Utilisation of Communal Organic & Green Waste- Brochure

Sun & Wind Energy 10/201298Bioenergy Utilisation of commUnal organic and green wasteIn the European Union, 38 % of all communal waste still ends up in landfill. Eurostat has revealed that in Bulgaria and Romania, virtually all household waste is dumped. In the other EU countries in eastern and south-eastern Europe the dumping rate is around 75 %. In the coming years there needs to be vast in-vestment in these countries in particular, considering the dumping and waste management policy within the European Union stipulates a drastic reduction in the amount of waste being dumped. To achieve this, the waste economy must be over-hauled according to the following priorities: avoid-ance of waste production, recycling, utilisation to generate energy and finally, dumping – which should be seen as a last resort. If moist organic waste is col-lected separately and treated correctly, it can be used to produce biogas and fertiliser. If biodegradable res-idential waste is utilised in this way, the atmosphere is spared the harmful methane gas that would other-wise have been generated if the waste had simply been dumped.Biogas can be generated through either wet or dry fermentation. However, wet fermentation can be problematic for the fermentation of communal organ-ic and green waste because the pump and agitator technology is sensitive to objects that could cause wear and tear. As a result, in Germany dry fermenta-tion with a TS (total solid) content of between 20 and 40 % has proven much more successful. Each ton of input material generates around 80 to 140 m³ of biogas. The amount of methane produced is around 50 to 75 %, depending on the amount of energy stored within the raw material.The process depends on how the biogas and digestate will be utilisedAround 300 kW can be generated from a material throughput of 10,000 t/a (tons per annum) of com-munal organic waste. There are two options for carry-ing out dry fermentation: the non-continuous “batch” process using box digesters and the continuous pro-cess using plug flow digesters. Germany, the EU’s most populous country, has been turning organic and green waste (i.e. garden waste and waste from land-If communal organic waste is simply dumped, it is harmful to the environment. But if it is used to produce biogas, it can become a significant source of energy. Currently, there are two dry fermentation processes available. Organic waste is composted – or, to get even more out of it, it is fermented first to generate biogas. This fermentation plant in Switzerland has been oper­ating since 2011 and processes 20,000 tons of waste in each year to produce biogas. Photo: Axpo KompogasFerment first, then compostSun & Wind Energy 10/2012 99scaping) into compost since the 1990s. Over the last few years composting plants have increasingly been additionally fitted with upstream dry fermentation systems to utilise the substrate to produce compost and generate energy. This has no discernible effect on the quality of the compost and the upstream fermentation system also reduces the smell and in-creases the composting plant’s capacity, as the final composting stage is completed more quickly. “Composting plants that are capable of process-ing at least 10,000 t/a are most suitable for the inte-gration of a fermentation system,” says Thomas Raussen from the Witzenhausen-Institut für Abfall, Umwelt und Energie GmbH (Witzenhausen Institute for Waste, Environment and Energy). According to a study carried out by the IFEU Institute in Heidelberg, Germany, a combined system including fermentation produces up to 160 kg fewer CO2 emissions per ton of organic waste than a composting plant. But which process is right for which location? “To answer this question, you tend to start with the technical and eco-nomic considerations. However, experience suggests that first, you should check how the digestate and biogas are going to be used,” recommends waste ex-pert Raussen. For example, if the digestate is a liquid (which is often the case with the continuous process) is there even a market for it at the proposed location? The region’s existing supply of fertiliser and demand from the local agricultural industry should also be taken into account, as well as the cost of preparing the digestate. For Raussen, the choice between the two biogas processes depends on the options available for using the waste heat of a thermal power station. If there is no external heat recovery at the plant location, there are two alternatives to consider: a micro gas pipeline to a suitable heat customer further away and the op-eration of a satellite thermal power station, or processing and supply to the gas network. However in both cases, thermal heat and part of the electricity generated by the biogas will usually be required for the operation of the plant. For the production of bio-methane, Raussen says that at least 20,000 tons of organic waste would be required annually. In addi-tion, fluctuation in the quality and amount of gas is particularly common with the non-continuous process and can be problematic for the operation of a gas processing plant.Discontinuous batch process However, the German company Eggersmann Anlagen-bau GmbH has now built a plant according to the discontinuous batch principle that both processes the gas it produces and feeds it into the gas network. 70,000 tons of organic waste from the city’s more than 10,000 green bins will soon be processed in the plant to generate 2.5 million m³ of bio-methane and 35,000 tons of quality compost each year. It is the tenth project featuring the “Kompoferm” process with “tunnel digesters” that Eggersmann has successfully overseen. Tel. +33 (0)4 78 176 219 batiment@gl-events.com bepositive-events.com @bepositiveevent Document not contractually binding - RCS Lyon 380 552 97619/22 FEBRUARY 2013EUREXPO LYON FRANCEENRTHE RENEWABLE ENERGY EXHIBITIONWhere all of tomorrow’s energies are rolled outThe meetingpositive energy buildingFerment first, then compostBioenergy Utilisation of commUnal organic and green wasteSun & Wind Energy 10/2012100 Eggersmann. This way, the procedure does not nega-tively affect the processing of the gas. The digesters are filled with wheel loaders. After a short aerobic treatment via an aeration floor, the substrate is irri-gated with pre-heated process water (“percolate”) and the actual fermentation process can begin. The methane-producing microorganisms need just a few days to fully establish themselves in the fermentation tunnel. The gas production subsides after about three weeks. The system is then emptied and reloaded. The percolate is recycled using the heated percolate digester and the resulting digestate, which has a con-sistency thick enough to allow it to be stacked, is then decomposed and turned into saleable compost.Like other suppliers, Eggersmann has continued developing their process and now also offers a thermophilic operation option at 55 °C made possible by more efficient heat use. This means the digestate can already be sufficiently hygienisated during the fermentation process. Automated loading is also optionally available. Eggersmann has developed a system called Smartferm that features a container design and four digesters that can be used to process around 3,000 to 3,600 t/a.Continuous process with a plug flow digesterCompared to the batch process where the concentra-tion of dry material in the substrate is usually over 30 %, the continuous process has a solid content of between 20 and 30 % for the dry fermentation pro-cess. A leading manufacturer of continuous plants is Axpo Kompogas AG. The Swiss company has been building these kinds of organic waste digesters since the 1990s. “There are over 65 Kompogas plants worldwide and most of them are in Germany, Switzer-land and the Netherlands,” says Axpo company spokesperson Daniela Biedermann. They are now also constructing a plant in Zurich to supply gas to the gas network, which is due to start operating in 2013.The Kompogas process involves shredding the organic waste down to a maximum particle size of The batch process is slightly newer than the continuous process and can ferment substrate with a dry material content of over 30 %. Source: Eggersmann AnlagenbauAxpo Kompogas has been building plants with this technology since the early 1990s. They ferment substrate with a solid content of between 20 and 30 %. Graphic: Axpo KompogasContinuous process with a plug flow digester “The waste is fed into the 21 digesters staggered over time according to a specific schedule and the digestate is then removed. The discontinuous biogas production of each of the digesters is completely levelled through a suitably sized gas storage facility on the roof of the plant,” says Michael Harms from Discontinuous process with box digesters Sun & Wind Energy 10/2012 10160 mm. The input material is thinned using press water from the digestate processing to ensure an optimal TS content in the digester. It is then trans-ported to the digester via a screw conveyor. To inoculate and accelerate the fermentation process, around a third of the output material is reintroduced into the system and mixed with the raw substrate. A special heating system in the digester maintains a process temperature of 55 °C. The plant’s operation is based on the plug flow process, in which the substrate is moved horizontally through the fermen-tation room like a plug or cork. A slowly turning agitator driven by a planetary transmission ensures it is properly mixed and the gas is released from contents of the digester. “The high TS content of 30 % prevents the mate-rial from being mixed in a longitudinal direction,” explains Biedermann. 850 kg of digestate is pro-duced per ton of organic waste. A screw press divides this roughly in half, into solid and liquid parts. Part of the liquid is then recirculated for the pulping of the new material, so there is no need for additional water. According to Biedermann, the above average gas yield, stable process biology and high availability are the major advantages of the Kompogas process.Cost comparisonSimilarly, Thomas Raussen views the high degree of automation and generally higher gas yields as the biggest benefits of the continuous process. However, these benefits come at a higher cost: an upstream system on a composting plant with an annual input amount of 20,000 tons will require an investment of 250 to 480 €/t, compared to € 160 to 320 for discon-tinuous dry fermentation. The operating costs are typically between 18 and 38 €/t (discontinuous between 15 and 30 €/t). The system’s profitability depends on the respective country’s legal framework and subsidies. “Germany has the ideal conditions for setting up and operating a cost-neutral upstream system,” says the organic waste expert. According to the new Closed Substance Cycle and Waste Management Act, separate collection of organic waste will be rolled out throughout the entire country by 2015. This federal government policy could potentially result in the collection of a further 2 to 3 million tons of organic and green waste. There are also hopes for similar initiatives in other EU coun-tries. This could open up new markets, depending on the political developments in waste management in those countries. The European Commission has shown positive signs in this regard, as it has taken Bulgaria, Hungary, Poland and Slovakia to the European Court of Justice for not complying with the Waste Framework Directive.Christian DanyFurther information:Eggersmann Gruppe: www.f-e.de, www.kompoferm.deAxpo Kompogas: www.axpo-kompogas.chWitzenhausen-Institut: www.witzenhausen-institut.dePARC DES EXPOSITIONS MONTPELLIER - FRANCE5 > 7 DÉCEMBRE 2012www.energaia-expo.com• 500 exposants• Conférences internationales• Rencontres d’affaires• Job forum• Trophées innovation• : Focus sur le BâtiSolutions & Innovationspour de Nouvelles EnergiesSalon International des Energies Renouvelables et des Applications BâtimentParc des Expositions Montpellier - France6 e é d i t i o n- Septembre 2012Votre badge d’accès gratuit sur www.energaia-expo.comEnjoy12-Energaia-102X297.indd 1 18/09/12 10:09