The Case for Cogeneration and Cogen based Eco-industrial Networks
Single purpose thermal electric power plants reject between 50% and 65% of the fuel heat to rivers, lakes, the ocean or the atmosphere. The heat rejected by single purpose thermal power plants may cause thermal pollution. Cogeneration systems use this rejected heat for purposes such as paper drying, chemical processing, food processing etc., as well as space heating or cooling (absorption chillers). Cogeneration enhances industrial competitiveness through cost reduction. It reduces emissions.
Many industrial and institutional plants use interruptible natural gas with sulphur bearing Heavy Fuel Oil (HFO) as an alternate. The HFO has a far greater adverse environment impact that does natural gas. When gas turbine or combined cycle cogen takes over the HFO is gone.
Cogeneration produces given amounts of electricity plus process heat with much less fuel than when they are produced separately. Significant reductions in GHG and other emissions are assured. Transmission losses are reduced. With appropriate arrangements Cogeneration systems and selected loads can be kept running during grid failures (blackouts) avoiding costly shutdowns. Many cogeneration systems serve a single steam user such as an industrial plant, a university or a hospital. The aim should be to group thermal energy users in Eco Industrial Networks. This achieves economies of scale. in the cogen system serving the network.

Cogeneration-based Eco - Industrial Networks are the right road to Sustainable Industrial Development. This concept involves co-locating electric power producing facilities near groups of industrial processes using electrical and thermal energy. Outputs and waste from one process become inputs to other processes in the network. A single cogeneration Page 2 plant serves the entire network achieving Economies of Scale as noted.. Steam cannot be transmitted more than 4 or 5 km. However, heat can be transported much further in low temperature hot water, or higher temperature heat transfer fluids such as Dow Therm, Therminol or hot oil. Some processes more distant from Cogen system and industrial waste heat sources can be included in the network. Industrial Development people should locate Businesses and Light Industrial parks or near plants with available waste heat to take advantage of the waste heat and heat from the Cogeneration system for heating and cooling.

Natural gas, coal, wood residues, garbage, heavy (residual) fuel oil, petroleum coke, byproduct gases, liquid biofuels etc. can be used for steam turbine cogeneration. A much better approach, if the fuel can be used in a gas turbine, is to use the gas turbine exhaust to generate high pressure steam for an extraction condensing steam turbine. This combined cycle approach yields much more electricity worth about 3 times as much as the heat equivalent. Reciprocating engines fit some situations.

The case for flexible natural gas combined cycle cogeneration. All natural gas combined cycle systems should have a base loaded cogeneration component. Flexible combined cycles provide firm power, peaking power and spinning reserve. The flexibility is provided by using an extraction condensing steam turbine. The condenser rejects heat at the at a temperature so low that it has limited use. There may be processes in the network which can use this very low grade heat in cold weather. Steam should be lost at the condenser only during peak loads The flexibility of a combined cycle system can be substantially increased by using a burner between the gas turbine and the heat recovery steam generator (HRSG). In one case the steam turbine has a capacity of about 12 MW without auxiliary firing and 30 MW when the auxiliary burner between the gas turbine and the HRSG is fully on. The gas turbine exhaust is roughly 15% oxygen so combustion air need not be heated. As a result the natural gas is burned at an efficiency some 10% higher than it would be with a conventional boiler. Gas turbine exhaust can be used directly in Yankee dryers on paper machines and some other drying processes such as clay drying

. Heavy industrial parks - Paper machines, chemical processes, oil refining, food processing etc. are well suited to relatively large scale Cogeneration based Eco Industrial Networks. Good examples of chemical/ petrochemical/ oil refining networks are the TransAlta, Sarnia 400 MW combined cycle system serving 4 large petrochem. complexes and the Joffre AB, 450 MW cogen plant serving a major petrochemical complex.
The Alberta Industrial Heartland near Edmonton has several major combined cycle cogeneration systems. Examples of Forest products complexes with cogeneration are Catalyst in Campbell River, Bowater in Thunder Bay and Irving Pulp and Paper/Irving Tissue in St John NB.








Polygeneration - adds a new dimension to chemical, petrochemical and oil refining complexes. Integrated Gasification Combined Cycle IGCC Systems can gasify coal, petroleum coke and other inputs to produce electricity and process heat as well as hydrogen which can be converted to ammonia used to produce a variety of chemicals products such as nitrogenous fertilizer. Pure sulphur can also be produced. This approach is particularly well suited to Sarnia where the coal fired The Ontario Power Lambton Generating station has major coal handling facilities An IGCC ploygenration Page 3 plant could be built on that site. . Pure CO2 would flow from the stack. This can be sequestered by pipeline according to a recent study of Sarnia by sequestration experts. The Hydrogen could be used for fuel cells and in nearby chemical plant and oil refineries.. .

Perhaps the best example of an Institutional Eco Industrial network is the General Campus of the Ottawa Hospital. A TranAlta 70 MW combined cycle cogeneration system supplies thermal energy to a large hospital complex. One of the hospitals more than a kilometre away from the Cogen plant is both heated and cooled by a single low temperature hot water loop from the cogen plant. Absorption coolers handle summer air conditioning.

Cogeneration should also be encouraged for light industrial parks where non energy synergies or symbiosis may be more important. There are many of these. An example is the Burnside Eco-Industrial Park in Dartmouth (Halifax) Nova Scotia. Thermal energy can now be used for both heating and cooling (trigeneration) which can help reduce both summer and winter peak loads on the grid. Reciprocating engines using light liquid fuels or natural gas can cogenerate for smaller systems.

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Bio Energy can be used for steam turbine cogeneration by burning wood residues or pulping liquor. There are many of these in pulp and paper mills. A system by Dynamotive and Orenda in West Lorne Ontario uses liquid fuel made from saw mill residues in a gas turbine cogeneration system producing The outputs are 2.5 MW of electricity and steam for the lumber kiln. The benefit of cogeneration depends on the fuel displaced from a single purpose power plant by the electrical output of the cogeneration plant. Hydro will not be displaced due to storage and export options. Biomass steam generation without cogeneration produces no more emissions per unit of fuel burned than would be produced if the material were incinerated or allowed to decay. Biomass cogeneration displaces fossil fuel otherwise used to generate electricity at single purpose plants. It reduces emissions. Much more electricty can be produced when biomass can be gasified for use in gas turbine combined cycles. Likely in the near future.

Anaerobic Digesters. Biogas from these can be used in cogeneration systems based on municipal waste treatment, manure etc.
Fuel Cells produce both electricity and reject heat (cogeneration). They can use byproduct hydrogen from petrochemical processes. Nuclear plants can produce hydrogen off peak. It can be made from natural gas, coal etc. There are many applications.
Nuclear Cogeneration. Steam can be extracted from the steam turbines of nuclear power plants. This was done at Tiverton, Ontario at the Bruce nuclear power plant. A standby fossil fuel plant can be used during periods of peak loads on the grid.