Objective
To extract, dewater and utilize biogas produced in a controlled urban and industrial waste landfill either as primary fuel (when needed) in an incinerator for industrial toxic wastes or to generate electricity by otto-cycle gas motors to supply the needs of the industrial wastes treating plants located near the landfill area.
A remarkable number of short-term plant breaks were generated by an unexpected high number of micro-interruptions and power fluctuation (dued to in-line works) which affected negatively process computer fuctionality.
Even if gas production was initially intended mainly for direct combustion as auxiliary fuel in the toxic wastes incinerator, the delay in the completion of it has made electricity production the only available outlet for the gas.
During the test run of the plant electric measurements have been made and the yeld figures appear very interesting.
With regard to gas motor, electro/thermic functionality measurements have been made with power set at 50%, 75% and 100 % of nominal power.
At 100% of nominal power, that is with an electric power of 215 kW gas consumption was measured as 143 NMc/h which, being methane percentage equivalent to 51.63 gives a yeld of 2,577 Kcal/kWh.
Electricity produced is primarily self-used within the area and only a minor surplus is poured inthe municipal network.
Landfill gas capacity during plant exploitation has shown itself remarkably constant with a gas concentration highly reliable.
Methane concentration in the landfill gas has been constantly measured for more than one year by means of an infra-red analyzer, further data have been collected giving the following average figures :
CH4 57% C02 36.5%
02 0.01% N2 0.3%
H2S 0.0005 Mercaptans 0.002
A top capacity figure has been reached as 174,8 Nmc/h.
Besides these figures a keen attention has been reserved to the possibility of any interaction between environment and landfill parameters.
While no correlation has been recorded with external temperature, an interesting parallel pattern appears between rain and methane concentration.
With regard to single components, it is remarkable the good electricity yeld of gas motors and the reliability of the gas extraction system.
The Municipal Solid Wastes landfill of Modena is located in the outskirts of the city, nearly two kilometers from the beginning of urban area.
The landfill was started in 1973 and closed in 1985 and is developed completely in elevation; it covers an area of about 70.000 s.m. and the volume in about 1.200.000 c.m. reaching a maximum height of about 37 meters.
Between 1973 and 1985 there were disposed about 700.000 tons of M.S.W. which exceeded the capacity of the municipal incinerators as well as refuse with high organic content coming from separate collection.
At first (1981) the project was to utilise the gas (expected 5.000 c.m. per day from a smaller landfill expected not to exceed 450.000 tons) directly by combustion in a brick factory nearby; the decision (1982) to locate the Industrial Toxic Wastes Treating plants in that area as well as the increased capacity of landfill gas (now expected about 9.000 c.m. per day) led the proposers, first to change the user of the plant, now the municipality itself, second to fit the plant to user's needs at best, that is to add to gas extraction, dewatering and distribution sections a further step of electricity production.
A first lot of 7 bore holes have been drilled and connected to the collecting network giving a capacity of about 120 cu.m per hour while the maximum suction rate is fixed in 3.44 cu.m per hour per meter of pit; the second lot will tip the capacity of 9.000 cu.m per day from 20 wells.
The power house now contains one DEUTZ BGA 8 M otto-cycle water cooled gas motors which supplies 217 Kw electric while two more motors will be installed in 1988; when landfill gas will be needed as primary fuel from the incinerator of organic toxic wastes the shortage of fuel will exclude the motors automatically.
Particular care has been given to the measure and control system both of the suction plant and the motor which are fully computerized.
The whole plant is developed in order to be completely automatic.
Theprocess computer operates the plant through :
- methane and oxigen percentage indicators, recorders and controllers through pit-valve opening, scanning each single pit connected to the network plus the feeder giving thus highly constant gas composition, with alarm and automatic pit shut-off in case of malfunctioning;
- suction head control unit.
An exaust gas oxigen meter operates through a PLC in order to optiimize fuel-air ratio in conncetion to motor load.
Gas meters are placed before each user while power meters will measure electricity produced by each gas motor; other meters placed before plant distribution switchboard which is parallel connected to the local network will enable to get a continuous energy balance of the system.
Programme(s)
Topic(s)
Call for proposal
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DEM - Demonstration contractsCoordinator
41100 Modena
Italy