A New Waste Disposal Technology-plasma arc Pyrolysis System

Plasma Science & Technology, Vol.5, No.2 (2003)A New Waste Disposal Technology-plasma arc Pyrolysis System*HUANG Jian-junl,2 (黄建军), SHI Jiabiao' (施嘉标),LIANG Rongqing' (梁荣庆): LIU Zheng zhi+(刘正之)1 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, Chinaz Department of Applied Physics, Shenzhen University, Shenzhen 518060, ChinaAbstract This paper introduces a new waste disposal technology with plasma arc. Beingdifferent from conventional combustion or burning such as incineration, it is based on a proccsscalled controlled pyrolysis-t hermal destruction and recovery process. It has four advanlages. theyare completely safe, clean, high-energy synthesis gas, non-toxic vitrified slag and netal.Keywords: plasma arc, pyrolysis, incineralor .PACS: 52.80Mg; 82.30Lp1 Introductionstroyed and gasificd to colvert the waste into valu-able products through a process called controlled py-The new waste disposal tcchnology provides a rev-olutionary way of dealing with two very pressingAdditionally, the controlled pyrolysis of organicproblens faced with today's society: waste treat-materials allows the systen wo handle inorganic 1a-ment and disposal, and clean sources of energy. It isterials (glass, soil, metals, and ash), if they aresuperior over competing methods of waste treatmentpresent. Thesc conponents, common in Iany wasteand disposal because of its economic and environ-streams are melted and normally seperated into twonental advantages and its potential to be used acrosslayers to forn a molten bath. The gasified organica wide variety of applications, including distributedcompounds are reacted with steam and oxygen topower production. These advantages provide a lowerproduce a hydrogen-rich synthcsis gas.cost of waste processing for the customer, an op-Furthermore, the proprietary process control sys-tional on-site power generation, a greater utilizationtem minimizes the possibility of the reformed com-of waste materials for couumnercial products, a valu-plex pollutants. The escape of volatile metals andable secondary revenue stream out of these products,acid gases are minimized to the level that can meetfriendly opcrations to the environment and a mini-the mosl stringent air enmission!1,2]mized future liability for the waste. The historicallyThe plasna based pyrolysis system can dispose ofprecdominant industrial treatment methods, e.g. in-these wastes such as municipal waste, incineratedcineration and land- flling, cannot set up such claims.ash, waste contaninated with dioxins, medical waste,This system uses a unique, but effective thermaltires, asbestos, mnetals, plastics, glass, paper, elec-treatment process powered by a plasma arc, whichtronic parts (such as computers and circuit boards),ensures that all complex organic cornpounds arc de-comp中国煤化工terials, labora“This project supported by the Scicnce and Technology Fund of AnhuiTYHCNMHG1743HUANG Jian-jun et al. : A New Wastc Disposal Technology-plasma arc Pyrolysis Systemtory wastes, laboratory animal carcasscs, radioac-mental metals, and glassy material remains. Plasmative wastes, biological warfare agents, chemical andpyrolysis generally produces a glassy slag or vitri-petrochemical process wastes, including chlorinatedfied aggrcgate, and its mass and volume are reducedcompounds and amino compounds.as much as ( 90 ~ 98) percent. Pathogens are notexpccted to survive under very high temperatures.2 Principles of burn andHowever, even with extremely high temperatures,the heat lransfer characteristics in a plasma chambernon-burn technologymay not necessarily mcan a uniform heating at ele-vated temperaturcs. In plasma-based pyrolysis op-Burning refers to combustion that the rapid oxi-erating at a much higher temperature than inciner-dation of a combustible material results in the gen-ation, the glass and other inorganic naterial fromeration of heat and fire, and the release of gaseousbyproducts. If the combustible material cont ainsthe waste are melted and turn into a non-leachableitrified slag.carbon, a solid carbonaceous residue will remain.The two layers are a glass layer and a metal layer.Combustion takes place in an incinerator (from theThe glass layer serves as not only a barrier fromGreek word for “buru to ash"). In a completcvolatile metals, but also a mcdiurn for chemicallycomnbustion process, water and carbon dioxide arbinding many netals in a non-leachable manner byformed. However, in a typical medical waste inciner-vitrification. Wastc strearns that are preduninantlyator, undesirable pollutants and products of incom-metallic in form can usually be processed to promoteplete cornbustion are alsu produced, including par-metal recovery.ticulate matters, carbon monoxide, acid gases, heavymetals, dioxins and furans, and other organic com-pounds.3 Plasma-based pyrolysisIf the waste is heated in absence of air or in thesystempresence of an inert gas, such as helium or nitro-3.1 Overview of the technologygen, pyrolysis dominates. Unlike the combustionwhich is exothernic (generating heat), the pyroly-In the plasma state, the ionized gas can conductsis is endothermic (requiring heat) and involves aelectric current, but due to its resistance, the electricdifferent set of chermical reactions that produce dif-energy is converted to the heat producing tempera-ferent reaction products, such as methane, hydrogenture ranging from 1650 °C to as high as 10000 °C.and monoxide. The resulting of-gas has a low-to .Most systems luse a plasma arc torch to gencrate themedium -heat content and can be used as a supple-plasma energy- In a plasma torch, an arc is estab-mental fuel. In actual practice, the process takeslished between two electrodes. A carrier gas, which.place, not in the complete absence of oxygen, butmay be inert or have some heating value, passes be-in an oxygen-depleted environment, where oxygen istween the electrodes and transfer the energy to thestill present among the molecules that cormprisc the .waste material. In a ntrarsrerring system, the an-waste material or pockets of air trapped in the waste.ode and cathode are both part of the plasma torch.Thus, carbon monoxide is also produced along withAnother design is to use DC (direct current) plasmaa snall arnount of NOx, SOx, dioxins, and furansarc, wherein the arc formed betwcen the two graphite(at levels much lower than in combustion).electrodes directly transfers to the molten glass andThe solid residues from pyrolytic process vary. Inmetal in a molten bath where the waste is formed insome cases, a mixture of inert carbon residue, ele-the中国煤化工: system will be .YHCNMHG1744Plasma Science & Technology, Vol.5, No.2 (2003)WasteAC. volumetricDC- plasma . arcTesitance (joule)electrodesERIOOESPlasma- archeating zoneVolumetricresistanceheatingzone.Fig.1 Process chanber of pyrolysisintroduced later.the other clectrode al the opposite polarity.Components of the plasma- basedA stable plasma are is then Tormed between thepyrolysis systemmolten bath and the arcing electrodes. The secondsource of energy to the process charmber is siuppliedA typical plasma-based pyrolysis systen, such asdirectly to the molten glass via a graphite joule-PEMTMI, has the fllowing 4 components, they are:heating electrode submerged in the melt. A threea process chamber of pyrolysis, a waste feed sub-phase AC potential is placed across the joule-heatingsystemn, a glass and netal recovery subassembly andelectrode, which results in a current flow through theprocess gas cleaning subassembly.glass. The molten glass acts as a rcsistor such that3.2.1 Process chamber of pyrolysispower is supplied directly to the molen glass.Fig.I shows the process chamber of pyrolysis,which is the heart of the PEMTM systern, and is the3.2.2 Waste feed subsystemsite where waste materials are processed to producehydrogen-rich syuthesis gas, a glassy product andThe design of the waste feed systerm is dependentmetal. Two sources of energy are utilized to processupon the nature and type of wastc to be processcd.the waste: One is the DC (direct current) arc plasmaThe fllowing Fig. 2 depicts a typical bulk feed sctup,zone, and the other is the AC (alternating current)where the wastc is fed into a hopper and is meteredjoulc-heating zone. The DC plasma arc is created byinto the process chamber via an al1ger mechanismn.applying a DC potential across the graphite arcing中国煤化工electrodes with a single electrode at one polarity and3.2.HC N M H Gy subassembly1745HUANG Jian-jun et al. : A New Waste Disposal Technology-plasma arc Pyrolysis Systempresent. After the wet scrubber, an additional fil--Bulk teed hopperWaste intering may be required to remove any remnant tracehopper- Feeding augerelements of particulates and mist being carried overfrom the wet scrubbing systemn. The final element-Waste intoof the gas cleaning system is a blower to provide aprocess chambercontinuous drawing stream of gas from the processchamber.4 Operational advantages ofFig.2 A typical bulk waste feed systemthe systemOperational advantages of the systems, comparedThe function of the glass and metal recovery sub-with other waste treatment and disposal methods areassembly is to discharge the molten product fromnumerous. These advantage are as follows.the process chamber and to provide confinement dur-ing product recovery. Molten glass is discharged via1.1 Clean energya side drain while metals are discharged through aThe energy value of the organic components of thebottom drain of the process chamber. The follow-waste material can be recovered through the produc-ng ilustration depicts a glass draining arrangetion of a clean hydrogen-rich gas during the opera-ment. Vitrified product, with typical temperaturesion. The speifcally controlled plasma heating sub-of 1200 °C to 1400 °C, is poured from the processsystem facilitates the production of this clean gas,charnber via the side or bottom drain, into steel-which may be used to produce electricity. The elec-receiving canisters. Fig. 3 is the ilustration of glasstrical power generated not only may be enough todischarged via the side drain.maintain the system operation and, in the case ofMolten metals are poured from the bottom of thea certain waste stream, but also can provide sub-process chamber. The following Fig. 4 depicts a sam-stantial excess power that could be sold to powerple metal removal arrangement.generators or energy brokers.3.2.4 Process gas cleaning subassembly4.2 Salable commercial productsThe gas cleaning subassembly is designed to beThe glass byproduct of PEMTM for processingcompatible with the wastes to be processed. Thewaste can have commercial usage. Industrial appli-volume of of-gas that is produced is very small, typ-cations of the glass product include the use as a sub-ically around 10% of that of an incinerator. Thestitute for sand blasting material, which has beenlow amount of off-gas allows for a high-efficiencyproven highly cost-effective in tests for customers;gas clcaning system ensuring the effective removaldecorative tiles such as roofng material; insulatingof volatile heavy metals such as mercury.panels; construction blocks; aggregate for road build-Typically, the gas cleaning system is comprised ating, and other commercial products. It is also possi-minimum of three gas cleaning operations. The firstble to recover metal from certain waste streams. Thsystern is generally a hot filter device for particu-value of the recovered metal will depend on the va-late removal. The next is a wet scrubber, being usedrietyA stream withto reove additional particulates and acid gases ifa Co1中国煤化Iroduce. a mealTYHCNMHG1746Plasma Science & Technology, Vol.5, No.2 (2003)Side drain-Glass levelspoutMolten glassTo glassreceptacleSystem hearthFig.3 llustration of glass discharged via the side drainGrasslevelMo the mlalaye [“....Metal drainSystesystemhearthTo metalreceptaclFig.4 ilustration of metal discharged via the bottom drainby-product with a highly recycling value.rich gas is created by pyrolisis, not by combustion,and is cleaned prior to the use in energy gencra-4.3 Low emissions /reduced pollutiontion, undesirable products associated with combus-tion, such as dioxin and furans, are virtually elimni-nated. Air enissions from metal are also greatly reAir emissions from PEMTM systems are consider-duced, as comnpared to incineration, providing powerably lower than the polluting emissions from incin-production very clean, very low emission with,eration or the greenhouse gases generated by land-flling. This virtual elirnination of pollution occurs4.4 Safe, stable byproductsbecause the waste is processed by plasma heating,rather than by combustion of the waste in the case ofThe volume of the solid byproducts fie, glassincineration or by physical degradation (rotting), as .produc中国煤化工ed by PEMTMis the case with land-illig. Because the hydrogen-processYHCNMHGpercentofthe1747HUANG Jian-jun et al. : A New Waste Disposal Technology-plasma arc Pyrolysis Systemvolume of the original waste stream, depending onwaste (including municipal solid waste, biomedicalthe type of waste. As mentioned above, the glasswaste and hazardous waste) in a safe and reliablematerial produced by PEMTM systems is very stablemanner. Plasma-based pyrolysis system is a non-and, therefore, if no commercial application is cho-incinerating thermal process under extremely highsen, the glass material does not require any specialtemperatures in an oxygen-starved environment tdisposals (except in the case of radioactive waste).completely decompose input waste material into veryThis is due to the stable nature of the material thatsimple molecules. The byproducts of the process arecreates no threat of leaching and contamination ofa combustible gas, an inert slag and metal. Plasmasurrounding soil, water and air.based pyrolysis system consistently exhibits a muchlower environmental level for both air emissions and4.5Cost competitivenessslag leachate toxicity than competing technologies,The reduction of air pollution, the elimination ordemonstrating convincingly that the system reprereduction of undesirable solid waste products andsents a far more environumentally friendly method ofthe recovery of energy and materials at competitivedisposing waste than any other competing technolo-costs are important factors that can lead to the de-gies.mand for the systems. These features will help cus-tomers meet currcnt environmental standards in theUnited States and other developed countries. More-over, more stringent standards and public concernsReferencesabout the environment are proved to be a continuing1 Goles R w, Whyatt Ga, Mrrill R A, et al.trend worldwide.Engineering-scale DC arc furnace testing sum-mary. Mixed waste focus area, TTP No. RL3-5 Summary6-MW-51, Sep. 1998?Environmental and technology verification re-Plasma-based pyrolysis system is a technologi-port fro the plasma enhanced melter, preparedclly advanced and environmentally friendly pro-by the environmental technology evaluation cen-cess of disposing of waste materials converting themter (EVTEC), a service center of CERF/IIEC,to commercially usable byproducts. The intenseCERF/IIEC report: #40633, May 2002and versatile heat generation capabilities of plasma(Manuscript received 22 October 2002)arc technology enable the system to dispose of allE- mail address of HUANG Jian-jun:huangjj@szu.edu.cn中国煤化工MYHCNMHG1748