Field of the Invention

The present invention relates to a heater for use in hazardous environments, particularly where there is a risk of a vapour phase or dust explosion.

Background

Working environments need to maintained within a temperature range that is comfortable and safe for personnel working in that environment. As it can be difficult to adequately heat larger areas using radiative heaters, space heaters or similar heaters, that produce a stream of heated gases, are often used to provide heating for larger enclosed areas such as warehouses or factories. Generally, heaters of this type use a resistance element that is heated by passing an electrical current through the element, and a fan which operates to force a flow of air over the heated element, so that the heated air is distributed throughout the workspace. In some working environments, such as for example chemical factories or refineries, hazardous or inflammable material may be present and the atmospheric air within the working environment may contain flammable vapour or dust. As this can significantly increase the risk of fire or explosion, the use of exposed heating elements such as those used on standard space heaters may not be appropriate.

It is an object of the present invention to provide a heater that goes at least some way towards overcoming the abovementioned problems, or which at least, provides the public, with a useful choice. Summary of the Invention

Accordingly, in a first aspect the invention may broadly be said to consist in a heater, generally comprising a heater, comprising: a casing comprising a tubular interior portion with an opening at each end, configured to allow gases to flow therethrough;

a heating means configured to heat gases within the casing;

a gases circulation means configured to circulate gases through the casing, gases entering the casing at one open end and leaving through the other, the gases circulation means being spaced between 50 and 500mm from the heating means; the casing further comprises integral leg assemblies that extend from the casing, the leg assemblies configured to support the casing above a surface. The heater is suitable for heating enclosed working areas in which there is a risk of vapour or airborne particle ignition. The tubular casing provides improved energy usage and heat distribution.

Preferably, the leg assemblies are configured to support the heater with the tubular interior portion aligned at any angle between substantially horizontal and substantially 45° away from horizontal to increase stability.

Preferably, each of the leg assemblies comprise a leg portion and a foot, the assemblies configured such that the position of the foot portion on the leg portion can be altered. This allows the heater to be located on an uneven surface.

Advantageously, the casing is formed from a material suitable for use with heating temperatures substantially up to 240°C. Further advantageously, the casing is substantially formed from a plastics material. Alternatively further advantageously the casing is substantially formed from metal. The casing is therefore relatively easy to manufacture and provides good safety margins if overheating occurs.

Preferably, the heater further comprises a handle configured to allow a user to pick up the heater. Advantageously, the heater further comprises guards, located at each of the open ends and configured to allow the free passage of gases through the tubular interior portion while preventing access by personnel and reduce the risk of injury. Optionally, the heater comprises at least one enclosure, located within the tubular interior portion and configured to house and isolate electrical heater components to increase the safety of the heater. Further optionally, the at least one enclosure comprises at least one threaded cable entry, each of the threaded cable entries fitted with a cable gland. Yet further optionally, the at least one enclosure comprises at least two enclosures affixed to one another.

Preferably, the at least one enclosure comprises a steel enclosure and an aluminium enclosure. Further preferably, the aluminium enclosure has openings at each end, and threaded side entries configured to protect sparking electrical components located within the enclosure. Yet further preferably, the steel enclosure has a single opening configured to protect sparking electrical components and heating element terminations located within the enclosure.

Preferably, the at least one enclosure further comprises a heatshield configured to protect the enclosures and any items within the enclosures from radiant heat.

Preferably, the heating means comprises at least one electrical heating element. Further preferably, the at least one electrical heating element is configured for optimum fit across the cross-section of the tubular interior portion. Yet further preferably, the surface watt density of the at least one electrical heating element is selected to ensure that hazardous area temperature limits are not exceeded. Optionally preferably, the at least one element comprises a plurality of electrical heating elements arranged in concentric rings and/or multiple rows. Preferably, the at least one electrical heating element comprises a laterally curved and finned element. Further preferably the fins of the heating elements are pitched. Yet further preferably, the pitch is between 1 mm and 100mm. Optionally preferably, the pitch is substantially 6mm. Preferably, the at least one electrical heating element comprises 80/20 Nickel-Chromium resistance wire embedded in insulating material and housed in a metallic sheath.

Preferably, the gases circulation means comprises a motor and impeller. Further preferably, the motor and impeller form an assembly, the assembly configured to locate substantially on the axis of the tubular interior portion.

Optionally, the motor has a rating of up to 1 kW. Conveniently the motor and impeller are configured to operate across an AC Voltage range between substantially 100V to 1000V. Further conveniently the motor and impeller are configured to operate across an AC Voltage range between substantially 1 10V and 690V.

Preferably, the motor is configured to have an output rotation in a range between 800rpm and 3000rpm. Further preferably, the motor is configured to have an output rotation in a range between 1300-1600rpm.

Preferably, the impeller is affixed to the motor shaft via at least two grub screws combined with a keyway.

Optionally, the blades of the impeller are sized and configured such that they have an outside diameter that spaces the blade tips between 2mm and 20mm away from the inner surface of the tubular interior portion. Conveniently, the impeller blades have a pitch substantially between 30° and 45° to increase efficient gas flow. Further conveniently the impeller blades have a pitch of substantially 35°.

Preferably, the blades are formed from plastic with anti-static and self-extinguishing properties to increase safety towards fires and explosion.

Preferably, the impeller is oriented so that in use gases are directed across the motor before being heated by the heating means again minimising the risk of ignition. Preferably, the heater comprises an electrical supply cable and plug socket configured for connecting the heater to an external power supply. Further preferably, the electrical supply cable comprises multiple cores configured to allow single and polyphase operation. Yet further preferably, the electrical supply cable and plug socket further comprise a protective earthing system.

Conveniently, the heater comprises electric circuitry configured to prevent temperatures exceeding the rated limits. Further conveniently, the electric circuitry comprises a temperature sensor positioned so as to read the highest temperature of the heating means, the electric circuitry configured to decrease the power to the heating element if the temperature exceeds a pre-set maximum. Yet further conveniently, the electric circuitry further comprises a thermostat configured and positioned to monitor the ambient temperature, the circuitry configured to de-energise the heater if the ambient temperature exceeds a pre-set limit.

Brief Description of the Drawings

The invention is now described with reference to the accompanying drawings which show, by way of example only, one embodiment of a heater. In the drawings:

Figure 1 shows a perspective view from one end and to the side of an embodiment of the heater of the present invention, the heater comprising a cylindrical casing with integral supporting legs, the casing containing an electric motor/impeller assembly, heating elements, electrical enclosures, and circuitry interconnecting the components;

Figures 2a and 2b are respectively a perspective view and a side view of a heater with the outer casing removed;

,ures 3a and 3b are the views of Figures 2a and 2b with the heating elements removed. Description of the Invention

An embodiment of the heater of the present invention, and variations thereof, will now be described with reference to the figures. Although primarily intended for use in industrial areas as a space heater to ensure for example that materials are maintained at a temperature suitable for their use (e.g. do not freeze), the heater can also be utilised as a comfort heater. Fittings utilised, such as bolts or washers are preferably formed of a stainless steel material and also to have a yield strength greater than 300MPa. An embodiment of the heater of the present invention is generally shown as heater 1 in figure 1. The heater 1 has an outer casing 2 with the overall or general form of a cylinder, open at each end so as to provide a path for gases through the outer casing, and which surrounds and encloses a number of the other components which form the heater 1. The outer casing 2 is in two parts an upper portion 2a and a lower portion 2b. The lower portion 2b is formed with four integral leg assemblies 3 that extend outwards from the cylindrical portion of the outer casing 2 and which are configured so that the heater 1 can be positioned on a flat surface such as a floor, with the cylindrical portion raised above the floor and aligned such that the central axis of the cylindrical portion is generally parallel to the floor. The leg assemblies 3 are arched which provides additional strength and also allows an isolator to be included in the leg assembly. In this embodiment, the outer casing 2 is formed by plastic moulding or similar, with the leg assemblies 3 formed integrally with the cylindrical portion. However, in variations, the outer casing 2 could be formed from a suitable metal, and/or by any suitable means. In all the embodiments and variations, the material from which the outer casing 2 is formed is suitable for use with heating temperatures up to 240°C. As examples of materials from which the casing can be formed are polyamides such as PA66 or a polyphenylene sulphide (PPS). A plastics material can include carbon fibres, glass fibres to enhance the physical properties. In addition, a coating can be applied to the plastics material to resist the build-up of static charge on the heater. The casing material can in any event be chosen to prevent any build-up of static charge, for example being formed of an electrically conductive material having a resistivity of < 1.10 ⁶ Ohm. In this embodiment, the leg assemblies 3 comprise a leg portion 3', and tilting/adjustable feet 5 on the outer ends of the leg portion 3', the feet 5 forming part of the overall leg assembly 3. The position of each foot 5 is adjustable relative to the remainder of the associated leg portion 3' to allow alteration of the overall height of the heater 1, and also to allow the outer casing 2 to be angled away from the horizontal so as to allow angled operation of the heater, at any angle between substantially horizontal as outlined above, to an angle of 45° away from the horizontal. In an alternative embodiment, not illustrated, casters can be utilised in place of the feet to allow the heater to be more easily moved between locations. In either embodiment the feet or casters provide a gap of at least 10mm through air and 12mm across surfaces.

In an alternative embodiment, not illustrated, the heater can be wall mounted. In this embodiment a wall bracket, known in the art, can be secured to one or both of the ends of the outer casing 2 as required. Additionally, flexible ducting can be attached to a bracket. The ducting can be used to vent air from another area as and when required and when fitted to the inlet. The ducting can provide fresh air, free from potential flammable materials or other undesirable materials, or which has a higher temperature than the one around the heater. Alternatively, ducting can be used to direct warm air directly onto an employee working in an area or onto an area which requiring drying, such as a painted area. Said ducting is preferably operable within the temperature range of from -40°C to +80°C and formed of an anti-static material. The surface resistance of the ducting is selected to be below 1.10 ⁹ Ohm.

A handle 6 is located at the top of the outer casing 2 (i.e. on the opposite side from the legs 3). The handle 6 can be integrally formed with the outer casing 2, or attached/connected post-forming. The handle 6 can be formed from any suitable material, such as for example metal or a plastics material. Additionally, the heater can include a plurality of handles, with at least one handle being incorporated into the lower portion of the casing to aid in the heater being carried for longer distances.

The open ends of the outer casing 2 are covered by fan guards or grilles 4. In the embodiment shown in figure 1, these are formed from profiled sheet steel. The steel used to form the fan guards and grilles, and other components where applicable, is preferably suitable for use in marine environments, to resist corrosion from sea water. Alternatively these can be formed from wound wire, or plastic. The grilles 4 are bolted or screwed to the outer casing 2. The grilles 4 allow the free flow of gases through the outer casing, but prevent larger debris from entering the interior of the outer casing 2, and prevent personnel from inadvertently accessing the interior of the outer casing and injuring themselves on rotating and/or heated parts contained within the outer casing's interior. Additionally, guard elements (not illustrated) can be included to prevent small objects and debris, for example of a size of around 8-50mm, from entering the outer casing.

A combination of adhesive and steel name plates can be affixed to the exterior surface of the outer casing 2 to warn the operator(s) of dangers including but not limited to hot surfaces, sparking parts, weight, avoidance of obstruction, certification etc.

The components that form the remainder of the heater 1 comprise four main groups: heating elements, a gases circulation means, electrical enclosures, and connecting electronic circuitry configured to connect with and between the interior components. The connecting electronic circuitry also enables connection to a power source so that power is provided to the heater 1. In this embodiment, this is by way of an electrical supply cable and plug socket suitable for connecting the heater to an external power supply such as a mains power supply. In the preferred form, the cable comprises multiple cores to allow single and polyphase operation. A protective earthing system is also provided. The internal cabling is also preferably selected to be operable up to 125°C, and for example, has a multi-stranded tin-copper conductor, with an extruded and electron-beam cross- linked polyolefin copolymer sheath. In general terms the cabling is halogen free, weatherproof, oil-resistant and resistant to thermal pressure. The cable terminals ensure that gaps between live and conducting parts are sufficient to allow the operation of the heater in a hazardous area.

In order to improve the safety, a heater includes an isolator which can be used in energising or de-energising the heater. The isolator can be fitted either locally or remotely to the heater.

The component groups are described in detail below. Enclosures

In this embodiment, the heater 1 has two internal enclosures: an extruded aluminium enclosure, and a fabricated steel enclosure. The enclosures house and/or substantially isolate certain of the heater components and are designed to run preferably below 60 ^° C. The enclosures also act to prevent ignition of the external atmosphere.

Each of the enclosures is located within the outer casing 2, connected to the inner surface of the cylindrical portion of the outer casing 2. The extruded aluminium enclosure has openings at either end, and threaded side entries to protect the sparking electrical components. Typically, the aluminium enclosure has a wall thickness of 3mm so that in the event of a spark igniting an internal volume of gas, the explosion is retained within the heater and does not transfer to the outside of the heater, potentially igniting a larger volume of gas. The aluminium enclosure can be coated, for example by anodising to produce a coating which is >25μιη in thickness.

The fabricated steel enclosure has a single opening to protect the non-sparking electrical equipment and heating element terminations. The two electrical enclosures are affixed to one another, and cables that form part of the circuitry pass through threaded cable entries on the enclosures. The cable entries can be fitted with a suitable or certified component to prevent sparking. Such a component can be a cable gland, or a line bushing designed for hazardous environments. In this embodiment, a heatshield is also be incorporated, the heatshield forming part of the housing assemblies. The heatshield protects the main parts of the housings (and their contents) from damage from heat from the heating elements. For example, the aluminium enclosure is protected from radiant heat by the heatshield and the electronic circuitry is protected from overheating. The heatshield is also advantageously profiled to drive air- flow across the heating elements. In some embodiments, a secondary heatshield can be used around the external perimeter of the heating elements to further reduce the external surface temperature of the casing. Heating Elements

In order to provide heating, at least one and preferably multiple electrical heating elements 20 are included within the heater 1. In this embodiment, the electrical elements are laterally curved and finned elements which are configured for optimum fit within the circular cross-section of the tubular interior portion of the outer casing 2. To ensure that hazardous area temperature limits (e.g. 200°C and 135°C) are not exceeded, the surface watt density of the heating elements 20 is selected appropriately and such that the temperature of the element does not exceed 400 ^° C. The elements 20 are most preferably arranged in two or three concentric rings 21, three rows deep. However, they can be arranged in concentric rings of one or more elements in multiple rows from two to five deep.

To reduce the risk of initiating an explosion, the heating elements are constructed from 80/20 Nickel-Chromium resistance wire, which is embedded in insulating material and housed in a metallic sheath, with the fins 22 hard brazed into position. The insulating material can be selected form magnesium oxide or boron nitride. Threaded ferrules are also hard brazed to each end of each element 20 to allow firm securing to the electrical enclosure. Linkage between elements 20 can be by means of copper links or a cable. Copper links, in the form of a strip of copper, allow for greater current flow resulting in a cooler component during operation.

Sealing of the heating elements 20 can be through the use of a sealant such as a vulcanised silicone such as RTV silicone, an epoxy material. The seals are present to ensure that the insulation resistance of the heating elements remains high enough to operate the heater 1. A value in excess of 100 MOhms is desirable. Further protection for the seal is provided by means of an insulating bead which improves the safety of the heating elements. The bead provides that the distance which the electricity would have to run is at least 8mm to create an arc from the live terminal to the element sheath. The bead material is selected from a ceramic material, preferably such as Steatite C221 or a plastics material such as an acetal co-polymer or other material with a tracking index of 600.

Additionally, the heating elements are sealed against water ingress. The fins 22 of the heating elements 20 are pitched to suit the air flow supplied from the motor/impeller assembly (described in detail below). The pitches can vary from 1 mm to 100mm, although 6mm is preferred. Gases Circulation Means

The gases circulation means acts to draw gases (usually the ambient atmosphere) into the heater, across the heating elements, before discharging the heated gases to the surroundings. As exemplified in the preferred embodiments, the gas circulation means is a motor/impeller assembly which is positioned so as to sit inside the innermost concentric ring of the elements 20 described above. It is preferred that the motor 30 is rated up to 1 kW (e.g. the motor used is rated at 0.09kW, or 0.55kW, etc.). As it is envisaged that the heater 1 may be required to operate in locations which have different electrical supply parameters, the motor 30 and impeller 31 (and the electronic circuitry as described in detail below), are configured to operate across an AC Voltage range between substantially 100V to 1000V. This ensures that the heater 1 delivers a heat duty of substantially up to 100kW. Within the AC Voltage range outlined above a preferred operating range is between 1 10V and 690V, which allows the heater to provide a heat duty of up to 6kW, suitable for most uses, although a heat duty of up to 50kW is achievable within this voltage range. The motor 30 is preferably configured to have an output rotation in a range between 800rpm and 3000rpm, although it is preferred that the actual range used is substantially between 1300-1600rpm.

The impeller 31 is affixed to the motor shaft via at least two and preferably three grub screws combined with a keyway. The blades 32 of the impeller are sized and configured such that they have an outside diameter that spaces the blade tips between 2mm and 20mm away from the inner surface of the outer casing 2. The impeller blades 32 have a pitch substantially between 30° and 45°, and are most preferably pitched at 35°. The blades 32 are manufactured from plastic with anti-static and self-extinguishing properties. The Watt density of a heating element 20 is selected such that in a given air flow, the heating element 20 remains within the acceptable operating temperature range. Typically, an air-flow of at least 1 ms ¹ is maintained across the heating elements to ensure the elements remain within their operating parameters. As an example an air-flow of 3.5 ms ¹ is maintained for a heating element of 4W/cnr ² . The assembly is oriented so the impeller 31 is spaced substantially between 50mm and 500mm away from the heating elements. The impeller is oriented with the shaft aimed away from the elements, so that as the motor operates in use, cool air is directed across the motor before this air is heated by the elements. One or more profiled flow-directors can be included between the impeller 31 and the heating elements 20 to laminarise the air-flow within the heater. This provides a more even surface temperature on the heating elements 20 allowing the heating elements to run more efficiently. Electronic Circuitry

The electronic circuitry has a basic function of providing a conduit between the power source and the motor/impeller assembly and the heating elements. Protection for electronic circuitry and other water or dust-sensitive components is provided in the form of gaskets. For example, gaskets to at least IP54 rating, but also up to IP68 or IP69k can be used. The circuitry also provides any other internal connections between the components as required. The circuitry also comprises a protective circuit that is configured to prevent temperatures exceeding the rated limits. The protective circuit comprises a temperature sensor, directly fixed to the heating element positioned furthest from the impeller. This ensures that the highest temperatures are read. If the temperature exceeds a pre-set maximum, then the circuitry acts to decrease the power to the heating element. A separate thermoregulator, which can be digital is fixed to the heater 1 at a suitable position to monitor the ambient temperature. The thermoregulator is adapted to allow use down to a temperature of -40°C and also such that as the temperature rises, condensation does not affect the electrical circuitry within. The circuitry will act to de- energise the heater when the ambient temperature as read by the thermostat exceeds allowable limits. Where deemed desirable the temperature of other heater elements can also be controlled. In general, the electronic circuitry is positioned within the core of the heater in what would, in conventional heaters be dead space. This allows firstly for a more compact heater to be designed. Moreover the air-flow is increased across the heating elements allowing for greater duties to be applied whilst maintaining the maximum allowable surface temperature. Alternatively a further additional sub-circuit can be used to control the duty of the heater 1, so as to maintain a pre-set room temperature. A separate isolator unit may also form part of the circuitry, preferably fixed to the outer casing 2, and configured to allow safe de-energising of the heater 1. For example, where a fault or careless operation occurs (for example an air inlet being covered) the entire heater can be de-energised. Earthing positions are also included, and are connected in such a way to ensure the heater remains electrically safe. Should a fault arise, in which the current grounds itself, the heater is configured to de-energise to allow repair.

A heater such as the heater 1 described above is especially suited for applications where portability is required. A heater formed in this manner can be formed to weigh less than 30kg. However, larger units weighing more than this are not excluded from the scope of the invention. A heater such as the heater 1 described above is suitable for use in environments where the temperature ranges from between around -60°C to +80°C, and most preferably suitable for environments where the temperature ranges between -40°C and 40°C.