WO1988008758A1

WO1988008758A1 - Device for supplying a flow of heated air

Info

Publication number: WO1988008758A1
Application number: PCT/GB1988/000368
Authority: WO
Inventors: Trevor Willis
Original assignee: B T Sales And Services Limited
Priority date: 1987-05-12
Filing date: 1988-05-12
Publication date: 1988-11-17
Also published as: GB2228076B; GB8925650D0; GB8711167D0; GB2228076A; AU1704888A

Abstract

There is disclosed a device for supplying a flow of heated air for scavenging the interior of emptied liquid-containing tanks and comprising an electrically driven fan (5, 6), an air filter (11) fitted to an inlet of the fan, ducting (12) connecting an outlet from the fan to an inlet of a heating chamber (14) which houses one of more electrical heating elements (30), ducting (19) connecting an outlet from the heating chamber (14) to an inlet (20) of a hose reel (21), a hose wound on the reel and connected to the hose reel inlet (20), a thermostat (54) in the air path downstream of the heating elements (30), a connection box (40) for the heating elements (30) which is spaced from the heating chamber (14), and guide means in the form of tubes (36, 38) enclosing ends of the heating elements (30) and guiding these from the heating chamber (14) to the connection box (40). A control box (50) houses electrical controls for the fan and the heating elements; and the electric motor (6), the connection box (40), the control box (50) and all the connections thereto are flameproof. A device according to the invention is therefore particularly useful for scavenging fuel tanks which have contained volatile material, so as to deliver air at a temperature which is sufficiently low that there is no danger of ignition of any residual volatile elements, while being sufficiently high to promote evaporation and therefore clearance of less volatile or non-volatile material, such as water.

Description

DEVICE FOR SUPPLYING A FLOW OF HEATED AIR

This invention relates to a device for supplying a flow of heated air.

In the past, the scavenging of aircraft fuel tanks has been a major problem, requiring a significant amount of work over a long period under conditions which ensure that no sparks can occur which may ignite the residual volatile materials in the tanks. However, scavenging involves not only the removal of such volatile materials, but also the removal of water and solid contaminants that may have been present in the fuel and which are left in the tank. Removal of these other materials continues to be a problem, and the present invention seeks to mitigate this problem.

According to the invention there is provided a device for supplying a flow of heated air and which comprises a fan, an electric motor for driving the fan, an air filter fitted to an inlet of the fan, ducting connecting an outlet from the fan to an inlet of a heating chamber which houses an electrical heating element, ducting connecting an outlet from the heating chamber to an inlet of a hose reel, a hose wound on the reel and connected to the hose reel inlet, a thermostat in the air path downstream of the heating element, a connection box for the heating element, the connection box being spaced from the heating chamber, guide means enclosing ends of the heating element and guiding these from the heating chamber to the connection box; and a control box which houses electrical controls' for the fan, and the heating elements; the electric motor, the connection box, the control box and all connections thereto being flameproof.

A device as aforesaid can be used in the scavenging of aircraft fuel tanks, and indeed of any other tanks which may have contained volatile materials. The device is capable of delivering air at a temperature that is pre-set and under thermosta ic control, the temperature being sufficiently low that there is no danger of ignition of the volatile elements, and yet sufficiently high that it will promote evaporation and thus clearance of less volatile or non-volatile material, such as water. It is particularly important when air is supplied to an atmosphere that contains volatile constituents that any danger of sparks being carried into the atmosphere by the air flow is prevented, and the flameproofing of the electric motor, the connection box, the control box and all connections thereto are such as positively to prevent the creation of sparks capable of being carried in the heated air flow. If sparking should occur in any of these components then it is wholly confined within the respective area of the component. The flameproofing may be carried out to any required degree, even to the extent of making the particular component or containment area substan ially explosion-proof. It is also important that there should be no carriage into the volatile atmosphere of solid particles that may either spontaneously cause ignition, or that may be catalytic to such ignition occurring. Accordingly, the provision of the filter on the inlet of the fan is desirably such that it gives complete protection against the ingress of particulate material.

Desirably the connection box is mounted above the heating chamber, and the guide means are tubes extending vertically between the heating chamber and the connection box. The physical separation between the connection box and the heating chamber is of importance in reducing heat transfer between these two areas, and of promoting air cooling of the external surfaces of, respectively, the heating chamber and the connection box. The vertically separated confi uration of the two regions is particularly preferred, as it assists in promoting a compact arrangement of the equipment. By making the guide means of tubular form the complete enclosure and protection of the heating elements and the connections thereto is enhanced.

Desirably the heating chamber contains a plurality of heating elements, and the control box includes means for supplying power via the connecting box to selected ones of the heating elements. In this way the upper limit of the heat energy which may be imparted to the air flow is set without any problem concerning control by the thermostat.

Preferably the fan is a centrifugal fan mounted for rotation about a first axis, the fan has a central inlet and a peripheral outlet, the ducting from the fan outlet includes a 90° bend section for directing air into the heating chamber, which has an axis parallel to that of the fan, the ducting from the heating chamber to the hose reel inlet includes a further 90° bend section, and the axis of the hose reel is perpendicular to the axes of the fan and the heating chamber. Again, this assists in the attainment of a compact configuration for the device. The configuration also makes possible the arrangement of the ducting in such a way that back pressure on the centrifugal fan is kept to an acceptably low level in order that desired air flow figures may be attained. In order that the desired amount of heat may be provided, the cross- sectional area of the heating chamber is preferably greater than that both of the fan outlet and of the hose reel inlet .

Conveniently the device includes a wheeled trolley, the fan being mounted adjacent to a first end of the trolley, the hose reel being mounted adjacent to a second end of the trolley, the heating chamber and connection box being mounted adjacent to a first side of the trolley, and the control box being mounted adjacent to a second side of the trolley and between the fan and the hose reel. The device is thus made readily portable and can be arranged within an optimally small area.

Desirably the control box includes interlock means for preventing operation of the heating element unless the fan is running, and for maintaining operation of the fan for a predetermined period after switching off the heating element. Such interlocks act to prevent overheating of the air, and the explosion risk that would be attendant on overheating.

In order that the invention may be better understood a specific embodiment of the device in accordance therewith will now be described in more detail, by way of example, with reference to the accompanying drawings in which: - Figure 1 is a plan view of the device; Figure 2 is an elevation of one side of the device; Figure 3 is a perspective view of the other side of the device;

Figure 4 is a sectional view on the line IV-IV of Figure 1 ; and

Figure 5 is a part section, part elevation of a heating chamber and a connection box of the device of Figure 1.

Referring now to the drawings the device is mounted on a trolley 1 having wheels 2 fitted onto casters in order that the trolley is both portable and fully manoeuvrable. The trolley comprises a framework from which there is upstanding a support assembly 4 with a section 5 supporting a bearing and a fan housing 6. The casing 7 of an electric motor is secured by appropriate bolts to the section 5, and the fan housing Is also bolted to the section 5. The motor has its own internal bearings, and the motor output shaft passes through the bearing in the section 5 and is coupled to the shaft of the fan. The fan is a centrifugal fan having backward curved blades, with air being taken in through an inlet 8 at the centre of the fan, and the air being discharged through a peripheral outlet 9. Mounted on the fan inlet by bolts 10 is a filter 11 through which air is drawn into the fan. The filter incorporates filter elements that are effective to remove all particulate material from the incoming air down to a size of microns, so that substantially clean air enters the fan itself. The filter is formed in accordance with known techniques to give the required filtration rating, and if necessary it may incorporate a downstream microfilter barrier in order to prevent carry-over of particulate material that may be incorporated in or entrained in the upstream filter material.

The outlet from the fan is connected by a 90° bend pipe section 12 to a ducting manifold 13 that flares outwardly in the downstream direction of flow. The downstream end of the manifold is bolted to the inlet side of a heating chamber 14. Suitable gaskets are incorporated at the locations 15 to 17 between all joint regions of the ductin .

The downstream end of the heating chamber is similarly connected by a manifold 18 that tapers inwardly in the downstream direction and that is connected at its downstream end to a further 90° bend pipe 19, bolted at its other end to the inlet 20 to a hose reel 21. Again, suitable gaskets are included at the joints in this downstream ducting.

The hose reel has an axial through pipe 22, with a rotary coupling incorporated at the downstream end thereof, so that air can flow from the axial passageway into the upstream end of a hose 24 that is wound onto the reel. The hose may be of any suitable material, typically a neoprene rubber that has low heat conductivity, and the hose may be of any suitable length. The reel may be of any suitable configuration, but will conveniently be spring-loaded to a position wherein the hose is fully wound onto the reel, and provided with a ratchet mechanism whereby any desired length of hose can be pulled from the reel, the reel being locked at the required hose length by the ratchet. The reel is journalled for rotation in bearings that are supported by supports 26, 28 upstanding from the framework of the trolley.

The heating chamber 14 contains a plurality of serpentine heating elements 30 extending across the direction of the air flow. Each heating element is of solid construction and has two ends, each of which pass through a pressure-resistant gland 32, 34 at opposite sides of the heating chamber. Tubes 36, 38 extend upwardly from each of the glands to the lower face of a control box 40, into which ends of the heating elements pass, again through suitable pressure-resistant glands.. The connection box 40 is supported above the heating chamber by pillars 42. Positive and negative connections to the free ends of the heating elements are made within the connecting box. Supply cables for the heating elements extend through pressure-resistant glands in one side of the box. Those cables extend to a control box 50, and enter the control box through further pressure-resistant glands. The control box has means whereby it can be connected to a source of electrical power, and also includes suitable electrical control elements enabling both the fan and the heating elements to be controlled from external switches 52 mounted on one face of the control box.

A main thermostat 54 responsive to air temperature extends across the outlet from the heating chamber 14 to the manifold 18, and a connector 56 is supported externally of the chamber, from which a cable is taken to the control bcx 50. A secondary thermostat 58 for monitoring element temperature is connected to one of the elements, and its end passes through a further tube 60 to the connection box 40.

The electric motor that is used is a flameproof electric motor in accordance with BS 5000-99, and the electrical cables to the motor are fully shrouded and protected by appropriate connectors. Those cables extend from the control box, and at the interface between the cables and the control box the cables are again protected by similar connectors. Appropriate connectors also protect cables leaving the control box and Dassin to the connection box, with similar connectors again being provided at the interface into the connection box. The control box and the connection box are each of massive construction with massive lids secured in position by an appropriate number of bolts, in order that the boxes are flameproof to the required degree, and preferably so that the boxes are explosion-proof in accordance with the requirements of BS 5501. By mounting the connecting box above and remote from the control box it will be seen that any sparking that may occur within the connection box cannot be transmitted into the heating chamber, and accordingly that no sparking can be conveyed by the air flow to the region that is being scavenged by the air flow. Furthermore, if any sparking should occur in the connecting box or in the control box it will positively be contained within the appropriate box due to the flameproof construction thereof, so that again hazard within an area containing volatile gases is positively prevented. The provision of the filter at the fan inlet is effective to remove substantially all particulate material from the incoming air, so that no particles can pass into the volatile atmosphere which may themselves cause ignition or which may have a catalytic effect in assisting ignition.

The control box incorporates interlocks that will ensure that power cannot be supplied to any of the heating elements unless the fan is already running, and also that will ensure that the fan runs for a predetermined length of time after the last of the heating elements has been switched off. In this way overheating of the air can positively be prevented, again with a consequent increase in safety standards. The control box also incorporates suitable circuitry responsive to the thermostats, in order that current to the elements is controlled in relation to the air flow so that the air delivered at the downstream end of the hose is of a required temperature. A typical requirement may be to deliver air at 25° C at the free end of a ten metre length neoprene hose of 75 mm diameter. This may readily be achieved using a 5.5 HP motor driving the fan at 2,900 rpm with an air throughput of 600 cfm. Six heating elements each rated at 1833 watts will then be more than adequate to impart the required heat to the air, air temperature being regulated by the setting of the thermostat.

It will be appreciated that the equipment particularly described is capable of modification.

Claims

CLA I MS

1. A device for supplying a flow of heated air and which comprises a fan, an electric motor for driving the fan, an air filter fitted to an inlet of the fan, ducting connecting an outlet from the fan to an inlet of a heating chamber which houses an electrical heating element, ducting connecting an outlet from the heating chamber to an inlet of a hose reel , a hose wound on the reel and connected to the hose reel inlet, a thermostat in the air path downstream of the heating element, a connection box for the heating element, the connection box being spaced from the heating chamber, guide means enclosing ends of the heating element and guiding these from the heating chamber to the connection box; and a control box which houses electrical controls for the fan, and the heating elements; the electric motor, the connection box, the control box and all connections thereto being flameproof.

2. A device according to Claim 1, in which the connection box is mounted above the heating chamber, and the guide means comprises upright tubes extending between the heating chamber and the connection box.

3. A device according to Claim 1 or 2, in which the heating chamber contains a plurality of heating elements, and the control box includes means for supplying power via the connection box to selected ones of the heating elements.

4. A device according to any one of Claims 1 to 3, in which^': the fan is a centrifugal fan mounted for rotation about a first a is, the fan having a central inlet and a peripheral outlet: the ducting from the fan outlet includes a 90° bend section for directing air into the heating chamber, which has an a is parallel to that of the fan; the ducting from the heating chamber to the hose reel inlet includes a further 90° bend section; and, the axis of the hose reel is perpendicular to the axes of the fan and the heating chamber.

5. A device according to Claim 4, in which the cross- sectional area of the heating chamber is greater than that of both of the fan outlet and of the hose reel inlet.

6. A device according to Claim 1 and mounted on a wheeled trolley, in which the fan is mounted adjacent to a first end of the trolley; the hose reel is mounted adjacent to a second end of the trolley; the heating chamber and the connection box are mounted adjacent to a first side of the trolley; and the control box is mounted adjacent to a second side of the trolley and between the fan and the hose reel .

7. A device according to Claim 1, in which the control box includes interlock means for preventing operation of the heating element unless the fan is running, and for maintaining operation of the fan for a predetermined period after switching-off the heating element.