JPH0419885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to steam, particularly geothermal steam used to operate turbines.
This invention relates to a method for removing hydrogen sulfide (H ₂ S) from steam. It was established in 1978 that geothermal steam containing _H2S can be purified by contacting the steam with metal compounds that form insoluble metal sulfides.
U.S. Patent No. 4123506 dated October 31 and May 1980
Known from US Pat. No. 4,202,864 dated 13th. Geothermal steam containing _H2S can be purified by oxygenation and passing through a bed of activated carbon, as disclosed in U.S. Pat. No. 1, April 1, 1980.
Also known from number 4196183. In December 1982, it was discovered that geothermal steam containing H ₂ S can be purified by the reaction of steam with hydrogen peroxide and a ferrous catalyst.
Further known from US Pat. No. 4,363,215, dated 14. Various methods of _H2S control in geothermal steam are
Energy Report by FBStephens et al. #
Outlined by the US Subcommittee of DOE/EV-0068 (March 1980). ferric chelate from sulfur compound-containing gases and sulfur compound-containing water.
The removal of H ₂ S by
No. 4009251, No. 4091073 and No. 4076621. The present invention is a geothermal steam power plant.
A method is directed to purifying residual steam containing H ₂ S before it is released into the atmosphere. The process of the invention comprises the steps of: (A) converting the steam directly or indirectly with an aqueous solution in a condensation zone at a temperature low enough to convert the steam into an aqueous solution containing dissolved hydrogen sulfide and its ions; (B) freeing by contacting the aqueous sulfide solution with an aqueous solution of ferric chelate containing a sufficient amount of ferric chelate to completely oxidize the sulfide ions to sulfur; (C) converting the ferrous chelate solution with air in a cooling zone to an aqueous solution containing ferric chelate; and (D) converting the ferrous chelate solution to an aqueous solution containing ferric chelate. recycling the chelate solution to the condensation zone. In the method of the invention, H ₂ S in geothermal steam
Approximately 20% to 80% of the gas is absorbed into the aqueous phase of the steam condenser depending on whether a direct contact condenser or a surface condenser is used, whereby the dissolved _H2S is absorbed into the ferric chelate. ) to produce finely divided sulfur. Uncondensed or unabsorbed H ₂ S can be discharged to the atmosphere or, if zero discharge is desired or required, H ₂ S gas can be converted into conventional H ₂ S
It can be absorbed with absorbents, such as aqueous alkanolamine solutions or potassium carbonate solutions or caustic solutions, or it can be oxidized to sulfur using the Stretford process. A direct contact steam condenser with an atomizing head can be used to absorb approximately ₈₀ % of the _H2S into the geothermal steam condensate, but other It may be advantageous to condense the steam using indirect condensers or surface condensers such as shell and tube condensers if the system is readily available. The advantage of using surface condensers is that about 20% of the incoming _H2S
About 80% remains in the non-condensable gas, while only about 80% is absorbed in the condensate, and its purification is more economical. Therefore less ferric chelate is required to react with dissolved H ₂ S and/or its ions. Furthermore, since the condensate fluid is not mixed with the condensate, the total liquid volume for processing is less. FIG. 1 shows the application of the present invention to the oxidation of hydrogen sulfide contained in a liquid stream produced by the condensation of geothermal steam in a direct contact condenser, and which is itself toxic and noxious. 1 illustrates a method for eliminating environmental pollution problems associated with the discharge of containing effluent streams. FIG. 2 illustrates a similar method using indirect capacitors. In FIG. 1, geothermal steam from line 2 is used to power a steam turbine 4 connected to a power generator 6. In FIG. Turbine 4 discharges via line 8 to direct contact condenser 10 . Cooling water containing chelated iron (ferric chelate) from line 12 is sprayed into condenser 10 for this condensation and from condenser 10 via line 14 to 38-52°C (100-126〓). It is sent to the hot well 16 operated by the hot well 16. Non-condensable gases such as CO ₂ , N ₂ , O ₂ and H ₂ S are removed from the main condenser 10 via line 18 by two steam jet evacuators 20 and 34 and associated condensers 26 and 42. . Ejectors 20 and 34 are operated by steam supplied by lines 22 and 36, respectively. These ejectors create a partial vacuum or low pressure zone. The exhaust steam from the ejector 20 is transferred to the condenser 2 by a line 24.
6 and is conveyed by line 32 to a second ejector 34. Exhaust steam from ejector 34 is conveyed by line 40 to condenser 42. Cooling water from line 12 is supplied to each of condensers 26 and 42 by lines 28 and 44, respectively. Condensed steam from condensers 26 and 42 is routed to lines 30 and 4.
6 to the hot well 16. The non-condensable gases and exhaust steam are then exhausted via line 48 to a conventional caustic scrubber, alkanolamine or potassium carbonate unit for removal of _H2S gas. A pump 58 is used to pump the combined condensed geothermal steam and cooling water from the hot well 16 via line 60 to an induced-draft cooling tower 62 by an intermediate spray head 66. Ru. spray head 6
At 6, an amount of water equal to about 80% of the condensed steam is evaporated by an air flow through the column stripping all of the dissolved hydrogen sulfide from the liquid and it is When not in use, it will be exhausted to the environment by air flow 64. Excess condensed steam that is not evaporated is sent to cooling tower 6 for disposal via line 80.
Wear cough at the base of 2 (not shown)
overflow. The rest of the cold water is on line 68.
through to a relatively cool well 70 operating at 24-29°C (75-85°). Pump 50 pumps condensers 42, 26 and 1 from cold well 70.
Used to pump low temperature water to 0. Hot well 16 is separated from cold well 70 by weir 72 . In the air flow flowing from the top of the cooling tower 62,
Chelated iron is added to the circulating water in an amount greater than the stoichiometric amount required to oxidize the dissolved hydrogen sulfide in the hot well 16 to prevent release of dissolved hydrogen sulfide to the environment. In this method, dissolved hydrogen sulfide is removed from water in line 6.
0 to the top of the cooling tower 62. The contact time between the air flow and the air and water in the cooling tower 62 ensures that the ferrous chelate resulting from the oxidation of dissolved hydrogen sulfide in the hot well 16 and associated piping 56 and 60 is in the cooling tower 62.
long enough to be reoxidized to the active ferric state as it passes downward through the ferric state. The finely divided solid form of elemental sulfur produced by this method circulates freely throughout the system and can be recovered from the overflow line 80 by conventional means. Such recovery methods may cause the sulfur to agglomerate into a heavy slurry, after which the supernatant can be recovered by decantation, centrifugation, filtration, or the like. To maintain at least the stoichiometric amount of iron chelate needed for this process, an amount of new iron chelate equal to the amount lost in overflow line 80 is added to pump 76 and inlet line 7.
8 from storage container 74. In Figure 2, the component parts and their functions are
1 except that the illustrated condenser 110 is an indirect condenser with a cooling coil indicated schematically by 113. Cooling water enters condenser 113 via line 113 and is removed via line 115. In this embodiment, steam condensate containing _H2S drains down line 114 to hot well 116. Because cooling water does not mix with geothermal steam and from geothermal steam
This is because H ₂ S is not scrubbed. Due to this reduced amount of _H2S in the condensate entering hot well 116 from line 114, the amount of ferric chelate used or added will be less than the required ratio of ferric chelate to _H2S in the hot well. can be made much less while retaining the stoichiometric proportions and the amount lost in overflow 180 is less. The Geysers
Known Geothermal Resource Area (KGRA)
(“The Geysers” is a region in the U.S. state of California that is noted for its geothermal activity, including the Geysers.) Geothermal steam from It was found that it contains impurities. Gas range average H ₂ S 5-1600 222 CO ₂ 290-30600 3260 CH ₄ 13-1447 194 NH ₃ 9-1060 194 N ₂ 6-638 52 H ₂ 11-218 56 One object of the present invention is to , to reduce or eliminate hydrogen sulfide (H ₂ S) from condensed geothermal steam after the steam is used to power a turbine. The present invention is useful for other systems that rely on liquid-dominated resources as an energy source.
It can also be applied to KGRA′S. In these cases, the geothermal fluid is processed directly, thus eliminating the condensation step. In the process of the present invention, the amount of ferric chelate used for sulfide conversion ranges from about 1.0 moles to about 6.0 moles, preferably from about 1.2 moles to about 3.0 moles of ferric chelate per mole of _H2S . It was found that it should be. The temperature range for the sulfide conversion process is from about 1.0°C to about 99°C
C. preferably should be in the range of about 25.degree. C. to about 60.degree. The sulfide conversion step is about 5 to about 10, preferably about
It should be performed at a pH ranging from 6.8 to about 8.3. The temperature range of the condensation zone should be from about 1.0°C to about 99°C, preferably from about 25°C to about 65°C. The temperature range of the chelate conversion zone should be from about 1.0°C to about 99°C, preferably from about 25°C to about 65°C. Chelating agents useful in producing chelates useful in producing the ferric chelates of the present invention include:
Includes chelating agents or complexing agents that form water-soluble chelates. Representative of such chelating agents are aminocarboxylic acids such as nitrilotriacetic acid, N-hydroxyethyliminodiacetic acid, ethylenediaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, cyclohexanediaminetetraacetic acid, triethylenetetraacetic acid, etc. Amine hexaacetic acid, etc., and salts thereof are also included. Among such chelating agents are ethylenediaminetetraacetic acid, N-
Hydroxyethylethylenediaminetriacetic acid and N-hydroxyethyliminodiacetic acid are most advantageously used to prepare the ferric chelates used in the present invention. Detailed examples of the invention are presented below for the purpose of further illustrating the invention. Examples 1-4 Versenol iron, a fully chelated iron solution containing 4% iron
(The Dow Chemical Company, Midland,
Michigan, USA)
Prepared from trisodium salt of hydroxyethylethylenediaminetriacetic acid (Na ₃ HEDTA) and ferric nitrate. After baseline data is obtained for hydrogen sulfide release in the absence of iron chelate (ie, control) using the apparatus of FIG. 1 of the accompanying drawings, a drum of Versenol iron concentrate is rapidly added to the cold well 70. Thereafter, pump 76 was used to meter additional iron chelate at a rate of approximately 2 pounds iron per hour to balance that lost in overflow 80. This maintained an iron concentration in the circulating water of about 20 ppm in hot well 16, slightly above the stoichiometric requirement of 14 ppm. Immediately after the addition of iron chelate to the system, hydrogen sulfide emissions from the cooling tower became immeasurably small and could not be detected in this stream for the entire remainder of the test. The data obtained during this test are given in Table 1. Although these data demonstrate that the present invention is highly effective in removing hydrogen sulfide from aqueous streams, a relatively constant percentage of hydrogen sulfide in the noncondensable gas stream 48 is It was shown that it had almost no effect. 【table】

[Brief explanation of drawings]

Figure 1 shows H ₂ S in steam by application of the present invention.
FIG. 2 is a flowchart showing a method for oxidizing and removing the oxidizing agent, and FIG. 2 is a diagram showing a similar method using an indirect condenser. In the figure, 2...geothermal steam line, 4...
...Steam turbine, 10...Direct contact condenser, 20,34...Steam jet ejector, 26,42...Associated condenser, 16...
...High temperature well, 58 ... Pump, 62 ... Cooling tower, 64 ... Air flow, 70 ... Low temperature well, 72
...Cough, 80...This is an overflow line.

Claims (1)

[Claims] 1. A method for purifying H ₂ O containing H ₂ S, comprising: (A) dissolving the steam portion of the H ₂ O directly or indirectly in an aqueous solution in a condensation zone; (B) converting the aqueous sulfide solution to an aqueous solution containing hydrogen sulfide and its ions in a conversion zone, which may be a condensation zone; The aqueous sulfide solution containing free sulfur and ferrous chelate by contacting with an aqueous solution of ferric chelate containing a sufficient amount of ferric chelate to completely oxidize the ferric chelate. (C) converting the ferrous chelate solution to an aqueous solution containing ferric chelate with air in a cooling zone; and (D) recycling the ferric chelate solution to the conversion zone. A method consisting of: 2. The method of claim 1, wherein the amount of ferric chelate used ranges from 1.0 to 6.0 moles of ferric chelate per mole of _H2S . 3 The ferric chelate range is ferric per mole of H ₂ S.
The method according to claim 1, wherein the amount is 1.2 to 3.0 mol. 4. The method according to claim 1, wherein ferric chelate is added as necessary to maintain the sufficient amount. 5. The method of claim 1, wherein a portion of the stream is directly condensed, and the condensed fluid is an aqueous solution of ferric chelate. 6. The method of claim 5, wherein the amount of ferric chelate used ranges from 1.0 to 6.0 moles of ferric chelate per mole of _H2S . 7. The method of claim 5, wherein the amount of ferric chelate used is in the range of 1.2 to 3.0 moles of ferric chelate per mole of _H2S . 8. The method of claim 5, wherein said sulfide conversion is carried out at a temperature in the range of about 1.0°C to 99°C and a pH in the range of 5 to 10. 9. The method of claim 5, wherein the sulfide conversion is carried out at a temperature in the range of about 25°C to 60°C and a pH in the range of 6.8 to 8.3. 10. The method of claim 5, wherein ferric chelate is added as necessary to maintain the sufficient amount.