Plasma Gasification

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Plasma gasification is a phrase heard often when discussion plasma-arc treatment or waste-to-energy technologies, however this entry looks to give a closer look as to what plasma gasification is and its associated reactions. Plasma gasification is a thermal chemical conversion process designed to optimize the conversion of waste into the synthetic gas or (“syngas”). The chemical reactions take place under oxygen starved conditions. The ratio of oxygen molecules to carbon molecules can be less than one in a plasma gasification reactor (sometimes a stoichiometric amount of oxygen to achieve pyrolysis).

The following simplified chemical conversion formulas describe some of the thermo-chemical processes that are typically occurring in gasification.

Equation 1. C (fuel) + O2 →CO2 + heat (exothermic)
Equation 2 C + H2O (steam) → CO + H2 (endothermic)
Equation 3 C + CO2 → 2CO (endothermic)
Equation 4 C + 2H2 → CH4 (exothermic)
Equation 5 CO + H2O → CO2 + H2 (exothermic)
Equation 6 CO + 3H2 → CH4 + H2O (exothermic)

Some of the waste undergoes partial oxidation by precisely controlling the amount of oxygen fed into the plasma reactor (see first reaction above). The heat released in the above exothermic reactions provide additional thermal energy for the primary gasification reaction (endothermic formulas above) to proceed very rapidly.

At higher temperatures (around 3,600°F) the endothermic reactions are typically favored. Some plasma companies (not PEAT however) introduce supplementary fuels such as coal, petroleum coke or even other hot gases generated by plasma torches (sometimes referred to as plasma-assisted gasification) to maintain the desired plasma gasification temperatures in the reactor.

Additionally, plasma gasification currently appears to be the option being promoted most widely for larger scale waste-to-energy applications mainly because of its ability to produce the syngas from which energy can be recovered in high efficiency recovery units so offsetting the high energy requirements of plasma gasification.

The reducing atmosphere within the plasma gasification reactor avoids the formation of oxidized species such as sulfur dioxide (SO2) and nitrogen oxide (NOx). Instead, sulfur and nitrogen (organic-derived) in the feedstock are primarily converted to hydrogen sulfide (H2S) and nitrogen. Finally, typical halogens in the feedstock are converted to inorganic acid halides (HCl, HF, etc.)

Potential pharmaceutical waste rule change

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EPA officials recently proposed adding hazardous pharmaceutical wastes to the Universal Waste Rule as part of a larger effort to protect public health and the environment. In addition, the agency has called for a simpler, more streamlined system for disposal that will make it easier for generators to safely collect and dispose of hazardous wastes. The proposed rule would apply to pharmacies, hospitals, physicians and dentists offices, outpatient care centers, ambulatory health care services, veterinary clinics and other facilities that generate hazardous pharmaceutical wastes.

The rule would also make it possible for generators to dispose of non hazardous pharmaceutical waste as universal waste, and thus remove unregulated waste from wastewater treatment plants and landfills. The collection of personal medications from the public for proper disposal would be facilitated at various locations across the nation. Currently, the Universal Waste Rule includes such items as batteries, pesticides and a variety of other items found in industrial and household settings.

Thermal treatment solutions will be required to make this proposal work. Plasma Thermal Destruction and Recovery is ready for the challenge. In addition to the information posted two weeks in this blog forum, unlike incineration or metal-bearing waste stabilization, PEAT’s plasma gasification process does not create any secondary solid wastes that would require further treatment or landfilling. For example, incinerators produce large quantities of bottom and fly ash that are toxic in nature and require further treatment (with stabilization agents); the resulting post-treated materials (whose volume may have increased significantly) will also require final disposal, sometimes in specially designed hazardous waste landfills.

Ultimately the commercial success of the PEAT’s plasma gasification technology lies in its ability to generate a favorable net present value based on existing market prices, industry dynamics and metrics. Using a conservative price point for pharmaceutical waste at $0.50 per pound, important financial benefits can be seen. PEAT’s waste-to-energy systems designed for on-site treatment (PTDR-100 and PTDR-500) have the ability to process feedstock on a continuous basis, feeding 21 hours a day with three hours reserved for maintenance and inorganic vitrification/pre-heating. Using 340 days per year, this indicates 8,165 operational hours per year and payback returns under three years.

You can read more about PEAT’s plasma gasification solutions with regards to pharmaceutical waste in the below article.

http://www.peat.com/other/IPT-PEAT-APRIL09.pdf

As was written in that article, waste treatment and alternative energy generation are two of the most difficult challenges facing many industries today. An ever-increasing global output, coupled with the rapid industrialization seen in many developing countries, is forcing the world to not only rethink how it handles waste, but how it views waste as a resource. Plasma gasification – and specifically PEAT’s waste-to-energy PTDR technology – allows companies to do just that.

More detail on Plasma-Arc

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Plasma can be described as an electrically-charged gas where a specific amount of energy is added to separate the molecules into a collection of ions, electrons and charge-neutral gas molecules. Plasma indicates a gas volume with sufficient energy supplied (electromagnetic, electric and/or thermal) so that electrons that normally exist in specific numbers and at distinct energy level orbiting around the nucleus are freed from their orbital bonds. This plasma, with its constituents of individual molecules and electrons acts as a conductor of electricity, the resistance of which converts electrical energy to heat.

Depending on the amount of energy added, the resulting plasma can be characterized as thermal or non-thermal.

Thermal plasma heating technologies were widely developed in the early 1960’s in conjunction with space exploration and military applications programs in the United States (NASA) and the former Soviet Union. In particular, plasma torches were developed to provide an effective method to test the effectiveness and durability of heat shields required for space vehicle re-entry.

Plasma-arc systems have been widely used for destruction of hazardous wastes.
This extreme heat from this temperature breaks down wastes, forming synthesis gas (hydrogen and carbon monoxide) and a rock-like solid byproduct called slag.

The significant difference between plasma-arc systems and other thermal waste processing technologies is that the heat required for waste degradation is generated by the plasma itself and not via combustion of all or part of the waste.

 
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