Patent Application
20230416089
The present invention pertains to improved systems and methods for producing SO2 and to use thereof in plants for producing H2SO4.
Sulfur dioxide is a commonly produced industrial chemical for use as a reactant in various other chemical processes. It is produced in both pure SO2 gas and/or liquefied SO2 form for sale and as a gas mixture for use in downstream processes. A major industrial application for sulfur dioxide is in the production of sulfuric acid which is one of the most produced commodity chemicals in the world and is widely used in the chemical industry and commercial products.
Nowadays, the contact process is the primary process used to produce sulfuric acid commercially (developed in 1831 by P. Phillips). Typically, this involves obtaining a supply of sulfur dioxide by combusting a supply of sulfur with ambient air and then oxidizing the sulfur dioxide with oxygen in the presence of a catalyst (typically vanadium oxide) to accelerate the reaction in order to produce sulfur trioxide. The reaction of sulfur dioxide to sulfur trioxide is reversible and exothermic and it is important to appropriately control the temperature of the gases over the catalyst in order to achieve the desired conversion without damaging the contact apparatus which comprises the catalyst.
The produced sulfur trioxide is then converted to sulfuric acid by absorption into a concentrated sulfuric acid solution with subsequent water addition to the now more concentrated acid to maintain the acid concentration. This indirect reaction of the sulfur trioxide with water avoids the consequences of directly dissolving sulfur trioxide into water which is a highly exothermic reaction. The absorbing of the sulfur trioxide is usually done in one or more absorption towers.
Distributors are used in the absorption towers to distribute strong sulfuric acid solution across the top of a packed bed within the tower. Sulfur trioxide gas flows through the tower in generally counter-current flow to the solution, but it can also flow co-currently. The strong sulfuric acid solution is used to absorb the flowing sulfur trioxide. In CA2802885, an improved energy efficient system was disclosed for producing sulfuric acid that employs an intermediate absorption subsystem comprising a spray tower, an energy recovery subsystem, and an intermediate absorption tower comprising a packed bed. This and similar systems are commercially available under the trade-mark ALPHA™.
In WO2008/052649, a process was disclosed for the continuous catalytic complete or partial oxidation of a starting gas containing from 0.1 to 66% by volume of sulfur dioxide plus oxygen, in which the catalyst is kept active by means of pseudoisothermal process conditions with introduction or removal of energy. The related apparatus is for the continuous catalytic complete or partial oxidation of a starting gas containing sulfur dioxide and oxygen, and is characterized by at least one tube contact apparatus which is an upright heat exchanger composed of at least one double-walled tube whose catalyst-filled inner tube forms a reaction tube, with heat being transferred cocurrently around the reaction tube and an absorber for separating off SO3 being installed downstream of the tube contact apparatus. The reactivity of the catalyst is preset by mixing with inert material. This process and apparatus are commercially available under the trade-mark CORE™ Large volumes of sulfuric acid are required to produce phosphate based fertilizer. Large companies exist in the industry that are located in areas with an abundance of phosphate rock and which employ large integrated fertilizer complexes for the production thereof. Outputs between 4000 and 5000 mtpd now come from such sulfuric acid plants and as the plants continue to become larger, it is getting uneconomic to fabricate the converters, absorbing towers and gas-gas exchangers involved. The result is that multiple sulfuric acid plants are required to meet the increasing demand.
To address this problem, sulfuric acid plants and processes have recently been disclosed that practically allow for capacities in excess of 10,000 mtpd. For example, this technology is disclosed in Canadian patent application CA3021202 titled Sulfuric Acid Plant and published Dec. 24, 2018 and also The “MEGA” Sulphuric Acid Plant, by R. Dijkstra, Chemetics Inc., Vancouver, BC, Canada, Presented at Sulphur 2018 International Conference & Exhibition (Gothenburg 5-8 Nov. 2018). Here, sulfur is combusted to sulfur dioxide using oxygen instead of air and using submerged combustion to manage the heat which is generated. The design offers lower capital expenditure as well as enhanced energy recovery.
Notwithstanding that the use of oxygen instead of air has long been considered to combust sulfur to sulfur dioxide (e.g. EP2330075 & EP2507164) historically, commercial sulfur burning, sulfuric acid plants have always used ambient air as the source of the oxygen required in the process. The use of ambient air is inexpensive and the conventional process operating at approximately 11-12 vol % SO2 into the converter perfectly balances the O2:SO2 ratio required for high conversion and the maximum allowable temperature in the first catalyst bed. The disadvantage of using air is that each required molecule of oxygen also comes with approximately four molecules of inert gas (mainly N2 and argon) which must also flow through the plant, therefore requiring very large equipment to handle to entire gas flow.
In the sulfuric acid plants disclosed in the aforementioned CA3021202, submerged combustion is primarily used to produce sulfur dioxide. However, due to the relatively low latent heat of sulfur, a large amount of sulfur is evaporated from the combustion bath along with the sulfur dioxide vapour produced (approx. 23 kg sulfur vapour for every kg of sulfur reacted to sulfur dioxide). Thus, large gas volumes have to be handled and the substantial amount of sulfur vapour present practically must be recovered, along with associated heat energy, using a sulfur condensing step in a sulfur condenser. In this sulfur condensing step, sulfur is recovered as liquid sulfur and the remaining gas mixture consists mainly of sulfur dioxide and a now modest amount of residual sulfur vapour. This modest amount of residual sulfur vapour then undergoes a secondary combustion to essentially convert it all to sulfur dioxide too. (Secondary combustion techniques for the combustion of sulfur to sulfur dioxide have long been known to those skilled in the art; e.g. as disclosed in U.S. Pat. No. 3,803,298.)
The sulfur condenser in such plants needs to operate at either high or low temperature to avoid operating at the viscosity peak for sulfur at 170° C. (e.g. as discussed in U.S. Pat. No. 5,204,082). Operation of the sulfur condenser at temperatures below the viscosity peak temperature only allows recovery of low grade energy in the form of low pressure steam and/or hot water which is undesirable given the large quantity of energy available. Operating the sulfur condenser at temperatures above the viscosity peak temperature allows useful energy to be recovered (e.g. 40 barg steam), but in this case not all sulfur vapor is condensed and even at the expected operating temperature of 275-300° C., the condensed liquid sulfur has undesirably high viscosity. This makes the sulfur more difficult to condense and because the condensed sulfur liquid flows slowly, oversized piping is required. Thus, the sulfur condensing step is relatively complex and the associated sulfur condenser is a relatively large and expensive piece of equipment. It is therefore highly desirable to reduce the amount of sulfur that must be condensed and recovered.
The chemistry of sulfur is quite complex and numerous allotropes can exist in molecules which differ in both the arrangement of atoms and the number of atoms. Under common or standard conditions, sulfur is a solid material and forms molecules with 8 sulfur atoms, i.e. S8. However, allotropes Sn are known to exist in the liquid and vapor phase in which n can range from 1 to 8 and even higher. The allotrope diagram for sulfur is complex and the thermodynamic properties of each allotrope differs. Additionally, the conversion between the various allotropes either requires or releases energy. For simplicity, in developing and engineering chemical processes and equipment involving sulfur, the presence of various sulfur allotropes—other than the primary allotrope involved—and the various differences in their associated properties are frequently not taken into account in their entirety.
There remains a desire for continual improvement in plant design and operation for the production of sulfur dioxide, and particularly for the efficient and cost-effective production of ever larger volumes of sulfuric acid therefrom. The present invention addresses this desire and provides other benefits as disclosed below.
In the production of sulfur dioxide using submerged combustion and pure oxygen or oxygen enriched air as a reactant, it has been discovered that a very substantial reduction in the amount of sulfur vapour needing to be condensed can be achieved, along with a significant improvement in energy recovery, by incorporating an additional vapour phase combusting step and taking advantage of the types, amounts, and properties of the various sulfur allotropes involved.
Specifically, an inventive system for the production of sulfur dioxide gas comprises a submerged combustion reactor, a vapour phase combustion chamber, and apparatus for cooling a gas and for condensing sulfur vapor into liquid sulfur. The submerged combustion reactor is for the combustion of molten sulfur to sulfur dioxide and comprises an inlet for a supply of molten sulfur, an inlet for a supply of oxygen at ≥90% purity by volume, an inlet for condenser sulfur, and an outlet. The vapour phase combustion chamber is for the combustion of sulfur vapour to sulfur dioxide and comprises an inlet connected to the outlet of the submerged combustion reactor, an inlet for a supply of oxygen at ≥90% purity by volume, and an outlet. The apparatus for cooling a gas and for condensing sulfur vapor into liquid sulfur comprises an inlet connected to the outlet of the vapour phase combustion chamber, an outlet for liquid sulfur connected to the condensed sulfur inlet of the submerged combustion reactor, and an outlet for a gas mixture comprising sulfur dioxide and residual sulfur vapour.
In general, the apparatus for cooling a gas and for condensing sulfur vapor into liquid sulfur may involve a single piece of equipment that can accomplish both functions (e.g. in smaller systems). More typically however, the two functions would be accomplished in separate processing components, namely a heat exchanger for cooling a gas and a sulfur condenser for condensing sulfur vapour into liquid sulfur. In such a case, the heat exchanger comprises the inlet connected to the outlet of the vapour phase combustion chamber, and an outlet. The sulfur condenser comprises an inlet connected to the outlet of the heat exchanger, the outlet for liquid sulfur connected to the condensed sulfur inlet of the submerged combustion reactor, and the outlet for a gas mixture comprising sulfur dioxide and residual sulfur vapour.
The aforementioned system advantageously may successfully employ a smaller sulfur condenser than that in the prior art. For instance, the sulfur condenser can be sized to condense less than 10 times the mass of molten sulfur supplied to the submerged combustion reactor. As a further advantage, due to the higher temperatures in the heat exchanger more energy is recovered at high temperature thus making the recovered energy more valuable.
The sulfur dioxide production system may be used to produce sulfur dioxide gas or liquefied sulfur dioxide for a variety of purposes in which case a further sulfur condenser operating at low temperature is required to remove the residual sulfur vapor from the sulfur dioxide gas. It is however particularly suitable for use in a sulfuric acid plant, and more particularly a single contact, single absorption sulfuric acid plant. Generally, such a sulfuric acid plant comprises the aforementioned sulfur dioxide production system, a secondary combustion chamber, a contact apparatus, and an absorption system. The secondary combustion chamber is for the combustion of residual sulfur vapour to sulfur dioxide and comprises an inlet connected to the outlet of the sulfur condenser for the gas mixture, an inlet for an oxygen containing gas (preferably oxygen at >90% purity but any oxygen containing gas including air could be used), and an outlet for process gas consisting essentially of sulfur dioxide and oxygen. The contact apparatus is for converting sulfur dioxide to sulfur trioxide and comprises an inlet connected to the process gas outlet of the secondary combustion chamber and an outlet for sulfur trioxide. The absorption system is for converting sulfur trioxide to sulfuric acid and comprises an inlet connected to the sulfur trioxide outlet of the contact apparatus, and an outlet for sulfuric acid.
A suitable contact apparatus for the sulfuric acid plant is a tubular reactor cooled by molten salt. Optionally, the submerged combustion reactor, the vapour phase combustion chamber, and the secondary combustion chamber may share a common supply of oxygen at ≥90% purity by volume.
The secondary combustion chamber in the instant sulfuric acid plant can desirably comprise an inlet for recycle gas from the absorption system wherein the recycle gas comprises sulfur dioxide, oxygen and accumulated inert gases. The secondary combustion chamber can thus simultaneously reheat the recycle gas without the need for additional heat exchangers.
In the associated method of the invention, sulfur dioxide is produced by combusting molten sulfur with oxygen at >90% purity by volume using submerged combustion to produce a first gas mixture comprising sulfur dioxide and sulfur vapour comprising molecules of sulfur Sn wherein n≥2, then vapour phase combusting the sulfur vapour in the first gas mixture with oxygen or oxygen enriched air to produce a second gas mixture comprising sulfur dioxide and sulfur vapour in which the concentrations of sulfur dioxide and sulfur vapour in the second gas mixture are greater and less respectively than the concentrations in the first gas mixture, then cooling the second gas mixture to produce a third gas mixture comprising sulfur dioxide and sulfur vapour, and then condensing sulfur vapour into liquid sulfur from the third gas mixture to produce a fourth gas mixture comprising sulfur dioxide and residual sulfur vapour. The method is characterized in that the average number naverage of the sulfur atoms in the sulfur molecules in the second gas mixture is at least 20% lower than the naverage of the sulfur atoms in the sulfur molecules in the first gas mixture.
In a desirable exemplary method of the invention, the average number naverage of the sulfur atoms in the sulfur molecules in the second gas mixture is more than 50% lower than the naverage of the sulfur atoms in the sulfur molecules in the first gas mixture.
In the method, the cooling step can be performed at a temperature above the dewpoint of sulfur and the cooling can remove more than 50% of the energy released during the combustion of sulfur in the submerged combustion and vapour phase combusting steps.
In a representative embodiment, 30 to 50% of the total oxygen combusted in the submerged and vapour phase combusting steps is combusted in the submerged combusting step and 50 to 70% of the total oxygen is combusted in the vapour phase combusting step.
In other representative embodiments, the average number of sulfur atoms of the Sn molecules for all n≥2 in the first gas mixture can be in the range from 6.4 to 7.0. Further, the average number of sulfur atoms of the Sn molecules for all n≥2 in the second gas mixture can be in the range from 2.1 to 3. Further still, the average number of sulfur atoms of the Sn molecules for all n≥2 in the third gas mixture can be in the range from 6.4 to 7.0.
In yet other representative embodiments, the temperature of the first gas mixture can be in the range from 440 to 500° C. Further, the temperature of the second gas mixture can be in the range from 650 to 700° C. Further still, the temperature of the third gas mixture can be in the range from 400 to 475° C.
As mentioned above, the invention may be used to produce sulfur dioxide gas or liquefied sulfur dioxide for numerous purposes, but is particularly suitable for use in producing sulfuric acid in a sulfuric acid plant. In such an embodiment sulfur dioxide is produced according to the aforementioned method, after which conventional steps for producing sulfuric acid therefrom may be employed.
Unless the context requires otherwise, throughout this specification and claims, the words “comprise”, “comprising” and the like are to be construed in an open, inclusive sense. The words “a”, “an”, and the like are to be considered as meaning at least one and are not limited to just one.
The words “oxygen” or “pure oxygen” are to be considered as meaning oxygen in concentrations equal to or exceeding 90% by volume.
Herein, the average number naverage of the sulfur atoms in the sulfur molecules in a given gas mixture is defined as the sum of all sulfur atoms contained in the sulfur molecules in the gas mixture divided by the total moles of sulfur in the gas mixture.
The trade-marks CORE-S™ and CORE-SO2™ refer to the molten salt cooled tubular reactor and the processes of the invention respectively.
The present invention represents a significant improvement to the sulfur dioxide generation portion of the system and methods disclosed in CA3021202. While this disclosure was directed specifically to use in sulfuric acid production plants, the sulfur dioxide generation portion may instead be employed to generate pure SO2 gas or liquefied SO2 (by condensing the SO2 in the gas mixture in a SO2 liquefaction system) directly for sale or for use in other applications. (Note: a difference between use for sulfuric acid production is that not all sulfur content of the gas has to be removed in this application, for instance being allowed to contain up to 10-20 mol % sulfur (expressed as S1), whereas for use as pure SO2 or liquefied SO2, cooling to a lower temperature to condense all sulfur, e.g. to <1 mole % sulfur (expressed as S1) from the gas would typically be required.)
In the submerged combustion step of molten sulfur with oxygen, it has been discovered that the significant presence of the variety of sulfur allotropes in the gas mixture produced can be advantageously used to reduce the ultimate amount of sulfur that needs to be condensed in the process and also to simplify and improve energy recovery in the process. This is a consequence of the amounts and thermodynamic properties of the different sulfur allotropes present.
In the primary combustion stage of the process involving submerged combustion, all the oxygen supplied is consumed and excess sulfur remains in the gas mixture produced. In the prior art process where the entire primary combustion is accomplished by submerged combustion, a gas mixture comprising sulfur dioxide and sulfur gases is created with a very large relative amount of sulfur vapour (approximately 7-9 kg sulfur vapour for every kg of sulfur dioxide formed). It was realized that if an initial portion of the supplied oxygen were used to generate this mixture, the additional remaining portion of oxygen could be used to convert part of the sulfur in the vapour to SO2 (while still consuming all the supplied oxygen), while at the same time the reaction energy from the vapour phase combustion of sulfur to SO2 would be taken up by the gas mixture. This energy would be used to convert S8 allotrope molecules to four S2 molecules and in a like manner convert other n≥2 sulfur allotropes to S2 (e.g. S6 molecules to three S2 molecules). This conversion of the sulfur molecules results in a much lower gas temperature rise than would otherwise be expected due to the endothermic nature of the conversion of larger sulfur molecules into multiple smaller sulfur molecules and thus most of the total oxygen used in the primary combustion stage can actually be used in the vapour phase combusting step rather than in the submerged combusting step. Having a large portion of the associated energy in the hot gas mixture then readily allows this energy to be recovered at a high temperature (via a conventional heat exchanger) without having to condense sulfur which is not only more complicated but also only allows energy to be recovered at lower temperature. Consequently, a significantly smaller amount of sulfur needs to be condensed and smaller amount of energy has to be recovered from the condensing sulfur allowing the sulfur condenser to be sized significantly smaller than in the prior art. In the preferred embodiment of the invention less than 3 kg of sulfur is condensed for every kg sulfur dioxide produced
In SCSA plant 1 of
The remaining components shown in
In
While SCSA plant 1 provides many advantages, undesirably a substantial amount of sulfur vapour needs to be condensed in sulfur condenser 6.
A SCSA plant of the invention is next illustrated in the schematic of
As is evident from
Comparing
In embodiments of the invention, any known or conventional vapour phase combustion chamber types may be considered for use as vapour phase combustion chamber 6. Further, any known or conventional gas-gas (e.g. steam superheater) or gas-liquid (e.g. steam boiler or molten salt cooler) heat exchangers may be considered for use as heat exchanger 18. In other embodiments however, the function of the heat exchanger 18 and sulfur condenser 6 can be carried out in a single, integrated piece of equipment. Further still, the various supplies of pure oxygen can be obtained from a common supply (e.g. a vacuum swing absorption unit, typically 90-93% purity, or a cryogenic air separation unit, typically >98% purity, are likely sources) or alternatively more than one supply may be considered.
A characteristic of the present invention is that the apparatus and operation results in the average number naverage of the sulfur atoms in the sulfur molecules in the second gas mixture 5b being at least 20% lower than the naverage of the sulfur atoms in the sulfur molecules in the first gas mixture 5a. More particularly, the average number naverage of the sulfur atoms in the sulfur molecules in the second gas mixture 5b may be more than 50% lower than the naverage of the sulfur atoms in the sulfur molecules in the first gas mixture 5a. Further, sulfur condenser 6 can be sized smaller than that used in the prior art, e.g. sized to condense less than 10 times the mass of molten sulfur supplied to the submerged combustion reactor.
In the operation of the SO2 production system of the invention, the cooling performed in heat exchanger 18 may preferably be carried out at a temperature above the dewpoint of sulfur and such cooling can remove more than 50% of the energy released during the combustion of sulfur in the submerged combustion and vapour phase combusting steps.
In the representative embodiments shown in the Figures and in the following Examples, it is seen that 30 to 50% of the total oxygen combusted in the submerged and vapour phase combusting steps can be combusted in the submerged combusting step and 50 to 70% of the total oxygen can be combusted in the vapour phase combusting step. Further, the average number of sulfur atoms of the Sn molecules for all n≥2 in the first, second, and third gas mixtures can be in the ranges from 6.4 to 7.0, 2.1 to 3, and 6.4 to 7.0 respectively. Further still, the temperature of the first gas mixture can be in the range from 440 to 500° C., the temperature of the second gas mixture can be in the range from 650 to 700° C., and the temperature of the third gas mixture can be in the range from 400 to 450° C.
However, those of ordinary skill will appreciate that the amounts, temperatures, and desired operating conditions (such as operating pressure) may need to be modified somewhat in accordance with differing situations and plant apparatus. It is expected however that those of ordinary skill will be able to make such modifications using the disclosed teachings and the following Examples for guidance.
In general terms, a main advantage of using submerged combustion using enriched air or pure oxygen at >90% concentration is that the temperature of the combustion products are limited to the boiling point of sulfur (e.g. ˜450° C. at 0.5 barg & ˜575° C. at 4 barg). However, due to the relatively low latent heat of sulfur, a large amount of sulfur is evaporated from the bath resulting in large gas volumes that have to be handled. Thus, large amounts of sulfur need to be condensed from the SO2 gas before it is sent for further use. The sulfur condenser in the system needs to operate at either high or low temperature to avoid the sulfur viscosity peak at 170° C., but even at the expected operating temperature of 275-300° C., the condensed liquid sulfur has high viscosity. This makes the sulfur more difficult to condense and the condensed sulfur liquid flows slowly requiring oversized pipes.
Additionally, for larger plant capacities the large amounts of oxygen gas that must be distributed into the molten salt bath require large equipment to ensure good gas/liquid contact. Existing submerged sulfur combustion systems have been limited to approx 50 tpd sulfur capacity. To meet the larger demand for sulfuric acid, capacities of up to 3000 tpd sulfur are foreseen. The present invention addresses this in part by accomplishing some of the combusting in the vapour phase instead of via submerged combustion. Advantage is taken of the fact that at low temperatures, most of the sulfur vapour exists in the form of S6, S7 and S8 molecules whereas at high temperatures, the superheated sulfur vapour exists primarily as S2 molecules. The conversion of S6, S7 and S8 molecules into S2 molecules requires significant amounts of energy resulting in a gas that heats up significantly slower than is expected based on the normal heat capacity of the mixture. The reaction of S6, S7 and S8 to S2 is reversible and when the gas is cooled down, the reaction energy is released again.
The present invention splits the sulfur combustion into two portions, namely submerged and vapour phase combustion. The released reaction energy in the latter is used to heat the sulfur vapour and produce S2 molecules. Due to the reaction of S6, S7 and S8 to S2 molecules, the vapour has a very high apparent heat capacity and the vapour only increases relatively modestly in temperature to (e.g. to ˜700° C. instead of the ˜2000° C. that would be expected based on conventional heat capacity alone). The process temperature (and hence oxygen addition) is preferably limited to about 700° C. to ensure some of the sulfur molecules remain in the S6, S7 and S8 form which prevents temperature spikes in case of process fluctuations. The reaction of sulfur to sulfur dioxide in the gas phase has the additional benefit that significantly less sulfur remains in the gas before it is cooled resulting in smaller equipment for condensing the remaining sulfur.
The reversible reaction of S6, S7 and S8 to S2 takes place essentially entirely in the vapour phase and the heat exchanger required to remove the majority of the reaction energy (up to 75% of the total sulfur combustion energy) can operate above the sulfur dewpoint and therefore does not need to be designed to handle liquid sulfur. This simplifies the design and allows higher grade energy to be recovered. The remaining sulfur combustion energy is recovered in a sulfur condenser.
It should be clear that although the aforementioned description has focused on sulfur dioxide production for use in sulfuric acid plants with large capacity, the same process and economic benefits exist for smaller plants and for other applications using sulfur dioxide.
The following Examples have been included to illustrate certain aspects of the invention but should not be construed as limiting in any way.
Computer modeling was used to calculate the expected compositions and temperatures of the various gas mixtures involved in using submerged combustion and oxygen to produce sulfur dioxide for a commercial scale SCSA sulfuric acid plant (similar to that shown in
Three cases were modeled, the first (Comparative example) being based on the plant and method disclosed in the aforementioned CA3021202 and as depicted in
Values for the prior art SCSA plant or Comparative example during exemplary operation were obtained and are tabulated in Table 1. Specifically, the temperatures, pressures, mass flows, and compositions of the various streams depicted in
With reference to
In the secondary combustion, the 182.5 kg/hr gas mixture primarily containing SO2 from
For comparison, the two Inventive examples were based on a similar SCSA to that shown in
With reference to
Inventive example 2 shows the same inventive process but differs from Inventive example 1 in that the sulfur condenser is operated at a temperature below the sulfur viscosity peak. It also illustrates that the inventive process can be operated at different pressures. Values for Inventive example 2 are tabulated in Table 3 below.
It is apparent from this modeling that the sulfur condenser required in the inventive embodiments of Inventive examples 1 and 2 can be sized much smaller than that of the Comparative example. The ratio of mass supplied to the sulfur condenser in
As mentioned, the calculated heat loads (i.e. the amount of energy that is removed from the process) from sulfur condenser 6 and from the heat exchanger 18 are shown in Tables 1 through 3. The total heat load in Inventive example 1 is the same as that in the Comparative Example, but importantly in this inventive process, more than 70% of that total heat load can be recovered in heat exchanger 18 which operates at a temperature above 400° C. and less than 30% of the heat load is recovered from sulfur condenser 6 at much lower temperature. The energy recovered from heat exchanger 18 is recovered at higher temperature and has more economical value and can be used for high pressure (e.g. 60 barg) steam production and/or steam superheating. No condensation occurs in heat exchanger 18 and thus no viscous liquid needs to be dealt with to recover this energy.
The total heat load shown in Table 3 for Inventive example 2 is higher compared to the other examples as due to the lower condensing temperature in the sulfur condenser there is less sulfur vapour leaving in stream 5d and therefore more of the molten sulfur in stream 1 is converted into sulfur dioxide. However, as for Inventive example 1, approximately 70% of the total heat load can be recovered in heat exchanger 18.
For illustrative purposes,
From the above Examples, it is clearly apparent that the invention allows for a substantial reduction in the size, complexity, and cost of the sulfur condensing equipment used in this process and also for a significant improvement in high temperature energy recovery.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, particularly in light of the foregoing teachings. Such modifications are to be considered within the purview and scope of the claims appended hereto.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/045989 | 8/13/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63076165 | Sep 2020 | US |
