ASTM D6781-02(2007)

Standard Guide for Carbon Reactivation

ABSTRACT
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. The equipment used for thermal reactivation process usually consists of rotary kilns, vertical tube furnaces, fluidized beds, or a multiple hearth furnace. All of these can be fired directly or indirectly. Auxiliary equipment to the furnace or kiln consists of feed screws, dewatering screws, direct feed bins, dust control equipment, product coolers, screening equipment, off-gas pollution abatement equipment, and tankage.
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.
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.
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.

General Information

• Status: Historical
• Publication Date: 30-Sep-2007
• ICS: 71.060.10 - Chemical elements
• Technical Committee: D28 - Activated Carbon
• Drafting Committee: D28.02 - Liquid Phase Evaluation

Relations

• Replaces: ASTM D6781-02 - Standard Guide for Carbon Reactivation
• Effective Date: 01-Oct-2007

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D6781 − 02(Reapproved 2007)
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 3.1.1 reactivated carbon—spent activated carbon that has
gone through a thermal reactivation process.
1.1 This set of guidelines is offered to users of activated
carbon to provide a better understanding of the reactivation 3.1.2 spent activated carbon—activated carbon that has
process and some of the problems associated with sending seen service in some application, and that has some adsorbate
carbon off-site or to a third party for thermal reactivation. It is on the carbon.
not intended to serve as an operating procedure for those
3.1.3 virgin carbon—activated carbon produced from a raw
companies or persons that actually operate reactivation facili-
material carbon source that has never seen service.
ties. This is true because each reactivation facility is unique,
using different types of furnaces, using various operating and
4. Procedure
performance requirements, and running spent activated car-
4.1 Thermal Reactivation Process :
bonseitherinaggregatepools(combiningdifferentsuppliersof
4.1.1 In order to appreciate the parameters or properties of
carbon) or in custom segregated lots. Additionally, proprietary
the spent activated carbon that influence the success of the
information for each facility relative to the particular equip-
reactivation process, one must have a basic understanding of
ment used cannot be addressed in a general set of guidelines.
the reactivation process and the equipment used therein.
1.2 This standard does not purport to address any environ-
Basically, the equipment and process used for reactivation is
mental regulatory concerns associated with its use. It is the
similar, if not identical, to those same items used for activation
responsibility of the user of this standard to establish appro-
of coal, coconut, wood, or other chars, into activated carbon,
priate practices for reactivation prior to use.
post devolatilization and carbon fixation (which are necessary
1.3 This standard does not purport to address all of the
steps in virgin carbon manufacture).
safety concerns, if any, associated with its use. It is the
4.1.2 The equipment used for these types of processes
responsibility of the user of this standard to establish appro-
usually consists of rotary kilns, vertical tube furnaces, fluidized
priate safety and health practices and determine the applica-
beds, or a multiple hearth furnace. All of these can be fired
bility of regulatory requirements prior to use.
directly or indirectly. Auxiliary equipment to the furnace or
kiln consists of feed screws, dewatering screws, direct feed
2. Referenced Documents
bins, dust control equipment, product coolers, screening
2.1 ASTM Standards:
equipment, off-gas pollution abatement equipment, and tank-
D2652 Terminology Relating to Activated Carbon
age.
2.2 Other Standard:
4.1.3 The spent carbon can come from either liquid or gas
AWWA B605-99 Standard for Reactivation of Granular
phase service. Thus, the spent carbon will contain more or less
Activated Carbon
water (or other liquids) depending on its service—less for gas
phase service compared to liquid phase service. Additionally,
3. Terminology
the carbon could be fed to the furnace as a water slurry if
3.1 Definitions: received in a bulk load, or if the spent carbon was slurried out
of adsorbers. Gross dewatering of such a slurry is normally
done by gravity separation of the water from the carbon in an
This guide is under the jurisdiction of ASTM Committee D28 on Activated inclined dewatering screw.
Carbon and is the direct responsibility of Subcommittee D28.02 on Liquid Phase
4.1.4 Once the spent carbon is introduced into the reactiva-
Evaluation.
tion furnace, the carbon undergoes a three-step process.As the
Current edition approved Oct. 1, 2007. Published November 2007. Originally
spent carbon progresses through the furnace and is heated up,
approved in 2002. Last previous edition approved in 2002 as D6781 – 02. DOI:
10.1520/D6781-02R07.
the carbon first loses moisture and light volatiles; then the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
carbon loses heavier volatiles by a combination of
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
vaporization, steam stripping, and thermal cracking of heavies
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. into a pseudo-char which deposits in the pores of the carbon;
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6781 − 02(Reapproved 2007)
and then, the char is removed from the pores by gasification
with
D6781 − 02 (2007)
steam. This three-step process normally relies on the carbon spent carbon as possible before charging to the reactivation
being heated from ambient temperature to a temperature furnace. Otherwise, the sugars will caramelize inside the pores
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) being the furnace.
typical. The steam ratio used is normally 1:1, with the pounds
4.2.2.2 Similarly, carbon used for decaffeination of coffee
of steam added to the furnace equal to the discharge rate of
must also be thoroughly “sweetened off” before charging to the
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. Addition-
this is done by a combination of devolatilization, steam
ally, the economics can be influenced by whether these carbons
stripping, thermal cracking, and gasification. Thus, anything
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, silox-
carbon loading (that is, the amount of contaminants to be
anes, 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 refractory material
test reactivation be done on these carbons to determine if
(that is, material inert to devolatilization or gasification) makes
reactivation can be done economically. Additionally, the eco-
the reactivation process less effective, even unattractive, in
nomics can be influenced by whether these carbons are run in
terms of yield, cost effectiveness, or product quality for reuse.
a segregated, or pool, manner.
Ideally, reactivation leads to optimally restoring the adsorptive
4.2.2.5 Carbons that retain large am
...