Technologies for Sulphuric Acid Production
Desmet Ballestra plants are based on different technologies.
DuPontTM MECS® Single
Contact Single Absorption or Double Contact Double Absorption leading
technology for large integrated H2SO4 plants
Proprietary know-how (which uses DuPontTM MECS® catalyst
and key components) Single Contact Single Absorption process for low
capacity plants (up to about 200 TPD
Several fields of application
Sulphuric acid is widely used in different business areas such as:
Waste gas treatment
The processes that Desmet Ballestra makes available can produce
sulphuric acid from several sources:
Elemental sulphur, based on dry air combustion (conventional process)
Exhaust SO2 gas, coming from roasting/smelting of pyrites,
copper, zinc, lead, nickel ores and similar
Spent acid or sludge obtained from alkylation processes
H2S and SO2 off gas from various other chemical
Possibility to produce high quality H2SO4 for
special applicationslike battery grade, analytical grade,electronics and others.
Option for production of Oleum as
well as liquid SO2 and liquid SO3.
Waste heat recovery by steam
production, with steam turbine power generationsystems to increase theoverall
plant efficiency and boost the return on investment.
DuPontTM MECS® HRSTM
technology to maximize
theheat recovery from the plant.
Wide range of production capacities, 2 from small size of 8 TPD for
local or very specific applications to large industrial production units up to
more than 2,000 TPD.
Compact plant layout, for
investment cost optimization (e.g. piping and duct routing), taking into account
safety / maintenance / operation principles and according to customer site
Air pollution control system, to contain the plant emissions to the
minimum level required by the most stringent laws and standards.
High quality construction materials and
use of acid resistant specialalloys.
High yield of conversion, granted by the best available technology
together with DuPontTM MECS® catalysts
allowing for an extended life time, low pressure drop and low screening losses.
Conventional Process (Dry route) Principle
Process technology is based on the production of Sulphur dioxide (SO2)
by Sulphur burning using dry air, followed by catalytic conversion to produce
Sulphur trioxide (SO3) which is finally absorbed in water (H2O)
to obtain sulphuric acid (H2SO4)
All the above reactions are extremely exothermic at high temperatures and
therefore the recovery of the heat generated during the process is highly
The typical converter configuration is based on 4 stages of catalytic
Single or Double absorption
According to the requested production capacity, the selected conversion yield,
the specific plant requirements, flexibility, startup time, the plant can be
Single Contact Single Absorption (SCSA) – Ballestra technology.
Single Contact Single Absorption (SCSA) - DuPontTM MECS® technology.
Double Contact Double Absorption (DCDA) - DuPontTM MECS® technology.
The conversion factor for a Ballestra SCSA plant is 98.5%, typically requiring a
tail gas scrubber to control the SO2 stack emissions. This plant is
specifically designed to achieve a very fast startup, thus granting a high
DuPontTM MECS® DCDA
are designed for higher conversion factor, typically >99.8%, thus granting SO2 emissions
at stack within the limit of 280- ppmV without the need for a tail gas scrubber.
Minimization of gaseous emissions
Improvement of SO2 stack emissions can be achieved by a combination
of the following:
Cesium-based catalyst instead of Vanadium-based ones.
5 stages catalytic conversion.
Dedicated Acid Tank and cooler for Final Absorption Tower.
The solutions above allow to have SO2 emissions
at stack within the limit of 100 ppmV (equivalent to a conversion factor over
99.92%) without the use of a tail gas scrubber.
Waste Heat Recovery
Energy recovery is extremely important in the economics of new sulphuric acid
Desmet Ballestra can offer sulphuric acid plants based on the conventional heat
recovery systems as well as on the DuPontTMMECS® HRSTMsystem.
The heat recovery system of a conventional sulphuric acid plant recovers most of
the heat produced during the sulphur combustion and the SO2 -> SO3 conversion,
producing 1.2 ÷ 1.3+ tons of MP superheated steam (at 25 ÷ 42 bara and about
400°C) per ton of sulphuric acid.
The steam produced can feed a turbogenerator for electric power production or
can be delivered at unit battery limits, according to the plant requirements.
Turbogenerator units can be condensing steam turbines, to maximize electric
power generation, or backpressure steam turbines, to still have exhaust steam
available as utility at unit battery limits.
DuPontTM MECS® HRSTM
DuPontTM MECS® HRSTM is
a system designed to enhance the Sulphuric Acid Plant performances in terms of
waste heat recovery.
The system consists of the HRS tower and its ancillaries that replace the
interpass absorbing tower and allow the recovery of the heat generated during
the interpass absorption reducing thus the heat that would have been lost to
cooling water. As a result, additional LP saturated steam is produced and, as a
collateral benefit, size of cooling water system (e.g. cooling towers) is
reduced together with relevant consumptions.
With DuPontTM MECS® HRSTM system,
the heat recovered can be increased to 90% of the total reaction heat produced
in the Sulphuric Acid Unit.
P steam ton / H2SO4 ton
HRS steam ton / H2SO4 ton
Up to 0.40 ÷ 0.48
Total Heat Recovered
Up to 90% approx
Oleum and SO3 Production
The Oleum and the SO3 production are strictly connected to the H2SO4 production
Liquid SO3 is
produced by evaporation of Oleum and subsequent cooling and condensation.
Oleum can be produced by absorbing part of the SO3 leaving
the sulphuric acid converter in a circulation of Oleum at the required strength
and maintaining a steady concentration by adding sulphuric acid at 98.5% w.
This absorption is carried out in a dedicated Oleum tower installed immediately
upstream the absorption tower.
Typical grade of Oleum is at 20÷35% or 65% free SO3.
Desmet Ballestra preferred design for liquid SO2 is
based on the cryogenic condensation process.
The feed is an SO2 rich gaseous stream produced in a sulphur furnace
that is fed to an absorption tower for SO3 entrainments
removal. Then the gas is sent to a chilling group for SO2 condensation.
The condensed fraction flows to battery limit, while the uncondensed gas stream
is sent to a SO2 converter
for H2SO4 production.
The cryogenic condensation process is strictly connected to the H2SO4 production,
hence the unit can be a stand-alone plant or a secondary product package unit
installed within a large scale H2SO4 production
Wet gas technologies
The MECS® Sulfox
wet gas technology is an alternative process to the conventional “dry” sulphuric
This process is designed to produce H2SO4 acid
from SO2 or H2S
off-gas, spent acids, sulphates regeneration feedstocks or organic wastes
The Sulfox technology can effectively process the wet gas without gas drying
upstream of the reaction section.
The core process consists of a reaction section that converts the wet stream of
SO2 into a wet stream of
SO3, followed by a column that condenses H2SO4.
A final mist precipitator grants low acid mists emissions at the stack.
When the feedstock is H2S rich gas, a waste liquid or a spent acid, a
preliminary oxidation section (both thermal or catalytic) is added to obtain the
SO2 inlet stream.
The Sulphuric acid concentration from a Sulfox plant depends on the feedstock
composition. Typically 96%÷98% concentration is achievable.
MECS® Sulfox process is an
effective alternative to “dry” processes for specific concentration of the gas
feedstocks, based on the conditions detailed below.