Chemical Engineering March 2017 - 40

Technology Profile
Sulfuric Acid Production from Sulfur
By Intratec Solutions
S
ulfuric acid (H2SO4) is among
the most important industrial
chemicals, with large-scale
uses in several industry sectors,
such as basic chemicals, fertilizers,
petroleum refining, metals, explosives,
detergents and plastics. H2SO4
is broadly used in different concentrations
and grades. Major applications
include its use as a dehydrating agent,
catalyst, reactant in chemical processes,
solvent and absorbent.
The process
The following paragraphs describe a
double-contact process for
sulfuric
acid production (Figure 1) in which elemental
sulfur is the source of sulfur
dioxide (SO2). SO2 can also be obtained
from several sulfur-bearing raw
materials, including spent H2SO4 and
smelter off-gases.
Sulfur burning. Elemental sulfur (in
molten form) and dried air are fed
into a combustion furnace, in which
the sulfur is burned to produce SO2.
The proportion of airflow relative to
sulfur feedrate is controlled so that a
sufficient concentration of oxygen is
maintained in the process gas. This
ensures proper conversion of SO2 to
SO3 in the subsequent steps. This
combustion furnace is equipped with
a waste-heat boiler that cools down
the reaction gas and generates highpressure
steam, which, in turn, is fed
to a turbine for generating electricity.
The cooled reaction product gas is directed
to the SO2 converter.
Double-contact process. In the SO2
converter, SO2 is oxidized to SO3 in
five catalyst beds within a single verSteam
Sulfur
BFW
1
6
Exhaust
steam
3
Sulfur dioxide
(SO2)
Elemental sulfur
Spent sulfuric
acid
Double contact
process
Sulfur burning +
double contact
Decomposition +
double contact
Sulfuric
acid
Gas treatment +
double contact
Wet gas process
H2O2 abatement
FIGURE 2. Several production pathways are available for sulfuric acid, a major industrial chemical
n Raw material n Pathway n Main product
tical converter. The gases from the
third bed leave the reactor and are directed
to an intermediate absorption
step downstream, in which part of the
SO3 formed reacts with existing water
in the recirculating H2SO4, forming
more H2SO4. After this intermediate
absorption step, the column off-gas is
routed to the fourth and fifth beds for
the last catalytic oxidation stages.
The oxidation product is sent to the
final absorption step, which is analogous
to the intermediate absorption.
The concentrated H2SO4 is then fed
to the intermediate absorption circuit.
The final product (98.5 wt.% H2SO4)
is discharged from the intermediate
absorber circuit.
H2SO4 production pathways
The double-contact process is currently
the most widely employed process
for producing H2SO4. However, SO2
starting material can be obtained from
several sources, depending on local
availability. Aside from elemental sulfur,
spent H2SO4 and smelter off-gases
are the main sources (Figure 2).
Economic performance
The process described here was considered
in an economic assessment
Electricity
4
Water
targeting the construction of a H2SO4
plant in the U.S. The analysis was
based on a production capacity of 1.5
million metric ton/yr, and from economic
data from the 4th quarter 2013. The
estimated capital investment required
would be about $160 million. This figure
includes production units, storage
installations, utilities facilities and auxiliary
buildings, as well as working capital
and additional capital requirements.
Due to the large scale of this plant,
the raw material costs represent a
significant portion of H2SO4 production
cost.
According to
the
aforementioned
analysis, gross raw material
costs were about $30 per ton of
H2SO4 produced.
This column is based on " Sulfuric
Acid Production from Sulfur via Double-Contact
Process - Cost Analysis, "
a report published by Intratec. It can
be found at: www.intratec.us/analysis/
sulfuric-acid-production-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. Combustion furnace
2. Drying column
3. SO2
converter
4. Intermediate absorption
5. Final absorption
6. Turbine generator
7. Cooling tower
2
Air
FIGURE 1. The diagram shows the production of sulfuric acid
from elemental sulfur via double-contact process
40
CW
7
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
MARCH 2017
Tail gas
Water
5
CW Cooling water
BFW Boiler feedwater
Sulfuric acid
Smelter offgasses
Hydrogen
sulfide
gases
SO2-rich
tail gas

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Chemical Engineering March 2017

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