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Garbage In, Power Out: How Trash Can Power Ethanol Plants

A win-win situation for the local government, utilities, and industry.

Fortnightly Magazine - February 2007

the process, but recent technological advances have reduced this usage to 200 kWh/ton of MSW. 10 The vitrified slag or rock residue produced is 400 pounds.

The above-simplified representation of the MSW pyrolysis step can be shown as a simplified process flow diagram 8 but the fuel/gas could be used for generation of electricity, steam and/or for synthesis of chemicals (see Fig.2).

A simplified process-flow diagram 14 is shown here for a typical ethanol plant converting the raw material, corn, into ethanol: (see Diagram 1).

The capital cost for a plasma arc gasification process to produce electricity and a vitrified slag can be deduced from the following figure (see Figure 3) of capital cost versus capacity. 5

Thus, with the information presented so far, a preliminary evaluation and economics can be deduced for a plasma-arc plant using MSW 12 with sufficient capacity to supply both electricity and steam for an adjacent ethanol plant producing 50 million gallons of ethanol per year from corn. 11

Consequently, we evaluate the following economic cases: (see Table 1) .

Basis

A plasma arc gasification facility operates at 706 tons/day capacity 1,2,3 for treatment of MSW with a “total” capital investment of $97,344,000. 5 This plasma plant capacity supplies sufficient energy as electricity and steam to an ethanol plant for the production of 50 million gallons of ethanol per year. 11

Capital cost of the ethanol plant is $65 million. 11 Capital financed for both plants would be at 5.75 percent interest for 20 years, making two payments per year. The plasma-arc facility would generate 30,000,000 kWh/year 4 of electrical energy (renewable energy) for sale to the ethanol plant at 4.5 cents/ kWh. A 2.0 cents/kWh revenue from green tags associated with renewable energy electrical production was used in the financial analysis for the plasma arc plant.

In addition, the plasma arc plant would supply 1,421,405,000 lbs/year steam for sale to the ethanol plant at a sale price of $5.50/1,000 lbs steam. The byproduct rock material would be sold as a road construction material at $15/ton. 1 On the ethanol facility, 18,518,500 bushels/year of corn are purchased at $3.75/bushel. 11 A byproduct, dried distillers grain with solubles (DDGS), is produced at 166,667 tons/year and sold as a cattle feed for $90/ton. 11

Cost considerations for operations and maintenance, a capital budget reserve, process water, and sewer have been considered in the economic evaluation. More than 100 jobs would be created by a combined plasma and ethanol facility. The combined facility is self-sufficient in electrical and steam energy requirements, since this energy is produced internally from a renewable raw material, MSW.

Economic Cases

From these “initial” economic analyses, one likely approach to a business plan is for a cooperative effort among a local utility, local industry, and local governmental entities. Thus, the local government participates in the MSW treatment part of the plasma-arc facility while the local utility participates in the electrical and steam energy (renewable energy) producing part of the facility. A local industrial/business entity could own/operate the ethanol facility. Thus, the local government remains in the