SEPTEMBER 2009

Commercialized plasma gasification of solid waste offered by S4 Energy

Click to Enlarge - InEnTec's Plasma Enhanced Melter plant in Richland, Washington.
E-mail the author

One need not be a physicist or chemical engineer to understand what plasma gasification can mean to the future of solid waste. This intriguing technology for converting solid waste into chemicals and energy has been in the demo phase since the mid-80s. But in May it took a major step forward towards commercial deployment when Waste Management (WM) and InEnTec announced a joint venture to form S4 Energy Solutions. S4 plans to build plasma gasification plants and WM has the nationwide infrastructure to deliver a smooth flow of segregated feedstock.

WM, North America’s largest waste management company, is embracing plasma gasification for the first generation of commercial facilities. “We are choosing some sites right now and have a few identified. Short term, we are looking at three to five different locations. Long term we are going to be looking at the majority of the 50 states. We expect to announce our first plant in three to six months. At that time we will expect to have already started construction. We are beginning the permitting process in a few cases and doing prep work for those facilities,” stated Jeff Surma, president and CEO of S4.

“The point lost on a lot of people is that this technology has been around for a while. From a chemistry perspective it works,” said Joe Vaillancourt, senior vice president of S4 Energy Solutions. “What no one had done in the past is put together a model where the collection of waste can be done efficiently, routed and pre-processed efficiently. This collaboration allows the technology to marry a very large WM infrastructure that from an economic standpoint allows it to work commercially.” 


This is how InEnTec’s Plasma Enhanced Melter (PEM) technology works. Solid waste is fed into an oxygen deprived chamber and heated to temperatures reaching 10,000 degrees Fahrenheit using an electricity-conducting plasma arc gas. Intense heat rearranges the molecules and transforms organic, carbon-based material into a synthesis gas, called syngas. Syngas is then converted into fuels such as ethanol and diesel, and into hydrogen and methanol that can be substituted for natural gas to make heat or electricity.

Molten waste created by the InEnTec's Plasma Enhanced Melter.

Recovered pure hydrogen can also be sold to commercial customers or used for fuel cell technology. In a secondary stage of the process, inorganic materials like glass and rock are drawn off as slag which can be incorporated into a number of construction materials.

The PEM process has been field proven in a number of small pilot plants, including a plant in Taiwan for the past four years that treats medical wastes and NiCad batteries. InEnTec also sold a system to Kawasaki in Japan, which was used to process hazardous waste and asbestos containing waste materials. Kawasaki continues to develop opportunities in Japan for the PEM technology. For the past nine months, InEnTec’s 25 ton per day plant in Richland, Washington has been running tests on various solid waste feedstocks for analytical purposes. “Once you have the analysis of syngas relative to waste composition and energy content you can calculate what you can do with the various energy off-take options,” said Surma. The syngas produced from the Richland plant is not actually used for chemicals or energy, rather disposed though an EPA approved combustion process.

Permitting and emissions do not seem to pose problems for this type of plasma gasification configuration. “We have actually permitted a number of these plants. Even though they were small we did not have any permitting issues,” Surma said.

Beside the Richland plant, InEnTech has had five other United States permits issued. Another in Washington to process radioactive and toxic wastes, one in California and another in Hawaii for medical wastes and two in Nevada, one for a municipal solid waste system and the other for medical waste. Permits usually take from 90 to 180 days. The direct emissions from the PEM system itself are negligible. Primary emissions from the PEM system would be those of the generator itself if the syngas was used to generate electricity, in which case all emissions would comply with EPA standards,” Surma claimed.

The initial S4 plants will handle 25 tons per day and will be co-located at landfills or recycling centers, or as independent facilities close to feedstock supplies. In the near term, S4 will concentrate on processing high-value, high tipping fee materials such as medical waste and other commercial segmented waste streams.

Short term, medical waste will be S4’s primary focus. Long term, as they prove out the technology, plants will be scaled up to 125 tons per day, which will be the common size for a plant. These will be deployed to sites as single or parallel units depending on the nature of feedstocks. Once S4 reaches the 125 ton scale they will be able to handle larger streams from industrial sites such as auto shredder residue. Eventually, S4 hopes to prove out the technology to process general residential waste.

“Whether we are talking about the very small 25 ton per day, or even the larger plants, they are still of the size that allows us the flexibility to site them as close to waste generation points as possible. So even with a larger facility, it is still significantly smaller than other alternatives,” Vaillancourt noted. The 25 ton per day plant has a relatively small footprint, about 7,500 square feet and can be run 24/7/365 with a staff of 12 to 15, even fewer if co-located with another facility that has maintenance and operations staff. The PEM process itself can be operated by as little as two people.

InEnTec’s Richland pre-commercial plant provides insight into material segregation before entering the PEM process. Municipal solid waste was received from the City of Richland landfill in raw form. Prior to a course shredding, large ferrous and non-ferrous metals, aluminum cans and large rocks were removed. Rocks, glass and other inorganic materials have no recovered energy value and result in slag. While the demo plant has run a number of different feed streams, it has been running municipal residential waste to understand how the technology performs. It has also processed rubber tires, wood waste, auto shredder residue and industrial non-hazardous solid waste streams like cardboard and plastic. The plant has not run medical waste because InEnTec has extensive experience with this material at its other facilities.

When it comes to recovering energy from waste, WM is not putting all its eggs in one basket. They are, after all a leading developer of waste-to-energy incineration and landfill gas-to-energy facilities in the United States. As to the economics of plasma gasification, Joe Vaillancourt characterized it this way: “Instead of looking at a thumbnail on the cost of energy production, what we are proposing is a service where our pricing is competitive to market, both on the disposal and on the energy side. Where we have customers who have a need, we can come in very competitively and provide them a disposal way of creating energy.”

Since the plasma arc process uses large amounts of electricity and uses some natural gas to heat vessels, the question is what is cost of energy consumed to the resulting value of the energy and products produced? It largely depends on material input. Waste streams heavily laden with plastics, cardboard or rubber will naturally have a higher BTU value. “Generally between the variability of the incoming waste and efficiency of conversion to different types of energy, the system uses 30 to 50 percent and we have a 50 to 70 percent net energy positive conversion. In addition to the energy recovered, we are also subsidized by tipping fees on the high value materials,” said Surma.

“Our S4 initiative is being driven by a number of factors. Certainly the cost of energy has a significant impact on why people are starting to look at alternatives for the conversion of what used to be considered waste stream with no energy value to a resource that does have energy value. That’s primarily the factor for looking at conversion technology like this.”

An interesting aspect of PEM technology is that it allows S4 to mix a variety of wastes while giving WM the flexibility to deliver the types of waste mixtures as the plants need them. When co-located at either a landfill or recycling center or at a customer facility there are several segmented streams that could be combined efficiently. “It’s a technology that we feel is very flexible and adaptable to customers’ particular economical, environmental, and logistical needs. These units can be put close to the generator. They will become especially cost effective for customers who have high transportation costs and high tipping fees.” Vaillancourt pointed out.