DIESEL & GAS ENGINE DEVELOPMENT
Expanding waste line8 April 2004
The Walloon region of Belgium is struggling to address carbon issues while fighting to reduce its expanding energy consumption and emissions rate. The imminent inauguration of new biogas installations at the Mont-Saint-Guibert landfill site will increase its capacity to 9 MWe and help the country to meet its Kyoto commitments.
Mont-Saint-Guibert landfill received its first Perkins biogas gensets in 1996 when six 4016 TESI
726 kW gas engine powered modules were brought to the site. The project was engineered, built and installed by Belgian company EVW.
In June 2002 a seventh Perkins 4016 unit was installed, then in December 2003 a further six were added to extend the existing power station. Today, from the mountain of 300 000 tonne of waste created every year in the region, they generate 9 MW of electricity, amounting to more than 200 million kWh annually.
This kind of green project, currently receiving more attention than ever from investors and operators, has been rendered economically viable by the availability of green power certificates. In this area Belgium is taking a leading role. Electric utilities are obliged to match the gap between power produced in traditional power plants and the green power quota imposed on them, with the certificates available on the market and supplied by green producers such as Shanks Group, owner of CETeM who operate the Mont-St-Guibert site. The quotas have been set for the next ten years and are designed to encourage the creation of a great many more waste-to-energy projects, in a national context that sees the country going backwards in its race toward the 2012 EU deadline. After Kyoto, Europe committed itself to reducing its GHG emissions to 92% of 1990 levels by 2008-12. Belgium for its part fixed its reduction level at 7.5%. However in Belgium as in many other countries GHG emissions actually increased between 1990 and 1998.
Wallonia is a major consumer of energy. In 1998, its per capita gross internal consumption was nearly 50% higher than the European average. Its average production of CO2 is nearly 15 tonne/year/inhabitant compared to 12 tonne for Belgium as a whole and 9 tonne for the average European. Under a continuation of existing policies, energy consumption and therefore the production of GHG will continue to increase – by around 8% by 2010.
To get back on track, the Walloon region, as part of its draft plan for the sustainable control of energy, is studying strategies that include a greater use of renewables. Sources of renewable energy in the EU currently contribute nearly 6% of total gross internal energy. In Wallonia the figure is only 4%, and less than 1% in Belgium as a whole.
Wallonia’s objective is to achieve green electricity production of 8% by 2010, an objective was set on the basis of a study estimating renewable energy potential in the Walloon Region (see chart, below left).
To be ‘green’ in this context, electricity must be produced in a way that reduces by at least 10% its CO2 emissions compared to conventional generation (reckoned as a steam or gas turbine generator) producing the same quantity of kWh. Power from biogas combustion is categorised as renewable, and makes possible a saving in CO2 that is substantially higher than the required 10%.
According to EU projections, by 2050 the energy landscape in Europe will look totally different – energy prices are expected to rise considerably and consumption to decrease. A significant proportion of the power generated will be derived from biogas.
The technology employed reflects the nature and quality of the biogas, whose composition depends on whether it originates from landfill, wastewater treatment or biomass. For sludge gas, by contrast, production as well as quality directly depends on the wastewater treatment process. But with a methane content of approximately 50%, landfill gas is an excellent fuel. One of its advantages is the inertia of the composting process, resulting in steady production.
Landfill gas is higher quality if it origninates from domestic waste; accordingly since February 2003 the Mont-Saint-Guibert site has rejected industrial waste. But still a distinction is being made between ‘poor’ and ‘rich’ gases. Rich gases contain more methane and are suitable for biogas engines. For the poor gases, though, Shanks has other plans – they are considering burning it to dry the sludge from wastewater treatment and then using the briquettes to fuel an installation capable of generating another 4 MWe.
Contribution of the CETeM plant
The CETeM plant is designed for a biogas output of about 5500 Nm3/h with a methane content of between 40% and 60%. The engines were designed on the basis of a CH4 content of 50%. The site has 13 engines, each developing 726 kWe gross, 9438 kWe in total. Surplus biogas is flared off.
Currently CETeM can generate up to around 72 GWh/year of green electricity, or a little more than 40% of the Wallonia biogas objective for 2010.
In addition the technology meets demanding performance criteria relating to atmospheric waste (complies with TA-Luft norms) and sound pollution (ie it meets Walloon regulations).
A network of sink holes in the mass of waste collects the biogas produced by the decomposition of household waste and similar products. To these shafts are connected tubes that converge towards extractors that pressurise the gas via high density polyethylene (PEHD) tubes.
Boosters force the biogas into 450 mm diameter PEHD collectors leading to the recovery station. The entire system is monitored directly by computer, allowing permanent control of the pressure in the catchment network and prevention of passive biogas emissions.
The biogas is then piped to the gas engines and flares. Depending on its methane concentration, the biogas is either burned off at 1200°C or recovered as electricity. After pre-filtration biogas intended for recovery is compressed by variable speed boosters up to around 70 mbar. During pre-filtration this biogas undergoes dehumidification, dust extraction and final filtration in one of the 2 pre-processing stations.
Each engine is equipped with a low voltage air cooled alternator (400 V triphase 50Hz). The voltage is raised to the network level (11 kV) by 13 individual 1000 kVA transformers.
All the generators are equipped with protection and control equipment and mains paralleling facilities. All data on operation, security and co-ordination of the different units are downloaded to a central control and monitoring unit to ensure automatic control when required. HV power production is sent to the electrical distributor station at Louvain-La-Neuve by a 4 km underground line.
In the case of sludge gas, by contrast, production as well as quality directly depends on the wastewater treatment process.
The chart on page 71 traces the expected change in 2005 and 2010 for electricity production based on renewable sources and their respective percentages with regard to total electricity consumption in Wallonia, considered constant until 2010.
Currently 0.1% of electricity consumption in Wallonia is produced from waste. With the same rate of consumption the Plan proposed by the Wallonia government forecasts growth of nearly 0.9% in the energy contribution of biogas.
After Kyoto Europe committed itself to reduce its GHG emissions to 92% of 1990 levels by 2008-12. Belgium for its part fixed its reduction level at 7.5%. However in Belgium as in many other countries GHG emissions actually increased between 1990 and 1998, which suggests that the Kyoto objectives will not be reached unless additional measures are implemented. MOVED
The fact that the actual state of affairs fails to chime with national commitments emphasises the need for an energy policy combining rational management of energy resources with effective control of the effects of energy use on the environment.
It wants on the one hand to use energy better, and on the other to use better energy. The development of renewables fits into the second category.
, 9.6% for biomass and 4% of the total estimated amount of electricity produced from renewable sources.