Chemical Engineering March 2019 - 31

Technology Profile
Calcium Carbide Production from Limestone
By Intratec Solutions
C
alcium carbide is the most
industrially relevant carbide
because of its important
role as the basis of the
acetylene industry. In locations where
there is a shortage of petroleum, calcium
carbide is used as the starting
material for the production of acetylene,
which, in turn, can be used as a
building block for a range of organic
chemicals, such as vinyl acetate, acetaldehyde
and acetic acid.
The process
The following describes a process
for calcium carbide production from
limestone and coke (Figure 1).
Feed preparation. Initially, coke is
dried with hot air in a tray dryer to
reduce moisture in the coke. After
drying, the coke is transferred to
the electric
furnace. Limestone is
crushed in a jaw crusher into a uniform
particle-size range. Some gross
impurities originating from the limestone
are separated in a screener.
Lime kiln. The crushed limestone
is calcined in a vertical-shaft lime
kiln. The calcium carbonate present
in the limestone is decomposed
into calcium oxide (CaO, or lime)
and carbon dioxide, which is used
to preheat the limestone feed. The
resulting CaO is passed through a
screener for the removal of gross impurities.
Then the CaO is conveyed,
along with dry coke, to an electric
furnace, which contains electrodes
through which high current passes
to provide heat.
Electric furnace. The lime-coke
mixture flows down the furnace until
Coke
Limestone
1
3
6
5
4
CW
ST
7
8
Calcium
carbide
FIGURE 1. The process diagram shown here outlines a process for the production of calcium carbide from limestone
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9
10
CW Cooling water
ST Steam
2
1. Limestone crusher
2. Dryer
3. Lime kiln
4. Electric furnace
5. CO scrubber
6. Gas holder
7. Calcium carbide crusher
8. Product silo
9. Steam boiler
10. Cooling tower
Limestone, coke
Calcination,
electrothermic
reduction
Calcium carbide
Limestone,
lignite
Calcination,
electrothermic
reduction
Calcination,
electrothermic
reduction
Limestone,
charcoal
FIGURE 2. Several production pathways exist for calcium carbide, depending on the carbon source
n Raw material n Process n Main product n Byproducts
reaching the high-temperature reaction
zone, where molten CaO reacts
with coke and generates molten calcium
carbide. The reaction zone is a
packed bed of coke, where empty
space is filled with molten calcium
carbide and gaseous byproduct
carbon monoxide. The CO gas from
the electric furnace is fed to a water
scrubber for removal of any residual
particles. The gas is then temporarily
stored in a gas holder before it is
fed through a blower to the dryer
and the lime kiln upstream, where it
is used as fuel.
The molten calcium carbide product
is removed from the furnace by
means of continuous tapping, and
it falls into a water-cooled cylinder,
where the products solidifies.
Finishing. The solid calcium carbide
is transferred to the carbide crusher,
where it is sieved and crushed until it
reaches the desired particle size for
the final product. The crushed product
is screened to remove impurities
and then conveyed to silos that feed
the packing section.
Other production pathways
Calcium carbide production consists
of the reaction of CaO (obtained
from limestone) with a carbon material.
There are several different routes
to manufacturing, related to the different
sources of carbon (Figure 2).
Economic performance
The total operating cost (raw materials,
utilities, fixed costs and depreciation
costs) estimated to produce
calcium carbide was about $1,000
per ton of calcium carbide in the first
quarter of 2015. The analysis was
based on a plant constructed in the
U.S. with the capacity to produce
80,000 metric tons per year of calcium
carbide.
This column is based on " Calcium
Carbide Production from Limestone
- Cost Analysis, " a report published
by Intratec. It can be found at: www.
intratec.us/analysis/calcium-carbide-production-cost.
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.
Calcination,
electrothermic
reduction
Limestone,
anthrocite
n

http://www.intratec.us/analysis/calcium-car http://www.intratec.us http://www.intratec.us/che http://WWW.CHEMENGONLINE.COM

Chemical Engineering March 2019

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