As discussed earlier in this blog, a vitrified matrix or slag is the primary solid byproduct of plasma arc waste-to-energy processing. The vitrified matrix from plasma arc processing contains the mineral matter associated with the feed materials in a vitrified form – a hard, glassy-like substance. The amount of matrix produced is a function of how much non-combustible mineral matter is present in the feedstock.

This matrix is the result of operating temperatures within the plasma arc reactor above the melting temperature of the mineral matter. Under these conditions in the plasma arc reactor, non-volatile metals and metal oxides bind together in molten form until it is cooled via natural heat loss or via a pool of water, where it would fracture and granulate.

The compressive strength of a slag sample generated from fly ash from coal-fired power plant as well as some sodium carbonate (fluxing agent) was 480 kg/cm2, while its average mortar strength was tested at 169 kg/cm.

The vitrified matrix or slag generated by plasma arc treatment is primarily made up of silicon dioxide (SiO2), aluminum oxide (Al2O3) and calcium oxide (CaO). Toxicity Characteristic Leaching Procedure (TCLP) tests are designed to determine the mobility of both organic and inorganic analytes present in the slag. The most recent TCLP results conducted in March 2013 on the vitrified matrix from the plasma arc waste-to-energy system located in Shanghai is presented in the below table along with previous results from processing refinery sludge.

Also, here are recent pictures of this system.

http://www.peat.com/ptdr_pictures.html

According to the US EPA, in 2010 the US produced almost 250 million tons of municipal solid waste (MSW), of which only 12% was diverted towards waste-conversion (example: waste to energy) facilities. This generated approximately 14 million megawatt hours of electricity.

Landfilling is still the largest single means of trash disposal as more than half of all MSW produced in the US was sent to landfill in 2011 (The average American produces 4.4 pounds of waste per day with landfill diversion targets becoming more widespread and stringent). Diverting waste from a landfill to generate value from it is in itself a compelling reason to invest in waste conversion and/or waste to energy, however it also reduces greenhouse gas emissions.

In 2009, 17% of all human-related methane emissions in the US came from landfills. Further, the scarcity of land around urbanized areas means some municipalities are forced to transport waste long distances for disposal. For example, New York’s Department of Sanitation spends in excess of $300 million per year moving waste by truck to landfill and waste disposal facilities outside of the city.

PEAT’s TVRC is an innovative waste to energy technology that combines a thermal volume reduction (“TVR”) system on the front end with a core plasma-arc, plasma gasification PTDR system on the back-end for ash treatment. This combination maximizes electricity generation and minimizes residual by-product treatment.

Finally, in 2007, the EPA stated that waste to energy facilities comply with stringent air emissions standards and produce electricity with less environmental impact than almost any other source of electricity.

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.

Any fly ash generated in a Thermal Volume Recovery and Conversion System is converted on-site into a vitrified matrix product, thus converting an unusable by-product from the high temperature boiler/reactor system into a usable end-product.

As previously discussed in this blog section as well as on PEAT’s website, the vitrified matrix could be used in a variety of commercial applications including concrete aggregate, insulation, roadbed/fill construction and even in decorative and non-decorative tiles. Independent laboratory tests (i.e. “TCLP”) have proven that the vitrified matrix does not leach, is totally benign and safe for any re-utilization.

PEAT has conducted a range of testing on this material include Toxicity Characteristic Leaching Procedure (TCLP) tests. A summary of the test results can be seen below when fly ash was processed:

The most recent TCLP results on the vitrified matrix from PEAT’s plasma-arc plasma gasification PTDR system previously located at a China refinery is presented in the below table.