US3767362A

US3767362A - Sterilisation of materials

Info

Publication number: US3767362A
Application number: US00150640A
Authority: US
Inventors: M Griffin; B King
Original assignee: Gardeners of Gloucester Ltd
Current assignee: Gardeners of Gloucester Ltd
Priority date: 1970-06-10
Filing date: 1971-06-07
Publication date: 1973-10-23
Anticipated expiration: 1990-10-23
Also published as: DE2128805A1; GB1335557A; DE2128805B2

Abstract

A method of sterilising powders and other fine-grained pulverulent or granular materials employs a gaseous sterilising agent. An upwardly extending closed treatment chamber is partially filled with the material to be sterilised, and the gaseous sterilising agent is admitted to the lower end of the chamber in such manner that the material is flung upwardly into free space at the top of the chamber and substantially allowed to settle again whereafter the process is repeated. Thus, the material is displaced by the sterilising agent and allowed to settle and stand again, or at any rate to complete its settling movement at least to a fluid state, several times. The sterilising agent escapes from an outlet at the top of the chamber, and it is desirably admitted to the latter in a series of pressure shocks of short duration, and in such manner that the material is whirled upwardly by the shock pulses in an ascending peripheral vortex so that the particles are in a state of suspension from which they fall downwards again in an inner vortex axially of the chamber.

Description

[ STERlLlSATlON OF MATERIALS Inventors: Michael John Griffin, Hucclecote,

Gloucester; Brian Clarence King, Gloucester, both of England [73] Assignee: Gardeners of Gloucester Limited,

Gloucester, England [22] Filed: June 7, 1971 [21] A pl. No.: 150,640

[30] Foreign Application Priority Data June 10, 1970 Great Britain 28,010/70 [52] US. Cl 21/58, 21/57, 21/D1G. 4 [51] Int. Cl. A611 1/00, A611 13/00 [58] Field of Search 2l/D1G. 4, 56, 58,

[56] References Cited UNITED STATES PATENTS 3,068,064 12/1962 McDonald 21/D1G. 4 3,069,734 12/1962 Leuthner 21/D1G. 4 3,088,179 5/1963 Leuthner.. 21/D1G. 4 3,341,280 9/1967 Eolkin 21/D1G. 4 3,341,335 9/1967 Eolkin et al. 21/58 X 3,477,807 11/1969 Ernst 2l/D1G. 4 3,600,127 8/1971 Kereluk et a1... 21/58 3,407,029 10/1968 Krahe 21/56 X Great Britain 2l/D1G. 4

993,757 6/1965 Great Britain 2l/D1G. 4

Primary Examiner-*Barry S. Richman Attorney-Young & Thompson 57 ABSTRACT A method of sterilising powders and other fine-grained pulverulent or granular materials employs a gaseous sterilising agent. An upwardly extending closed treatment chamber is partially filled with the material to be sterilised, and the gaseous sterilising agent is admitted to the lower end of the chamber in such manner that the material is flung upwardly into free space at the top of the chamber and substantially allowed to settle again whereafter the process is repeated. Thus, the material is displaced by the sterilising agent and allowed to settle and stand again, or at any rate to complete its settling movement at least to a fluid state, sev- 6 Claims, 3 Drawing Figures PATENIEUnmza ma SHEEI 10F 3 6km Cums/v05 k/A a INVENTORS 8%"? M ATTORNEYS PATENTED UN 2 3 I973 SHEET 2 OF 3 STERILISATION OF MATERIALS This invention relates to the sterilisation of materials, for example powders and other fine-grained pulverulent and granular materials, that is to say the treatment of such materials with gaseous sterilising agents with a view to destroying or preventing bacterial growths or the like.

Hitherto, such sterilisation has been carried out, gen erally speaking, with the materials in the prepacked state, for example in sealed plastic bags, or with the material exposed in shallow layers on open trays, in a sealed chamber or vault. This method of procedure requires long exposure times, for example of the order of 16 to 48 hours, with the attendant risk of degradation of the product by the gaseous sterilising agent. It has, however, been proposed to sterilise material in bulk by passing the gaseous sterilising agent through a body of the material in a tumbling-type unit which assists in obtaining intimate contact between the gaseous sterilising agent and the particles of powder. Even so, the sterilising time required may be of the order of 4 hours.

More recently it has been proposed to effect bulk sterilisation of powders by separating the particles of the powder in a stream of the gaseous sterilising agent which fluidises a bed of the powder to be sterilised. With that process the treatment time is claimed to have been reduced to between 5 and 20 minutes duration with the gaseous sterilising agent streaming continuously during that period.

The main object of the present invention is to provide improvements in the sterilisation of powders and other fine-grained pulverulent or granular materials which enables the materials to be sterilisedin bulk in a reasonably short period of time depending on circumstances while using minimal quantities of the gaseous sterilising agent and ensuring complete removal of the gas from-the product, thereby avoiding all possibility of degradation of the latter.

According to the invention a method of sterilising powders and other fine-grained pulverulent or granular materials comprises, partially filling an upwardly extending closed treatment chamber with the material, admitting a gaseous sterilising agent to the lower end of the treatment chamber in such manner that the mate-- rial is flung upwardly into the free space'at the top of the chamber and substantially allowed to settle again whereafter the process is repeated, the gaseous sterilising agent escaping from an outlet at the top of the chamber. I

Thus, the material is displaced and allowed to settle and stand again, or at any rate to complete its settling movement at least to a fluid state, several times by the gaseous sterilising agent as compared with the fluidisingof a bed of material by a continuous stream of the gaseous sterilising agent previously proposed.

If desired the gaseous sterilising agent may be admitted in a series of pressure shocks of short duration and at such pressure that the foregoing effect is achieved. Preferably the manner of admission of the gaseous sterilising agent to the treatment chamber and the form of the latter are such that the material is whirled upwardly. by the shock pulses of the pressurised gaseous sterilising. agent in an ascending peripheral vortex so that the particles are in a state of suspension from which'they fall downwards again in an inner vortex axially of the chamber The gaseous sterilising agent may be one which destroys by chemical action the bacteria and/or other organisms in respect of which sterility is to be achieved. Ethylene oxide, either alone or in a carrier gas such as nitrogen, and formaldehyde are examples. Preferably the sterilisation is carried out with control of the material and gas temperatures, humidity and pressure. For example in a typical case a temperature of around 122F and a relative humidity of about 45 percent to 5 0 percent may be established in the treatment chamber.

The invention also covers apparatus for carrying the foregoing method steps into effect. For the admission of the gaseous sterilising agent to the treatment chamber in the aforesaid series of pressure shocks of short duration a plurality, preferably a multiplicity, of separate nozzles are provided at the lower end of the treatment chamber and to and from which the pressurised gaseous sterilising agent is intermittently fed and cut off under the control of a timing device. Preferably the nozzles are arranged in a ring at equiangular separation around a frusto-conical lower end wall of the treatment chamber, the axes of the nozzles being parallel to the frusto-conical wall but slanted in order to impart the aforesaid whirling motion to the gaseous sterilising agent.

By way of example, the application of the invention to the sterilisation of talc will now be described with reference to the accompanying drawings, inwhich:

FIG. 1 is a flow diagram illustrating one typical arrangement of the tale sterilising plant,

FIG. 2 is a similar view of an alternative exemplary sterilising plant, and 7 FIG. 3 is a flow diagram illustrating a sterilising gas supply rig, suitable for use with either of the foregoing plants but shown more particularly as associated with that of FIG. 1.

The talc is initially ground to a fine impalpable powder in which state it is stored in a large silo 11. From the bottom of the silo 11 the powder is removed by means of a discharge worm 12 to the lower end of a pneumatic elevator 13 from the upper end of which it is delivered, in the plant of FIG. 1, to duplex powder heaters 14' andlS, which may be steam or oil jacketed chambers, in which the powder is preheated to a temperature of [00F to 180F, for example 140F. From the

heaters

14 and 15 the talc is fed into a single sterilising chamber 16, the feed means being such that the chamber 16 is filled to an extent of approximately 60 percent of its capacity.

The sterilising chamber 16 is substantially cylindrical in shape with its axis vertical and has a frusto-conical lower end or base 16a.- At its upper end the sterilising chamber has a gas outlet 17 (see FIG. 3) embodying filtering means. The opening of the frusto-conical base of the sterilising chamber is closed by an upwardly c'oned element 18 which serves to deflect the material within the chamber to the outer periphery of the frustoconical base 16a of the latter and is capable of being raised to provide an annular opening through which material may be discharged through a short outlet pipe 19. Surrounding the base of the coned element 18 is a ring main 20 having a series of equiangularly separated nozzles (not shown) leading therefrom and opening on to the lower wall of the frusto-conical base' 16a of the sterilising chamber.

To the ring main 20 through an admission conduit 22 a 10 percent ethylene oxide and percent nitrogen mixture is fed. From the ring main 20 the gas mixture passes through a multiplicity of radially directed bores each of which leads to one of the aforesaid nozzles. There may be, for example, ten such bores and nozzles at equiangular separation around the frusto-conical base 16a of the chamber 16. The nozzles may be of Laval type arranged with their axes parallel to the frusto-conical bottom portion of the sterilising chamber but slanted so that the separate jets of gas mixture issue therefrom with an upwardly directed circulatory movement.

Entry of the gas mixture to the ring main 20 occurs through the intermediary of a control valve 23 which operates as a timing device. As a result, powerful but very brief shocks of pressure gas issue from the nozzles in a circular movement in order to whirl the talc freely upwards within the chamber 16 until it is in a state of suspension, the pressure gas shocks following one another only at such time intervals that the talc can settle again between each two pressure shocks at least to a fluid state. Usually the talc is allowed to settle and stand for some minutes to allow the chemical sterilising action to proceed before the next pressure shock. The upward whirling movement of the talc takes place in the vicinity of the cylindrical wall of the sterilising chamber 16 into the free space at the top of the latter where the tale is in a state of suspension and whence it falls spirally near the centre of the chamber at the termination of each blast which is of only a few seconds duration. On falling to the bottom of the chamber the talc is deflected by the central upwardly coned element 18 towards the peripheral wall of the frusto-conical base 16a and then whirled upwardly again by the next succeeding blast from the nozzles.

After the foregoing procedure has been repeated several times the cone 18 is raised penumatically to allow the sterilised talc to be discharged through the annular opening already mentioned and the outlet pipe 19 into a buffer hopper 24 from the lower end of which it is discharged by a worm through a rotary seal 26 and pneumatically conveyed along a duct 27 to a storage silo (not shown). The treatment time may be, for example, of the order of l to 3 hours.

Referring now more particularly to FIG. 3, a cylinder 28 of ethylene oxide is pressurised from a cylinder 29 of nitrogen, thereby delivering the ethylene oxide through a flow-control valve 30 to a heating and humidifying reservoir 32. A bank of nitrogen cylinders 33 also deliver to the reservoir 32 through pressure and flow-

control valves

34 and 35, the flows from the

valves

30 and 35 joining at the region of an inlet/outlet pipe 36 of the reservoir. I

The reservoir is heated by an electrical heating jacket 37, which is thermostatically controlled, and the internal reservoir gas temperature is monitored by a pyrometric sensing element 38 connectable to a temperature indicator 39. The indicator 39 is alternatively connectable to a pyrometric sensing element 40 in the chamber 16, whereby to monitor the treatment temperature. The pipe 36 is jacketed to prevent undue heat loss and supplies the valve 23 through flow and

pressure control valves

42 and 43.

A pressure gauge 44 monitors the internal reservoir pressure, and humidifying steam is admitted through a flow-control valve 45. A hygrometer indicator 46 is alternatively connectable to a humidity sensing head 47 in the reservoir 32 and a similar head 48 in the treatment chamber 16. This enables the steam flow to be controlled to maintain appropriate humidity in the treatment zone, and the reservoir 32 is also fitted with a drain valve 49.

A source of compressed air can be connected to the described heating and humidifying means through a flow-control valve 50 connected to the reservoir 32. Thus by appropriate operation of the various flowcontrol valves compressed air may be admitted to the treatment chamber for a cleaning run, and through the various pipe-lines for purging purposes.

The alternative arrangement of the talc sterilising plant of FIG. 2 enables continuous preheating of the talc to be carried out notwithstanding the batch sterilisation and discharge of the tale from the sterilising chamber 16 in the manner already described. This is achieved by delivering the powder from the upper end of the pneumatic elevator 13 to a battery of, for example five as shown, continuous powder heaters 52 arranged in cascade. From the lowermost powder heater 52 the talc passes through a rotary seal 53 to a pneumatic conveyor 54 along which air is blown by a blower 55, this air being heated in a heat exchanger 56 in order to avoid chilling of the preheated talc. The pneumatic conveyor 54 feeds the preheated tale to one or other of two sterilising chambers 16 of the construction already described and arranged in parallel so that one of the chambers is being filled while powder is undergoing sterilisation in the other. The latter chamber 16 is then discharged and refilled while the talc in the first chamber is undergoing the sterilisation treatment.

The gas mixture is passed through heating and humidifying means as before but passes thence to a selector valve 57 which determines which of the two sterilising chambers 16 it enters by way of

respective admission conduits

58,59. It will be understood that the selector valve 57 operates in timed relation to a valve 60 which determines which of the sterilising chambers 16 is being filled at a given time. From the bottoms of the sterilising chambers the sterilised powder passes through respective short outlet pipes into a common pipe 19 leading to a buffer hopper 24 as already described.

A pneumatic timer control unit 62, shown in FIG. 3, controls the valve 23 of each chamber 16 so that the gaseous sterilising agent is admitted to the chambers 16 in the described pulsed manner. In either plant the storage silo 11 may be replaced by an automatic bag opener to which the talc is brought by way of a'bag conveyor and whence the material is fed into a transfer hopper, this modification not being shown in the drawings. The transfer hopper would then deliver to the discharge worm 12 of the plants as illustrated.

To provide even distribution of the tale in the or each chamber 16, the latter may include at the top end a rotary discharge spreader of generally volute form on to which the talc is delivered. From this spreader the talc is then distributed so that it delivers into the chamber in the form of an even curtain.

We claim:

1. A method of sterilising powders and other finegrained pulverulent or granular materials comprising partially filling an upwardly extending closed treatment chamber with the material, admitting a gaseous sterilising agent to the lower end of the treatment chamber at a flow rate in excess of that required to fluidize said material and in such manner that the material is flung upwardly into the free space at the top of the chamber while the gaseous sterilising agent escapes from an outlet at the top of the chamber, and then discontinuing the flow of said gaseous sterilizing agent into said treatment chamber whereby said material is allowed to settle whereafter further gaseous sterilising agent is admitted to repeat said flinging and settling procedure.

2. A method according to claim 1, wherein the gaseous sterilising agent is admitted in a series of pressure shocks of short duration.

3. A method according to claim 1, which includes pre-heating the material prior to delivery thereof to the treatment chamber and effecting controlled heating and humidifaction of the gaseous sterilising agent prior to admission thereof to the treatment chamber, said heating and humidification being carried out in a reservoir which contains thermostatically controlled electrical heating means and to which steam is fed 4. A method of sterilising powders and other finegrained pulverulent or granular materials comprising partially filling an upwardly extending closed treatment chamber with the material, admitting a gaseous sterilising agent to the lower end of the treatment chamber at a flow rate in excess of that required to fluidize said material and in such manner that the material is whirled upwardly by the gaseous sterilising agent in an ascending peripheral vortex from which the particles of said material fall downwards in an inner vortex axially of the chamber upon termination of the flow of said gaseous sterilising agent, the gaseous sterilising agent being allowed to escape from an outlet at the top of the chamber discontinuing the flow of said gaseous sterilizing agent into said treatment chamber until settling of said material is substantially complete and admitting further gaseous sterilising agent into said treatment chamber to repeat said whirling and falling procedure when settling of the material is substantially complete.

5. A method according to claim 4, which includes effecting controlled heating and humidification of the gaseous sterilising agent prior to admission thereof to the treatment chamber.

6. A method according to claim 4, which includes pre-heating the material prior to delivery thereof to the treatment chamber.

Claims

2. A method according to claim 1, wherein the gaseous sterilising agent is admitted in a series of pressure shocks of short duration.
3. A method according to claim 1, which includes pre-heating the material prior to delivery thereof to the treatment chamber and effecting controlled heating and humidifaction of the gaseous sterilising agent prior to admission thereof to the treatment chamber, said heating and humidification being carried out in a reservoir which contains thermostatically controlled electrical heating means and to which steam is fed.
4. A method of sterilising powders and other fine-grained pulverulent or granular materials comprising partially filling an upwardly extending closed treatment chamber with the material, admitting a gaseous sterilising agent to the lower end of the treatment chamber at a flow rate in excess of that required to fluidize said material and in such manner that the material is whirled upwardly by the gaseous sterilising agent in an ascending peripheral vortex from which the particles of said material fall downwards in an inner vortex axially of the chamber upon termination of the flow of said gaseous sterilising agent, the gaseous sterilising agent being allowed to escape from an outlet at the top of the chamber discontinuing the flow of said gaseous sterilizing agent into said treatment chamber until settling of said material is substantially complete and admitting further gaseous sterilising agent into said treatment chamber to repeat said whirling and falling procedure when settling of the material is substantially complete.
5. A method according to claim 4, which includes effecting controlled heating and humidification of the gaseous sterilising agent prior to admission thereof to the treatment chamber.
6. A method according to claim 4, which includes pre-heating the material prior to delivery thereof to the treatment chamber.