogas plants. Also, will be given representative examples of biogas plants used in European countries. 2. REPRESENTATIVE EXAMPLES OF BIOGAS PLANTS USED IN EUROPEAN STATES Biogas installations processing agricultural substrates are some of the most important applications of anaerobic digestion today. Thousands of agricultural biogas plants are in operation in Europe and North America [1]. A biogas plant is a complex installation, consisting of a variety of elements. Depending on the type, size and operational conditions of each biogas plant, various technologies for conditioning, storage and utilisation of biogas are possible to implement [2]. The biogas plants have a common principle layout: manure is collected in a pre-storage tank, close to the digester and pumped into the digester, which is a gas-tight tank, made of steel or concrete, insulated to maintain a constant process temperature. Digesters can be or vertical, usually with stirring systems, responsible for mixing and homogenising the substrate, and minimising risks of swimming-layers and sediment formation or horizontal. Apart from the digester, equipped with stirring system, the plant can include pre-storage for fresh biomass, storage for digested biomass and for biogas, and even a CHP unit [2]. Further, there is presented a representative examples of a farm biogas plant, with horizontal digester of steel [6].
Figure 1: Shematic representation of a farm biogas plant, with horizontal digester [6] 148
Figure 2: Biogas plant for biomas and animal manure (Austria, 2004) [7] Figure 3 shows the Denmark’s largest biogas plant, located in Lemvig which started production in 1992. The plant processes yearly about 226,000 tons of biomass, consisting of 183,000 tons of annual manure and slurries and 43,000 tons suitable industrial waste (maximum 25 % of the total feedstock mixture). The produced biogas it converted into electricity and heat by the CHP-unit of the biogas plant. In 2013, an additional new Caterpillar biogas-engine (1560 kW-el) was installed. More than 21 million kWh of electricity is generated every year and sold to the local grid. The surplus heat from the gas engine cooling system exceeds 18 million kWh per year and is sold for distributed to more than 1000 households in the area [8].
Figure 3: Example of co-digestion plant built in Denmark [8] Many European countries have established favorable conditions for electricity production from biogas. Germany has a leading role in Europe with almost 4000 biogas plants, most of them on farms for cogeneration [9]. In Europe, other than market leader Germany, Sweden, Italy, Denmark and Poland have announced plans to increase their biogas markets substantially. Plans in Denmark include the construction of what will be the world’s largest biogas facility [10]. 149
Figure 4: Biogas plant south of Hanover, Germany [10] In Romania the biogas sector is in an early stage of development. Romania is a country with many areas appropriate for biogas production. Bihor county is just an example, with 12 areas where people can get rid of harmful waste, and receive instead heat, electricity, bio fertilizer and a clean environment. The first bioethanol and biogas plant in Romania will be built and completed until 2013, in Remetea, Harghita. The plant will produce ethanol using agricultural products in the area, and the resulting pulp will produce biogas [11]. The core of a biogas plant is the digester - an air proof reactor tank, where the decomposition of feedstock takes place, in absence of oxygen, and where biogas is produced. Common characteristics of all digesters, apart from being air proof, are that they have a system of feedstock feed-in as well as systems of biogas and digestate output. In European climates anaerobic digesters have to be insulated and heated. There are a various types of biogas digesters, operating in Europe and around the world [2].
Figure 5: Vertical digesters built in Germany Horizontal digesters have a horizontal axis and a cylindrical shape. This type of digesters are usually manufactured and transported to the biogas plant site in one piece, so they are limited in size and volume.
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Figure 6: Horizontal digester, built in Denmark The biogas is usually used soon after generation without storage, but there are situations in which the gas must be stored. Various types of biogas storage facilities are available today. The simplest solution is the biogas storage established on top of digesters, using a gas tight membrane, which has also the function of digester cover. For larger biogas plants, separate biogas storage facilities are established, either as stand-alone facility or included in storage buildings. The biogas storage facilities can be operated at low, medium or high pressure [2]. Figure 6 presents gas storage tanks with double membrane. Double membrane storage tanks are composed of an external membrane, which forms the outer shape of the tank, and an inner membrane, which is the actual space for biogas. Continuously, pressurized air is supplied in the space between the two membranes, in order to apply a constant pressure on the inner membrane (this ensures the pumping of biogas into the outlet pipe at constant pressure and volume) and to withstand external loads (given by snow and wind) [12].
Figure 6: Gas storage tank with double membrane A – external membrane; B – internal membrane; C – air flow system; D – rope system; E – anchor ring; F – non return valve; G – blower; H – low pressure valve; I – excess pressure valve; J – inspection window
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3. CONCLUSIONS Biogas techology is recognized as one of the most advanced possibilities for obtaining energy from renewable sources and valuable fertilisers. Biogas energy has an important role in the proper choice of scopes aproved by European Directive for Energy from renewable sources (RED, 2009/28/CE), which states that 20% of final energy consumption must be ensured from renewable sources until 2020. According to a study of the European Environmental Agency the potential from agricultural is still largely unexploited and this sector is expected to have the highest growth rates in the coming years. Digestion of animal manure and organic waste has contributed to solve a substantial environmental problem in the majority states of European Union. Biogas installations, processing agricultural substrates, are some of the most important applications of anaerobic digestion today. In our country the biogas sector is in an early stage of development. References [1] EBA - European Biogas Association, Biogas- simply the best, Renewable Energy House, Brussels, Belgium. [2] Al Seadi, T., Rutz, D., Prassl, H., Köttner, M., Finsterwalder, T., Volk, S., Janssen, R., BIOGAS – Handbook, University of Southern Denmark, 2008, ISBN 978-87-992962-0-0. [3] Al Seadi, T., Lukehurst, C., Quality management of digestate from biogas plants used as fertiliser, IEA Bioenergy, May 2012. [4] Arogo Ogejo, J., Wen, Z., Ignosh, J., Bendfeldt, E., Collins, E.R., Biomethane Technology, Virginia Cooperative Extension, College of Agriculture and Life Sciences, Virginia Polytechnic Institute and State University, 2009. [5] Rutz, D., Sustainable use of the thermal energy of biogas, Renewable Energies, Munchen, Germany, 2012. [6] Hjort-Gregersen, K., Danish Farm Scale Biogas Concepts- at the point of commercial break trough, Danish Institute of Agricultural and Fisheries Economics, Proceedings of the International Conference Würzburg, Germany: Biomass for Energy and Industry, 8-11 June 1998, p 641-643. [7] Lipp, R., Advanced Biogas Technology for the Food Processing Sector, Lipp GmbH73497 Tannhausen Germany. [8] Lemvig Biogas, An example of successful centralized co-digestion in Denmark, IEA BIOENERGY TASK 37 Energy from Biogas, February 2013. [9] Edita Vagonyte, European biomass association, Biogas & Biomethane in Europe. [10] www.greentech-opportunities.com [11] NRG Energy News, Biogas - Important Resource for Renewable Energy Development in Romania. [12] Sattler Brochure, Biogas storage tanks for each plant design. Available online at http://www.sattlerag.com/sattler-web/static/media/pdf/Broschuere_UT_EN.pdf.
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