Rotary kilns are used for many different processes involving thermal conversion of free flowing, granular bulk solids. Once inside the rotary kiln, bulk solids can be calcined (lime), sintered (cement), roasted (phosphate), expanded (expanded clay), regenerated (lime slurry), or their crystalline structure can be changed (aluminium oxide). The bulk solid is brought into contact with the hot gas using a counter flow. The thermal energy is supplied by hot gas, that is fed into the kiln at its end. The hot gases can either be produced using a primary energy source (gas, oil or coal), or by using waste fuel, which is more common nowadays due to reasons of energy recovery. The dimensioning of the rotary kiln is determined by the quantification of the procedural possibilities in relation with properties of the bulk solid.
The tyres support the weight of the rotary kiln on the carrying rollers and the stand. Depending on the length of the kiln they are supported at least twice. The tyres can be either welded to the kiln or teethed to it. Another option are loose tyres in the direction of rotation. This can be used to counterbalance the differences of the diameters of the kiln and the tyres due to thermal changes by offering some slip. The carrying rollers can be produced either with a rolling or an anti-friction bearing. Pressure bearings or a hydraulic longitudinal kiln guidance reduce the displacement due to inclination of the kiln and thermal-induced differences in length.
Rotary kilns are driven via chains or girth gear/pinion drives, or via friction drives. To prevent unwanted air entering from the kiln, seals with sliding sealing faces are attached at the kiln inlet and outlet. The sliding sealing faces absorb the longitudinal movement of the kiln. We mostly use pneumatic seals or pull-rope seals. All our rotary kilns are walled. Which fire-proof materials we use is determined by the thermal stress it will be put under, the intensity of wear due to bulk solids and the chemical aggressiveness of the occurring gases. If the material charge is provided as bulk solids dissolved in water, the front part of the kiln will take the function of a dryer. To intensify the thermal process, either cross-shaped inserts or chain screens can be used.
Specific advantages of rotary kilns are:
- equipment that is applicable in many ways to carry out thermal processes alone or in combination with other operations;
- Application for large flowing rates and long required wait times
A Rotary Kiln built by ZADCON
Heat transfer takes place in tubes, that are located in the drum* of the tube cooler. These tubes can either have a smooth or ribbed surface. Ribbed tubes increase the area where heat is being transferred, which significantly increases the heat transfer. The smaller the grains of the bulk solids are, the more efficient the cooler gets. Bulk solids can thus be cooled down from around 300°C (572°F) to 60°C (140°F). The coolant can either be air or water.
The bulk solids are continuously fed into the cooler with either co- or counter-current flow, using a feed chute. The bulk solids are dispensed through a discharge housing*. Both the feed chute and the discharge housing are sealed actively. When the bulk solid is passed through the rotating tube cooler, it gives off its heat to the coolant. The coolant is being delivered and discharged with a centre tube. Distributing chambers ensure the equal distribution of the coolant to the tubes. The tube cooler is sealed air-tight by means of a discharge housing with a rotary valve.
Tube coolers are horizontally lying, welded cylinder on rotating bearings. The cylinder is supported horizontally by two tyres on carrying rollers with double bearings (rolling or anti-friction). We usually use electro motors to power our drives. For drives we use girth gear drives, pinion drives, friction wheels drives or v-belt drives. The rpm of the cooler can be controlled. The coolant is delivered and discharged by means of a sealed centre tube. This centre tube is both flexible and elastically mounted.
Specific advantages of tube coolers are:
- a large heat transfer area in a very small space
- high cooling capacity
- exchangeable tubes
- can be adjusted very well
The direct cooling drum belongs to the family of direct cooling drums as the coolant and the dry bulk solids have immediate contact. The coolant used is air. The air cooler can use co-current or counter-current flow. The usage of co-current flow is more efficient. This requires a more steeply inclined positioning of the drum. The bulk emits its heat directly to the stream of cooled air and leaves the cooling the drum with the desired temperature.
The cooling drum is a horizontally positioned, welded drum cylinder which is stored spinning. The cylinder of the cooling drum is supported and stored horizontally by two ball races in roller stations with dual bearings (roller or plain bearing). The propulsion of the cooling drum is achieved with an electric motor and can be implemented with the help of a chain wheel, a gear drive, a V-belt drive, or a friction wheel drive. The rotational speed is adjustable. The extraction of the bulk out of the drum is accomplished by tilting of the drum and by the usage of internal fixtures in the drum cylinder. The internal fixtures intensify and raise the heat exchange considerably. The internal fixtures of the cooling drum can be in the form of lifting blades, cross or square fixtures. The direct rotary tubular cooler is walled in partially or completely depending on the temperature of the entering dry bulk.
The cooling with air in a cooling drum makes safe and high-quality storage possible even without too harsh* drying. Thus the product is of higher quality. In addition the exiting of warmth during the cooling process causes further drying of the bulk.
Direct Cooling Drum
The sectional cooler consists of a welded drum cylinder in which four to eight continuous chambers are installed in a specific form. The cylinder of the sectional cooler is supported and stored horizontally and without incline by two ball races in roller stations with dual bearings (roller or plain bearing). The propulsion of the sectional cooler is achieved an electric motor and can be implemented with the help of a chain wheel, a gear drive, a V-belt drive, or a friction wheel drive. The rotational speed of the sectional cooler is adjustable. Provisions are made between the rotary and stationary water supply lines for a special design of a stuffing box seal*. The dry bulk that is to be cooled arrives in the sectional cooler by way of an inlet chute. The inlet chute can be equipped with water cooling if the process engineering* calls for it. The dry bulk that is to be cooled is moved through the sectional chambers lengthwise and toward the exit of the cooling drum emitting itss heat into the cooling surfaces. The cooling medium used in the sectional cooler is preferably water. It enters the sectional cooler via a stuff box* at the output end* and flows up to the input end of the drum steadily absorbing heat. The cooling fluid flows through the hollow spaces* between the sectional chambers. These hollow spaces* are connected with the central space in such a way that the spinning of the sectional cooler causes a constant exchange of the cooling fluid. From there the water returns through a centre pipe back to the output end of the sectional cooler. Here it exits the drum presurelessly. The sectional cooler can either use co-current or counter-current flow. The sectional cooler is used with dry bulk that needs gentle care.
Specific advantages of the sectional cooler are:
- intensive and yet gentle treatment of the dry bulk
- effective cooling even with high amounts of throughput
- optimal energy usage
- very well adjustable
Examples thereof are pyrolysis of used tires, scrap wood, coconut shells, used car battery housings, brown coal, bio mass, chicken droppings, sunflower shells, sewage sludge, aluminium shreds and much more.
The principle of the classification is based on the varying sinking speeds in various trajectories of air currents with particle size dependant resisting forces of the particles surrounded by the air flow. A ventilator wheel creates a field of currents in the classification chamber by overlapping a drain current and a swirl flow. The dry bulk that is to be divided is spun against the air flow and across a disperser. The fine particles are carried up with the air current and the larger particles are carried out the bottom under the influence of gravitational and centrifugal forces. The centrifugal system that is arranged above the disperser makes the air current into a swirl flow. The fine bulk is transported into the fine bulk separation chamber by the fan wheel and slides down the exterior wall into the fine bulk output. The shaft-mounted fan wheel with disperser and centrifugal system is powered by an angular gear with a rev-adjustable engine. The classification chamber is protected against wear by an anti-wear lining.
Single gasket segments are pressed against the seal band radially by weight-loaded cables, guided into the housing axially or made taught with springs.
The seal is achieved through bent stainless steel sheets that drag on the seal band. With or without impact airflow.
Seal in radial direction with flange rings that are pressurized by pneumatic cylinders. Seal in axial direction by sealing strip.
We deliver hydraulic longitudinal adjustments of kilns or ones powered by electric motors. These can be executed with the help of one or two pressing rollers.
Hydraulic Longitudinal Adjustments to Kilns
Type ZAD OLV H 1
- hydraulic cylinder is fitted in the kiln axis
- includes integrated adjustment measurer in the hydraulic cylinder
- controls according to actual distance of adjustment
Type ZAD OLV H 2
- hydraulic cylinder powered slide
Electric Motor Operated Longitudinal Adjustments to Kilns
Typ ZAD OLV E
- powered by electric motors
- predominantly suited for smaller systems
Longitudinal Adjustment of Kilns
The rotary tubular dryers make the efficient drying of coarse-grit as well as fine-grit dry bulk such as agricultural products such as sugar beet slices, green fodder and wheat possible. The dry bulk is injected into the dryer with or against the current of the drying gas, which is preferably smoke from an external hot gas generator.
The cylinder of the dryer is supported and stored horizontally by two ball races in roller stations with dual bearings. The propulsion of the cooling drum is achieved with an electric motor and can be implemented with the help of a chain wheel, a gear drive, a V-belt drive, or a friction wheel drive. The rotational speed is adjustable. The gasket system we have developed reduces the inflow of false air and thus the use of thermal energy.
In order to intensify the exchange of material and warmth the rotary tubular dryer can be equipped with various fittings.
Specific advantages of the rotary tubular dryer are:
- high specific water evaporation
- high drying temperatures
- sparing treatment of the material when using direct current
Rotary Tubular Dryer
Air Current Mills: The method used by the air current mills called gravity grinding is one tested and tried that has proven itself again and again. The ground material is immediately blown out of the milling process by the air current.
Single Chamber Mills: Are predominantly constructed with diameters from 1,0 to 5,4 meters. When specifically demanded they can also be constructed in larger dimensions. They are not partitioned.
These mills are suited for coarse or preliminary grinds as well as the fine grinding.
Multi-Chamber Mills: With the help of a variable amount of partitioning walls the camber is divided into at least two separate chambers. These are used as:
- throughput mills
- mills using bucket conveyors with output at the end
- mills using bucket conveyors with output in the middle
We deliver complete drive systems for the rotary tubular kilns, drums and tubular mills among others in the forms of central drive, sprocket drive, chain drive and friction wheel drive. We also deliver single parts of these drive systems such as for example:
- sprocket wheels
- chain wheels
- friction wheels either with steel or rubber surface
The built-in components for the rotary tubular kilns, dryers, drums and tubular mills are designed, constructed and finished according to the technical specifications given. Our mounting parts include the partitioning and discharge walls and preliminary drying chambers for the mills, chains, buckets, cell fittings and installations made of cast iron.
Flap boxes find their use as single pendulum or double pendulum boxes or as a combination of these. They are used to insert or discharge fine or coarsely grained bulk solids and to seal processing spaces hermetically. The pendulum claps are usually controlled by weights, in case of the more demanding sealing of processing spaces the flaps are opened and closed automatically.
We deliver bearing stations both mounted in anti-friction bearing and plain bearing for rotary kilns, drums and tubular mills.
Our rolling bearings come in all standard sizes and are products from reputable German manufacturers. The housings for these bearings are in part in-house creations.
The plain bearings in form of hydrodynamic or hydrostatic bearings are in-house productions that can be outfitted with water cooling. The housings hereof are mainly welded constructions. The lubrication is achieved either by splash or pump lubrication with oil. The bearing shells for the intake of the axles are manufactured out of specific alloys.
The bearings for the mills can be in the form of spherical roller bearings, slide/free-wheel bearings with bearing shells (trunnion bearing) or slide shoe bearing on the mill cylinder depending on the technical or economic parameters.
Rotary drums are outfitted with two or three, depending on the length of the drums, predominantly one-piece raceways that are themselves are on track rollers. The strain on the rotary tube is directed over the track rollers to the raceways and into the foundation. Therefore track rollers and raceway are subject to great strains. These are meticulously designed based on ZADCON's experience in this field.
We produce the fitting pipelines with the necessary accessories for various amounts of various media whether air, hot gases, technical gasses or mixes of gas and solid matter.
- welded: the raceway is welded onto the kiln cylinder parallel to the kilns axis
- lose: the raceway is fixed on the kiln cylinder parallel to the kilns axis in such a manner that it rotate around the cylinder
- gusset fastening: the raceway is fixed and welded onto the drum mantle with the help of axially adjustable wedges and can be gaplessly oriented or centred
- sprocketed raceway: the raceway is connected interlockingly with the kiln cylinder in peripheral direction via its internal gearing. The kilns entire weight is supported by the internal gearing tangentially. Due to the tangential load transfer the kiln cylinder is kept perfectly circular in all operating conditions.
- screwed on: the raceway is screwed onto the kiln cylinder parallel to the kilns axis
Such as sprocket covers, heat shields on charging stations, protective installations on moving parts etc.
The inlet is crafted out of heat resistant segments that, depending on operating conditions, are of steel and when appropriate walled out and cooled to reduce wear. The segmented construction allows for the expansion that comes with the high temperatures.
The outlets need to withstand even more strain due to the materials that leave the kiln and the heat that they are exposed to. Accordingly ZADCON uses highly heat resistant output protector segments that can be stresslessly assembled to a double-mantle. Support arms connect the segments with the kiln shell. The thus created face can be cemented and so made especially durable. The double-mantle is then cooled from the outside with cool air as coolant.
Recuperators are installed in front of rotary kilns and are used for the same diverse dry bulk. ZADCON's recuperators that are designed, constructed and built with process engineering in mind are classic, multi-stage cyclone preheaters* that are connected with a calcining line* when required.
The warmth exchange takes place according to the counter flow principle with intensive mixing and partial neutralization. The rest of the neutralization can take place in the calcinatory or in the calcining zone of the rotary kiln. Furthermore the standpipe dryer is used as a recuperator.
- The material is heated in a vertical pipe with the help of preheated air, hot gasses or even exhaust gasses. The preheating material is then separated out in the cyclone.
- Low spacial requirement
- Preheating flexible and with low maintenance
- Input material must be sufficiently pourable or the input needs to take place with a centrifuge drum, in order to break up larger clumps.
- Cement Plant Bernburg, Germany
- Cement Plant Karsdorf, Germany
- Cement Plant Deuna, Germany
- Cement Plant Nowing, Poland
- Cement Plant Malogoszcz, Poland
- Cement Plant Musulmiye I, Syria
- Cement Plant Hama, Syria
- Cement Plant Adra, Syria
- Cement Plant Tartous 1+2, Syria
- Cement Plant Beli Isvor, Bulgaria
- Cement Plant Fabrica Cementa „Sharr“, Kosovo
- Cement Plant Cienfuegos, Cuba
Additionally ZADCON can produce parts for installations and systems out of all other industrial branches where rotary tube technology is used.
Spare Parts for ZADCON-built ore ZAB-built installations
Our experienced designers use CAD workstations and modern software to work on a broad range of problems like designing machines or different components, optimizing spare parts or different fields of research and development.
At ZADCON, our own experts work at procedural dimensioning of rotary machines and their accessories. Furthermore we work closely with the Institute of Fluid Mechanics and Thermodynamics of the Otto von Guericke Universität in Magdeburg, and with Prof.Dr.-Ing. Specht and Jprof.Dr.-Ing. Herz in particular, and a number of other universities, colleges, research facilities and specialized companies.
ZADCON is not bound to any particular manufacturers, even though we work closely with several excellent partners, some of them near our headquarters. Because of our way of working, we have both: quality and short distances. Production control and inspection is being handled by our specialist engineers.
Our products are shipped worldwide and assembled locally by specialist installation companies.
Our support writes expertises for existing plants, replaces broken or wear parts and optimizes facilities. They also work at assembling our machines, and offer advice on questions concerning process engineering. Furthermore they are active around the world to support operators of plants, that have been built by ZAB Dessau.
We ship spare parts and constructional components for mechanical and systems engineering around the world. Spare parts include pinions, bearings, shafts, tyres, carrying rollers, girth gears and many more.