A rotary vessel (kiln or drum) is a shell with two or more rings. Each ring is supported on two rollers and the vessel shell is in constant rotation.
Roller supported rotary process equipment differs from ‘fixed’ equipment in many important ways. We can think of rotary equipment as being ‘dynamic; and fixed equipment as being ‘static’.
Static can be defined as ‘lacking in movement, action or change’.
In this group, we would include equipment which is slow moving, sliding or not in continuous operation.
A dictionary definition of dynamic is ‘a process characterised by constant change’.
Most dynamic machinery has enclosed parts and is rotating or reciprocating at high speed; the constant changes are usually consistent with each movement and can easily be accommodated in the design stage. The dynamic process of drums and kilns is of constantly changing magnitude due to many influences.
Dynamic
These constant changes are taking place continuously over time as this equipment normally operates 24 hours a day, seven days a week, which exaggerates the effects of the changes.
The changes originate from three sources:
1. Process: which may include, changes in product throughput; rotational speed; temperature of the product; feed size; and internal build-up or partial blockages inside the rotary kiln or drum.
2. External: for example, the impact of weather on equipment which is outside; the atmosphere and operating environment of the equipment; misalignment of support rollers;
feed and discharge seals; extreme temperatures of equipment; vibration from equipment
installed close-by; failures of the foundations, frames and piers; the design and location of the drum
or kiln can also be a source of potential problems.
3. Material of construction of the drum: due to its own weight, the shape of the tyre and the
shell not being round, the diameter measured on the horizontal plane will be larger than the
diameter measured on the vertical plane. This is referred to as ‘Ovality’.
This shape is constantly changing with the rotation of the drum, which will cause problems
relating to fatigue on the material of the shell.
This is considered during the equipment design process as it has a major influence on
the life expectancy and reliability of the drum.
All these changes increase the loads and stresses which always exist on rotary equipment.
In contrast Static
Static process equipment, by definition, has little or no movement of parts and there is no significant change in shape or molecular structure of the metals. Static equipment is, therefore, is much easier to control by design.
All these important issues relating to dynamic rotary equipment are discussed in depth during our training seminar programmes, along with exploration of the causes, effects, inspection procedures, symptoms, measurement and adjustment techniques, allowable failure limits and solutions for successful operation and maintenance.