Analysis of return feed
in closed-circuit comminution equipment

1 Common quartz particles (250 µm) in a raw mix (SEM)

2 High chrome heat treated white cast iron (SEM)

3 Material circulations inside a VRM.

4 22 raw mixes were chosen from different parts of the world

5 Laboratory VRM

6 Particle size distribution of the acid insoluble residue from the separator sample

7 Wear rate vs total acid insoluble residue

8 Wear rate vs + 90 µm quartz content

Relativer Verschleiß zu relativem Härteverhältnis

Common return feed sample
from closed circuit VRM process

Summary: 22 cement raw mix samples from different parts of the world were analyzed to assess the influence of hard particles such as quartz on the wear in closed-circuit comminution equipment. So far, the main belief has been, that the concentration of quartz in the separator sample will (return feed) result in a strong correlation to the wear rate, and that limestone will act as a diluting agent alone. This study shows, that the total acid insoluble components show inadequate correlations. However as expected, quartz alone will result in the best correlations when determining the wear (R²=0.60). Considering the influence of other hard components such as iron oxides and sillimanite did not further improve the correlations. From the results obtained, it is questioned whether the quartz content in the separator samples should be used for predicting and verifying the wear rate with a high degree of accuracy. Nevertheless, a series of possible discrepancies have been identified.

1 Introduction

1.1 Background

Traditionally, ball mills (tube mills) have been used for the comminution of raw materials and clinker in the cement industry. However lately, vertical roller mills (VRMs) have become increasingly popular because they use approx. 40 % less power compared to a traditional ball mill [1]. Unfortunately, the setup and operation of a VRM is more complicated compared to a ball mill and high wear rates quickly change the overall performance. The focus of this study are raw material VRMs because they experience an unpredictable wear ranging from 0.1 to approx. 30 g/t....