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ESS – natural gas and biogas thermal power stations generate electricity and heat

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The thermal power plants of ESS Energie Systeme & Service GmbH are tailor-made for applications in the medium capacity range, in municipalities, businesses and in industry, as well as in agricultural enterprises. Since 2008, ESS has been a member of the Viessmann Group, which operates the power plants manufactured by ESS under the „Vitobloc“ brand.

The idea of decentralised, heat-led thermal power plants is at the forefront of ESS installations. In the compact units, on the one hand, electricity is generated for internal needs and, on the other, the incidental exhaust heat of the engine is used largely without loss for heating and is not discharged into the environment. Electricity which is not required is fed into the public network.

Thermal plants are extremely efficient. While conventional power plants achieve overall efficiency of barely 40%, for thermal plants, this figure is over 90%. Through the deployment of a thermal plant, primary energy consumption is reduced by well over 30% and CO2 emissions by up to one third. A thermal plant can be operated with biogas or with biomethane (raw biogas which is processed and fed into the natural gas network) in a particularly environmentally friendly way, since it works on a CO2-neutral basis. Through it, agricultural enterprises can become independent of fossil fuels such as natural gas, since the biogas can be generated from raw materials which grow in the region. The „Vitobloc“ thermal plants produced by ESS are available with electricity generating capacities of 20 to 401 kW and with heat generating capacities of 39 to 549 kW.

At AGRITECHNICA in Autumn 2011, ESS will offer a biogas-fuelled thermal plant in the 75 kW capacity class, which is extremely attractive for many farmers. The new installation is specially designed for deployment close to farms and for enhanced fermentation of liquid manure. The Renewable Energies Law (EEG) 2012 codifies the promotion of small biogas installations fuelled by liquid manure, with capacities of up to 75 kW. The remuneration for feeding in electricity through this installation will rise in 2012 to an attractive 25 cents/kWh.

ESS delivers each individual installation in turnkey condition. The customer can also assemble a tailor-made service package, ranging from commissioning to training to complete operation. ESS staff are always happy to help when it comes to commissioning, maintenance, service, repair work or overhauling of engines. Various maintenance contracts provide a balanced price to performance relationship and risk-free all-round service. All central power plants can be monitored and controlled remotely by the ESS service. Within Germany, ESS maintains a factory service with some 30 support points. Outside it, the service is carried out by reliable partner firms.

ESS thermal plants deploy gas engines of leading manufacturers, such as MAN or Toyota. The engines should be operated exclusively with a gas engine oil with special additives, approved by the OEM. According to the type of engine and gas, the overall or volume ranges from 35 to 220 litres. For engines operated with natural gas, oil is predominantly changed at fixed intervals. In biogas installations and in turbo systems with heavy loads, ESS recommends changing the engine oil as a function of its condition. The optimal time is defined by OELCHECK with analyses of lubricants.

Gas engines represent a genuine challenge for their engine oils. Ultimately, the facilities operate on a continuous basis, at high process temperatures and frequently under full load. For operation with biogases, individual and highly variable qualities of gas are added. The composition of biogas depends on the respective fermented organic material. In addition, it is hardly ever pure. In addition to 50- 75% methane, biogas contains nitrogen, carbon dioxide, water and oxygen. Very frequently, mainly for the fermentation of liquid manure, hydrogen sulphide is also present and can form aggressive hydrogen sulphide (H2S). This can generate corrosive wear and tear on pistons, cylinders and in the valve train. A further risk for gas engines and a major challenge for engine oil is posed by sulphuric acid, generated in the combustion process for the gas. The gas engine oil must have a high alkaline performance reserve in order to neutralize these acid components, as well as to neutralise the hydrogen sulphide. The acid-buffering additives must be ash-poor and cannot be added in excessively high doses, since otherwise, the performance of the catalyst will be impaired. If it does not succeed in striking a balance between few additives and good neutralisation capacity, the oil can no longer lubricate the engine reliably and protect against wear and tear, corrosion and deposits

ESS deploys regular lubricant analyses by OELCHECK to monitor the gas engine oil and to determine the condition-dependent oil changing interval. Analysis set 4 was specially devised for gas engine oils, deployed in engines powered by biogas, landfill gas or sewage gas. In this way, fractions of wear metals, any impurities and additives, as well as the general condition of the oil are determined. On combustion of the gases, acidic products accrue, which must be neutralised by the engine oil. If the oil is incapable of this task due to its performance or an urgently due oil change is not carried out, the extremely aggressive acids attack the components of the engine. This predetermines corresponding damage and even the complete failure of the engine. In order to exclude such risks, the degree of acidity of the oil is monitored. For this purpose, the values of the BN, AN, i-pH and if necessary, the SAN as well, are displayed in the laboratory report for biogas engine oils, under the heading „supplementary tests“. The BN (base number) states the alkaline reserve of a lubricant for the neutralisation of acids. By comparison with the new oil values, the AN (acid number) permits conclusions to be drawn regarding the oxidation of the oil and the breakdown of oil additives. In gas engines operated with variable gas qualities, the i-pH value (initial or original pH value) provides supplementary information on the degree of acidification of the gas engine oil. The SAN (Strong Acid Number) is only determined if, as is made clear by an i-pH of below 4, exceptionally aggressive acids are present in the oil.

Thanks to the regular deployment of OELCHECK lubricant analyses, the gas engine oils in thermal plants fuelled by biogas are changed by ESS depending on their condition. The operator thereby benefits from reduced maintenance costs and the maximum operating safety of their installation.

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