As you may know from reading this blog, in plasma arc, plasma gasification, waste is broken down at temperatures around 1,500°C. While this form of gasification can be energy intensive, it ensures that the plasma gasification syngas produced is cleaned of residue tar, which makes it a higher value product. Another major benefit of plasma arc, plasma gasification is that it creates little to no emissions. This blog entry attempts to take a quick look at some of the other waste to energy technologies available.

Conventional gasification slightly differs from plasma arc, plasma gasification in that the temperatures inside its primary reactor are lower and the fuel source may be natural gas. However conventional gasification is similar to plasma arc, plasma gasification in that both are thermo-chemical processes in which waste is heated in an oxygen deficient environment to produce syngas which contains hydrogen, carbon monoxide and sometimes methane. This gas can be used as fuel for electricity generation or to produce chemicals or biofuels.

Pyrolysis is sometimes linked to plasma arc, plasma gasification. Pyrolysis is also a thermo-chemical process, however here the waste is heated in the complete absence of oxygen. The products are olefin liquid, syngas-type product, and char. The liquid fuel can be used as an input to produce gasoline, while the char can be recovered or passed along to a gasification process.

Other waste to energy alternatives include landfill gas recovery that convert methane gas from decomposing trash in to power. Methane is collected through a series of pipes and compressed for electricity generation. There are also waste to biofuels and waste to chemical processes. These are similar to aforementioned waste to energy technologies as they may utilize gasification or other thermo-chemical processes. Appropriate waste feedstocks include soybean straw, wood waste and used oils/fats.

Finally, there is anaerobic digestion (AD). This differs greatly from the other waste to energy technologies mentioned here in that AD uses microorganisms to convert organic waste into a biogas (primarily methane) and digestate. This biogas can be used to generate electricity, while the digestate has applications as a fertilizer. Anaerobic digestion is limited to wet organic wastes (including manure and sewage) or food waste. As such it requires that these materials to be separated from regular waste.

The innovative and patented core Plasma Thermal Destruction & Recovery waste to energy solution is a gasification technology. Gasification is a process that converts organic based carbonaceous materials into carbon monoxide (CO), hydrogen (H2) and carbon dioxide (CO2) by reacting the material (i.e. waste) at high temperatures (minimum 700°C) without combustion with a controlled amount of oxygen and/or steam. The resulting gas mixture is called syngas (from synthesis gas) and is itself a fuel.

PEAT uses the heat generated by plasma-arcs to first pull apart (dissociate) the molecules that make-up the organic portions of the waste, then, depending on the composition of the waste stream, oxygen is added to reform the dissociated elements of the waste into the syngas The syngas can then be used in a variety of ways: as a fuel for thermal and/or electricity production or as a feedstock for the production of liquid fuels, such as ethanol.

Waste, when heated to a very high temperature in the controlled atmosphere of the reducing plasma reactor undergoes predictable physical and chemical changes. This high temperature, over 1,250°C (2,280°F) prevents the formation of complex organic molecules and breaks down organics into a gas. Our operations reflect that the formation of dioxins or furans is practically impossible inside the plasma reactor due to the unique process features, including high uniform temperatures and a lack of excess oxygen within the system.

This hot gas is then fed through a gas cleaning and conditioning system (The gas that comes out of a plasma reactor has a trace of contaminants compared to huge quantities in the stand-alone incinerator), where it is rapidly cooled and cleaned to remove any entrained particulate and/or acid gases prior to potential re-use.

Any inorganic constituents of the waste are melted (vitrified) into an environmentally safe, leach resistant, glass matrix. Plasma Thermal Destruction & Recovery waste to energy plasma reactors are designed to collect the molten metal and glass. The glass and metal layers are removed through controllable tap ports into a slag/metal collection system. Removal of the molten glass or metals presents no hazards of any kind to personnel, requires no special tools and does not disrupt the operating process. The metal layer settles on the bottom of the basin in the processing reactor below the molten glass. Both layers are tapped as necessary, depending on the metal/inorganic content of the waste stream.

The vitrified product can be used in a variety of commercial applications including concrete aggregate, insulation, roadbed construction, and even in decorative tiles. The metal layer can contain relatively pure amounts of iron, copper and aluminum.

It is important to note that the composition of end-products varies with the waste being processed. For example, processing medical waste, with a relatively high percentage of paper and plastic or pharmaceutical manufacturing waste with high levels of carbon-based constituents would produce meaningful levels of syngas, and a lesser amount of glass product. Conversely, processing fly ash from the high temperature boiler in a TVRC would produce lower amounts of syngas and relatively more vitrified product.

Plasma Thermal Destruction & Recovery waste to energy systems are driven by proprietary, state-of-the-art instrumentation and computerized control systems. The Plasma Thermal Destruction & Recovery waste to energy process is a unique, cost-effective and environmentally effective technology that is superior to other mainstream methods of waste treatment:

• The Plasma Thermal Destruction & Recovery waste to energy process can utilize virtually any type of feedstock containing combinations of organic, inorganic and/or heavy-metal constituents thus the pre-processing, staging and management costs are minimized thereby reducing processing costs and enhancing recycling designations.

• Unlike incineration or metal-bearing waste stabilization, the Plasma Thermal Destruction & Recovery waste to energy process is designed to not create any secondary solid wastes that will require further treatment or land filling. As indicated, stand-alone incinerators produce large quantities of bottom and fly ash which are toxic in nature, require further treatment (with stabilization agents) and the resulting post-treated materials (often time whose volume has been doubled) will require final disposal, sometimes in specially designed hazardous waste landfills.

It is also important to note however that through a previous partnership with the Russian Academy of Science, PEAT utilized an AC plasma torch into earlier Plasma Thermal Destruction & Recovery waste to energy systems. The AC plasma torch, which generates the plasma field by utilizing AC electric current directly from the grid without the need for rectifiers (a device, such as a diode, that converts alternating current to direct current). Patents behind the Plasma Thermal Destruction & Recovery waste to energy technology would allow for usage of an AC plasma torch, giving PEAT some additional flexibility. Like electrodes, the AC plasma torch can be more tolerant of a wide range of waste streams (organic and inorganic) and is less expensive to build and to operate than a DC plasma torch. The NCKU facility represented the first applications where an AC plasma torch was utilized in a commercial plant anywhere in the world.

There are a number of perceptions within the marketplace regarding plasma arc treatment and plasma arc gasification processes. Last week, this blog addressed the idea/claim regarding the plasma arc technology’s ability to generate significant useable recyclable end-products and energy with no residual waste.

This week we address some aspects of the environmental footprint associated with plasma arc gasification processes

The high temperatures within plasma arc gasification reactors do facilitate higher thermal destruction with regards to volatizing organic material in the feedstock and breaking them down to simple molecules, however some plasma arc gasification systems require a secondary reactor or cracking stage to accomplish this breakdown indicating that not all reactions occur within the “blackbox.”

With regards to lower emissions claims, specifically dioxins for example, the high temperature within the plasma arc gasification reactors, while important, alone does not ensure little to no dioxin formation, the rapid cooling of the syngas as it leaves the plasma arc gasification reactor is equally important to ensure these complex compounds do not reform.

As discussed in this blog entry:

Plasma Arc Gasification and Wastewater Other Residuals

http://www.peat.com/blog/plasma-arc-gasification-and-wastewater-other-residuals/

other by-products generated during the gas cleaning and conditioning require proper handling. In some plasma arc gasification process configurations, it is feasible to re-inject the by-products collected/generated during this stage into the plasma arc gasification reactor to be vitrified, however this requires planning during the early design stages. If these by-products cannot be re-fed, then secondary treatment would be mandatory.