1、Designation: D6781 02 (Reapproved 2014)Standard Guide forCarbon Reactivation1This standard is issued under the fixed designation D6781; 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 parenthe
2、ses indicates the year of last reapproval. Asuperscript epsilon () 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 assoc
3、iated with sendingcarbon 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 furnac
4、es, using various 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 a
5、ddressed in a general 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 purp
6、ort to address 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:2D2
7、652 Terminology Relating to Activated Carbon2.2 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 carb
8、on that hasseen 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 ofth
9、e spent activated 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 activatio
10、nof coal, coconut, 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
11、 hearth furnace. 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, screeningequipment, off-gas pollution abatement equipment, and tank-age.4.1.3 The spent ca
12、rbon can come 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 bul
13、k load, or if 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
14、 process. As thespent 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 ofvaporization, steam stripping, and thermal cracking of heaviesinto a pseudo-char which deposits in the pores of
15、the carbon;1This 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 July 1, 2014. Published September 2014. Originallyapproved in 2002. Last previous edition approved in 2
16、007 as D6781 02 (2007).DOI: 10.1520/D6781-02R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright AST
17、M International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1and then, the char is removed from the pores by gasificationwith steam. This three-step process normally relies on thecarbon being heated from ambient temperature to a tempera-ture approaching 1010C
18、(1850F), with a reactivated carbondischarge temperature of 871 to 954C (1600 to 1750F) beingtypical. The steam ratio used is normally 1:1, with the poundsof steam added to the furnace equal to the discharge rate ofreactivated carbon leaving the furnace. This ratio can beadjusted up or down depending
19、 on the relative quality of 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
20、service or are easy toreactivate 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 devolati
21、lization, steamstripping, 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 re
22、fractory material(that is, 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 granul
23、ar activated carbon while 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
24、in mechanical strength and 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
25、or metallic bed support material,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 servi
26、ces toachieve good yields and good product quality. These applica-tions include potable water dechlorination, taste and odorremoval, underground tank remediations, standard wastewatertreatment applications, most fugitive emission controlapplications, most solvent recovery applications, and mostchemi
27、cal purification applications. A good reference for reac-tivation of granular activated carbon used in the drinking watermarket is standard AWWA B605-99. However, there areseveral applications that require special care in the use ofreactivation services, or that may not be able to be reactivatedecon
28、omically. The following 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
29、 will caramelize inside 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 a
30、mounts ofinorganic salts, 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 reac
31、tivatedcarbon). They may 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 c
32、arbons todetermine if reactivation can be done economically.Additionally, the economics can be influenced by whetherthese carbons are run in a segregated, or pool, manner.4.2.2.4 Carbons that are contaminated with silanes,siloxanes, or organosilicones may cause problems with furnaceslagging, and aft
33、erburner slag formation. 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
34、 sludge or oilsfrom their applications represent handling problems to reacti-vators that result in higher handling costs and reducedthroughputs, and thus, increased overall costs.Additionally, thesludge or oil may polymerize into a refractory coke that wouldreduce product quality. It is suggested th
35、at a test reactivation bedone on 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 shou
36、ld be taken to 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 pro
37、blems.4.2.2.7 Carbons 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-bas
38、ed carbonsand may 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 wheth
39、erthese carbons are run in a segregated, or pool, manner.D6781 02 (2014)24.2.2.8 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 the
40、ir pores filledirreversibly with the polymerization product of the ketone (forexample cyclohexanone) being used and may be unsuitable forthermal reactivation. Activated carbon used for ketone solventrecovery should be very thoroughly steamed before removalfrom the adsorber bed and submitted for reac
41、tivation. It issuggested that a test reactivation be done on these carbons todetermine if reactivation can be done economically.Additionally, the economics can be influenced by whetherthese carbons are run in a segregated, or pool, manner.4.2.2.9 Carbons that have long service lives, such as gaso-li
42、ne vapor recovery units, 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 fro
43、m thereactivator of whether 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 w
44、ith reactivated carbon “bleed“of 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 pre
45、vent passing styrene 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 sugges
46、ted thatthese carbons 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 tr
47、eatment aspectsassociated 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 fluoride
48、s, such asrefrigerants, 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 dispo
49、sal costs aswell. It 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 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 thereactiv
