Final manufacturing process
The final manufacturing process for cement has numerous steps. Raw-meal is grounded into a fine powder and burned in the kiln. The blending is done in silos. The raw-meal is continuously circulated and blended in the first silo. It’s passed on to the second silo for further homogenization—the perfect blending and mixing of various constituents.
Pre-heating stage and the kiln
The blend is heated in a rotary kiln. Gas, oil, or pulverized coal are used to ignite the flame at one end of the kiln. The clinker from the kiln passes into a cooler, where convective airflow cools the clinker for subsequent handling and grinding.
Today, only the dry heat treatment process is used. In the past, the wet process, semi-wet process, and semi-dry process were used.
In the dry process, the kiln feed has a moisture content of ~0.5%. The feed is put into a suspension pre-heater. The formed clinker nodules are in a molten state. Then, the clinkers are put into a cooler.
Cement is produced by grinding the cooled clinker with gypsum—hydrated calcium sulfate. Gypsum is added to regulate the cement’s setting time. The clinker is ground in vertical roller mills.
Usage of fly ash and slag in blended cement
In the last few years, blended cement has increased in popularity among manufacturers including CRH plc (CRH), Cemex, SAB de CV (CX), Eagle Materials Inc. (EXP), and James Hardie Industries SE (JHX). It has advantages such as increased production, low cost of production, and less pressure on natural minerals like limestone.
Typically, there are two types of blending materials that are used:
- Fly ash—residual of burnt coal, mainly sourced from thermal power plants
- Slag—a non-metallic by product produced at iron and steel plants
Investors can access the cement industry through the Vanguard FTSE Emerging Markets ETF (VWO).
Continue reading the next part of the series to learn about the cost elements of cement.