Project Green District Energy Feasibility Study - Partners in Project ...

TRCA Pearson Eco-Business Zone District Energy Feasibility Study 10 April 2012
Appendices
higher efficiency due to higher evaporation temperature as raw sewage may be at higher
temperatures than an alternative geothermal field lower overall capital from not having to drill
multiple deep bore holes as for geothermal
However, these factors must be checked for local site conditions.
It must be emphasized that the relative success of the heat pump in Vancouver is partly due to
B.C. enjoying a much more moderate climate than other parts of Canada. This allows the
buildings to be supplied at a lower temperature more of the time. However, another factor is
that the SFC system serves new development designed for lower district heating supply
temperature; this aspect might be emulated elsewhere for new developments. In fact, FVB
recently considered this heat source for other clients and as a result, there may be a similar
project proceeding in the GTA within the next few years.
One of the important requirements is access to a relatively high constant sewage flow, e.g. in
the order of 200 litres/second for 3 MWt. Therefore, due to the low population density of Project
Green there may be physical capacity limits, similar to geothermal and solar, which would
prevent this technology from serving a large portion of the potential heat demand.
13.6 Biogas
Biogas consists of approximately 50-60% methane (as compared with 97% for natural gas), with
the balance being mostly carbon dioxide. There are also some trace contaminants, notably
water vapour and hydrogen sulphide (H2S). After relatively simple drying and H2S removal
biogas can be used in boilers and reciprocating engines for CHP much like natural gas. In fact
equipment can be retro-fitted to accept natural gas if originally designed to use natural gas. It
may be viewed as a potential future substitute for natural gas.
Biogas is recovered from landfills and in anaerobic digesters at wastewater treatment plants.
Another source is from facilities for processing the source separated organic fraction of
municipal solid waste or animal waste on farms. Landfill gas has some challenging
contaminants, such as siloxanes, but can still be used for power or heat generation.
Waste cooking fats and oils collected from food processors and restaurants are expected to
become another major source of organics for energy production. In fact, Organic Resource
Management Inc. one of the largest companies in this business in Canada has its head office in
Woodbridge, on Steeles Avenue West. They currently collect from over 8,000 customers, dewater
the material locally then ship it to Quebec for composting. Energy production via biogas
from anaerobic digestion is seen as the highest value use for such material.
In some European DES, biogas is piped for several kilo-metres from the digesters to CHP units
in DEC’s. This practice could be emulated in Project Green, especially given the proximity of
industrial areas to the planned new commercial development.
Another approach that FVB has suggested to other clients is to purchase “green gas” from
remotely located biogas producers in an analogous way to purchasing “green power”.
Green gas, also called pipeline gas, is biogas that has been upgraded by removal of carbon
dioxide and other contaminants to the quality of natural gas and injected into the natural gas
distribution system. The City of Toronto is proceeding with two pipeline gas projects at their
planned new anaerobic digesters at the Disco and Dufferin Transfer Stations. The City of
Toronto has internal uses for the green gas and is therefore not in the market as a supplier.
However, there may be other potential green gas producers, e.g. farmers, which the DES could
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