1、Designation: D 6781 02Standard Guide forCarbon Reactivation1This standard is issued under the fixed designation D 6781; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates th
2、e year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This set of guidelines is offered to users of activatedcarbon to provide a better understanding of the reactivationprocess and some of the problems associated with send
3、ingcarbon off-site or to a third party for thermal reactivation. It isnot intended to serve as an operating procedure for thosecompanies or persons that actually operate reactivation facili-ties. This is true because each reactivation facility is unique,using different types of furnaces, using vario
4、us operating andperformance requirements, and running spent activated car-bons either in aggregate pools (combining different suppliers ofcarbon) or in custom segregated lots. Additionally, proprietaryinformation for each facility relative to the particular equip-ment used cannot be addressed in a g
5、eneral set of guidelines.1.2 This standard does not purport to address any environ-mental regulatory concerns associated with its use. It is theresponsibility of the user of this standard to establish appro-priate practices for reactivation prior to use.1.3 This standard does not purport to address
6、all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory requirements prior to use.2. Referenced Documents2.1 ASTM Standards:D 2652 Terminology
7、 Relating to Activated Carbon22.2 Other Standard:AWWA B605-99 Standard for Reactivation of GranularActivated Carbon3. Terminology3.1 Definitions:3.1.1 reactivated carbonspent activated carbon that hasgone through a thermal reactivation process.3.1.2 spent activated carbonactivated carbon that hassee
8、n service in some application, and that has some adsorbateon the carbon.3.1.3 virgin carbonactivated carbon produced from a rawmaterial carbon source that has never seen service.4. Procedure4.1 Thermal Reactivation Process:4.1.1 In order to appreciate the parameters or properties ofthe spent activat
9、ed carbon that influence the success of thereactivation process, one must have a basic understanding ofthe reactivation process and the equipment used therein.Basically, the equipment and process used for reactivation issimilar, if not identical, to those same items used for activationof coal, cocon
10、ut, wood, or other chars, into activated carbon,post devolatilization and carbon fixation (which are necessarysteps in virgin carbon manufacture).4.1.2 The equipment used for these types of processesusually consists of rotary kilns, vertical tube furnaces, fluidizedbeds, or a multiple hearth furnace
11、. All of these can be fireddirectly or indirectly. Auxiliary equipment to the furnace orkiln consists of feed screws, dewatering screws, direct feedbins, dust control equipment, product coolers, screening equip-ment, off-gas pollution abatement equipment, and tankage.4.1.3 The spent carbon can come
12、from either liquid or gasphase service. Thus, the spent carbon will contain more or lesswater (or other liquids) depending on its serviceless for gasphase service compared to liquid phase service. Additionally,the carbon could be fed to the furnace as a water slurry ifreceived in a bulk load, or if
13、the spent carbon was slurried outof adsorbers. Gross dewatering of such a slurry is normallydone by gravity separation of the water from the carbon in aninclined dewatering screw.4.1.4 Once the spent carbon is introduced into the reactiva-tion furnace, the carbon undergoes a three-step process. As t
14、hespent carbon progresses through the furnace and is heated up,the carbon first loses moisture and light volatiles; then thecarbon loses heavier volatiles by a combination of vaporiza-tion, steam stripping, and thermal cracking of heavies into apseudo-char which deposits in the pores of the carbon;
15、andthen, the char is removed from the pores by gasification withsteam. This three-step process normally relies on the carbonbeing heated from ambient temperature to a temperatureapproaching 1010C (1850F), with a reactivated carbondischarge temperature of 871 to 954C (1600 to 1750F) beingtypical. The
16、 steam ratio used is normally 1:1, with the poundsof steam added to the furnace equal to the discharge rate of1This guide is under the jurisdiction of ASTM Committee D28 on ActivatedCarbon and is the direct responsibility of Subcommittee D28.02 on Liquid PhaseEvaluation.Current edition approved Oct.
17、 10, 2002. Published June 2003.2Annual Book of ASTM Standards, Vol 15.01.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.reactivated carbon leaving the furnace. This ratio can beadjusted up or down depending on the relative quality o
18、f thespent activated carbon and the relative reactivated carbonquality being produced, with higher quality (for example,higher iodine numbers, higher carbon tetrachloride numbers,etc.) and harder to reactivate carbons demanding more steam.Spent carbons that have seen light service or are easy toreac
19、tivate will demand less steam.4.2 Reactivation Guidelines:4.2.1 The purpose of the reactivation process is to removethe accumulated contaminants from the activated carbon poreswithout damaging the carbon backbone. As described above,this is done by a combination of devolatilization, steamstripping,
20、thermal cracking, and gasification. Thus, anythingthat increases the severity of the operation in terms of spentcarbon loading (that is, the amount of contaminants to beremoved), the tendency of the contaminants to create char, thepresence of higher boiling materials, or refractory material(that is,
21、 material inert to devolatilization or gasification) makesthe reactivation process less effective, even unattractive, interms of yield, cost effectiveness, or product quality for reuse.Ideally, reactivation leads to optimally restoring the adsorptiveproperties of the granular activated carbon while
22、maintainingthe carbons physical properties (especially mechanicalstrength, density, and particle size). These two requirements doconflict to some extent: for example, reactivation conditionssevere enough to optimize adsorption properties may result inunacceptable decreases in mechanical strength and
23、 density atthe same time. This means that an optimal balance has to befound between restoring adsorption properties and maintainingphysical properties. Additionally, any non-carbon material thatis introduced with the spent carbon into the furnace, forexample, sand, ceramic or metallic bed support ma
24、terial,sludges, oils, etc., reduces the final product quality in terms ofadsorptive capacity.4.2.2 With this in mind, the normal applications for carbonthat cover a broad spectrum of applications and industries donot present any restrictions to the use of reactivation services toachieve good yields
25、and good product quality. These applica-tions include potable water dechlorination, taste and odorremoval, underground tank remediations, standard wastewatertreatment applications, most fugitive emission control applica-tions, most solvent recovery applications, and most chemicalpurification applica
26、tions. A good reference for reactivation ofgranular activated carbon used in the drinking water market isstandard AWWA B605-99. However, there are several appli-cations that require special care in the use of reactivationservices, or that may not be able to be reactivated economi-cally. The followin
27、g guidelines apply:4.2.2.1 Carbon used in sweetener applications must bethoroughly “sweetened off,” that is, have as much residualsugar or other large size organic molecules washed off thespent carbon as possible before charging to the reactivationfurnace. Otherwise, the sugars will caramelize insid
28、e the poresduring reactivation and lessen product quality and rate throughthe furnace.4.2.2.2 Similarly, carbon used for decaffeination of coffeemust also be thoroughly “sweetened off” before charging to thereactivation furnace.4.2.2.3 Carbons that are contaminated with large amounts ofinorganic sal
29、ts, gangue, fused salts, calcium oxide, or waterhardness solids by contact with process waters or solutions alsomake poor quality reactivated products. There may also bepotential leaching problems from the reactivated product (forexample, accumulated aluminum from alkaline reactivatedcarbon). They m
30、ay also cause problems with furnace slagging,and afterburner slag formation. (Slag is the formation of fusedinorganic materials, that may result in large masses that mayplug up the furnace or afterburner flow passages.) It issuggested that a test reactivation be done on these carbons todetermine if
31、reactivation can be done economically. Addition-ally, the economics can be influenced by whether these carbonsare run in a segregated, or pool, manner.4.2.2.4 Carbons that are contaminated with silanes, silox-anes, or organosilicones may cause problems with furnaceslagging, and afterburner slag form
32、ation. It is suggested that atest reactivation be done on these carbons to determine ifreactivation can be done economically. Additionally, the eco-nomics can be influenced by whether these carbons are run ina segregated, or pool, manner.4.2.2.5 Carbons that retain large amounts of sludge or oilsfro
33、m their applications represent handling problems to reacti-vators that result in higher handling costs and reduced through-puts, and thus, increased overall costs. Additionally, the sludgeor oil may polymerize into a refractory coke that would reduceproduct quality. It is suggested that a test react
34、ivation be doneon these carbons to determine if reactivation can be doneeconomically. Additionally, the economics can be influencedby whether these carbons are run in a segregated, or pool,manner.4.2.2.6 The inclusion of foreign material in any spentcarbon should be avoided. Care should be taken to
35、minimizethe amount of sand, gravel, support material, trash, packaging,etc. contained in any spent carbon that is shipped off-site. Thismay require close supervision of contract or plant personnelthat provide removal services for the carbon, or that haul thecarbon to prevent these problems.4.2.2.7 C
36、arbons that are wood-based, including those usedin gasoline vapor recovery units, present some problems toreactivators due to the fact that wood-based carbons are softerthan coal based carbons, and thus suffer higher attrition losses,and because they are lower in density than coal-based carbonsand m
37、ay float in water slurries. Overall yields and handlingcosts may suffer as a result. It is advisable to get someindication from the reactivator of whether these concerns willhave a negative impact before committing to reactivation.Additionally, the economics can be influenced by whetherthese carbons
38、 are run in a segregated, or pool, manner.4.2.2.8 Some solvent recovery unit carbons, particularlythose that are used in magnetic tape applications, suffer frompoor quality outputs from reactivation. Additionally, carbonsused in solvent recovery of ketones can have their pores filledirreversibly wit
39、h the polymerization product of the ketone (forexample cyclohexanone) being used and may be unsuitable forD6781022thermal reactivation. Activated carbon used for ketone solventrecovery should be very thoroughly steamed before removalfrom the adsorber bed and submitted for reactivation. It issuggeste
40、d that a test reactivation be done on these carbons todetermine if reactivation can be done economically. Addition-ally, the economics can be influenced by whether these carbonsare run in a segregated, or pool, manner.4.2.2.9 Carbons that have long service lives, such as gaso-line vapor recovery uni
41、ts, and carbons that have been exposedto high abrasive service, usually have a high fines content.These fines may present handling problems whether unloadedby slurry or by vacuum. Overall yields and handling costs maysuffer as a result. It is advisable to get some indication from thereactivator of w
42、hether these concerns will have a negativeimpact before committing to reactivation. Additionally, theeconomics can be influenced by whether these carbons are runin a segregated, or pool, manner.4.2.2.10 Carbons used in liquid phase styrene removalapplications present a problem with reactivated carbo
43、n 9bleed9of residual styrene even after processing. This is not true ofcarbons used in vapor phase styrene removal applications. It issuggested that the reactivation of the liquid phase carbons bedone via custom segregated reactivation, rather than poolreactivation, so as to prevent passing styrene
44、into streamswhere it would not normally be present.4.2.2.11 Some carbons have been used as inoculation sitesfor bacteria to perform specialized chemical recoveries. Othercarbons have been exposed to services wherein bacterial ororganic plant growth has been rampant. It is suggested thatthese carbons
45、 not be reactivated, but rather disposed of.4.2.2.12 Carbons that have been used for organic removalfrom hydrochloric acid can be exposed to iron pickup duringreactivation. Users of reactivation services should be aware ofthis possibility.4.2.2.13 There are some environmental treatment aspectsassoci
46、ated with reactivation that may add significant costs -highly loaded carbons with significant amounts of halides orsulfur compounds engender additional treatment and disposalcosts when these compounds are removed from the spentcarbon. Carbons loaded with high amounts of fluorides, such asrefrigerant
47、s, hydrogen fluoride, etc., may engender additionalcosts for processing by attacking furnace refractories, whichwill require replacement, as well as increasing treatment costs.Carbons loaded with high amounts of metals engender lowerthroughputs and additional treatment and disposal costs aswell. It
48、is advisable to get some indication from the reactivatorof whether these concerns will have a negative impact beforecommitting to reactivation. Additionally, the economics can beinfluenced by whether these carbons are run in a segregated, orpool, manner.4.2.2.14 If any reactivation of carbon used in
49、 nuclearapplications is undertaken, special precautions are necessary tocontrol any radiological offgassing. Therefore, reactivation ofcarbon from nuclear applications may require special consid-erations. It is advisable to get some indication from thereactivator of whether these concerns will have a negativeimpact before committing to reactivation.5. Keywords5.1 activated carbon; guidelines; reactivationASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expre
