Patent GB-405354-A (GB)
Title: Electrically sterilizing food products or the like
IPC: A23L3/26
Filed: 1932-08-16
Abstract: <PICT:0405354/III/1> <PICT:0405354/III/2> <PICT:0405354/III/3> <PICT:0405354/III/4> <PICT:0405354/III/5> <PICT:0405354/III/6> <PICT:0405354/III/7> <PICT:0405354/III/8> Insect life in food products, such as milled cereals, is destroyed by passing the material, which is usually packaged, through a stressed air dielectric obtained by the application of an electric alternating potential so arranged that the higher permittivity of the material causes a local breakdown of the dielectric without complete rupture thereof.  The products are passed by means of a conveyer belt 17 of insulating material such as asbestos, canvas or cotton between electrodes 27 and 28 maintained at high potential and the lower part 32 of the frame 10 maintained at earth potential, the spacing between the electrodes 27 and 28 and the belt 17 being so small, and the spacing between the belt and the low potential frame being so large that a corona discharge occurs between the high tension electrodes and the material to be treated on the belt without a discharge occurring between the belt and the frame.  The high tension electrodes consist of two or more disc-like members suitably insulated and rotated in opposite directions by motors 23 and 24 at a speed of approximately 1800 r.p.m.  Each disc carries on its lower face a number of electrode members 28a of the form shown in Figs. 3 and 4, the tips z being the trailing portions.  A potential of the order of 170,000 volts and a frequency of the order of 640 cycles per second is applied to these electrodes by a suitable alternator.  Due to the rotation of the electrodes, the tips z give the effect of a horizontal plane having a multiplicity of discharge points, and thus give a high potential drop immediately beneath the electrodes, e.g. approximately 90 per cent of the total potential difference applied. The height of the electrodes above the belt may be suitably adjusted in accordance with the voltage applied and the size of the article to be treated, e.g. in the case of corn-meal in packages having a vertical dimension of two inches, the high potential electrodes are about \ba3/8\be inches above the surface of the packets and about 36 inches from the ground 32.  The belt 17 passes over a supporting framework 20 of insulating material such as synthetic resin, preferably having circular openings 20a and 20b immediately below each electrode, the size of the openings being approximately twice the diameter of the electrode members, thus avoiding the interposition of material having a permittivity higher than air, except the material to be treated, between the high and low potential electrodes.  The length of the conveyer belt between the rollers 15 and 16 is made as long as possible to reduce the leakage path. These rollers are preferably made of cast iron containing a stationary magnetic core with a number of poles past which the roller moves. Windings on the poles are energized by alternating current, thus rotating the rollers, and the heat produced by hysteresis losses and eddy currents in the roller keeps the belt free from moisture.  The low potential electrode may be alternatively constituted by a plate parallel to the plane of the conveyer and capable of being raised or lowered, or by two separate plates 50c and 50d (Fig. 10) which are in below the two openings in the support 20.  This form of construction prevents stray leakage beyond the edges of the plates and enables a lower voltage to be used to effect the sterilization.  The dielectric flux may also be concentrated by placing material of high permittivity such as fused quartz or glass known under the Registered Trade Mark "Pyrex" in the openings in the support 20 beneath the rotating electrodes: this is stated to increase the effective voltage applied to the material to be treated.  This high permittivity material may be in the form of flat plates fitting the openings, or of the form shown in Fig. 14 comprising members 68, 69, 70, 71, 72, 73 forming closed cylinders which may be filled with air or paraffin wax and which rest on a earthed metallic member 67 capable of being raised or lowered.  This apparatus may coact with a single condenser plate or separate plates 50 and 50d or these members may be omitted. Concentration of the dielectric flux is also achieved by forming the support 20 as a continuous surface and placing between the upper and lower surfaces of the belt 17 (see Fig. 18) a circular group of gaseous discharge tubes 161, e.g. containing neon gas at low pressure, beneath the upper rotating electrodes.  These tubes are held in recesses in a ring-shaped solid dielectric member 172 in a circle substantially the same as that described by the upper electrodes. Their lower ends contain an electrode 162 attached to conducting spheres 167, 168 and 169 which function as the plate of a condenser and coact with plate 50 or its equivalent.  The spheres may be replaced by a flat conducting plate.  When the high tension voltage is applied, these tubes become ionized and conducting and have a relatively small fall of potential across them, thus giving the effect of two condensers in series.  In the arrangement shown in Fig. 24, the high potential electrodes comprise flat discs 27 and 28 which are rotated by suitably arranged motors and are supported by an insulating member 113 of the form shown in Fig. 25.  The discharge points consist of a number of sharp points 105 arranged in a number of circles.  These electrodes coact with groups 115 and 116 of gaseous discharge tubes as previously described, preferably arranged to form a hollow cylinder of approximately the same diameter as the upper electrodes and which are slowly rotated in opposite directions, e.g. by motor 126, and with earthed condenser plates 50c and 50b. The belt 17 passes over quartz plates 127 and 128 arranged immediately above the discharge tubes.