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Health and safety: Working in cyclone-preheaters

World Cement,

Occupational health and safety has top priority within the cement industry. Hot areas and cyclone-preheaters in particular are among the most dangerous places in a cement plant. Dealing with hot meal can especially be a potential source of severe injury. Special attention therefore has to be directed towards working safely in these areas.

Coatings and blockages can often occur in the cyclone preheaters of rotary kiln plants for burning cement clinker. They result from the combined action of recirculating materials (alkalis, chlorides, sulfates), intermediate compounds from the decomposition of raw meal that have a tendency to stick together, and an extremely high dust loading in the atmosphere in the preheater. Blockages in the cyclone area or in meal ducts can be caused by the gradual closure of narrow cross-sections (e.g. top outlet ducts in cyclones) or through a sudden fall of coating which, for example, closes the cyclone outlet or meal duct. The frequency of cyclone blockages strongly depends on the specific situation onsite and can vary between the extremes of several times daily and a few times per year depending on the raw materials and the plant technology. Many plants therefore have widely differing experience in dealing with the dangers involved when removing these disruptions to plant operation. There is no uniform technical equipment for preventing the disruptions arising and no generally recognized procedure for removing the blockages. Figure 1, for example, shows the removal of coating with a pneumatic hammer.

Figure 1. Removing coating with a pneumatic hammer.

Serious accidents due to hot meal

Coating and blockages in a cyclone preheater are often the causes of serious accidents due to the hot meal that emerges suddenly at temperatures of up to 800 °C from the rodding openings during cleaning work and when removing the blockages. In addition, meal surges that are associated with considerable danger can occur. Due to cyclone blockages and kiln rings, and during starting and stopping large amounts of hot free-flowing material with great momentum can be released. It can flow from the kiln outlet into the clinker cooler and basement areas.

When meal has escaped it is usually difficult to detect (Figure 2). This is extremely dangerous since stepping into the meal can lead to serious injury. The connected accidents are mainly attributable to inappropriate actions by the personnel in charge of removing the coatings and cyclone blockages rather than to a lack of safety equipment. As well as the plant accidents in the maintenance sector, accidents in the clinker production sector are also particularly numerous and severe.

Figure 2. Basement area after an escape of hot meal.

There is therefore a pressing need for the further improvement of occupational safety, especially in these areas. Typical injuries that can occur are burns due to the hot meal, dust-related eye injuries and mechanical injuries resulting from the handling of rodding equipment. In many cases these accidents can be avoided by simple measures, for instance by ensuring that no-one must ever stand underneath an open cleaning flap. It can therefore be assumed that a significant number of accidents can be avoided through organisational measures and proper instruction. In order to provide a safe working environment inside the preheater, however, various aspects have to be taken into account. These include the design of openings, staging and platforms, the handling of rodding tools or air blasters, procedures for the removal of coatings and blockages, and the selection and use of appropriate personal protective equipment. Figure 3, for example, shows a suit intended for use in work areas where there is a high probability that hot meal will escape.

Figure 3. Suit for use when there is a high risk of meal escape.

Code of practice for hot meal

Different codes of practice exist that describe procedures and measures for the safe removal of coating and blockages in cyclone  preheaters as well as possible ways to recognise blockages. Furthermore, strategies for dealing with meal surges and recommendations for the use of personal protective equipment have been developed. The wealth of information available shows the complexity of the influencing factors and the number of causes for possible accidents, but it also illustrates that there are numerous successful solutions for creating a safe workplace.

The persistent application of all measures, together with the constant motivation of the entire personnel with regard to safety, can enable the accident-free operation of a cyclone-preheater. Not least because nearly all accidents with hot meal lead to severe injury, it is necessary to reduce the number of such incidents to zero. Even experienced staff who are aware of the possible dangers can become involved in accidents due to their working routine, as many years of practice without incidents can create a feeling of “invulnerability”. Maintaining awareness and ensuring safe working procedures is therefore a constant challenge for us all.

Written by the European Cement Research Academy.

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