Recycling Waste Heat Via Cogeneration  

Solve Climate has an interesting post on cogeneration in the US and the - Co-Generation: Clean as Wind, Reliable as Coal. The title isn't strictly true - while it can improve the efficiency of many forms of power generation, CHP still relies on the burning of fossil fuels (except when hydrogen is used) and is just increasing the efficiency with which we harness the energy generated - it isn't carbon free and thus shouldn't really be compared with solar, wind and other true clean energy sources.

We think we could make about 19 to 20 percent of U.S. electricity with heat that is currently thrown away by industry.

Tom Casten, chairman, Recycled Energy Development

There are different types of co-generation, but the concept is simply this: take energy that is being wasted on an industrial scale and find a way to put it to use. Do that, and co-generation could provide up to 20% of the nation's electrical generation, replacing a large number of our coal plants at a lower cost and with roughly the same reliability.

Another name for co-generation is combined heat and power (CHP). We have enough potential CHP to replace 40% of coal-fired generation. Producing 20% of our electricity from CHP would put it on par with our fleet of nuclear reactors, which also produce about 20%. CHP is also as clean as wind power, reliable enough to use as base-load power and has the lowest construction cost of any power source.

The DOE and EPA in 2001 put together a road map to double the amount of CHP. It said,

CHP is a win-win-win solution for energy users, energy and equipment suppliers, and society-at-large and produces measurable national benefits for energy efficiency, environmental protection, and economic growth.

A typical coal plant has an efficiency in the low 30% range, meaning 65% or more of the energy is wasted. CHP can improve the plant efficiency to the 60%-80% range. Waste heat is commonplace in heavy industry too: for example a West Virginia Alloys silicon plant uses high heat to refine the metal. For now, when they're done refining metal, they just let the heat dissipate. Recycled Energy Development (RED) is developing the CHP needed to capture that heat and drive a steam turbine that will produce 40 to 44 Megawatts of electricity. No additional fuel is used - all the power that is generated comes from capturing the heat that would've been wasted. Since there's no extra fuel, there's no extra fuel expense and no extra CO2 generated, making this as clean as wind or solar power.

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The heat from a power plant, instead of being lost in a cooling tower or surrendered to the atmosphere, can be used for local heating via underground hot water or steam pipes to nearby businesses, homes or industry. There's a limit on how far the heat can travel, hence the name, district heating. Once more common, today in the US this is mostly limited to college campuses and a few old downtown neighborhoods.

Anytime there is a pressure drop in a pipe, a backpressure turbine generator can capture the lost energy. For example, long distance natural gas pipelines operate at high pressure and when the pressure is reduced for local distribution, some of the significant energy originally used to pressurize the pipe can be recovered. This is sort of like regenerative braking for gas lines. An investment of $8 to $10 billion could capture 6.5 GW, another bargain at $1,250 to $1,500/kW. Steam pipelines are more numerous and have even more potential. The college campuses with district heating mentioned above could also be producing some fuel-free power where ever the steam pressure is reduced from transmission pressures to the pressure used in buildings.

Many industrial processes have leftover gas or create some low quality gas that can be burned. Quite often, this is simply flared ( that is, burned ) at the top of a smokestack. I watched flaring gas coming off steel mill blast furnaces for years as a kid in Gary, Indiana without knowing what it was. In any event, I was awed by 15 foot high tongues of flame dancing on top of a 300 foot high stack. Other sources are oil refineries, auto painting plants, carbon black plants and ethanol refiners.

One more advantage of CHP is that the electricity usually doesn't have to travel far and rarely requires new transmission lines. Unlike many large utility plants sited far away from population centers, most CHP installations are already where there are people and power demand.

Barriers

If this is such a great idea, and it is, why haven't we used more of this fuel-free, cheap-to-build and reliable power? The biggest barriers are legal. In part because many of our state and federal laws are out-of-date and in part because monopoly power companies have tilted regulations in their favor, it can be the hardest part of implementation. In the DOE/ EPA road map, the main issue wasn't financing, technology or finding good projects, it was legal barriers. This is what the report said about eliminating regulatory and institutional barriers:

This set of actions is the centerpiece of this Roadmap. There are CHP systems that are commercially viable today but that developers have trouble getting installed because of roadblocks in siting, permitting, and interconnecting.

In most of the country, it is illegal for anyone but the power company to sell you power, reducing the market of CHP electricity to what you can use in your own plant. In the entire country, it's illegal for anyone but the electric company to run a power line across a street, making it even harder. When a company does consider a co-generation project, the local electric company can discourage it with high fees for interconnections, backup power and other services that make it uneconomical. This is far thornier than it appears at first. Check out RED's excellent blog for a real power industry insider's view of this and other issues.

If you've been worrying about meeting the Gore Challenge and you didn't know about CHP, you should feel like you just found a $1,000 bill laying on the sidewalk. Or, even better, 100 GW of high availability generation nearly ideal to provide 20% of our electrical generation and replace 40% of our coal plants.