GB2105607A

GB2105607A - Gas scrubbing

Info

Publication number: GB2105607A
Application number: GB08223196A
Authority: GB
Inventors: Douglas House
Original assignee: BRISTOL PNEUMATIC Ltd
Current assignee: BRISTOL PNEUMATIC Ltd
Priority date: 1981-08-12
Filing date: 1982-08-12
Publication date: 1983-03-30
Also published as: GB2105607B

Abstract

A mixture of gases is scrubbed of gas components soluble in a liquid by mixing the mixture of gases and liquid in a scrubbing unit 1. The liquid is introduced into the unit by a spray 4 which extends through a dome- shaped member 6. The outlet 7 for the scrubbed gas is situated at the periphery of the dome-shaped member. Liquid containing dissolved gas components is removed from the unit through outlet 5. The scrubbed gas is caused to swirl between the outside of the spray of liquid and the interior of the member 6 such that liquid vapour containing dissolved gas components is condensed from the scrubbed gas mixture on the interior surface of the dome-shaped member 6 before the scrubbed gas mixture leaves the unit through the outlet 7. <IMAGE>

Description

SPECIFICATION Gas scrubbing This invention relates to scrubbing a mixture of gases of gas components soluble in a liquid.

The invention includes a method of scrubbing a mixture of gases of gas components soluble in a liquid, comprising causing the mixture of gases and liquid to mix in a scrubbing unit, removing liquid containing dissolved gas components from the unit, and condensing liquid vapour containing dissolved gas components from the scrubbed gas mixture in the unit before the scrubbed gas mixture leaves the unit through a gas outlet.

The invention also includes apparatus for scrubbing a mixture of gases of gas components soluble in a liquid, comprising a scrubbing unit, first and second inlet means introducing the mixture of gases and the liquid respectively into the unit for mixing therein, first and second outlet means for removing the scrubbed gas mixture and liquid containing dissolved gas components from the unit, and means for condensing liquid vapour containing dissolved gas components from the scrubbed gas mixture in the unit before the scribbed gas mixture leaves the unit through said first outlet means.

We have found that condensing liquid vapour containing dissolved gas components from the scrubbed gas mixture greatly improves the efficiency of gas scrubbing.

In order that the invention may be well understood, an embodiment thereof, which is given by way of example only will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagram of a scrubbing apparatus indicating operating conditions; and Figure 2 is a detail of the apparatus showing a spray inlet and gas outlet thereof.

The illustrated apparatus is used for scrubbing carbon dioxide and hydrogen sulphide from sewer gas which comprises approximately 65% methane, 33% carbon dioxide and 2% hydrogen sulphide, and is able to produce a scrubbed gas which comprises up to 98% methane with 2% carbon dioxide. The apparatus makes feasible the commercial extraction of methane from sewer gas.

The illustrated apparatus is shown in Figure 1 between the second and third stages of a four stage compressor plant and as operating at a pressure of 200 psi.

The apparatus comprises a scrubbing unit 1 which accommodates a basket 2 which contains small pieces of a material such as polypropylene which is inert in the sewer gas. Sewer gas from the second stage compressor enters the unit at an inlet 3 beneath the basket and flows up the unit through the polypropylene pieces in the basket.

The polypropylene pieces provide tortuous flow paths for the sewer gas. At the same time water supplied through a water inlet system 20 is sprayed onto the top of the basket through a spray inlet 4 and flows along the tortuous paths provided by the polypropylene pieces, in the opposite direction to the sewer gas. Carbon dioxide and hydrogen sulphide are dissolved in the water which is subsequently removed from the unit through drain outlet 5 and a drain system 30.

The spray inlet 4 extends through the centre of a substantially dome-shaped member 6 and a gas outlet 7 is situated at the periphery of the member 6. More specifically, the gas outlet 7 comprises an annular opening 8 of a chamber 9 defined between the exterior of the dome-shaped member 6 and an end cap 10~which is also domeshaped of the unit. The chamber 9 is connectible to the third stage compressor through an opening 11 provided in a boss 12 on the end cap 10 and the end cap 10 is provided with another boss 13 for mounting a safety valve 14.

Advantageously, a wad, or pieces, of polypropylene or other inert material is located in the chamber 9 adjacent opening 8 to form a restricting element 15 restricting flow through the gas outlet.

In use, sewer gas which has been scrubbed by the sprayed water during its passage through the basket 2 is caused to swirl in the interior of the dome-shaped member 6 between the outside of the spray and the interior surface of the member (as diagrammatically illustrated in Fig. 2) such that water vapour present in the scrubbed gas condenses on the interior surface of the domeshaped member before the gas leaves the unit via the opening 8. As water vapour, which would contain dissolved hydrogen sulphide and carbon dioxide, is removed from the gas prior to its exit from the unit, the gas which passes from the unit to the third stage compressor contains a higher percentage of methane - up to 98%~than it would otherwise.The presence of the element 1 5 in the chamber 9 also provides surfaces on which water vapour can condense, further increasing the efficiency of the unit.

The overall operation of the apparatus is summarised as follows: In order to set up the apparatus for operation, an inlet bypass valve A and a drain valve B of the inlet system 20 are fully opened. Next water isolating valve D is opened and pump P is started.

Valve A is adjusted until a desired reading for example 26 gallons per minute, on flowmeter F is achieved. Valve B of the drain system is then adjusted until the water level is seen to slowly rise in the column of level indicator L. The compressor is then started and when the operating pressure of the scrubbing unit 1 is achieved, the readings of the flowmeter F and level indicator L are checked and if necessary valves A and B re-adjusted to achieve the desired flow rate and a slowly rising water level. Valves A and B are then locked to prevent unauthorised adjustment.

The operating sequence of the apparatus is as follows. Isolating valve D of the water inlet system and an isolating valve E in the drain system are opened and the pump P started. A flow switch FS in the drain system downstream of the isolating valve E provides a signal which starts the compressor. The water in the scrubbing unit 1 rises until its level is sensed by a level sensor LS which provides a pressure signal to cause a bypass valve C in the drain system to be opened to allow a faster drainage rate. Thus, the water level in unit 1 falls and thereafter the level sensor LS provides a signal to close valve C. As will be appreciated the water level will then rise again and the level sensor will operate to cause valve C to re-open. Thus, the level of water in the unit 1 will be automatically limited by the level sensor and the valve C.The level sensor and the valve C are linked by a pneumatic control circuit generally referenced 40 in Figure 1 but not described herein in detail as its understanding is not essential to the understanding of the apparatus so far as the invention is concerned.

When the compressor is stopped, the valves D and E are closed and the water level and pressure in the unit 1 are maintained.

If during operation the supply of water through the inlet system 20 fails, a non-return valve NR in the inlet system prevents gas entering the water supply line. The water level will, of course fall but the flow switch FS will signal the compressor to stop.

As will be apparent from Figure 1 , the piping of the drainage system 40 is such as to provide a minimum water level M before the water unit 1 can activate the flow switch FS to start the compressor.

Whilst, we have disclosed the use of a domeshaped member for condensing water vapour from the scrubbed gas before it leaves the unit, it is envisaged that other members or means could be provided to so condense water vapour from the scrubbed gas. Furthermore whilst the illustrated apparatus has been described in connection with scrubbing sewer gas, it is to be understood that the present invention is not so restricted.

Claims

1. A method of scrubbing a mixture of gases of gas components soluble in a liquid, comprising causing the mixture of gases and liquid to mix in a scrubbing unit, removing liquid containing dissolved gas components from the unit, and condensing liquid vapour containing dissolved gas components from the scrubbed gas mixture in the unit before the scrubbed gas mixture leaves the unit through a gas outlet.

2. A method as claimed in claim 1 ,wherein the liquid is introduced into the unit for mixing with the mixture of gases by a spray means extending through a substantially dome-shaped member, and the scrubbed gas mixture is caused to swirl between the outside of the spray and the interior of the member such that liquid vapour in the scrubbed gas mixture condenses on the interior surface of the member before the scrubbed gas mixture leaves the unit through said outlet.

3. A method as claimed in claim 1 or 2, wherein said liquid is water and said mixture of gases comprises sewer gas.

4. Apparatus for scrubbing a mixture of gases of gas components soluble in a liquid, comprising a scrubbing unit, first and second inlet means introducing the mixture of gases and the liquid respectively into the unit for mixing therein, first and second outlet means for removing the scrubbed gas mixture and liquid containing dissolved gas components from the unit, and means for condensing liquid vapour containing dissolved gas components from the scrubbed gas mixture in the unit before the scrubbed gas mixture leaves the unit through said first outlet means.

5. Apparatus as claimed in claim 4, wherein the first and second inlet means are arranged to cause the mixture of gases and liquid to flow in generally opposite directions in the unit.

6. Apparatus as claimed in claim 4 or 5, wherein the second inlet means comprises a spray inlet which extends through the centre of a substantially dome-shaped member and the first outlet means is situated at the periphery of the member, the arrangement being such that in use the scrubbed gas is caused to swirl in the interior of said substantially dome-shaped member between the outside of the spray of liquid and the interior surface of the member whereby liquid vapour in the scrubbed gas mixture condenses on the interior surface of the member before the scrubbed gas mixture leaves the unit through said first outlet means.

7. Apparatus as claimed in claim 6, wherein the first outlet means comprises an annular opening of a chamber defined between the exterior of the substantially dome-shaped member and an end cap of the unit.

8. Apparatus as claimed in claim 7, wherein said end cap is substantially dome-shaped.

9. Apparatus as claimed in any one of claims 4 to 8, wherein restricting means are provided in or adjacent said first outlet means for restricting flow therethrough.

10. Apparatus as claimed in claim 9, wherein said restricting means comprises a restricting element extending across said first outlet means.

1 Apparatus as claimed in claim 10, wherein said restricting element comprises a wad of an inert material.

12. Apparatus as claimed in claim 10, wherein said restricting element comprises pieces of an inert material.

13. Apparatus for scrubbing a mixture of gases of gas components soluble in a liquid, substantially as herein described with reference to the accompanying drawings.

13. Apparatus as claimed in claim 1 1 or 12, wherein said inert material is polypropylene.

14. A method of scrubbing a mixture of gases of gas components soluble in a liquid, substantially as herein described with reference to the accompanying drawings.

1 5. Apparatus for scrubbing a mixture of gases of gas components soluble in a liquid, substantially as herein described with reference to the accompanying drawings.

New claims or amendments to claims filed on 16 December 1982 Superseded claims 1-1 5 New or amended claims:~

1. A method of scrubbing a mixture of gases of gas components soluble in a liquid, comprising causing the mixture of gases and liquid to mix in a scrubbing unit, removing liquid containing dissolved gas components from the unit, and condensing liquid vapour containing dissolved gas components from the scrubbed gas mixture in the unit before the scrubbed gas mixture leaves the unit through a gas outlet, wherein the liquid is introduced into the unit for mixing with the mixture of gases by a spray means extending through a substantially dome-shaped member, and the scrubbed gas mixture is caused to swirl between the outside of the spray and the interior of the member such that liquid vapour in the scrubbed gas mixture condenses on the interior surface of the member before the scrubbed gas mixture leaves the unit through said outlet.

2. A method as claimed in claim 1, wherein said liquid is water and said mixture of gases comprises sewer gas.

3. Apparatus for scrubbing a mixture of gases of gas components soluble in a liquid, comprising a scrubbing unit, first and second inlet means introducing the mixture of gases and the liquid respectively into the unit for mixing therein, first and second outlet means for removing the scrubbed gas mixture and liquid containing dissolved gas components from the unit, and means for condensing liquid vapour containing dissolved gas components from the scrubbed gas mixture in the unit before the scrubbed gas mixture leaves the unit through said first outlet means, wherein the second inlet means comprises a spray inlet which extends through the centre of a substantially dome-shaped member and the first outlet means is situated at the periphery of the member, the arrangement being such that in use the scrubbed gas is caused to swirl in the interior of said substantially dome-shaped member between the outside of the spray of liquid and the interior surface of the member whereby liquid vapour in the scrubbed gas mixture condenses on the interior surface of the member before the scrubbed gas mixture leaves the unit through said first outlet means.

4. Apparatus as claimed in claim 3, wherein the first and second inlet means are arranged to cause the mixture of gases and liquid to flow in generally opposite directions in the unit.

5. Apparatus as claimed in claim 4, wherein the first outlet means comprises an annular opening of a chamber defined between the exterior of the substantially dome-shaped member and an end cap of the unit.

6. Apparatus as claimed in claim 5, wherein said end cap is substantially dome-shaped.

7. Apparatus as claimed in any one of claims 3 to 6, wherein restricting means are provided in or adjacent said first outlet means for restricting flow therethrough.

8. Apparatus as claimed in claim 7, wherein said restricting means comprises a restricting element extending across said first outlet means.

9. Apparatus as claimed in claim 8, wherein said restricting element comprises a was of an inert material.

10. Apparatus as claimed in claim 8, wherein said restricting element comprises pieces of an inert material.

1 Apparatus as claimed in claim 9 or 10, wherein said inert material is polypropylene.

12. A method of scrubbing a mixture of gases of gas components soluble in a liquid, substantially as herein described with reference to the accompanying drawings.