This invention relates to a method and an apparatus for use in the drying and/or processing of materials.

GB 2281383 describes apparatus for use in the continuous drying of moist materials in an atmosphere made up largely of superheated steam. The apparatus comprises a chamber from which extend inlet and outlet ducts through which materials to be dried pass to enter and, once dried, leave the chamber. The ducts extend downwardly and, in use, temperature and density differential stratification layers form in the ducts and serve effectively as seals, resisting the ingress of external air or other gases into the chamber and resisting the escape of superheated steam or other gases from the chamber. Some ingress or escape resulting from gases being entrained with the materials entering or leaving the chamber may occur, but typically only at a low level.

PCT/GB02/01497 describes high temperature processing of materials in a similar apparatus. It will be appreciated that, in such arrangements, drying and/or processing can be undertaken in an environment substantially free of oxygen.

In both cases, it is known to provide a rotating cylinder within the chamber within which the materials to be dried or processed are positioned. Unless the cylinder is of louvered form, the pumped recirculation of the atmosphere within the chamber will usually result in the formation of a relatively high pressure region towards one end of the cylinder and a lower pressure region towards the other end of the cylinder as a result of the restriction to the flow formed by the cylinder and its contents. If the pressure at the high pressure end becomes too high then there is a risk that gases from within the chamber may blow out of the duct adjacent the high pressure end, and external air may enter the chamber through the other duct, negating the effect of the stratification layers as seals. Obviously this is undesirable as it will allow the introduction of free oxygen into the chamber which may lead to breakdown or combustion of the materials therein.

The use of louvered cylinders, although reducing sealing problems, may require the operating temperature of the system to be reduced to avoid overheating of the materials about to leave the cylinder. Instead of using a relatively low weight of high temperature gases, a greater quantity of lower temperature gases is used leading to increased fan or blower requirements and increased motor operating costs.

It is desirable for the drying and/or processing to be undertaken in an atmosphere substantially free of free oxygen or in which the quantity of free oxygen can be controlled so as to be maintained at a low, or desired level. Objects of the invention are to provide methods and apparatuses whereby this can be achieved.

According to one aspect of the invention there is provided a method of drying and/or processing materials comprising using fan means to route a proportion of a process gas entering a higher pressure region of a chamber through a venturi device to reduce the pressure at a duct opening into the higher pressure region of the chamber.

By routing the process gas in this manner, the application of sufficiently high pressures to cause gases to blow out of the chamber through the duct can be avoided whilst maintaining the rate at which process gases pass through the chamber at a desired level to permit efficient drying and/or processing.

The invention also relates to a drying and/or processing apparatus having a chamber, fan means for routing a proportion of a process gas entering a higher pressure region of the chamber through a venturi device so as to reduce the pressure at a duct opening into the high pressure region of the chamber.

The process gas are preferably routed around a recirculation path including heater means, the heater means being arranged to introduce little, if any, free oxygen into the process gas. The heater means may be an indirect heater. Alternatively, a direct heater or burner may be used. The direct heater or burner is preferably a proportional burner whereby the quantity of oxygen supplied to the burner is controlled to ensure that little, if any, free oxygen is introduced into the process gas.

An oxygen sensor is preferably provided to monitor oxygen levels within at least part of the chamber. The output of the oxygen sensor is preferably used to control the introduction of water, for example through an atomiser, into the chamber, In such an arrangement, if unacceptably high free oxygen levels are sensed, water can be introduced to assist in the rapid formation of quantities of superheated steam in the process gas, reducing the free oxygen content of the process gas.

The invention further relates to a drying and/or processing apparatus comprising a chamber containing, in use, a process gas, heater means for heating the process gas whilst introducing little, if any, free oxygen into the process gas, an oxygen sensor, and water delivery means operable to introduce a quantity of water into the process gas in the event that the sensed free oxygen level exceeds a predetermined threshold.

The apparatus maybe a batch processing apparatus or a continuous processing apparatus. It will be appreciated that the aforementioned venturi device may be provided.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic view illustrating an apparatus in accordance with one embodiment of the invention; and

Figures 2 to 4 illustrate some alternative embodiments.

Referring firstly to Figure 1 there is illustrated a drying and/or processing apparatus comprising a drying and/or processing chamber 10 within which a cylinder

12 is supported for rotation by appropriate bearings (not shown) and arranged to be driven by an associated motor (not shown). The chamber 10 houses a recirculation fan 14 arranged to draw process gases along the cylinder 12, and supplying the gases along a recirculation path 16 in which a heater device 18 is located. The fan 14 may take a range of forms.

The chamber 10 includes a downwardly extending inlet duct 20 through which materials to be dried or processed enter the chamber 10, and a similar outlet duct 22 whereby dried or processed materials can exit the chamber 10. Conveyor means 24 are provided to carry the materials through the inlet duct 20 to the interior of the cylinder 12. Similar conveyor means may be provided to transport materials out of the chamber 10. However, in this embodiment the dried and/or processed materials simply fall from the chamber 10 through the outlet duct 22 under the action of gravity.

The chamber 10 is provided with a vent 26 which exhausts at a vertical height aligned with parts of the ducts 20, 22 with the result that, in use, temperature and density differential stratification layers 28 will tend to form in the ducts 20, 22 which, in use, serve effectively as seals preventing or restricting the entry or exit of gases into or from the chamber 10 whilst permitting the introduction or exit of materials in a relatively simple manner.

With such an arrangement, in use, the end of the chamber 10 closest to the inlet duct 20 will typically be at a higher pressure than the end closest to the outlet duct 22 and there is a risk that, as a result, gases may be blown from the chamber 10 through the inlet duct 20, and gases may enter the chamber 10 through the outlet duct 22, negating the effect of the stratification layers 28.

In accordance with the invention, in order to avoid or reduce the risk of such operation, a proportion of the re-circulating gases are supplied via a fan device 30 to a venturi device 32 located close to the inlet duct 20, i.e. adjacent the higher pressure end of the chamber 10. The fan device 30 may take a range of forms. For example it may comprise a bladed fan, a blower, a compressor or the like. The venturi device may take a range of forms and in this embodiment comprises an annular flow passage 34 surrounding an end part of the conveyor 24 whereby materials are delivered to the cylinder 12. The delivery of gases at high speed by the fan device 30 through the venturi device 32 together serve to form a reduced pressure at or close to the inlet duct 20, countering the higher pressure in that part of the chamber 10 and so reducing the risk of gases being blown out of the chamber 10 through the inlet duct 20. It will be appreciated that the shapes of the flow passage 34 and end part of the conveyor 24 are not critical. For example, they could be of rectangular section if that lends itself conveniently to the shapes and sizes of the materials to be conveyed.

The operation of the fan device 30 may be controlled in such a manner as to achieve a desired level of 'suction' at the higher pressure part of the chamber 10. For example, a thermocouple may be provided to permit sensing of the inlet duct temperature, if the sensed temperature increases, suggesting that hot gases are being blown down the inlet duct 20, then the operation of the fan device 30 maybe increased to increase the level of 'suction'. Rather than alter the operating speed of the fan device 30, a baffle or other movable flow restrictor could be provided to permit such control. If the duct temperature is decreasing then the fan device 30 may be slowed. Rather than use duct temperature in regulating the operation of the fan device, a pressure sensor may be used, or a gas flow sensor sensitive to gas flow along the duct could be used. Similarly, if desired, a sensor may be provided to sense the level of the temperature and/or pressure at the outlet duct, and the output of the sensor used in controlling the operation of the fan device 30, or the recirculation fan 14, to avoid external air entering through the outlet duct.

The cylinder 12 is preferably of internally flighted form to assist in uniform drying and/or processing. If desired it may be of louvered form to reduce the pressure differential along the chamber 10. However, it will be appreciated that this need not always be the case. Further, depending upon the nature of the materials to be processed, it may be preferred not to use a cylinder and for the materials to simply be conveyed through the chamber 10 by a suitable conveyor arrangement.

The heater 18 may take a range of forms, but it is, in this embodiment, designed to be of the type that results in little, if any, free oxygen being introduced into the re-circulating process gases with the result that the process gases are, in use, substantially inert. For example, the heater 18 may be of the indirect type. Alternatively, a direct heater or burner may be used in which case the air or oxygen supply to heater or burner is preferably matched to the fuel supply thereto with the result that efficient combustion of the fuel does not result in significant quantities of free oxygen being introduced. By using such a heater to ensure that little or no, free oxygen is introduced, it will be appreciated that the drying and/or processing can be undertaken in a reduced oxygen environment.

An oxygen sensor 36 is located within the chamber 10 to monitor the quantity of free oxygen within the process gases. The sensor 36 is illustrated as located within the re-circulation path but this is not essential and it could be located elsewhere. The output of the sensor 36 is monitored and if the sensed free oxygen levels fall above a predetermined level than a quantity of water is injected into the chamber 10, via an atomiser 38 to aid in the rapid introduction of a quantity of superheated steam into the process gases, reducing the proportion of the process gases made up of free-oxygen. It will be appreciated that such an arrangement permits control over the free-oxygen content of the process gases in a closed loop manner. This is advantageous in that the introduction of too little water could leave sufficient free-oxygen to permit deterioration of the material being dried or processed. Introduction of too much water results in unnecessary cooling reducing the efficiency of the apparatus.

Although described hereinbefore in connection with a continuous drying and/or processing apparatus, it will be appreciated that the heater, sensor and water injection arrangements could also be used in batch processing arrangements, for example in which a chamber is sealed by one or more doors, and the invention extends to such arrangements. Further, the venturi device may be used to lower the pressure at a duct housing a mechanically sealed door, reducing the pressure that the seal must withstand, in use.

In the arrangement of Figure 1 , the venturi device 32 is arranged such that the proportion of process gases routed by the fan device 30 flow at relatively high speed flows through an annular flow path 34 surrounding the end part of the conveyor 24. Figure 2 illustrates an alternative in which the material is conveyed through an annular path 24a surrounding a tapering flow passage 34 for the gas supplied by the fan device 30. In this case, the path 24a takes the form of a hopper to which materials to be dried or processed are supplied by the conveyor 24. This arrangement is particularly suitable for use with materials of granular or particulate form, but other materials may also be dried or processed using the apparatus.

Another difference between the arrangement of Figure 2 and that of Figure 1 is that in Figure 2 the cylinder 12 is not located within the chamber 10, but rather is sealed thereto by seals 40 which allow the cylinder 12 to rotate. In this arrangement the cylinder 12 is not of louvered form as such louvers would allow the escape of process gases. Figure 3 illustrates another variant, in this case the cylinder 12 being omitted and the materials to be dried and/or processed passing through the chamber 10, for example upon a suitable conveyor.

Figure 4 illustrates the application of the invention to a batch process in which the chamber 10 includes a duct 20 provided with a door 21. The door 21 is sealed in a closed position, in use, by mechanical seals (not shown). The venturi device 32 of this arrangement serves to reduce the pressure at the duct 20, reducing the pressure differential across the seals thereby reducing the sealing requirements or permitting continued use of partially worn seals.

It will be appreciated that a number of modifications can be made to the arrangements described hereinbefore without departing from the scope of the invention.