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Understanding how to balance the cement production process for lower cost mode of operation  
Cutting costs doesn’t have to involve a huge system overhaul and it shouldn’t only be a directive from above. The responsibility for seeking out and implementing opportunities to reduce cost per tonne generally lies with the Process Engineer and the Production department. Here, I look at one of my preferred approaches to establishing the lowest cost mode of operation.

Do you know what efficient operation looks like?
Before you start on such a project, it’s worth reflecting on the basic parameters at the core of efficient operation. These are too often forgotten over time, as equipment ages and personnel get used to working around under-performance. Changes in the raw materials, fuels and final product specification also have an impact that needs to be borne in mind.

If you can answer the question ‘why isn’t this equipment operating efficiently’, you’re halfway to a solution, but in order to do this you need to first establish what efficient operation looks like for your plant. Read my previous post about performance analysis for more on this.

Balancing every stage of the process
Cement production is a delicate operation. Everything in this linear process needs to work well for the whole process to be truly efficient. Therefore, a good approach to identifying the lowest cost mode of operation is to ensure that the process parameters between each stage of the process are in balance.

Output: from quarry to kiln
This is the first parameter that most plants will have balanced. The quarry, crusher and raw mill output needs to produce sufficient feed at the right chemical and physical specification for the kiln to keep running at its optimum level. The balance between the kiln and cement mill is less important, since the clinker store acts as the natural buffer through seasonal variations in cement demand. However, the kiln must be capable of producing sufficient clinker to see the plant through the peak sales months or customers will be lost.

In new plants that have been well designed, the output should be balanced at the desired chemical and physical target parameters. But what happens as the plant ages? Or the raw materials change? Or the fuels change? The process becomes unbalanced.

Case study: ball mill
Let’s look at an example from a real plant. Over time, the ball mill output had been steadily decreasing, due to a lack of attention to the media grading and inleaking air around the circuit, which resulted in inadequate mill ventilation. The plant got to the stage where there was no overtaking capacity in the mill and therefore, to achieve the required mill output, the raw meal 90 micron residue was increased.
As the 90-micron residue was siliceous, the fuel consumption of the kiln increased, the kiln output dropped and the clinker was much harder burnt, which resulted in a knock-on effect in the cement quality.

This example shows how a lack of attention to process engineering and maintenance issues in the raw milling department created a chain of events that affected the whole process, including the final product quality. Examples like this are numerous and often include upratings, where parts of the process have been modified without considering all of the plant. Such actions will create imbalance in the process.

Understanding your process is key to cost-cutting success
At each stage of the process, there are both chemical and physical parameters that will impact the operation and productivity of the following stage and therefore affect the cost of production. The chemistry of the raw meal affects kiln operation and clinker quality; fuel properties influence the flame characteristics, again impacting on clinker quality and kiln operations; clinker quality affects the chemical and physical targets of the cement mill operation, and the quantity of materials such as limestone and pozzolan than can be used in the cement. In an intricate process, everything is interconnected. Knowing where cost reductions can be made really comes down to understanding your production process.

Sadly, due to staff cuts during mergers and acquisitions, and a lack of new talent entering the industry, many cement plants lack the skilled staff capable of this level of understanding. Fortunately, however, performance analysis can easily be outsourced with tools such as JAMCEM Consulting’s Performance Analysis and Diagnostics System and Virtual Technical Centre. If you’d be interested in learning where your efficiency is dropping out, get in touch.