Clinker is the primary ingredient in cement production. A mixture of limestone, clay, silica, iron oxide, and a small amount of alumina, the nodular material is produced in the kilning stage at the cement plant.
Clinker allows for much less difficult conveying and shipping than would be required for cement powder. Once cooled and then ground into powder in mills, the clinker is used as the binder in making cement.
Clinker nodules are typically 3-25 mm in diameter when transporting. When they are ground with a certain amount of gypsum, they produce Portland cement. When ground with specified portions of gypsum and other pozzolanic materials, they make blended cements such as ground granulated blast furnace slag cement, pozzolona cement, and silica fume cement.
The gypsum helps control the flash settings and supplies the cement’s chief property, compressive strength. It also contributes to easier grinding of the clinker by preventing agglomeration and coating of the powder on the surface of clinker balls and mill walls.
Cement clinker can be dry-stored for long periods without degradation of quality. This allows it to be traded globally and used by cement manufacturers when raw materials are unavailable or scarce.
While clinker is integral to cement production, it can also cause operational issues if not properly contained. In its kiln-fired form, clinker produced is marble-like with a highly abrasive surface due to its mineral and material composition. If it spills from conveyor belts into walkways, it can create slip, trip, and fall hazards.
Clinker’s abrasive properties also can hasten attrition of wear liners and transfer chutes. Other problems often include chute pluggage and excess airborne clinker dust during handling operations. Some of clinker’s challenges are similar to those of working with taconite pellets used to make steel.
More about Cement Clinker
Portland cement clinker was first produced in the 19th century in a rectified form of the traditional static lime kiln. The undeveloped kiln was equipped with a beehive structure that provided an extension for raising draft and attaining the temperatures needed to make the clinker.
The kiln was surrounded in size by the strength of the lumps of the raw mix. If the charge in the kiln collapsed under its weight, the kiln would be off. Beehive kilns therefore could not complete more than 30 tons of clinker per batch. Because a batch required about seven days to turn around, the kiln might produce around 1,500 tons per year. This form of manufacturing lasted for almost 50 years.
While today’s kilns are much more efficient and productive, creating clinker still involves fundamental properties. Limestone and clay are sintered at elevated temperatures without melting to the point of liquefaction. The raw meal is fed into the kiln, where first the calcium carbonate calcination occurs. The resulting calcium oxide then is burned at high temperatures with silica, alumina, and ferrous oxide to form the clinker.
Once cement clinker arrives at a bulk material handling facility, having the proper material transfer and containment solutions in the load zone will ensure the clinker does not plug chutes, damage liners and chutes, release clinker dust, and spill onto the walkways.
Cement Clinker: Engineered Transfer Chutes
An advanced-flow transfer chute with an adjustable discharge can minimize production problems with clinker at cement plants.
In developing the transfer chute for a cement plant, Benetech applies state-of-the-art Discrete Element Modeling (DEM) flow analysis to evaluate each clinker transfer point design. This pre-installation computer-modeling process anticipates the cement plant’s potential material flow problems both at discharge and farther downstream.
All computer modeling also includes the latest multi-phase material flow and airflow engineering analysis based on Conveyor Equipment Manufacturers Association (CEMA) criteria. This enables precisely defined and controlled material movement from the head of the belt conveyor through discharge to the receiving conveyors.
In contrast to a traditional chute’s square corners, a rounded/chamfered chute design prevents dust generation rather than just passively trying to control it. The rounded/chamfered loading “spoon” also helps achieve soft loading of clinker and minimizes displaced air in the load zone.
Once the custom-designed transfer chute is in place, a cement facility gains more control over plugged or choked flow, clinker spillage and dust, high-impact areas, the life of load-zone equipment, and the interval length between service and maintenance.
Cement Clinker: Effective Sealing
Keeping clinker material and dust contained requires a conveyor skirting system that can be built to any length on the belt. The sealing system also should be interchangeable, let one person make skirt-rubber seal adjustments, and enable personnel to manage maintenance from outside of the belt.
Load zone clamps will ensure the skirt provides a consistent seal and an economical solution for load-point spillage. Quick-release clamps will allow for maintenance without the use of tools.
Different options of sealing type and material (e.g. rubber, polyurethane) can give cement facility operators more versatility for problem-solving in the load zone as well.
Cement Clinker: Wear Liners
Wear liners protect the conveyor skirting system and the chute wall from the abrasive wear and tear of cement clinker as it moves through the load zone. Achieving optimum performance requires that they be placed inside the skirtboard.
Installed inside the skirting system, wear liners provide a protective surface against the friction and abrasion caused by the clinker material. The wear liner also assists to manage the side-loading forces from reaching the skirting rubber seals as well.
Optimizing the performance of wear liners is best achieved by selecting a system that can be easily serviced, with internal liners that can be adjusted externally. Elimination of the need for confined space entry, as well as allowing liners to be perfectly aligned quickly and easily reduces maintenance downtime and improves safety. Properly aligned wear liners ensure that material entrapment will not damage the conveyor belt. Wear liners further support the center loading of bulk material on the conveyor and reduce the material’s pressure on skirt rubber seals, which adds to their lifespan.
Beyond maximizing the belt edge for sealing, the right wear liner can be made of a material such as AR 400, ceramic, UHMW, chromium carbide, or stainless steel for reducing early wear and erosion of skirt rubber caused by clinker’s abrasive properties.
The wear liner also can be installed in a straight or deflector style with a standard thickness of one-half inch or a custom length and thickness as needed.
Cement Clinker: MaxZone® and MaxZone® Plus
Proper material flow and containment are critical to preventing the operational challenges of cement clinker. Benetech’s MaxZone Modular Skirtboard and Belt Support System seal the load zone to keep clinker in the material stream, reduce clinker dust, and lessen abrasive impact on the conveyor belt.
Providing an economical transfer point and load zone solution in lieu of a full replacement, the system’s modular design allows cement plant operators to replace components without special permits or extended shutdowns. The system also can be retrofitted to accommodate and enhance an existing one. Installation is simple, and limited welding is required.
In the event a cement plant is contending with off-center conveyor loading of clinker, the MaxZone Plus system resolves a misaligned transfer point chute without requiring a costly chute redesign.
With cement clinker, improper or off-center loading can load it to either side of the conveyor belt, creating extra spillage and dust while also threatening to mistrack the belt. The MaxZone Plus system corrects this with a deflector and adjustable side kicker plates that move the clinker forward onto the moving belt to correctly center-load the material for a smoother transition.
The system also includes 6” removable side panels for the chute configuration, allowing it to be installed easily into an existing MaxZone® as well as retrofitted to other containment systems.
Benetech: Your Ally in Bulk Material Handling
Benetech supports cement bulk material handlers with the engineering and load zone sealing solutions for greater, safer productivity with less housekeeping, maintenance, and downtime. To find out more about how our custom conveyor skirting systems can enhance your operation, contact us at info@benetechusa.com to speak with a specialist.
Posted in Dust Control, and Material Handling