MXPA00010958A - Method for hydrogen sulfide abatement - Google Patents

Abstract

Methods for abating hydrogen sulfide, e.g. from geothermal brine, by introducing an H2S-containing gas into a bioscrubber, the bioscrubber containing sulfur bacteria, and reversing the flow of said gas stream after a certain period of time.

Description

METHOD FOR THE DECOMPOSITION OF HYDROGEN SULFIDE TECHNICAL FIELD The invention is concerned with the field of the abatement of toxic and / or harmful gases, particularly the field of abatement of hydrogen sulfide gas. The invention is also concerned with the production of sulfuric acid from hydrogen sulfide gas. The invention is further concerned with the conversion of hydrogen sulfide gas into geothermal brine to sulfuric acid.

BACKGROUND OF THE INVENTION Hydrogen sulfide gas has a variety of undesirable properties. At low concentrations (that is, less than 10 parts per million), the gas has a strong odor of "rotten eggs". Paradoxically, at concentrations greater than 100 parts per million (ppm), the gas can no longer be smelled, but will induce dizziness. Concentrations greater than about 500 ppm can be fatal to humans. Hydrogen sulfide can also be oxidized to sulfur dioxide, a chemical that contributes to acid rain. Hydrogen sulfide gas (H2S) can be released through a variety of sources. Biologically generated hydrogen sulfide is generally the product of anaerobic digestion of organic matter and can be Ref: 124967 released by sewage treatment facilities, solid waste embankment, paper mill waste, livestock feed lots, poultry farms and other industries that employ anaerobic digestion for processing. H2S is also released by oil drilling operations, oil refinery operations and operations using geothermal brines, such as power generation. Geothermal brines are of interest for several reasons. Geothermal formations containing brines heated to high temperature can be accessed by conventional drilling technology and are found in a variety of locations including California. When a geothermal brine is brought to the surface and subjected to "flash evaporation", live steam is generated that can be used to drive turbines for the production of electricity. The brines also contain large quantities of commercially valuable metals, for example lead, silver and zinc. However, when the geothermal brines are subjected to instantaneous evaporation, they also release non-condensable gases in which H2S is included. H2S concentrations in non-condensable gas streams from geothermal brines can be quite high, reaching levels of over 4000 ppm.

Depletion (this is removal or transformation of H2S) can be carried out by chemical or biological means. The purpose of the H2S abatement systems is to convert the H2S gas to elemental sulfur, a solid that can be easily collected. An older chemical process for the abatement of H2S, the Claus process, uses heat and oxygen to oxidize H2S to elemental sulfur. This process is not particularly efficient however and produces sulfur dioxide. Thus, a catalytic step is required to react the remaining H 2 S and the sulfur dioxide to form elemental sulfur. The company Dow Chemical and U. S. Filter Engineered Systems are suppliers of newer technologies (sold under the trade names SulFerox ™ and ARI LO-CAT II ™, respectively). Both of these technologies use patented iron catalysts in liquid reactors for the conversion of hydrogen sulfide to elemental sulfur. Biological technologies for H2S abatement are also available. Sulfur bacteria (that is, bacteria that are able to metabolize sulfur compounds) can be used in "biofilter" or "biodepurator" reactors to oxidize H2S to sulfates. Biofilter and biodepurator plants are normally designed to produce elemental sulfur. In this process, the H2S gas is passed over the bioreactor bed under aerobic conditions, leading to the reduction of H2S to elemental sulfur that is deposited intracellularly and extracellularly as a solid in lumps or granules. This elemental sulfur must be mechanically separated periodically from the bioreactor bed or the reactor will be clogged. Sulfur deposited, once separated, can be discarded or used in industrial and / or agricultural processes. Additional oxidation of sulfur by biofilter or biodepurator reactors has been considered undesirable. Sulfuric acid, a strong acid, is the main product of the further oxidation of elemental sulfur by sulfur bacteria. Sulfuric acid has not been a desirable product because it is highly corrosive (sulfuric acid produced by sulfur bacteria generally has a pH of 1 to 2). In addition, sulfate ions are so undesirable that bioreactor technology is available (for example, from THIOPAQ Sulfur Systems BV) for the biological conversion of sulfate to elemental sulfur. In this technology, anaerobic bacteria are used to reduce sulfate to H2S, which is then oxidized by aerobic sulfur bacteria to form elemental sulfur. Lanting et al., "Biological Removal of Hydrogen Sulfide from Biogas", presented at the 46th Annual Purdue Industrial Waste Conference, May 14-16, 1991 describe methods for the use of biological systems for the abatement of H2S from biological sources. The methods disclosed are concerned with the biological abatement of H2S by conversion to elemental sulfur. In this method, gas containing H2S is passed over a support medium coated with sulfur bacteria. Water and a nutrient fluid are circulated through the bioreactor bed. H2S is oxidized to elemental sulfur and sulfate, although elemental sulfur is the desired end product. Sulphate production is indicated and actions are suggested to reduce or eliminate sulphate production. In the Lanting method, the elemental sulfur is separated from the bioreactor by periodically washing the reactor.

DESCRIPTION OF THE INVENTION It is an object of the invention to provide a method for the abatement of hydrogen sulfide gas using biological processes wherein the sulfuric acid is the final resultant product desired. In one embodiment, a gas stream containing H 2 S is passed through a biodepurator, the biodepurator comprising at least one bioreactor container containing sulfur bacteria adhering to a support medium, while a fluid stream is sprayed on the support medium in the bioreactor vessel. For oxygen deficient gas streams, the air is mixed with the gas stream before it is introduced into the biodepurator. The gas stream is inverted on a regular basis to facilitate the distribution of elemental sulfur throughout the biodepurator and complete the conversion of elemental sulfur to sulfuric acid. The good distribution of sulfur optimizes the conversion of sulfur to sulphate.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of the reversible flow biodepurator system. Figure 2 shows the conversion efficiency of elemental sulfur to sulfuric acid using the method of the invention.

MODES FOR CARRYING OUT THE INVENTION A variety of genera of sulfur bacteria are suitable for use in the method of the present invention. The "sulfur bacteria" include species of Beggiatoa Thiothrix and Thiobacilli, although any acidophilic sulfur-oxidizing bacteria can be used. Appropriate sulfur bacteria can be obtained from a variety of sources, which include sediments from sulfur hot springs, soil and channel samples and cooling tower packages associated with industries that use geothermal wells. The biodepurator and associated equipment for use in the method of the present invention are preferably constructed of materials highly resistant to corrosion. Sulfuric acid is produced in the process of abatement of H2S present and consequently portions of the biodepurator that come in contact with this product (such as the bioreactor container and the collection system of blown) must be resistant to sulfuric acid, as it will be evident to those of ordinary experience in the art. Gas supply lines, conduits and gas gates must also be resistant to corrosion, since gases containing H2S can be corrosive. Portions of the biodepurator in contact with corrosive compounds are preferably constructed of materials such as glass fiber, molded fiber, polyvinyl chloride and other plastics and the like. The sulfur bacteria are inoculated into a biodepurator comprising at least one bioreactor container packed with a support medium. The support means is preferably retained within the bioreactor vessel by a permeable alkaline flux, disk or filter or other apparatus that retains the support medium, while allowing the passage of gas and liquid. Suitable support means may include any material that is resistant to corrosion, in which metal, plastic, ceramics, soil, coke and the like are included. The support means preferably has a large surface area to withstand a large growth of bacterieis. A preferred support medium is polypropylene, such as Jaeger Tripac®. During inoculation, the elemental sulfur can be added with the bacterial inoculant or sprayed onto the support medium to aid in the establishment and growth of the sulfur bacteria. Once the biodepurator is inoculated with sulfur bacteria, a nutrient solution is supplied. The nutrient solution contains the basic elements required for the growth and survival of sulfur bacteria that are not supplied by any other source. The main nutrients required by the sulfur bacteria are nitrogen, carbon, potassium, phosphorus and sulfur. Micronutrients are also provided, as will be apparent to one of ordinary skill in the art. The nitrogen is preferably supplied as ammonia and can be supplied during the inoculation and establishment phases. In one embodiment, the geothermal brine condensate is used as a source of nitrogen. Because many gas streams containing H2S (such as non-condensable gas streams from geothermal brines subject to flash evaporation) contain ammonia, nitrogen supplementation may not be required after the biodepurator is operational. Carbon can be supplied in the form of C02. Sufficient C02 may be available in air and gas streams containing H2S may contain additional amounts of C02, so that no carbon supplementation is necessary. Potassium and phosphorus are preferably supplied by the addition of potassium phosphate to the nutrient solution. Solid elemental sulfur can be added to the bioreactor during initial inoculation with sulfur bacteria, but gas streams containing H2S will supply all of the sulfur needed during the operation. Micronutrient supplementation may not be necessary if tap or industrial water is used to produce the nutrient solution. However, micronutrients can be added, where one or more micronutrients are present in a sufficient amount, as will be apparent to one of ordinary skill in the art. A nutrient solution is sprayed preferably to the biodepurator under moderate pressure. The sulfur bacteria are usually bonded to the carrier medium and are therefore easily dislodged by a strong spray. The spraying can be indirect, for example using a relatively strong or sprayed stream directed against the walls of the bioreactor container which "bounce off" the walls of the container to spray the support medium. A preferred method of spraying uses one or more spray nozzles suspended above the support means. A nutrient solution is used to supply nutrients to the sulfur bacteria and to maintain moisture levels in the biodepurator. The nutrient solution is preferably mixed in a tank and then pumped into the biodepurator, but systems that use in-line mixing and / or utility water pressure are also useful. The flow must be controlled to maximize the removal of H2S from the gas stream containing H2S. The flow velocity will be determined by the size and configuration of the biodepurator. Preferably, the nutrient solution is sprayed to the biodepurator at a flow rate of approximately 378.5 liters per minute 100 gallons per minute to approximately 757 liters per minute (200 gallons per minute) or 0.75 to 3 gpm / square foot. The biodepurator temperature should be maintained at approximately 24-25 ° C. Preferably, the biodepurator is maintained at about 35-40 ° C. If necessary, the temperature can be maintained by circulating a controlled temperature fluid within a jacket or jacket that surrounds the core of the bioreactor vessel, heating or cooling the air space within the bioreactor vessel, heating or cooling the stream of gas containing H2S in line or by heating or cooling the nutrient solution or any combination thereof. It is unlikely that cooling is necessary, unless the ambient temperature in the biodepurator area is high or the gas stream containing H2S is very hot. Alternatively, heating may not be necessary where either the ambient temperature or the gas stream containing H 2 S provides sufficient heat to maintain the temperature of the biodepurator within the preferred operating range. The gas stream containing H23 must contain enough oxygen to allow complete oxidation of H2S to sulfuric acid. Many gas streams containing H2S do not contain enough oxygen to support the oxidation of H2S to sulfuric acid, such that gas streams containing H2S sources may require oxygen supplementation. Oxygen supplementation can be carried out by adding oxygen gas to the gas stream containing H2S source or by mixing air with the gas stream containing H2S source. Preferably, a stream of gas containing source H2S that lacks sufficient oxygen is supplemented by mixing with air.

After the sulfur bacteria are established in the biodepurator, the gas stream containing H2S is directed through gas supply lines to the biodepurator. The gas stream containing H2S is directed through a first gas gate to the bioreactor vessel where it flows over the support medium. Sulfur bacteria on the support medium in the bioreactor vessel oxidize the H2S to elemental sulfur. The elemental sulfur is deposited as granules intra- and extra-cellularly. The gas exhausted from H2S is directed to a gas outlet through a second gas gate. The gas dampers can be installed in any arrangement, such as top / bottom, sides or axial / peripheral. A top / bottom gas damper arrangement is preferred. A gas stream containing H2S is introduced through the first gas gate by one cycle. The duration of a cycle is from about 12 hours to about 5 days or from about 36 hours to about 3 days or from about 24 hours to about 3 days or from about 24 hours to about 2 days or from about 12 hours to about 2 days . At the end of the cycle, the gas flow is reversed (that is, the gas stream containing H2S is introduced via the second gas gate and the exhausted H2S gas is directed to a gas outlet via the first gate) by a second cycle. The cyclic operation is continued throughout the operation of the biodepurator and the gas flow is reversed at the end of each cycle. The inversion of the gas flow is preferably carried out by changing the valves located in the conduits between the gas supply, the gas outlet and the first and second gates. The conduits can be arranged in such a way that separate conduits and valves control the flow from the gas supply to the two gas gates and from the two gas gates to the gas outlet. This type of arrangement allows the use of simple "on / off" type valves to control the gas flow. Another design links the gas supply and the gas outlet to multi-position valves, where a single valve can be used to select either the first or second gas gate. An additional design places multi-position valves on the first and second gas gates, each allowing the selection between the gas supply and the gas outlet conduits. The reversal of the gas flow results in a better distribution of sulfur in the support medium, thereby resulting in a more efficient oxidation of the elemental sulfur to sulfuric acid. Sulfuric acid greatly reduces the pH of the nutrient flow to approximately 1 to 2, greatly reducing or eliminating the growth of non-acidophilic sulfur bacteria in the bioreactor. The nutrient stream containing sulfuric acid is drained to the bottom of the bioreactor vessel. This liquid is separated from the bioreactor vessel by an outlet drain of the liquid located at the bottom of the vessel. Sulfuric acid can be collected and used in industrial processes that require sulfuric acid. The bioreactor container can be of any shape, although the walls of the container are preferably substantially vertical. Preferably, the bottom surface of the interior is inclined or curved to channel the blown liquids into a blown liquid drain. The preferred bioreactor vessel has a shape that provides good distribution of gas and liquid through the support means. The method of the present invention can be employed in biodepurators containing one or more bioreactor containers. The bioreactor containers can be put into operation separately or they can be connected. If the bioreactor vessels are connected, the gas gates can be linked in series (ie, the second gas damper of the biodepurator 1 linked to the first gas damper of the biodepurator 2) or in parallel (that is, each gate of the bioreactor). gas 1 is connected to a first manifold and each gas gate 2 is connected to a second manifold). All patents and publications disclosed herein are incorporated by reference in their entirety.

EXAMPLES Example 1: Operation of the biodepurator Non-condensable gases (NCG) in the ventilation stream enters the plant at approximately 1.08 Kg / cm absolute square (14.8 psia). Blowers are used to increase the gas inlet pressure by approximately 106.7 cm (42") of water column in order to drive the gas through the reactors that were connected in series.Air ambient was filtered and introduced to the system by means of After the air and the (NCG) in the ventilation stream were mixed at a ratio of approximately 1: 4, the gas mixture was distributed to the first bioreactor, reactor A in figure 1, which was 73.62 cubic meters (2600 cubic feet) and packed with 44.79 cubic meters (1582 cubic feet) of Jaegere TripacTM 2.5 cm (1 inch) spherical shape.The reactor temperature should be approximately 37.7 ° C (100 ° F) - 48.9 ° C (120 ° F) In order to maintain the temperature above 37.7 ° C (100 ° F), a steam line of 0.70 Kg / cm square (10 psig) injects steam into the NCG / Air mixture. Circulating solution 1 was pumped at 567.7 liters per minute (150 gallons per nuto) at 757 liters per minute (200 gallons per minute) at the top of the reactor and sprayed moderately on top of the bioreactor bed. The circulating solution that flows downwards wetted the support medium and in a cycle was placed in countercurrent contact with the gases that flow upwards. The hydrogen sulfide present in the gases was absorbed by the circulating solution, oxidized to elemental sulfur by the bacteria present on the support medium. Then the elemental sulfur was deposited on the support medium. The circulating solution exited from the bottom of the reactor and was pumped back to the top of the reactor by means of spray nozzles. A small blowing or purging stream 2 was divided from the circulating solution stream pumped to separate the sulfuric acid from the system. The remaining pH of the circulating solution was maintained at about 1.0 to 2.0 by introducing water 4 into the circulating solution. An injection system supplied a nutrient solution to the bacteria resident in the bioreactors in an amount of approximately 0.802 gallons per hour (0.212 gallons per hour). A solution of potassium phosphate salt nutrient 3 was pumped into the circulating solution lines to mix with the circulating solution and supply the bacteria with the necessary nutrients as the support medium was wetted. After the contact of the circulating solution on the support medium in reactor A, the clean gas exits to reactor B. The first reactor in the series, in this example reactor A, accumulates the elemental sulfur while in the second reactor , reactor B, the elemental sulfur is converted to sulfuric acid. After a period of time, this is 0.5 to 2 days, the flow of non-condensable gases to the reactors was reversed and the second cycle was continued for approximately the same period of time. This method, which employs an inversion of the non-condensable gas stream, results in a conversion of approximately 99.999% of the hydrogen sulfide gas present in the vent stream to sulfuric acid, a surprisingly unexpected improvement in the conversion of sulfur hydrogen to sulfuric acid in comparison with the known methods as shown in figure 2. It is noted that, in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is that which is clear of the present description of the invention.

Claims (8)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A method for producing sulfuric acid from a stream of gas containing hydrogen sulfide (H2S), characterized in that it comprises: introducing a stream containing hydrogen sulfide (H2S) and oxygen-containing gas to a biodepurator through a first gas gate and venting spent hydrogen sulfide gas (H2S) through a second gas gate, the biodepurator comprises at least a container of bioreactor and sulfur oxidizing bacteria, acidophilic, adhering to a support medium contained in the container; invert the gas flow after a period of time that fluctuates from about 12 hours to about 5 days, such that the gas stream containing hydrogen sulfide (H2S) and oxygen is introduced to the biodepurator through the second gate Gas and hydrogen sulfide depleted gas (H2S) is vented through the first gas gate and collect the sulfuric acid.
2. 2. The method according to claim 1, characterized in that the period of time fluctuates from about 24 hours to about three days.
3. 3. The method according to claim 1, characterized in that the period of time ranges from about 36 hours to about two days.
4. 4. The method according to claim 1, characterized in that the biodepurator comprises at least two bioreactor vessels.
5. 5. The method of compliance with the claim 4, characterized in that the bioreactor vessels are connected in series.
6. 6. The method according to claim 4, characterized in that the bioreactor vessels are connected in parallel. The method according to claim 1, characterized in that the gas stream containing hydrogen sulfide (H2S) and oxygen is separated from geothermal brine. 8. The method of compliance with the claim 1, characterized in that the sulfur-oxidizing, acidophilic bacteria are a species of Beggiatoa, Thiothrix or Thiobacilli.