Chemical Engineering January 2018 - 35

Technology Profile
Activated Carbon Production
By Intratec Solutions
A
ctivated carbon, also known
as activated charcoal or activated
coal, is an inert solid
composed mostly of carbon
atoms, processed to have porous
structure and a large internal surface
area. These unique characteristics
impart adsorptive properties
that make activated carbon attractive
for use in a range of liquid- and gasphase
applications.
The process
The following
paragraphs
describe
activated carbon production from coconut
shells, which involves two main
steps: carbonization of coconut shells
into shell charcoal, followed by steam
activation at high temperatures. Figure
1 presents a simplified flow diagram of
the process.
Carbonization.
Initially, coconut
shells are fed to a crusher, where the
size of the shells are reduced. The
crushed material is fed to a flash dryer
to remove moisture, and then fed to a
rotary kiln to be carbonized. The shell
fragments are heated under nitrogen
in such a way that non-carbonaceous
material - elements such as hydrogen
and oxygen - is volatilized and
eliminated from the precursor. Carbonization
produces
charcoal,
with
bio-oil vapors, steam and incondensable
gases as byproducts. At this
point, a carbon skeleton possessing
a latent pore structure is formed. Oils
and tars separated as byproduct are
used for fuel.
Steam activation. In a fluidized-bed
reactor, the charcoal is activated by
reaction with steam at a temperature
Coconut shells
1
Tar
2
3
FIGURE 1. Shown here are the major process steps
in the production process for activated carbon
ST
Air
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
4
5
6
Powdered
activated
carbon
JANUARY 2018
Off-gas
Coconut shell
charcoal
Activation
Powdered activated
carbon
Coal
Carbonization/
activation
Carbonization/
activation
FIGURE 2. The diagram shows several possible production pathways for activated carbon
n Raw material n Pathway n Main product
of 900-1,100°C under controlled atmosphere.
The activation promotes
the elimination of volatile components
and the simultaneous oxidation of the
outer surface of the charcoal, forming
active sites. The gas escapes from
the charcoal, leaving behind pores in
the carbon solid. Air is also fed to the
reactor, for the combustion of the carbon
monoxide and hydrogen formed
during activation. Carbon monoxide
and H2 are converted to steam and
carbon dioxide.
Then the activated carbon undergoes
a sequence of steps in which it
is cooled and ground to the desired
particle size. The activated carbon is
cooled to ambient temperature by indirect
cooling, and then ground into
powder of specified mesh size. At
this point, the finished powdered activated
carbon is directed to a packing
system.
Production pathways
Activated carbon can be produced
from several carbon-rich raw materials,
such as coal, lignite, wood,
pitches and agricultural and forestry
wastes. When it comes to manufacturing
processes, there are basically
two main activation methods: chemical
activation, based on the dehydrating
action of chemicals; and physical
activation, based on the use of gases,
such as steam or carbon dioxide.
Several different pathways for activated
carbon are presented in Figure 2.
Economic performance
The total operating cost (raw materials,
utilities, fixed costs and depreciation
costs) estimated to produce activated
carbon was about $2,400 per ton of
activated carbon in the first quarter
of 2014. The analysis was based on
a plant constructed in the U.S. with
capacity to produce 10,000 metric ton
per year of activated carbon.
This column is based on " Activated
Carbon Production Process - Cost
Analysis, " a report published by Intratec.
It can be found at: www.intratec.us/analysis/activated-carbonproduction-cost.
n
Edited
by Scott Jenkins
Editor's note: The content for this column is supplied by Intratec
Solutions LLC (Houston; www.intratec.us) and edited by
Chemical Engineering. The analyses and models presented are
prepared on the basis of publicly available and non-confidential
information. The content represents the opinions of Intratec only.
More information about the methodology for preparing analysis
can be found, along with terms of use, at www.intratec.us/che.
1. Crusher
2. Dryer
3. Carbonization reactor
4. Activation
5. Product refinement
6. Packing
7. Steam boiler
8. Cooling tower
CW Cooling water
ST Steam
ST
CW
7
8
Wood
Carbonization/
activation
Coconut shell
33
http://www.in http://www.tratec.us/analysis/activated-carbon http://www.intratec.us http://www.intratec.us/che http://WWW.CHEMENGONLINE.COM
Chemical Engineering January 2018

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