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Mechanical kiln inspection Improves and ensures kiln availability by optimisation of: ■ Kiln axis ■ Kiln shell ovality ■ Axial balance ■ Kiln crank
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MECHANICAL
KILN
INSPECTION
Introduction
MAIN FEATURES • Ensures high kiln availability • Reduces maintenance costs • Short payback time • Performed during normal kiln operation • Extended lifetime of refractory lining and other key kiln components • Backed up by F.L.Smidth´s in-house engineering departments • Based on more than 120 years of experience in kiln design • Performed by highly experienced F.L.Smidth kiln specialists
Kiln inspections
F.L.Smidth
Regular kiln inspection is required to ensure optimum availability of the kiln installation and to verify that the kiln operates within the load and stress parameters laid down by the kiln designer. Today’s state of the art methods of inspection performed during normal operation of the kiln are based on advanced measuring techniques and evaluated by highly experienced kiln specialists. Although the vast majority of cement plants employ a very experienced maintenance staff, it is not economically and technically viable for the individual plant to invest in the measuring instruments and develop the computer software required, acquire and maintain the skills necessary to perform these advanced inspections, process the data and evaluate the results. Therefore it is an accepted practice in the cement industry worldwide to call on an outside company to carry out these comprehensive kiln inspections at regular intervals.
F.L.Smidth is the world's largest supplier of rotary kilns, spare parts and services to the cement industry. With more that 120 years of experience as kiln designers, F.L.Smidth possesses a huge technical know-how on rotary kilns and employs a group of highly experienced field engineers, who work daily as kiln specialists at cement plants all over the world backed up by the entire F.L.Smidth organisation. The Hot Kiln Alignment method was introduced into the cement industry in 1981 allowing a full inspection of the kiln to be performed during normal operation. Since then, F.L.Smidth has continuously updated and improved the method, measuring instruments and computer software to provide our clients with the best possible tools to evaluate the consequences of the kiln’s present operating condition in respect of the availability.
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Symptoms and root causes
Symptoms Hot bearings
Root causes
Cracks
Wear
On bearing On thrust journal collar
In kiln shell
In supporting roller shaft
On suppt. roller and tyre
Kiln axis
Kiln axis
Kiln axis
Kiln axis
Kiln shell ovality Kiln crank
Kiln crank
Between the tyres
Under the tyres Kiln axis
Kiln shell ovality Kiln crank
Axial balance Lubrication
Between tyre and kiln shell
Lining loss
Kiln shell ovality Kiln crank
Axial balance Corrosion
Operation Lining qualities
The F.L.Smidth concept The inspection concept innovated by F.L.Smidth focuses on the following four elements: • Kiln axis • Kiln shell ovality • Axial balance • Kiln crank The root causes of the vast majority of the failures of kiln installations originate from one or more of these elements, thus posing a serious threat to the availability of the kiln. In addition, the F.L.Smidth concept includes a thorough inspection of the drive station, kiln shell profile analysis, and a general inspection of the mechanical condition of the other key kiln components. Very often the load condition of a kiln changes over the years due to e.g. increased capacity, change of fuel and/or changes of refractory lining quality. To compensate for such changes, F.L.Smidth recommends that the kiln be recalculated based on the present load conditions and that the optimum kiln axis be determined taking the load distribution between the individual supports and the stress levels in kiln shell, tyres and rollers, as well as the bearing loads into consideration.
F.L.Smidth inspection types F.L.Smidth markets the following three standard inspections covering all types of rotary kilns: • Comprehensive kiln inspection • Two-support kiln inspection • Hot kiln alignment check The F.L.Smidth standard inspections consist of individual modules, most of which are optional, enabling the client in co-operation with
F.L.Smidth to tailor an inspection to meet his specific needs. The results of the F.L.Smidth inspection are presented in a written report and/or on a CD-Rom, with recommendations of measures to be taken. Additionally, any adjustments to the kiln recommended by F.L.Smidth can, at the client’s request, be supervised and verified by an F.L.Smidth field engineer in continuation of the inspection.
Benefits The comprehensive kiln inspection performed on a regular basis in co-operation with F.L.Smidth provides the client with the knowledge necessary to prolong the lifetime of the refractory lining and expensive kiln components and reduces the risk of unscheduled stoppages, thus ensuring high kiln availability. Empirically, the payback time of a comprehensive kiln inspection is very short as the expenditure on this inspection is very marginal as compared with the cost of refractory lining and components to be replaced as a result of avoidable mechanical failures as well as the cost of the consequential production losses incurred.
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Side 4
Elements Kiln axis The kiln axis is defined by the position of the supporting rollers. It determines the distribution of the kiln weight load between the supports and thus the distribution of the longitudinal bending stresses in the kiln shell. Misalignment of the kiln axis may result in overloading of supports, excessive stresses in kiln shell, tyres and supporting rollers as well as bearing overload. The kiln axis is measured during normal kiln operation using two electronic theodolites, connected to a computer calculating the horizontal and vertical kiln axis by specially developed software. Additionally, the “Comprehensive kiln inspection” includes a complete recalculation of the kiln, based on the axis measured and the present load conditions, to determine the optimum kiln axis, taking both load distribution on the supports, the stress levels in kiln shell and tyres, and the kiln axis into consideration.
Kiln shell ovality The dynamic ovality is defined by the degree of deformation of the kiln shell and determines the distribution of the cyclic, circumferential bending stresses in the kiln shell. Excessive ovality can result in circumferential bending fatigue in the kiln shell and refractory lining failures. The ovality is either calculated on the basis of the tyre migration or measured via the Shell Test method.
Axial balance Although a rotary kiln is always in axial balance, the axial balance can be established either between large forces or preferably, in order to ensure the availability, between small forces. The state of axial balance is defined by the degree of parallelism between the kiln axis and the axes of the individual supporting rollers determining the magnitude and directions of the axial frictional forces between the tyres and supporting rollers and on the thrust roller(s). Large axial forces may result in hot supporting roller bearings, failure of the thrust device(s) or damaged end seals.
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Side 5
Elements Kiln crank A kiln crank, whether mechanical or thermal, can cause excessive, extra, cyclic loads between supporting rollers and tyres and stresses in the kiln shell. A mechanical crank is caused by a permanent deformation in the kiln shell, whereas a thermal crank is caused by temperature variations along the circumference of the kiln shell, and so it is present only during operation of the hot kiln. Excessive crank formation can lead to failure of contact surfaces, supporting roller shafts, tyres, kiln shell and lining. The kiln shell is checked for crank formation by measuring the variations in the deflection of the supporting roller shafts, which has to stay within certain limits.
Kiln drive An examination of the kiln drive constitutes another important element of a kiln inspection. The condition of the kiln drive is determined by measurering of the axial and radial wobbling of the girth gear as well as evaluation of the mesh and root clearance between the girth gear and pinion(s). Further, the condition of the tooth profiles, the lubrication of the gears, as well as the stud bolt connections between the girth gear and the spring plates and the welds between the spring plates and the kiln shell are examined. To complete the examination of the kiln drive, the operating temperature and vibration levels of the main gear unit are checked.
Kiln shell profile analysis A kiln shell profile analysis is made to investigate the degree of deformation of the kiln shell. Such deformation may have no influence on the loads on the supporting rollers but can contribute to refractory lining and kiln shell failures.The kiln shell profile analysis is based on an evaluation of the kiln cross-section geometry measured at regular intervals along the length of the kiln. The analysis is presented graphically.
General inspection The general inspection of the kiln comprises a visual examination of the condition of other key kiln components not included in any of the above activities, but the possible poor condition of these components can also pose a threat to the availability of the kiln.
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Side 6
Calculation of longitudinal stress distribution in kiln shell
Calculation of current loads on supports
General mechanical condition
Ultrasonic testing of supporting roller shafts
Surface condition of tyres and supporting rollers
Kiln shell profile analysis
Check of supporting rollers and bearings
Check of girth gear / kiln drive and main gear unit
Check of thrust device(s)
Check for tyre wobbling
Verification of axial balance
Check for kiln crank
Inspection types
Check for kiln shell ovality
Inspection modules
Verification of kiln axis
Standard kiln inspections
Comprehensive kiln inspection Inspection of two-support kiln Hot kiln alignment check ) Included in the standard inspection
*) Optional
www.flsmidth.com Up-to-date addresses of worldwide subsidiaries and sales offices are available from our website
DENMARK
USA
INDIA
F.L.Smidth A/S Vigerslev Allé 77 DK-2500 Valby Copenhagen Tel: +45 36 18 10 00 Fax: +45 36 30 18 20 E-mail:
[email protected]
F.L.Smidth Inc. 2040 Avenue C Bethlehem, PA 18017-2188 Tel: +1 610-264-6011 Tel: +1 800-523-9482 Fax: +1 610-264-6170 E-mail:
[email protected]
F.L.Smidth Ltd. Capital Towers 180, Kodambakkam High Road Nungambakkam Chennai 600 034 Tel: +91 – 44-52 191234 Fax: +91 – 44-2827 9393 E-mail:
[email protected]
12-04-258 Bazement Grafisk Design ApS
Data in this brochure is intended for preliminary project planning only. Manufacturer reserves the right to modify equipment details and/or specifications without notice.
