EP0000251B1 - Production of hydrogen sulfide from sulfur dioxide obtained from flue gas - Google Patents

Production of hydrogen sulfide from sulfur dioxide obtained from flue gas Download PDF

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Publication number
EP0000251B1
EP0000251B1 EP78300044A EP78300044A EP0000251B1 EP 0000251 B1 EP0000251 B1 EP 0000251B1 EP 78300044 A EP78300044 A EP 78300044A EP 78300044 A EP78300044 A EP 78300044A EP 0000251 B1 EP0000251 B1 EP 0000251B1
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EP
European Patent Office
Prior art keywords
sodium
solid
conveying
slurry
sulfite
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Expired
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EP78300044A
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German (de)
English (en)
French (fr)
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EP0000251A1 (en
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Ralph Miller
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/16—Hydrogen sulfides
    • C01B17/164—Preparation by reduction of oxidic sulfur compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/48—Sulfur compounds
    • B01D53/50—Sulfur oxides
    • B01D53/501—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/60—Simultaneously removing sulfur oxides and nitrogen oxides

Definitions

  • This invention is concerned with the economic conversion of sulfur dioxide initially contained in a gas mixture in which the S0 2 was a very minor component to gaseous hydrogen sulfide as a major component in a gas mixture. Although this invention is useful in a variety of circumstances, it is of especial utility in flue gas desulfurization-FGD.
  • sulfur dioxide is detrimental to the well-being of animal, aquatic and plant life.
  • sulfur dioxide is converted to sulfuric acid by the oxygen and moisture in the air, which conversion takes place readily, sulfur dioxide is responsible for the corrosion of many materials of construction including steel and concrete.
  • Aqueous Carbonate Process AGP
  • a carbonate FGD process is disclosed in French Patent Specification FR-A 2162630 for the removal and its subsequent recovery as hydrogen sulfide, of the bulk of the sulfur dioxide contained in a flue gas, which process includes the steps of
  • the S0 2 absorption step is normally carried out so as to produce a dry mixture of solid particles of sodium sulfite, sodium sulfate and sodium carbonate suspended in the S0 2- denuded gas. These particles have to be substantially completely removed from the flue gas to avoid contaminating the atmosphere with particulate material and excessive consumption of sodium carbonate. This involves the use of complex and expensive procedures such as banks of cyclones followed by an electrostatic precipitator installation.
  • Said French specification also refers briefly to an alternative process in which the S0 2 absorption step produces a solution of alkali metal sulfite and sulfate. Again this results in the need for a relatively complex and expensive separation process such as evaporation. Yet another alternative involving the use of particles of solid sodium carbonate in the absorption step is described in the French specification as requiring a relatively long contact time which in most applications is generally not available.
  • regenerable process for the removal, and its subsequent recovery as hydrogen sulfide, of the bulk of the sulfur dioxide contained in a flue gas containing oxygen comprising the steps of:
  • aqueous slurry containing solid sodium sulfite and sodium sulfate may be very simply and economically separated by mechanical means such as those described hereinbelow from the treated flue gas and so as to provide solid sodium sulfite and sodium sulfate.
  • the present invention provides a system for removing the sulfur dioxide contained in a flue gas, comprising:
  • the ability of the absorbent to continue to absorb S0 2 is maintained by the subsequent addition of sodium carbonate.
  • the sodium bisulfite reacts with the carbonate as follows:
  • the second series of reactions of the process involve the reduction of the sodium sulfite and sodium sulfate to sodium sulfide by means of a readily available reducing agent. In most instances this will be a carbon-containing reducing agent such as bituminous coal. Other inexpensive carbon-containing reductants such as coke, or wood, or heavy oil also work satisfactorily.
  • the overall reactions, when carbon containing reducing agents which are particularly convenient, are used can be summarized as: If sodium nitrate is present it is converted to sodium carbonate and nitrogen. The overall reaction is:
  • the principal reaction following the reduction reactions is the generation of hydrogen sulfide from sodium sulfide and sodium bicarbonate.
  • the overall reaction is: It will be noted that the sequence of the reduction reactions followed by the H Z S generation step results in the regeneration of the sodium carbonate used in the S0 2 absorption step.
  • Any convenient, low cost source of CO 2 can be used such as for example the gas resulting from the reducing step where a carbon-containing reducing agent has been used, or the SO 2 -free flue gas.
  • Figure 1 is a flow diagram depicting the relationship of the various steps to each other when the invention is practised at a site where space is available for all the necessary equipment and the SO 2 -containing flue gas is washed with water to remove particulates prior to the S0 2 removal step. Under less preferable conditions certain steps of the process can be physically separated. Although not desirable, in some instances it is necessary to carry out certain steps of the process at two different locations.
  • One of the advantages of the invention is that a split operation is technically. feasible. This mode of operation is employed when it provides economic advantages compared with the use of any other process for freeing flue gas from pollutants prior to venting it to the atmosphere.
  • the invention can be understood by following each step starting with the sulfur compound as it enters the process as sulfur dioxide and finally leaves as gaseous hydrogen sulfide in concentrated form.
  • the S0 2- containing flue gas is scrubbed with water by means not shown to remove the bulk of the particulate solids.
  • the gas then flows into the lower gas inlet of a first absorption zone or gas-contacting device (1) by means of duct (2).
  • the gas is contacted by an aqueous slurry, the liquid phase of which is an aqueous solution containing mostly dissolved sodium sulfite and sodium sulfate, minor amounts of other sodium salts, e.g. sodium nitrate, plus a small amount of sodium carbonate.
  • the solid phase is essentially mixed crystals of sodium sulfite and sodium sulfate-the bulk of the solids being composed of sodium sulfite.
  • the temperature of the scrubbing step is controlled so that the anhydrous salt crystallizes i.e. the temperature is maintained at such a temperature that the solid salts which precipitate are free from water of crystallization.
  • a suitable temperature range is between 40°C and 50°C.
  • the purpose of maintaining the scrubbing solution at the indicated temperature is to minimize the fuel cost in a subsequent step of the process. It does not affect the ability of the solution to absorb S0 2 or oxides of nitrogen. The undesirable oxidation of sulfite to sulfate takes place primarily in this first absorption zone.
  • the solids in the slurry always contain some sodium sulfate mixed with the sodium sulfite. Whenever solid sodium sulfite is mentioned below it must be understood that it will be mixed with some sodium sulfate. Similarly, it should be understood that the liquid phase of the absorbent slurry will always contain some dissolved sodium sulfate but the predominant solute will be sodium sulfite.
  • the oxides of nitrogen of the flue gas are also. absorbed in this first absorption zone to a greater or less degree depending upon the amount of NO and N0 2 present. If there are equimolar concentrations, most of oxides will be absorbed and form sodium nitrite.
  • the solution is fortified by the continuous or periodic addition of sodium carbonate the source of which is described below.
  • the slurry used to contact the S0 2 - concentrating gas in the first absorption zone enters it at one end through pipe 3 by means of a pump not shown.
  • the slurry flows through the zone counter-current to the S0 2- containing gas flowing in the opposite direction.
  • the S0 2 is absorbed by the liquid phase of the slurry as the gas leaves the zone through vent pipe 22.
  • additional solid sodium sulfite forms since the solution is maintained in a saturated condition.
  • the slurry leaves the first absorption zone by means of first conveying means in the form of an outlet pipe 4 which conducts it into a settler 5 of a separating means.
  • the larger crystals in the slurry sink to the lower section of the settler and form a more dense magma.
  • the smaller crystals and the bulk of the liquid phase leave the settler through overflow line 6 through which it empties into surge tank 7.
  • the magma formed in the base of the settler leaves through its bottom outlet and flows by means of pipe 8 into centrifuge 9. In centrifuge 9 most of the solids are separated from their accompanying liquid phase.
  • the liquid phase is directed to surge tank 7 by means of pipe 10. Crude sodium carbonate is also fed to surge tank 7 by means of belt 17.
  • the mixture formed in tank 7 is circulated through the absorption zone 1 by means of the pump, not shown, mentioned previously.
  • the moist solids separated in centrifuge 9 are conveyed by second conveying means including a belt 11 into a feed hopper 12.
  • feed hopper 13 is periodically replenished with pulverized bituminous coal.
  • Pulverized coal constituting a carbon-containing reducing agent is removed from hopper 13 by means of screw conveyor 14 and to mixer 15.
  • Crude moist sodium sulfite is withdrawn from feed hopper 12 by means of feeder 16 and also fed to mixer 15.
  • Crude moist sodium sulfite and coal are intimately mixed in mixer 15 and the mixture fed by means of a screw conveyor 18 of second conveying means into the feed end of a reducing means comprising a direct fired rotary kiln 19.
  • the solid mixture formed in the rotary kiln is withdrawn through the kiln's discharge outlet by means of a third conveying means comprising a screw conveyor 23 equipped with means, not shown, to prevent air from contacting the hot solid sodium sulfide-containing mixture.
  • Screw conveyor 23 delivers the sodium sulfide-containing mixture to mixing means comprising a continuous mixer-grinder 24 in which it is blended with the stoichiometric quantity of moist sodium bicarbonate the source of which is described below.
  • the mixer-grinder converts the mixture into small particles thoroughly commingled.
  • Mixer-grinder 24 is equipped with seals to prevent the escape of any vapours formed during the blending operation. To ensure that vapours do not escape mixer-grinder 24 is maintained under a slight negative pressure.
  • the mixture resulting from the blending of the bicarbonate and sodium sulfide-containing solid flows out of the mixer-grinder's outlet into fourth conveying means in the form of a screw conveyor 25 which delivers it to a heating means comprising a steam tube rotary calciner 26.
  • the steam tube calciner is heated by high pressure steam e.g. steam at a pressure between 27.6 and 31 bars.
  • the bulk of the sodium bicarbonate and the bulk of the sodium sulfide are heated to a temperature of about 200°C. Under these conditions they react to form crude sodium carbonate and gaseous hydrogen sulfide.
  • the water vapour and gaseous hydrogen sulfide leave the calciner's gas outlet and by means of fifth conveying means in the form of a pipe 27 are conveyed to a recovering means including a condenser, not shown, in which the bulk of the water vapour is separated from the H Z S and in a Claus process plant not shown in which the separated H Z S is converted to sulfur.
  • the crude sodium carbonate-containing solid formed in the calciner leaves the calciner's discharge outlet and by means of a screw conveyor 28 and sixth conveying means in the form of a screw conveyor 29, respective portions of crude sodium carbonate are fed to surge tank 7 via belt 17, and to a dissolver 30 of an adding means.
  • Sodium bicarbonate-containing solution whose source is described below is also fed to the dissolver 30 by means of line 32.
  • the slurry formed in dissolver 30 is piped via a pipe 31 of seventh conveying means to a filter 37.
  • the concentrated filtrate separated from the solids by means of filter 37 is pumped by a pump, not shown, through line 33 into surge tank 34. Wash water is introduced to the washing section of filter 37 by means of water feed line 35.
  • the wash liquor containing the remaining water soluble components of the mixture entering dissolver 30 flows out of filter 37 and by means of line 36 is directed to dissolver 30 via pipe 12.
  • the washed solids, free from water soluble components, leaves filter 37 and by means of screw conveyor 38 is mixed with the fuel fed to the boiler, not shown, in which the sulfur dioxide-containing products of combustion are formed.
  • the solution and suspended solids contained in surge tank 34 which consists in large part of a mixture of sodium bicarbonate and sodium carbonate is circulated by means of pipe 54 to the liquid inlet of a second absorption zone 40 of the adding means.
  • Carbon dioxide-containing gas is fed to inlet of absorption zone 40 by means of pipe line 41.
  • the source of the carbon dioxide gas is described below.
  • carbon dioxide is absorbed by the sodium carbonate-containing solution which is maintained saturated with sodium bicarbonate.
  • sodium carbonate is converted to sodium bicarbonate which crystallizes from solution.
  • the slurry leaving absorption zone 40 is directed into a second separating means in the form of a settler 42 by means of line 43 of the seventh conveying means.
  • the larger particles of solid sodium bicarbonate in the slurry settle into the lower section of the settler 42.
  • the smaller particles and the bulk of the solution leave the settler from its top outlet and by means of pipe 44 is delivered to surge tank 34.
  • the magma formed in the lower section of settler 42 is fed to centrifuge 45 by means of pipe 46.
  • Centrifuge 45 separates the slurry feed into two fractions one of which is the centrifuge cake consisting in large part of moist sodium bicarbonate and the other consisting of the bulk of the solution contained in the slurry.
  • the moist sodium bicarbonate cake is transported by eighth conveying means in the form of a belt conveyor 47 to the mixer-grinder 24.
  • the solution leaving the centrifuge flows by means of pipe 48 into surge tank 34.
  • the carbon dioxide fed to absorption zone 40 is preferably obtained from the exhaust gas from kiln 19 by means of duct 49 via pipe 41. Should this gas be unavailable as a result of local conditions or should the quantity of CO 2 be insufficient for any reason, then carbon dioxide can be obtained from the gas leaving absorption zone 1.
  • CO 2 is fed to absorption zone 40 from the gas leaving absorption zone 1, it is piped from vent pipe 22 by means of pipeline 50 into pipe 41 which leads to absorption zone 40.
  • Carbon dioxide-containing gas exiting from absorption zone 1, not needed for absorption in zone 40 is vented to the atmosphere by means of vent pipe 51. No matter the source of the carbon dioxide entering absorption zone 40, the CO 2 will be mixed with a preponderance of nitrogen. The nitrogen plus all of the remaining unabsorbed gas leaves zone 40 by means of vent pipe 52.
  • a soluble slurry absorbent i.e. an aqueous solution saturated with sodium sulfite containing suspended sodium sulfite crystals
  • hydroclones can be used instead of settlers.
  • filters can be used instead of centrifuges.
  • the filter cake is mixed with the fuel fed to the boiler.
  • the weight of filter cake is only a small fraction of the weight of fuel. Because the weight of filter cake is so small compared with the weight of the fuel, adding the filter cake to the fuel does not affect the operation of the burner but it prevents fuel from being wasted.
  • This process is particularly advantageous when used to control the pollutants in the flue gas of a coal burning large steam raising installation used to generate electricity.
  • various sodium salts are formed and then converted to other salts in sequence, other than coal, only utilities are consumed and they are all readily available and relatively inexpensive at such a location.
  • the slurry circulated will contain suspended water soluble sodium sulfur salts and the particulates.
  • the moist filter cake obtained by the centrifugation operation will contain the water insoluble particulates which had been suspended in the flue gas and sodium salts i.e. sodium sulfite, sodium sulfate, along with minor amounts of sodium nitrite and sodium nitrate.
  • sodium salts i.e. sodium sulfite, sodium sulfate, along with minor amounts of sodium nitrite and sodium nitrate.
  • the filter cake is transported by some convenient means to a location where there is sufficient land to install the rest of the equipment required to carry out the process. Much of the equipment has already been described. Additional facilities wil be needed, however. These facilities will consist primarily of a dissolver and filter with means to wash the water soluble sodium salts out of the filter cake using a minimum of water.
  • the insoluble particulates are separated from the mixed sodium salts.
  • the end results consists of two filter cakes.
  • One is composed of innocuous, water insoluble, solids essentially the ash resulting from the burning of the fuel.
  • the other is a moist filter cake composed principally of sodium sulfite and sodium sulfate.
  • the sodium salt filter cake is processed as has already been described to recover the sulfur values and to regulate sodium carbonate. Part of the crude sodium carbonate formed in the H Z S formation step is shipped back to the scrubbing operation for additional S0 2 absorption.
  • This device is useful when absorbing CO 2 as well as SO 2 .
  • the NH 3 enters the vapor phase, reacts with the acidic gas to form a salt particle that quickly absorbs water vapor so that it is enlarged and easily wetted.
  • the moist particle is rapidly dissolved by the scrub liquor.
  • ammonia vaporizes and the cycle is repeated.
  • the savings in pressure drop resulting from the maintenance of a small concentration of ammonia in the scrubbing system is larger than the cost of the ammonia that has to be continuously supplied.
  • the reduction can be carried out in a direct fired rotary kiln or a multiple hearth furnace.
  • the reactor can be a refractory lined pot with means for adding the sodium salts to be reduced and the reductant. Air can be blown into the mixture to burn some of the reductant to provide the necessary heat.
  • the reaction between sodium sulfide and sodium bicarbonate to evolve H 2 S and sodium carbonate is carried out conveniently at a temperature between about 180°C and 220°C. Even lower temperatures can be used by increasing the amount of water in the initial mixture.
  • the rotary steam tube calciner is a particularly useful piece of equipment in which to carry out this reaction when high pressure steam is available.
  • a high boiling liquid heat transfer fluid such as the well-known Dowtherms can be used in place of high pressure steam.
  • Other equipment can also be employed provided the intimate mixture of Na 2 S and NaHC0 3 is heated to the reaction temperature under substantially muffle conditions.
  • a multiple hearth muffle furnace can be used as well as an indirectly heated rotary kiln.
  • One of the factors which influences the economics of this invention is the amount of energy required to recover a pound of H 2 S.
  • This item is strongly influenced by the moisture content of the mixture of Na 2 S and NaHC0 3 which is heated to evolve H 2 S. The higher the moisture content, the lower the temperature to which the mixture has to be heated. In most instances the moisture content is controlled so that two to three pounds of water are vaporized per pound of H 2 S evolved although under some circumstances it is advantageous to vaporize three times this quantity. If it is convenient to heat the mixture above 200°C, good conversions are obtained when somewhat less water is present in the initial mixture.
  • this invention provides an improved process for the recovery of the sulfur values from an S0 2- containing flue gas while simultaneously purifying it so that it may be exhausted to the atmosphere as a substantially clean and harmless effluent. Variations can be employed with respect to procedures and proportions without changing the scope of the invention as defined by the following claims.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Biomedical Technology (AREA)
  • Environmental & Geological Engineering (AREA)
  • Analytical Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Treating Waste Gases (AREA)
EP78300044A 1977-06-16 1978-06-14 Production of hydrogen sulfide from sulfur dioxide obtained from flue gas Expired EP0000251B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US807044 1977-06-16
US05/807,044 US4141961A (en) 1977-06-16 1977-06-16 Production of H2 S from SO2 obtained from flue gas

Publications (2)

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EP0000251A1 EP0000251A1 (en) 1979-01-10
EP0000251B1 true EP0000251B1 (en) 1982-07-28

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EP78300044A Expired EP0000251B1 (en) 1977-06-16 1978-06-14 Production of hydrogen sulfide from sulfur dioxide obtained from flue gas

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US (1) US4141961A (it)
EP (1) EP0000251B1 (it)
JP (1) JPS546897A (it)
CA (1) CA1090534A (it)
DE (1) DE2861967D1 (it)
IT (1) IT1159729B (it)
ZA (1) ZA783400B (it)

Families Citing this family (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5819327B2 (ja) * 1978-06-28 1983-04-18 呉羽化学工業株式会社 排ガスの処理方法
JPS5520608A (en) * 1978-07-28 1980-02-14 Kureha Chem Ind Co Ltd Treating method for waste gas absorption product
US4241041A (en) * 1979-01-22 1980-12-23 Mei Systems Inc. Methods for the recovery of sulfur components from flue gas and recycle sodium sulfite by reduction-smelting and carbonating to strip hydrogen sulfide
US4588567A (en) * 1985-01-28 1986-05-13 Ralph Miller Recovery of concentrated H2 S from SO2 contained in flue gas
US4837001A (en) * 1986-03-03 1989-06-06 T-Thermal, Inc. Production of sulfur from sulfur dioxide obtained from flue gas
US4758371A (en) * 1986-03-11 1988-07-19 Nl Industries, Inc. Process and composition for removal of mercaptans from gas streams
US4917874A (en) * 1988-06-24 1990-04-17 The University Of Tennessee Research Corporation Desulfurization process
US5059406A (en) * 1990-04-17 1991-10-22 University Of Tennessee Research Corporation Desulfurization process
FR2681796B1 (fr) * 1991-09-30 1994-05-20 Solvay Et Cie Procede pour epurer un gaz contenant de l'oxyde nitrique .
US20120323714A1 (en) * 2011-06-16 2012-12-20 Surendra Saxena Modified steam-methane-reformation: Hydrogen production with carbon sequestration
CN102762502B (zh) 2010-02-25 2015-08-12 阿尔法拉瓦尔股份有限公司 排气和气体洗涤器流体清洁设备及方法
DK2402288T3 (en) * 2010-07-02 2017-02-06 Alfa Laval Corp Ab GAS SCRUBBER FLUID CLEANING EQUIPMENT
CA3009451A1 (en) * 2015-12-27 2017-07-06 Metoxs Pte, Ltd. System for generating h2s in an alkaline medium and method of using the same
CN108043211A (zh) * 2018-01-24 2018-05-18 东莞市升佳净水材料有限公司 一种脱硫增效剂及其制备方法
US10617999B2 (en) 2018-07-12 2020-04-14 AECOM Technical Services, Inc. Process for removing SO2 from flue gases using liquid sorbent injection
JP6970070B2 (ja) * 2018-10-22 2021-11-24 フタバ産業株式会社 排気熱回収器

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1692878C3 (de) * 1966-05-25 1974-04-04 Oy Tampella Ab, Heinola (Finnland) Verfahren/um Auskristallisieren von Alkali als Karbonat aus der bei der Zellstoffablaugen-Aufarbeitung anfallenden Schmelz lösung
US3932587A (en) * 1971-12-09 1976-01-13 Rockwell International Corporation Absorption of sulfur oxides from flue gas
US3832444A (en) * 1972-05-18 1974-08-27 Trw Inc Recovery of so{11 {11 and so{11 {11 from flue gases
GB1411330A (en) * 1973-09-19 1975-10-22 Tsukishima Kikai Co Process for desulphurisation of waste gas
US3932586A (en) * 1973-10-12 1976-01-13 The University Of Delaware Removal of oxides of sulfur from gases
US3966418A (en) * 1974-01-16 1976-06-29 The Dow Chemical Company Gas treatment apparatus
US3987147A (en) * 1974-02-21 1976-10-19 The University Of Delaware Process to desulfurize gas and recover sulfur
US4003985A (en) * 1976-01-30 1977-01-18 Allied Chemical Corporation Production of sodium sulfite

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Publication number Publication date
JPS546897A (en) 1979-01-19
ZA783400B (en) 1979-06-27
IT7868405A0 (it) 1978-06-16
CA1090534A (en) 1980-12-02
DE2861967D1 (en) 1982-09-16
IT1159729B (it) 1987-03-04
US4141961A (en) 1979-02-27
EP0000251A1 (en) 1979-01-10

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