GB2158235A

GB2158235A - Water pollutant monitor

Info

Publication number: GB2158235A
Application number: GB08510421A
Authority: GB
Inventors: Graham Penrose Evans; Clive Withell
Original assignee: Water Research Centre
Current assignee: Water Research Centre
Priority date: 1984-05-01
Filing date: 1985-04-24
Publication date: 1985-11-06
Also published as: GB8510421D0; GB2158235B

Abstract

A monitor for detecting volatile pollutants (such as petroleum-based products) in a water supply comprises means (10, 12, 14) for heating the water, means (25) for purging the heated water with gas to remove at least some of any volatile pollutant therefrom, and means (32) for sensing pollutant in the gas. The preferred gas is air which is preferably passed counter- current to a flow of the heated water in the form of bubbles therein. <IMAGE>

Description

SPECIFICATION Water pollutant monitor This invention relates to a monitor arranged especially (but not exclusively) for a continuous on-line detection of petroleum-based products or other volatile pollutants in water.

In accordance with this invention, there is provided a pollutant monitor comprising an inlet for water, a heating means for heating the water, means for purging the water with air or other gas to remove into said air or gas at least a portion of any volatile pollutant in the water, and sensing means for responding to the concentration of pollutant in said air or gas.

The heating means advantageously brings the water to a constant temperature and also increases the volatility of any hydrocarbons or other volatile pollutants in the water.

The invention also provides a method of monitoring water for the presence of volatile pollutants therein, which comprises heating the water and purging it with a gas to remove at least at a portion of any volatile pollutant therein, and sensing the presence and/or concentration of any said pollutant in the gas.

In the monitor (and method) of the invention, the sample water is preferably heated indirectly by heat exchange. The amount of heating desirable will depend, among other things, upon the likely pollutant present and its volatility, but usually it is satisfactory to heat to a temperature of about 40"C (lower and higher temperatures can be used).

The gas purging can be effected in a variety of ways. We prefer to pass the gas through a diffuser into a vessel containing the heated sample water, at or near the bottom of the vessel, so that the gas bubbles rise up through the sample. The gas is then collected above the water surface and led to the sensing means (preferably via a water trap). Most preferably, especially when the monitor is used on a continuous (as opposed to batch) basis, the sample water flows in a downwards direction through the vessel countercurrent to the rising gas bubbles.

An embodiment of this invention will now be described by way of example only, with reference to the accompanyng drawing, the single Figure of which is a diagrammatic front elevation of said embodiment of monitor.

The monitor illustrated comprises a heat exchanger which includes a vertical tube 10 housing a coiled pipe 1 2. A thermostatically controlled heater 14 circulates heated water vertically through the tube 10, thus serving to heat water to be monitored, which is pumped by a peristaltic pump (not shown) into the bottom end of the coiled pipe 1 2 and finally flows out of the top of this coil. Typically the water to be monitored will be heated to 40"C.

In the drawing, the various arrows indicate liquid and gas flow directions, respectively.

The monitor further comprises a vertical outer tube 1 6 into the side of which the top end of the coil 1 2 is connected. An outlet pipe 1 8 for the water passes from the bottom of the tube 1 6 to a vessel 20 which is positioned alongside the bottom of the tube 16, has an overflow outlet 22 and is adjustable in height to control the level of water in the tube 1 6.A pipe 24 is connected to a supply of compressed air and passes through a stopper at the top of tube 1 6 to communicate with a sintered gas distribution tube 25 which extends to the bottom of the outer tube 1 6. Gas emerges from the enlarged bottom end of tube 25 (at a typical rate of 1.25 litres/min.) and into the sample water with which the outer tube 1 6 is partly filled.

The air rises up the outer tube 16, in the opposite direction to the flow of sample water, and serves to purge the water of any volatile pollutants which may be present in the water.

The gas then passes out of the top of the outer tube 1 6 via a pipe 26 to a water trap 28, then through a pipe 30 to a gas sensor box 32. The trap 28 has a tap 34 which may be opened to drain trapped water to the vessel 20. The gas sensor box contains three stannic oxide semi-conductor sensors and the volatile component in the gas is absorbed onto the surface of these sensors, causing a measurable change in surface conductivity which can be detected as a voltage change for amplification to provide a signal indicative of the amount of volatile pollutant present in the water. The signal produced is continuously monitored and passed via wire 36 to a microcomputer for on-line analysis.

It is to be understood that the illustrated monitor is merely one example of a monitor of the invention, and that various changes and modifications can of course be made. For example, the air used can be drawn from the atmosphere using a compressor, or may be supplied from air bottles or cylinders, or it may be recirculated after suitable cleaning, e.g. by passage through a carbon filter.

Another example of changes concerns the output signal from the gas sensor box. This can be monitored, for example, using analogue meters of by using the signal to activate relay contacts.

1. A water pollutant monitor comprising an inlet for sample water, heating means for heating the water, means for purging the water with a gas to remove into the gas at least a portion of any volatile pollutant in the water, and sensing means for responding to the presence and/or concentration of pollutant in said gas.

2. A monitor according to claim 1, wherein the heating means comprises a heat exchanger for heating the sample water indi

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Water pollutant monitor This invention relates to a monitor arranged especially (but not exclusively) for a continuous on-line detection of petroleum-based products or other volatile pollutants in water. In accordance with this invention, there is provided a pollutant monitor comprising an inlet for water, a heating means for heating the water, means for purging the water with air or other gas to remove into said air or gas at least a portion of any volatile pollutant in the water, and sensing means for responding to the concentration of pollutant in said air or gas. The heating means advantageously brings the water to a constant temperature and also increases the volatility of any hydrocarbons or other volatile pollutants in the water. The invention also provides a method of monitoring water for the presence of volatile pollutants therein, which comprises heating the water and purging it with a gas to remove at least at a portion of any volatile pollutant therein, and sensing the presence and/or concentration of any said pollutant in the gas. In the monitor (and method) of the invention, the sample water is preferably heated indirectly by heat exchange. The amount of heating desirable will depend, among other things, upon the likely pollutant present and its volatility, but usually it is satisfactory to heat to a temperature of about 40"C (lower and higher temperatures can be used). The gas purging can be effected in a variety of ways. We prefer to pass the gas through a diffuser into a vessel containing the heated sample water, at or near the bottom of the vessel, so that the gas bubbles rise up through the sample. The gas is then collected above the water surface and led to the sensing means (preferably via a water trap). Most preferably, especially when the monitor is used on a continuous (as opposed to batch) basis, the sample water flows in a downwards direction through the vessel countercurrent to the rising gas bubbles. An embodiment of this invention will now be described by way of example only, with reference to the accompanyng drawing, the single Figure of which is a diagrammatic front elevation of said embodiment of monitor. The monitor illustrated comprises a heat exchanger which includes a vertical tube 10 housing a coiled pipe 1 2. A thermostatically controlled heater 14 circulates heated water vertically through the tube 10, thus serving to heat water to be monitored, which is pumped by a peristaltic pump (not shown) into the bottom end of the coiled pipe 1 2 and finally flows out of the top of this coil. Typically the water to be monitored will be heated to 40"C. In the drawing, the various arrows indicate liquid and gas flow directions, respectively. The monitor further comprises a vertical outer tube 1 6 into the side of which the top end of the coil 1 2 is connected. An outlet pipe 1 8 for the water passes from the bottom of the tube 1 6 to a vessel 20 which is positioned alongside the bottom of the tube 16, has an overflow outlet 22 and is adjustable in height to control the level of water in the tube 1 6.A pipe 24 is connected to a supply of compressed air and passes through a stopper at the top of tube 1 6 to communicate with a sintered gas distribution tube 25 which extends to the bottom of the outer tube 1 6. Gas emerges from the enlarged bottom end of tube 25 (at a typical rate of 1.25 litres/min.) and into the sample water with which the outer tube 1 6 is partly filled. The air rises up the outer tube 16, in the opposite direction to the flow of sample water, and serves to purge the water of any volatile pollutants which may be present in the water. The gas then passes out of the top of the outer tube 1 6 via a pipe 26 to a water trap 28, then through a pipe 30 to a gas sensor box 32. The trap 28 has a tap 34 which may be opened to drain trapped water to the vessel 20. The gas sensor box contains three stannic oxide semi-conductor sensors and the volatile component in the gas is absorbed onto the surface of these sensors, causing a measurable change in surface conductivity which can be detected as a voltage change for amplification to provide a signal indicative of the amount of volatile pollutant present in the water. The signal produced is continuously monitored and passed via wire 36 to a microcomputer for on-line analysis. It is to be understood that the illustrated monitor is merely one example of a monitor of the invention, and that various changes and modifications can of course be made. For example, the air used can be drawn from the atmosphere using a compressor, or may be supplied from air bottles or cylinders, or it may be recirculated after suitable cleaning, e.g. by passage through a carbon filter. Another example of changes concerns the output signal from the gas sensor box. This can be monitored, for example, using analogue meters of by using the signal to activate relay contacts. CLAIMS

2. A monitor according to claim 1, wherein the heating means comprises a heat exchanger for heating the sample water indi rectly.

3. A monitor according to claim 1 or 2, which also comprises a vessel for receiving the heated water, and wherein the gas purging means comprises means for supplying said gas into the vessel.

4. A monitor according to claim 3, wherein the gas purging means comprises a gas-diffuser so mounted as to be below the water level in the vessel (in use).

5. A monitor according to claim 3 or 4, wherein the vessel has a sample inlet and a sample outlet so that (in use) said sample water flows in a direction from said inlet to said outlet, and wherein said gas purging means is arranged to supply gas to travel through said sample in a countercurrent direction.

6. A monitor according to any of claims 1 to 5, which also includes a water trap to remove water from the gas before the gas enters the sensing means.

7. A monitor according to any of claims 1 to 6, wherein means are provided to clean the gas exiting from from the sensing means and to recirculate the cleansed gas to the gas purging means.

8. A water pollutant monitor substantially as herein described with reference to the accompanying drawing.

9. A method of monitoring water for the presence of volatile pollutants therein, which comprises heating the water and purging it with a gas to remove at least a portion of any volatile pollutant therein, and sensing the presence and/or concentration of any said pollutant in the gas.

10. A method according to claim 9, wherein the gas is air.

11. A method according to claim 9 or 10, wherein the pollutant is or includes one or more petroleum-based products.

1 2. A method according to claim 9, 10 or 11, which is operated on a continuous basis.