GB2272513A

GB2272513A - Determining the concentration of solid particles in a liquid

Info

Publication number: GB2272513A
Application number: GB9223179A
Authority: GB
Inventors: Phillip Warren Napper
Original assignee: Apv Rosista Ltd; APV Rosista Ltd
Current assignee: Apv Rosista Ltd; APV Rosista Ltd
Priority date: 1992-11-05
Filing date: 1992-11-05
Publication date: 1994-05-18
Anticipated expiration: 2012-11-05
Also published as: GB9622933D0; GB9223179D0; GB2304188B; GB2304188A; GB2272513B

Abstract

The apparatus comprises an instrument head, 1, and a calculation means, the instrument head comprising an aperture, 2, through which the liquid can pass, a light source, 3, arranged to direct light into the aperture, and a number of photodetectors, 5, 6, 7, for detecting light scattered from solid particles suspended in the liquid in the aperture and each producing an output signal dependent on the intensity of light incident upon it, and the calculation means being arranged to calculate the concentration of solid particles from the output signals of the photodetectors. In one example, the apparatus includes a dosing pump to add filter aid to the liquid depending upon the concentration of solid particles in the liquid. <IMAGE>

Description

MEASURING APPARATUS The present invention is directed to an apparatus and a method for determining the concentration of solid particles in a liquid, and more particularly for the determination of the concentration of solid particles in beer to enable the accurate calculation of the optimum concentration of filter aid which should be added to the beer.

In breweries, beer often needs to be filtered to obtain an acceptable clarity by removing solid particles such as yeast and other haze forming particles from the beer. Such filtration occurs after the beer has been brewed, but before the beer fills bottles or kegs. For filtration to take place, a filter unit is required, and virtually all of these units in the brewing industry, and in particular for beer, use Kieselguhr as the filter medium.

Kieselguhr is a diatomaceous earth in powder form, which because of its inert nature can be safely dosed as a slurry together with the unfiltered beer. The Kieselguhr is retained on a filter screen which can take various shapes and forms, for example plate and frame, horizontal leaf, vertical leaf and candle, and in doing so forms a cake bed or filter medium. This bed is continually built up by more Kieselguhr to maintain the require porosity or flux for the liquid being filtered. The solid particles, which are smaller than the particles of Kieselguhr, become trapped within the filter medium. Blinding or blockage occurs if the porosity of the bed surface gets too small, for example if there is insufficient Kieselguhr for the amount of solid particles suspended in the liquid.

To ensure efficient filtering, a fine balance must be maintained between the quantity of Kieselguhr dosed and the concentration of solid particles suspended in the liquid.

Too little Kieselguhr will cause blinding of the filter to occur, and too much is firstly uneconomical and secondly fills the available volume for bed formation more quickly reducing the run time of the filter. To ensure optimum efficiency, the rate of addition of filter aid should be strictly controlled in accordance with: (a) the concentration of solid particles in the beer, (b) the fluid flow characteristics, (c) the physical properties of the filter aid and yeast particles.

In general, the greater the concentration of solid particles, the more filter aid should be added to the beer.

Conventionally, the concentration of solid particles in the beer has been determined using a turbidimeter. This type of meter measures the intensity of light that either passes through or is scattered back by the unfiltered beer, and compares that to the initial beam intensity. The greater the concentration of, or the greater the size of the particles suspended within the beer, the higher the turbidity reading. However, these turbidimeters cannot differentiate between lots of small particles and a few large particles very accurately. Due to this, turbidimeters are unsuitable for use in an accurate automated dosing system for which this information is required. Further, turbidimeters often take the form of inserted probes in a pipeline, which can be a hygiene risk and act as an obstacle to fluid flow.

According to a first aspect of the present invention, an apparatus for determining the concentration of solid particles in a liquid comprises an instrument head and a calculation means, the instrument head comprising an aperture through which the liquid can pass, a light source arranged to direct light into the aperture, and a number of photodetectors for detecting light scattered from solid particles suspended in the liquid in the aperture and each producing an output signal dependent on the intensity of light incident upon it, and the calculation means being arranged to calculate the concentration of solid particles from the output signals of the photodetectors.

Preferably the different photodetectors are arranged to detect light scattered at different respective angles, and the calculation means are arranged to calculate a parameter dependent on the concentrations of particles of different sizes from the different respective outputs of the photodetectors.

The measurement of the concentration of solid particles suspended in the liquid according to the present invention is improved over other methods in that it is a non-invasive method and so the calculation does not effect the free flow of the liquid, and in that the accuracy of the determination of the concentration of and characterisation of size of solid particles suspended in the liquid is improved over conventional turbidimeters.

Preferably the instrument head is arranged to be coupled to a pipe carrying the liquid, with the aperture coaxially aligned with the pipe.

Preferably the light source is a semi-conductor laser.

Preferably, the instrument head houses three photodetectors which are arranged to detect light scattered by angles of 00, 150 and 900. The instrument head may include further optical elements such as mirrors, prisms and lenses for directing the light into the liquid, and directing light scattered by solid particles in the liquid to the photodetectors.

Preferably, the apparatus is able to determine the concentrations of two or more different types of particle, for example the concentration of yeast and that of haze forming compounds, where the liquid is beer.

The apparatus may form part of a larger system comprising a dosing pump for selectively adding a filter aid to the liquid, and a filter to remove the solid particles from the liquid.

According to a second aspect of the present invention, a method of determining the concentration of solid particles in a liquid comprises the steps of irradiating the liquid with a light beam, and determining the amount of light scattered in each of a number of directions by solid particles suspended in the liquid, and determining the concentration of solid particles suspended in the liquid from the relative quantities of light detected in each direction.

Preferably, the light is detected in three directions, preferably at 00, 150 and 900.

Figure 1 shows an instrument head which can be used in the present invention. The instrument head 1 can be included in a pipe through which the liquid is flowing and includes an aperture 2 through which the liquid can flow.

A laser source 3 emits a beam of laser light towards a prism 4 which directs the light into the liquid flowing through the aperture 2. When this light is incident upon a solid particle suspended in the liquid, for example yeast or a haze forming compound in beer, the light will be scattered. The amount that the light is scattered is dependent upon the size of the particles that the light is incident upon. The light will scatter by a larger angle for larger particles such as yeast as opposed to smaller haze forming compounds. The light transmitted through the beer is detected by photodetectors 5,6,7 which detect light scattered by angles of 00, 150 and 900 respectively. The light is collimated onto the photodetector 5,6,7 by collimating lenses 8 and a mirror 9. The photodetectors 5,6,7 produce an output signal dependent upon the intensity of light incident upon them. This signal is supplied to the calculation means which calculates the concentration of solid particles in the liquid, and is able to calculate the concentrations of different size particles based on the relative intensity of light incident upon different photodetectors.

The instrument head and calculation apparatus can be included in a system for filtering solid particles from a liquid such as beer. An instrument head 1 is included in a pipeline through which beer passes prior to filtration and bottling. As described above, the concentration of solid particles in the beer is calculated, and from this the amount of filter aid required to be added to the beer for optimum filter performance is calculated. Generally, the higher the concentration of solid particles in the liquid, the more filter aid should be added, and conversely if there is a low concentration of solid particles then less filter aid is required. The calculation means produces a control signal dependent upon the amount of filter aid required and this controls a dosing pump which adds the appropriate quantity of filter aid to the beer before this is filtered.

Claims

1. An apparatus for determining the concentration of solid particles in a liquid comprising an instrument head and a calculation means, the instrument head comprising an aperture through which the liquid can pass, a light source arranged to direct light into the aperture, and a number of photodetectors for detecting light scattered from solid particles suspended in the liquid in the aperture and each producing an output signal dependent on the intensity of light incident upon it, the calculation means being arranged to calculate the concentration of solid particles from the output signals of the photodetectors.

2. An apparatus according to claim 1, in which the different photodetectors are arranged to detect light scattered at different respective angles, and the calculation means are arranged to calculate a parameter dependent on the concentrations of particles of different sizes from the different respective outputs of the photodetectors.

3. An apparatus according to claim 1 or 2, in which the instrument head is arranged to be coupled to a pipe carrying the liquid, with the aperture co-axially aligned with the pipe.

4. An apparatus according to any one of the preceding claims, in which the light source is a semiconductor laser.

5. An apparatus according to any one of the preceding claims, in which the instrument head houses three photodetectors which are arranged to detect light scattered by angles of 00, 150 and 900.

6. An apparatus according to any one of the preceding claims, in which the instrument head includes mirrors or prisms for directing the light into the liquid in such a way that the light source and the photodetectors are located on the same side of the instrument head.

7. An apparatus according to any one of the preceding claims, in combination with a dosing pump for selectively adding a filter aid to the liquid, and a filter to remove the solid particles from the liquid.

8. An apparatus substantially as described with reference to the accompanying drawing.

9. A method of determining the concentration of solid particles in a liquid comprising the steps of irradiating the liquid with a light beam, and determining the amount of light scattered in each of a number of directions by solid particles suspended in the liquid, and determining the concentration of solid particles suspended in the liquid from the relative quantities of light detected in each direction.

10. A method according to claim 9, in which the light is detected in three directions, at substantially 00, 150 and 90" to the incident light.

11. A method substantially as described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. An apparatus for determining the concentration of solid particles in a liquid and selectively adding filter aid to the liquid, comprising an instrument head having an aperture through which the liquid can pass, a light source arranged to direct light into the aperture, and a number of photodetectors for detecting light scattered from solid particles suspended in the liquid in the aperture and each producing an output signal dependent on the intensity of light dependent upon it, a calculation means being arranged to calculate the concentration of solid particles from the output signals of the photodetectors, and a dosing pump for selectively adding filter aid to the liquid.

5. An apparatus according to any one of the preceding claims, in which the instrument head houses three photodetectors which are arranged to detect light scattered by angles of 00, 15 and 900.

7. An apparatus for determining the concentration of solid particles in liquid comprising an instrument head and a calculation means, the instrument head comprising an aperture through which the liquid can pass, a light source arranged to direct light into the aperture, a number of photodetectors for detecting light scattered from solid particles suspended in the liquid in the aperture and each producing an output signal dependent on the intensity of light incident upon it, and mirrors or prisms for directing the light into the liquid in such a way that the light source and photodetectors are located on the same side of the instrument head, the calculation means being arranged to calculate the concentration of solid particles from the output signals of the photodetector.

10. A method according to claim 9, in which the light is detected in three directions, at substantially 00, 150 and 900 to the incident light.