In the last blog entry it was mentioned that 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. This entry looks to discuss in slightly more in depth the differences between these types.

In the updraft (sometimes referred to as “counter current”), air/oxidant is injected from the bottom and the material enters at the top. Following gravity, the material is dried then reduced to char (pyrolyis) and finally any ungasified solid remnant is burned. This type has a high energy efficiency because of the heat exchange between the rising gas and descending material. The main issue is the high concentration of oils and/or tars in the syngas, which must be cleaned prior to any utilization, which can decrease the overall efficiency. Updraft gasifier usage is generally focused to direct heating applications as little to no gas cleaning is necessary. PEAT’s plasma-arc plasma gasification process is configured similarly in that the feedstock material is fed from the top, however it also has similarities to a fluidized bed (see below) in that the vitrified material in PEAT’s plasma-arc plasma gasification is maintained in a somewhat molten form.

In a downdraft gasifier (or co current), the gas is drawn out from below through a combustion zone. The material and oxidant flow in the same direction. Compared to the updraft configuration, the gas tends to be cleaner with fewer tars – the reason being in a downdraft configuration the tars (product from any pyrolysis phase) have to pass through a higher-temperature oxidization zone. The key I in a downdraft design is temperature maintenance and if the feedstocks vary in composition and moisture content, this can be difficult to achieve. The gas must rapidly cooled prior to be used.

Finally, a fluidized bed, which is more common in large plants, has a hot bed of sand located at the bottom of the gasifier. Gas clean-up is key as many times tar and ash can be found in the syngas. Waste is typically shredded or pulverized prior to being fed from the top.

PEAT International has successfully commissioned a Plasma Thermal Destruction and Recovery (PTDR) systems in Shanghai, China. The system was designed to deconstruct medical waste and oil refinery sludge.

PEAT International, Inc. (PEAT), a plasma-thermal waste destruction company, has installed a PTDR system in Shanghai, China. The 60 kg/hr system was specifically designed for the treatment of medical waste and oil refinery sludge for Abada Plasma Technology Holdings, Ltd.

“This is end-stage technology and sets the standard for clean hazardous waste remediation. Only with plasma can you achieve temperatures high enough for waste destruction in a single-staged process,” said Joseph Rosin, PEAT International chairman. “It’s a 21st century solution that addresses three important needs: significant volume reduction, full pollution control and competitive pricing. We are currently preparing for other projects already under contract.”

PEAT’s PTDR “single stage” plasma-thermal process transforms hazardous waste through molecular dissociation at 1,500°C (2,732°F) into recoverable, non-toxic end-products, synthetic gas and heat (sources for energy recovery), metals, and a vitrified glass matrix. Emissions are below the most stringent environmental standards.

PTDR systems are in operation in California, Taiwan, and China. For more information and to watch a video of operations, please click here.

Northbrook, Illinois & Shanghai, China – October 10, 2013 – PEAT International, Inc., (“PEAT”) a leader in plasma-thermal waste destruction systems, announced the successful commissioning of a Plasma Thermal Destruction and Recovery (“PTDR”) system in Shanghai, China. The 60 kg/hr system – designed for medical waste and oil refinery sludge – was installed for Abada Plasma Technology Holdings, Ltd. – an Asian-based renewable energy project developer.

PEAT’s PTDR “single stage” plasma-thermal process transforms hazardous waste through molecular dissociation at 1,500°C (2,732°F) into recoverable, non-toxic end-products, synthetic gas and heat (sources for energy recovery), metals and a vitrified glass matrix. Emissions are below the most stringent environmental standards used anywhere.

“This is end-stage technology and sets the standard for clean hazardous waste remediation. Only with plasma can you achieve temperatures high enough for waste destruction in a single-staged process,” said Joseph Rosin, PEAT International Chairman. “It’s a 21st century solution that addresses three important needs: significant volume reduction, full pollution control and competitive pricing. We are currently preparing for other projects already under contract.”

PTDR systems are in operation in California, Taiwan and China. Go to http://www.peat.com/chinasystem.html for a video of operations and acceptance test run data.

About PEAT International

PEAT International, Inc., headquartered in Northbrook, Illinois, with offices in China, Taiwan and India, is a waste-to-energy (“WTE”) company with its two proprietary technologies – the Plasma Thermal Destruction and Recovery™ (“PTDR”) technology for the treatment and recycling of industrial, medical and other hazardous waste streams and the Thermal Volume Reduction & Conversion™ (“TVRC”) technology for municipal solid waste. For more information, contact Daniel Ripes, dripes@peat.com, at 847-559-8567 and visit www.peat.com.

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.

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