GB2052055A - Gas Sampling Apparatus - Google Patents

Abstract

Gas sampling apparatus for sampling blast furnace gas or coke oven gas comprises a double-acting pump (14) for drawing on a source of said gas and discharging the gas to an accumulator for subsequent determination of any one of a multiplicity of components of that gas. The pump has a pair of variable gas containers (20, 21) and valves (23 to 25) sequentially controlled in conjunction with the pump such that a gas source continuously feeds the accumulator whereby to obtain a more truly representative sample for analysis at any time. <IMAGE>

Description

SPECIFICATION Gas Sampling Apparatus This invention relates to gas sampling apparatus, and more particularly relates to apparatus for sampling blast furnace gas or coke oven gas.

Blast furnace top gas analysis is becoming increasingly important both as a predictive tool and a means of measuring the operating efficiency of the furnace and although a variety of reliable techniques exist for obtaining this analysis problems do exist in regard to obtaining truly representative samples on which these measurements can be conducted.

It is an object of this invention to provide apparatus for sampling gas substantially continuously whereby to obtain a more truly representative sample for analysis at any time.

The present invention provides an automatic gas sampling apparatus comprising a double acting pump for continuously drawing on a source of said gas and discharging the gas to an accumulator for analysis of any of a multiplicity of components thereof, the pump having a pair of variable gas containers and means for varying the capacity thereof such that as the capacity of one container increases the other decreases, and vice versa, and valve means controlled in conjunction with the pump such that the gas source is always connected to whichever container is increasing in capacity and the accumulator is always connected to the container decreasing in capacity.

Preferably the variable gas containers are cylinders and the means for varying their capacity are pistons associated with them; the valve means may conveniently be solenoid operated.

Additional valve means may be provided for isolating the pump and the accumulator in response to a deficiency in the gas source and/or the power supply.

A comprehensive gas filtration/conditioning system is provided for cleansing the gas submitted to the pump.

In order that the invention may be fully understood one embodiment thereof will now be described by way of example with reference to the accompanying drawings in which: Figure 1 schematically illustrates that part of the apparatus in which the gas to be sampled is cleansed; and Figure 2 schematically illustrates the pump and valve mechanisms.

Referring now to Figure 1 blast furnace top gas is extracted from a dirty gas main 1 by a probe 2 which extends through the main wall and is conducted via a valve 3 to a 10 ft. effective water seal 4 which is principally operative to remove moisture from the gas but also ensures some constancy in pressure within the ongoing ducting 5. The major pressure stabilisation is effected in a stabiliser 6 which collects any water carried along with the gas but is principally effective as a surge tank to increase the available volume of the system; the pipework is such however that the gas flow does not normally enter the cavity within the stabiliser housing to any substantial degree.

This prevents a long residence time in the system.

The water collected is periodically tapped off via the valve 7; From here the gas is conducted to a filter 8 housing stacked perforated stainless steel gauze elements primarily for removing dust. The gas is then passed through a small trap 9 within which any remaining water is condensed and collected and is then conducted to a vertical drying column 10 loaded with cotton wool. A substantially dry dust-free gas is thus presented to the pump (see fig. 2) via the duct 11.

A steam duct-cleansing circuit 12 may be provided for cleansing that area of the duct vulnerable to build up of residue on the walls.

Referring now to Figure 2, the pump and valve mechanism is conveniently housed in a selfcontained portable unit. In particular the major portion of the cleansed gas conducted along the duct 11 is bled off through an alarm rotameter 13 which provides an indication of gas flow. It ensures that a representative sample of gas is always available since in the event of blockage or an off-blast period then it actuates a control system to ensure that the pump is isolated as will be described shortly.

The pump 14 is driven by a motor 1 5 via gearing 1 6 which continuously and unidirectionally rotates a crankpin 1 7 commonly connected to two pistons 18 and 19 which reciprocate in cylinders 20 and 21 respectively.

As shown the pistons are moving in the direction of the arrows which means that the gas is being drawn in through the normally open solenoid valve 22, the common open (but directional) solenoid valve 23 and through the suction/exhaust valve 24 - set for suction.

Likewise, the gas in the cylinder 21 from the previous half cycle is being slowly exhausted through suction/exhaust valve 25 - set for exhaust -- and the common, normally open, solenoid valve 26 to the gas collection vessel (accumulator) for analysis.

At the completion of the half cycle one (27) of a pair of limit switches 27 and 28 actuates a controller 29 which sets solenoid valve 25 for suction (the quadrature position shown dotted), the solenoid valve 24 for exhaust (as shown dotted) and the directional control valve 23 into its opposite sense (again as shown dotted). As the cycle continues the pistons move in the opposite direction and the gas is now drawn into cylinder 21 and exhausted from cylinder 20.

A typical cycle time would be 5 minutes with cylinders of the order of 25 cc in capacity, the cycle being completed upon the limit switch 28 actuating the controller 29 again to restore the solenoids 23, 24, 25 to the original positions shown.

A continual supply of gas is thus provided to the accumulator for whatever period is required and the gas stored is periodically removed and analysed by any convenient method, e.g. by chromatography. The accumulator itself may comprise a pair of low diffusion polypropylene based bags double coated with polyvinyl chloride -PVDC-either clear or (preferably) frosted which have been found to exhibit the lowest gas ingress diffusion rates, i.e. an oxygen diffusion rate of plus 0.003% per hour. This is achieved by having one bag sited inside the other so that the inner bag is well shielded from oxygen contamination.

As mentioned above provision is made for the pump to be arrested and the associated lines isolated in the event of a blockage or an off-blast period; this is effected by the rotameter 13 since, if the rate of flow falls below a certain critical value an alarm signal is transmitted along circuit 30 which actuates the controller to close solenoid valves 22 and 26 through circuits 31, 32 respectively, thereby preventing contamination of the gas sample, and switching off the motor 1 5.

Although the sampler described is operative continuously it can readily operate for periodic sampling if desired; a timer 33 is provided for this purpose, it is effective to actuate the controller 29 which starts and stops the pump at predetermined intervals the circuits 31,32 being controlled in accordance with the on/off increments required.

The invention thus provides gas sampling apparatus including robust, portable pumping equipment which is simple in construction, requiring only input and output pipework and mains voltage supply, and is yet very reliable in operation, with an effective gas filtration system for supplying clean gas to this equipment. The accumulator, in which the gas is stored for analysis has been designed from specially selected PVDC bags having extremely low oxygen diffusion rates sited one within the other minimising contamination from the atmosphere and thus further ensuring truly representative samples.

Notwithstanding this, various modifications may nevertheless be introduced without departing from the scope of this invention. For example, a simple pressure switch alarm may be provided instead of the rotameter in the event of the pressure falling below the minimum value required.

Claims (8)

Claims

1. Gas sampling apparatus comprising a double acting pump for continuously drawing on a source of said gas and discharging the gas to an accumulator for analysis of any of a multiplicity of components thereof, the pump having a pair of variable gas containers and means for varying the capacity thereof such that as the capacity of one container increases the other decreases, and vice versa, and valve means controlled in conjunction with the pump such that the gas source is always connected to whichever container is increasing in capacity and the accumulator is always connected to the container decreasing in capacity.

2. Apparatus according to claim 1, in which each variable gas container is a cylinder and the means for varying the capacity thereof is a piston, the two pistons for the pair of cylinders being coupled together to a common unidirectional drive.

3. Apparatus according to claim 1 or claim 2 in which the valve means comprises a first valve for sequentially coupling the source gas to second and third valves respectively, each of the second and third valves being selectively operable to complete a gas path between different ones of the two gas containers and either the accumulator or (via the first valve) the said gas source, the arrangement being such that whilst gas is inspired from the source into the one container via the second valve the gas in the other container is exhausted to the accumulator via the third valve, the functions of the second and third valves alternating in unison with that of the two gas containers.

4. Apparatus according to claim 3, in which the valves are solenoid operated, the solenoids being controlled by switches actuated when the pistons are at the limit of their stroke.

5. Apparatus according to claim 3 or claim 4, comprising additional valve means for isolating the gas flow path between the source and the accumulator as desired or in response to control failure or the flow rate from the source dropping below a predetermined rate.

6. Apparatus according to any one of claims 1 to 5, in which the accumulator comprises a plastics bag, or a doublewalled plastics bag, constructed from a material having a very low oxygen diffusion rate.

7. Apparatus according to any one of claims 1 to 6, comprising a gas filtration/conditioning system for cleansing the gas submitted to the pump.

8. Gas sampling apparatus, substantially as herein described with reference to the accompanying drawings.