The Other Green Energy: Recycled energy is often overlooked, but has huge potential
Posted by Dick Munson on July 8th, 2010
Fox News shines a light on recycled energy as a clean and low-cost source of power that could make an enormous difference in our country, yet is often overshadowed by “sexier” and more expensive forms of clean energy. Fox reports that policy makers have overlooked “a power source boasting far greater reliability and intensity than both solar and wind power.”
Fox visited the energy recycling project at the Arcelor Mittal steel plant in Indiana, and notes that recycled energy, which it calls “The Other Green Energy,” has massive potential to slash energy costs and carbon emissions at the same time. Fox interviewed RED’s Tom Casten, who said, “What they’ve done at this plant produces about twice the amount of clean energy as all of the solar collectors in the U.S.” Tom explained that as a nation we are allowing hundreds of billions of dollars worth of energy to literally go up in smoke as wasted heat that could be captured and turned into useful, clean power. “We are the Saudi Arabia of waste heat,” he said. “You can either use it or lose it.”
As a mechanical engineer, I would like to see better and more specific information provided by your organization. “Using energy twice” as an example is a catch phrase and an accurate description of energy utilization processes. Recovering waste energy really means two things; Getting more heat out of the flue stack or making use of the latent energy in condensing steam. Neither one is high quality heat. I was part of the team that designed a new central utility plant for a mid-sized university. I repeatedly was called by an economizer maufacturer who wanted me to put his condensing economizers on our boilers. The trouble is, unless we were heating a whole bunch of greenhouses or a really big swimming pool, (a pretty pretty small group of choices) the economizers wouldn’t even work.
Oops…I meant NOT an accurate description of energy utilization processes.
In response to Mike Hromanik’s post, I concur entirely with his view that the heat from latent energy in condensing steam is not high quality. With a thermal gradient in the cooling circ water ranging somewhere between 15 and 28 degrees F its usefulness is indeed limited.
However, an energy conversion system capable of operating cost-effectively from such a heat source could capture much of the 40% heat normally dissipated by the cooling system. My company has such a technology, but the political and societal roadblocks that stand in the way of full scale demonstration and commercialization are immense. I’m sure the Casten father/son team
are well aware of such a situation!
Another viable application for low-grade heat is to dry out the woodchip fuel. Humidity in this form of biomass is notoriously high and has a significant impact on the heat rate of the facility.
Alan Belcher.
Alan and Michael,
Your thermodynamic concerns are well taken, and it is certainly not practical to recover the low temperature heat from a typical cooling tower at a thermal power plant to make useful energy. However, that only highlights the problems with a paradigm that starts by maximizing power output.
Our approach when designing a typical “topping cycle” cogen plant is to maximize efficiency and operating margins by making a bit less power than one might make in a power-only approach so as to leave high value residual heat in the tail exhaust that can be more fully used. Note that this gets substantially more useful energy out since the customer who needs high grade heat needs the full heat of vaporization (effectively, the lumber mill/chemical plant/etc. becomes a cooling tower, using the full ~1000 Btu/lb available rather than just the few degrees of latent heat.)
In a waste heat recovery facility, we do the reverse, taking high grade heat that is being dissipated from a manufacturing facility to generate heat and/or power that would otherwise require the use of additional fossil fuel.