by E. Gary Cook
The global chemical industry has always had the challenge of disposing of chemical wastes, by-products and residuals by legal, safe and economically effective means. Traditionally, the primary disposal methods have been landfill, deep well injection, and incineration. Responsible chemical companies all over the world have strived to dispose of these chemicals, especially hazardous ones, in keeping with national and state regulations. In hindsight, we have discovered that methods formerly thought to be safe and permanent have proven otherwise, as leaching, groundwater contamination, air quality issues, and other problems were discovered. Superfund legislation was enacted to identify sites needing remediation to avoid harm to the environment and to the public, and many of the sites identified met every environmental regulation at the time they were in use. Incineration, once believed to be the safest and most environmentally friendly way to dispose of chemical wastes, has its limitations as well.
 Figure 1. Schematic of the G500 PEM system |
Historically, many chemical companies operated their own incinerators, but as emissions standards continued to tighten over the years, only very large incinerators could justify the high capital cost of installing appropriate emission controls. As a result, incineration capacity continues to fall, and conventional wisdom says no significant new hazardous waste incineration capacity will be built. Existing hazardous landfills are reaching capacity and permitting such new landfills has become difficult, very time consuming, and in many jurisdictions, impossible. Transportation costs for chemical residuals continue to rise and there are regulatory, environmental, and consumer pressures to reduce the movement of such products through public corridors. In addition, the chemical companies themselves have set goals to reduce their carbon footprints (the amount of CO2 and other greenhouse gases produced by operations and transportation) and have established internal sustainability goals which seek to reduce the residuals produced in every process and to recycle and reuse as much material as possible.
Today, a new answer is commercially available to address all of these issues. The Plasma Enhanced Melter (PEMTM) gasification technology uses chemical wastes, by-products and residuals as feedstock and converts them into useful products returned to the chemical companies or sold to the broader market. PEM technology was invented by scientists and engineers working at the Battelle Pacific Northwest National Laboratory and the Massachusetts Institute of Technology, and commercialized by InEnTec LLC. These inventors found a unique way to combine a DC plasma arc with an AC glass melter to provide an efficient, cost-effective and environmentally sound process for converting waste materials into useful products.
Waste or chemical residuals (solid or liquid) are fed into the primary vessel, contacting the plasma zone which reaches temperatures of 3000°–10,000°C. A plasma is a highly ionized gas, sometimes referred to as the fourth state of matter. Extreme examples of plasmas experienced in every day life are fluorescent lights and lightning. The PEM plasma is created by DC carbon arcs, which are consumed by the process and are automatically and continuously fed via a proprietary mechanism to the PEM. The glass bath is heated via AC resistance heating, just like a burner on an electric range. The combination of DC Plasma with an AC glass bath is unique and allows the energy to be balanced between the two zones in the most efficient manner. Oxygen and steam are fed into the PEM along with the waste at levels calculated, to provide reducing conditions such that high oxides cannot be formed. In short, within the PEM, a steam reforming reaction occurs almost instantaneously. Power requirements are generally proportional to the carbon content of the feedstock. The energy balance for typical wastes results in about one-third of the energy produced to be used to power the PEM and two-thirds are available for downstream use.
The refractory is proprietary and has shown excellent lifetimes, generally a minimum of three years, including exposure to high halogen containing wastes. Operation is highly automated, with numerous feedback loops and interlocks to ensure efficient and safe operation.
Organic materials are immediately converted to their elemental state and recombined to form synthesis gas (a mixture of hydrogen and carbon monoxide – see box). Most inorganic materials are dissolved or entrained in the glass. The glass can be collected on a batch or continuous basis and has been found to have useful properties. Metals may end up as part of the glass or in the case of heavier metals, pass through the glass to be collected separately. Halogens, sulphur, mercury, and other elements are removed from the synthesis gas in the gas treatment system, resulting in a very high purity synthesis gas that can be converted into a variety of products, such as hydrogen, methanol, ethanol, and dimethyl ether (DME).
The process has been subjected to numerous tests and has been found to meet or exceed all environmental regulations. Because it is not a combustion process, the PEM process is not conducive to the formation of dioxins, furans and other pollutants.
A number of PEM units have been built and operated commercially. Today, a unit in Taiwan processes a mixture of industrial and medical wastes, generally operating 24/7. Another unit was sold in Japan and used to demonstrate PCB destruction for the Japanese government, and then relocated to demonstrate asbestos reduction. Based on those tests, an agency of the Japanese government has ordered two more units for PCB destruction.
Systems to be deployed for the chemical industry are supplied by InEnTec Chemical LLC, a joint venture of InEnTec LLC and Lakeside Energy LLC. Lakeside Energy has committed up to $150 million in equity funding to build PEM-based projects. Systems for the municipal waste industry are supplied by InEnTec Energy Solutions LLC, a wholly owned subsidiary of InEnTec.
The first on-site unit in the chemical industry in the US is currently under construction at Dow Corning Corporation’s facility in Midland, Michigan. This project will use chlorosilane residuals as its feedstock and return HCl and synthesis gas to Dow Corning for use as a raw material and to displace natural gas usage. It is expected to be operational by the end this year. During 2008, using a portable PEM unit transportable on two semi-trailers, the versatility and utility of the PEM were demonstrated to a number of major chemical companies who brought samples of their hazardous waste to the temporary site. Each was provided detailed analysis showing degree of destruction and purity of the synthesis gas produced. InEnTec Chemical has several other projects in various stages of development with these and other major global chemical companies.
Use of the PEM in the chemical industry creates a true paradigm shift. Chemical wastes are no longer problems to be managed but are now the raw material for a new chemical process. In certain applications under US EPA regulations, if materials that would otherwise be hazardous waste are used as ingredients to produce other chemical products, they are excluded from RCRA regulation and are simply considered chemical feedstocks. Materials used as feedstock to the PEM process qualify for this exclusion.
A typical build, own, operate installation will be built on or contiguous to the chemical company plant site. Frequently the feedstocks are fed directly to the PEM and the new products are returned to be used by the host site. In this closed loop mode, emission sources are minimized and can be drastically reduced. In addition to useful products, other installations capture the energy value of the feedstocks as a ‘waste to energy’ installation, and, at the same time, reduce CO2 and NOx emissions exponentially. The PEM provides a new economic model as well. In return for a long-term contract to supply the raw material (waste or other residuals) and a long-term contract to take the products produced, a PEM system will be built at no capital cost to the chemical company.
Next-generation technologies such as PEM offer a new paradigm and a new vision for the chemical process industry. For the first time, a broadly applicable, economically viable and environmentally sound solution to the problem of chemical waste is commercially available. The PEM process is poised to become a major factor in helping the chemical industry move toward true sustainability.
E. Gary Cook is CEO of InEnTec Chemical LLC, Oregon, USA
e-mail: egcook@aol.com
Synthesis gas to energy or clean fuels
When wastes are introduced into the PEM, they are broken down by the extraordinarily high temperatures of the plasma zone into their basic molecules, which recombine to reform the elements present. The organic materials are converted into synthesis gas, a combination primarily consisting of hydrogen and carbon monoxide along with minor quantities of other elements present in the organic wastes. This mixture goes through a gas cleaning train and the resulting product is a very high quality synthesis gas.
Synthesis gas may be used directly as a fuel, usually replacing natural gas. Synthesis gas may be further processed in a standard PSA reaction to recover the hydrogen, useful in hydrogen fuel cells. It also can be converted via catalytic reactions to alcohols, including methanol or ethanol. Another option is conversion to dimethylether, which can be used as a direct substitute for propane. Finally, synthesis gas from the PEM, just like synthesis gas from a coal gasification process, can be converted into diesel fuel via a Fischer-Tropps reaction.
The synthesis gas from the PEM process is of exceptional purity compared to other gasification processes and is therefore useful in a broad variety of downstream processes that are sensitive to contaminants.
