JPH0134922B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the recovery of sulfur, and more particularly to the recovery of sulfur as vapors of elemental sulfur, droplets of liquid elemental sulfur and sulfur as hydrogen sulfide and sulfur dioxide, all present in dilute concentrations in the entrained gas. It relates to the removal of sulfur present in various forms including mixtures of compounds. In particular, the present invention is aimed at removing a significant proportion of sulfur combined with elemental sulfur from the effluent gas of a Claus process plant which is operated primarily to convert hydrogen sulfide to elemental sulfur for recovery.

Claus process plants are used to convert toxic hydrogen sulfide released from petroleum refining operations or removed by scrubbing natural gas (collected from some gas wells, which contains 25% to 40% hydrogen sulfide). used in industries such as refineries and natural gas processing plants. The Claus process involves reacting hydrogen sulfide with air to produce elemental sulfur and water as the main products. The elemental sulfur thus formed condenses from the vapor state and passes from some uncondensed sulfur vapor, unreacted hydrogen sulfide and sulfur dioxide and the charge to the Claus plant operation (or produced in the Claus process plant). It is recovered well from the uncondensed gases, which are mainly water vapor and nitrogen, along with some carbon disulfide and carbonyl sulfide.

The uncondensed effluent gas from a Claus process plant is typically incinerated, resulting in the residual sulfur being exhausted from the incinerator stack as dilute sulfur dioxide. The total emission of sulfur dioxide is measured in the chimney and it is this emission that is subject to limits set by the Environment Agency. Despite the considerable progress made today in reducing the proportion of sulfur in its various forms that passes into the effluent gas and is finally emitted as sulfur dioxide, the final chemical and physical equilibrium puts an upper limit on plant efficiency and must be further recovered by another plant process where operating conditions permit additional sulfur recovery. Several such processes are known in the art;
Some are operated commercially.

Although water washing of effluent gas streams is widely practiced, attempts to apply this method to Claus process effluent gases encounter significant difficulties, namely the tendency to form colloidal sulfur in the aqueous medium. Colloidal sulfur is formed when sulfur vapor comes into contact with water. Colloidal sulfur is also produced by a series of chemical reactions that occur when hydrogen sulfide and sulfur dioxide react in the presence of water. In this series of reactions, thiosulfuric acid and polythionic acid are formed, some of which exhibit intermediate stability and gradually decompose with the formation of colloidal elemental sulfur. In this form, sulfur is not easily separated from water. In addition, colloidal sulfur can cause serious problems in plant equipment by plating out (the formation of a thin layer of sulfur on the internal surfaces of the processing equipment), causing all plant equipment to shut down.

The problem of controlling the deposition of elemental sulfur from pre-existing vapors of elemental sulfur or from the aqueous reaction of hydrogen sulfide and sulfur dioxide can be solved by aqueous washing of certain catalytic solids in the form of finely divided powders. It has now been discovered that this can be solved by adding it to the medium. These catalytic solids are solids known in the art for their ability to catalyze the gas phase reaction of hydrogen sulfide and sulfur dioxide in systems operating above the dew point of water, namely alumina and activated carbon. . however,
The presence of these catalytic solids, for practical purposes, substantially completely inhibits the series of aqueous reactions cited above and leading to the formation of colloidal sulfur in the bulk aqueous phase, or It could not be predicted that such catalytic solids would not necessarily prevent the formation of colloidal sulfur when elemental sulfur vapor contacts an aqueous system. It has now been discovered that such an inhibitory effect occurs in the presence of the catalytic solid particles described above.
Based on this knowledge, it became possible to discover a method for cleaning the Claus process effluent gas stream using an aqueous slurry of activated carbon or alumina.

destroys the finely divided catalyst solids which are effective for the present invention but result in reduced effectiveness by depositing sulfur while carrying out the process; It has also been discovered that a significant portion of it can be regenerated and returned to its original activity without being consumed.

Accordingly, the present invention involves bringing a gas stream into intimate contact with an acidic aqueous suspension of finely divided catalytic materials of the group of alumina and activated carbon, and the acidity of the suspension is such that the acidity of the gas stream increases. said gas for removing sulfur vapor and a mixture of hydrogen sulfide and sulfur dioxide, entrained by droplets of liquid sulfur present in dilute concentrations in said gas stream, resulting from the absorption of components; There is a way to handle the flow.

The present invention also provides for (1) separating the finely divided catalytic material from an aqueous medium in which the material is contacted with a gas stream; and (2) separating the absorbed sulfur from the catalytic material so that the catalytic material is a liquid for sulfur at a temperature sufficient to dissolve the sulfur when the fluid is a liquid solvent and to melt and volatilize the sulfur when the fluid is a gas until the activity is sufficiently restored. finely divided with an accumulation of sulfur deposited by a method for treating a gas stream as described above, consisting of passing the material through a fluid of the group consisting of a solvent and a gas that does not react with the catalyst material; The present invention provides a method for regenerating a solid material having a catalytic action. The invention further provides for regenerating the finely divided catalytic solid material by the method described above and using the regenerated catalyst in the form of an aqueous dispersion as a catalyst in the method for treating a gas stream as described above. It's about bringing it back.

Intimate contact between the gas stream and the aqueous slurry according to the method of the present invention is accomplished using any suitable type of gas-liquid contacting device. Such equipment includes, for example, washing columns such as packed and perforated or bubble columns, cyclone scrubbers, jet scrubbers, spray scrubbers, cascade scrubbers and ventilure scrubbers. A ventilate scrubber is preferred as the most practical device for contacting the gas with the slurry.

The aqueous suspension or slurry of alumina or activated carbon used may be, for example, the commercially available finely divided grade of alumina used in Claus process converters or the various types of powdered or relatively fine alumina on the market. It can be easily prepared using granular activated carbon. The proportion of suspended solid material in the aqueous suspension in the process of the invention generally ranges from substantially 1% to substantially 10% by weight, with lower proportions containing sulfur in various forms. The ability to remove the slurry from the slurry is low and it is uneconomical, and if the ratio exceeds the above, there is a risk of problems in handling the slurry. The preferred range of solids in the aqueous suspension is 3% to 7%.

In the process of the invention, during the contacting step the finely divided catalytic material not only acts as a deposition site for the sulfur extracted from the gas stream, but also catalyzes the reaction between hydrogen sulfide and sulfur dioxide; There is a limit to the amount of sulfur that can be removed from the gas stream by a given amount of catalyst material before the accumulated sulfur must be removed from the catalyst material. Generally, the practical limit for sulfur deposition on catalyst material is a weight equal to the dry weight of the catalyst material itself, which can then be regenerated by removing and separating the sulfur from it for reuse. is convenient. The catalytic material can then be redispersed in water and the suspension used to contact a gas stream for sulfur removal according to the invention.

Since the gas stream from which sulfur needs to be removed is generally at a temperature above the boiling point of water at atmospheric pressure and is not saturated with water, a significant amount of heat is transferred to the aqueous suspension and a significant amount of heat is then transferred to the aqueous suspension. water evaporates. The operating temperature of a particular slurry can be established at such a temperature that evaporation of water from the slurry is virtually zero. This temperature can be maintained, for example, by providing a heat exchanger in the slurry circulation circuit.
Alternatively, heat can be removed by evaporating water from the slurry and using makeup water to maintain the volume of the slurry. The features of this alternative method can also be used in combination. The cooling equipment preferably keeps the temperature of the contacting suspension between 60°C and 80°C.
℃, most preferably maintained at a temperature range of 65°C to 75°C.

The efficiency of removing all forms of sulfur from a gas stream by the method of the present invention depends on several factors.
These factors include, among other things, the efficiency of the gas-liquid contacting device used to achieve the desired intimate contact;
The specific type and proportion of the catalyst material in the suspension and the loading rate of sulfur loaded onto the catalyst material from the previously contacted gas are included. Under efficient operating conditions, 50% or more of sulfur in all forms is removed from the Claus Process plant effluent gas stream, so that no sulfur that must be incinerated and vented to the atmosphere or further passed through sulfur recovery equipment is removed from the Claus process plant effluent gas stream. It can be expected that the amount of sulfur required will be reduced by more than half.

Because there is a limit to the amount of sulfur that a given amount of catalytic material can remove from the gas before it becomes useless, the catalytic material must be regenerated to restore its capacity if the process is to operate economically. It is. heating the catalytic material above the melting point of the sulfur with a stream of, for example, air, superheated steam, other inert gases or mixtures thereof, in order to expel the sulfur in a gas stream capable of condensing the sulfur; Thus, once the catalyst is separated from the aqueous phase, its regeneration is easily accomplished. Superheated steam or a mixture of hot combustion gas and superheated steam avoids its consumption by partial combustion of the carbon, and therefore such gases are preferably used in the regeneration of activated carbon. Sulfur is removed from the catalytic material by dissolving the sulfur from the catalytic material with a suitable liquid solvent of sulfur, e.g. carbon disulfide or xylene, in a suitable extraction process and then separating the solid catalytic material from the liquid solvent, e.g. by filtration. However, the catalyst material can also be regenerated thereby. The overall method for recovering regenerated catalyst from an aqueous suspension of sulfur-deposited solid catalyst material is such that the solid catalyst material is easily separated from the aqueous suspension by filtration;
and in situ on the material (if desired), for example by passing one or more hot inert gases through the material to drive off the sulfur, or by passing a liquid solvent for the sulfur through the material to dissolve the sulfur. The catalytic material can then be recovered from the material by such operations, reslurried in water and recycled for intimate contact again with the gas stream containing sulfur and sulfur compounds. This is facilitated by the fact that

The following examples are presented to illustrate the operability and utility of various aspects of the invention and are not intended to limit the invention as defined in the claims below. isn't it. These embodiments separately and individually remove a mixture of hydrogen sulfide and sulfur dioxide from a gas stream without developing colloidal sulfur in the aqueous phase, and also remove sulfur vapor from the gas stream. The operability and effectiveness of aqueous suspensions of solid catalysts have been demonstrated.
The examples further demonstrate the recyclability of the solid catalyst material after it has been loaded with sulfur removed from a sulfur-containing gas stream in a form that deposits free sulfur on the solids. All percentages expressed herein are weight percentages unless otherwise indicated.

The following example illustrates the effectiveness of an aqueous suspension of activated carbon in removing sulfur vapor from a gas stream.

Example 1 In order to prepare a suspension of activated carbon, "Aqua Nutia" was prepared in a vigorously stirred container at room temperature.
1.0 g of activated carbon was dispersed in 100 ml of water. Introducing a stream of preheated nitrogen gas flowing at a rate of 1.2/min over a molten sulfur body held at 182°C (360〓), and bringing the resulting dilute sulfur vapor stream to a temperature of 160°C. A heated tube was introduced into the vigorously stirred suspension. The gas from the suspension was passed through a glass wool stopper at room temperature in a 2.5 cm diameter glass tube to retain any sulfur that was not absorbed through the aqueous suspension. After 2 hours of operation, the suspension was passed through paper to yield a clear liquid, indicating the absence of colloidal sulfur formed from contact of sulfur vapor with water. Activated carbon and sulfur filter cake 110
℃ for 2 hours and then extracted with carbon disulfide solvent in a Soxhlet apparatus for 2 hours. It was found that 0.244 g of solid sulfur was obtained from the extract and that 0.166 g of solid sulfur was then obtained by extracting the plug of glass wool with carbon disulfide in a Soxhlet apparatus. Therefore, the efficiency of removing sulfur from a gas stream by an aqueous suspension of activated carbon is
It was 59.5%.

The following example illustrates the effectiveness of bauxite (alumina) in an aqueous suspension for removing a dilute mixture of hydrogen sulfide and sulfur dioxide from a gas stream.

Example 2 5 with inlet line for gas flow, outlet line and downcomer for removing aqueous slurry
in a laboratory-scale flask with a top opening for connection to the bottom of a contactor consisting of a 2-inch (5 cm) internal diameter commercial laboratory-scale vacuum jacketed distillation column with perforated plates; Fine bauxite, prepared by grinding 2.5 g of a commercial pellet catalyst of the Claus process, was dispersed in 250 ml of water. The slurry is continuously withdrawn from the flask and pumped to the top of the distillation column, from where it is allowed to fall by gravity into the column and returned to the flask, while the gases pumped into the flask through the gas inlet are A positive displacement pump of the "Moyno" type is connected to the flask to raise the flow in the column and into contact with the slurry over the perforated plate and thence to the vent tube. Adjusting the test gas flow by continuously metering nitrogen gas, hydrogen sulfide gas and sulfur dioxide gas into the inlet line at rates of 3/min, 60 ml/min and 30 ml/min respectively. , this ratio resulted in a mixture essentially containing 2% by volume hydrogen sulfide, 1% by volume sulfur dioxide and 97% by volume nitrogen. A stream of test gas is passed through the flask and up the distillation column to form a continuously circulating slurry.
The contact period was 50 minutes, during which time heat was applied to the flask to maintain the temperature of the circulating slurry at 77°C. At the end of that period, the slurry was strained and found to be clear and free of colloidal sulfur. When the recovered bauxite is dried and then extracted with carbon disulfide, it contains 17.5% free sulfur (based on the weight of the original dry sulfur-free bauxite) removed from the free sulfur-free test gas. It has been found. The efficiency of removing sulfur from the test gas was calculated to be 6.6%, and this relatively low efficiency is due at least in part to the ineffectiveness of alumina as a catalyst in the present invention, and is also likely due to the simple 5-plate inclusion. This may also be due to the lack of sufficient intimate contact between the test gas and the circulating slurry in the contact tower.

The following example illustrates the effectiveness of activated carbon in an aqueous suspension for removing a dilute mixture of hydrogen sulfide and sulfur dioxide from a gas stream, and is also sufficiently loaded to be extensively loaded with absorbed free sulfur. The regeneration of activated carbon to reuse it in the above operations after a long period of use is described. By using suitable convenient equipment, this example also illustrates the possibility of carrying out continuous absorption and regeneration of activated carbon.

Example 3 The relatively simple apparatus for this example consisted essentially of a glass tube (4.4 cm outside diameter) with a sintered glass plate at the bottom approximately 25 cm from the top. The joining of the top and bottom of the tube is accomplished by introducing an aqueous suspension of activated carbon at the top of the sintered plate, introducing a gas flow below the sintered plate to bubble into the aqueous suspension, and at the top. This coupling also made it possible to introduce water vapor or other regeneration fluids above the sintered plates and to withdraw the fluid medium below the sintered plates for the regeneration stage. . The device was surrounded by heating equipment, which allowed the temperature to be raised to high temperatures during the regeneration of the activated carbon on the sintered plates. To start the operation, a nitrogen gas flow of 1.3/min was created in the tube from the bottom, and a suspension of 5 g of Nuchar SN (trade name) activated carbon in 100 ml of water was sintered. It was added to the top of the plate where the gas bubbled through it. Heat was supplied by heating equipment to maintain the aqueous suspension at a substantially constant temperature of 70°C. Hydrogen sulfide and sulfur dioxide flows were then increased to 40 ml/min and 20 ml/min, respectively.
minutes to the nitrogen flow in the tube and continued operation for a precisely timed period of 2 hours, during which time the concentration of sulfur dioxide in the outlet gas released from above the suspension was determined by Milan ( Continuous monitoring was performed using a Miran® infrared analyzer. This slight increase in the monitored concentration occurring during the 2 hour period indicated that the sulfur dioxide conversion efficiency was substantially uniform and decreased only slightly during the conversion period. During this period, the volume of the suspension was maintained at substantially about 100 ml, and 2.3 ml of water was added to the suspension from time to time to replace the water lost in the gas stream due to evaporation. Sulfur compounds were removed from the charge gas during its passage through the activated carbon suspension by periodic iodometric analysis of samples of both the charge gas and the outlet gas emanating from above the aqueous suspension. The efficiency is 41.5%
It was calculated that At the end of the 2 hour operation, the flow of the charge gas is stopped and the water in the aqueous suspension is forced onto the sintered plate, leaving a filter cake of activated carbon containing absorbed sulfur on the sintered plate. A slight pressure was applied on top of the liquid. A water-cooled condenser was then attached to the bottom of the tube, and the substantially
A stream of superheated steam is introduced over the activated carbon in the tube whose temperature has been raised by the superheated steam to 900°C (482°C), thereby melting, evaporating and entraining the sulfur deposited on the activated carbon. The water vapor and sulfur were transferred to a condenser, and below the condenser the condensed water vapor and sulfur were recovered in the form of a dispersion in which the sulfur was dispersed in the water in the form of a white milk. At the end of 2 hours of steaming, regeneration of the activated carbon by removal of sulfur was deemed appropriate, and 100 ml of water was added to the activated carbon on the sintered plate, giving the same flow rate as before and as a suspension medium for the loose activated carbon powder. was added to reestablish a gas flow of a mixture of nitrogen, hydrogen sulfide, and sulfur dioxide. Continuously monitoring the sulfur dioxide concentration of the outlet gas for the next two hours with an infrared analyzer again shows that the concentration increases only slightly and the conversion efficiency decreases only slightly during this period. It was done. Periodic iodometric analysis of samples of the charge and outlet gases revealed that the efficiency of conversion of sulfur compounds to free sulfur in the suspension during this period was 50
It was determined that %. At the end of this period the water of the aqueous suspension was passed through a sintered plate and the activated carbon filter cake was again treated with a stream of superheated steam for 2 hours as before to remove the sulfur from the activated carbon filter cake. . This was followed by creating a stream of mixed gas again as described above, and with it water was added to the activated carbon on the sintered plate to form a suspension, into which the stream of gas was continued for a further 2 hour reaction period. The mixture was bubbled inside and the exit gas was monitored by a continuous infrared analyzer. During the 2-hour run, this monitoring again showed only a slight decrease in conversion efficiency, and periodic iodometric analysis of the charge gas and outlet gas streams revealed a conversion efficiency of 45.5% during the run. Indicated. These conversion efficiency values are within a reasonable range of the same level;
And it is well established that activated carbon can be regenerated and reused without loss of efficiency. To confirm the correctness of the sulfur removal efficiency in three consecutive 2-h reaction periods, the milky sulfur suspension in water obtained from the condenser was separately collected during the first two regeneration periods. The sulfur in the residue was weighed and the activated carbon containing the absorbed sulfur from the third 2 hour reaction period was extracted with carbon disulfide in a Soxhlet extractor and the carbon disulfide was then evaporated. The weight of the sulfur residue was then measured. The weight of sulfur thus recovered from three successive regeneration stages was in good agreement with the calculated value of sulfur removed from the charge gas based on analysis of the composition of the charge gas and discharge gas.

The following example also illustrates the effectiveness of activated carbon in an aqueous suspension for removing dilutely mixed hydrogen sulfide and sulfur dioxide from a gas stream, and as in Example 3 above. The paper additionally describes the regeneration of activated carbon for reuse in the operations described above after the activated carbon has been used long enough to become extensively loaded with free sulfur absorbed by the activated carbon in hot liquid xylene. Regeneration is carried out by extracting sulfur from.

Example 4 A device for removing thin gases of sulfur compounds from a gas stream is similar to Example 3, consisting of a glass tube with a sintered glass plate at the bottom, for discharging and introducing an aqueous medium and a regeneration medium. It included a top connection and a bottom connection for the introduction of the charge gas and the withdrawal of the liquid extractant. In the same way as in Example 3, add "Nuchar" to 100 ml of water on a sintered plate.
SN” Nitrogen gas 1.3 to a suspension containing 5 g of activated carbon
/min, hydrogen sulfide 40ml/min and sulfur dioxide 20ml/min
A flow of ml/min was introduced to create bubbles, and the suspension was maintained at substantially 70°C by means of heating equipment around the tube, and also to maintain the volume of the suspension at approximately 100 ml. Water was added occasionally. As before, 9.4 g of sulfur in the form of gaseous sulfur compounds were introduced into the activated carbon suspension during each of these two hour reaction periods. The sulfur dioxide concentration of the outlet gas was monitored during the 2 hour reaction period and was found to increase only slightly during each 2 hour run. At the end of each of five such consecutive absorption runs, the flow of the charge gas was stopped and the filtration was started with supplemental application of inert gas upstream of the activated carbon suspension.
At the end of this operation a wet activated carbon filter cake remained on the sinter plate. At this point, the bottom of the reaction tube was connected through a water trap to a tared liquid collection flask, and a stream of xylene vapor from a boiling source of xylene was combined with the top of the tube. As the xylene condenses onto the activated carbon, the xylene vapor forces residual water through the sintered plate and the xylene passes through the carbon filter cake and sintered plate in turn into the collection flask. The hot xylene condensate dissolves the sulfur absorbed by the activated carbon when passed through the filter cake, and the xylene vapor flow is reduced to a temperature within the filter cake of 260〓 (127
C), ie, well above the boiling point of the water-xylene azeotrope, was maintained until all the water was removed from the filter cake and the activated carbon was completely contacted by the xylene. When the xylene flow was stopped, the liquid xylene in the recovery flask was removed from the flask for reuse by distillation, and the sulfur residue extracted from the activated carbon and remaining in the flask during the regeneration period was weighed. The weights of sulfur thus obtained during five consecutive regeneration periods following five absorption runs were 5.2, 3.9, 3.9, 4.2 and 4.4 g, respectively.
The weight of these is 2 prior to each regeneration period.
55.3% of the sulfur (as sulfur compounds) charged into the suspension of activated carbon during absorption operation for hours, respectively
They corresponded to 41.5%, 41.5%, 44.7% and 46.8%.
These sulfur recoveries not only established the effectiveness of hot liquid xylene for removing adsorbed sulfur from activated carbon, but also increased the efficiency even though the initial high value of sulfur removal efficiency was not fully maintained in regeneration. The decline was acceptable but not continuous, and the recovery (and corresponding removal efficiency) apparently leveled out at a satisfactory level of about 50%.

The above examples illustrate various aspects of the invention. Furthermore, it may be pointed out that the invention can be applied to reduce the total amount of sulfur present as dilute concentrations of sulfur dioxide, for example in furnace stack gas or in the sulfide ore incubation process effluent. After primary treatment, such a gas stream that still normally contains sulfur dioxide but no hydrogen sulfide will first have a stoichiometric proportion of sulfide in the stream to form elemental sulfur, which is reacted with sulfur dioxide. It can be treated according to the invention by adding hydrogen and then intimately contacting the expanded stream with an aqueous suspension of solid catalyst material according to the process of the invention as described above.

Many modifications may be made to the specific measures shown herein without departing from the scope of the invention as defined in the claims.

Claims (1)

Claims: 1. A method for removing at least one of sulfur vapor, entrained liquid sulfur droplets, and a mixture of hydrogen sulfide and sulfur dioxide present in dilute concentrations in a gas stream. A method of treating a gas stream in which the gas stream is brought into intimate contact with an acidic aqueous suspension of finely divided catalyst material or regenerated catalyst material, wherein the acidity of the suspension is such that the gas a process as described above, characterized in that the catalytic material comprises at least one of alumina and activated carbon. 2 The aqueous suspension contains finely divided catalytic material from 1 to
The method according to claim 1, characterized in that it contains 10% by weight. 3. Process according to claim 1 or 2, characterized in that the aqueous suspension of catalyst material is maintained at a temperature in the range from 60°C to 80°C. 4. The method according to claim 3, wherein the temperature is in the range of 65°C to 75°C. 5. A method according to any of claims 1 to 4, characterized in that the intimate contact between the gas stream and the aqueous slurry is achieved using a ventilate scrubber. 6. A method according to any one of claims 1 to 5, characterized in that the finely divided catalyst material is activated carbon. 7. The regenerated catalyst material: (1) separates the finely divided catalyst material from the aqueous medium when the finely divided catalyst material is contacted with a gas stream in the aqueous medium; and (2) adsorbs the finely divided catalyst material. when the fluid is a liquid solvent, at a temperature sufficient to dissolve the sulfur, and when the fluid is a gas, to melt the sulfur for a time sufficient to separate the sulfur from the finely divided catalyst material; The fluid, which can be either a liquid solvent for sulfur or a gas that does not react with the catalytic material, is passed downwardly through the catalytic material at a temperature sufficient to cause the sulfur to volatilize. A method according to claim 1, characterized in that it is obtained by regenerating. 8. The method of claim 7, wherein the fluid is hot liquid xylene. 9. The method according to claim 7, wherein the fluid is superheated steam.