ASTM D6781-02(R2021) pdf free download

ASTM D6781-02(R2021) pdf free download.Standard Guide for Carbon Reactivation
1. 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 offsite 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 facili- ties. This is true because each reactivation facility is unique, using different types of furnaces, using various operating and performance requirements, and running spent activated car- bons either in aggregate pools (combining different suppliers of carbon) or in custom segregated lots. Additionally, proprietary information for each facility relative to the particular equip- ment used cannot be addressed 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 the responsibility 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 all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.4 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
4. Procedure
4.1 Thermal Reactivation Process: 4.1.1 In order to appreciate the parameters or properties of the spent activated carbon that influence the success of the reactivation process, one must have a basic understanding of the reactivation process and the equipment used therein. Basically, the equipment and process used for reactivation is similar, if not identical, to those same items used for activation of coal, coconut, wood, or other chars, into activated carbon, post devolatilization and carbon fixation (which are necessary steps in virgin carbon manufacture). 4.1.2 The equipment used for these types of processes usually consists ofrotary 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 tank- age. 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 phase service compared to liquid phase service. Additionally, the carbon could be fed to the furnace as a water slurry if 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 inclined dewatering screw. 4.1.4 Once the spent carbon is introduced into the reactiva- tion furnace, the carbon undergoes a three-step process. As the spent carbon progresses through the furnace and is heated up, the carbon first loses moisture and light volatiles; then the carbon loses heavier volatiles by a combination of vaporization, steam stripping, and thermal cracking of heavies into a pseudo-char which deposits in the pores of the carbon; and then, the char is removed from the pores by gasification with steam. This three-step process normally relies on the carbon being heated from ambient temperature to a tempera- ture approaching 1010 °C (1850 °F), with a reactivated carbon discharge temperature of 871 to 954 °C (1600 to 1750 °F) being typical. The steam ratio used is normally 1:1, with the pounds of steam added to the furnace equal to the discharge rate ofreactivated carbon leaving the furnace. This ratio can be adjusted up or down depending on the relative quality of the spent activated carbon and the relative reactivated carbon quality 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 to reactivate will demand less steam.