Cogeneration Plant

Cogeneration Defined

Cogeneration is the simultaneous production of electricity and heat, both of which are used for beneficial purposes. A cogeneration plant is a single source for electricity and thermal energy, located close to the point of use.

The conventional approach to energy operations for a campus of Amherst College's size and complexity is to obtain all electricity from the local utility company via the "grid", at only 30% efficiency, and to generate all of the thermal needs for heat and hot water via central steam boilers. This traditional process is inherently inefficient, as shown in the diagram below, because only so much electrical energy can be derived from the energy input, and the balance is wasted as heat rejection to the atmosphere. At best, this process is 45% efficient.

The benefit of cogeneration is that locating the plant adjacent to the point of use allows for increased efficiency of energy conversion and use.The waste heat from the combustion process is captured and processed through a "heat recovery steam generator" that extracts energy from the waste heat and uses it to produce steam.The diagram below demonstrates how capturing this waste heat increases the overall efficiency to 75% or more.

 

Conventional System
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Cogen Diagram
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Learn more about Amherst College Cogeneration Plant

 
 

General Benefits of Cogeneration

  • Increased efficiency of energy conversion and use results in a significant net reduction in energy input to create an equivalent output.
  • Lower emissions to the environment, in particular CO2, because less fuel is burned.
  • Significant cost savings--an investment in a cogeneration plant is an attractive capital investment that has a lucrative rate of return.
  • A more reliable power source. The electricity generated at the point of use is backed up by the utility grid.
  • Additional steam generation capacity, which allows reduced capacity requirements for the main steam boilers.

Amherst College Cogeneration Plant

Amherst  College's cogeneration system consists of a 1250-kW gas turbine generator that burns natural gas or diesel fuel. The turbine, similar in design to a small aircraft engine, will turn an electrical generator connected to the campus electrical system and send its hot exhaust to a heat recovery steam generator (HRSG).
 
The HRSG can make steam directly from the hot turbine exhaust, or burn additional fuel to make more steam to satisfy campus heat loads and keep the existing boilers off-line.

A 500-kW steam turbine is also installed as part of the project, generating electricity by taking the high-pressure steam produced by the HRSG and boilers and reducing the pressure for campus distribution. Previously, this pressure reduction was performed by valves under the old heating plant.

The cogeneration system occupies the space reserved for a future boiler in the existing heating plant, and a small addition has been created to house the turbines.

The cogeneration system supplies approximately 55% of the annual electricity usage. We purchase the rest from the local utility as usual. The steam output satisfies approximately 30% of the campus heating needs, with the existing boilers used to supply the rest.

The overall reduction in source energy substantially reduces the campus carbon emissions. Other emissions, such as NOx and SO2 that cause smog and acid rain, are greatly reduced because of the cogeneration system's cleaner fuels and state-of-the-art pollution controls.

The cogeneration plant produces over 11 million kWh per year, enough to power 1,000 homes. The carbon reduction is more than 22,000 tons of CO2, approximately 20% of the College's pre-cogen greenhouse gas footprint.

System Capacity

Electrical

  • Gas turbine: 1250 kW
  • Steam turbine: 500 kW
  • Total electrical output: 1750 kW
  • Total annual output: 12,000,000 kWh
  • Total CO2 saved by operating co-gen plant: 6,000 tons

Steam

  • Heat recovery steam generator: 8,000 to 20,000 lbs. of steam per hour

Gallery

 Cogen Plant        Gas Turbine  
Cogeneration Plant  

Gas Turbine Engine: the heart of our combined heat-and-power plant

 
 GT Pipes         HRSG Front  
Gas Turbine Pipes: This is not a screen saver.  

Heat Recovery Steam Generator: the heat end of the combined heat-and-power deal

 
SCR Emissions Controls         Boiler Feed Pumps   

Emissions Control NOx Reduction Unit: the smog saver

  New Boiler Feedwater Pumps: C3PO's cousins