Waste treatment plant operators have begun to employ plasma arc technology for the treatment of municipal solid waste (MSW), as an alternative to establishing and/or extending a landfill. This recent development could eliminate or minimize landfill volumes. To accomplish an economic evaluation of the technology, the Linn County treatment plant near Marion, Iowa, with a 500 ton per day output of MSW, was selected as a prototypical facility.

Plasma arc gasification for the treatment of MSW is a pyrolysis type of process (7,200 to 12,600˚F) whereby organic wastes are converted to a synthesis gas and inorganic solids to produce a rock-like byproduct. Synthesis gas is often called syngas and is predominantly composed of various concentrations of CO and hydrogen.

The inorganic and mineral constituents in the MSW are converted to a vitrified slag, typically of metals and silica glass. This vitrified material is basically non-leaching, exceeds EPA standards, and can be used to produce metals and other byproducts, including rock wool, floor tiles, roof tiles, insulation, landscaping blocks, road aggregate or even metallic content. The synthesis gas can be used to produce electricity, thanks to byproducts such as hydrochloric acid and sulphur formed via the gas cleanup step.

Enlarge this picture Figure 1: A simplified representation of the MSW pyrolysis step.

For the purposes of this evaluation, the synthesis gas was used to generate electricity and the slag as a road material (see Figure 1). It should be noted that 1 ton of MSW used 500 kWh of the total electricity produced by the process, but recent technological advances have reduced this usage to 200 kWh per ton of MSW. The vitrified slag or rock residue produced was 400 pounds. The simplified representation of the MSW pyrolysis step in Figure 1 can be shown as a simplified process flow diagram (see Figure 2). In the diagram, only the gas could be used for generation of electricity and/or for synthesis of chemicals.

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Figuring cost

Enlarge this picture Figure 2: Process flow diagram of plasma gasification as applied to municipal solid waste.

The capital cost for a plasma arc gasification process to produce electricity and a vitrified slag was deduced from a comparison of capital cost versus capacity (see Figure 3). Thus, Linn County’s 500 tons per day of MSW, with an excess of electrical energy produced for sale at 800 kWh per ton of MSW, economic Cases 1 and 2 apply at break-even.

Now, if the excess electrical energy for sale is 600 kWh per ton of MSW, then the following economic Cases 3 and 4 apply at break-even.

If the government incentive payment of 1.8 cents per kWh is replaced with a 1.8 cents per kWh tax credit -- similar to that used for wind energy -- and a utility company sold the energy produced, a break-even Case 5 applies:

The plasma arc gasification facility operating at 500-tons/day capacity for treatment of MSW showed a total capital investment of almost $79.2 million. Capital financed for the project would be at 5.75-percent interest for 20 years, making two payments per year. A government incentive of 1.8 cents per kWh revenue to produce a renewable energy up to maximum payment of $750,000 per year, and a 1.0 cent per kWh revenue from green tags associated with renewable energy production were used in the financial analysis.

In Cases 1 and 2, the facility would generate 146 million kWh per year of electrical energy for sale to the grid system at 2.5 cents per kWh. In Cases 3 and 4, the facility would generate 109.5 million kWh per year of electrical energy for sale to the grid system at 2.5 cents per kWh. The byproduct slag material would be sold as a road construction material at $15 per ton. Such cost considerations for operations and maintenance and a capital budget reserve have been considered in the economic evaluation. Over 50 jobs would be created by the new plasma facility.

The basis for Case 5 is similar to Case 4 except a government tax credit of 1.8 cents per kWh is used rather than a cash incentive payment. Also, the utility company sells the excess power generated at 6.72 cents per kWh for a break-even tipping fee of $35.00 per ton of MSW.

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Economic cases

Enlarge this picture Figure 3: A chart showing anticipated capital costs versus capacity.

From these initial economic analyses, one business plan is to seek a cooperative effort between the local utility and governmental entities. Thus, the local government participates in the MSW treatment part of the plasma arc facility, while the local utility participates in the renewable energy-producing part of the facility, i.e., the local government remains in the MSW business while the utility stays in the electrical energy business. This appears to be a win-win situation for both parties.

Case 1 presented the preliminary economics of a plasma arc gasification facility for Linn County, producing 800 kWh per ton MSW for sale as excess energy. Private industry invested 61.5 percent of the total capital, and a governmental grant covered the remaining 38.5 percent of the facility’s capital requirements. The cooperative venture resulted in a tipping fee for the MSW of $35 per ton at the break-even point.

Case 2 presented an economic evaluation similar to the previous case but private industry finances accounted for 100 percent of the total capital requirements of $79.2 million. The net result at break-even was for the tipping fee to be increased to $49.20 per ton MSW. If, however, Case 2 had the electrical energy produced sold at 4.5 cents per kWh, the break-even price for the tipping-fee would be about $33 per ton MSW.

Case 3 presented the preliminary economics of a plasma arc gasification facility for Linn County, producing 600 kWh per ton of MSW for sale as excess energy. Private/industry invested 42.5 percent of the total capital and a governmental grant covered the remaining 57.5 percent of the capital requirements. The cooperative venture resulted in a tipping fee for the MSW of $35 per ton at break-even.

Case 4 presented an economic evaluation similar to the previous case but private industry finances handled 100 percent of the total capital requirements of nearly $79.2 million. The net result at break-even was for the tipping fee to be increased to $56.17 per ton of MSW. If, however, Case 4 had the electrical energy produced sold at 4.5 cents per kWh, the break-even price for the tipping-fee would be about $44 per ton of MSW.

Case 5 is similar to Case 4 except a government tax credit of 1.8 cents per kWh was used rather than a cash incentive payment. Also, the utility company sold the excess power generated at 6.72 cents per kWh for a break-even tipping fee of $35 per ton of MSW. Additionally, the utility company generated a tax credit of over $1.97 million per year. With the tax credit considered as a revenue source, the break-even selling price for energy produced became 4.92 cents per kWh.

Logical approach for future progress

A logical approach is to take initial economics presented for a particular area and periodically update the analysis by a cooperative effort between one or more governmental bodies and industrial entities, so that both parties will have a fully transparent involvement and trust in the final economic analysis. This factual, transparent, updated economic analysis will therefore determine the final approach taken by both government and industry when determining if plasma arc gasification is an economically and environmentally attractive alternative to a landfill.

The attractiveness of plasma arc gasification technology is the generation of renewable electrical energy and the production of a useful byproduct with environmentally acceptable properties. Thus, the state of the local economic climate for renewable energy and recycled products has a direct influence on the economic viability of the technology.

A utility company in partnership with a local government would likely be the more economical combination with a more positive benefit to the environment. Keep in mind that plasma processing of MSW is an emerging technology, and that this economics study is purely preliminary. Such evaluations are site-specific, and thus should be repeated for each case. Yet the study suggests that with proper diligence, a viable business plan can be developed, an encouraging sign for the future of plasma arc technology.