FR2543015A1 - PROCESS FOR THE PURIFICATION OF BURNED GAS EXIT FROM A CLAUS INSTALLATION - Google Patents

Abstract

IN A PROCESS FOR CLEANING BURNT GAS COMING OUT OF A CLAUS INSTALLATION BY CATALYTIC REDUCTION OF BURNT GAS, ACCOMPANIED BY THE FORMATION OF HYDROGEN SULPHIDE, COOLING OF THE GAS, CONDENSATION AND SEPARATION OF WATER FROM THE BURNT GAS, ADJUSTING THE NECESSARY HSSO RATIO THE REACTION CLAUS LATER, THIS ADJUSTMENT BEING OBTAINED BY COMBINING THE BURNT GAS AND A GAS OBTAINED BY COMBUSTION AND CONTAINING SO, AND PASSING THE GAS UNIT BY A FIRST CONTACT STAGE CLA 22 BELOW THE DEW POINT OF SULFUR, THE GAS SOOT CONTAINER IS COOLED TO A REGENERATION OR COOLING TEMPERATURE AND TAKES TO GO THROUGH A SECOND CONTACT STAGE CLAUS 23 RESPECTIVELY CHARGED OR CLEARED WITH SULFUR, SO AS TO REGENERATE OR COOL THIS STAGE.

Description

I Process for purifying burnt gas leaving a Claus La installation

  present invention relates to a process for purifying burnt gas leaving a Claus installation, while simultaneously obtaining sulfur, by catalytic reduction

  gas burnt at high temperature with the formation of hydrogen

  sulfur-free, by cooling the gas, condensation and separation of water from the burnt gas, adjustment of the molar ratio H 2 S / 502 necessary for a subsequent Claus reaction, this adjustment being carried out by combining the burnt gas and a gas containing SQ 2 and obtained by combustion of a gas containing H 2 S, and by passing the qaz thus united by a first Claus contact stage below the sulfur dew point, while a second Claus contact stage is regenerated doing

pass a hot gas.

  From the German patent application DE AS 21 01 112 there is known a purification process for burnt gases leaving Claus installations, in which water is removed from the gases after their hydrogenation, before subjecting them to a reaction. subsequent in a subsequent Claus stage The formation of sulfur by the Claus reaction is certainly favored by the elimination of water However, since the Claus stage operates above the dew point of sulfur, the sulfur yield does not is not optimal since the equilibrium state of the reaction is not established in a completely favorable manner This yield is indicated as being 98 to 99.5% In the German patent application DE OS 2 134 742 is described a substantially identical process in which the hydrogenated Claus burnt gas and to a large extent freed from water is mixed, in the molar ratio% S / 502 necessary for the Claus reaction, with a gas containing SO 2 and obtained by combustion of a gas containing H 2 S Dan s in this case the additional Claus stage also operates above the sulfur dew point so

  that the disadvantage cited is present here too.

  German Patent No. 2,923,895 describes a process for removing hydrogen sulfide and sulfur dioxide from burnt gases leaving Claus plants, in which the burnt gases are separated into two partial streams; the first partial stream is caused to pass, at temperatures above the dew point of sulfur, through a bed of catalyst loaded with sulfur and the bed is thus regenerated; the vaporized sulfur is separated from this partial stream by cooling and condensation; this partial stream and the second partial stream are combined and the combined partial streams are caused to pass, at temperatures below the dew point of sulfur, through a second bed of catalyst Although the sulfur yield is brought to about 98 , 5% thanks to this additional cold bed stage, the pollution of the atmosphere, that is to say the loss of sulfur, is still considerable by

  so the process needs to be improved.

  Finally, there is described in European patent application N O O 059 548 a process for purifying burnt gas leaving Claus installations in which the sulfur components contained in the burnt gas are transformed into hydrogen sulfide by reducing them catalytically; water is removed from the noisy gas by condensation and then, after adding a quantity of a gas containing 502 necessary for the subsequent Claus reaction, this subsequent reaction is carried out on a cold bed below the dew point sulfur In this case it is necessary to make a hot regeneration gas to

regenerate the charged cold bed.

  The object of the present invention is to enable the

  separation of sulfur from the burnt gas leaving an installation

  tion Claus to be improved quantitatively using a Claus contact stage mounted downstream This is in particular to allow a purification of burnt gases leaving a Claus installation by means of Claus stages at low temperature, in which the regeneration gas for the Claus stages is made available by the process in such a way that its temperature can be regulated in a heat exchanger according to the phases of

  regeneration and cooling.

  This object is achieved according to the invention, with regard to the purification process mentioned above for burnt gases leaving Claus installations, by the fact that the gas containing 502 and-produced by combustion is

  cooled to a regeneration temperature

  tion and / or cooling and is brought to pass through the second contact stage charged with sulfur or freed from sulfur and this stage is thus respectively regenerated or cooled, that the sulfur collected during the regeneration phase is brought by cooling to condense from the gas containing 502 and is separated and that the gas containing 502 is then, after having been combined with the burnt gas, brought to pass through the first contact stage with a view to the formation and separation of

  sulfur The process according to the invention not only allows.

  to further improve the yield which, thanks to the prior separation of water, is in any case already good in the case of Claus contact stages at low temperature, but offers

  in addition, significant operating advantages

  In fact, since the burnt gas containing 502 is available at a high temperature, it is no longer necessary to bring a cold gas to the regeneration temperature. A flexible temperature pipe depending on the regeneration and cooling phases. is easily achievable because the burnt gas containing 502 is hot thanks to the process itself Finally, the Claus reaction on a cold bed offers the advantage that the cold burnt gas due to condensation and the separation of water does no longer needs to be brought to a high temperature

  sulfur yield is about 99 to 99.8%.

  According to a preferred embodiment of the process of the invention, the burnt gas containing 502 is brought back during the regeneration phase to a temperature between 160 and 3600 C and during the cooling phase to a temperature between 100 and 'C The gas containing 502 1 as it results from combustion, for example has a temperature of 400 to 450 * C Cooling is advantageously carried out by passing the hot gas containing 502 before entering the second contact stage, for the adjustment of the regeneration or cooling temperature by a heat exchanger equipped with an adjustable bypass duct By adjusting the tap of the bypass duct, the cooling action of the heat exchanger traversed by the gas and, consequently, the temperature of the gas at the outlet of the heat exchanger and at the inlet of the second contact stage (to be regenerated or cooled)

  can be varied and adapted to the phase concerned.

  According to the preferred embodiment of the process of the invention, the gas containing 502 is obtained by combustion of part of the gas burned from Claus installations, after reduction and separation of water, and optionally part of the gas acid brought to the Claus installation The combustion of burnt gas from Claus installations, this gas having been dehydrated, provides a gas containing 502 and whose water content is consequently low If this gas, after having been combined with the part remaining of the burnt gas leaving Claus installations and containing H 2 S, is used in the Claus stage with a cold bed, suddenly obtains that the gases thus combined also have a low water content and that the equilibrium of the Claus reaction lies in

consequence favorably.

  The flow of gas containing 502 through the Claus contact stages is reversed when the second stage is cooled after being regenerated and the first stage is charged with sulfur The burnt gas containing H 2 S is added each time to the stream of gas containing SQ 2, which flows to the contact stage located in the reaction phase The reaction temperature of the combined gases is advantageously determined by the temperature to which the burnt gas containing

of Hi -

  The burned gas containing SO is preferably produced by partial combustion of the gas containing H 2 S Due to the substoichiometric combustion it still remains

  H 2 S in the burnt gas, which makes this gas special-

  suitable for regeneration.

  The invention is described in more detail below with the aid of the appended drawing o the flow diagram of an installation is shown for the implementation of a mode of

realization of the process.

  The burnt gas from a Claus installation delivered at 'C by a pipe 1 is brought to an in-line burner 2 in which its temperature is brought to 3500 C. In the burner 2, combustible gas is burned with air, the combustible gas and air being supplied respectively by conduits 3 and 4 Hydrogen is at the same time supplied, as a reducing gas, by conduit 5 Passing through conduit 6, a mixture of H 2 S, SQ 2, COS,

  C 52, S, H 2 as well as N 2 reaches the hydrogen enclosure

  tion 7 in which the SQ 2 as well as the sulfur compounds of carbon and the elemental sulfur are hydrogenated so as to form H 2 S The hydrogenation chamber is equipped with a cobalt / molybdenum catalyst The reduction takes place around 3000 C The stream leaving the hydrogenation enclosure is first cooled in the heat exchanger 8 with the cold dehydrated burnt gas and then in the tubular boiler 9 with feed water from the boiler supplied by the conduit 10,

  with vapor formation, up to 1600 Cc At this temperature-

  re the hydrogenated gas arrives in a cooling tower h 1 in which it is further cooled to about 400 C by direct cooling with water In the cooling tower 1 l most of the water present

  in the hydrogenated burnt gas after leaving the installation

  tion Claus condenses The water is constantly recirculated and thus maintained by cooling in the refrigerant 12 at a temperature as close as possible to ambient temperature The quantity of condensed water is drawn off in 13 The H 2 S dissolved in the water is discharged into a drive column (not shown) and returned to

the Claus installation.

  The dehydrated burnt gas leaves the cooling tower at 400 C for 1 hour and is brought to 140 ° C in the heat exchanger 8 About 1/3 of this gas arrives, via the conduit 14, at a burner 15 in which combustible gas supplied through line 16 is burned with air supplied through line 17 Acid gas from the Claus installation can at the same time be brought through line 18 The combustion gas containing 502 and having at the outlet of the burner 15 a temperature of 400 to 450 ° C. arrives in a heat exchanger 19 provided with a hot bypass duct 26 and in which it can be cooled, with the formation of vapor, variably to temperatures between 140 and 3600 C The gas stream containing SQ 2 and cooled for example to 3500 C is then used first to regenerate, passing through the conduit 25, the contact stage Claus 22 charged with elemental sulfur, this gas stream being for this purpose brought to pass through the stage so as to rec ueill the sulfur in the process of vaporization The gas stream containing SQ 2 and charged with sulfur then passes through the sulfur condenser 21 where it is cooled to about 1400 C with formation of vapor and condensation and separation of sulfur The gas stream is then combined with the remaining 2/3 of the burned gas Claus dehydrated, supplied by line 20, and brought to 1400 C at the contact stage Claus 23 The H 25 and the SQ 2 contained in the gas mixture are thus in a large measurement transformed into sulfur which is deposited on the catalyst of this stage Then the burnt gas thus desulfurized

  leaves the installation via conduit 24.

  When the catalyst in stage 22 has been regenerated

  re by vaporization of the sulfur, the temperature of the gas

  of SQ 2 is lowered by opening the bypass duct

  tion provided on the exchanger 19, so that the catalyst of stage 22 is cooled below the dew point of sulfur When the catalyst in stage 22 is cooled and that the catalyst of stage 23 is charged with sulfur, the temperature of the gas containing 52 in the conduit 25 is raised again by closing the tap in the bypass conduit 26 of the exchanger 19 Then the gas stream containing 50 is directed to the contact stage Claus 23 in order to regenerate this stage The Claus reaction and the sulfur separation are then carried out in stage 22 The liquid sulfur separated in the sulfur condenser 21 is withdrawn, according to the direction of flow of the gas containing 502, in 21 or 21 The operation of the Claus stages with cold beds 21 to 25 corresponds, except for the composition of the gas streams, to that of the installation described in

German patent 2,923,895.

EXAMPLE

  Burnt gas delivered at a rate of 37,000 Nm / h by a Claus installation and containing 0.8% by volume of H 28, 0.4% by volume of SQ 2 0.2% by volume of COS + C 52, 1 , 4% by volume of Hz and 1.5 g / Nm of elemental sulfur, which is at a temperature of 130 OC under a pressure of 1.3 bar (abs), is brought to 3000 C in an in-line burner by combustion of 420 Nm 3 / h of combustible gas Before this heating are added to the burnt gas 135 Nm 3 / h of gas rich in H 2 * The mixture reacts in the presence of a Co Mo catalyst, on an alumina support, at 3200 C Thus the 502 is hydrogenated and the sulfur-containing carbon compounds undergo a hydrolysis to form hydrogen sulphide The gas released contains 1.36% by volume of H 2 S and still traces of COS The gas is cooled, first indirectly and then by direct heat exchange with water brought to circulate, up to 400 C Thus are condensed 7.62 t / h of water which is evacuated from the water circuit The gas coming from the direct refrigerant is heated ffé, with the gas from the hydrogenation stage, up to 140 ° C in a heat exchanger

gas / gas heat.

  Of the 30,900 Nm / h of hydrogenated and dehydrated gases, which contain 551 Nm 3 / h of H 2 SD are separated approximately 40% The separated gas stream is heated in a burner in line, o 460 Nm 3 / h of acid gas (60% by volume of H 25) are burned, up to approximately 410 ° C. so as to produce the necessary quantity of SQ. 14,655 Nm / h of combustion gas are thus obtained containing 1.87% by volume of 502 and

1.50% by volume of H 25.

  This gas is cooled, in a heat exchanger provided with a bypass duct, to 350 ° C, then immediately brought to pass through a contact stage Claus charged with sulfur Thus the sulfur vaporizes from the catalyst so to be carried away by the hot gas stream containing So 2 ', which stream is then cooled in a sulfur condenser to 1400 C, thus allowing the sulfur to condense again and to be separated from the gas stream Then the gas containing SQ 2 is combined with the remaining 60% of the gas containing H 2 S, so as to give the mixture the temperature of 1400 C suitable for the Claus reaction at low temperature Then the mixture is brought to pass through another contact stage Claus in which sulfur is formed and deposited on the solid catalyst The gas stream with a flow rate of 33 195 Nm 3 / h passing through this other contact stage Claus contains 1.66% by volume of H 2 S, 0, 83% by volume of SO 2 and approximately 5.3% by volume of H 20 As a result of the sulfur conversion carried out in this contact stage, the content of sulfur compounds in the burnt gas is reduced to 600 ppmv

of Si and 1200 ppmv of H 25.

  When the deposited sulfur is volatilized so as to be completely eliminated from the first Claus contact stage, the temperature of the gas entering this stage and containing 502 is lowered to 1400 C so as to cool the first contact stage to at around 1400 C After cooling of the first contact stage and

  full charge of the second contact stage temperature-

  re gas containing SOS is again raised to 3500 C, and the gas containing 502 is directed to the second Claus contact stage in order to regenerate it, while at the same time the Claus reaction and the accumulation of

  sulfur take place in the first contact stage.

Claims (3)

CLAIMS l Process for purifying burnt gas leaving a Claus installation, while obtaining sulfur at the same time, by catalytic reduction of the burnt gas at high temperature with formation of hydrogen sulfide, by cooling of the gas, condensation and separation of water of the burnt gas, adjustment of the H 2 S 502 molar ratio necessary for the subsequent Claus reaction, this adjustment being obtained by combining the burnt gas and a gas containing 502 and produced by combustion of a gas containing H 2 S, and by passage of the gases thus united by a Claus contact stage below the sulfur dew point, while a second Claus contact stage is regenerated by passing a hot regeneration gas through it, characterized in that the gas produced by combustion and containing S 2 is cooled to a regeneration or cooling temperature and is brought to pass through the second contact stage respectively charged or freed of sulfur so as to regenerate or cool c and contact stage, in that the sulfur collected in the regeneration phase is separated from the gas containing SQ 2 by being condensed by cooling and the gas containing 502 is then, after having been combined with the burnt gas, brought through the first contact stage to allow sulfur to form and settle.   2 Method according to claim 1, characterized in that the burnt gas containing SQ 2 is cooled, during the regeneration phase, to a temperature between 160 and 3600 C and, during the cooling phase, up to a temperature between 100 and 1600 C. 3 Method according to claim 1 or 2, characterized in that the burnt gas containing 502, before entering the second contact stage, is caused to pass through an exchanger heat to adjustable bypass duct in order to communicate the temperature of   regeneration or cooling.   4 Process according to any one of the claims   tions above, characterized in that the gas containing SO 2 is obtained by combustion of part of the burnt gas from a Claus installation, after separation of water from it, and optionally part of the acid gas supplied at the Claus facility.   Process according to any one of the claims   above, characterized in that the direction of flow-   gas containing SO 2 through the Claus contact stages is reversed when the second stage is located   cooled and the first stage loaded.   6 Method according to any one of the claims   above, characterized in that the combustion gas   tion containing 502 is obtained by partial combustion of a gas containing H 25.