Opportunities to recycle waste energy
A variety of industrial waste energy streams can be recycled into useful heat and power. These
include hot exhaust gases, low-grade fuels (some of which are typically flared), and high-pressure
steam and gas. Proven technology can profitably convert the energy in hot exhaust (300 degrees
F or higher) from any process into steam that drives turbine generators and produces electricity.
Coke ovens, glass furnaces, silicon production, refineries, natural gas pipeline compressors,
petrochemical processes, and many processes in the metals industry vent hot exhaust that can be
profitably recycled to produce fuel-free power.
Another way to recycle waste energy is by burning presently flared gas from blast furnaces,
refineries, or chemical processes to produce steam and electricity. Factories producing carbon
black (used in tire manufacturing) typically waste enough flared gas to produce three times their
The energy potential in pressurized gases also can be recycled into electricity. Examples of
pressurized gas include steam, process exhaust, and compressed natural gas in pipelines. Gas
pressure drop can be converted to mechanical energy with expanders, which then drive an
electric generator. Many industrial producers generate streams of high-pressure gas that can
power a backpressure turbine connected to an electric generator in order to produce fuel-free
power, with zero pollution.
For example, most industrial and commercial boiler plants were designed to generate steam at
high pressures to pack the distribution pipes. This approach allows the plant to install smaller
distribution pipes, reducing first cost. These plants then deflate steam pressure at points of use by
means of valves. A backpressure turbine can convert the pressure drop into fuel-free power. Nearly
every college and university campus, as well as most industrial complexes, could produce some
fuel-free power from steam pressure drop with a backpressure turbine generator.
Gas transmission pipelines burn approximately 8 percent of the gas being transported to drive
compressors that pack the remaining natural gas into transcontinental pipes. The gas pressure is
then reduced at each city gate with valves, typically wasting the potential energy of the pressure
drop. Gas expanders can recycle this pressure drop at the points of gas flow into local distribution
systems. Capturing this natural gas pressure drop across the United States would require roughly
$8-10 billion of new investment and would result in 6,500 megawatts of clean energy. The
resulting generation would produce roughly 28 trillion kilowatt-hours per year of fuel-free power
with zero pollution. At present, we know of only two locations in North America that capture this
opportunity. To achieve a comparable amount of clean energy would require 22,000 megawatts
of new solar collectors (at a current capital cost of $130-170 billion) or 6-7 nuclear plants.
Many industrial processes—such as catalytic crackers at petroleum refineries and blast furnaces at
steel mills—also emit hot exhaust at above atmospheric pressure. Top-gas recovery turbines could
produce 15 to 35 megawatts of fuel-free power at every blast furnace and every oil refinery. The
overwhelming majority of U.S. blast furnaces and oil refineries currently waste this potential clean
energy due to their focus on their “core business” and corresponding underinvestment in energy
Recycling industrial waste energy enables us to tackle a major challenge of our time—global
warming—while reducing energy costs for our customers and creating profits for our investors.
Greenhouse gas reduction and profitability are mutually sacrosanct to our business. Without the
former, we leave the world a worse place than we found it. Without the latter, we won’t grow.
USG will develop industrial energy projects that either recycle waste energy from a host's industrial processes to produce electricity and
thermal energy, or it will build new on-site electrical generation that converts fuel to electricity and then recycles the associated waste heat to
displace the host's boiler fuel (a process known as cogeneration or combined heat and power). Recycled energy is useful energy derived from:
* Exhaust heat from any industrial process or from electric power generation;
* Industrial tail gas that would otherwise by flared, incinerated or vented; or
* Pressure drop in any gas.
Understanding the potential to recycle energy or cognerate requires three pieces of information:
* First, manufacturing processes and electric power generation convert only a portion of their available energy input into useful work. Both
discard the remaining potential energy. The electric power generation system, on average, discards two thirds of its input energy as waste.
Many industrial processes also discount significant quantities of potential energy. This energy carries a significant cost of procurement and
conversion. Investments in energy recycling, therefore, create substantial economic savings.
* Second, much of the waste energy discarded by manufacturing and power generation can be profitably recycled into useful heat and power—
but only if the energy recycling facility is located at or near users. Thermal energy, which is the form of much of present waste, does not travel
far without losing its value.
* Third, the electric power industry has largely ignored energy recycling, focusing instead on remote central generation plants that cannot
capture waste heat. This bias results from cost-plus utility regulation, which for several decades provided a guaranteed return on a monopolist’s