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Fuel cells project_maree
1. Fuel Cells Project
Maree
Introduction
The purpose of this project is to propose a sustainable use of fuel cell technology.
The Western Treatment Plant at Werribee, Victoria is more than 11, 000 hectares in area
and treats 52% of Melbourne's sewage. The site was first developed in 1892 and the first
Melbourne homes were connected to the sewerage system in 1897. Today it treats about
485 million litres of sewage each day, serving 1.6 million people in the central, northern
and western suburbs. The sewage comes from toilets, sinks and laundries in homes
across Melbourne, as well as wastewater or tradewaste produced from businesses and
factorires. 99% of the sewage is water. The treatment process separates the solid
material from the water and the 1% of solids tht remain from the treatment process are
further treated using biological processes to reduce the disease-causing pathogens and
stabilise remaining organic matter.
The Western Treatment plant uses large lagoons of ten ponds (1.5 km x 200 metres in
size). Each lagoon can hold up to 6200 million litres of sewage. The first pond in each
lagoon system includes membrane covers to eliminate odour and trap about 20,000
cubic metres of methane gas each day. Capturing this methane gas means that Western
Treatment plant halves their greenhouse gas emissions. AGL Pty Ltd uses the methane
gas to fire gas engines to generate electricity for the plant. These power generation
facilities are were initially capable of producing 3.7 MW of electricity and have since been
upgraded to a electricity production capacity of 8MW.
Each methane cover is made from high-density, 2.5 mm thick polyethyline. Each cover
takes up four hectrares and consists of a foam layer in the middle of two outer plastic
layers. The cover is anchored around the perimeter of the pond and held down by
2. weighted pipes. The cover traps methane, which can be stored for up to height hours,
allowing the gas generators to draw on it when needed. This program reduces operating
costs, and reduces greenhouse emissions and eliminates odour. Similar covers are used
in sewage treatment plants in parts of North America, but few are quite as large.
The gas generators operate up to 24 hours a day, with each lagoon producing enough
electricity to supply a small suburb. The covers collect around 40,000 cubic metres of
gas each day. The composition of the cover is:
• Methane 80%
• Carbon dioxide 10%
• Nitrogen 5%
• Hydrogen sulphide 0.5%
• Water 4.5%
The biogas is scrubbed to produce methane which is fed to the gas turbines.
Western Treatment Plant also produces biosolids (dried, stabilised matter that remains
made up of both oragnic and inorganic compounds) as a by-product of the sewage
treatment process. The plant's operators are currently seeking new and sustainable uses
for this renewable resource and one of the reuse options open to the plant is using
biosolids as fuel.
Werribee Western Treatment Plant produces 30 tonnes of methane per day.
Problem
Western Treatment Plant has the potential to increase sustainability and enhance energy
production from waste products it processes. Currently it produces electricity from
biogas on site with gas turbines and stockpiles biosolids. Both the biogas and biosolids
are potential renewable sources of energy.
The gas turbines which use methane from scrubbed biogas are currently only run during
peak times due to the economics of the peak-load energy market. The rest of the time
biogas (which is about eighty percent methane) is flared to the atmosphere as carbon
dioxide to reduce the greenhouse potential of the gas.
The digesters (part of the methane production system) require heat to increase methane
production efficiency. The temperature range for best production is 37-41 degrees
celcius. Temperatures in the area during winter months may limit the temperature to
below the optimum temperature range.
Proposal
The proposal is that of adding a fuel cell system (electricity generation plant) to the
Western Treatment plant, including gas storage, to enhance peak load energy generation
and enable this renewable power to be used more onsite for driving plant equipment and
charging electric vehicles.
The second part of the proposal is to add a pyrolysis plant to process biosolids and
generate syngas. The syngas is high in hydrogen which will be able to be fed into the
fuel cell. Biosolids are already stored on site. The pyrolysis process will be able to be run
on demand to produce syngas at times when the fuel cell demand is not covered by
biogas production from the existing biogas production processes (such as maintenance
work), or time of peak energy demand for the grid or onsite.
Another addition will be gas storage over a 24 hour period. The large space available at
3. Western Treatment plant means that pressurised storage is not necessary. The use of
gas bags will allow gas storage over a 24 hour period to be done at low cost. Existing
onsite pumping and gas transport systems can be enhanced or duplicated to meet the
extra demand.
Waste heat from fuel cell can be used to ensure the digesters operate within the
optimum temperature range for methane production.
Fuel cell system requirements
Costing
Fuel cell system costing
Capital cost estimates of US $400/kW.
10 MW fuel cell system cost estimate of US $4,000,000 (AUD $4,325,260) comprising 10
Ballard 1 MW PEM fuel cell systems.
Gasbags (for 24 hour storage of methane), extension to existing pumping equipment,
site infrastructure estimated $500,000 AU.
$4,825,260.
Lifetime
40,000 hours (5 years +)
Sustainability
• Reduced flaring of biogas, leading to reduced carbon dioxide emissions that have
not been first used for producing electricity.
• Heat used to increase efficiency of bioas production and other processes
• Use of biosolids to produce syngas for electricity production and biochar for
roadbases and agricultural uses (soil improvement)
Conclusion
The addition of a fuel cell system at Western Treatment Plant at Werribee will allow more
energy to be produced for onsite use and grid-export, which means electricity from a
renewable source will offset use from non-renewable and polluting sources. Better use of
the methane resource (less flaring) will mean less CO2 is escaped to the atmosphere
without first being used to generate electricity.
Bibliography
• http://www.melbournewater.com.au/content/sewerage/
western_treatment_plant/western_treatment_plant.asp?bhcp=1
• http://www.melbournewater.com.au/content/publications/fact_sheets/sewerage/
biosolids.asp
