Patent Description:
This patent relates to methods and systems to remove sulfur-containing compounds from a gaseous stream, for example sulfur-containing streams generated during wellbore drilling or in a gas-oil separation plant.

As governmental environmental restrictions become increasingly stringent, the removal of sulfur-containing compounds from emissions is increasingly important. In some instances, sulfur recovery minimums are as high as <NUM>%. A simplified and reliable tail gas treatment of sulfur recovery units is therefore needed.

<CIT> describes a process plant that includes a Claus reaction furnace, a means of Claus gas cooling, a Claus conversion section, a means for Claus tail gas oxidation and a sulfuric acid section. A sulfuric acid outlet of the sulfuric acid section is in fluid communication with an inlet of said Claus reaction furnace, as well as a related process.

Provided herein are systems and methods for removing the sulfur-containing compounds from a gas stream, for example, from the tail gas of a Claus process.

A method for treating a tail gas of a Claus process to remove sulfur-containing compounds includes combusting a tail gas of a Claus process in an excess of oxygen gas is defined in claim <NUM>, wherein the excess of oxygen gas includes a number of moles of oxygen exceeding the number of moles of oxygen required to fully combust the sulfur-containing compounds. Combusting the tail gas of the Claus process in an excess of oxygen gas yields a thermal oxidizer effluent, wherein the thermal oxidizer effluent includes sulfur dioxide, water vapor, and oxygen. The method includes cooling the thermal oxidizer effluent to yield a cooled thermal oxidizer effluent, flowing the cooled thermal oxidizer effluent to a quench tower, contacting the cooled thermal oxidizer effluent in the quench tower with a dilute aqueous acid quench stream to condense water vapor and dissolve the sulfur dioxide to yield sulfurous acid, hydrated sulfur dioxide, or a combination of sulfurous acid and hydrated sulfur dioxide, oxidizing the sulfurous acid or hydrated sulfur dioxide with oxygen from the thermal oxidizer effluent to yield a produced dilute aqueous acid stream that includes sulfuric acid, cooling the produced dilute aqueous acid stream to yield a cooled dilute aqueous acid stream, splitting the cooled dilute aqueous acid stream into the dilute aqueous acid quench stream and a dilute aqueous acid buffer stream, and flowing the dilute aqueous acid quench stream to the quench tower.

This aspect, taken alone or combinable with any other aspect, can include the following features. The method further includes flowing the dilute aqueous acid buffer stream to a water treatment unit, wherein the water treatment unit yields a permeate that is substantially water and a retentate that is concentrated sulfuric acid.

This aspect, taken alone or combinable with any other aspect, can include the following features. Contacting the cooled thermal oxidizer effluent in the quench tower with a dilute aqueous acid quench stream to condense water vapor and dissolve the sulfur dioxide to yield a produced dilute aqueous acid stream that includes sulfurous acid, hydrated sulfur dioxide, or a combination of sulfurous acid and hydrated sulfur dioxide yields a produced dilute aqueous acid stream that includes between about <NUM> and about <NUM> wt% sulfuric acid.

This aspect, taken alone or combinable with any other aspect, can include the following features. Splitting the cooled dilute aqueous acid stream into the dilute aqueous acid quench stream and the dilute aqueous acid buffer stream includes splitting the cooled dilute aqueous acid stream into the dilute aqueous acid quench stream and a dilute aqueous acid buffer stream, wherein the dilute aqueous acid buffer stream includes approximately the same volume as the water condensed from the thermal oxidizer effluent.

This aspect, taken alone or combinable with any other aspect, can include the following features. Splitting the cooled dilute aqueous acid stream into the dilute aqueous acid quench stream and a dilute aqueous acid buffer stream includes splitting the cooled dilute aqueous acid stream evenly, wherein the dilute aqueous acid quench stream and the dilute aqueous acid buffer stream each comprise approximately <NUM>% of the cooled dilute aqueous acid stream.

This aspect, taken alone or combinable with any other aspect, can include the following features. The method further includes contacting the sulfur dioxide with a fresh water stream, oxidizing sulfurous acid, hydrated sulfur dioxide, or both into sulfuric acid with the excess of oxygen in the thermal oxidizer effluent, recovering a portion of the fresh water stream, monitoring the pH of the recovered water, and in response to a pH of the recovered water that is less than <NUM>, flowing the recovered water to the water treatment unit.

This aspect, taken alone or combinable with any other aspect, can include the following features. The method further includes flowing the permeate of the water treatment unit to the quench tower as the fresh water stream.

This aspect, taken alone or combinable with any other aspect, can include the following features. The retentate of the water treatment unit is flowed to a sulfur recovery unit to enrich a Claus furnace in oxygen.

A system for removing sulfur-containing compounds from a gas includes a thermal oxidizer configured to receive a gas comprising sulfur-containing compounds and to combust the sulfur-containing compounds in an excess of oxygen gas is defined in claim <NUM>, wherein the excess of oxygen gas comprises a number of moles of oxygen exceeding the number of moles of oxygen required to fully combust the sulfur-containing compounds, to yield a thermal oxidizer effluent that contains sulfur dioxide. The system includes a waste heat recovery system coupled to the thermal oxidizer and configured to cool the thermal oxidizer effluent to yield a cooled thermal oxidizer effluent. The system includes a quench tower coupled to the waste heat recovery system and configured to receive the cooled thermal oxidizer effluent, and contact the cooled thermal oxidizer effluent with a dilute aqueous acid quench stream to dissolve the sulfur dioxide to sulfurous acid, hydrated sulfur dioxide, or a combination of sulfurous acid and hydrated sulfur dioxide, oxidize the sulfurous acid, hydrated sulfur dioxide, or both to sulfuric acid, and yield a produced dilute aqueous acid stream comprising sulfuric acid. The system includes a cooler system coupled to the quench tower, wherein the quench tower is configured to flow the produced dilute aqueous acid stream to the cooler system. The cooler system is configured to receive the produced dilute aqueous acid stream, cool the produced dilute aqueous acid stream to yield a cooled dilute aqueous acid stream, split the cooled dilute aqueous acid stream into the dilute aqueous acid stream, split the cooled dilute aqueous acid stream into the dilute aqueous acid quench stream and a dilute aqueous acid buffer stream, and flow the dilute aqueous acid quench stream to the quench tower.

This aspect, taken alone or combinable with any other aspect, can include the following features. The system includes a water treatment unit, wherein the water treatment unit is coupled to the cooler system and configured to receive the dilute aqueous acid buffer stream from the cooler system, and wherein the water treatment unit is configured to yield a permeate stream that is substantially water and a retentate stream that is concentrated sulfuric acid.

This aspect, taken alone or combinable with any other aspect, can include the following features. The system includes a buffer tank coupled between the cooler system and the water treatment unit, wherein the buffer tank is configured to receive the dilute aqueous acid buffer stream and to flow the dilute aqueous acid buffer stream to the water treatment unit.

This aspect, taken alone or combinable with any other aspect, can include the following features. The buffer tank includes a vent, wherein the vent is coupled to the quench tower and configured to flow undissolved gases to the quench tower.

This aspect, taken alone or combinable with any other aspect, can include the following features. The waste heat recovery system is configured to cool the thermal oxidizer effluent to a temperature of about <NUM> °F (<NUM>).

This aspect, taken alone or combinable with any other aspect, can include the following features. The dilute aqueous acid quench stream has a temperature between about <NUM> °F (<NUM>) and about <NUM> °F (<NUM>).

This aspect, taken alone or combinable with any other aspect, can include the following features. The produced dilute aqueous acid stream comprises between about <NUM> and about <NUM> wt% of sulfuric acid.

This aspect, taken alone or combinable with any other aspect, can include the following features. The water treatment unit is a reverse osmosis membrane treatment unit, and wherein the reverse osmosis membrane treatment unit yields a permeate that is substantially water and a retentate that is about <NUM> to about <NUM> wt% sulfuric acid.

This aspect, taken alone or combinable with any other aspect, can include the following features. The retentate is flowed to a sulfur recovery unit to enrich a Claus furnace in oxygen.

This aspect, taken alone or combinable with any other aspect, can include the following features. The quench tower includes an upper section, a mid-section, and a lower section, wherein the upper section and the lower section are connected in the mid-section by a perforated plate, wherein the perforated plate redistributes the dilute aqueous acid quench stream on the lower section of the quench tower.

This aspect, taken alone or combinable with any other aspect, can include the following features. The quench tower includes an upper section, a mid-section, and a lower section, wherein the upper section and the lower section are connected in the mid-section by a plate, wherein the plate comprises bubble caps, wherein the plate is configured to collect liquid and allow gas to pass through the plate.

This aspect, taken alone or combinable with any other aspect, can include the following features. The system includes a second buffer tank coupled between the quench tower and a second cooler, wherein the second buffer tank is configured to receive recovered water from the quench tower, and wherein the second buffer tank includes a second vent, and the second vent is coupled to the quench tower and configured to flow undissolved gases to the quench tower. The system includes a fresh water stream, wherein the fresh water stream enters the quench tower at the upper section of the quench tower, and wherein the plate is configured to recover fresh water and flow the recovered water to the second buffer tank. The system includes a second cooler, wherein the second cooler is configured to cool the recovered water from the second buffer tank and flow the cooled recovered water to the quench tower as the fresh water stream. The system includes a pH monitor configured to monitor the pH of the recovered water, wherein the second buffer tank is configured to flow the recovered water to the buffer tank via a valve when the pH of the recovered water is below <NUM>, and wherein the water treatment unit is configured to flow the permeate stream to the quench tower as the fresh water stream.

The details of one or more implementations of the disclosure are set forth in the accompanying drawings and the description that follows.

Reference will now be made in detail to certain embodiments of the disclosed subject matter, examples of which are illustrated in part in the accompanying drawings. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.

Provided in this disclosure, in part, are methods and systems for removing sulfur compounds from a gas stream, for example, the tail gas of a Claus process. The techniques described in this disclosure can be implemented to more efficiently treat the tail gas of a Claus process compared to currently available methods. Compared to currently available methods, the techniques described here offer higher percentage of sulfur recovery and are comparatively less expensive.

A Claus process is a method of removing the hydrogen sulfide from natural gas, crude oil, or other industrial fluids or gases. The Claus process consists of two steps: <MAT> <MAT>.

The tail gas of a Claus process contains sulfur dioxide (SO<NUM>), hydrogen sulfide (H<NUM>S), carbon dioxide (CO<NUM>), nitrogen gas (N<NUM>), hydrogen gas (H<NUM>), water (H<NUM>O), carbon monoxide (CO), carbonyl sulfide (COS), traces of carbon sulfide (CS<NUM>), and allotropes of sulfur (S<NUM>, S<NUM>, and S<NUM>). Treatment or separation of the components of the tail gas is difficult.

Described herein are methods and systems for treating the tail gas that contains sulfur compounds, for example the tail gas of a Claus process. The methods and systems are capable of removing a multitude of different sulfur-containing compounds from a tail gas by converting the sulfur compounds to SO<NUM>, contacting the SO<NUM> with an aqueous solution dissolve the SO<NUM>, and oxidizing the hydrated SO<NUM> to sulfuric acid. The produced sulfuric acid can then be monetized or used in subsequent processes. For example, the produced sulfuric acid can be used in dyes, paper, glass, astringents, batteries, drain cleaners, metal processing, and fertilizer manufacture.

In some implementations, the tail gas of a Claus process is combusted with a fuel gas, for example, CH<NUM> or C<NUM>H<NUM>, in a thermal oxidizer. The combustion occurs with an excess of oxygen gas. An excess oxygen gas includes a number of moles of oxygen exceeding the number of moles of oxygen required to fully combust the sulfur-containing compounds. In some implementations, the oxygen gas is supplied by ambient air. The thermal oxidizer yields an exhaust gas, i.e., a thermal oxidizer effluent, that contains about <NUM>-<NUM> vol% of O<NUM>, along with SO<NUM>, CO<NUM>, N<NUM>, H<NUM>O, and traces of CO. This effluent is cooled by contact with a chilled acidic water. This contact also condenses water vapor in the exhaust gas. Further, SO<NUM> from the thermal oxidizer effluent dissolves and hydrates in water, and, in the aqueous phase, reacts with the excess of oxygen present in the thermal oxidizer effluent to yield to a mixture of sulfurous acid (H<NUM>SO<NUM>) and sulfuric acid (H<NUM>SO<NUM>). The oxidation of SO<NUM> is thermodynamically allowed in water, however, this reaction will not occur in the gas phase. The generated sulfurous and sulfuric acids in the chilled acidic water yield an aqueous sulfurous/sulfuric mixture acid stream. The aqueous sulfurous/sulfuric acid stream is cooled further and split into two streams. A first stream is sent back into the quench tower as the chilled acidic water coolant. A second stream is processed to yield a weakly acidic water and a concentrated sulfurous/sulfuric acid stream. The weakly acidic water can be send to an evaporation pond or reused. The concentrated sulfurous/sulfuric acid stream can be monetized or sent to a sulfur recovery unit (SRU) to enrich a Claus furnace in oxygen. In some implementations, this can help a plant, business, commercial enterprise, or other emissions-producing entity achieve sulfur recovery or emission targets.

Advantageously, this approach is capable of removing a wide variety of sulfur-containing species in the tail gas of a Claus process by transforming sulfur-containing species into sulfur dioxide via combustion, followed by subsequent transformation into sulfuric acid in a quench tower via absorption and oxidation with an excess of oxygen.

<FIG> is an example schematic of a system <NUM> for removing sulfur-containing compounds from a gas. The system <NUM> includes a one-stage quench tower <NUM> for SO<NUM> removal from thermal oxidizer effluent <NUM>. The thermal oxidizer effluent <NUM> is the result of the complete combustion of hydrogen sulfide and other sulfur-containing compounds, for example, COS and CS<NUM>, in a thermal oxidizer <NUM>. The thermal oxidizer effluent <NUM> contains N<NUM>, SO<NUM>, O<NUM>, H<NUM>O, CO<NUM>, and CO. The stars (*) shown in <FIG> indicate the relative concentrations of the species in the stream, wherein four stars (****) represents a high concentration, three stars (***) represents a high-intermediate concentration, two stars (**) represents a low-intermediate concentration, and one star (*) represents a low concentration. The thermal oxidizer effluent <NUM> includes a high concentration of N<NUM>, a high-intermediate concentration of H<NUM>O and CO<NUM>, a low-intermediate concentration of O<NUM>, and a low concentration of CO and SO<NUM>. In some implementations, the concentration of SO<NUM> in the thermal oxidizer effluent <NUM> is <NUM> - <NUM> mol%. In some implementations, the concentration of O<NUM> in the thermal oxidizer effluent <NUM> is <NUM>-<NUM> vol%.

The thermal oxidizer effluent <NUM> exits the thermal oxidizer <NUM> at a temperature of about <NUM> °F (<NUM>). In some implementations, the thermal oxidizer effluent is cooled to a temperature of about <NUM> °F (<NUM>) using a waste heat recovery system <NUM> before entering the quench tower <NUM>. The thermal oxidizer effluent <NUM> is routed to the bottom section <NUM> of a quench tower <NUM>. The thermal oxidizer effluent is then contacted by the dilute aqueous acid quench stream <NUM>. The thermal oxidizer effluent is further cooled by contact with the dilute aqueous acid quench stream <NUM>.

The dilute aqueous acid quench stream <NUM> enters from the upper section <NUM> of the quench tower <NUM>. The dilute aqueous acid quench stream <NUM> has a temperature between about <NUM> °F (<NUM>) and about <NUM> °F (<NUM>). In some implementations, the dilute aqueous acid quench stream <NUM> has a temperature of about <NUM> °F (<NUM>).

In the quench tower, sulfur dioxide from the thermal oxidizer effluent <NUM> hydrates and reacts readily with the excess oxygen present in the thermal oxidizer effluent (E° =+<NUM> V), as shown in Equation <NUM>: <MAT>.

The product of this reaction is sulfuric acid. The rate of the reaction is dependent on the concentration of hydrated sulfur dioxide and independent on the concentration of oxygen, whether the oxygen is dissolved or not. The rate of the oxidation reaction can be expressed as in Equation <NUM>: <MAT>.

The rate constant, k, with units of <MAT>, can be expressed as in Equation <NUM>: <MAT> where R is the ideal gas constant and T is the temperature in Kelvin. The rate of the reaction shown in Equation <NUM> increases as the temperature of the reaction increases. However, the rate of the reaction is not altered by the presence of sulfuric acid. The reaction as shown in Equation <NUM> takes place in the packing zone of the quench tower <NUM>. The packing zone is a section that offers a large surface to facilitate contact between the liquid phase, i.e., the acidic water, and the gas phase. This also facilitates the removal of SO<NUM> from the gas phase. A packing zone can vary in material (e.g. plastic, ceramic, metal), in morphology (e.g. rings, beads, saddles), and in organization (i.e. structured or random). The packing zone also induces mixing in each phase, to avoid any concentration polarization in the gas phase and/or the liquid phase. After hydration of the SO<NUM>, oxidation of the SO<NUM> occurs in the water phase. Other species present in the thermal oxidizer effluent (N<NUM>, unreacted O<NUM>, uncondensed H<NUM>O, and CO<NUM>) exit the top of the quench tower as the quench tower effluent <NUM>. The stars in <FIG> indicate the relative concentrations of these species, as discussed herein. The quench tower effluent <NUM> is sent to a flare stack, mitigating any SO<NUM> breakthrough that can occur during upset conditions. Upset conditions occur when SO<NUM> is not successful treated in the quench tower, for example, when a portion of the SO<NUM> remains in the gas phase due to poor contacting between the gas and liquid phases (e.g. channeling of the gas stream or lowering of liquid-to-gas ratio).

The cooling action of the dilute aqueous acid quench stream <NUM> also condenses water vapor in the thermal oxidizer effluent <NUM>. The mixture of the produced sulfuric acid in the condensed water and the dilute aqueous acid quench stream yields a produced dilute aqueous acid stream <NUM>. The mass concentration of sulfuric acid in the produced dilute aqueous acid stream <NUM> is between about <NUM> and about <NUM> wt%. The produced dilute aqueous acid stream <NUM> exits the lower section of the quench tower and is sent to a cooler <NUM> using a pump <NUM>. In some implementations, the cooler <NUM> is a heat exchanger. In some implementations, the cooler <NUM> is an air cooler. The produced dilute aqueous acid stream <NUM> is cooled from about <NUM> °F (<NUM>) to about <NUM> °F (<NUM>) to yield a cooled dilute aqueous acid stream <NUM>. The cooled dilute aqueous acid stream <NUM> exits the cooler <NUM> and is split into the dilute aqueous acid quench stream <NUM> and a dilute aqueous acid buffer stream <NUM>. In some implementations, this split is performed by monitoring the flowrate of the cooled dilute aqueous acid stream <NUM> and by diverting a part of this flow using a controller and controlled valve (not shown). The split can be based on the desired concentration of sulfuric acid in the produced dilute aqueous acid stream <NUM>, which in turn determines how much of the dilute aqueous acid quench stream <NUM> is required in quench tower <NUM>. Most of the cooled dilute aqueous acid stream <NUM> (approximately <NUM> - <NUM> wt%) is sent back to the upper section <NUM> of the quench tower <NUM> as the dilute aqueous acid quench stream <NUM>. The dilute aqueous acid buffer stream <NUM> includes the remaining small portion (approximately <NUM> - <NUM> wt%) of the cooled dilute aqueous acid stream <NUM>. This small portion is approximately the same as the amount of water condensed in the quench tower <NUM>, ensuring that the amount of water in the quench tower remains constant, and that the produced dilute aqueous acid stream <NUM> maintains a constant concentration of sulfuric acid.

The dilute aqueous acid buffer stream <NUM> is sent to a buffer tank <NUM>. Any unreacted SO<NUM> will continue to react readily in the aqueous acid buffer stream with O<NUM> from the air. The buffer tank <NUM> includes a vent <NUM>. If the concentration of the SO<NUM> and sulfuric acid in the dilute aqueous acid buffer stream is low, the buffer tank can be vented to the open air. The venting process can ensure that any liquid sent to a subsequent membrane process is free from gas and minimizes degassing in a subsequent membrane process. In addition, the vent can be used to equilibrate the pressure in the buffer tank when the second pump <NUM> is in operation. In some implementations, the vent <NUM> can be connected to the quench tower <NUM>, and vented gases <NUM> can be routed to the upper section <NUM> of the quench tower <NUM>. The vented gases <NUM> enter the quench tower <NUM> below the dilute aqueous acid quench stream <NUM>. Venting the buffer tank <NUM> to the quench tower <NUM> recycles undissolved gases, for example, CO<NUM> or traces of SO<NUM>, to the quench tower and increases the yield of sulfuric acid in the produced dilute aqueous acid stream <NUM>. In some implementations, in order to avoid any SO<NUM> emission, the vent <NUM> is equipped with a small column where a clean water stream is circulated, or a water trap. In some implementations, a blanket of inert atmosphere is injected into the buffer tank via the vent <NUM>.

In some implementations, the dilute aqueous acid buffer stream <NUM> in the buffer tank <NUM> exits the buffer tank and is routed to a water treatment unit <NUM> using a second pump <NUM>. The water treatment unit <NUM> is configured to remove sulfurous and sulfuric acids from the dilute aqueous acid buffer stream <NUM>. In some implementations, the water treatment unit <NUM> is a reverse osmosis membrane treatment unit, a nanofiltration unit, or a combination of nanofiltration and reverse osmosis membranes. The water treatment unit can concentrate sulfuric acid up to <NUM>-<NUM> wt%. The water treatment unit can yield a permeate <NUM> that is mainly water. The permeate <NUM> can have a concentration of sulfuric acid that ranges from <NUM>-<NUM> wt%, with a pH that ranges from about <NUM> to about <NUM> respectively. The permeate <NUM> can be reused in the facility or sent to an evaporation pond. The water treatment unit also yields a retentate stream <NUM> that is mainly concentrated sulfuric acid (approximately <NUM>-<NUM> wt%). The retentate <NUM> can be monetized or sent to a sulfur recovery unit (SRU) to enrich a Claus furnace in oxygen.

In some implementations, the water treatment unit <NUM> is an electrodialysis unit. The electrodialysis units can be used to concentrate the sulfuric acid up to <NUM>-<NUM> wt%.

In some implementations, dilute aqueous acid buffer stream <NUM> is concentrated by distillation in the water treatment unit <NUM>, using part of the steam generated from the thermal oxidizer <NUM>, or by utilizing the heat from a waste heat recovery system installed downstream of the reaction furnace of the Claus process. For example, steam can be generated by utilizing the hot thermal oxidizer effluent gas (temperature > <NUM>°F (<NUM>)) to heat up boiler feed water in a waste heat recovery heat exchanger downstream of the thermal oxidizer. The steam can then be used to concentrate the dilute aqueous acid buffer stream by boiling off water with the steam.

<FIG> is an example schematic of a system <NUM> for removing sulfur-containing compounds from a gas. A thermal oxidizer effluent <NUM> exits a thermal oxidizer <NUM>. The thermal oxidizer effluent <NUM> is the product of the complete combustion of hydrogen sulfide and other sulfur-containing compounds in the thermal oxidizer. The thermal oxidizer effluent <NUM> contains N<NUM>, SO<NUM>, O<NUM>, H<NUM>O, CO<NUM>, and CO. The stars (*) shown in <FIG> indicate the relative concentrations of the species in the stream, as discussed herein. The thermal oxidizer effluent <NUM> includes a high concentration of N<NUM>, a high-intermediate concentration of H<NUM>O and CO<NUM>, a low-intermediate concentration of O<NUM>, and a low concentration of CO and SO<NUM>. In some implementations, the concentration of SO<NUM> in the thermal oxidizer effluent is <NUM> - <NUM> mol%. In some implementations, the concentration of O<NUM> in the thermal oxidizer gas is <NUM>-<NUM> vol%.

The thermal oxidizer effluent <NUM> exits the thermal oxidizer <NUM> at a temperature of about <NUM> °F (<NUM>). The thermal oxidizer effluent <NUM> is cooled using a waste heat recovery unit <NUM> before entering the bottom section <NUM> of the quench tower <NUM>. The quench tower includes an upper section <NUM>, a mid-section <NUM>, and a lower section <NUM>. The upper section <NUM> of the quench tower and the lower section <NUM> of the quench tower <NUM> are fluidly connected in the mid-section <NUM> by a perforated plate <NUM>. The perforated plate <NUM> redistributes the water from a fresh water stream <NUM> on the packing of the lower section <NUM>. The perforated plate is configured to redistribute the falling liquid on the top of the packing in the lower section <NUM>, as well as to allow gas to pass through from the upper to the lower section. The perforated plate can be made of plastic, ceramic, or metal. In some implementations, the perforated plate can be a splash-plate or channel-type plate.

The dilute aqueous acid quench stream <NUM> is sprayed on the packing of the lower section <NUM>. The packing zone in the lower section <NUM> can vary in material (e.g. plastic, ceramic, metal), in morphology (e.g. rings, beads, saddles), and in organization (i.e. structured or random). The packing zone offers a large surface to facilitate contact between the liquid phase, i.e., the acidic water, and the gas phase. This also facilitates the removal of SO<NUM> from the gas phase. The packing zone also induces mixing in each phase, to avoid any concentration polarization in the gas phase and/or the liquid phase.

The thermal oxidizer effluent <NUM> is further cooled in the quench tower by contact with the dilute aqueous acid quench stream <NUM> and the fresh water stream <NUM>. The dilute aqueous acid quench stream <NUM> enters the quench tower <NUM> at the mid-section <NUM> of the quench tower <NUM>. The dilute aqueous acid quench stream <NUM> has a temperature between about <NUM> °F (<NUM>) and about <NUM> °F (<NUM>). In some implementations, the diluted sulfuric acid stream <NUM> has a temperature of about <NUM> °F (<NUM>). The fresh water stream <NUM> enters the upper section <NUM> of the quench tower <NUM>. The fresh water stream <NUM> has a temperature between about <NUM> °F (<NUM>) and about <NUM> °F (<NUM>). In some implementations, the fresh water stream <NUM> has a temperature of about <NUM> °F (<NUM>).

The oxidation of hydrated sulfur dioxide into sulfuric acid occurs in the packing zones of the quench tower, in the upper and lower sections <NUM> and <NUM>. As described herein, sulfur dioxide in the thermal oxidizer effluent <NUM> hydrates in water and reacts readily with the excess oxygen present in the thermal oxidizer effluent, as shown in Equation <NUM>. The product of this reaction is sulfuric acid. The rate of the reaction is dependent on the concentration of hydrated sulfur dioxide. The cooling action of the dilute aqueous acid quench stream <NUM> and the fresh water stream <NUM> condenses water vapor contained in the thermal oxidizer effluent <NUM>. SO<NUM> from the thermal oxidizer effluent dissolves and hydrates in water, and, in the aqueous phase, reacts with the excess of oxygen present in the thermal oxidizer effluent to yield to a mixture of sulfurous acid (H<NUM>SO<NUM>) and sulfuric acid (H<NUM>SO<NUM>). The generated sulfurous and sulfuric acids in the chilled acidic water yields a produced sulfuric acid stream. The resulting produced sulfuric acid stream maintains a mass concentration of sulfuric acid between <NUM> and <NUM> wt% at the bottom of the quench tower. Other species present in the thermal oxidizer effluent (N<NUM>, unreacted O<NUM>, uncondensed H<NUM>O, and CO<NUM>) exit the top of the quench tower as the quench tower effluent <NUM>. The stars in <FIG> indicate the relative concentrations of these species, as discussed herein. The quench tower effluent <NUM> is sent to a flare stack, mitigating any SO<NUM> breakthrough that can occur during upset conditions.

The produced dilute aqueous acid stream <NUM> exits the lower section of the quench tower <NUM> and is routed to a cooler <NUM> using a pump <NUM>. In some implementations, the cooler <NUM> is a heat exchanger. In some implementations, the cooler <NUM> is an air cooler. The produced dilute aqueous acid stream <NUM> is cooled by the cooler from about <NUM> °F (<NUM>) to about <NUM> °F (<NUM>) to yield a cooled dilute aqueous acid stream <NUM>. The cooled dilute aqueous acid stream <NUM> is split into the dilute aqueous acid quench stream <NUM> and a dilute aqueous acid buffer stream <NUM>. In some implementations, this split is performed by monitoring the flowrate of the cooled dilute aqueous acid stream <NUM> and by diverting a part of this flow using a controller and controlled valve (not shown). The split can be based on the desired concentration of sulfuric acid in the produced dilute aqueous acid stream <NUM>, which in turn determines how much of the dilute aqueous acid quench stream <NUM> is required in the quench tower <NUM>. In some implementations, the cooled dilute aqueous acid stream <NUM> is split evenly, i.e., the dilute aqueous acid quench stream <NUM> and the dilute aqueous acid buffer stream <NUM> each contain <NUM> wt% of the cooled dilute aqueous acid stream. The dilute aqueous acid quench stream <NUM> is routed back to the mid-section <NUM> of the quench tower <NUM>. The dilute aqueous acid buffer stream <NUM> is sent to a buffer tank <NUM>. Any unreacted SO<NUM> will continue to react readily in the aqueous acid buffer stream with O<NUM> from the air. The buffer tank <NUM> is fitted with a vent <NUM>. If the concentration of the SO<NUM> and sulfuric acid in the dilute aqueous acid buffer stream <NUM> is low, the buffer tank can be vented to the open air. The venting process can ensure that any liquid sent to a subsequent membrane process is free from gas and minimizes degassing in a subsequent membrane process. In addition, the vent can be used to equilibrate the pressure in the buffer tank when the second pump <NUM> is in operation. In some implementations, the vent <NUM> can be connected to the quench tower <NUM>, and vented gases <NUM> can be routed to the mid-section of the quench tower <NUM>. The vented gases <NUM> enter the quench tower <NUM> below the dilute aqueous acid quench stream <NUM>. Venting the buffer tank <NUM> to the quench tower <NUM> recycles undissolved gases, for example, SO<NUM> and CO<NUM>, to the quench tower and increases the yield of sulfuric acid in the produced dilute aqueous acid stream <NUM>.

In some implementations, in order to avoid any SO<NUM> emission, the vent <NUM> is equipped with a small column where a clean water stream is circulated, or a water trap. In some implementations, a blanket of inert atmosphere is injected into the buffer tank via the vent <NUM>.

The dilute aqueous acid buffer stream <NUM> can be routed from the buffer tank <NUM> to a water treatment unit <NUM> using a second pump <NUM>. The water treatment unit <NUM> is configured to remove sulfurous and sulfuric acid from the dilute aqueous acid buffer stream <NUM>. In some implementations, the water treatment unit <NUM> is a reverse osmosis membrane treatment unit, a nanofiltration unit, or a combination of nanofiltration and reverse osmosis membranes. The water treatment unit can concentrate the sulfuric acid in the dilute aqueous acid buffer stream <NUM> up to <NUM> - <NUM> wt%. The permeate <NUM> of the water treatment unit is mainly water. The permeate <NUM> can have a concentration of sulfuric acid that ranges from <NUM>-<NUM> wt%, with a pH that ranges from about <NUM> to about <NUM> respectively. Most of the permeate (about <NUM>-<NUM> wt %) is sent to the upper portion <NUM> of the quench tower <NUM> as the fresh water stream <NUM>. A small portion 218b (about <NUM>-<NUM> wt %) of the permeate <NUM> is removed. This portion 218b corresponds to roughly the amount of water condensed in the quench tower <NUM>, ensuring that the amount of water in the quench tower remains constant, and the produced dilute aqueous acid stream <NUM> maintains a constant concentration of sulfuric acid. This portion 218b can be reused in the facility or send to an evaporation pond.

The retentate <NUM> of the reverse osmosis treatment unit is concentrated sulfuric acid (<NUM> - <NUM> wt %). The retentate can be monetized or sent to a sulfur recovery unit (SRU) to enrich a Claus furnace in oxygen.

In some implementations, the water treatment unit <NUM> is an electrodialysis unit. The electrodialysis unit can be used to concentrate the sulfuric acid up to <NUM>-<NUM> wt%.

In some implementations, dilute aqueous acid buffer stream <NUM> is concentrated by distillation in the water treatment unit <NUM>, using part of the steam generated from the thermal oxidizer, or by utilizing the heat from a waste heat recovery system installed downstream of the reaction furnace of the Claus process.

<FIG> is an example schematic of a system <NUM> for removing sulfur-containing compounds from a gas. A thermal oxidizer effluent <NUM> is sent to the bottom section <NUM> of a quench tower <NUM>. The thermal oxidizer effluent <NUM> is the result of the complete combustion of hydrogen sulfide and other sulfur-containing compounds in a thermal oxidizer <NUM>. The thermal oxidizer effluent <NUM> contains N<NUM>, SO<NUM>, O<NUM>, H<NUM>O, CO<NUM>, and CO. The stars (*) shown in <FIG> indicate the relative concentrations of the species in the stream, as discussed herein. The thermal oxidizer effluent <NUM> includes a high concentration of N<NUM>, a high-intermediate concentration of H<NUM>O and CO<NUM>, a low-intermediate concentration of O<NUM>, and a low concentration of CO and SO<NUM>. In some implementations, the concentration of SO<NUM> in the thermal oxidizer effluent <NUM> is <NUM> - <NUM> mol%. In some implementations, the concentration of O<NUM> in the thermal oxidizer effluent is <NUM>-<NUM> vol%.

The thermal oxidizer effluent <NUM> exits the thermal oxidizer <NUM> at a temperature of about <NUM> °F (<NUM>). The thermal oxidizer effluent is cooled to about <NUM> °F (<NUM>) using a waste heat recovery unit <NUM> before being routed to the quench tower <NUM>. In the quench tower <NUM>, the thermal oxidizer effluent is further cooled by contact with a dilute aqueous acid quench stream <NUM> and a fresh water stream <NUM>. The dilute aqueous acid quench stream <NUM> enters the quench tower <NUM> at the mid-section <NUM> of the quench tower <NUM>. The dilute aqueous acid quench stream enters the quench tower at a temperature of about <NUM> °F (<NUM>). The fresh water stream <NUM> enters the quench tower <NUM> at the upper section <NUM> of the quench tower. The fresh water stream <NUM> enters the quench tower at a temperature of about <NUM> °F (<NUM>).

The upper section <NUM> of the quench tower <NUM> are fluidly connected to the lower section <NUM> of the quench tower <NUM> by a plate <NUM> in the mid-section <NUM> of the tower. The plate <NUM> includes bubble caps. The bubble caps allow gas upwards through the plate. The plate <NUM> also collects fresh water from the fresh water stream <NUM>. The fresh water can be recovered from the plate <NUM>.

The oxidization of hydrated sulfur dioxide into sulfuric acid, as described in Eq. <NUM>, occurs mainly in the packing zone of the lower section <NUM> of the quench tower <NUM>. Other species present in the thermal oxidizer effluent (N<NUM>, unreacted O<NUM>, uncondensed H<NUM>O, and CO<NUM>) exit the top of the quench tower as the quench tower effluent <NUM>. The stars in <FIG> indicate the relative concentration of these species, as discussed herein. The quench tower effluent <NUM> is sent to a flare stack, mitigating any SO<NUM> breakthrough that can occur during upset conditions.

The produced dilute aqueous acid stream <NUM> exits the lower section of the quench tower and is sent to a cooler <NUM> using a pump <NUM>. In some implementations, the cooler <NUM> is a heat exchanger. In some implementations, the cooler <NUM> is an air cooler. The produced dilute aqueous acid stream <NUM> enters the cooler and is further cooled from about <NUM> °F (<NUM>) to about <NUM> °F (<NUM>) to yield a cooled dilute aqueous acid stream <NUM>. The cooled dilute aqueous acid stream <NUM> is split into the dilute aqueous acid quench stream <NUM> and a dilute aqueous acid buffer stream <NUM>. In some implementations, this split is performed by monitoring the flowrate of the cooled dilute aqueous acid stream <NUM> and by diverting a part of this flow using a controller and controlled valve (not shown). The split can be based on the desired concentration of sulfuric acid in the produced dilute aqueous acid stream <NUM>, which in turn determines how much of the dilute aqueous acid quench stream <NUM> is required in the quench tower <NUM>. About <NUM> to <NUM> wt% of the cooled acidic aqueous stream <NUM> is sent back to the mid-section of the quench tower as the dilute aqueous acid quench stream <NUM>. A small portion (about <NUM> to <NUM> wt %) of the cooled acidic aqueous stream <NUM> is sent to a buffer tank <NUM> as the dilute aqueous acid buffer stream <NUM>. This small portion corresponds roughly to the amount of water condensed in the quench tower <NUM>, ensuring that the amount of water in the quench tower remains constant, and that the produced dilute aqueous acid stream <NUM> maintains a constant concentration of sulfuric acid. Any unreacted SO<NUM> will continue to react readily in the aqueous acid buffer stream with O<NUM> from the air.

The buffer tank <NUM> is fitted with a vent <NUM>. If the concentration of SO<NUM> and sulfuric acid in the dilute aqueous acid buffer stream is low, the buffer tank can be vented to the open air. The venting process can ensure that any liquid sent to a subsequent membrane process is free from gas and minimizes degassing in a subsequent membrane process. In addition, the vent can be used to equilibrate the pressure in the buffer tank when the second pump <NUM> is in operation.

In some implementations, the vent <NUM> can be configured to route vented gases <NUM> to the lower section <NUM> of the quench tower. The vented gases <NUM> enter the quench tower below the dilute aqueous acid quench stream <NUM>. Venting the buffer tank <NUM> to the quench tower <NUM> recycles undissolved gases, for example, SO<NUM> and CO<NUM>, to the quench tower and increases the yield of sulfuric acid in the produced dilute aqueous acid stream <NUM>. In some implementations, in order to avoid any SO<NUM> emission, the vent <NUM> is equipped with a small column where a clean water stream is circulated, or a water trap. In some implementations, a blanket of inert atmosphere is injected via the vent <NUM>.

The dilute aqueous acid buffer stream <NUM> exits the buffer tank <NUM> and is routed to a water treatment unit <NUM> using a second pump <NUM>. The water treatment unit <NUM> is configured to remove sulfurous and sulfuric acid from the dilute aqueous acid buffer stream <NUM>. In some implementations, the water treatment unit <NUM> is a reverse osmosis membrane treatment unit, a nanofiltration unit, or a combination of nanofiltration and reverse osmosis membranes. The water treatment unit can concentrate sulfuric acid up to about <NUM> - <NUM> wt%. The permeate <NUM> of the water treatment unit is mainly water. The permeate <NUM> can have a concentration of sulfuric acid that ranges from <NUM>-<NUM> wt%, with a pH that ranges from about <NUM> to about <NUM> respectively. The permeate <NUM> can be reused in the facility or sent to an evaporation pond via valve <NUM>. The retentate <NUM> of the water treatment unit is mainly concentrated sulfuric acid, about <NUM> - <NUM> wt%. The retentate <NUM> can be monetized or sent to a sulfur recovery unit (SRU) to enrich a Claus furnace in oxygen.

In some implementations, the dilute aqueous acid buffer stream <NUM> is concentrated by distillation in the water treatment unit <NUM>, using part of the steam generated from the thermal oxidizer, or by utilizing heat from a waste heat recovery system installed downstream of the reaction furnace of the Claus process.

As discussed herein, the plate <NUM> is configured to collect and recover water from the fresh water stream <NUM>. In some implementations, the recovered fresh water <NUM> is sent to a second buffer tank <NUM>. The second buffer tank <NUM> is fitted with a second vent <NUM>. If the concentration of SO<NUM> and sulfuric acid in the recovered fresh water <NUM> is low, the second buffer tank <NUM> can be vented to the open air. The venting process can ensure that any liquid sent to a subsequent membrane process is free from gas and minimizes degassing in a subsequent membrane process. In addition, the vent can be used to equilibrate the pressure in the buffer tank when the third pump <NUM> is in operation. In some implementations, the second vent <NUM> can be connected to the upper section <NUM> of the quench tower <NUM>. The vented gases <NUM> enter the quench tower <NUM> below the fresh water stream <NUM>. Venting the second buffer tank <NUM> to the quench tower <NUM> recycles undissolved gases, for example, SO<NUM> and CO<NUM>, to the quench tower and increases the yield of sulfuric acid in the produced dilute aqueous acid stream <NUM>.

In some implementations, the second vent <NUM> is equipped with a small column where a clean water stream is circulated, or a water trap, to prevent SO<NUM> from being released to the atmosphere. In some implementations, a blanket of inert atmosphere is injected into the second buffer tank via the second vent <NUM>.

In some implementations, the fresh water stream <NUM> exits the second buffer tank and is maintained at a temperature of about <NUM> °F (<NUM>) by a heat exchanger <NUM> before being directed to the top of the quench tower.

As described herein, the oxidation of hydrated sulfur dioxide into sulfuric acid occurs mainly in the packing zone of the lower section <NUM> of the quench tower <NUM>. However, if there is a variation or upset in the composition or flowrate of the thermal oxidizer effluent <NUM>, or if a production upset generates a large amount of SO<NUM> that cannot be handled by the lower section of the quench tower, breakthrough can occur and SO<NUM> gas enters the upper section <NUM> of the quench tower <NUM>. The breakthrough SO<NUM> is absorbed by fresh water coming from fresh water stream <NUM> to yield sulfurous and sulfuric acid in the upper section <NUM> of the quench tower <NUM>. The fresh water stream <NUM> cools and dissolves the sulfurous and the sulfuric acid. The sulfurous and sulfuric acid generated by the breakthrough of the SO<NUM> is recovered in the fresh water stream <NUM>.

Therefore, when breakthrough of sulfur dioxide occurs, the pH of the recovered fresh water <NUM> decreases. Without breakthrough, the pH of the fresh water <NUM> is between <NUM> and <NUM> (respectively <NUM>-<NUM> wt% of sulfuric acid). When breakthrough occurs and the pH reaches about <NUM>, as measured by an in-line or bypass pH probe, the recovered water stream <NUM> that exits the second buffer tank <NUM> is diverted to the buffer tank <NUM> via line <NUM> and valve <NUM>. In some implementations, the valves can be controlled manually. In some implementations, the valves can be controlled with a controller linked to pH meters and liquid level meters in the buffer tank <NUM> and the second buffer tank <NUM>. The recovered water stream is therefore held in the buffer tank <NUM> and subsequently treated using the water treatment unit <NUM>. The permeate <NUM> of the water treatment unit is then sent back to the upper section <NUM> of the quench tower <NUM> via line <NUM> and valve <NUM> and the third pump <NUM>. Accordingly, the system <NUM> mitigates the breakthrough by treating the recovered water <NUM> to remove sulfuric acid.

In some implementations, system <NUM> includes an alternative arrangement of lines and valves. For example, the recovered water stream <NUM> that exits the second buffer tank <NUM> can pass through line <NUM> and valve <NUM> to pump <NUM>. In this implementation, line <NUM> is connected to the bottom of the second buffer tank <NUM>. In this implementation, fresh water from the water treatment unit <NUM> is routed into tank <NUM> through valve <NUM> and line <NUM>, where line <NUM> is connected to the top of the second buffer tank <NUM>. In this implementation, the valves can be controlled manually, or the valves can be controlled with a controller linked to pH meters and liquid level meters in the buffer tank <NUM> and the second buffer tank <NUM>.

<FIG> shows an example method <NUM> of treating a tail gas of a Claus process to remove sulfur-containing compounds. At <NUM>, the tail gas of a Claus process is combusted in a thermal oxidizer in an excess of oxygen gas to yield a thermal oxidizer effluent that contains sulfur dioxide, water vapor, and oxygen. At <NUM>, the thermal oxidizer effluent is cooled to about <NUM> °F (<NUM>). At <NUM>, the cooled effluent is routed to a quench tower.

At <NUM>, the thermal oxidizer effluent entering the quench tower is contacted with a dilute aqueous acid quench stream to condense water vapor and dissolve the sulfur dioxide to yield sulfurous acid, hydrated sulfur dioxide, or both. At <NUM>, the sulfurous acid or hydrated sulfur dioxide is oxidized with oxygen from the thermal oxidizer effluent to yield a produced dilute aqueous acid stream that includes sulfuric acid. In some implementations, the produced dilute aqueous acid stream contains between about <NUM> and about <NUM> wt% sulfuric acid.

At <NUM>, the produced dilute aqueous acid stream is cooled to about <NUM> °F (<NUM>) to yield a cooled dilute aqueous acid stream. At <NUM>, the cooled dilute aqueous acid stream is split to yield the dilute aqueous acid quench stream and a dilute aqueous acid buffer stream. In some implementations, the dilute aqueous acid buffer stream is approximately the same volume as the water condensed from the thermal oxidizer effluent. In some implementations, the cooled dilute aqueous acid stream is evenly split, such that the dilute aqueous acid quench stream and the dilute aqueous acid buffer stream each comprise approximately <NUM>% of the cooled dilute aqueous acid stream.

At <NUM>, the dilute aqueous acid quench stream is routed to the quench tower. In some implementations, the dilute aqueous acid buffer stream is routed to a water treatment unit. In some implementations, the water treatment unit is a reverse osmosis membrane treatment unit, a nanofiltration unit, or a combination of nanofiltration and reverse osmosis membranes. The water treatment unit can concentrate sulfuric acid up to <NUM>-<NUM> wt%. The water treatment unit can yield a permeate that is mainly water. The permeate can have a concentration of sulfuric acid that ranges from <NUM>-<NUM> wt%, with a pH that ranges from about <NUM> to about <NUM> respectively. The permeate can be reused in the facility or sent to an evaporation pond. The water treatment unit also yields a retentate stream that is mainly concentrated sulfuric acid (approximately <NUM>-<NUM> wt%). The retentate can be monetized or sent to a sulfur recovery unit (SRU) to enrich a Claus furnace in oxygen.

In some implementations, the water treatment unit is an electrodialysis unit. The electrodialysis units can be used to concentrate the sulfuric acid up to <NUM>-<NUM> wt%.

In some implementations, dilute aqueous acid buffer stream is concentrated by distillation in the water treatment unit, using part of the steam generated from the thermal oxidizer, or by utilizing the heat from a waste heat recovery system installed downstream of the reaction furnace of the Claus process. For example, steam can be generated by utilizing the hot thermal oxidizer effluent gas (temperature > <NUM>°F (<NUM>)) to heat up boiler feed water in a waste heat recovery heat exchanger downstream of the thermal oxidizer. The steam can then be used to concentrate the dilute aqueous acid buffer stream by boiling off water with the steam. The water treatment unit yields a permeate that is substantially water and a retentate that is concentrated sulfuric acid.

In some implementations, the method includes contacting the sulfuric acid with a fresh water stream. The fresh water stream is recovered. In some implementations, the recovered water is reused as the fresh water stream. If the pH of the recovered water drops below <NUM>, the recovered water can be routed to the water treatment unit. The permeate of the water treatment unit can be routed to the quench tower or to an evaporation pond. The retentate of the water treatment unit can be monetized or sent to an SRU to enrich a Claus furnace in oxygen.

The term "about" as used in this disclosure can allow for a degree of variability in a value or range, for example, within <NUM>%, within <NUM>%, or within <NUM>% of a stated value or of a stated limit of a range.

The term "substantially" as used in this disclosure refers to a majority of, or mostly, as in at least about <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or at least about <NUM>% or more.

As used in this disclosure, "weight percent" (wt%) can be considered a mass fraction or a mass ratio of a substance to the total mixture or composition. Weight percent can be a weight-to-weight ratio or mass-to-mass ratio, unless indicated otherwise.

As used in this disclosure, "volume percent" (vol%) can be considered a volume fraction or a volume ratio of a substance to the total volume of the mixture or composition.

Claim 1:
A method (<NUM>) for treating a tail gas of a Claus process to remove sulfur-containing compounds, the method comprising:
combusting (<NUM>) a tail gas of a Claus process in an excess of oxygen gas, wherein the excess of oxygen gas comprises a number of moles of oxygen exceeding the number of moles of oxygen required to fully combust the sulfur-containing compounds, to yield a thermal oxidizer effluent (<NUM>, <NUM>, <NUM>), wherein the thermal oxidizer effluent comprises sulfur dioxide, water vapor, and oxygen;
cooling (<NUM>) the thermal oxidizer effluent to yield a cooled thermal oxidizer effluent;
flowing (<NUM>) the cooled thermal oxidizer effluent to a quench tower (<NUM>, <NUM>, <NUM>);
contacting (<NUM>) the cooled thermal oxidizer effluent in the quench tower with a dilute aqueous acid quench stream (<NUM>, <NUM>, <NUM>) to condense water vapor and dissolve the sulfur dioxide to yield sulfurous acid, hydrated sulfur dioxide, or a combination of sulfurous acid and hydrated sulfur dioxide;
oxidizing (<NUM>) the sulfurous acid or hydrated sulfur dioxide with oxygen from the thermal oxidizer effluent to yield a produced dilute aqueous acid stream (<NUM>, <NUM>, <NUM>) that comprises sulfuric acid;
cooling (<NUM>) the produced dilute aqueous acid stream to yield a cooled dilute aqueous acid stream;
splitting (<NUM>) the cooled dilute aqueous acid stream into the dilute aqueous acid quench stream and a dilute aqueous acid buffer stream (<NUM>, <NUM>, <NUM>); and
flowing (<NUM>) the dilute aqueous acid quench stream to the quench tower.