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

Medical and pharmaceutical waste comes from hospitals, doctors/dentists offices, skilled & unskilled nursing care, group practices, specialized out-patient services and veterinarians. Examples of medical waste are: soiled or blood soaked bandages, culture dishes and other glassware, discarded surgical gloves, and instruments (e.g. scalpels), needles, cultures, stocks, swabs used to inoculate cultures, removed body organs and lancets used to draw blood samples.

For medical waste generators (medium and large hospitals/health clinics or medical waste collectors), the current trend is clearly in the direction of greater efficiency in sorting. The pressure for cost containment has grown in the health care industry and the price for medical waste treatment and disposal has increased. It has been estimated that hospitals and long-term care (LTC) facilities in the US waste generate at least 125 million pounds of pharmaceuticals annually. Our research reflects that medical waste treatment systems are expected to experience high growth due to a growing and aging population, a rising incidence of chronic disease, and new requirements for disposal in community and home settings.

PEAT’s PTDR plasma-arc plasma gasification system in Sacramento, CA is currently permitted for sanitized medical waste treatment, among other waste streams. The PTDR plasma-arc plasma gasification technology has received numerous regulatory approvals throughout the globe, including the California Department of Public Health, which certified the technology as an alternative to incineration for medical waste treatment.

Since October 2011, PEAT has been performing small medical waste treatment campaigns. Most recently in August, PEAT hosted potential clients from Utah to witness a medical waste treatment campaign on waste supplied from the San Jose area.

PEAT’s plasma-arc plasma gasification system consists of DC-powered plasma-arc graphite electrodes rather than plasma torches, typically marketed by other companies. There are a number of benefits associated with using DC-powered plasma-arc electrodes.

Minimization of capital costs as plasma-arc graphite electrodes generate plasma-arcs directly with exposed anodes and cathodes without requiring an independent torch. Plasma torches are expensive and increase the capital costs associated with overall systems.

Minimization of operational costs as plasma-arc graphite electrodes require no water cooling or any externally-supplied carrier gas (i.e. argon or nitrogen). This increases the electrical to thermal conversion rates (typically seen around 85-90% in PTDR plasma-arc plasma gasification systems).

Plasma torches require water cooling, carrier gases and have lower efficiencies as their power output can be as low as 50% of the power input for small torches. This means that one half of the electricity of the plasma torch is dissipated to the cooling water or efficiency of the plasma-arc power supply.

Plasma pyrolysis and plasma-arc plasma gasification, like incineration, are options for recovering value from waste by thermal treatment. Both pyrolysis and plasma-arc plasma gasification convert feedstocks/wastes into energy by heating the waste under controlled conditions. Whereas incineration converts the input waste into a combusted flue-gas that can then be used to recover thermal energy (usually in the form of steam) and ash, pyrolysis and plasma-arc plasma gasification deliberately limits the conversion so that combustion does not take place directly. Instead, they convert the waste into potentially valuable intermediates that can be further processed for materials recycling or energy recovery. Pyrolysis and plasma-arc plasma gasification offer more scope for recovering products from waste than incineration.

One of the benefits associated with plasma-arc plasma gasification is that plasma-arc plasma gasification reactors do not require moving grates and the smaller volume of gases generated means that the plasma-arc plasma gasification reactors can accommodate the required minimum residence times in a smaller volume. Further, the smaller gas production and reducing environment within plasma-arc plasma gasification reactors does facilitate smaller sized air pollution control systems.

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.

Plasma-arc systems have been widely used for destruction of hazardous wastes. This extreme heat from the plasma-arc breaks down wastes, forming synthesis gas (hydrogen and carbon monoxide) and a rock-like solid byproduct called slag. The significant difference between pure plasma-arc plasma gasification systems (like PTDR systems) and other thermal waste processing technologies is that the heat required for waste degradation is generated by the plasma-arc itself and not via combustion of all or part of the waste.

PTDR plasma-gasification systems derive its energy from graphite plasma-arc electrodes thus wastes with little or no calorific value can be effectively and efficiently treated. Graphite plasma-arc electrodes are more effective than plasma-arc torches (typically marketed by other plasma-based companies) in that they reduce capital costs versus plasma-arc torches and have significantly higher electric-to-thermal energy conversion efficiencies (90-95% vs. 65-70%) thereby reducing operational costs when compared to plasma-arc torches