IE41818B1

IE41818B1 - Sampling gas for analysis

Info

Publication number: IE41818B1
Application number: IE2317/75A
Authority: IE
Original assignee: British Steel Corp
Priority date: 1974-10-28
Filing date: 1975-10-24
Publication date: 1980-03-26
Also published as: ZA756720B; NL7512621A; JPS5185780A; LU73657A1; FR2289899B1; GB1500508A; DK483475A; IT1047246B; FR2289899A1; IE41818L; BE834914A; DE2541285A1

Abstract

1500508 Sampling gases BRITISH STEEL CORP 28 Oct 1975 [28 Oct 1974] 46432/74 Heading G1B A method for the rapid transfer of gas from a sampling probe at a source of the gas to a gas analyzer remote from the gas source, comprises passing the gas from the probe along a first gas sampling duct intercommunicating with a second gas sampling duct which transfers a gas sample to the gas analyzer, the first gas sampling duct being relatively long compared with the second gas sampling duct and the gas being transferred along the first duct at a high gas transfer rate relative to the transfer rate along the second duct, a proportion of the gas in the second gas sampling duct being vented to the atmosphere immediately prior to the analysis of the remaining gas. In an example a steelmaking vessel 10 is shown with a hood 11 and an oxygen lance 12. The hood draws the hod exhaust gases into a waste gas duct 14. Waste gas sampled through the probe 15 passes at about 56 litres per minute along a first sampling duct 16 through filter 17 and cooler 18 to vacuum pump 19. In the filter fume particles are removed, and in the cooler the gas temperature is reduced to ambient temperature. Beyond the pump 19 the sampled gas continues along the duct 16 at a positive pressure until the duct leads into an analysis room 20. The duct 16 passes through the analysis room and the bulk of the sampled gas is exhausted to atmosphere at 24. A second sampling duct 25 branches from the first duct 16 within the analysis room and part of the sampled gas is drawn along the second duct 25 and through a further filter 26 at about 5 litres per minute by pump 27. From pump 27 the second sampling duct leads through a further cooler 28, to remove any residual moisture in the gas, to three gas analysers e.g. a paramagnetic oxygen analyzer 31 and infrared analyzers 32 and 33 for carbon monoxide and carbon dioxide respectively. From these analyzers the gas is exhausted through a duct 35. The analyzers 31, 32 and 33 require a gas supply rate of about one litre per minute. A bleed line 36 is provided in the second gas sampling duct 25 prior to the analyzers to vent excess gas to the atmosphere. It is possible to operate the steelmaking process with a time lag of as little as 10 to 15 seconds between sampling the waste gas and obtaining an analysis of its oxygen, carbon monoxide and carbon dioxide content. Pump 19 transfers gas at about 56 litres per minute along duct 16 at a pressure of about 22mm. mercury gauge. Duct 16 is unrestricted and of 12À7mm. internal diameter. The second gas sampling duct 25 is of 6À3 mm. internal diameter and is provided with gas from pump 27 at a pressure of approximately 60 mm. mercury gauge.

Description

This invention relates to sampling gas for analysis.

It is particularly concerned with taking a sample of a gas which requires continuous monitoring by analysis and transferring the sample rapidly to analysers which are remote from the gas sampling point.

In many processes involving chemical change and giving rise to waste or exhaust gases, the chemical composition of the exhaust gases provides a useful indication of the progress of the reactions taking place in the process. One such process is the conversion of iron into steel by lancing it with oxygen, in which the decarburisation reactions which occur during the conversion can be monitored by analysing the evolved gases for oxygen, carbon monoxide and carbon dioxide.

In such a system the degree of control which can be exercised over the process is in part dependent upon the speed with which information about a process event can be extracted and made available to the controller. One factor which affects the speed of response is the time taken for the sampled gas to reach the gas analysers.

In the BOS process evolved gases and fume are collected in a hood over the steel-making vessel at a temperature of the order of 15OO°C. These process gases are ducted away to be cleaned, cooled and discharged. In order to provide good accessibility and the controlled and stable environment which the gas analysers require it is convenient to site the analysers well away from the steel-making vessel and its exhaust system. However, a gas analyser may typically require a gas supply rate of about one litre per minute, and this implies a long transfer time and a correspondingly long time for the analyser to respond to a process event.

In accordance with the present invention there is provided a method for the rapid transfer of gas from a sampling probe at a source of the gas to a gas analyser remote from the gas source, comprising passing the gas from the probe along a first gas sampling duct intercommunicating with a second gas sampling duct which transfers a gas sample to the gas analyser, the first gas sampling duct being relatively long compared with the second gas sampling duct and the gas being transferred along the first duct at a high gas transfer rate relative to the transfer rate along the second duct, a proportion of the gas in the second gas sampling duct being vented to the atmosphere immediately prior to the analysis of the remaining gas.

The invention also provides a system for the rapid transfer of gas from a sampling probe at the gas source to a gas analyser remote from the gas source comprising a first gas sampling duct connected to the sampling probe and a second gas sampling duct communicating with the first gas sampling duet and providing a passage for flow of a sample of gas from the first gas sampling duct to the gas analyser, said first sampling duct being relatively long compared with said second sampling duct and being adapted to transfer gas at a high gas transfer rate as compared with the gas transfer rate in the second sampling duct, and vent means provided in the second sampling duct immediately prior to the gas analyser.

The excess gas not passed along the second duct may be exhausted as convenient, for example to atmosphere beyond the connection of the first gas sampling duct to the second sampling duct. The gas in the -second sampling duct may be cooled prior to venting. The first and/or second gas sampling duct are suitably provided with a filter and a pump. The first gas sampling‘duct may have a cross-sectional area approximately four times that of the second sampling duct.

One embodiment of the invention is shown by way of example in the accompanying drawing, which shows schematically and not to scale a BOS vessel With its exhaust system, an exhaust gas sampling line and analysing equipment.

The steelmaking vessel 10 is shown with a hood 11 and an oxygen lance 12. The hood draws the hot exhaust gases into a waste gas duct 14, through which they are removed from the process.

A sampling probe 15 is set into the waste gas duct wall at a point which is close to the vessel, to reduce gas transit time, but at which adequate mixing of the waste gases is assured. This point might be about 25 metres above the hood 11, and the gas temperature will have fallen to about 1300°C.

Waste gas sampled through the probe 15 passes at a rate of about 56 litres per minute along a first sampling duct 16 through a filter 17 and a cooler 18 to a vacuum pump 19.

In the filter fume particles are removed, and in the cooler the gas temperature is reduced to normal ambient temperature. Beyond the pump 19 the sampled gas continues along the duct 16 at a positive pressure until the duct leads into an analysis room 20 some distance from the sampling point. The duct 16 passes through the analysis room and the bulk of the sampled gas is exhausted to atmosphere at 24. No restriction is included in the exhaust line beyond the analysis room which might create back pressure and thereby increase gas transport time.

A second sampling duct 25 branches from the first duct 16 within the analysis room and part of the sampled gas is drawn along the second duct 25 and through a further filter 26 at a rate of about 5 litres per minute by a pump 27. From the pump 27 the second sampling duct leads through a further cooler 28, to remove any residual moisture in the gas, to three gas analysers constituted by a paramagnetic oxygen analyser 31 and infrared analysers 32 and 33 for carbon monoxide and carbon dioxide respectively. From these analysers the gas is exhausted through a duct 35.

The analysers 31, 32 and 33 each require a gas supply rate of about one litre per minute. A bleed line 36 is therefore provided in the second gas sampling duct 25 immediately prior to the analysers to vent the excess gas to the atmosphere.

It has been found possible to operate the steelmaking process with a time lag of as little as 10 to 15 seconds between sampling the waste gas and obtaining an analysis of its oxygen, carbon monoxide and carbon dioxide content by the utilisation of this invention.

The pump 19 transfers gas at about 56 litres per minute along the duct 16 at a pressure of about 22mm mercury gauge, pressures between 5 or lo and 50mm mercury gauge being considered generally suitable. The duct 16 is Unrestricted and of 12.7mm internal diameter.

The second gas sampling duct 25 is of 6.3mm internal diameter and is provided with gas from the pump 27 at a pressure of approximately 60mm mercury gauge.

The whole sampling and analysis system is operated under positive pressure at all times.

Claims

1. CLAIMS: 1. A method for the rapid transfer of gas from a sampling probe at a source of the gas to a gas analyser remote from the gas source, comprising passing the gas from the probe along a first gas sampling duct intercommunicating with a second gas sampling duct which transfers a gas sample to the gas analyser, the first gas sampling duct being relatively long compared with the second gas sampling duct and the gas being transferred along the first duct at a high gas transfer rate relative to the transfer rate along the second duct, a proportion of the gas in the second gas sampling duct being vented to the atmosphere immediately prior to the analysis of the remaining gas.

2. A method as claimed in claim 1 wherein the gas is mixed waste gas from a basic oxygen steelmaking process.

3. A method as claimed in claim 1 or claim 2 wherein the gas is passed along the sampling ducts at a pressure of between 5 and 50 millimetres mercury gauge.

4. A method as claimed in any preceding claim, in which the gas in the second sampling duct is cooled prior to venting.

5. A system for the rapid transfer of gas from a sampling probe at the gas souroe to a gas analyser remote from the gas source comprising a first gas sampling duct connected to the sampling probe and a second gas sampling duct communicating with the first gas sampling duct and providing a passage for flow of a sample of gas from the first gas sampling duct to the gas analyser, said first sampling duct being relatively long compared with said second sampling duct and being adapted to transfer gas at a high gas transfer rate - 7 41818 as compared with the gas transfer rate in the second sampling dupt, and vent means provided in the second sampling duct immediately prior to the gas analyser.

6. A system as claimed in claim 5 in which the first gas sampling duct vents to the atmosphere beyond its connection with the second gas sampling duct.

7. A system as claimed in claim 5 or 6 including a cooler in the second gas sampling duct positioned prior to the vent means.

8. A system as claimed in any of claims 5 to 7 wherein the sampling probe is situated in the waste gas duct of a basic oxygen furnace.

9. A system according to any one of claims 5 to 8 wherein the first and/or the second gas sampling duct is provided with a filter and a pump.

10. A system according to any one of claims 5 to 9 wherein the first gas sampling duet has approximately four times the cross-sectional area of the second gas sampling duot.

11. A system according to claim 5 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

12. A method according to claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.