The main aspect of gasification, whether it is plasma-arc plasma gasification or “traditional” gasification is to raise carbon–rich materials or waste to a high temperature in an oxygen–deficient reactor, where the materials break down thermochemically versus combustion.

This process is more efficient than incineration, has a significantly lower environmental footprint, while the syngas can be transformed into a number of end products (liquid fuels, power, chemicals, etc.).

The feedstocks for traditional gasification processes range from coal, the organic components of municipal waste and biomass while the range is even greater for plasma-arc plasma gasification processes, which can handle just about any waste stream with the exception of radioactive materials.

Due to the fact that gasification occurs pre-combustion (assuming the syngas would be burned to generate electricity), it supports easier carbon capture than incineration where the chemistry can be more complex.

Plasma-arc plasma gasification is just one type of gasification. Other common forms include (1) updraft, (2) downdraft, (3) fixed bed and (4) fluidized bed. The first two are quick similar with exception of the gas flow. More on the differences in the next posting.

Previously, this forum has demonstrated how plasma arc plasma gasification nearly eliminates dioxin formation, semi-volatile heavy metal compounds and other air emissions when processing various forms of industrial waste or hazardous waste.

Below is a summary of a June 2013 third party emissions testing conducted on the PTDR-100 plasma-arc, plasma gasification system located in Shanghai. The summary also compares the results to current European air emission regulations.

ND =”Not Detectable” with Limit in parentheses

It is worth noting that the above emissions for the PTDR plasma arc, plasma gasification system were measured when the syngas was thermally oxidized. It is worth noting that if the syngas is utilized in a gas engine or other syngas utilization equipment, then the only gas emissions associated with a PTDR plasma arc, plasma gasification system would be the exhaust from the engine or boiler, etc.

Previously, we discussed and demonstrated how plasma arc plasma gasification nearly eliminates dioxin formation, this entry looks to address semi-volatile heavy metal compounds and other air emissions.

The high temperatures at which the plasma-arc plasma gasification processes operate can result in the generation of volatile inorganic constituents (i.e. metals and metal oxides), sometimes at a higher level than compared to convention thermal treatment processes, particularly if the waste feedstock comes in direct contact with the very hot plasma-arc plasma gasification plume as these compounds may become volatilize and carried downstream with the syngas generated. While many are removed by the gas cleaning and conditioning systems, in plasma-arc plasma gasification processes where the off gases are not cooled (i.e. plasma combustion, which is not utilized by PEAT) these heavy metal compounds could be carried out in the stack gases, increasing the levels of potential contaminants that are emitted.

Downstream of any quench system or syngas cooler, any entrained particulate matter and/or acid gases (H2S, HCl, etc.) are scrubbed with water typically using either a packed-bed tower/Venturi scrubber or through a dry filtration system. Additional equipment in the form of HEPA or baghouse filters may also be utilized.

The results presented in the below reflect emissions from PEAT International plasma-arc plasma gasification waste-to-energy systems where the syngas was not utilized and ultimately processed in a thermal oxidizer or secondary reaction chamber.

All of the high temperature boiler/reactors – a key component of the TVRC technology –  installed and operating to date required an air permit from the applicable regulatory body. Typically, these systems are designed to comply with emissions levels for particulate matter (150 μg/m3), NOx (0.04 PPMV), SOx (0.03 PPMV) and carbon monoxide (9 PPMV), as well as the other typical reference pollutants as they pertain to air emissions.

Below is a summary of the most recent third party emissions testing conducted on a recently commissioned PTDR plasma-arc, plasma gasification. The test was conducted for medical waste treatment. The summary also compares the results to current United States air emission regulations.

The following parameters were also tested but were found to be non detectible (Detectible limit in parentheses) Chlorides as Cl (1.4 mg/m3), Ammonia (5 mg/m3), Hydrogen Sulfide (1.4 mg/m3). With regards to Volatile Organic Compounds (VOCs), the testing for Benzene, Ethyl Benzene, Toluene and Xylene were all below the detectible limit (1 mg/m3). Finally, with regards to heavy metals with the exception of cadmium, which is listed above, all were below the detectible limit of 1 μg/m3 (antimony had a detectible limit of 5 μg/m3).

It is worth noting that the above emissions for the PTDR plasma-arc, plasma gasification were measured when the energy recovery system (gas engine was not operating and thus the syngas was thermally oxidized. It is noted that if the syngas is utilized in a gas engine or other syngas utilization equipment, then the only gas emissions associated with the PTDR plasma-arc, plasma gasification system would be the exhaust from that source.

According to the United States Environmental Protection Agency’s “Solid Waste Management and Greenhouse Gases: A Lifecycle Assessment of Emissions and Sinks”, disposing of 650,000 tons per year in a landfill without gas collection, could reduce its Greenhouse Gas (GHG) emissions by about 260,000 Metric Tons Carbon Equivalent (MTCE) per year by managing waste in a mass burn combustor unit. For this preliminary discussion, this equates to 0.40 MTCE/ton avoided from landfilling.

However, the EPA’s document uses a combustion system efficiency of 550 kWh per ton of mixed MSW. The high temperature boiler/reactor system in the TVRC system, which combines a high temperature boiler/reactor with a plasma-arc, plasma gasification sytem, has an efficiency of approximately 690 kWh per ton – 25% greater efficiency; thus the high temperature boiler/reactor has the potential to generate approximately 0.50 MTCE/ton avoided from landfilling or in total up to 82,500 MTCE, when assuming 500 TPD.

Additionally, the EPA estimates greenhouse gas (GHG) emissions range from 10 to 20 million metric tons, depending on the different methods used to estimate the biogenic fraction of MSW. EPA’s eGrid (a database of information on electrical generators in the United States) indicates about 53% of the energy generated by MSW combustion facilities is from biogenic sources and 47% is fossil-fuel derived power. If we take that 53% and presume the same percent of GHG emissions are from biogenic sources, then MSW combustion facilities generate less GHGs than fossil-fuels.

EPA estimates the GHG savings from WTE to be about 1 on of GHGs saved per ton of MSW combusted.