DK1674732T3

DK1674732T3 - Explosion protection for a non-electrical appliance.

Info

Publication number: DK1674732T3
Application number: DK05023602.5T
Authority: DK
Inventors: Jochen Skatulla
Original assignee: Ksb Ag
Priority date: 2004-12-21
Filing date: 2005-10-28
Publication date: 2015-10-26
Also published as: EP1674732A2; ES2550427T3; SI1674732T1; EP1674732B1; HUE026420T2; PL1674732T3; CY1116857T1; DE102004061366A1; PT1674732E; EP1674732A3

Description

Explosion protection for non-electric device

The subject matter of the invention is an explosion protection for a non-electric device or unit that is hot in the operating state, in particular for a centrifugal pump for hot delivery media. GB-A-2 075 643 discloses an enclosed machine unit in a noise- and/or heat-insulated machine casing. The enclosed machine unit comprises a diesel motor and a compressor which are arranged in a sound-absorbing casing. The inner wall of the casing is covered with an insulating material layer. For cooling of the unit, the inner wall is provided with cooling surfaces which are connected to a coolant supply.

The explosion protection, in short: ex-protection, for devices or units was based in the past substantially on the ex-protection-compliant selection of electric components and non-sparking material combinations of devices. As a result of a new European Directive (ED 94/9 EC), non-electric devices are now also regarded as an ignition source in terms of their risk potential and correspondingly measures are required for safe use in the ex-region. It must thus, among other things, be ensured that the surface temperature of the device or unit lies below the maximum permissible ignition temperature of the respective ex-region. In this case, the ignition temperatures are normally divided into temperature classes.

As a result of the regulations which now apply, measures for ex-protection must also be taken in some cases for centrifugal pumps with high medium temperatures. This applies, for example, to pumps, the medium temperature of which exceeds 200°C, but which should be operated in temperature class T3 with a maximum permissible temperature of 200°C. At first glance, various measures lend themselves to this but must be rejected under certain circumstances on various grounds: an isolation of the pump is not permissible since a risk of ignition could arise as a result of leakage and concentration; an effective cooling of the pump by a foreign medium, e.g. water, requires high additional outlay which can often not be provided; a "vapour-inhibiting encapsulation" according to European Standard EN13463-3 can frequently not be used in certain ex-zones and as a result of the complex geometry of the article to be sealed off.

The object on which the invention is based is thus to provide an explosion protection for a non-electric device or unit that is hot in the operating state, which ensures a high level of safety with little outlay.

The set object is achieved according to the invention by an enclosure that only encloses partial regions, in particular a hot zone, of the surface of the device or unit at a distance, wherein a non-explosive, heat-dissipating gas under positive pressure is fed into the enclosure and is removed from the enclosure by way of openings, wherein gaps remain between the surface of the device or unit and the enclosure.

Here, the invention relies on a technology which is already known in terms of its principle, but was previously used for other purposes and with a different configuration: the encapsulation of machine units which was used in particular to reduce noise emission. For this purpose, the capsule was also provided with a sound-insulating layer usually on its inner wall.

The earthed enclosure, preferably composed of metal, of the invention shields the hot surface of the device or unit from the surroundings, wherein various effects are generated by the gas delivered into the enclosure: an ex-free zone is generated around the device or unit. Since a positive pressure is generated in the enclosure by the gas, no gas, i.e. also no ex-atmosphere, can penetrate from the outside. On the contrary, a continuous flow of the delivered gas to the outside is maintained, as a result of which a continuous flow for removing heat is also produced which in turn keeps the surface temperature of the enclosure below the required threshold value.

The actuation of the inner space of the enclosure is preferably carried out by an inert gas. For example, nitrogen can be used. However, system air or non-ex ambient air can also be conducted by a suitable delivery system into the enclosure.

The removal of the introduced gas out of the enclosure can be carried out in various manners and on various paths. There are preferably non-contacting gaps between the surface of the device and the enclosure. This has the advantage that temperature-resistant seals between the hot surface and the enclosure can also be omitted such as a separate device for the removal of the gas introduced.

In order to achieve increased safety, it is recommended to provide a device for monitoring the surface temperature of the device and the enclosure. As a result of this, not only the adherence to a prescribed maximum temperature is ensured. Moreover, faults which can become noticeable as a result of a temperature increased can be detected at an early stage, which in turn enables the transmission of a fault signal and/or the early switching off of the relevant device or unit.

Moreover, a device for monitoring the pressure inside the enclosure is recommended. This results in a warning device which responds very early and which, among other things, already responds to an impairment in the delivery of the gas which removes the heat. An impermissibly high pressure build-up in the enclosure is prevented as a result of this.

Finally, a device for monitoring any leakages of the device or unit can also be beneficial since this also allows an early response to potential faults.

The invention will be explained on the basis of an exemplary embodiment. The drawing shows a centrifugal pump 2 driven by a separately set-up electromotor 1, which centrifugal pump 2 serves to deliver a medium which has a temperature of greater than 200°C.

As a result of the delivery medium which enters via a suction piece 3 and escapes via a pressure piece 4, casing 5 of centrifugal pump 2 is heated to a maximum value after a certain period of delivery, which maximum value would also be above 200°C in the absence of cooling. In order to be usable in ex-temperature class T3, however, the surface temperature exposed to atmosphere 6 of the unit composed of electromotor 1 and centrifugal pump 2 must not exceed the threshold of 200°C at any point. In order to satisfy this delivery, the surface of casing 5 must be shielded from atmosphere 6. This can nevertheless not occur in a manner as in the case of the pipes - not represented here - connected to suction piece 3 and pressure piece 4 of centrifugal pump 2, namely by an isolation attached to the surface. Were a leakage, which cannot be ruled out with certainty, namely to occur at pump casing 5, there would be a risk of ignition.

The shielding off of casing 5 from atmosphere 6 is carried out by an enclosure 7 which encloses the hot zone and an adjoining cooler region of centrifugal pump 2, without, however, having contact with the various surface regions. In actual fact, there remain gaps 8 between the surface of centrifugal pump 2 and enclosure 7.

Enclosure 7 forms an ex-protected space 9 which is supplied via a pipe 10 with a nonexplosive gas from a source, not represented. It is ensured here that the pressure in space 9 is always above the pressure of surrounding atmosphere 6. Therefore, no air can flow out of the surroundings into enclosure 7. Above all, however, a constant leakage of the gas flowing out via gaps 8 out of space 9 into the surroundings is produced. As a result of the also continuous subsequent flow of gas into space 9, a continuous gas flow is thus generated which removes part of the heat present in space 9 into surroundings 6. The initial temperature and quantity of the gas pushed into space 9 are selected so that the surface temperature of enclosure 7 always remains below 200°C. This is monitored with the aid of a thermometer 11.

The surface temperature of pump casing 5 is monitored by a thermometer 12. This monitoring allows an early response to any faults since an increase in the temperature of the medium is detected earlier at this point than at enclosure 7. Moreover, the point in time at which enclosure 7 may be opened can be determined on the basis of the temperature measured here: this is the case if the pump temperature is 195°C or lower.

Finally, a pressure monitor 13 is also provided with which the pressure in space 9 is monitored. A fault in the system which supplies the gas for space 9, excessive leakage out of space 9 or an impermissible pressure increase are displayed early so that remedial measures can be initiated in a timely manner.

Claims

1. Explosion protection for a non-electric appliance or unit which is hot in a state of operation, in particular for a centrifugal pump (2) for hot media, characterized by a housing (7) which encloses only a sub-region at a distance, in particular a hot zone , of the surface of the appliance or assembly (2), in which a non-explosive gas which can dissipate heat is passed into the housing (7) with overpressure and discharged out of the housing (7) via openings (8) where gaps between the surface of the apparatus or assembly (2) and the housing (7).

Explosion protection according to claim 1, characterized in that an inert gas is fed into the housing (7).

Explosion protection according to claim 1 or 2, characterized in that the gaps (8) are provided between the surface of the apparatus or the assembly (2) and the housing (7) for the discharge of the introduced gas.

Explosion protection according to claim 1 or 2, characterized in that the gaps (8), which exist between the surface of the apparatus or the assembly (2) and the housing (7), are closed with a temperature-resistant insulating sealant for the discharge of the gas is provided as a separate device.

Explosion protection according to one of the preceding claims, characterized by a device (11, 12) for monitoring the surface temperature of the apparatus or assembly (2) and the housing (7).

Explosion protection according to one of the preceding claims, characterized by a device (13) for monitoring the pressure in the housing (7).

Explosion protection according to one of the preceding claims, characterized by a device for monitoring any leaks of the apparatus or unit (2).

Explosion protection according to one of the preceding claims, characterized in that the housing (7) comprises metal and is grounded.