GB1578002A

GB1578002A - Production of sulphur and sulphuric acid from hydrogen sulphide

Info

Publication number: GB1578002A
Application number: GB1597078A
Authority: GB
Original assignee: Ght Hochtemperaturreak Tech
Current assignee: Ght Hochtemperaturreak Tech
Priority date: 1977-04-21
Filing date: 1978-04-21
Publication date: 1980-10-29
Also published as: FR2387903B1; DE2717633A1; FR2387903A1; NL7803901A; JPS53131996A

Description

(54) PRODUCTION OF SULPHUR AND SULPHURIC ACID FROM HYDROGEN SULPHIDE (71) We, GHT, GESELLSCHAFT FUR HOCHTEMPERATURREAKTORTECH NIK MBH, a German Company, of 5060 Bergisch Gladbach 1, Friedrich-Ebert-Strasse, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for the production of sulphur and sulphur dioxide by combustion of hydrogen sulphide more particularly in large sized plants in which waste gases having a high proportion of hydrogen sulphide are to be converted partially to elemental sulphur and partially to sulphuric acid.

In the so-called Claus process, hydrogen sulphide is converted to elemental sulphur by partial oxidation and by subsequent reaction between hydrogen sulphide and sulphur dioxide on bauxite. Since the conversion achieved in the Claus reactor does not amount to more than 98% and cannot be increased by using any commercially feasible means, a waste gas is produced containing H2S, COS, CS2 and SO2, as well as a proportion of sulphur vapour in accordance with the sulphur partial pressure in the reactor employed. On account of the poisonous nature of the H2S and organic sulphur compounds, the waste gas from the Claus reactor is burnt in a subsequent combustion furnace before being released into the atmosphere.At this stage, there is just a waste gas containing from about 5,000 to 6,000 ppm SO,. Because of the need to avoid atmospheric pollution, it is generally desirable to reduce the SO2 content of waste gases from the combustion furnace. Hence, for example, downstream of the last Claus reactor takes place a further reaction stage in the liquid phase.

In this way it has been possible successfully to reduce the SO2 content of waste gas to 1,000 ppm. With large scale plants, this still represents, however, an enviromental hazard.

According to the present invention there is provided a process for the production of sulphur and sulphuric acid from hydrogen sulphide which comprises the steps of subjecting the hydrogen sulphide to partial combustion in a first furnace in which a partial pressure of air exists which is sufficient to partially oxidise the hydrogen sulphide to sulphur but insufficient to further oxidise a major proportion of the sulphur produced, subjecting the combustion products to indirect heat exchange to remove heat of combustion therefrom, separating off by condensation elemental sulphur thereby produced, subjecting residual gases from which said sulphur has condensed out to complete combustion in a second furnace in an atmosphere having a sufficiently high partial pressure of air to yield sulphur dioxide and utilising the sulphur dioxide in the production of sulphuric acid.By varying the processing conditions employed. it is possible readily to vary the proportions of sulphur and sulphuric acid obtained from the initial hydrogen sulphide. The process of this invention is particularly applicable to the treatment of hydrogen sulphide-containing waste gases from industrial plant.

In the process of this invention there first takes place combustion with a low air partial pressure in accordance with the following reaction: 2 H2S + O2 = 2 S + 2 H2O At this stage, conversation of hydrogen sulphide right through to sulphur dioxide according to the following reaction only takes place to a small extent: H25 + 3/2 2 = SO2 + H20 By operating in this manner, it is readily possible to convert the major proportion of the hydrogen sulphide to elemental sulphur, with only a small proportion being converted to sulphur dioxide. In general, up to 70% of the total amount of hydrogen sulphide will be converted to elemental sulphur.The heat of combustion is then substantially withdrawn from the gas stream by indirect heat exchange, preferably in a steam generator, the withdrawn heat serving to produce steam at a temperature and pressure level suitable for commercial use. Sulphur is then removed from the reaction product, generally in a sulphur condenser in which the gas is further cooled down. In this way, the major proportion of the elemental sulphur formed is condensed at relatively low temperatures and removed in liquid form. The heat discharged here can generally be employed for operation of the steam generator at low temperature or pressure level. The gas leaving the sulphur condenser contains H2S, COS, CS2, SO2, as well as small quantities of elemental sulphur in vapour form.These gases are passed to a second furnace in which they are mixed with air which is used in amounts such as to provide the major partial pressure and the gases are completely burnt to SO2. This SO2 is cooled in a second heat exchanger again preferably a steam generator, and is subsequently converted to sulphuric acid using any convenient process, for example making use of a double absorption arrangement or a wet catalyst arrangement.

The process of this invention is preferably carried out using an apparatus which comprises a by-pass circuit which branches off from a main flow line before the first furnace, the by-pass circuit opening into the second furnace before the position of entry of the sulphur dioxide-containing gases resulting from the partial combustion in the first furnace. It is thus possible, on occasion, for hydrogen sulphide to pass directly to the second furnace, missing but the first furnace.This is desirable on occasion when the gases entering the first furnace contain only small amounts of H2S, or for example, when, as a result of the break down of main plant producing H2S-containing gas, a gaseous effluent from the plant contains an amount of H2S which has decreased to a low level such that the combustion temperature in the second furnace would, without additional heating, not suffice for complete combustion.

If a partial stream of the H,S-containing gas is fed directly into the second furnace through this by-pass line, there is always guaranteed a sufficient combustion temperature there and, correspondingly, a complete conversion to SO2. Moreover, by increasing the volume flow in this by-pass line, it is possible to increase the amount of SO2, and hence sulphuric acid, produced with respect to the amount of elemental sulphur produced.

For a better understanding of the invention, and to show how the same can be carried into effect, reference will now be made, by way of example only, to the accompanying drawing, which is a flow scheme showing an arrangement suitable for use in carrying out the process of the invention.

Referring to the drawing, a first combustion chamber 1 serves for the combustion of hydrogen sulphide-containing gas fed thereto together with air such as to yield a low air partial pressure. Combustion products from furnace 1 are fed to a steam generator 2 in which a large proportion of the heat of combustion produced in chamber 1 is utilised for generation of steam from water fed thereto. A small amount of elemental sulphur condenses out and is withdrawn in liquid form from the colder part of the steam generator.

The uncondensed gases pass on to a vertical sulphur condenser to which further water is supplied such as to maintain the temperature in the sulphur condenser within the narrow range of from 120 to 140"C necessitated by the special flow properties of elemental sulphur.

A very large proportion of the sulphur is separated off in the sulphur condenser 3 in liquid form as the heat of condensation thereof is taken up by the cooling water which is vaporised. The gases leaving the sulphur condenser 3 are burnt completely to SO2 in a subsequent combustion chamber 4 to which air is admitted in such an amount as to provide a major part of the gas partial pressure. The gaseous combustion products from combustion chamber 4 are fed to a steam generator 5 in which they are cooled and thence to a sulphuric acid plant 6, the construction of which does not form part of this invention and is not described herein. in which the combustion products are converted to sulphuric acid. The waste gases leaving the sulphuric acid plant 6 are completely free from hydrogen sulphide and contain only very small amounts of sulphur dioxide. If the temperature reached in the furnace 4 is insufficient for the required complete combustion, or if the sulphuric acid production must be increased at the expense of sulphur production, a by-pass line 7 leading from the inflow side of the furnace 1 to the inflow side of the furnace 4 is opened and more hydrogen sulphide is supplied for burning in the furnace 4.

The following example illustrates this invention: Example 12,600 Nm3/h of gas having the following composition: 10700 Nm3/h H25 252 Nm3/h C2H6 1018 Nm3/h CO2 630 Nm3/h H20 were obtained in a gas desulphuriser in an oil refinery.

This gas was first subjected to combustion with 5,350 Nm3/h oxygen which corresponded to 25,500 Nm3/h air. A reaction gas containing 10,700 kg/h sulphur as well as 1,070 Nm3/h SO3 was produced. The combustion temperature employed was about 1,500 C. This combustion took place in furnace 1 of plant of the type referred to above with reference to the accompanying drawing. The gaseous combustion product was then cooled to about 320"C in the steam generator 2 and in this way steam at 30 bar and at the same temperature was produced. Gas leaving the steam generator 2 was further cooled to 140"C in the sulphur condenser 3 at which steam at 0.8 bar under the corresponding temperature was produced.

About 10,500 kg/h of sulphur condensed out in the sulphur condenser 3. The gas leaving the sulphur condenser 3 was then burnt in the furnace 4 with a large amount of air to yield a gas which contained 7.5% by volume SO2 and 1.5% by volume 02. This gas was cooled in the steam generator 5, freed from acid vapours and mixed with air so that a gaseous mixture containing 5.66% by volume SO2 and 5.24% by volume 2 was supplied to the sulphuric acid plant 6, these being optimum proportions of SO2 and 02. 95 to 98% by weight acid was produced in the sulphuric acid plant. The waste gas discharging from the plant 6 contained less than 350 ppm SO2.

WHAT WE CLAIM IS: 1. A process for the production of sulphur and sulphuric acid from hydrogen sulphide which comprises the steps of subjecting the hydrogen sulphide to partial combustion in a first furnace in which a partial pressure of air exists which is sufficient to partially oxidise the hydrogen sulphide to sulphur but insufficient to further oxidise a major proportion of the sulphur produced, subjecting the combustion products to indirect heat exchange to remove heat of combustion therefrom, separating off by condensation elemental sulphur thereby produced, subjecting residual gases from which said sulphur has condensed out to complete combustion in a second furnace in an atmosphere having a sufficiently high partial pressure of air to yield sulphur dioxide and utilising the sulphur dioxide in the production of sulphuric acid.

2. A process as claimed in claim 1, wherein the amount of air supplied to the first furnace is such that up to 70% of the total amount of hydrogen sulphide supplied thereto is converted to elemental sulphur.

3. A process as claimed in claim or 2, wherein combustion gases from the first furnace are passed to a steam generator for absorption of the heat of combustion of the hydrogen sulphide.

4. A process as claimed in any one of the preceding claims, wherein elemental sulphur produced in said first furnace is condensed out of the gas produced therein in a sulphur condenser in which the heat of condensation is used to convert water to steam.

5. A process as claimed in any one of the preceding claims, wherein gases from the second furnace are discharged to a steam generator for achieving cooling thereof.

6. A process as claimed in any one of the preceding claims, which is carried out using apparatus including a by-pass circuit extending from a feed line for said hydrogen sulphide-containing gas to said first furnace to said second furnace to supply gas from said feed line to said second furnace at a position in advance of the position of entry of gases from the first furnace thereinto.

7. A process as claimed in claim 4 or either of claims 5 and 6 when appended to claim 4, wherein the sulphur condenser is operated so as to cool gases introduced thereinto to a temperature in the range of from 120 to 1400C.

8. A process as claimed in any one of the preceding claims, wherein air is mixed with sulphur dioxide-containing gas from the second furnace so that a gas containing 5.66% by volume SO, and 5.24% by volume 02 is supplied to the sulphuric acid plant.

9. A process for the production of sulphur and sulphuric acid from hydrogen sulphide, substantially as described herein with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

hydrogen sulphide is supplied for burning in the furnace 4.

The following example illustrates this invention: Example 12,600 Nm3/h of gas having the following composition:

10700 Nm3/h H25

252 Nm3/h C2H6

1018 Nm3/h CO2

630 Nm3/h H20 were obtained in a gas desulphuriser in an oil refinery.

This gas was first subjected to combustion with 5,350 Nm3/h oxygen which corresponded to 25,500 Nm3/h air. A reaction gas containing 10,700 kg/h sulphur as well as 1,070 Nm3/h SO3 was produced. The combustion temperature employed was about 1,500 C. This combustion took place in furnace 1 of plant of the type referred to above with reference to the accompanying drawing. The gaseous combustion product was then cooled to about 320"C in the steam generator 2 and in this way steam at 30 bar and at the same temperature was produced. Gas leaving the steam generator 2 was further cooled to 140"C in the sulphur condenser 3 at which steam at 0.8 bar under the corresponding temperature was produced.

About 10,500 kg/h of sulphur condensed out in the sulphur condenser 3. The gas leaving the sulphur condenser 3 was then burnt in the furnace 4 with a large amount of air to yield a gas which contained 7.5% by volume SO2 and 1.5% by volume 02. This gas was cooled in the steam generator 5, freed from acid vapours and mixed with air so that a gaseous mixture containing 5.66% by volume SO2 and 5.24% by volume 2 was supplied to the sulphuric acid plant 6, these being optimum proportions of SO2 and 02. 95 to 98% by weight acid was produced in the sulphuric acid plant. The waste gas discharging from the plant 6 contained less than 350 ppm SO2.

WHAT WE CLAIM IS: 1. A process for the production of sulphur and sulphuric acid from hydrogen sulphide which comprises the steps of subjecting the hydrogen sulphide to partial combustion in a first furnace in which a partial pressure of air exists which is sufficient to partially oxidise the hydrogen sulphide to sulphur but insufficient to further oxidise a major proportion of the sulphur produced, subjecting the combustion products to indirect heat exchange to remove heat of combustion therefrom, separating off by condensation elemental sulphur thereby produced, subjecting residual gases from which said sulphur has condensed out to complete combustion in a second furnace in an atmosphere having a sufficiently high partial pressure of air to yield sulphur dioxide and utilising the sulphur dioxide in the production of sulphuric acid.
2. A process as claimed in claim 1, wherein the amount of air supplied to the first furnace is such that up to 70% of the total amount of hydrogen sulphide supplied thereto is converted to elemental sulphur.
3. A process as claimed in claim or 2, wherein combustion gases from the first furnace are passed to a steam generator for absorption of the heat of combustion of the hydrogen sulphide.
4. A process as claimed in any one of the preceding claims, wherein elemental sulphur produced in said first furnace is condensed out of the gas produced therein in a sulphur condenser in which the heat of condensation is used to convert water to steam.
5. A process as claimed in any one of the preceding claims, wherein gases from the second furnace are discharged to a steam generator for achieving cooling thereof.
6. A process as claimed in any one of the preceding claims, which is carried out using apparatus including a by-pass circuit extending from a feed line for said hydrogen sulphide-containing gas to said first furnace to said second furnace to supply gas from said feed line to said second furnace at a position in advance of the position of entry of gases from the first furnace thereinto.
7. A process as claimed in claim 4 or either of claims 5 and 6 when appended to claim 4, wherein the sulphur condenser is operated so as to cool gases introduced thereinto to a temperature in the range of from 120 to 1400C.
8. A process as claimed in any one of the preceding claims, wherein air is mixed with sulphur dioxide-containing gas from the second furnace so that a gas containing 5.66% by volume SO, and 5.24% by volume 02 is supplied to the sulphuric acid plant.
9. A process for the production of sulphur and sulphuric acid from hydrogen sulphide, substantially as described herein with reference to the accompanying drawing.
10. Sulphur or sulphuric acid whenever produced by the process as claimed in any one

of the preceding claims