Dry processing beats the wet clay

February 16, 2015 Morten Jakobsen

A carefully planned design concept helps the Tulacement plant reap the benefits of its rich raw materials

HeidelbergCement Russia opened its two million tpa plant, Tulacement, in 2011. Located close to the Gurovo-Beton quarry, there was a clear opportunity to benefit from the quarry’s rich source of raw materials.

But shortly after the kiln’s commissioning, it became apparent that the high clay content, which has a moisture content of 26 percent, would reduce plant productivity to unacceptable levels.

Problems observed
The concept of the raw material preparation at the plant was to crush limestone, clay and other additive in the same crusher and transport the mixture to a circular blending storage. However, particularly the stickiness of the clay caused problems at the stacker/reclaimer. At the entrance to the storage the raw materials would build-up in the central chute of the stacker leading to misalignment and slipping of the stacker belt and finally complete blockage of the chute. With the high moisture content in the mixture also the reclaimer faced difficulties. The high forces needed for reclaiming stressed the equipment thus requiring more maintenance. At the central discharge chute after the reclaimer further build-up occurred.

In fact, blockages were a key problem, also occurring at the conveyor belts chutes between the circular blending bed and the dosing station. The problems were compounded by severe discharge problems at the raw mill’s dosing silo.  The plant had had to use slag to be able to operate, resulting in low profit margins and high wear especially in the raw VRM mill.

Objective and feasibility studies
So in the spring of 2012, a few months after the plant was commissioned, HeidelbergCement approached FLSmidth to assist in developing a concept that would allow the plant to make full use of the quarry’s raw materials, despite their difficult composition. The objective was to determine whether wet clay or dry clay processing would be most efficient. 

Through a set of feasibility studies, ten different scenarios were developed based on criteria including investment required, operating costs, maintenance costs, complexity of the process, interference of the kiln operation, and chemical control. The results of the studies indicated that dry processing technologies would be the most suitable. Wet processing brought with it significant risks in materials handling, and the capacity of the wet clay equipment was severely limited.

Solution with innovative flow sheet 
Following the studies, FLSmidth was chosen to supply suitable dry processing equipment. The main concept of the solution is to treat the sticky clay separately and thereby improve the availability of the entire material handling department. This includes a double-rotor pre-crusher for clay, a special box feeder, and a hammer mill dryer, which is the heart of the process. While this solution fulfills Tulacement’s entire capacity requirements, its compact design also means it can be integrated into the plant’s limited space. 

The design concept is composed specifically to overcome the problem of wet clay, and can be summarized as follows:

  • The wet clay is fed by wheel loaders to the crusher inlet hopper
  • An apron feeder transports the clay to the roller crusher
  • After the crusher the clay is transported by a wide belt conveyor directly to the box feeder
  • The clay is dried to approximately 1% residual moisture in the hammer mill using hot gases from the kiln and cooler
  • The dry clay powder is then collected in two cyclones and stored in a small buffer bin
  •  The clay is added to the raw mill in the required ratio by dosing and feeding it to the conveyor belt to the raw mill together with the other raw materials.
  • The chemical composition of the mixture is monitored by a cross-belt analyzer installed before the drive station of the belt conveyor. The chemical control system adjusts the feed rate of each raw material to ensure the required chemical composition.

Dryer crusher in operation

Read more about the Dryer Crusher here>>

Direct feed concept
Whenever handling wet and sticky materials particularly in cold climates as well the layout and design should be made with the minimum number of equipment. Belt conveyors should run at low speed and transfer chutes should be avoided. In this design the crushed clay is transported directly to the box feeder without any transfer chute. 

Designed with vertical walls to reduce the risk of clay blockages, the box feeder serves three functions. First, it works as a small intermediate storage for the crushed clay, next it feeds the hammer mill with an even distribution of feed and finally it operates as an air sluice reducing the intake of false air.

Commissioning in 2015
FLSmidth delivered the equipment in the first quarter of 2015 and commissioning is scheduled for the third quarter.

           Dryer crusher and the complex gas duct installation

Although the overall concept of this solution has been used successfully within the Heidelberg Cement Group at other cement plants, this is the first time it has been applied to clay. In fact, this installation solution is a world-first in cement production. 

But thanks to the thorough, detailed planning of the engineers at Tulacement and FLSmidth, the owners are in no doubt that the challenges posed by the wet conditions will be overcome.

Read more about FLSmidth Crushing equipments here>>

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