Recycling Energy: The Fine Art of Rag Picking
by Thomas R. Casten
ecycling, once confined to rag pickers in poor countries, has gone mainstream. Over the past thirty years, competitive industries have learned to rag pick go through the trash and salvage steel, aluminum, paper and plastic. Recycling presently wasted energy could cut US fossil fuel purchases by $65 billion per year, postpone new electrical transmission and distribution, reduce emissions of various pollutants by 19 percent to 48 percent, and decrease electric system vulnerability to extreme weather and terrorist actions.
A variety of proven technologies lie in wait, but the industry assumption of the superiority of central generation blinds the world to the recycling opportunities from decentralized electric generation (DG).
How is energy recycled?
Industry groups have defined recycled energy as the useful energy derived from:
These waste streams are abundant in all industrial processes but only a small portion of the energy content of the fuel is incorporated in any product. Most of the energy is vented into the atmosphere. However, it is often profitable to recycle this energy by generating heat and power in relatively small, decentralized plants.
Process energy recycling potential
Industry vents heat from coke ovens, metal production, glass production, gas compressor drives, refineries and chemical production. Although the data is sparse, it is conservatively estimated that 13 gigawatts of electric capacity could be supplied from the heat energy presently vented to the atmosphere. (1 GW = 1,000,000 kilowatts)
US industry flares waste gas equivalent to 2.0 Tcf of natural gas/year. Flaring reduces certain emissions, but the resulting heat is generally vented. Picking these 'rags' could supply 19 GW of new electric-only capacity or support combined heat and power (CHP) with 12 to 15 GW of electric capacity and 45 to 50 GW of thermal capacity.
Steam boilers convert about 85 percent of the fuel to steam or hot water but heat-only production does not extract high value electricity. Most industrial and institutional complexes feed distribution systems with medium pressure steam, but then discard the pressure drop energy. The steam is deflated at points of use with pressure reducing valves instead of using backpressure turbines to convert this pressure drop into electricity.
These steam pressure drop rags could supply 12 to 20 GW of fuel-free electric capacity. In addition, if the boiler pressure and pressure differential are increased, the waste thermal energy produced could be used to generate another 50 GW of electricity. Similarly, natural gas which is compressed for transmission and then deflated at the local distribution system supply points could also supply 8-10 GW of fuel free electric capacity.
In total, US Industry could rag pick waste energy to supply 45 to 58 gigawatts of electric capacity and importantly, avoid the waste and environmental impact of burning 6.8 quadrillion Btu's (quads) of fuel per year 7.0% of total US fuel consumption.
Industrial recycled energy: Primary Energy
In 1994, NiSource formed a subsidiary, Primary Energy, to help economically challenged integrated steel companies recycle their waste heat and blast furnace gas. The new company invested $300 million in six waste energy facilities. Combined, these plants supply 440 MW of electric capacity and 460 MW of steam capacity.
The four steel mills owned by Ispat Inland, ISG and US Steel consume the recycled heat and power on-site. By recycling energy they have improved their competitive position by over $100 million per year and reduced yearly emissions of SO2 by 24,000 tons, NOX by 12,000 tons and CO2 by 3.4 million tons. The CO2 reduction is equivalent to the CO2 uptake of just under 1 million acres of new trees. Such rag picking is profitable. Recently the projects were sold for $335 million to Private Power.
Energy recycling: Decentralizing electric generation
The wasted heat from US central generation of electricity that could be recycled is five times the industrial process recycling potential described above. In 2001, 71 percent of total US power was generated with an aging fleet of fossil-fired central plants that delivered only 30.7 percent of the fuel energy to users as electricity. These plants made no use of nearly 70 percent of the fuel, thus wasting 25.2 quads.
After transmission and distribution (T&D) line losses (3.6 quads), and nonrecoverable boiler losses (5.6 quads), 16 quads of heat could have been recycled to replace thermal boiler fuel or electric heat. Generating the power in DG plants near the end users would have eliminated at least half of the T&D losses, raising the total recycling potential to 17.8 quads.
In 2001, commercial and industrial sector boilers consumed 25.9 quads of fuel with 85% efficiency. If all fossil-fueled electric generation had been replaced with thermally matched CHP plants, 21 quads of this fuel would have been saved.
Why don't central plants recover waste heat?
Recycling heat from central electric generation stations is prohibitively expensive due to the cost of piping steam and/or hot water long distances to thermal users. Ton van der Does, acknowledged by many as the father of CHP in the Netherlands, explained these economics with the rule of sevens.
He determined that it generally takes seven times more energy to move a unit of electric power a given distance than to move a unit of fuel the same distance. In addition, it takes seven times more energy to move a unit of thermal energy than to move a unit of electric energy. Thus it takes forty-nine times more energy to move a unit of thermal energy from point A to point B than to move the same energy as fuel.
To make recycling economic, generation must be decentralized, moving fuel to the thermal user, generating power in on-site CHP plants, and then moving the recycled heat short distances. The electricity will flow first to the thermal host and then to the nearest electric consumers, regardless of contracts. Decentralized generation would significantly reduce energy lost in transmission of fuel, heat and power.
Why continue central generation?
DG is severely limited by many legal and regulatory barriers that were originally enacted to protect early electric entrepreneurs from competition in order to speed electrification of every community. The rules remain, long after universal electrification, for two reasons: assumed economy of scale and inertia.
Today's best 500 MW combined cycle gas turbine electric only plant converts 60 percent of the fuel's energy to electricity. In 2001, T&amp;amp;D losses consumed 9.7 percent of centrally generated power, thus reducing delivered efficiency to 54 percent. A one MW, combined cycle, molten carbonate fuel cell is more efficient, delivering 57 percent of the fuel energy as electricity. More importantly, this fuel cell is twice as efficient as an average US coal-fired plant. It can also recycle waste heat to achieve 80-95 percent overall delivered efficiency.
But what of capital cost for new capacity? The commonly used measure of dollars per kW of generating capacity suggests major economies of scale; the 500 MW plant can be installed for $800 per kW versus $2500 per kW for the small fuel cell. A truer measure is the dollars per kW of delivered power at the peak load, which includes T&amp;D capital and peak period losses. The US transmission congestion is worsening, suggesting the need for new T&amp;D for every new kW of central generation, which is estimated to cost $1200 per kW, on average. New T&amp;D raises installed cost per kW from new central plants to $2000/kW. Only 80% of this new central capacity will reach users during peak periods, when line losses reach 20%. Thus, the total capital cost of a new central generation peak kW is $2500, the same as the fuel cell, which needs no new T&amp;D and has no peak load line losses.
Although the molten carbonate fuel cell is the most efficient DG technology today, several mature CHP technologies cost less than half as much per kW, offsetting their lower fuel-to-electricity conversion. A 5 to 20 MW combined cycle gas turbine converts 40% to 45% of the fuel to electricity and can achieve 85-95% overall efficiency by recycling most of the waste heat. Piston engine DG has comparable efficiencies. Both technologies cost $800 to $1,200 per kW, less than half the current cost of fuel cells, compensating up for their lower electric efficiency. All DG technologies will become cheaper and more efficient with mass production.
Using a variety of fuels, proven CHP technologies offer economic DG across a wide range from a few kW to several hundred MW. Combustion and reciprocating engines convert oil, natural gas and most off gasses to heat and power, while boilers with backpressure turbines burn virtually all fuels, including waste, biomass and coal.
In summary, today's CHP technologies offer a superior value proposition to central plants on a delivered kW basis with combinations of capital advantage and efficiency.
Why continue to operate and build expensive central plants when DG has such comprehensive advantages? In a word: inertia. Attitudes, habits of mind, obsolete regulations and the power of incumbent firms that profit from the status quo are all slow to change.
In competitive markets, insurgent firms push disruptive technology into niche markets, gradually overcoming the natural inertia and leading to the technology growing to dominate the overall market. But electricity is not a competitive market and many barriers to DG remain even in states with some easing of monopoly protection. Barriers will remain until all energy policy makers understand the advantages of DG and CHP.
Savings potential from recycling energy
Figure 1 shows the potential fossil fuel savings to the US economy from industrial recycling and replacing fossil fired central electric generation with thermally matched CHP. These two actions, fully deployed, would save 20.8 quads or 21.5 percent of US fossil fuel consumption. The calculations assume a mix of current CHP technologies with a 32 percent fuel-to-electricity efficiency and 88 percent overall fuel efficiency. In other words, 56% of the CHP fuel is recovered and recycled as heat. These numbers are consistent with the authors experience with over 150 thermally matched CHP plants ranging in size from 40 kW to 200 MW.
The weighted average cost of fuel in 2001 to the commercial and industrial sectors was $3.22/MMBtu and $1.88/MMBtu for central electric generation. Figure 2 shows the dollar and percentage fuel savings potential from recycling of $65 billion, which is 17 percent of the total US fuel expenditures.
Recycling reduces emissions in two ways, by burning less fossil fuel and by replacing old and relatively dirty generation with modern, clean production. The percentage reduction varies for NOX, SO2 and CO2 due to fuel mix changes and technology substitution. Figure 3 shows the percentage reduction for each at various levels of recycled energy deployment.
Modernizing energy policies will speed deployment of DG and CHP and yield large savings to consumers, manufacturers, the economy and the environment.
Energy rag picking can flourish by:
Despite abundant advantages, DG supplied only 6.5% of US electricity in 2001. Interstate differences ranged from none to 26% in California and 33% in Hawaii. Internationally, DG provided a low of 2-3% of electricity produced in France to over 40% in Finland, Denmark and the Netherlands.
Since each state and country has access to similar technologies and capital and fuel costs, the explanation for differences lies in local regulations and barriers. Where policy makers have encouraged utilities to support DG and have removed barriers to efficiency, energy recycling has flourished. The energy industry like competitive industries must put away its slippers and start sorting through the trash. It is time to embrace the fine art of rag picking.
Thomas R. Casten is Chairman, World Alliance for Decentralized Energy, and Chairman and CEO of Primary Energy Holdings, LLC