Patent Application
20240417256
The present invention relates to a process for production of sulfuric acid using an amount of O2 enriched gas, a process for co-production of sulfuric acid and other chemicals, especially ammonia and process plants for such processes.
The abundance of nitrogen in atmospheric air may result in excessive process equipment size for processes involving oxidation with atmospheric air as oxidant, as the inert nitrogen will require additional process volume, which is related to increased costs of equipment. At the same time the additional process volume also has the benefit of providing a heat sink for exothermal reactions, which may keep the temperature in a desirable range. While oxygen enriched air or pure oxygen has been used in select cases. commonly the cost of O2 is too high to be a commercially viable path for reduction of process equipment size. Furthermore, the high amount of heat released during the oxidation process will lead to excessive process temperatures, which commonly also is a problem requiring a solution.
We have now identified that the in a hydrogen-based society, the production of H2 by electrolysis and the use of NH3 as an energy vector will both provide an increased availability of O2 and O2 enriched gas at moderate cost, which motivates identifying beneficial application of O2 enriched gas. In sulfuric acid production, choosing a catalytically active material which is active at elevated temperatures, such O2 enriched gas may be used in the SO2 oxidation process, together with O2 from electrolytic sources or O2 from air separation for NH3 production.
In the following the term lean sulfuric acid shall be understood as sulfuric acid having the ability to absorb SO3, and not imply an explicit concentration of H2SO4.
In the following the term concentrated sulfuric acid shall be understood as any sulfuric acid having absorbed SO3 which depending on the conditions may be either below the concentrations matching trade definitions of concentrated sulfuric acid or be oleum, and thus not imply an explicit concentration of H2SO4.
In the following the unit Nm3 shall be understood as “normal” m3, i.e. the amount of gas taken up this volume at 0° C. and 1 atmosphere.
Where concentrations are stated in vol % this shall be understood as volumetric % (i.e. molar percentages for gases).
Streams may in the following be designated by a reaction, e.g. an oxidized process gas stream. Such terminology shall not be construed as a limitation to completely reacted streams, but merely as an identification of the stream for referencing.
A first aspect of the disclosure relates to a process for conversion of SO2 to H2SO4 comprising the steps of
Preferably said material catalytically active in oxidation of SO2 to SO3 comprises an active phase in which the weight ration of vanadium to other metals is at least 2:1 supported on a porous carrier comprising at least 25 wt % crystalline silica.
This has the associated benefit of such a process having a lower process volume compared to a similar process employing atmospheric air, and a potential for a process. The metals in the catalytically active material will mainly be vanadium and alkali metals, whereas other metals, including iron, are generally only present in trace amounts.
A second aspect of the disclosure relates to a process according to the first aspect further comprising the step of recycling an amount of oxidized process gas or desulfurized process gas to contact said first material catalytically active in oxidation of SO2 to SO3. This has the associated benefit of enabling temperature moderation by providing a heat sink by the recycled process gas.
A third aspect of the disclosure relates to a process according to an aspect above, wherein oxidation conditions involve a pressure above 2 Barg, 5 Barg or 10 Barg. This has the associated benefit of reducing the gas volume and thus the required volume and cost of process equipment.
A fourth aspect of the disclosure relates to a process according to an aspect above wherein oxidation conditions involve a pressure below 100 Barg, 50 Barg or 20 Barg. This has the associated benefit of operation at a pressure matching ammonia and methanol production while avoiding excessive demands and cost of process equipment.
A fifth aspect of the disclosure relates to a process according to an aspect above, wherein less than 100 Nm3 process gas per ton sulfuric acid produced, such as 50 Nm3/t or 10 Nm3/t is released to the atmosphere.
This has the associated benefit of minimizing the stack size and the perceived environmental impact.
A sixth aspect of the disclosure relates to a process according to an aspect above, wherein the first material catalytically active in oxidation of SO2 to SO3 is characterized by comprising vanadium pentoxide (V2O5), sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate, one or more alkali metals on a porous carrier comprising at least 50 wt % crystalline silica. This has the associated benefit of such a material being stable and catalytically active at elevated temperatures.
A seventh aspect of the disclosure relates to a process according to an aspect above wherein an amount of the process gas stream is provided from an O2 enriched gas stream comprising at least 50 vol % O2, such as at least 90 vol % O2, or at least 95 vol % O2. This has the associated benefit of providing a gas stream with an amount of O2 with reduced volume compared to atmospheric air with 21% O2.
An eighth aspect of the disclosure relates to a process according to an aspect above further comprising the step of directing an amount of elemental sulfur and the O2 enriched gas stream to a sulfur incinerator, to provide said process gas comprising SO2. This has the associated benefit of providing SO2 and heat from the elemental sulfur.
A ninth aspect of the disclosure relates to a process according to an aspect above wherein an amount of the O2 is provided by electrolysis of H2O. This has the associated benefit of the O2 enriched gas stream being provided as a side stream at moderate costs from hydrogen production.
A tenth aspect of the disclosure relates to a process according to the ninth aspect above wherein electrolysis of H2O is carried out in a process at a temperature above 400° C., such as a solid oxide electrolysis process. This has the associated benefit of the heat integration by transferring heat from sulfuric acid production to electrolysis is beneficial.
An eleventh aspect of the disclosure relates to a process according to an aspect above, wherein said process gas stream comprising at least 15 vol % SO2, originates from incineration of sulfur or sulfur recuperation from smelter operation. This has the associated benefit of efficiently providing a rich SO2 stream from a stable source.
A twelfth aspect of the disclosure relates to a process according to an aspect above wherein at least an amount of the O2 enriched gas stream is provided by separation of atmospheric air. This has the associated benefit the O2 enriched gas stream being provided as a side stream at moderate cost from air separation, e.g. in NH3 production.
A thirteenth aspect of the disclosure relates to a process for co-production of NH3 and H2SO4 involving a process for production of H2SO4 according to the twelfth aspect where the separation of atmospheric air further provides an N2 enriched gas stream which is directed to a plant for production of NH3, said process optionally involving the production of ammonium sulfate from NH3 and H2SO4.
This has the associated benefit of integration between the NH3 production process providing a stream of O2 enriched gas and a the H2SO4 production process consuming such a stream.
A fourteenth aspect of the disclosure relates to a process according to the thirteenth aspect wherein heat is released during oxidation of SO2 to SO3 and directed to be used in NH3 production. This has the associated benefit of reducing the cost of the energy intensive NH3 production process, by provision of energy to the NH3 production. The value of heat is typically higher, the higher the pressure or temperature steam.
A fifteenth aspect of the disclosure relates to a process for production of fertilizer comprising ammonium and phosphate, comprising a process for co-production of NH3 and H2SO4 according to the thirteenth or fourteenth aspect and the process of producing phosphate from a phosphor source, employing the produced H2SO4. This has the associated benefit of reducing the cost of the process by integration of the sub-processes.
A process plant for production of H2SO4 comprising a means for production of an O2 enriched stream having an O2 enriched stream outlet, an optional sulfur incinerator having at least one inlet and an outlet, a reactor containing a material catalytically active in SO2 oxidation at temperatures above 700° C. having an inlet and an outlet in fluid communication with the gas inlet of an absorber, having a liquid inlet for lean sulfuric acid, a liquid outlet for withdrawal of concentrated sulfuric acid and a gas outlet, characterized in the O2 enriched stream outlet being in fluid communication with the inlet of the reactor, or if the optional sulfur incinerator is present, with an inlet to the sulfur incinerator, having the outlet in fluid communication with the inlet of the reactor. This has the associated benefit of enabling a process with reduced process volume, due to the use of O2 enriched gas.
Sulfuric acid is the most abundantly produced chemical worldwide. One common process for production of sulfuric acid is known as the dry gas method. In general, for this process, elemental sulfur is combusted to form SO2 which is catalytically oxidized to SO3. The SO3 in the process gas is converted to concentrated sulfuric acid by absorption in lean sulfuric acid.
The combustion of sulfur and the catalytic oxidation of SO2 both require oxygen, typically supplied in the form of atmospheric air. However, if atmospheric air, containing inert N2, is used, a large amount of flue gas is released from the process. A typical dry gas sulfuric acid plant will release 1700 Nm3 flue gas/ton sulfuric acid produced. The flue gas will contain low levels of compounds of environmental concern, but will still be required to be released from a high stack, which will have CAPEX cost. In addition, thermal and mechanical energy will also be related to handling the large volume of inert gas.
By using oxygen enriched gas, the plant volume may be reduced, but a lower limit exists in this respect, since the SO2 oxidation process is exothermal and conventional SO2 oxidation catalysts with stable operation above 650° C. have not been available. Therefore, a practical limit of 14% SO2 has been common to stay under that temperature, which is operational with only moderate O2 enrichment. To control the temperature in the SO2 oxidation reactor, it has been proposed to recirculate an amount of cooled SO3 rich product gas, to function as a combined heat sink and reaction moderator, which may enable operation at 25 vol % SO2. The temperature may also be moderated by staged addition of O2. In addition, the reactor temperature is commonly controlled by cooling between beds of catalytically active material. This has the effect of withdrawing thermal energy to other processes, of protecting catalytically active material against excessive temperature peaks and of pushing the reaction towards additional conversion, as the SO2/SO3 equilibrium favors SO3 at lower temperatures.
As an alternative we have now identified that a material catalytically active in SO2 oxidation which may operate up to 750° C., also enables operation with 35 vol % SO2 or even higher SO2 concentrations with minor process modifications, as this would release an amount of thermal energy corresponding to this temperature. We have developed one such material catalytically active in oxidation of SO2 to SO3 and stable at elevated temperature comprising vanadium pentoxide (V2O5), sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate, one or more alkali metals on a porous carrier comprising at least 25 wt % crystalline silica or 50 wt % crystalline silica. Such a material catalytically active in SO2 oxidation at high temperature may be used in one bed or in multiple beds depending on the specific process conditions. In addition other, low temperature beds may operate with a standard material catalytically active in oxidation of SO2 to SO3 such as a catalyst comprising vanadium pentoxide (V2O5), sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate, one or more alkali metals on a porous carrier comprising at least silica in the form of diatomaceous earth—which provides a higher surface area—and thus activity compared to the catalytically active material comprising the more stable crystalline silica. In active use the V2O5 on the SO2 oxidation catalyst is in the form of a vanadium sulfate melt. Furthermore, noble metal based catalytically active materials are also known for use in the oxidation of SO2 to SO3, and while these may be partially deactivated at elevated temperatures, they may have sufficient activity for the initial conversion.
Such operation with 35 vol % SO2 may either be carried out by continuous admission of an amount of N2 or by recirculation of SO3 product or N2. Oxygen enriched gas may be provided, either from the outlet from electrolysis producing hydrogen from water and electricity, or from an air separation unit. Electrolysis will provide close to 100% O2, and an air separation unit may provide from 90% to 99.5% pure O2. If an amount of desulfurized process gas is recycled, an amount of inert process gas may build up, but may be minimized by releasing a minor amount as purge, which may be treated by scrubbing or other conventional methods. Assuming combined use of O2 enriched air and purge, such that the amount of N2 and O2 are equal, the process gas volume, and thus equipment size, may be reduced by more than a factor of 2. In addition, the recycling of product gas may also mean that such a process plant may be pressurized, since the release to the atmosphere of only a minimal amount of gas will also minimize the energy lost in pressurization. A pressure around 10 barg, will result in a factor 10 reduction of size of process equipment, but depending on the choice of material, higher pressure and increased reduction of size may be possible, but practical construction of equipment may limit the pressure to below 50 barg or 100 barg, which is required for compatibility with processes for production of methanol and ammonia. In total the volume of many parts of the plant may be reduced by a factor 20 by operation with pure O2 and a pressure of 10 barg. In theory, the process may operate with only release of sulfuric acid and no release of flue gas, but as mentioned, in practice a small purge may be required to withdraw impurities such as nitrogen and carbon dioxide inter alia originating from the combustion of sulfur, with an amount of impurities.
The operation at elevated temperature will mean that the temperature and/or pressure of steam collected is increased, to the benefit of the locations where steam is used. In addition, the lower process plant size and the lower amount of flue gas released (if any) will also mean that the thermal efficiency of the process is increased.
The recycle of the process gas leaving the absorber also has the benefit that the absorption does not need to be 100% quantitative, and thus only a single absorber is required.
As no water enters the process, the absorber with recirculating acid will require an addition of water to hydrate the sulfur trioxide to form sulfuric acid.
The process may also be configured for addition of water up to or slightly above a ratio of water and SO3 of 1:1, and condensation of an amount of the resulting sulfuric acid, prior to the absorption of SO3 in lean sulfuric acid. This has the benefit of enabling withdrawing heat of condensation and hydration separately from the absorption process, such that temperature control in the absorber is simplified.
The process plant for production of sulfuric acid will often be positioned in a factory for production of fertilizer, since the phosphate used in fertilizer is commonly produced by dissolving phosphate rock by use of sulfuric acid. In addition to phosphate, ammonium is a common constituent in fertilizer, which is produced from ammonia.
Ammonia production is carried out catalytically at elevated temperature from atmospheric nitrogen and hydrogen. Traditionally the hydrogen has been produced from fossil sources, but an alternative will be to produce sustainable hydrogen electrolytically from water and a sustainable source of electricity and will in addition to hydrogen provide oxygen. In addition, as nitrogen is produced by separation of air in oxygen and nitrogen, excess oxygen is available from an ammonia plant, which conveniently may be employed in a sulfuric acid plant as described above. Furthermore, the heat released in the exothermal sulfuric acid process may be transferred to the ammonia plant, operating at about 850° C., and if energy efficient solid oxide electrolyzers are used they will also conveniently be able to employ thermal energy to ensure operation at elevated temperature.
Furthermore, other hydrogen consuming processes may be relevant sources of pure oxygen—including methanol synthesis and synthetic fuel produced either from methanol or by the Fischer Tropsch process, as well as refineries hydrogenating renewable feedstocks with electrolytically produced hydrogen.
In
In
Two examples are presented, for comparison of traditional operation with operation according to the present disclosure.
In both examples 27 t/h sulfur is directed to the process which provides 83 t/h sulfuric acid.
Table 1 shows an example corresponding to
According to the example a purge is not carried out, but a presence of nitrogen is assumed. If the oxygen source is air separation, the oxygen enriched gas may comprise an amount of nitrogen, which increases with recycle. In this case a small purge is necessary. In practice the place of the nitrogen may be taken by recycled SO3, but for computational convenience a presence of nitrogen as diluent is assumed.
Depending on the impurities (which in addition to nitrogen, also may include CO2 and H2O from combustion of hydrocarbon impurities in the sulfur) of a small purge may be required. Assuming an impurity corresponding to 7% of the O2, the purge will be 3270 Nm3/h (12% of the recycle), and assuming 0.5%, the purge will be 234 Nm3/h (0.85% of the recycle), which is 40 Nm3/t sulfuric acid and 2.8 Nm3/t sulfuric acid respectively. The purged stream must be purified by scrubbing or other means, as it will contain some SO2 and SO3.
The total amount of catalyst is 206 m3, and due to the temperature the catalyst of beds 1 and 2 is of the type V2O5 sulfate on crystalline silica whereas the rest is V2O5 sulfate on diatomaceous earth.
The process pressure is 10 bar, and thus the volume of the incinerator, heat exchangers and the absorber may be reduced, but a pressure shell must be provided.
For comparison, Table 2 shows an example corresponding to
The total amount of catalyst is 405 m3, and all catalyst is of the type of V2O5 on non-crystalline silica, such as diatomaceous earth.
The process pressure is 1.3 bar, and thus the need for a pressure shell is avoided. The volume of purified process gas released to the environment is 137,217 Nm3/h, which is 1658 Nm3/t sulfuric acid.
When comparing the two examples, the use of a heat stable catalytically active material enables use of pure oxygen as oxidant. The result is a reduction of catalyst volume to almost half, due to a combination of increased reaction rate due to increased temperature, increased SO2 partial pressure and an acceptable lower conversion, due to the recycle. Furthermore, the use of pure oxygen reduces the volume of process gas released to the environment by 99.8%, which also is relevant for the size of the stack used in the plant.
As the temperatures of the process with pure oxygen are higher, the value of heat integration to other plants will also increase. This will be beneficial for ammonia production or methanol, and generally if the pure oxygen is obtained from a process plant, where hydrogen is produced electrolytically by high temperature electrolysis in a solid oxide electrolyzer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21205190.8 | Oct 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/080166 | 10/28/2022 | WO |
