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How do I tell if my carbon is spent?

The only sure way to tell when the carbon is spent is to test the outlet of the carbon column for the contaminant being removed. Once the concentration of the contaminant is above the acceptable emission or discharge limits, the activated carbon is considered spent. The activated carbon does not change color or shape as it adsorbs contaminants. Therefore, no visual inspection will tell you if the carbon is spent. Also, you cannot “test” the carbon for being spent using commercially available "carbon testers", as each situation is unique based upon the type and concentration of contaminants. The only way to determine if the carbon is spent is to detect the contaminant in the outlet of the carbon column.

How large should the system be?

The size of the system depends on the nature of the contaminant being removed. The contaminant has an adsorption potential that depends on the type of compound and its chemical structure. Some contaminants are strongly adsorbed; some are not. The more strongly adsorbed (the higher the adsorption potential) a contamination is, the less carbon is required to adsorb it. The amount of carbon required to remove the contaminant from its inlet concentration to the desired level is termed the mass transfer zone (MTZ). The system has to be at least as large as the MTZ for good carbon utilization. In situations where the MTZ is very large, the adsorber may need to be relatively large compared to the flowrate, not only to contain the MTZ, but also to get better utilization of the carbon.

Is there a benefit to operating fixed beds in series?

There is.
As the MTZ progresses through the carbon fixed beds, it reaches a point where the length of the MTZ is longer (deeper) than the remaining depth of the carbon in the vessel still capable of adsorption (not spent). At this point, the concentration of the contaminant begins to increase in the outlet of the carbon bed as the MTZ begins to exit the vessel. This is called breakthrough. If the vessel is taken out of service when this occurs, there may be a substantial amount of carbon that had not been fully utilized.

With fixed bed in series, the leading edge of the MTZ would progress into the second vessel. When the MTZ wave front completely exits the lead vessel, all of the carbon in that vessel would be spent. By operating in this manner, it is possible that 100% of the carbon capacity to adsorb the contaminant would be used.

When the lead (or first) carbon bed is spent, the vessel is removed from service and the spent carbon removed for reactivation. The vessel that had been in the second (or polish) position is placed in the lead position and another vessel containing fresh or reactivated carbon is placed on line in the trailing (or polish) position.

What is reactivated carbon?

Reactivated carbon is formed through a thermal treatment process in which adsorbed chemical constituents are removed from spent activated carbon to produce a recycled, reactivated product for beneficial reuse by Gowrishankar Chemicals’s customers.

How about pores in activated carbon?

A proper activated carbon has a number of unique characteristics: a large internal surface area, dedicated (surface) chemical properties and good accessibility of internal pores. According to IUPAC definitions three groups of pores are distinguished:

• Macropores (above 50 nm diameter)
• Mesopores (2-50 nm diameter)
• Micropores (under 2 nm diameter)

Micropores generally contribute to the major part of the internal surface area. Macro- and mesopores can generally be regarded as the highways into the carbon particle, and are crucial for kinetics. Macropores can be visualised using Scanning Electron Microscopy (SEM). The pore size distribution is highly important for the practical application; the best fit depends on the compounds of interest, the matrix (gas, liquid) and treatment conditions.
The desired pore structure of an activated carbon product is attained by combining the right raw material and activation conditions.

:: FAQ's


	• What types of applications are right for activated carbon?

	Activated carbon is principally used to remove low-levels (ppm or ppb level) of organic species from water, process liquids, or air. If the concentration is in the percentage level (1%, 5%, etc.), activated carbon may or may not be appropriate for the application. Please check with Gowrishankar Chemicals concerning these applications.

	• The following is a list of activated carbon applications:

	• Acid purification • Air stripper off-gas • Amine purification • Aquarium water treatment • Amine purification • Carbon dioxide purification • Catalyst protection • Catalyst support • Chloramines from drinking water • Citric acid purification • Corn syrup decolorization • Decaffeination of coffee • Dechlorination of drinking water • Gasoline vapor recovery • Glycerin purification • Glycol purification • Gold recovery • Groundwater remediation • High-purity hydrogen • Hydrogen sulfide from drinking water • Incinerator flue gas • Indoor air filtration for HVAC systems • Iron from drinking water • Mercury removal from liquid hydrocarbons • Organics from drinking water • Personnel protection respirators • Process water treatment • Product purification • Soil/sludge stabilization • Soil vapor extraction treatment • Tank venting • Taste and odor control for municipal water • Ultrapure water treatment • VOC’s from drinking water • Wastewater treatment