Grinding is a large and costly part of Portland cement manufacture. Prior to clinkering in the rotary kiln, raw materials are ground to a fineness of 80 to 90 pct passing 200 mesh. Then, after burning and cooling, the resulting clinker is ground to about 92 pct passing 325 mesh.
Open Circuit Clinker Grinding: Many early clinker grinding plants employed two-stage, open circuit grinding. Comparatively short mills of large diameter, loaded with balls 4 in. and smaller, first reduced the clinker to 95 pct passing 14 mesh. Tube mills of smaller diameter and greater length, loaded with balls 1 in. and smaller, carried out the fine grinding operation.
Oversize Particles: Open circuit mills, whether separate ball and tube mills or compartment mills, always encountered the problem of tramp oversize in the product. A small percentage of clinker survived passage through the first grinding stage as particlesperhaps 1/16 in. diamthat were too large for the smaller balls in the following stages to reduce to 200 mesh. When the feed rate was lowered to reduce tramp oversize, there were serious losses in grinding efficiency.
Closed Circuit with Air Separator: Although screens after the first stage of grinding largely solved the problem of tramp oversize, the final stage still remained in open circuit. With the passage of time, higher and higher cement finenesses were called for. Overheating and ball coating reduced grinding efficiency. It became increasingly costly to produce the new high-fineness cements in open circuit.
When the tailings from an air separator are returned to the mill, a circulating load is created. Although the circulating load contains a certain amount of fine particles, the material in transit through the mill is considerably coarser than in open circuit. This reduces the formation of coating on the small balls. It is also, possible to draw a large quantity of air through the air separator, exhausting it to a bag-type dust collector, thereby cooling both the tailings being returned to the mill and the finished cement. Imperfect as the air separator may be as an accurate sizer of fine particles, it has the following advantages, which become more pronounced with high-fineness cements: 1) elimination of oversize particles; 2) reduction of ball coating; 3) lowering of temperature of mill and product; 4) some gain in mill output.
It is entirely feasible first to grind the clinker in a preliminary mill, and then to follow it with a tube mill in closed circuit with an air separator. This is done in many older installations, in which air separators have been applied to existing tube mills. Once the air separator is employed, however, no advantage can be found in doing the preliminary grinding in a separate mill. Modern installations often use the closed circuit compartment mill, which is simpler.
Various arrangements of this equipment are possible. If the air separator is placed near the discharge end of the mill, the elevator can be conveniently located next to the air separator. The tailings must then be conveyed back to the feed end of the mill. If the tailings conveyor is located beneath the service crane, there is some restriction to the movement of the crane hook. If it is placed above the service crane, the air separator must be installed higher.
A Letter From Our President. During the current situation with the COVID-19 virus, Precision Roll Grinders remains open for business to meet all of our customers roll servicing needs. The health and safety of our employees, as well as our customers and partners, is of primary concern. We are monitoring the COVID-19 situation very closely, taking appropriate health measures, and are confident we can abide by locally imposed policies while continuing to seamlessly support and provide value to our customers business operations. If you have any questions about PRGs accessibility or operations please do not hesitate to contact us.
Even large-scale components built to withstand the rigors of heavy-duty industrial processes need occasional maintenance. Our roll grinding experts can keep even the largest trunnion assemblies such as for lime kilns, cement plants, paper mills or other heavy-duty industrial processes working properly. Our team handles repairs to mounts; bearings; arms; shafts; and lugs, pipes, rings and seals to help you address: Flat-spot damage resulting from a bearing lock-up while a kiln continues to turn Chatter marks (to eliminate additional chatter transfer to a larger drum ring) Damaged bearing seats and seal areas Journal gouges that are common following torch removal of bearing inner races Bearing fits for setups involving inner races Journal restoration to allow new bearing sleeves for sleeve-style bearings See our grinding and CNC lathe capacity.
Due to the rare incidence of trunnion repair, most facilities have only one spare trunnion to cover all positions in the manufacturing process. A proactive approach to maintenance can eliminate costly downtime. PRG offers emergency service as well as fabrication and grinding services for spare or new replacement trunnion assemblies to reduce downtime due to scheduled maintenance or unplanned equipment failure. We have four locations to best serve your plants needs. Well work with your plant to: Create amaintenance planthat works around your schedule. Guarantee faster, easier emergency repair in the event of unplanned downtime. Identify any possible areas of concern, along with your Operations Managers and Maintenance Supervisors
What are the costs for replacing a trunnion assembly? Can a trunnion assembly be repaired? Im seeing flat spot damage resulting from a bearing lock-up while a kiln continues to turn. Will chatter marks cause additional chatter transfer to a larger drum ring?
For grinding Portland Cement, the power consumption accounts for some 35% of the total consumption of electrical energy for producing cement, counting right from the quarry to the packing plant. It is therefore for very good reason that great efforts during the past years have been put into making cement grinding more efficient, thereby saving power.
In the traditional cement grinding installation, clinker of a maximum size of about 1 is being fed to a ball mill for grinding in 2 or 3 compartments with grinding media ranging in size from 3 to 4 down to about .
In an ordinary diaphragm the slots will normally have a width of 6 8 mm, due to strength and manufacturing requirements . This means that the slots are not narrow enough to ensure effective screening of the ground material. Consequently, the size of the grinding media in the last compartment must be big enough to effectively grind the material passing into it.
The screening plate is made out of thin plate with slots of 2 mm width only. This means that the plate can retain all particles exceeding the critical size, allowing the use of smaller grinding media of an optimum size of 5 7 grammes piece weight.
About 25% of the electrical energy consumed by the ball mill can be saved when increasing the efficiency of the separator from about 25% as found in the conventional air separator to about 80% which has been demonstrated in the SEPAX separators. The calculation is based on the same amount of particles in the range 3-30 , which according to general experience is equal to identical strength properties.
If the grinding charge in the fine grinding compartment is carefully dimensioned to the changed conditions in the mill, a further reduction of the specific power consumption can be expected, primarily due to decreased agglomeration in the mill. The combined effect of the high separator efficiency and reduced agglomeration corresponds to a proven increase of production of 30-40%.