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


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

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

Fortnightly Magazine - February 2007

Ethanol plants either are operating, under construction, or planned for several areas in the Midwest. These same areas also have municipal solid waste (MSW) produced daily in an existing landfill. In addition, these areas have a need for establishing or extending a landfill.

As an alternative to the existing concept of a landfill, plasma-arc technology has been applied to the treatment of MSW. Known as plasma-arc gasification for the treatment of MSW, this recent development would eliminate or minimize the need for a landfill.

Plasma-arc gasification can generate an abundant amount of energy and electricity, or steam. Nearby ethanol plants using corn require electricity and a large amount of steam for fermentation, distillation, and drying operations.

In this article, we offer a preliminary economic analysis of a joint process operation for a typical ethanol plant using corn, with a capacity of 50 million gallons/year with a plasma-arc plant processing MSW. A simplified schematic for such a hybrid process (combined plasma-arc plant and ethanol plant) is shown below.

Plasma arc gasification for the treatment of municipal solid waste (MSW) is a very high-temperature pyrolysis type of process (7,200 oF to 12,600 oF) whereby the organics of waste solids are converted to a synthesis gas, and the inorganic and minerals of the waste solids produce a rock-like byproduct. 1,4,6,8,9

The synthesis gas 6,7,9 is predominantly carbon monoxide (CO) and hydrogen (H 2). The inorganic material and minerals in the waste solids (MSW) are converted to a vitrified slag typically of metals and silica glass. This vitrified slag basically is non-leaching and exceeds EPA standards. Metals can be recovered from the slag and the slag can be used to produce other byproducts 1,4,6,8,9 such as rock wool, floor tiles, roof tiles, insulation, and landscaping blocks. One of the simpler recyclable uses of the slag is as a road material[ 1] but at much lower economic value. The synthesis type of gas can be used to produce electricity and the rock-like byproduct as a material for road construction, since it is environmentally acceptable. The fuel/synthesis gas produces byproducts hydrochloric acid (HCl) and sulfur via the gas cleanup step 8.

In this article, the economics are performed on a process for converting MSW by a plasma-arc gasification (a pyrolysis process) to a synthesis gas and a vitrified slag. The synthesis gas will be used to generate electricity—steam—and the slag will be used as a road material.

The bottom line: This process for treating MSW eliminates the need for a landfill and can be used to process existing landfill MSW sites.

MSW can be processed using the plasma arc gasification 1,4 process and simply represented in Figure 1.

Note, 1 ton of MSW uses 500 kWh of the total electricity produced by