Problem solving

Clean and safe

Explosion-protection extraction unit for waste incinerator

There are good reasons why a waste incinerator plant, just like any other industrial installation, has to be kept clean. Dirt can reduce operating efficiency and damage machinery and it is also a health and safety hazard for plant employees. Explosion protection directives also specify that the build-up of dust deposits should be prevented.

There are therefore plenty of good reasons why a waste incinerator building has to be cleaned thoroughly at regular intervals. At the MVA - Waste Incinerator Plant in Nürnberg, the plant operator uses three Ruwac industrial vacuums for this purpose. These vacuums are noticeably much larger than standard industrial vacuums for the simple reason that they have to deal with much, much greater quantities of dust.

The three vacuums operate in different areas of the plant. The entire waste incinerator plant is served by a pipeline with numerous connections for vacuum hoses. When several connections are in use at the same time, a second drive switches on automatically to deal with the extra load. Each vacuum has two 7.5 kW vacuum units.

The drives create the vacuum required and separate the dust into two bag filters mounted in-line one after the other. The separation rating achieved with this layout is Dust Class H. In practice this classification means that of the 20,000 very small particles vacuumed up by the equipment only one particle is allowed to pass through the filter; the remaining 19,999 must be trapped by the filter. Filters are dedusted automatically by a vibrator driven by an electric motor and controlled by a differential pressure sensor. The dust filtered out is collected in a 200-litre bin which can be picked up and emptied using a fork-lift truck. The entire unit - vacuum, filter and collection bin - is mounted on a solid steel frame on a trolley.

The vacuums installed meet the requirements of explosion protection directives. Explosion protection is an area where Ruwac has a lot of experience. Ruwac even produces vacuums for space station launch pads. Obviously the explosion hazard is at a somewhat lower level in a waste incinerator plant. The vacuums are designed with numerous features to prevent the creation of ignition sources such as sparks from mechanical and electrical components. One such feature is the "Q-tube" fitted to the filter. If, despite all the precautions, an explosion does occur inside the filter, it will be controlled by the Q-tube. The Q-tube prevents damage to the filter holder, contains the explosion inside the filter unit and prevents any chain reaction.

This particular feature means that under certain conditions it is possible to do without an expensive wet pre-separator. Ruwac has already used this solution in a large number of Ex-protection installations. In other cases, such as in the extraction of flammable light metal dusts, vacuums can be Ex-protected with a spark trap, a mechanical device for trapping and rendering sparks harmless. Despite the size of this application and the high-level of customisation required, Ruwac was able to build this installation using standard components from its modular range. The installation therefore consists of tried-and-tested components with a proven track record. This guarantees trouble-free operation and a high level of safety. The carefully-matched filters hold back the finest dust and are cost-effective and efficient. A further guarantee for full compliance with health and safety regulations. %error