USE OF BIOGAS MICROTURBINES FOR THE USE OF BIOGAS FROM DUMPSITE
For over ten months now, the waste processing centre at Thieulloy l’Abbaye has been producing heat and electricity using biogas produced by the decomposition of wastes. Eight turbines were installed for this purpose but they do not operate at full efficiency. In fact, only two turbines function because the storage pit of the non-recyclable wastes attached to the unit produces less biogas than expected. To overcome this problem, a second pit is planned to be connected shortly.
The plant using biogas at the waste processing centre of SMITOP (Syndicat Mixte Interdépartemental de Traitement des Déchets de l’Ouest Picard) situated at Thieulloy l’Abbaye was inaugurated on 30th September 2004. This is the first installation in Europe to have connected 8 turbines for making use of biogas to produce electricity and thermal energy.
SMITOP is responsible for the processing of domestic wastes of seven townships of Somme, four townships of Oise and one of Seine-Maritime. In total, the area covered by this organisation includes 262 communes and 96 800 inhabitants. The processing of wastes of this zone depends on their composition: the recyclable papers and packaging materials are sorted and recycled, the vegetable wastes are composted and the residual wastes are buried in a storage centre. From 1982 to 2002, the non-recyclable domestic wastes were buried in a pit with a capacity of 300 000 tonnes. Since 2002, another pit is used for the non-recyclable domestic wastes at the rate of 30 000 tonnes per year. The biogas is produced due to the decomposition of the wastes.
USE OF BIOGAS IN MICRO-TURBINES
Since June 11, 2001, the unit is subjected to a local authorisation act that makes it responsible for the collection and combustion of biogas. In order to take up this obligation efficiently, SMITOP asked the consulting firm BSDV to conduct a study to determine the possibility of using the biogas produced in its waste storage centre. As a result of this study, SMITOP decided to use its biogas by setting up eight micro-turbines, each having a capacity of 30 kWe and 52 kWth. The small size of the turbines allows for greater flexibility to match the quantity of gas produced.
The biogas is produced during the decomposition of the wastes. It is then collected and routed towards the turbines by an aspirator. Before sending the biogas to the turbines, it is essential to eliminate the contaminants (sulphur, chloride and fluorine) and the solid particles that it may contain. Then, the cooling of the gas enables the water contained in the biogas to condense. It is then that the gas is considered “clean” and contains only methane and carbon dioxide. The biogas is then compressed to a pressure of 4 bars and directed towards the turbines which generate electricity (27%) and heat (51%). This plant was installed by the company Euro Power Technology. It was a turnkey project for which the company supplied the micro-turbines (manufactured by Capstone), a biogas processing system capable of eliminating 99% of contaminants and a candelabra connected to the plant that automatically destroys the excess gas.
AN UNFORTUNATE DRAWBACK
In a technical waste disposal centre of this type, the biogas starts escaping after 3 to 5 years of operation. In the first pit functioning for 20 years, 9 wells were dug for improving the collection of gas. This vertical network is further complemented by a horizontal one that enables to drain more of biogas. However, because of a slightly premature loss of methane from the first pit, the plant is far from operating at its full capacity as anticipated in the study. Only two turbines are functioning. The connecting of the second pit during the year 2005 will enable the functioning of 4 to 6 turbines and when the pit attains its optimum gas producing capacity, all the 8 turbines are supposed to operate. This unexpected drawback distorts the financial data of the study. According to the study, an income of 121 000 Euros was expected (buy back by EDF) with the 8 turbines operating for 8000 hours per year and maintenance cost was projected to be 23 415 Euros per year (which represents an annual net income of 100 000 Euros, excluding depreciation). Had these projections come true, the return on investment would have taken 5 to 6 years. Now, it has become more difficult to estimate this period. However, SMITOP has not made a bad investment as the innovative character of this project helped it to find financing partners. Out of a total investment of 948 590 Euros, SIMTOP has invested 482 898 Euros (41%) and the rest comes from the partners: ADEME (219 405 Euros, i.e. 28%), the General Council (170 087 Euros, i.e. 21%) and the Regional Council (76 200 Euros, i.e. 10%). Moreover, for such installations, the benefit should not be seen only in terms of money, but its environmental contribution as it avoids emission of greenhouse gases.
Electricté = Electricity
Gaz = Gas
Air = Air
Gaz de Combustion = Combustion gas
Récupérateur = Recovery unit
Echangeur = Exchanger
Alternateur HF + Convertisseur AC/DC/AC = HF Alternator + AC/DC/AC Converter
Compresseur Gaz = Gas Compressor
Compresseur Air = Air Compressor
Unité Contrôle/Commande = Control Unit