TCL uses what is known in the industry as a wet process technology for the manufacture of cement. The process derives its name from the fact that the basic raw material, naturally occurring limestone, is crushed and mixed with water to form slurry. Though more modern plants utilize “dry process technology”, TCL is forced to maintain a wet process owing to the fact that limestone reserves are located in Mayo, which is approximately sixteen kilometers from the cement manufacturing facilities at Claxton Bay. The already simple cement manufacturing process can be conveniently classified into a number of simpler steps.
1. Limestone Quarrying
The quarrying of limestone, the main raw material used in the production of cement, is the first step in the manufacturing process. Trinidad Cement Limited obtains its limestone from its own quarry at Mayo, in Central Trinidad, which is one of three major deposits of “yellow” or impure limestone in Trinidad. It is estimated that this deposit will sustain TCL‘s proposed production rates for at least the next two hundred years. Traditionally, the limestone was obtained by blasting, which involved the use of explosives. Today, a heightened degree of environmental awareness coupled with greater consideration for the growing Mayo community, have lead us to review our methods. Limestone is now extracted from the quarry by literally ripping it out of the ground. TCL uses one of the largest tractor rippers in the Caribbean, the Caterpillar D11R, to rip and push raw limestone out for production.
The limestone is transported via dump trucks to a 530-tonne/hour Hazemag crusher, which reduces the limestone to an average size of 25mm. The limestone is separated according to high or low carbon content, then crushed and transported by conveyor to a large storage shed.
3. Raw Milling
The crushed limestone is extracted from storage and transported by conveyor to the Raw Grinding Mills where water is added for grinding. Based on the silica content of the raw material, it is sometimes necessary to add sand in the grinding process. This process is called wet grinding; the aim of which is to reduce the material size from 25 mm to 90 micron. The resulting mixture of limestone, water and sand resembles a thick soup, which is called slurry.
4. Slurry Storage & Pumping
Slurry is stored in one of two slurry tanks at the Mayo quarry. The stored slurry is finally pumped along a pipeline from Mayo to TCL’s works at Claxton Bay, straight into large concrete storage tanks commonly known as slurry basins where it is constantly agitated by compressed air and revolving mechanical paddles to prevent the slurry from settling. Slurry is moved to Claxton Bay through a continuous pipeline measuring 10-inches in diameter and approximately 9 miles in length. The slurry leaving Mayo for Claxton Bay must be of a consistently high quality. Any slurry that does not meet the stringent quality requirements is adjusted and recycled until correct.
5. Clinker Production
The slurry is pumped from mixers to rotary kilns, which are long, revolving steel cylinders lined with refractory bricks. Refractory bricks are insulators for the kiln shell and serve to protect the kiln against relatively high temperatures. At TCL, the largest of the kilns is 145m long and 5m in diameter. The company has two kilns with a combined production capacity of 2160 tonnes per day. TCL’s kilns are fueled by natural gas supplied by the National Gas Company. Slide 5. The slurry enters the “back end” of the kiln, which is sloped down to allow for the free passage of slurry from the inlet to the outlet. In the early stage, the slurry is dried off at a temperature of approximately 230 degrees Celsius. The semi-dry product continues along the length of the kiln where it is literally “cooked” at a temperature of about 1450 degrees Celsius. The slurry now takes the form of clinker.