Installation of High Efficiency Dynamic Separator for Raw Mill

Background

The Raw Mill is one of the important equipment in the Cement industry used for grinding Limestone into fine raw meal powder. The older plants had Ball Mills for this operation.

Consequently the energy efficient Vertical Roller Mills ( VRM ) came into being. The VRMs have comparatively 30 – 35 % lower energy consumption than the Ball Mills. In the older Cement plants the VRMs had a simple static separator installed for separation of the coarse and fine material. The separator was an integral part of the VRM.

In the conventional separators, the ground material is lifted to the separator by high velocity hot air at the louvres. The separator separates the coarse and fine particles and fine particles are carried away by the airflow to the dust collectors. The coarse material subsides through the raising freshly ground material. This creates additional pressure drop in the VRM and also leads to increased circulation inside the Mill. The particle size distribution is also wider with both very fine and coarse particles present.

The latest trend has been to install cage type high efficiency separator. In these separators, the material enters radially through a cage type separator. The coarse material after separation is collected in a cone just below the separator and is dropped on to the grinding table through a gravity air lock. In this manner the contact between the freshly ground material and the coarse is avoided. The advantages of these separators are as below.

Closer particle size distribution

Less pressure drop across the VRM

Higher output at the same fineness as before or finer product at the same output rate

Previous status

In a million tonne dry process pre-calciner plant, a Vertical Roller Mill ( VRM ) was being used for grinding raw meal. The VRM had a conventional static separator.

Energy saving project

The existing static separator was replaced with a new cage type dynamic high efficiency separator.

Implementation methodology & time frame

The new separator could not be accommodated in the Mill body. So the Mill casings were modified to accommodate the new separator. Hence, to save on time the drawings were prepared and the new separator assembled outside and kept ready for installation.

With all these preparations, the actual installation needed only 21 days of Mill stoppage.

Benefits of the project

There was an increase in the output of the Mill , finer product and reduction in the specific power consumption of the Mill. Additionally, the Mill vibration also got reduced resulting in trouble free operation. The comparison of the conditions and the power consumption before and after installation of the dynamic high efficiency separator are as below:

Parameter	Before Implementation	After Implementation
Feed Rate	200 TPH	225 TPH
Raw Meal Residue
• 90 Microns	18 – 18.5 %	17 – 18 %

• 212 Microns	2.2 – 2.5 %	2.0 – 2.2 %
Mill DP	500 – 520 mmWg	480 – 500 mmWg
Mill Vibration	1.6	0.75
Power Consumption	24.5 units / ton	22.0 units / ton

The power saving amounted to 2.5 units / ton of Raw meal or 3.0 units / ton of Cement which annually amounted to 18 lakh units / year.

Financial analysis

This amounted to an annual monetary saving (@ Rs 3.0 /unit) of Rs 54.0 lakhs. The investment made was around Rs 60 lakhs. The simple payback period for this project was 13 months.

Benefits of high efficiency separator

Closer particle size distribution

Low pressure drop across VRM

Higher output at same fineness (or) same output with finer product.

Cost benefit analysis

Annual Savings - Rs. 54.0 lakhs

Investment - Rs. 60.0 lakhs

Simple payback - 13 months