Obiettivo
The aim of the present EEC project is to demonstrate that gas, which is generated when organic matter decomposes in a landfill, can be recovered and exploited for energy purposes. This process is well known in the U.S.A. where gas is recovered from major landfills with several million tons of waste, however this project primarily aims at optimizing the recovery of gas in small-sized landfills i.e. with a waste capacity that may be considerably less than
1 million tons.
The demonstration project, which was preceded by a pilot-scale project, is a continuation of the Danish Ministry of Energy's research programme which was initiated in 1981.
The running-in period having come to an end, the followig results are noted:
Total average gas production: 110 m3/h, which is less than foreseen mainly because of problems of water accumulation in the wells.
Gas production rate, old part - 2.5 m3/ton waste x year
Gas production rate, new part - 3.9 m3/ton waste x year
Methane content - 41-43 % CH4
Boiler efficiency - 80-85 %
Stirling motor efficiency - 49-63 %
MWM motor efficiency - 80-90 %
System efficiency - 75-80 %
Energy production
The major part of the energy is used in a gas furnace which supplies hot water to a district heating network. The present production of approx. 1.5 GJ/h covers approx. 1 % of the district heating system's average energy consumption of 210 GJ/h and can ensure the heating of some 150 detached houses.
A small part of the landfill gas is used as fuel in 2 minor CHP units which, together, have an output of 32 kW. The electricity produced is sold to the grid.
Future prospects and replication
The results achieved until now have shown that the gas volume which can be expected in landfills with a relatively low filling height, is in the neighbourhood of 2-5 m3 landfill gas per year per ton waste over a period of
10-20 years from the time when the waste is discharged in the landfill.
The demonstration project has shown that it is technically feasible to exploit the gas from small-size landfills at a reasonable cost-effectiveness as compared with other alternative energy sources. The pay-back time calculated for a further replication based on heat production only is estimated at 8 years.
A measurement and adjustment system has been made to function and, among other things, controls the gas recovery in such a way that a constant methane percentage is attained at all times. The constant gas quality has proved of great value to the production plant, because a better output is obtained when the plant can be adjusted for optimum burning without having to allow for varying gas quality. A varying gas quality was among the arguments in favour for using the Stirling motor, but this aspect has in part become superfluous due to the automatic adjustment system. Numerous problems have been encountered with the Stirling motor in this project, and there is as yet not sufficient ground for a correct assessment of the qualities of the motor when it runs on landfill gas. However, the Stirling motor is still being developed, and biogas motors of a more recent date are said to have shown better results.
Based on the experience acquired from the demonstration plant, a standardized recovering plant has been developed. As compared with the demonstration project, the process equipment for measurement, adjustment and pumping is now joined in a container unit, which is manufactured centrally and only has to be connected to the piping system in situ | This mobile container can furthermore be moved to a new recovery site after completion of the project.
Recovery system
The landfill gas is recovered from approx. 375,000 tons of waste. The landfill has an older part, where waste was disposed of in the period 1971-81, and where the filling height was between 5 and 11 m, and a newer part, which has been used since 1981 and is still in use. In this part of the landfill, the filling height is 8-12 m.
The recovery plant has 20 vertical wells in the old landfill and 12 in the new one. The wells consist of perforated plastic pipes surrounded by gravel.
The gas is sucked out of the waste by means of a constant-volume pump (Roots principle). From each well a horizontal pipe leads to a measuring and adjustment shed, one on the older part and another on the newer part of the landfill, whence the gas is piped to the pump house.
Where the gas pipes from the individual wells enter the measuring and adjustment sheds, samples are taken automatically. After a predetermined scanning procedure the samples are pumped to the pump house for analysis. Incase of fluctuations of the calorific value, the gas flow from each well is adjusted automatically by means of a motorised valve; the purpose of this adjustment being to allow a swift change in conditions, as landfills with low filling height and slight top soil are easily affected by a change of pressure, weather, etc., and penetration by ambient air soon reduces gas production.
Before reaching the pump, the gas passes through a filter which removes particles. Once through the pump, the gas is cooled in an air cooler, so that condensate is removed before the gas is transferred to the production plant via a 2.5 km gas pipe.
Production plant
The landfill gas is used in a gas boiler which produces heat, and a minor part of the gas goes into 2 CHP units. The heat is sold to Viborg District Heating Station.
The boiler capacity is 2.6 GJ/h. It has a modulating burner which maintains a constant pressure, gas volume notwithstanding.
One of the motors is of special interest for the plant, being a Stirling machine with a power production of 6 kW only. The Stirling machine has the advantage of having a continuous combustion in a combustion chamber outside the cylinders. This means that corrosion of cylinders and pistons is avoided, lubricating oil is not contaminated, and cleaning the landfill gas is not necessary. Another advantage is that the combustion process can take place at varied calorific value with no adjustment required.
The other motor is an ordinary gas motor, manufacture MWM, which serves as a reference motor for the Stirling machine.
Measurement and registration system
The plant has more than 200 measuring points where measurements are taken automatically and registered on computer disks. The measurements comprise temperature, pressure, flow and gas compositions in each well, total gas volume, power/thermal efficiency for the utilization system and, also, meteorological parameters.
A mass spectrometer is also used to measure the composition of the gas.
Campo scientifico (EuroSciVoc)
CORDIS classifica i progetti con EuroSciVoc, una tassonomia multilingue dei campi scientifici, attraverso un processo semi-automatico basato su tecniche NLP. Cfr.: Il Vocabolario Scientifico Europeo.
CORDIS classifica i progetti con EuroSciVoc, una tassonomia multilingue dei campi scientifici, attraverso un processo semi-automatico basato su tecniche NLP. Cfr.: Il Vocabolario Scientifico Europeo.
Questo progetto non è ancora stato classificato con EuroSciVoc.
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Meccanismo di finanziamento (o «Tipo di azione») all’interno di un programma con caratteristiche comuni. Specifica: l’ambito di ciò che viene finanziato; il tasso di rimborso; i criteri di valutazione specifici per qualificarsi per il finanziamento; l’uso di forme semplificate di costi come gli importi forfettari.
Coordinatore
8800 Viborg
Danimarca
I costi totali sostenuti dall’organizzazione per partecipare al progetto, compresi i costi diretti e indiretti. Questo importo è un sottoinsieme del bilancio complessivo del progetto.