Patent Application
20250033967
The present invention pertains to improved systems and methods for producing SO2, SO3 and H2SO4 therefrom. The invention also pertains to similarly improved systems and methods for producing liquefied SO2.
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 SO2form 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 catalyst and/or 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 cocurrently. 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-marks CORE™ and CORE-S™.
U.S. Pat. No. 4,578,262 describes a method for the production of sulfur dioxide from a source of concentrated sulfur dioxide gas using a liquefaction system in which the tail gas from the liquefaction is returned to the sulfur combustion furnace. The sulfur combustion furnace is operated with ambient air.
In U.S. Pat. No. 3,803,298. a method for production of high purity sulfur dioxide with oxygen is described in which the sulfur reacts with oxygen in a plurality of combustion stages with cooling in between the combustion chambers at temperatures of 1700-2000° C. The resulting high purity sulfur dioxide is liquefied by cooling the gas below the sulfur dioxide boiling point.
Both U.S. Pat. No. 7,052,670 and U.S. Pat. No. 6,875,413 describe methods for the production of high purity sulfur dioxide by combustion of liquid sulfur with oxygen in a furnace. The furnace temperature is controlled by a recycle of SO2 gas after cooling and passing through an absorber for the sulfur trioxide removal. High purity SO2 product is obtained via liquefaction carried out on a portion of the gas after sulfur trioxide removal. The tail gas from the liquefaction unit is also recycled to the furnace.
Historically, commercial sulfur burning, sulfuric acid plants have 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 contact apparatus 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 the entire gas flow. To improve efficiencies and reduce emissions, commercial sulfuric acid plants using ambient air are often of the double contact, double absorption (DCDA) design. In a DCDA system, process gases are subjected to two contact and absorption stages in series, (i.e. a first catalytic conversion and subsequent absorption step followed by a second catalytic conversion and absorption step). Sulfur dioxide for the system can be produced by combusting sulfur with ambient air in a single reactor after which the reactor gases produced are cooled in a heat exchanger prior to being supplied to the contact apparatus. Details regarding the conventional options available and preferences for sulfuric acid production and the contact process are well known and can be found for instance in “Handbook of Sulfuric Acid Manufacturing”, Douglas Louie, ISBN 0-9738992-0-4, 2005, published by DKL Engineering, Inc., Ontario, Canada.
In an alternative approach, a staged combustion process may be employed to produce gases with a high sulfur dioxide concentration while minimizing the formation of nitrogen oxides (NOx) in the reactor. For instance, a two stage combustion process using ambient air may be employed in which a first combustion stage is performed below 1200° C. to keep NOx formation relatively low followed by a second combustion stage at higher temperature to produce gases with a relatively high sulfur dioxide concentration. The higher gas temperature desirably allows for a reduction in heat exchanger size. The staged combustion process is described for instance in U.S. Pat. No. 8,043,597.
The use of oxygen instead of air has long been considered to combust sulfur to sulfur dioxide as the use of oxygen can allow for a reduction in size for much of the equipment in the system in principle. However, the combustion process results in exceedingly high flame and reactor temperatures temperatures (>3900° C.) in a single reactor system. Such temperatures are much too high for the typical materials used for reactor construction and instead very expensive construction materials would be required. Further, substantial NOx formation occurs at such temperatures even from the little nitrogen that is typically present in “almost pure” oxygen (typically >0.2 vol % minimum). The NOx produced is a problem in the downstream process when the combustion product is used for either production of sulfuric acid or liquid sulfur dioxide.
The use of oxygen to-date has also been hindered by the cost of providing such oxygen and plants would have to offset the cost of oxygen against cost savings in the process. New and emerging technologies are now becoming available where oxygen or high purity oxygen is a by-product from the process (e.g., water hydrolysis to produce green hydrogen) and this can provide lower cost sources of oxygen with the potential for economic integration of various processes. One such example is described in published PCT application WO2021/118599 (application number PCT/US2019/066262).
A practical approach then for combusting sulfur with pure or almost pure oxygen then was to employ a staged combustion process in which heat removal between stages was used in order to reduce the temperatures in the sulfur reactors. Such an approach is described in EP2330075, EP2507164 and/or EP2507167. However, multiple combustion zones (reactors) and multiple heat exchangers are required and such a system is more expensive to build and more complicated to operate. Further, while the flame and reactor temperatures are kept below 2000° C. NOx formation is still likely despite these lower temperatures and nitrogen concentration.
In another approach for combusting sulfur with oxygen, reactor temperatures can be kept desirably low by recycling a portion of the gases following conversion in the contact apparatus (i.e. the flue gas). This approach is disclosed for instance in U.S. Pat. No. 4,046,866. Recycling this flue gas provides for an improved system design, but requires a very large recycle flow. Additionally, the concentration of nitrogen in the system is undesirably increased while the concentration of sulfur dioxide is undesirably decreased. Further, as the entire gas stream is cooled to a low temperature in the absorber, a significant amount of energy is no longer available to be recovered in the reactor heat exchanger. Further, such recycling requires an increase in the size of all the related equipment and power consumption for the significant recycling pump that is required. This recycling pump must overcome the pressure drop present in all the upstream equipment and requires more advanced designs. While the gas volume involved with this approach is lower than for conventional ambient air combustion, it is typically only about 30% smaller, thus eliminating much of the theoretical advantages of using oxygen.
In another approach for combusting sulfur with oxygen, reactor temperatures can be kept desirably low by recycling the reactor gases following cooling, sulfur trioxide absorption and sulfur dioxide liquefaction. This approach is disclosed for instance in U.S. Pat. No. 7,052,670. Recycling the gas in this manner provides for an improved system design, but as the gas is recycled after cooling and sulfur trioxide absorption, a substantial amount of energy is lost to the absorber liquid. Further, such recycling requires an increase in the size of all the related equipment and power consumption for the significant recycling pump that is required. This recycling pump must overcome the pressure drop present in all the upstream equipment and requires more advanced designs.
In a yet further approach then, a system comprising both staged combustion and a recycle of the flue gas has been considered. For instance, such a system may comprise two combustion stages in series, namely a first stage comprising a first reactor and heat exchanger followed by a second stage comprising a second reactor and heat exchanger. The gases obtained from the staged combustion are then supplied to a contact apparatus after which, and as above, a portion of the gases following conversion in the contact apparatus are recycled. Such an approach desirably reduces recycle flow, but there is still a relatively high nitrogen concentration in the reactors. While the flow involved is smaller and hence there is a smaller power and heat loss penalty, the system is more complicated and expensive than a single stage system.
Recently sulfuric acid plants and processes have been proposed in which sulfur combustion is carried out using pure oxygen and a submerged combustion process. In this process, oxygen is injected into a bath of molten sulfur. Energy released as the oxygen reacts with sulfur is used to evaporate sulfur from the bath. The sulfur evaporated is condensed in a downstream condenser to recover the energy and the condensed sulfur is returned to the bath. The advantage of submerged combustion is that the temperature of the combustion products are limited to the boiling point of sulfur which is ˜450° C. at pressure of 0.5 barg. This technology is disclosed in detail in Canadian patent application CA3021202 titled Sulfuric Acid Plant and published Dec. 24, 2018. The design offers lower capital expenditure as well as enhanced energy recovery and allows for practical production capacities in excess of 10,000 mtpd. The submerged combustion does not require a large gas recycle in order to control temperature. And minimal NOx formation is involved due to the low operating temperature. However, a submerged combustion system is relatively complex since it involves containment of sulfur vapor at high temperature and thus material concerns.
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.
Improved systems and related methods have been developed for producing sulfuric acid and liquefied sulfur dioxide. The improvements include reductions in equipment size and/or equipment complexity, reductions in power consumption, improved energy efficiency, and in suppression of nitrogen oxide (NOx) formation when compared to options in the prior art. The improvements involve recycling both a portion of the combustion gas obtained from combusting sulfur to sulfur dioxide and also a portion of the gases obtained following the conversion of sulfur dioxide to either sulfuric acid or to sulfur dioxide liquid in the case of sulfuric acid and liquefied sulfur dioxide production respectively.
With this approach, the reactor used for the combustion of sulfur can be operated at any desired temperature, e.g. a modest temperature in a range around 1200-1400° C. such that NOx formation is suppressed, while also avoiding the formation of SO3 which can lead to corrosion issues in other equipment.
Specifically, one embodiment of the invention is a system for the production of sulfuric acid comprising a reactor for the combustion of sulfur to sulfur dioxide, a reactor gases heat exchanger for cooling reactor outlet gases, a contact apparatus for the conversion of sulfur dioxide to sulfur trioxide, an absorption apparatus for absorbing sulfur trioxide into sulfuric acid to form more concentrated sulfuric acid, a first recycle circuit, and a second recycle circuit. The reactor comprises an inlet for a supply of sulfur, an inlet for a supply of oxygen at ≥90% purity by volume, a recycle inlet for recycle gases, and an outlet for reactor outlet gases comprising sulfur dioxide. The reactor gases heat exchanger comprises an inlet fluidly connected to the reactor outlet and an outlet for cooled reactor outlet gases. The contact apparatus comprises an inlet connected to the reactor gases heat exchanger outlet and an outlet for contact apparatus gases. The absorption apparatus comprises an inlet fluidly connected to the contact apparatus outlet, an outlet for the more concentrated sulfuric acid, and an outlet for unabsorbed contact apparatus gases. The first recycle circuit of the two recycle circuits comprises a first pump and fluidly connects the reactor gases heat exchanger outlet to the recycle inlet of the reactor, while the second recycle circuit comprises a second pump and fluidly connects the outlet of the absorption apparatus for unabsorbed contact apparatus gases to the recycle inlet of the reactor.
In this simplified embodiment, the reactor may consist of a single stage and may be the only reactor for the combustion of sulfur to sulfur dioxide in the system. Further, the system may be absent any submerged combustion reactor. Further still, the reactor gases heat exchanger may be the only reactor gases heat exchanger for cooling reactor outlet gases in the system.
The first and second pumps employed in the two recycle circuits can be selected from the typical group consisting of fans, blowers, ejectors and other types known to those in the art. The first recycle circuit can also comprise a recycle heat exchanger that, in a preferred embodiment, is located before the first pump in the first recycle circuit.
The invention, and in particular the above embodiment, is advantageous for application in a sulfuric acid plant, and allows for a single contact, single absorption plant design. Such a plant would comprise the aforementioned sulfur trioxide production system and at least one absorption system for converting sulfur trioxide to sulfuric acid. The absorption system would comprise an inlet connected to the contact apparatus outlet and an outlet for sulfuric acid.
Another embodiment of the invention is a system for the production of sulfur dioxide liquid comprising a reactor for the combustion of sulfur to sulfur dioxide, a reactor gases heat exchanger for cooling reactor outlet gases, an absorption subsystem comprising an absorption apparatus for the removal of sulfur trioxide by absorption into sulfuric acid to form more concentrated sulfuric acid, a liquefaction apparatus for the conversion of sulfur dioxide gas to sulfur dioxide liquid, a first recycle circuit, and a second recycle circuit. In a like manner to the previous embodiment, the reactor comprises an inlet for a supply of sulfur, an inlet for a supply of oxygen at ≥90% purity by volume, a recycle inlet for recycle gases, and an outlet for reactor outlet gases comprising sulfur dioxide. The reactor gases heat exchanger comprises an inlet fluidly connected to the reactor outlet and an outlet for cooled reactor outlet gases. In this embodiment however the absorption subsystem comprises an inlet fluidly connected to the reactor gases heat exchanger outlet, an outlet for unabsorbed reactor outlet gases, and an outlet for the concentrated sulfuric acid. Further, the liquefaction apparatus comprises an inlet connected to the absorption subsystem outlet, an outlet for unliquefied liquefaction apparatus gases, and an outlet for liquid sulfur dioxide. The first recycle circuit of the two recycle circuits again comprises a first pump and fluidly connects the reactor gases heat exchanger outlet to the recycle inlet of the reactor. Here, the second recycle circuit comprises a second pump and fluidly connects the outlet of the liquefaction apparatus for liquefaction apparatus gases to the recycle inlet of the reactor.
Related methods of the invention include methods for producing sulfuric acid in a sulfuric acid plant, and for producing sulfur dioxide liquid. In the first instance, the method comprises obtaining the aforementioned system for producing sulfuric acid and then the steps of supplying sulfur and oxygen at ≥90% purity to the sulfur inlet and the oxygen inlet of the reactor respectively, reacting the sulfur and oxygen in the reactor thereby producing reactor outlet gases comprising sulfur dioxide, directing the reactor outlet gases from the reactor outlet to the reactor gases heat exchanger inlet, cooling the reactor outlet gases in the reactor gases heat exchanger thereby producing cooled reactor outlet gases, directing a contact apparatus portion of the cooled reactor outlet gases to the contact apparatus inlet, pumping a recycle portion of the cooled reactor outlet gases to the recycle inlet of the reactor using the first pump in the first recycle circuit, converting sulfur dioxide in the contact apparatus portion of the cooled reactor outlet gases in the contact apparatus thereby producing contact apparatus gases comprising sulfur trioxide, directing the contact apparatus gases from the contact apparatus outlet to the absorption apparatus inlet, absorbing sulfur trioxide from the contact apparatus gases into sulfuric acid to form more concentrated sulfuric acid, and pumping a recycle portion of the unabsorbed contact apparatus gases to the recycle inlet of the reactor using the second pump in the second recycle circuit.
An advantage of the inventive method for producing sulfur trioxide is that the flow through the contact apparatus and subsequent equipment downstream (e.g. in a sulfuric acid plant) can be markedly reduced thereby reducing the size and cost of the associated equipment. For instance in a representative embodiment, the ratio of moles of gases in the contact apparatus portion of the reactor outlet gases to the total moles of gases in the reactor outlet gases may be less than 0.5. Further, the required flow of recycled contact apparatus gases is relatively low (i.e. the flow in the second recycle circuit) and thus the significant amount of equipment between the reactor gases heat exchanger and the second recycle pump can now be made much smaller. As a result of the reduced flow of contact apparatus gases, the amount of energy lost from the gas to the absorber liquid in the absorption subsystem or apparatus is reduced. In addition, the second recycle pump which needs to generate a relatively large pressure rise (and hence has a large power consumption) can be much smaller as well. For instance in a representative embodiment, the ratio of moles of gases in the recycled unabsorbed contact apparatus gases to the moles of gases in the reactor outlet gases is less than 0.2.
The present invention is also advantageous in that the reactor outlet gases comprise a relatively low concentration of nitrogen and a relatively high concentration of sulfur dioxide. In representative embodiments, the concentration of inert gases (predominantly nitrogen and argon) in the reactor outlet gases can be less than 30 mole %, while the concentration of sulfur dioxide in the reactor outlet gases can be greater than 30 mole %. Further, the ratio of moles of oxygen to moles of sulfur dioxide in the reactor outlet gases can be less than 0.65. And as mentioned above, the reactor can be operated at a modest temperature to suppress NOx formation, e.g. at a temperature less than 1500° C.
In a preferred embodiment of the invention, the first recycle circuit in the system comprises a recycle heat exchanger and the method comprises further cooling the recycle portion of the cooled reactor outlet gases in the first recycle circuit in the recycle heat exchanger.
As mentioned, the invention also includes methods for producing sulfuric acid in a sulfuric acid plant and for producing sulfur dioxide liquid. In the former, the method comprises producing sulfur trioxide according to the aforementioned steps, directing the contact apparatus gases comprising sulfur trioxide from the contact apparatus to at least one absorption apparatus, and then absorbing the sulfur trioxide in the contact apparatus gases using the absorption apparatus thereby producing sulfuric acid. In the latter, the method comprises obtaining the aforementioned system for producing sulfur dioxide liquid, supplying sulfur and oxygen at ≥90% purity to the sulfur inlet and the oxygen inlet of the reactor respectively, reacting the sulfur and oxygen in the reactor thereby producing reactor outlet gases comprising sulfur dioxide, directing the reactor outlet gases from the reactor outlet to the reactor gases heat exchanger inlet, cooling the reactor outlet gases in the reactor gases heat exchanger thereby producing cooled reactor outlet gases, directing a liquefaction apparatus portion of the cooled reactor outlet gases to the absorption subsystem inlet, pumping a recycle portion of the cooled reactor outlet gases to the recycle inlet of the reactor using the first pump in the first recycle circuit, absorbing sulfur trioxide from the liquefaction apparatus portion of the cooled reactor outlet gases into sulfuric acid to form more concentrated sulfuric acid and unabsorbed reactor outlet gases comprising sulfur dioxide,
directing the unabsorbed reactor outlet gases to the liquefaction apparatus inlet, liquefying sulfur dioxide in the unabsorbed reactor outlet gases to produce liquid sulfur dioxide and liquefaction apparatus gases, and pumping a recycle portion of the liquefaction apparatus gases to the recycle inlet of the reactor using the second pump in the second recycle circuit.
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.
The trade-mark CORE-S™ refers to the molten salt cooled tubular reactor of the technology disclosed in the aforementioned WO2008/052649.
The present invention provides improved systems and methods for producing sulfuric acid and/or liquefied sulfur dioxide. Compared with conventional options in the art, reductions in equipment size and/or equipment complexity, reductions in power consumption, and in suppression of nitrogen oxide (NOx) can be obtained. For instance, a system of the invention for producing sulfuric acid is easier to operate and of lower complexity and cost than systems employing submerged combustion or staged combustion. Due to the higher combustion temperature involved, the heat exchanger employed can be made smaller than that in a conventional DCDA sulfuric acid plant. However the temperature can be kept low enough to suppress the formation of NOx.
To obtain these benefits, appropriate portions of gases are recycled back to the sulfur combustion reactor from two different points further downstream in the system. In a first recycle, an appropriate portion of the combustion gas obtained from combusting sulfur to sulfur dioxide is recycled. In a second recycle, an appropriate portion of the gases obtained following the conversion of sulfur dioxide to either sulfuric acid or to sulfur dioxide liquid is recycled—in the case of sulfuric acid and liquefied sulfur dioxide production respectively.
With this relatively simple approach, high concentration sulfur dioxide gas can be produced at moderate temperatures. Power consumption can be minimized by cooling gas upstream of the hot gas recycling pumps. And because the combustion reactor is operated at a moderate temperature, NOx formation is suppressed.
The differences in structure between numerous conventional systems of the prior art and the present invention can be seen by comparing the system schematics shown in the following figures.
In sulfuric acid plant 1a, sulfur 12 and ambient air 13 are supplied to reactor 5a at inlets 5aA and 5aB respectively and are reacted together to form SO2. Reactor outlet gases containing this SO2 are obtained from reactor 5a at outlet 5aC and are directed to inlet 6aA of heat exchanger 6a in which these gases are cooled. The cooled reactor gases are then directed from heat exchanger outlet 6aB to contact apparatus 7a at inlet 7aA. In contact apparatus 7a, SO2 in the cooled reactor gases is converted to SO3 after which the gases from contact apparatus 7a are directed from outlet 7aB to absorption apparatus 8a at inlet 8aA. In absorption apparatus 8a, SO3 is absorbed into a weaker sulfuric acid solution to produce the desired, higher concentration sulfuric acid product. This higher concentration sulfuric acid is removed at outlet 8aB and the remaining unabsorbed gases from the contact apparatus are removed at outlet 8aC and then directed to additional equipment 9a to be subsequently processed in a conventional manner.
Another approach contemplated in the prior art is illustrated in the schematic of
In a yet other approach disclosed for instance in U.S. Pat. No. 4,046,866, pure oxygen can be used for combustion with the reactor temperatures being controlled with recycled flue gas.
Recently, another approach was disclosed in CA3021202 in which the improved sulfuric acid plant therein used submerged combustion and pure oxygen in the sulfur combustion and could also involve recycling a modest amount of flue gas after the absorption step. This arrangement is illustrated in the schematic of
In yet another approach which may be considered based on conventional approaches in the prior art,
A sulfuric acid plant of the present invention however can be very similar to the embodiment shown in
The advantages of this approach are numerous. Using first recycle circuit 30 results in a reduction in gas volume throughout the plant and hence the equipment involved can be sized much smaller (e.g. similar to that of the submerged combustion based embodiment of
In principle any type of pump may be considered for use as pumps 31 and 41 in the two recycle circuits, including blowers or fans (e.g. as per U.S. Pat. No. 4,552,747) or ejectors (e.g. as per U.S. Pat. No. 6,508,998 where in the instant case oxygen would be used as the active fluid). However, due to the larger pressure difference that pump 41 must deal with in second recycle circuit 40, pump 41 would likely need to be of more advanced design than pump 31 in first recycle circuit 30.
In system 2a, the temperature of reactor 5 and the size and outlet temperature of reactor gases heat exchanger 6 would be set as per teachings of prior art relating to the embodiment of
As shown in
Next,
While the above description discloses the general arrangement and operation of certain embodiments of the invention, those of ordinary skill will appreciate that certain specifics may need to be modified somewhat in accordance with differing situations and plant apparatus. It is expected however that those of ordinary skill will readily be able to make such modifications based on the disclosed teachings and the following Examples for guidance.
Further, those skilled in the art will recognize that a simplified system using only the first recycle circuit in the sulfur combustion (represented by the set of elements 5, 6, 30 and 31 in
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 and compare the expected flows and compositions in a variety of sulfuric acid plants of differing designs but with the same plant capacity for purposes of direct comparison. In this comparison, sulfuric acid plants based on each of the prior art designs shown in
In each case considered, the molten sulfur temperature was assumed to be 140° C. ambient air was assumed to be 75° C. and oxygen was assumed to be at 25° C. Further, in these illustrative computer modeled Examples, oxygen was assumed to be 99.5% pure oxygen with the remainder shown as nitrogen only for simplification of the inert species present. While such oxygen concentrations are typical of those obtained from a cryogenic air separation system, the remainder in such a case could almost entirely be argon and not nitrogen. Those of ordinary skill would of course be expected to readily be able to adjust these models according to the oxygen production unit employed and what species and concentrations are present. Conversion of SO2 to SO3 for cases with a gas recycle was limited to a maximum of 70% whereas a specific conversion rate for other cases was not used as the conversion value does not impact the results shown. This conversion was used to serve as a conservative comparison against the prior art and in no way implies that higher conversion is not contemplated for the inventive system. To calculate the energy lost from the hot gas as it is cooled in the absorption apparatus or subsystem, it was assumed that the absorption apparatus gas inlet temperature was 140° C.
The results of this computer modelling, namely gas compositions (shown in mole %) at various points in the gas stream, flow amounts (shown as number of moles of gas [rounded off]), and gas temperatures (shown in ° C.) appear on the aforementioned
From the above Examples, it is clearly apparent that the reactor temperature can be controlled independently and in a simple manner since only the amount in the first recycle circuit need be adjusted and hence there need be no impact on the rest of the process.
Further, more energy is recovered from the gas in the reactor gases heat exchanger since the gas volume entering the absorption apparatus or subsystem is reduced and less energy is transferred to the absorber acid as the gas is cooled from the gas inlet temperature to the absorber liquid temperature.
Further still, conversion of sulfur dioxide to sulfur trioxide in the sulfuric acid production system embodiment can be maximized in the contact apparatus without impacting reactor temperature thereby allowing complete freedom in the design and operation of the contact apparatus.
Note also that the mole ratios of gases in the second recycle circuit compared to the reactor outlet gases in the inventive embodiments of
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/CA2022/051649 | 11/8/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63285944 | Dec 2021 | US |
