Kiln and pyro equipment maintenance

What it is

Located at the point of transfer between the rotating element and the stationary hood or duct. Kiln seals are used to minimize drawing excess air and expulsion of kiln gases.

What to watch for

• Exessive run-out of the kiln shell
• Overheating of the seal
• Damaged or inverted seals
• Dust or gas escaping from the seal
• Wear and tear of the seal components

What you can do about it

• Start with performing visual inspections
• Take key health measurements - temperature, shell run-out
• Replace individual leaf seals or the complete assembly if work out
• Switch materials or upgrade to double or triple leaves

What it is   

Commonly referred to as a tire, the riding ring is located at every carrying station.  It wraps the kiln shell, providing radial stiffness and a contact area for kiln rotation.

What to watch for

• Visual wear patterns - check for shoulders, tapers, convex or rolled edges, flat-spotting, or grooving
• Physical damage - check for indentations, cracks, or spalling
• Contact wear - check the interface of retaining components or thrust face to the side of the tire

What you can do about it

• Start with performing visual inspections
• Take key health measurements – creep, temperature, diameter, tire axial runout
• Consider tire grinding, alignment, or potentially replacing the riding ring

What it is

Assembled sections of rolled steel, typically known as “can sections”. The overall length and diameter of kiln shells are determined by process needs.

What to watch for

• Physical damage - check for any visual cracks
• Loose or falling refractory
• Any shell deformations – kiln crank

What you can do about it

• Start with performing visual inspections
• Take key health measurements – temperature, ovality, shell profile, and run-out
• Consider repairing or potentially replacing the shell section

What it is

The burner provides the heat required within the process to dry or carry out a chemical reaction in the product within the kiln or dryer. Heat is generated by burning fuels that can be gas, liquid, or solid in the presence of oxygen, normally provided by an air supply.

What to watch for

• High emissions
• Internal damage to kiln
• Inefficient system performance
• Reliable and current safety systems

What you can do about it 

• Kiln/dryer survey and audit
• Burner tuning/optimization
• Burner upgrade
• Safety system upgrade

What it is

Located at load piers, the carrying station includes the base frame and all support mechanisms (bearing assemblies, trunnions, etc.).

What to watch for

• Overheating
• Contamination
• Excessive vibrations and noises
• Leaking oil
• Visual wear patterns on the roller - check for shoulders, tapers, concave or rolled edges, flat-spotting, grooving

What you can do about it 

• Start with performing visual inspections
• Take key health measurements – temperature, differential roller shaft deflection
• Lubrication/oil testing and analysis
• Perform trust adjustments
• Consider repairing or potentially replacing the component

What it is

The drive system enables the rotary kiln to rotate. It is comprised of the main gear, a drive pinion, and a motor/reducer assembly.

What to watch for

• Gear and pinion backlash
• Radial and axial alignment of the bull gear
• Excessive vibration
• Visual wear patterns - steps, tapers, offset, the contact pattern
• Proper lubrication

What you can do about it 

• Start with performing visual inspections
• Take key health measurements – temperature, axial/radial alignment, backlash
• Consider continuous monitoring, realignment, weld repairs, component replacement, or upgrade

Alignment of the shell or drum between the support piers, gear to pinion, and tires to support rollers, is necessary for all rotary units. The benefits of keeping key components in alignment include:

• Equalization or optimization of loads on support piers
• Reduced power consumption
• Lower component wear rates for riding rings, support rollers, gear and pinion, thrust roller, bearings, etc., resulting in greater sustainabiity
• Reduced refractory stress and wear 
• Reduced risk of shell damage by refractory failure
• Reduced unplanned stoppage risk 

Hot alignment and mechanical analysis

Hot alignment allows adjustment of the kiln to the optimum level without interrupting production for multi-pier, refractory-lined kilns. Using the latest technology, the analysis typically includes items such as shell profile and run-out, ovality measurement, differential roller shaft deflections, gear, and tire axial run-out, as well as roller and tire diameter measurements. Corrections to alignment are made on the run. Hot kiln alignments are also beneficial in determining the shell axis prior to shutdowns where major work is planned.

Cold alignment

Cold alignment is executed during a shutdown period to correctly realign the kiln in order to benefit production and safeguard your equipment. This is typically carried out on smaller units such as coolers, dryers, and carbon regeneration kilns, with or without refractory lining, and running spherical roller bearings.

Because OEMs and repair companies apply different methods to calculate kiln misalignment, you might find it challenging to evaluate the service proposals you receive from suppliers performing their version of a hot-kiln alignment. When looking for support in kiln alignment, there are a few considerations to
evaluate:

What is included in the alignment?

An Alignment Analysis of the unit is often combined with a Mechanical Survey in order to identify, diagnose, and correct any issues before they develop into major problems. Metso Alignment Analysis contains a range of measurements using different tools to ensure all key parameters are analyzed.

How experienced are the service providers?

The use of accurate and proven procedures, performed by experienced and qualified personnel should be of paramount importance to the operator. Metso has crews with many hundreds of hours of experience on all makes and types of rotary equipment.

Is the latest technology being employed?

Proper diagnostics tools and methods should be utilized. For example, some rely on measurements of the riding ring and the associated tire slip or creep. However, given that the tire surface can be irregular due to wear and is often contaminated with lubricant and dust, basing kiln alignment on tire measurements alone is of questionable accuracy. Metso uses state-of-the-art high-frequency laser equipment to capture data with a high degree of accuracy, calculating the position of the kiln shell rotational axis at each support. Calculations include allowance for flexure, shape distortion, and eccentricity of the shell.

Shell flex or ovality occurs at each pier. This condition is marked by a radial irregularity or deviation from the circular shape at the horizontal axis, and an assumed equal and opposite deviation at the vertical axis.

Causes of kiln shell ovality:

Undersized or worn tires

• Shell thickness and clearance between tire bore and shell outside diameter, also known as creep or diametrical clearance
• Misalignment causing excessive loads on support rollers

Effects of kiln shell flex

• Refractory crushing and failure
• Shell plate cracking (typically at a weld)

Tire migration, also known as tire creep, is the difference in the circumferential distance traveled between the tire and shell in one revolution i.e. the amount that the tire lags or “creeps” behind the shell.

Causes of kiln tire creep

• Wearing of kiln components that reduce the diametrical clearance between the tire and shell
• The thermal differential between the tire and shell

Effects of excessive kiln tire creep

• Increased ovality (refractory crushing, failure, and shell cracking)
• Component wear (filler bars, tire blocks, and tire bore)

Shell profile (or out-of-roundness) is a permanent deformation of the kiln shell. This is normally referred to as shell blisters, shell warp-age, shell twisting, or coke bottling.

Kiln shell run-out (or eccentricity), is the inaccuracy of kiln shell rotation about its true center. It is the radial offset about the true center of rotation of the kiln. This situation is commonly referred to as a kiln shell crank, dog leg, or a banana in the kiln shell.

Causes of shell out-of-roundness and run-out

• Overheating of kiln and components
• Loss of refractory
• Damage to the kiln shell
• Emergency shutdown, where proper cooling and slowing the kiln was not possible

Effects of shell out-of-roundness and run-out

• Physical distortions of both the refractory condition inside the rotary kiln and the integrity of the kiln shell
• Higher drive amps and excessive loading on carrying mechanisms
• High differential roller shaft deflection
• High ovality on the kiln shell

Gear axial runout and radial runout refer to the misalignment of the main gear as it rotates. Radial run-out is checked to ensure proper alignment between the gear and the pinion, while the axial runout is important to ensure proper face contact between the gear and pinion.

Causes of gear axial runout and radial run-out

• Improper installation
• The eccentricity of the kiln shell (shell runout)
• Shell deformation (shell profile)
• Kiln misalignment

Effects of gear axial runout and radial run-out

• Heavy tooth wear and damage
• Insufficient/excessive root clearance
• Excessive vibrations