DK201600438A1 - A process for the production of sulfuric acid from gases comprising H2SA - Google Patents

Abstract

A process plant for the production of sulfuric acid from a gas comprising H2S comprises an alkaline absorber for con- tacting a gas comprising H2S with a liquid ammonia absorbent solution and a dissolved material, that is catalytically active in the oxidation of H2S to elemental sulfur, separation means for producing an absorber liquid free of elemental sulfur to be returned to the absorber and a stream of elemental sulfur and purged absorber liquid to be introduced into an incinerator, air-free nozzles for receiving and atomizing the elemental sulfur and purged absorber liquid into an incinerator, means for cooling, a particulate removal device, a sulfur dioxide converter for oxidation of SO2 to SO3, and means for the provision of concentrated sulfuric acid.

Description

Title: A process for the production of sulfuric acid from gases comprising H2S

The invention relates to a process for removal of hydrogen sulfide and hydrogen cyanide from coke oven gas, with associated production of concentrated sulfuric acid. More specifically, the invention relates to a process for the production of sulfuric acid from a gas comprising H2S.

When coke oven gas is produced from coal, significant amounts of sulfur and nitrogen are also released, mainly in the form of H2S and HCN. These constituents must be removed from the coke oven gas before the coke oven gas is used as city gas or process gas. One process for cleaning the coke oven gas involves absorbing H2S and HCN in an alkaline scrubber and oxidizing H2S to elemental sulfur by means of a liquid catalyst, which typically is a quinone type compound in combination with a metal, such as vanadium, cobalt or iron, to promote the catalytic activity. The elemental sulfur is then separated from the slurry, and then it may either be sold as low quality sulfur, or it may be transferred to a sulfuric acid production plant, where it can be incinerated by the use of a support fuel, forming S02, filtered in a high temperature filter and transferred to a catalytic S02 to S03 conversion unit, and subsequently hydrated to H2SO4 and collected as concentrated sulfuric acid. Examples of such configurations may be found in the patents CN 101033060, CN 100497165 and CN 101092577, which involve dry filters and a wet sulfuric acid process, as well as CN 101734629 and CN 103072957, which involve a wet process gas cleaning unit and a dry gas sulfuric acid process .

In its broadest form, the present invention relates to a process for the production of sulfuric acid from a gas comprising H2S, said process comprising the following steps: (a) directing said gas to an alkaline absorber containing a liquid ammonia absorbent solution and a dissolved material, that is catalytically active in the oxidation of H2S to elemental sulfur, providing a liquid slurry comprising elemental sulfur and absorber liquid, (b) separating said elemental sulfur from the absorber liquid by mechanical means, providing a stream of absorber liquid, which is practically free of elemental sulfur to be returned to the absorber, and a stream of elemental sulfur and purged absorber liquid, (c) injecting said elemental sulfur and purged absorber liquid streams into an incinerator by means of an air-free nozzle, (d) feeding a support fuel and a first oxidant gas into an incinerator or into a point upstream from said incinerator, (e) incinerating the mixture, thereby obtaining an incinerated gas comprising S02, (f) removing inorganic dust in a filter unit, (g) contacting the process gas with a material, that is catalytically active in the oxidation of S02 to SO3, thereby providing an oxidized process gas, and (h) withdrawing concentrated sulfuric acid, either by cooling and condensation or by absorption of SO3 in H2SO4, providing oleum or concentrated sulfuric acid and a process gas reduced in sulfur, with the associated benefit of avoiding an emission of S02 and thus reducing the environmental impact of the process. In a further embodiment said material, which is catalyti-cally active in oxidation of H2S to elemental sulfur in step (a) , is taken from the group comprising picric acid, thioarsenate or quinones, such as a benzoquinone, naphthoquinone or anthraquinone compound, optionally with one or more further constituents in ionic form such as sodium, iron, vanadium or cobalt, with the associated benefit of catalysts having quinone structure or a similar structure being well known, tested, active, low cost, and known to generate only gaseous combustion products, such as C02, H20 and possibly N2, N0X and S02, if substituted with sulfur or nitrogen groups.

In a further embodiment, the process in step (a) further comprises the step of withdrawing a purge stream of said absorber liquid with the associated benefit of avoiding a build-up of sulfur-containing ions such as S2032~, SCN” and S042~ in the absorber liquid.

Other favourable embodiments of the process include the following: - At least a part of said purge stream is directed to the incinerator for conversion of sulfur containing anions to S02 and S03, with the associated benefit of the purge stream being converted to commercial sulfuric acid product instead of having to send the purge stream to a waste water treatment plant. - Step (b) is carried out at a temperature below 150°C, with the associated benefit of a low heating requirement, thus providing an energy efficient process. - The absorber liquid concentrated in elemental sulfur is atomized into the incinerator through pneumatic (steam), hydraulic or centrifugal nozzles. - One or both of said first and said second gas comprising oxygen is/are atmospheric air being pre-heated by heat exchange with a hot process stream, such as the oxidized process gas, with the associated benefit of contributing to an efficient thermal management of the process. - The process further comprises the step of cooling said incinerated gas to a temperature in the range of 300 to 450°C, preferably 380 to 420°C, with the associated benefit of the catalyst for selective NOx removal and the catalyst for S02 oxidation both being highly active at this temperature, while avoiding shifting the S02 + 0.5 02 <-> S03 equilibrium towards S02. - The process plant comprises addition of a selective NOx reductant, such as NH3, upstream a reactor configured for the process gas to contact a material, that is catalytical- ly active in the selective reduction of N0X, with the associated benefit of the conversion of N0X to N2 being more efficient and less demanding in terms of process conditions . - The material, that is active in oxidation of S02 to SO3 in step (g), comprises vanadium with the associated benefit of being a highly effective and robust S02 oxidation catalyst . - The H2O/SO2 ratio in the oxidized process gas is above 1.1, and the oxidized process gas is directed to a condenser for cooling and withdrawal of condensed concentrated sulfuric acid. The process optionally also includes the step of addition of water in any position upstream said condenser, with the associated benefit of providing the required amount of water for hydratization of S03 to H2S04 and complete condensation of the sulfuric acid.

The process gas comprises less than 60 ppm water, and the oxidized process gas is directed to an absorber for absorption of S03 in concentrated sulfuric acid and for withdrawal of concentrated sulfuric acid. The process also includes the step of removal of water in any position upstream the material, that is catalytically active in the oxidation of S02 to SO3, with the associated benefit of providing the correct conditions for acid mist free S03 absorption into concentrated sulfuric acid in the absorber and significantly reducing the sulfuric acid dew point temperature in the process gas. - The means for withdrawal of sulfuric acid is an absorber configured for receiving said oxidized process gas and a concentrated sulfuric acid and for absorbing S03 in said sulfuric acid providing a concentrated sulfuric acid and a desulfurized process gas, with the associated benefit of such a process plant being efficient in providing a highly concentrated sulfuric acid.

Further, the invention relates to a process plant for carrying out the process for the production of sulfuric acid from a gas comprising H2S, said plant comprising an alkaline absorber configured for contacting a gas comprising H2S with a liquid ammonia absorbent solution and a dissolved material, that is catalytically active in the oxidation of H2S to elemental sulfur, providing a liquid slurry comprising elemental sulfur and absorber liquid, means for separation configured for receiving said liquid slurry and configured for producing an absorber liquid free of elemental sulfur to be returned to the absorber and a stream of elemental sulfur and purged absorber liquid to be introduced into an incinerator, one or more air-free nozzles configured for receiving and atomizing said elemental sulfur and purged absorber liquid into the incinerator, an incinerator receiving the atomized elemental sulfur and purged absorber liquid together with a support fuel and a first gas comprising oxygen, thereby providing a process gas, a means for cooling, such as a waste heat boiler for reducing the process gas temperature, a particulate removal device for receiving said process gas and separating solid particles from the process gas, a sulfur dioxide converter configured for receiving said process gas and comprising a material active in oxidation of SO2 to SO3, configured for receiving said process gas and providing an oxidized process gas, and a means for the provision of concentrated sulfuric acid, configured for receiving said oxidized process gas and for providing concentrated sulfuric acid and a desulfurized process gas.

Preferably the compressed air-free nozzle for atomizing the elemental sulfur and the purged absorber liquid is of the hydraulic type or of the centrifugal type.

Coke oven gas (COG) from the gasification of coal goes through several cleaning steps before it can finally leave the gasification plant and be used for e.g. chemical synthesis, combustion and heating purposes.

In the desulfurization unit, H2S and HCN are efficiently absorbed into an alkaline absorbent liquid, in which a fraction of H2S is oxidized to elemental sulfur by means of a liquid catalyst. The catalyst is regenerated by air addition, which optionally may be carried out in a separate process step. As side reactions some of the H2S will be further oxidized to a wide range of sulfur oxides, including S2C>32~ and S042~, and HCN is converted into SOFT. With NH3 as the alkaline component, a wide range of water soluble salts, including (NH4)2S203, (NH4)2S04 and NH4SCN, may be formed in the liquid phase accounting for up to half of the sulfur in the H2S removed. The sulfur and dissolved NH4+ salts are fed to a unit, in which the elemental sulfur is separated from the NH4+ salts. Most of the salt solution is returned to the desulfurization unit, but a purge stream is withdrawn to control the concentration of dissolved salts.

This COG desulfurization process is cheap and effective, but the products are of poor quality and could be expensive to get rid of in an environmentally benign way. The process variants are numerous and known by trade names such as HPF, PDS, ZL, Perox, LoCat, Takahax, Thylox, Fumaks-Rhodacs and Stretford. The differences are primarily within the catalyst system and the alkaline compound.

In the prior art, a wide range of organic catalysts for the oxidation of H2S to elemental sulfur are known, typically having a quinone structure, such as a benzoquinone, naphthoquinone or anthraquinone, optionally with one or more non-metallic substituents, or the structurally similar picric acid or thioarsenate. Typically, these quinone-type catalysts are supplied to the process in the form of sodium salts or together with ions of metals such as iron, vanadium or cobalt.

The present invention involves a method to convert the poor quality sulfur and purged absorber liquid into a concentrated sulfuric acid of commercial quality by incineration followed by treatment in a sulfuric acid plant. All of the H2S captured in the desulfurization unit can be converted to sulfuric acid, not only the elemental sulfur formed in the coke oven gas desulfurization plant.

In the coke oven gas desulfurization plant, some of the captured HCN and H2S will be converted into water soluble salts, of which S2032~, SCN“ and SC>42~ are the most abundant, but other sulfur-containing ions will also be present in low concentrations. The formed elemental sulfur is easily separated from the aqueous solution. The concentration of salts will increase over time if a purge stream is not withdrawn from the coke oven gas desulfurization plant. A too high salt concentration will result in decreased desulfurization efficiency and risk of salt precipitation in the plant, with the associated risk of plugging pipes and other equipment.

If the purge stream is too large, the catalyst and fresh water consumption will become too high. The optimal salt concentration in the absorber liquid is around 300 g salts/1.

By mechanical means such as settling, centrifugation and filtration, the elemental sulfur can be separated from the liquid phase. This separation is not very efficient, and some liquid will be present together with the elemental sulfur. This is of less concern as a purge stream of coke oven gas absorber liquid is required to maintain a stable salt concentration in the absorber liquid. Optionally a fraction of the sulfur-free absorber liquid is mixed with the absorber liquid with a high concentration of elemental sulfur, such that the salt concentration in the absorber liquid returned to the absorber is kept constant and below the maximum allowable concentration.

As in the prior art, described in CN 101092577, the mixture of purged absorber liquid and elemental sulfur is fed to an incinerator via a single feed line and the feed is atomized into the incinerator by means of a nozzle, using compressed air to break up the feed into fine droplets.

According to the present invention, the stream of purged absorber liquid and elemental sulfur is fed to the incinerator via a feed line and the feed is atomized into the incinerator by one or more nozzles using hydraulic or centrifugal means, thereby providing a cost effective method to inject the feed into the incinerator.

Hydraulic nozzles atomize the fluid using the fluid pressure drop to accelerate the fluid and break up the high velocity fluid on the surfaces and/or edges in the nozzle. These hydraulic nozzles are also called pressure nozzles and are generally small in size, inexpensive and consume only little power. Other names for this family of pressure nozzles are hollow cone, solid cone, fan, vibrating and impact nozzles.

Centrifugal nozzles are also called rotating nozzles or spinning atomizers and comprise a cup or disc that is put into high speed rotation. In the rotating disc, the fluid is introduced through a center hole in the disc and is accelerated as it is forced to the outer periphery of the disc. At the disc edge the fluid is broken up into small droplets and mixed with gas/air flowing around the disc.

The fluid and air pressure does not need to be high. This type of nozzle is very well suited for slurries and fluids containing solid particles.

This family of nozzles consumes little power.

The nozzle described in the prior art is a gas atomization nozzle, also called a pneumatic nozzle or a two-fluid nozzle. Compressed air or steam is accelerated by reducing the pressure of the air or steam and the high velocity of the air or steam is used to break up the fluid. The compressed air driven nozzle consumes relatively much power as compression of air is a power intensive process. Air consumption is in the range 300-800 1 air/kg water atomized, and the pressure of the air is typically 1-5 bar gauge.

Support fuel which may be coke oven gas and oxygen is fed to the incinerator, whereby the elemental sulfur is oxidized to S02 and the sulfur containing NH4+ salts are decomposed into S02, CO2, N2 and ΝΟχ. The oxygen required for the combustion may be in the form atmospheric air, pure oxygen or any other gas rich in oxygen. This combustion air may beneficially be preheated, e.g. by using heated cooling air from the sulfuric acid condenser and optionally further preheated air in a designated heat exchanger, as this higher air temperature will reduce the amount of support fuel required.

After the incineration step the process gas may be cooled to 380-420°C in a waste heat boiler, producing saturated steam. Alternatively the process cooling can be carried out in a combination of waste heat boiler, producing saturated steam, and a combustion air heater, preheating combustion air to the incinerator.

The process gas then passes through a filtration device, which removes practically all dust from the process gas. If not removed, the dust will eventually plug the catalyst beds in the downstream SO2 reactor. The filtration device could e.g. be an electrostatic precipitator or a system of candle filters.

The ΝΟχ formed by incineration can be reduced in a process for selective reduction of N0X by NH3, by contacting the process gas with a catalyst comprising a carrier, such as titanium oxide, and active catalytic components which usually are either oxides of base metals (such as vanadium, molybdenum and tungsten), zeolites, or various precious metals (selective catalytic reduction (SCR)). The NH3 needed for the reaction may be obtained from a washing process step where NH3 is removed from the coke oven gas. Anhydrous ammonia, ammonia water (NH4OH) and urea ((NH2)2C0) are also frequently used as the source of NH3 for the SCR reaction.

Downstream the optional SCR reactor, the process gas enters the SO2 reactor where SO2 is oxidized by an appropriate catalyst, such as a vanadium-based S02 conversion catalyst supported on silica.

The S02 oxidation may take place in one, two or three catalytic beds with inter-bed cooling; the exact layout depends on the S02 concentration in the process gas and the degree of S02 conversion required. After the last bed of S02 con version catalyst, the gas is cooled in the process gas cooler, producing saturated steam.

One or more dust guard catalyst beds can be installed above the first catalyst bed in the S02 reactor, as it is described in EP 1 114 669. Such guard beds will prolong the up-time of the sulfuric acid plant in the case that small amounts of inorganic ash are present in the process gas.

The inter-bed coolers superheat the steam produced in the waste heat boiler and the process gas cooler, and the valuable superheated steam can be exported to other processes.

The process gas finally enters a sulfuric acid condenser, where the sulfuric acid is condensed by cooling with air and separated from the cleaned process gas. The hot cooling air from the sulfuric acid condenser may be used as an oxygen source in the incinerator as it is, or it may be further preheated in a heat exchanger, thus increasing the heat recovery and minimizing support fuel consumption.

The invention is illustrated further with reference to the Figures, where

Fig. 1 is a flow sheet of a process plant according to the prior art,

Fig. 2 is a flow sheet of a process plant according to a preferred embodiment of the present invention, and

Fig. 3 shows the details of the introduction of the elemental sulfur and the absorber liquid bleed into the incinerator .

In a process according to the prior art, as illustrated in Fig. 1, a coke oven gas 1 is directed to an alkaline absorber 2 fed with an alkaline solution with dissolved catalyst 4. On the gas side a desulfurized coke oven gas 3 is released from the absorber, and on the liquid side a coke oven gas absorber liquid 5 comprising elemental sulfur and dissolved ions comprising sulfur is withdrawn. In a reactor 7, the coke oven gas absorber liquid continues the sulfur forming reaction, and the catalyst is reoxidized by means of air addition 14. The formed slurry is skimmed from the coke oven gas absorber liquid in a mechanical separator 11 into sulfur sludge 15 and coke oven gas absorber liquid 12. The coke oven gas absorber liquid 12 is directed back to the alkaline absorber, possibly after being replenished with catalyst and alkaline solution 13. If the implicit purge of coke oven gas absorber liquid through line 15 is insufficient, an extra purge line 29 is required to maintain an acceptable low concentration of dissolved sulfur containing ions (e.g. S2032~, SC>42~, SCN“) in the coke oven gas absorber liquid.

The sulfur sludge, including the elemental sulfur and part of the coke oven gas absorber liquid 15 and extra purged absorber liquid, is injected into an incinerator 30 by means of air atomizing nozzles, using compressed air 28 to break up the feed into fine droplets.

Support fuel 31, such as coke oven gas, and (hot) combustion air 61 are also injected into the incinerator to provide energy and oxygen to ensure the complete oxidation of the feed.

The incinerated sulfur sludge and coke oven gas absorber liquid forms a process gas 31, which is cooled in a waste heat boiler 32 and directed to a hot filtration device 36, that efficiently removes the dust formed from the inorganic compounds present in the feed to the incinerator, e.g. inorganic catalyst compounds, dissolved ions from the process water, corrosion products and compounds absorbed from the coke oven gas .

The dust free process gas 38 enters the SCg oxidation reactor 44, in this case comprising three catalytic beds (45a, 45b and 45c) , two inter-bed coolers (46a and 46b) and an outlet heat exchanger 47. The SO3 in the oxidized process gas 50 reacts immediately with water present in the oxidized process gas (or optionally added to the oxidized process gas) to form H2S04, which is condensed as concentrated sulfuric acid 52 in a condenser 51, cooled with air 58. A fraction of the heated air 59 from the condenser 51 may be used as combustion air 61 in the incinerator 30. The remaining hot air 62 can be combined with the clean gas 53 released from the condenser, which will have a very low sulfur concentration, and may be released to the atmosphere via a stack 56.

Fig. 2 is a flow sheet of a process plant according to a preferred embodiment of the present invention. A coke oven gas 1 is directed to an alkaline absorber 2 fed with an al kaline solution comprising a catalyst 4. On the gas side, a desulfurized coke oven gas 3 is released from the absorber, and on the liquid side, coke oven gas absorber liquid 5, which comprises elemental sulfur and dissolved ions containing sulfur, is withdrawn. In a reactor 7 the coke oven gas absorber liquid reacts to form elemental sulfur and sulfur containing ions in the form of a slurry. The elemental sulfur is skimmed from the coke oven gas absorber liquid in a mechanical separator 11, producing an absorber liquid enriched in elemental sulfur 15 and an absorber liquid almost free of elemental sulfur 12. To ensure a constant salt concentration in the absorber liquid 12 to be returned to the absorber 2, a purge stream 29 of the absorber liquid can be withdrawn and combined with the absorber liquid enriched in elemental sulfur 15, producing the feed stream 17 to the incinerator 30 of the sulfuric acid plant.

To compensate for the loss of water and catalyst withdrawn with the purged absorber liquid, fresh water and catalyst 13 can be added before the absorber liquid is returned to the coke oven gas absorber 2 via lines 6 and 4.

The feed containing elemental sulfur and the purged absorber liquid 17 is injected into the incinerator 30 by hydraulic nozzle (s) or centrifugal nozzle(s), producing fine droplets of the feed without consumption of compressed air.

Support fuel 31 and preheated combustion air 61 are also fed into the incinerator 30 to provide energy and oxygen to ensure complete decomposition and oxidation of the feed.

The process gas leaving the incinerator 31 is cooled in a waste heat boiler 32 and (optionally) further cooled in a combustion air heat exchanger 34. Thereafter the process gas 35 passes through a filtration device 36 in which the inorganic and possibly organic dust, formed during the incineration process, is separated from the process gas and withdrawn. The cleaned process gas 38 is optionally mixed with a stream 39 containing ammonia and directed to a reactor 42 for selective catalytic reduction, in which N0X formed during incineration is selectively reduced to N2 in the presence of a material, that is catalytically active in selective reduction of N0X, providing a process gas having a reduced concentration of N0X. Downstream the selective catalytic reactor the process gas 43 having a reduced concentration of N0X is directed to a S02 oxidation reactor 44, in this case comprising three catalytic beds (45a, 45b and 45c), two inter-bed heat exchangers (46a and 46b) and an outlet heat exchanger 47. The S03 in the oxidized gas 50 reacts immediately with water to form H2SC>4 which is condensed as concentrated sulfuric acid 52 in a condenser 51, cooled with air 58. A fraction of the heated air 59 from the condenser 51 is directed to the combustion air heat exchanger 34, and the hot air 61 is then directed to the incinerator 30. This will reduce the support fuel consumption. As an option the hot air from the sulfuric acid condenser 59 can be injected directly in the incinerator 30.

The clean gas 53 released from the condenser will have a very low sulfur dioxide concentration, and may be released to the atmosphere via a stack 56, possibly after dilution with heated air 62, not reguired in the incinerator.

In one embodiment of the present disclosure the process does not employ cooling and condensation, but instead an absorber in which S03 is absorbed in sulfuric acid. Typically this is related to configurations in which the process gas is dried, often downstream the SCR reactor, since water is produced during incineration and selective reduction of N0X.

The invention is illustrated in more detail in the examples which follow.

Example 1

An example of a typical coke oven gas composition entering the coke oven gas desulfurization plant as well as the removal efficiencies of the coke oven gas desulfurization plant is shown in Table 1 below.

Table 1

Example 2

In an example according to the present invention a process, as shown in Fig. 2, involving an aqueous ammonia absorbent solution and a guinone type H2S oxidation catalyst is used. The typical coke oven gas parameters given in Table 1 are used to evaluate the power consumption for the different nozzle types used for atomizing the feed into the incinerator .

The overall process includes coke oven gas desulfurization, pre-treatment of the effluent from the desulfurization plant, incineration of the elemental sulfur sludge and coke oven gas absorber liquid, and sulfuric acid production in a wet type sulfuric acid plant.

In this example it is assumed that 50% of the H2S is converted into elemental sulfur, while the remaining 50% of the H2S is converted into salt forming ions, primarily S2O32 , SCN and SC>42~. All captured HCN is converted into SCN".

This produces a liquid feed to the sulfuric acid plant of 3900 kg/h, of which 2650 kg/h is water, 375 kg/h is elemental sulfur and 875 kg/h is dissolved salt with NH4+ as the cation. The anions are a mixture of S2C>32~, SCN” and S042^.

The feed has to be atomized into fine droplets when it is injected into the incinerator, such that a large surface area is generated for fast evaporation of the volatile species, oxidation of the sulfur and decomposition and oxida tion of the salts. Nozzles of the pneumatic, hydraulic and centrifugal type can be used for this atomization.

The power consumption required to atomize the feed is calculated for the three different nozzles, namely a compressed air atomizing nozzle (hydraulic) as used in the prior art, a pressure nozzle (hydraulic) and a rotating nozzle (centrifugal).

The formulas for power consumption have been taken from Perry's Chemical Engineers Handbook (4th edition) and from "Unit Operations of Chemical Engineering" (5th edition) by McCabe, Smith and Harriott.

For the compressed air atomizing nozzle, an air flow of 0.2 kg compressed air/kg slurry (corresponding to around 150 1/kg) is assumed sufficient for the atomization of the feed. A pressure drop of 4 bars for the compressed air is required to atomize the feed.

The rotating nozzle is a rotating disc having an outer diameter of 4 inches and an inner feed hole diameter of 0.5 inches; the disc rotates with 5,000 rounds per minute. Insignificant feed pressure is required to inject the feed into the center hole of the rotating disc.

For the pressure nozzle, a pressure drop of the liquid feed of 4 bar is used to atomize the feed.

Table 2 below illustrates the power requirements for atomization of a sulfur slurry from a 100000 Nm3/h coke oven gas desulfurization plant. The feed flow of sulfur and absorber liquid is 3900 kg/h.

Table 2

As seen in Table 2, the power consumption for operating the compressed air atomizing nozzles is considerably higher than those for operating the pressure nozzles and rotating nozzles, which have approximately the same operating cost. The reason for the high power consumption of the air atomizing nozzle is the power-intensive step of compressing atmospheric air to the high pressure which is required for the atomization.

Assuming an electricity cost of 0.1 USD/kWh, the cost savings by using the pressure nozzle and rotating nozzle is around 30,000 USD per year.

Claims (10)

Claims :

1. A process for the production of sulfuric acid from a gas comprising H2S, said process comprising the following steps : (a) directing said gas to an alkaline absorber containing a liquid ammonia absorbent solution and a dissolved material, that is catalytically active in the oxidation of H2S to elemental sulfur, providing a liquid slurry comprising elemental sulfur and absorber liquid, (b) separating said elemental sulfur from the absorber liquid by mechanical means, providing a stream of absorber liquid, which is practically free of elemental sulfur to be returned to the absorber, and a stream of elemental sulfur and purged absorber liquid, (c) injecting said elemental sulfur and purged absorber liquid streams into an incinerator by means of an air-free nozzle, (d) feeding a support fuel and a first oxidant gas into an incinerator or into a point upstream from said incinerator, (e) incinerating the mixture, thereby obtaining an incinerated gas comprising S02, (f) removing inorganic dust in a filter unit, (g) contacting the process gas with a material, that is catalytically active in the oxidation of SO2 to SO3, thereby providing an oxidized process gas, and (h) withdrawing concentrated sulfuric acid, either by cooling and condensation or by absorption of SO3 in H2SO4, providing oleum or concentrated sulfuric acid and a process gas reduced in sulfur.

2. Process according to claim 1, wherein step (b) is carried out at a temperature below 150°C.

3. Process according to claim 1, wherein the elemental sulfur and the purged absorber liquid are injected into the incinerator via a single feed line.

4. Process according to claim 1 or 2, wherein the elemental sulfur and the purged absorber liquid are injected into the incinerator by means of a hydraulic nozzle.

5. Process according to claim 4, wherein the pressure of the elemental sulfur and the purged absorber liquid is in the range of 0.5 to 10 bar gauge.

6. Process according to claim 1 or 2, wherein the elemental sulfur and the purged absorber liquid are injected into the incinerator by means of a centrifugal nozzle.

7. Process according to claim 6, wherein the centrifugal nozzle is a disc, and the speed of rotation is in the range of 500 to 50000 r.p.m.

8. A process plant comprising an alkaline absorber configured for contacting a gas comprising H2S with a liquid ammonia absorbent solution and a dissolved material, that is catalytically active in the oxidation of H2S to elemental sulfur, providing a liquid slurry comprising elemental sulfur and absorber liquid, means for separation configured for receiving said liquid slurry and configured for producing an absorber liquid free of elemental sulfur to be returned to the absorber and a stream of elemental sulfur and purged absorber liquid to be introduced into an incinerator, one or more air-free nozzles configured for receiving and atomizing said elemental sulfur and purged absorber liquid into the incinerator, an incinerator receiving the atomized elemental sulfur and purged absorber liquid together with a support fuel and a first gas comprising oxygen, thereby providing a process gas, a means for cooling, such as a waste heat boiler for reducing the process gas temperature, a particulate removal device for receiving said process gas and separating solid particles from the process gas, a sulfur dioxide converter configured for receiving said process gas and comprising a material active in oxidation of SO2 to SO3, configured for receiving said process gas and providing an oxidized process gas, and a means for the provision of concentrated sulfuric acid, configured for receiving said oxidized process gas and for providing concentrated sulfuric acid and a desulfurized process gas.

9.

Process plant according to claim 8, wherein the compressed air-free nozzle for atomizing the elemental sulfur and the purged absorber liguid is of the hydraulic type. 10. process plant according to claim 8, wherein the compressed air-free nozzle for atomizing the elemental sulfur and the purged absorber liquid is of the centrifugal type.