Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Sulfur or sulfur containing component
Reexamination Certificate
2000-08-10
2002-09-03
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Sulfur or sulfur containing component
C423S244090, C423S573100, C423S574100, C423S576000, C423S576800
Reexamination Certificate
active
06444185
ABSTRACT:
Process for virtually total removal of the sulphur compounds H
2
S, SO
2
, COS and/or CS
2
which are present in a residual gas from a sulphur plant, with recovery of the said compounds in the form of sulphur.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to a process for the virtually total removal of the sulphur compounds H
2
S, SO
2
, COS and/or CS
2
which are present in a residual gas from a sulphur plant, with recovery of the said compounds in the form of sulphur.
The residual gases originating from a sulphur plant in which sulphur is produced by the Claus process of controlled oxidation of a sour gas containing H
2
S, by means of a gas containing free oxygen, contain of the order of 0.2% to 4% by volume of sulphur compounds a large proportion of which consists of H
2
S, the remainder consisting of SO
2
, COS, CS
2
and sulphur vapour and/or vesicular sulphur.
Such residual gases are commonly treated in order to lower as much as possible the overall content of sulphur compounds therein, with the aim of making it possible to discharge them to the atmosphere, after they have been, burned, while meeting the standards imposed by legislation on atmospheric pollution and simultaneously of recovering these sulphur compounds in a form contributing to increasing the yield of upgradable products formed from the sour gas treated in the sulphur plant.
In citation EP-A-0346218 a process is proposed for the treatment of residual gases which originate from a sulphur plant, in which a controlled oxidation of H
2
S in a sour gas is carried out by means of a gas containing free oxygen, and which contain H
2
S, SO
2
, COS and/or CS
2
, the process making it possible to recover virtually all of the compounds COS and CS
2
in the form of sulphur. This process consists in bringing the residual gas originating from the sulphur plant into contact with a catalyst of hydrolysis of the compounds COS and CS
2
to H
2
S, placed in an oxidation and hydrolysis unit, the operation being carried out at a temperature which is sufficient to produce a hydrolysed residual gas containing H
2
S and SO
2
and substantially free from COS and CS
2
, in passing the hydrolysed residual gas into a purification unit, after having brought the temperature of the said gas to the value required for its flow into the purification unit, causing the compounds H
2
S and SO
2
in the hydrolysed residual gas to react with each other in the said unit to form sulphur and to obtain, at the exit of this unit, a substantially purified residual gas with a low residual content of sulphur compounds and in continuously adjusting the H
2
S:SO
2
molar ratio in the hydrolysed residual gas to a value substantially equal to 2:1 at the entry of the purification unit by varying the ratio of the flow rates of sour gas containing H
2
S and of gas containing free oxygen which are introduced into the sulphur plant.
In citation EP-A-0424259 an improvement to the abovementioned process is proposed which makes it possible to improve the quality of the control of the H
2
S:SO
2
molar ratio in the hydrolysed residual gas entering the purification unit and generally to limit or to reduce the H
2
S and SO
2
content of the said hydrolysed residual gas. The said improvement consists in maintaining the H
2
S:SO
2
molar ratio in the residual gas originating from the sulphur plant and entering the oxidation and hydrolysis unit at a value equal to or higher than 2:1 by varying the ratio of the flow rates of sour gas containing H
2
S and of gas containing free oxygen which are introduced into the sulphur plant, in introducing into the oxidation and hydrolysis unit a gas flow containing free oxygen and in performing in the said unit an oxidation of H
2
S to SO
2
and optionally to sulphur by means of the said gas flow in contact with a catalyst of oxidation of the H
2
S present in this unit and in maintaining the H
2
S:SO
2
molar ratio in the hydrolysed residual gas entering the purification unit at the value substantially equal to 2:1 by varying the flow rate of the gas flow containing free oxygen introduced into the oxidation and hydrolysis unit.
Citation EP-A-0218302 describes, inter alia, a process for the treatment of residual gases containing H
2
S and SO
2
in low concentrations and in an H
2
S:SO
2
molar ratio of at least 2.2:1 and additionally containing COS and CS
2
. In such a process the residual gas is first of all subjected to a catalytic hydrolysis carried out at a temperature of 200° C. to 350° C., so as to convert the compounds COS and CS
2
into H
2
S. The hydrolysed residual gas is next brought into contact with a catalyst operating at a temperature ranging from 80° C. to 150° C. in order to carry out the reaction between H
2
S and SO
2
producing sulphur (2 H
2
S+SO
2
⇄3S+2H
2
O) which sulphur is deposited on the catalyst, and a gaseous effluent containing H
2
S as the only sulphur compound. The said gaseous effluent to which an appropriate quantity of oxygen has been added in the form of air (approximately 1.5 times the stoichiometric quantity) is brought into contact with a catalyst of direct oxidation of the H
2
S to sulphur (H
2
S+½O
2
→S+H
2
O), also operating at a temperature of 80° C. to 150° C., producing sulphur, which is deposited on the catalyst, and a desulphurized residual gas.
BRIEF SUMMARY OF THE INVENTION
According to the invention a process is proposed for removal of the sulphur compounds H
2
S, SO
2
, COS and/or CS
2
which are present in a residual gas from a Claus-type sulphur plant, which constitutes an improvement to the processes described in the abovementioned citations and which results in a more thorough removal of the said sulphur compounds, the result being the possibility, in the case of the whole sour gas treatment unit combining the sulphur plant and the plant using the process according to the invention, of reaching overall sulphur recovery efficiencies of at least 99.9%.
The process according to the invention for the virtually total removal of the sulphur compounds H
2
S, SO
2
, COS and/or CS
2
which are present in a residual gas from a sulphur plant, which carries out a controlled oxidation of the H
2
S in a sour gas by means of a gas containing free oxygen, with recovery of the said sulphur compounds in the form of sulphur, is of the type in which the residual gas originating from the sulphur plant is brought into contact with a catalyst of hydrolysis of the compounds COS and CS
2
to H
2
S, placed in an oxidation and hydrolysis unit, the operation being carried out at a temperature which is sufficient to produce a hydrolysed residual gas containing H
2
S and SO
2
and substantially free from COS and CS
2
. the hydrolysed residual gas is passed into a purification unit after having brought the temperature of the said gas to the value required for its flow into this unit, and the compounds H
2
S and SO
2
in the hydrolysed residual gas are caused to react with each other in the purification unit to form sulphur and to obtain, at the exit of this unit, a substantially purified residual gas containing H
2
S as the only sulphur compound and the substantially purified residual gas is introduced into a catalytic oxidation unit containing a catalyst of selective oxidation of H
2
S to sulphur and the substantially purified residual gas is maintained in this catalytic oxidation unit in contact with the oxidation catalyst in the presence of a quantity of oxygen which is injected into the said catalytic oxidation unit in the form of a gas stream containing free oxygen in excess in relation to the stoichiometric quantity needed for oxidizing to sulphur the H
2
S in the substantially purified residual gas, the oxidation being carried out at temperatures lower than 150° C., and it is characterized in that the H
2
S and SO
2
concentrations, expressed as volume percentages (H
2
S) and (SO
2
), are maintained in the hydrolysed residual gas entering the purification unit at values such that the quantity (H
2
S)−2(SO
2
) is higher than 0.2% without exceeding
Nougayrede Jean
Philippe Andre
Savin-Poncet Sabine
Elf Exploration Production
Silverman Stanley S.
Townsend and Townsend / and Crew LLP
Vanoy Timothy C
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