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Great Northern Power is in the business of developing small cogen power plants under 10 MWs. We seek out opportunities to recover waste heat or to combust waste fuels such as:

- green biomass (bark/hog fuel)
- municipal solid waste (MSW)
- industrial waste wood (IWW)
- construction, demolition & renovation (CDR) waste
- oilfield waste

in order to produce electricity and thermal energy for the host facility.

Typical technologies used to produce the heat and power are:
  1. turbine driven generators with HRSG,
  2. steam based Rankine Cycle systems, or
  3. Organic Rankine Cycle systems
Regarding steam based power generation, the larger these systems are the more economic they are as the staffing requirements are typically fixed. Less than 10 MW steam systems are typically only economic if the site already has steam operators for another application. For projects under 10 MW’s that do not currently have steam operators, then ORC Cogen systems are ideal for on-site power generation. Typically, ORC systems have lesser requirements for government prescribed operators than steam systems and therefore are well suited for smaller projects.

ORC systems are usually designed and built in modular components that are factory assembled on skids. ORC skidded units are typically delivered by truck and ready for operation following minimum site installation. Factory assembly allows the ORC systems to be tested and meet industrial standards before shipping. Note the schematic below:



ORC systems are based on the Rankine Cycle, with a variety of hydrocarbon that can be used as the working fluid. Therefore, because no water is used in these closed systems, no provision is required for protection from freezing.

Although other technologies can produce ON-SITE power under 10 MW capacity, not many are economic. ORC systems are economic because of:
  1. Capability to produce both heat & power
  2. Low maintenance costs (few moving parts)
  3. Low staffing/operator costs
  4. No trucking of fuel (as little as 2 Tonnes/hour required)
  5. No pre-treatment of the waste
The basic components of ORC Cogen Systems are:

Component Function
Thermal oil heater Recovers energy from the energy source to heat thermal oil.
Turbine-generator set Converts the thermal energy in the vapour to mechanical energy to drive the generator and produce electricity.
Condenser Condenses the working fluid from vapour to liquid.
Accumulator tank Stores liquid leaving the condenser and serves as the head tank for the charge pumps.
Pump(s) Elevates the pressure of the working fluid from that maintained in the head tank to that required by the turbine.
Switchgear and controls Controls the power from the generator and provides protection for the system.
Transformer Matches the voltage of the generator to the load or the utility system.
The ORC technology is based on the concepts used and applied in generating electricity in geothermal projects. Hundreds of geothermal projects exist globally where power is generated using these types of systems, and the application to biomass primarily differs on the front end of the system — the source heat. In geothermal stations, the source of heat is hot water at 120°C to 170°C. In waste fuel applications the source of heat is much higher. Therefore operating temperatures and pressures in waste fuel applications are higher than in the geothermal projects, resulting in lower capital costs and higher operating efficiencies.


ORC systems have several other advantages over other power generating systems such as gas turbines and reciprocating engines.


© 2001 Great Northern Power.