ASTM D6781-02(2021)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D6781 − 02 (Reapproved 2021)
Standard Guide for
Carbon Reactivation
This standard is issued under the fixed designation D6781; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 Other Standard:
AWWA B605-99 Standard for Reactivation of Granular
1.1 This set of guidelines is offered to users of activated
Activated Carbon
carbon to provide a better understanding of the reactivation
process and some of the problems associated with sending
3. Terminology
carbon offsite or to a third party for thermal reactivation. It is
3.1 Definitions:
not intended to serve as an operating procedure for those
3.1.1 reactivated carbon—spent activated carbon that has
companies or persons that actually operate reactivation facili-
gone through a thermal reactivation process.
ties. This is true because each reactivation facility is unique,
3.1.2 spent activated carbon—activated carbon that has
using different types of furnaces, using various operating and
seen service in some application, and that has some adsorbate
performance requirements, and running spent activated car-
on the carbon.
bonseitherinaggregatepools(combiningdifferentsuppliersof
carbon) or in custom segregated lots. Additionally, proprietary
3.1.3 virgin carbon—activated carbon produced from a raw
information for each facility relative to the particular equip-
material carbon source that has never seen service.
ment used cannot be addressed in a general set of guidelines.
4. Procedure
1.2 This standard does not purport to address any environ-
4.1 Thermal Reactivation Process:
mental regulatory concerns associated with its use. It is the
4.1.1 In order to appreciate the parameters or properties of
responsibility of the user of this standard to establish appro-
the spent activated carbon that influence the success of the
priate practices for reactivation prior to use.
reactivation process, one must have a basic understanding of
1.3 This standard does not purport to address all of the
the reactivation process and the equipment used therein.
safety concerns, if any, associated with its use. It is the
Basically, the equipment and process used for reactivation is
responsibility of the user of this standard to establish appro-
similar, if not identical, to those same items used for activation
priate safety, health, and environmental practices and deter-
of coal, coconut, wood, or other chars, into activated carbon,
mine the applicability of regulatory limitations prior to use.
post devolatilization and carbon fixation (which are necessary
1.4 This international standard was developed in accor-
steps in virgin carbon manufacture).
dance with internationally recognized principles on standard-
4.1.2 The equipment used for these types of processes
ization established in the Decision on Principles for the
usually consists of rotary kilns, vertical tube furnaces, fluidized
Development of International Standards, Guides and Recom-
beds, or a multiple-hearth furnace. All of these can be fired
mendations issued by the World Trade Organization Technical
directly or indirectly. Auxiliary equipment to the furnace or
Barriers to Trade (TBT) Committee.
kiln consists of feed screws, dewatering screws, direct feed
bins, dust control equipment, product coolers, screening
2. Referenced Documents
equipment, off-gas pollution abatement equipment, and tank-
2.1 ASTM Standards:
age.
D2652 Terminology Relating to Activated Carbon
4.1.3 The spent carbon can come from either liquid or gas
phase service. Thus, the spent carbon will contain more or less
water (or other liquids) depending on its service—less for gas
This guide is under the jurisdiction of ASTM Committee D28 on Activated
phase service compared to liquid phase service. Additionally,
Carbon and is the direct responsibility of Subcommittee D28.02 on Liquid Phase
the carbon could be fed to the furnace as a water slurry if
Evaluation.
received in a bulk load, or if the spent carbon was slurried out
Current edition approved June 1, 2021. Published June 2021. Originally
of adsorbers. Gross dewatering of such a slurry is normally
approved in 2002. Last previous edition approved in 2014 as D6781 – 02 (2014).
DOI: 10.1520/D6781-02R21.
done by gravity separation of the water from the carbon in an
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
inclined dewatering screw.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
4.1.4 Once the spent carbon is introduced into the reactiva-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. tion furnace, the carbon undergoes a three-step process.As the
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6781 − 02 (2021)
spent carbon progresses through the furnace and is heated up, several applications that require special care in the use of
the carbon first loses moisture and light volatiles; then the reactivation services, or that may not be able to be reactivated
carbon loses heavier volatiles by a combination of economically. The following guidelines apply:
vaporization, steam stripping, and thermal cracking of heavies
4.2.2.1 Carbon used in sweetener applications must be
into a pseudo-char which deposits in the pores of the carbon;
thoroughly “sweetened off,” that is, have as much residual
and then, the char is removed from the pores by gasification
sugar or other large size organic molecules washed off the
with steam. This three-step process normally relies on the
spent carbon as possible before charging to the reactivation
carbon being heated from ambient temperature to a tempera-
furnace. Otherwise, the sugars will caramelize inside the pores
ture approaching 1010 °C (1850 °F), with a reactivated carbon
during reactivation and lessen product quality and rate through
discharge temperature of 871 to 954 °C (1600 to 1750 °F)
the furnace.
being typical. The steam ratio used is normally 1:1, with the
4.2.2.2 Similarly, carbon used for decaffeination of coffee
pounds of steam added to the furnace equal to the discharge
must also be thoroughly “sweetened off” before charging to the
rate of reactivated carbon leaving the furnace.This ratio can be
reactivation furnace.
adjusted up or down depending on the relative quality of the
4.2.2.3 Carbonsthatarecontaminatedwithlargeamountsof
spent activated carbon and the relative reactivated carbon
inorganic salts, gangue, fused salts, calcium oxide, or water
quality being produced, with higher quality (for example,
hardnesssolidsbycontactwithprocesswatersorsolutionsalso
higher iodine numbers, higher carbon tetrachloride numbers,
make poor quality reactivated products. There may also be
etc.) and harder to reactivate carbons demanding more steam.
potential leaching problems from the reactivated product (for
Spent carbons that have seen light service or are easy to
example, accumulated aluminum from alkaline reactivated
reactivate will demand less steam.
carbon). They may also cause problems with furnace slagging,
and afterburner slag formation. (Slag is the formation of fused
4.2 Reactivation Guidelines:
inorganic materials, that may result in large masses that may
4.2.1 The purpose of the reactivation process is to remove
plug up the furnace or afterburner flow passages.) It is
the accumulated contaminants from the activated carbon pores
suggested that a test reactivation be done on these carbons to
without damaging the carbon backbone. As described above,
determine if reactivation can be done economically.
this is done by a combination of devolatilization, steam
Additionally, the economics can be influenced by whether
stripping, thermal cracking, and gasification. Thus, anything
these carbons are run in a segregated, or pool, manner.
that increases the severity of the operation in terms of spent
4.2.2.4 Carbons that are contaminated with silanes,
carbon loading (that is, the amount of contaminants to be
siloxanes, or organosilicones may cause problems with furnace
removed), the tendency of the contaminants to create char, the
slagging, and afterburner slag formation. It is suggested that a
presence of higher boiling materials, or r
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