Reclaim waste heat from Power plants

Want to take a 1-minute course on power generation? Great! There is a little mathematics mixed in, but it’s not too difficult.

The key to understanding efficiency is realizing that the energy used from the fuel exceeds the electrical energy produced.

1 kWh (kilowatt-hour) is the basic unit of power measurement and is equal to 3412 BTU’s (British thermal units). One barrel of heavy oil, costing roughly $50 / barrel, contains 6.2 milllion btu’s. So that barrel should produce a tremendous amount of energy when burned and it does. But a considerable amount of the energy is released as heat and not usefully converted into electricity.

Heavy oil or coal is burned to create steam that turns turbines. Once through the turbine, water from the ocean cools down the steam to allow a pressure difference and more hot steam to flow. On it goes around the circle and power is produced.

It actually takes roughly 10,000 BTU’s to create 1 kWh (3412 BTU’s) which is 34% efficiency conversion. The remaining 6,588 BTU’s of energy are lost out of the steam and flows into the ocean.

So how did we end up with thermal power generation that produces 1 unit of electrical energy and throws out nearly 2 units of heat? The simple answer is that power plant design evolved from a time when oil was cheap, less than $10 per barrel. Secondly, huge demand for energy required more than hydropower was able to fulfill and windpower was not a cost-effective option back then. Thirdly, power companies were never mandated to look at the energy efficiency of the whole process or to cooperate with private industry or the community to use the waste heat.

Public Utility Boards are the utilities oversight committees but sometimes they don’t see the larger picture either. To make matters worse, utilities built plants in isolated areas to avoid public controversy, making it difficult to use the waste heat for homes, industry or agriculture. Such is the benefit of hindsight. What a terrible waste of energy!

There are instances in North America where CHP (combined heat and power) is used for process heat to increase the efficiency of the system to roughly 85%, similar to the level when we burn oil in an efficient home furnace.

Europeans are way ahead of us in this regard. The Beznau nuclear plant in Switzerland distributes roughly 75 Megawatts of waste heat to homes and businesses.

The economics of oil generation are not too good lately. One barrel of heavy oil = 6.2 Million BTU’s / 10,000 BTU’s per kWh = 620 kWh’s per barrel. $50 CAN per barrel / 620 = 8 cents per kWh just for the fuel. If we add another 3 cents for the annual capital cost of the plant and the operational cost, then oil isn’t looking very good at 11 cents per kWh and it’s just going to get worse price wise in coming years. And we haven’t even mentioned greenhouse gas emissions from an oil plant.

So the future of the Coleson Cove plant in New Brunswick, the Tuft Cove plant in Nova Scotia isn’t bright and Maritime Electric’s plant on the Island only runs when absolutely necessary anyway. So probably oil fired plants are not going to be running much in coming years. But how would we use some of the enormous waste from coal and nuclear plants that will be running for the long term?

  • Install massive agricultural greenhouses in the Lepreau or Belledune area in New Brunswick. Similar installations in Nova Scotia are possible. Commercial operators of greenhouses would see low cost heat as a real incentive to locate close to a power plant.
  • Invite industrial enterprises to use the excess process heat at reasonable cost.
  • Consider the possibility of an indoor water theme park with wave pools, and other attractions. The low cost heat provides the economic incentive. In the future, gas prices will kill long distance tourism and the only method to satisfy the human desire for a getaway vacation may be a unique local tourism destination.
  • Where economically possible, install district-heating loops to feed residential homes from existing power plants.
  • Use of the waste steam heat to economically separate hydrogen for use as a fuel.

To put this into perspective, the heat wasted from Belledune coal fired power station is the equivalent of 3.9 billion kWh’s. (400 Megawatts x 60% load factor x 8760 hours per year x 65/35% efficiency) This is 3.5 times the annual power usage of the residents of Saint John. If we price this at 5 cents / kWh, then we have $195 Million of heat wasted each year. The waste heat from Point Lepreau would be equivalent to 7.8 billion kWh ($390 Million) per year. Could a portion of this heat be saved and used for good purposes?

In the future, should we rethink some of the principles related to power plant siting and design so that waste heat becomes part of the energy solutions that we so desperately need? When Public Utility Boards evaluate proposals for new power plants, should they include planning for use of the waste heat as part of the process? Should greenhouse gas emissions be part of the economic evaluation? I certain hope so.


One comment

  1. Hans Oomes · September 13, 2007

    Went to a tech school in Rotterdam, Netherlands from 1951-1953. I studied electro-mechanical stuff. A ring of well insulated pipes, supply and return, were installed in the ground and houses with hotwater radiators were hooked up to that system. The pipes were fed with the waste heat of a nearby power station. Apparently it worked very well.

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