ASTM D6781-02
(Guide)Standard Guide for Carbon Reactivation
Standard Guide for Carbon Reactivation
SCOPE
1.1 This set of guidelines is offered to users of activated carbon to provide a better understanding of the reactivation process and some of the problems associated with sending carbon off-site or to a third party for thermal reactivation. It is not intended to serve as an operating procedure for those companies or persons that actually operate reactivation facilities. This is true because each reactivation facility is unique, using different types of furnaces, using various operating and performance requirements, and running spent activated carbons either in aggregate pools (combining different suppliers of carbon) or in custom segregated lots. Additionally, proprietary information for each facility relative to the particular equipment used cannot be addressed in a general set of guidelines.
1.2 This standard does not purport to address any environmental regulatory concerns associated with its use. It is the responsibility of the user of this standard to establish appropriate practices for reactivation prior to use.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.
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Designation:D6781–02
Standard Guide for
Carbon Reactivation
This standard is issued under the fixed designation D 6781; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.3 virgin carbon—activated carbon produced from a raw
material carbon source that has never seen service.
1.1 This set of guidelines is offered to users of activated
carbon to provide a better understanding of the reactivation
4. Procedure
process and some of the problems associated with sending
4.1 Thermal Reactivation Process:
carbon off-site or to a third party for thermal reactivation. It is
4.1.1 In order to appreciate the parameters or properties of
not intended to serve as an operating procedure for those
the spent activated carbon that influence the success of the
companies or persons that actually operate reactivation facili-
reactivation process, one must have a basic understanding of
ties. This is true because each reactivation facility is unique,
the reactivation process and the equipment used therein.
using different types of furnaces, using various operating and
Basically, the equipment and process used for reactivation is
performance requirements, and running spent activated car-
similar, if not identical, to those same items used for activation
bonseitherinaggregatepools(combiningdifferentsuppliersof
of coal, coconut, wood, or other chars, into activated carbon,
carbon) or in custom segregated lots. Additionally, proprietary
post devolatilization and carbon fixation (which are necessary
information for each facility relative to the particular equip-
steps in virgin carbon manufacture).
ment used cannot be addressed in a general set of guidelines.
4.1.2 The equipment used for these types of processes
1.2 This standard does not purport to address any environ-
usually consists of rotary kilns, vertical tube furnaces, fluidized
mental regulatory concerns associated with its use. It is the
beds, or a multiple hearth furnace. All of these can be fired
responsibility of the user of this standard to establish appro-
directly or indirectly. Auxiliary equipment to the furnace or
priate practices for reactivation prior to use.
kiln consists of feed screws, dewatering screws, direct feed
1.3 This standard does not purport to address all of the
bins, dust control equipment, product coolers, screening equip-
safety concerns, if any, associated with its use. It is the
ment, off-gas pollution abatement equipment, and tankage.
responsibility of the user of this standard to establish appro-
4.1.3 The spent carbon can come from either liquid or gas
priate safety and health practices and determine the applica-
phase service. Thus, the spent carbon will contain more or less
bility of regulatory requirements prior to use.
water (or other liquids) depending on its service—less for gas
2. Referenced Documents phase service compared to liquid phase service. Additionally,
the carbon could be fed to the furnace as a water slurry if
2.1 ASTM Standards:
received in a bulk load, or if the spent carbon was slurried out
D 2652 Terminology Relating to Activated Carbon
of adsorbers. Gross dewatering of such a slurry is normally
2.2 Other Standard:
done by gravity separation of the water from the carbon in an
AWWA B605-99 Standard for Reactivation of Granular
inclined dewatering screw.
Activated Carbon
4.1.4 Once the spent carbon is introduced into the reactiva-
3. Terminology tion furnace, the carbon undergoes a three-step process.As the
spent carbon progresses through the furnace and is heated up,
3.1 Definitions:
the carbon first loses moisture and light volatiles; then the
3.1.1 reactivated carbon—spent activated carbon that has
carbon loses heavier volatiles by a combination of vaporiza-
gone through a thermal reactivation process.
tion, steam stripping, and thermal cracking of heavies into a
3.1.2 spent activated carbon—activated carbon that has
pseudo-char which deposits in the pores of the carbon; and
seen service in some application, and that has some adsorbate
then, the char is removed from the pores by gasification with
on the carbon.
steam. This three-step process normally relies on the carbon
being heated from ambient temperature to a temperature
This guide is under the jurisdiction of ASTM Committee D28 on Activated
approaching 1010°C (1850°F), with a reactivated carbon
Carbon and is the direct responsibility of Subcommittee D28.02 on Liquid Phase
discharge temperature of 871 to 954°C (1600 to 1750°F) being
Evaluation.
typical. The steam ratio used is normally 1:1, with the pounds
Current edition approved Oct. 10, 2002. Published June 2003.
Annual Book of ASTM Standards, Vol 15.01. of steam added to the furnace equal to the discharge rate of
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6781–02
reactivated carbon leaving the furnace. This ratio can be 4.2.2.2 Similarly, carbon used for decaffeination of coffee
adjusted up or down depending on the relative quality of the must also be thoroughly “sweetened off” before charging to the
spent activated carbon and the relative reactivated carbon reactivation furnace.
quality being produced, with higher quality (for example,
4.2.2.3 Carbonsthatarecontaminatedwithlargeamountsof
higher iodine numbers, higher carbon tetrachloride numbers,
inorganic salts, gangue, fused salts, calcium oxide, or water
etc.) and harder to reactivate carbons demanding more steam.
hardnesssolidsbycontactwithprocesswatersorsolutionsalso
Spent carbons that have seen light service or are easy to
make poor quality reactivated products. There may also be
reactivate will demand less steam.
potential leaching problems from the reactivated product (for
example, accumulated aluminum from alkaline reactivated
4.2 Reactivation Guidelines:
carbon). They may also cause problems with furnace slagging,
4.2.1 The purpose of the reactivation process is to remove
and afterburner slag formation. (Slag is the formation of fused
the accumulated contaminants from the activated carbon pores
inorganic materials, that may result in large masses that may
without damaging the carbon backbone. As described above,
plug up the furnace or afterburner flow passages.) It is
this is done by a combination of devolatilization, steam
suggested that a test reactivation be done on these carbons to
stripping, thermal cracking, and gasification. Thus, anything
determine if reactivation can be done economically. Addition-
that increases the severity of the operation in terms of spent
ally, the economics can be influenced by whether these carbons
carbon loading (that is, the amount of contaminants to be
are run in a segregated, or pool, manner.
removed), the tendency of the contaminants to create char, the
4.2.2.4 Carbons that are contaminated with silanes, silox-
presence of higher boiling materials, or refractory material
anes, or organosilicones may cause problems with furnace
(that is, material inert to devolatilization or gasification) makes
slagging, and afterburner slag formation. It is suggested that a
the reactivation process less effective, even unattractive, in
test reactivation be done on these carbons to determine if
terms of yield, cost effectiveness, or product quality for reuse.
reactivation can be done economically. Additionally, the eco-
Ideally, reactivation leads to optimally restoring the adsorptive
nomics can be influenced by whether these carbons are run in
properties of the granular activated carbon while maintaining
a segregated, or pool, manner.
the carbon’s physical properties (especially mechanical
4.2.2.5 Carbons that retain large amounts of sludge or oils
strength, density, and particle size).These two requirements do
from their applications represent handling problems to reacti-
conflict to some extent: for example, reactivation conditions
vators that result in hi
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