NZ623437B2 - Sulphuric acid production with recycle of desulphurized gas - Google Patents
Sulphuric acid production with recycle of desulphurized gas Download PDFInfo
- Publication number
- NZ623437B2 NZ623437B2 NZ623437A NZ62343712A NZ623437B2 NZ 623437 B2 NZ623437 B2 NZ 623437B2 NZ 623437 A NZ623437 A NZ 623437A NZ 62343712 A NZ62343712 A NZ 62343712A NZ 623437 B2 NZ623437 B2 NZ 623437B2
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- New Zealand
- Prior art keywords
- gas
- sulphuric acid
- process gas
- stream
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- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 title claims abstract description 70
- 239000001117 sulphuric acid Substances 0.000 title claims abstract description 61
- 235000011149 sulphuric acid Nutrition 0.000 title claims abstract description 61
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 11
- 238000000034 method Methods 0.000 claims abstract description 181
- 239000007789 gas Substances 0.000 claims abstract description 138
- 238000009833 condensation Methods 0.000 claims abstract description 37
- 230000005494 condensation Effects 0.000 claims abstract description 37
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 28
- 239000011149 active material Substances 0.000 claims abstract description 19
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 18
- 230000003647 oxidation Effects 0.000 claims abstract description 14
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 14
- RAHZWNYVWXNFOC-UHFFFAOYSA-N sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 claims abstract description 12
- 230000001590 oxidative Effects 0.000 claims abstract description 10
- 238000004064 recycling Methods 0.000 claims abstract description 6
- 239000001301 oxygen Substances 0.000 claims abstract description 4
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 4
- MYMOFIZGZYHOMD-UHFFFAOYSA-N oxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims abstract description 4
- NINIDFKCEFEMDL-UHFFFAOYSA-N sulfur Chemical group [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 36
- 239000005864 Sulphur Substances 0.000 claims description 33
- 238000002485 combustion reaction Methods 0.000 claims description 14
- 230000003197 catalytic Effects 0.000 claims description 12
- 239000003595 mist Substances 0.000 claims description 12
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 claims description 12
- 239000002253 acid Substances 0.000 claims description 8
- 239000000463 material Substances 0.000 claims description 6
- 238000010521 absorption reaction Methods 0.000 claims description 5
- 239000003546 flue gas Substances 0.000 claims description 5
- 238000003303 reheating Methods 0.000 claims description 5
- UGFAIRIUMAVXCW-UHFFFAOYSA-N carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 4
- 238000010438 heat treatment Methods 0.000 claims description 4
- 150000007513 acids Chemical class 0.000 claims description 2
- 230000000875 corresponding Effects 0.000 claims description 2
- 238000005367 electrostatic precipitation Methods 0.000 claims description 2
- 239000007788 liquid Substances 0.000 claims description 2
- 229910052717 sulfur Inorganic materials 0.000 claims description 2
- 239000011593 sulfur Substances 0.000 claims description 2
- 235000010269 sulphur dioxide Nutrition 0.000 claims description 2
- 239000004291 sulphur dioxide Substances 0.000 claims description 2
- -1 at least 10°C Chemical compound 0.000 claims 1
- AKEJUJNQAAGONA-UHFFFAOYSA-N Sulfur trioxide Chemical compound O=S(=O)=O AKEJUJNQAAGONA-UHFFFAOYSA-N 0.000 abstract description 14
- 238000006243 chemical reaction Methods 0.000 description 14
- 230000001603 reducing Effects 0.000 description 12
- 238000001816 cooling Methods 0.000 description 10
- 238000004140 cleaning Methods 0.000 description 9
- 238000002156 mixing Methods 0.000 description 8
- 238000010790 dilution Methods 0.000 description 6
- 231100000078 corrosive Toxicity 0.000 description 5
- 231100001010 corrosive Toxicity 0.000 description 5
- 238000007792 addition Methods 0.000 description 4
- 239000003054 catalyst Substances 0.000 description 4
- MHAJPDPJQMAIIY-UHFFFAOYSA-N hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- NMCUIPGRVMDVDB-UHFFFAOYSA-L Iron(II) chloride Chemical compound Cl[Fe]Cl NMCUIPGRVMDVDB-UHFFFAOYSA-L 0.000 description 2
- 229910052783 alkali metal Inorganic materials 0.000 description 2
- 150000001340 alkali metals Chemical class 0.000 description 2
- XKRFYHLGVUSROY-UHFFFAOYSA-N argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- RWSOTUBLDIXVET-UHFFFAOYSA-N dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- TVFDJXOCXUVLDH-UHFFFAOYSA-N Cesium Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 description 1
- 108060003095 GAS2 Proteins 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 229910052792 caesium Inorganic materials 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 150000004677 hydrates Chemical class 0.000 description 1
- 230000036571 hydration Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 230000000171 quenching Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000005201 scrubbing Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- KEAYESYHFKHZAL-UHFFFAOYSA-N sodium Chemical compound [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
- GRUMUEUJTSXQOI-UHFFFAOYSA-N vanadium dioxide Chemical group O=[V]=O GRUMUEUJTSXQOI-UHFFFAOYSA-N 0.000 description 1
- 229910001935 vanadium oxide Inorganic materials 0.000 description 1
- 239000002912 waste gas Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/202—Alkali metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/207—Transition metals
- B01D2255/20723—Vanadium
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2258/00—Sources of waste gases
- B01D2258/02—Other waste gases
- B01D2258/0283—Flue gases
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/48—Sulfur compounds
- B01D53/50—Sulfur oxides
- B01D53/501—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8603—Removing sulfur compounds
- B01D53/8609—Sulfur oxides
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/74—Preparation
- C01B17/76—Preparation by contact processes
- C01B17/765—Multi-stage SO3-conversion
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/74—Preparation
- C01B17/76—Preparation by contact processes
- C01B17/765—Multi-stage SO3-conversion
- C01B17/7655—Multi-stage SO3-conversion with intermediate absorption
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/74—Preparation
- C01B17/76—Preparation by contact processes
- C01B17/80—Apparatus
Abstract
Disclosed is a process for oxidation of sulfur dioxide to sulfur trioxide, for the production of sulfuric acid, and or for desulfurising a process gas, comprising the steps of (a) directing a stream of feed gas, being a process gas, comprising sulfur dioxide and oxygen, to a catalytically active material (b) oxidizing an amount of said sulfur dioxide in said process gas to sulfur trioxide in the presence of at least 0.1% water and the catalytically active material, providing a first oxidized process gas (c) reacting the sulfur trioxide with water in a condensing column, (d) condensing sulfuric acid in a condenser (e) withdrawing a first desulphurized process gas and a first stream of sulphuric acid; and (f) from the desulphurized process gas, withdrawing a recycle stream of desulphurized process gas wherein the recycle stream is added to said stream of feed gas or said first oxidized process gas. Also disclosed is a process plant for desulphurisation of a feed gas said process plant comprising a first bed of catalytically active material, a first condensation unit and a downstream desulphurisation plant, configured for recycling of a stream being withdrawn downstream said first condensation unit and optionally downstream the downstream desulphurisation unit, and being recycled to a process position upstream the first condensation unit, and optionally upstream said first bed of catalytically active material. erial (b) oxidizing an amount of said sulfur dioxide in said process gas to sulfur trioxide in the presence of at least 0.1% water and the catalytically active material, providing a first oxidized process gas (c) reacting the sulfur trioxide with water in a condensing column, (d) condensing sulfuric acid in a condenser (e) withdrawing a first desulphurized process gas and a first stream of sulphuric acid; and (f) from the desulphurized process gas, withdrawing a recycle stream of desulphurized process gas wherein the recycle stream is added to said stream of feed gas or said first oxidized process gas. Also disclosed is a process plant for desulphurisation of a feed gas said process plant comprising a first bed of catalytically active material, a first condensation unit and a downstream desulphurisation plant, configured for recycling of a stream being withdrawn downstream said first condensation unit and optionally downstream the downstream desulphurisation unit, and being recycled to a process position upstream the first condensation unit, and optionally upstream said first bed of catalytically active material.
Description
Title: Sulphuric Acid Production with Recycle of
Desulphurized Gas
The present invention relates to a method for production of
sulphuric acid by desulphurisation of an SO rich process
gas, including feed gases from combustion of a sulphur
source such as H S, sulphur and spent acid, and flue gases
from combustion plants. More specifically it relates to a
process with reduced equipment requirements involving
recycle of the desulphurised process gas.
Sulphuric acid can be produced from gases containing sulphur
oxides. One such process is based on the oxidation of SO to
SO in the presence of water vapour, followed by
condensation to H SO , and is sold under the trade name WSA
(the Wet gas Sulphuric Acid) by the company Haldor Topsøe
A/S of Denmark. The source of sulphur may either be an off-
gas with high sulphur content, or more typically, a gas
produced by combustion of a sulphur rich source, such as
elemental sulphur or hydrogen sulfide.
With increasing environmental concern, the regulations of
sulphur oxide emissions to very low concentrations has led
to the development of two WSA process plants configured in
series as disclosed in , hence the trade name
WSA-DC for dual condensation.
The WSA process operates with water concentrations in the
process gas close to or above stoichiometric concentrations
with respect to SO hydration. Therefore, the ability to
control condensation of sulphuric acid is critical, as
sulphuric acid is very corrosive. Condensation of sulphuric
acid occurs if the gas temperature is below the sulphuric
acid dew point, which is a function of partial pressures of
sulphuric acid and water. The conditions in the WSA process
downstream catalytic oxidation are typically chosen for
obtaining a given dew point of H SO , such that condensation
of H SO only occurs inside the condensation unit. With SO
2 4 3
concentrations in the oxidized process gas above about 5% by
volume this typically requires dilution of the oxidized
process gas, which is provided by adding excess air,
compared to the stoichiometric requirements for oxidation of
sulphur compounds to sulphur trioxide. This excess air will
lead to an excess flow of process gas and therefore to extra
cost and reduced heat recovery.
The material cost and operational cost of the
desulphurisation process is increased with increased total
molar flow in the plant. Therefore, it is desirable to
identify ways of reducing this flow. Furthermore, the amount
of heat recovered in the desulphurisation plant is also an
important economical factor for the plant.
For catalytic oxidation of SO it is required that the
temperature of the process gas is at least 370°C at the
inlet to the SO converter. This can be obtained e.g. by
tempering the process gas upstream the catalytic reactor in
which the SO is oxidized to SO . The exothermal reaction
typically requires temperatures above 370 to 390°C for
activation, but temperatures above this pushes on the other
hand the equilibrium between SO and SO towards SO such
2 3 2
that less sulphuric acid is formed.
Downstream the catalytic reactor the SO -rich gas is cooled
to 230-310°C and the SO is hydrated to H SO vapour in or
3 2 4
upstream a condenser in which the H SO vapour and most of
the SO is selectively condensed as concentrated sulphuric
acid.
relates to a process for producing sulphuric
acid from feed gases implemented as a dual desulphurisation
process, which employs two WSA process plants in series,
with the associated benefit of being able to operate each
combined process optimally at high and low SO levels,
respectively.
EP 0 972 746 and EP 2 330 075 relates to processes for
production of sulfuric acid, by the so called dry contact
process, in which a dried waste gas is recycled to the
sulphur burner. According to the dry contact process, SO is
oxidized to SO in a dry environment followed by absorption
of SO by contacting the gas with a water/sulphuric acid
absorbent, with the associated benefit of fewer demands to
the robustness of catalyst and with flexibility for the heat
exchanger designs due to the absence of condensable
sulphuric acid, but at the expense of requiring equipment
for drying the feed gas prior to oxidation. A sulphur
depleted gas is recycled for being fed upstream a sulphur
combustion unit, in order to control the combustion
temperature, increase sulphur removal and reduce equipment
size. Neither of these two disclosures realize the important
relations between dilution by recycled gas and the dew point
of a gas comprising water, sulphur trioxide and sulphuric
acid.
The present disclosure is aimed at reducing the investment
and operational cost of a dual desulphurisation plant by
reducing the molar flow of process gas in selected sections
of the WSA plant. This is done by configuring the
desulphurisation plant for recycle of a substream of a first
desulphurised process gas, such that the first
desulphurisation process operates with sufficient dilution
for avoiding sulphuric acid condensation outside the
condenser, while the remainder of the desulphurisation
process in which less or no dilution is required due to the
lower concentrations of SO may be reduced in size due to
the absence of the recycled gas in the flow. Similarly the
size of the sulphur combustor and other equipment upstream
the addition of recycled desulphurized gas may be reduced.
This also reduces the amount of energy required for heating
the feed gas to the second catalytic reactor.
Sections of the present application relates to a process
having two desulphurisation steps. In this respect, the
terms upstream or first desulphurisation process or
desulphurisation unit shall be understood as related to one
desulphurisation steps being most proximate to the feed gas,
and downstream, second or secondary to the other
desulphurisation step being most proximate to the stack.
Throughout the present text, trivial but critical elements
such as pumps, valves and heat exchangers may not be
mentioned explicitly, but such an omission shall not be
construed as an absence of the elements, unless explicitly
mentioned as such.
In a first embodiment the invention relates to a process for
oxidation of SO to SO comprising the steps of,
(a) directing a stream of feed gas comprising SO and O to a
catalytically active material,
(b) oxidizing an amount of said SO in said process gas to
SO in the presence of at least 0.1% water and the
catalytically active material, providing a first oxidized
process gas
(c) reacting SO with water,
(d) condensing H SO
(e) withdrawing a first desulphurized process gas and a
first stream of sulphuric acid
(f) from the desulphurized process gas withdrawing a recycle
stream of desulphurized process gas, wherein the recycle
stream is added to said stream of feed gas or said first
oxidized process gas with the associated benefit of reducing
the molar flow of process gas downstream withdrawal of the
recycle stream, and upstream the mixing point, with the
associated benefit of removing SO from a flue gas as
sulphuric acid, without having to dry the process gas and
subsequently add water to the gas, while maintaining non-
corrosive conditions in all of the process plant.
In a further embodiment the process further comprises the
secondary sulphur removal process steps of
(g) reheating the first desulphurized process gas,
(h) oxidizing an amount of the remaining SO in said first
desulphurized process gas to SO in the presence of a second
catalytically active material providing a second oxidized
process gas
(i) reacting SO with water,
(j) condensing H SO
(k) and withdrawing a second desulphurized process gas and a
second stream of sulphuric acid with the associated benefit
of further reducing the concentration of SO in the process
gas.
In a further embodiment the process further comprises the
process step of (l) heating the recycle stream of
desulphurized process gas to a temperature above the dew
point of sulphuric acid in the desulphurized flue gas with
the associated benefit of reducing the risk of condensation
of corrosive sulphuric acid, after mixing with the process
gas.
In a further embodiment the temperature of the recycle
stream is at least 10°C, preferably at least 30°C and even
more preferable at least 50°C above the dew point with
respect to sulphuric acid with the associated benefit of
reducing the risk of corrosion by ensuring ample margin to
the dew point of sulphuric acid.
A further embodiment involves one or more secondary sulphur
removal process steps taken from the group consisting of
(m) removal of sulphuric acid mist by collection of droplets
in a mist filter and withdrawal of collected sulphuric acid
droplets,
(n) removal of sulphuric acid mist by electrostatic
precipitation, and removal of precipitated sulphuric acid
(o) removal of sulphur oxides by absorption in a scrubber,
wherein said scrubber contains an alkaline solution and/or
an oxidative solution with the associated benefit of
providing the optimal means for reduction of SO
concentrations in the clean gas according to specific
process requirements.
In a further embodiment the recycle stream is withdrawn
downstream the secondary sulphur removal process step with
the associated benefit of a reduced molar flow upstream the
desulphurisation process, while high dilution is maintained
in all of the desulphurisation plant.
In a further embodiment the recycle stream is withdrawn
downstream the secondary sulphur removal process step with
the associated benefit of a reduced molar flow upstream the
desulphurisation process and in the secondary sulphur
removal process.
In a further embodiment the concentration of SO in the SO
rich gas is in the range 5-100% vol, preferably 5-30% vol,
allowing maximum benefit from removal of sulphur oxides in
two independent processes in series.
In a further embodiment at least 99% of the sulfur comprised
in the feed gas is in oxidised form such as SO or SO or the
corresponding acids, with the associated benefit of the
substantially all of the sulphur being condensable as acid
in the process.
In a further embodiment less than 50% of said desulphurized
process gas is withdrawn as a recycle stream of
desulphurized process gas, with the associated benefit of
avoiding a built up of inert gases, such as nitrogen and
argon.
In a further embodiment the volumetric concentration of
oxygen in said process gas being directed to contact the
catalytically active material is at least the same as the
volumetric concentration of sulphur dioxide, with the
associated benefit of providing an efficient oxidation
process with fast reaction due to the excess of oxygen.
In a further embodiment the temperature of said recycled gas
is above 200°C, with the associated benefit of the recycled
gas being maintained non-corrosive, even in the presence of
water and sulphur oxides.
A further aspect of the invention, relates to a process
plant for desulphurisation of a feed gas comprising a first
bed of catalytically active material, a first condensation
unit and a downstream desulphurisation plant configured for
recycling of a stream being withdrawn downstream said first
condensation unit and optionally downstream the downstream
desulphurisation unit and being recycled to a process
position upstream the first condensation unit, and
optionally upstream said first bed of catalytically active
material, with the associated benefit of reducing the molar
flow of process gas downstream withdrawal of the recycle
stream, with the associated benefit of providing a plant for
removing SO from a flue gas as sulphuric acid, without
having to dry the process gas, while maintaining non-
corrosive conditions in all of the process plant.
A further embodiment involves one or more additional sulphur
removal process units downstream the desulphurisation plant
taken from the group consisting of (i) a process unit
comprising a catalytic material for oxidation of SO to SO
and a condenser for condensation of sulphuric acid, (ii) a
mist filter for removal of sulphuric acid mist by collection
of droplets and withdrawal of collected sulphuric acid
droplets, (iii) an electrostatic precipitator for collection
of liquid sulphuric acid from sulphuric acid mist, and (iv)
a scrubber for removal of sulphur oxides by absorption in an
alkaline solution and/or an oxidative solution with the
associated benefit of providing the optimal means for
reduction of SO concentrations in the clean gas according
to specific process requirements.
A further embodiment is configured for recycling of a stream
being withdrawn downstream said first condensation unit and
upstream the downstream desulphurisation unit with the
associated benefit of reducing the molar flow inside the
downstream desulphurisation unit.
A further embodiment involves a combustion unit for a
sulphur rich material upstream said process plant in which
the stream being recycled is directed to a position upstream
or downstream said combustion unit, with the associated
benefit of independently providing a sulphur source for the
production of sulphuric acid.
Fig. 1 illustrates a process according to the prior art.
Fig. 2 illustrates a process according to an embodiment of
the present disclosure involving two WSA processes in
series.
Fig. 3 illustrates a process according to an embodiment of
the present disclosure involving a WSA process and a
scrubber process in series.
Fig. 4 illustrates a process according to an embodiment of
the present disclosure in which the recycled stream is
withdrawn downstream both desulphurisation processes.
A process as shown in Fig. 1, for removal of SO from
process gases, with associated production of sulphuric acid
is known from the prior art, and may be described as a
Double Conversion/Double Condensation process. In the
process a feed gas 2 containing SO may optionally, by
cooling or heating in an appropriate heat exchanger 4, be
provided as a process gas 6 at a temperature sufficient for
catalytic oxidation of SO to SO to be initiated such as
around 370-420°C. The tempered process gas 6 is directed to
a catalytic reactor 8 in which oxidation of SO to SO takes
place in the presence of an appropriate sulphuric acid
catalyst. A range of such sulphuric acid catalysts are known
to the person skilled in the art. One possible catalyst is
vanadium oxide supported on a silica carrier material and
promoted with alkali metals. Preferred alkali metals are
potassium, sodium, and/or caesium.
To avoid pushing the SO /SO equilibrium towards SO while
2 3 2
enjoying the benefit from high reaction rates at high
temperatures, the oxidation is often carried out in two or
three beds with intermediate heat exchangers, and followed
by a further heat exchanger.
At the outlet from the catalytic reactor a first oxidized
process gas 10 is available. This first oxidized process gas
contains water vapour which as temperature is reduced
hydrates SO to form gaseous H SO , sulphuric acid. The
3 2 4
oxidized and partly hydrated process gas is directed to a
condensation unit 12, in which the temperature is reduced to
below the dew point of sulphuric acid. The sulphuric acid
condenses and may be collected in concentrated form at the
bottom of the condensation unit 36. At the top outlet of the
condensation unit a desulphurised process gas 14 is directed
downstream to a further catalytic reactor 24 where most of
the remaining SO is oxidized, forming a second oxidized
process gas 26, which undergoes a similar condensation
process in 30, before it is directed to the stack 34 as a
clean gas 32.
Now according to the present disclosure with reference to
Fig. 2 and Fig. 3, it is desired to keep the oxidised
process gas 10 above the sulphuric acid dew point, while
ensuring a high level of sulphur removal and reducing the
size of equipment. This is obtained by keeping the
concentration of sulphur oxides low, by dilution of the feed
gas 6 with a first recycle stream 22 of desulphurised
process gas in a mixing point 40. The molar flow of the
recycle stream 22 is about the same as the amount of excess
air according to the prior art, and therefore overall
conditions, including the concentration of SO and H SO in
3 2 4
the first oxidized process gas 10 of this embodiment, are
equivalent to those of the prior art. The reduced molar flow
of desulphurised process gas 23, downstream the withdrawal
point 42 now constitutes a secondary process gas, which may
be desulphurised further in a downstream desulphurisation
process.
In a preferred embodiment illustrated in Fig. 2, the
downstream desulphurisation process is a second WSA process
configured for removal of a low level of sulphur oxides
comprising a catalytic reactor 24 and a condenser 30. This
downstream desulphurisation process may be significantly
smaller than the upstream desulphurisation process, since
the molar flow is much lower due to the withdrawal of the
recycle stream 22.
In an alternative embodiment illustrated in Fig. 3, the
first WSA Process is followed by an alternative process for
removal of low concentrations of sulphur oxides, such as a
scrubber 44,46 for collection of sulphur oxides in either
sodium hydroxide or hydrogen peroxide.
In a further embodiment illustrated in Fig. 4, the
withdrawal point may be positioned downstream the downstream
desulphurisation process. In this case a large molar flow
will be present in both desulphuration processes, but a
reduced molar flow will be present upstream the first
desulphurisation. This embodiment may be especially suited
for sulphuric acid production by combustion of a sulphur
source, as the sulphur combustor can be reduced in size,
compared to the prior art.
The addition of the recycle stream in the mixing point 40
may require careful mixing to avoid pockets of condensing
conditions, where corrosion may take place. This may
beneficially be implemented by an appropriate gas mixer such
as disclosed in WO2011/101038.
In a further embodiment the process may also include a
combustor receiving a sulphur rich feed, comprising e.g.
hydrogen sulphide, spent acid, or sulphur, and the recycle
stream may be added to the feed gas upstream this combustor.
Such addition upstream a sulphur combustor shall be
considered equivalent to the addition of a recycle stream
downstream said sulphur combustor.
EXAMPLES
In order to evaluate embodiments of the prior art and
embodiments of the present disclosure, performance and
design parameters has been evaluated for 3 sulphuric acid
processes designed for production of 600 metric ton
sulphuric acid per day (calculated as 100% H SO ). The
processes produce 98% (w/w) H SO , with a SO conversion of
2 4 2
99.83%. Outside the desulphurisation plant steam may be
converted into electrical power. For the process the feed is
100% H S gas and the ambient conditions are pressure 1001
mbar abs at 25°C, 65% RH.
Example 1
The process unit is designed according to Fig. 1, i.e.
Double Conversion/Double Condensation. The following process
steps apply with reference to elements of Fig. 1:
Combustion (not shown)
Cooling (4)
1 Conversion and Cooling (8)
1 Condensation and acid withdrawal (12, 36)
Reheating (18)
2 Conversion and Cooling (24, 18)
2 Condensation and acid withdrawal (30, 38)
Clean Gas to stack (34)
From the data in Table 1, it can be seen that the unit is
performing according to the performance requirements with a
clean gas flow of 73500 Nm /h.
Example 2
The process unit is designed as a Double Conversion Double
Condensation unit according to an embodiment of the present
disclosure, i.e. desulphurised process gas is recycled
downstream reheating 18 to upstream the SO converter 8
according to Fig. 2.
Combustion (not shown)
Cooling (4)
Mixing process gas with recycle gas (6,22,40)
1 Conversion and Cooling (8)
1 Condensation and acid withdrawal (12,36)
Reheating (18)
Withdrawal of recycle gas (22,42)
2 Conversion and Cooling (24,18)
2 Condensation and acid withdrawal (30,38)
Clean Gas to stack (34)
From Table 1 it is evident that the sulphur emission is as
low as for the prior art process of Example 1. In addition,
the process gas molar flow before the recycle gas mixing
point 40 and after the recycle gas withdrawal point 42 have
been reduced by more than 20% to a clean gas flow of 56500
Nm /h resulting in a smaller and more cost efficient layout.
Example 3
The process unit is designed according to Fig. 3 as a Single
Conversion Single Condensation unit with a quenching unit 44
and a hydrogen peroxide tail gas scrubber 46 and process gas
recycle.
Combustion (not shown)
Cooling (4)
Mixing process gas with recycle gas (6,22,40)
1 Conversion and Cooling (8)
1 Condensation and acid withdrawal (12, 36)
Withdrawal of recycle gas (42)
Process gas cooling (Quench) (44)
Process gas scrubbing (46)
From Table 1 it can be seen that performance is good
according to the specification and that it is possible to
reduce the molar flow about 20% outside the recycle loop
42,22,40 again resulting in a more cost efficient unit than
if constructed according to prior art.
Table 1
Example 1 Example 2 Example 3 Unit
no recirculation Single
recirculation conversion,
recirculation
& scrubber
Feed Flow 5731 5731 5731 Nm3/h
Combustion 85600 68600 71000 Nm3/h
Air (-20%) (-17%)
PG before 88400 71400 74400 Nm3/h
recycle (-19%) (-16%)
PG inlet 88400 88600 92100 Nm3/h
SO (0%) (+4%)
converter
Recycle 0 17100 17700 Nm3/h
Process 74400 57400 59400 Nm3/h
gas after (-23%) (-20%)
recycle
Clean Gas 73500 56500 61700 Nm3/h
(-23%) (-17%)
Power 13.3 13.6 13.7 MW
production (+2.5%) (+3.0%)
Sulphur in 50 50 50 kg/h
clean gas
as SO
SO 99.83 99.83 99.83 %
removal
Claims (15)
1. A process for oxidation of SO to SO comprising the steps of 5 (a) directing a stream of feed gas, being a process gas, comprising SO and O , to a catalytically active material (b) oxidizing an amount of said SO in said process gas to in the presence of at least 0.1% water and the catalytically 10 active material, providing a first oxidized process gas (c) reacting SO with water in a condensing column, (d) condensing H SO in a condenser (e) withdrawing a first desulphurized process gas 15 and a first stream of sulphuric acid; and (f) from the desulphurized process gas, withdrawing a recycle stream of desulphurized process gas wherein the recycle stream is added to said stream of feed gas or said first oxidized process gas.
2. A process according to claim 1 further comprising the secondary sulphur removal process step of (g) reheating the first desulphurized process gas, (h) oxidizing an amount of the remaining SO in said first 25 desulphurized process gas to SO in the presence of a second catalytically active material providing a second oxidized process gas (i) reacting SO with water, (j) condensing H SO 30 (k) and withdrawing a second desulphurized process gas and a second stream of sulphuric acid
3. A process according to claim 1 or 2 further comprising the process step of (l) heating the recycle stream of desulphurized process gas to a temperature above the dew point of sulphuric acid in 5 the desulphurized flue gas, such as at least 10°C, preferably at least 30°C and even more preferable at least 50°C above the dew point with respect to sulphuric acid in said recycle stream. 10
4. A process according to any one of claims 1 to 3 further comprising one or more secondary sulphur removal process steps taken from the group consisting of (m) removal of sulphuric acid mist by collection of droplets in a mist filter and withdrawal of collected sulphuric acid 15 droplets, (n) removal of sulphuric acid mist by electrostatic precipitation, and removal of precipitated sulphuric acid (o) removal of sulphur oxides by absorption in a scrubber, wherein said scrubber contains an alkaline solution and/or 20 an oxidative solution.
5. A process according to any one of claims 2 to 4, wherein the recycle stream is withdrawn downstream the secondary sulphur removal process step.
6. A process according to any one of claims 2 to 4, wherein the recycle stream is withdrawn upstream the secondary sulphur removal process step. 30
7. A process according to any one of claims 1 to 6, wherein the concentration of SO in the feed gas is above 5 % vol, and below 100% vol, preferably below 30% vol.
8. A process according to any one of claims 1 to 7 in which at least 99% of the sulfur comprised in the feed gas is in oxidised form such as SO or SO or the corresponding acids.
9. A process according to any one of claims 1 to 8 in which less than 50% of said desulphurized process gas is withdrawn as a recycle stream of desulphurized process gas.
10 10. A process according to any one of claims 1 to 9 in which the volumetric concentration of oxygen in said process gas being directed to contact the catalytically active material is at least the same as the volumetric concentration of sulphur dioxide.
11. A process according to any one of claims 1 to 10 in which the temperature of said recycled gas is above 200°C.
12. A process plant for desulphurisation of a feed gas 20 said process plant comprising a first bed of catalytically active material, a first condensation unit and a downstream desulphurisation plant, configured for recycling of a stream being withdrawn downstream said first condensation unit and optionally 25 downstream the downstream desulphurisation unit, and being recycled to a process position upstream the first condensation unit, and optionally upstream said first bed of catalytically active material. 30
13. A process plant according to claim 12, in which said downstream desulphurization unit is taken from the group consisting of (i) a process unit comprising a catalytic material for oxidation of SO to SO and a condenser for condensation of sulphuric acid, (ii) a mist filter for removal of sulphuric acid mist by collection of droplets and withdrawal of collected sulphuric acid droplets, (iii) an electrostatic precipitator, for collection of liquid 5 sulphuric acid from sulphuric acid mist, and (iv) a scrubber for removal of sulphur oxides by absorption in an alkaline solution and/or an oxidative solution.
14. A process plant for desulphurisation of a feed gas 10 according to claim 12 or 13, configured for recycling of a stream being withdrawn downstream said first condensation unit, and upstream the downstream desulphurisation unit.
15. A process plant for production of sulphuric acid 15 comprising a combustion unit for a sulphur rich material upstream a desulphurisation process plant according to claim 12, 13 or 14, in which the stream being recycled is directed to a position upstream or downstream said combustion unit. HALDOR TOPSOE A/S WATERMARK PATENT AND TRADE MARKS ATTORNEYS P38477NZ00
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PCT/EP2011/004860 WO2013044937A1 (en) | 2011-09-29 | 2011-09-29 | Sulphuric acid production with recycle of desulphurized gas |
EPPCT/EP2011/004860 | 2011-09-29 | ||
PCT/EP2012/069099 WO2013045558A1 (en) | 2011-09-29 | 2012-09-27 | Sulphuric acid production with recycle of desulphurized gas |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ623437A NZ623437A (en) | 2016-07-29 |
NZ623437B2 true NZ623437B2 (en) | 2016-11-01 |
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