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We were discussing “Cements and its types” and “Safety requirement in cement industries” in our previous posts. We have also seen the concept of “cement kiln firing system” industry in our recent post. 

Today we are going to start here one very important topic i.e. Cement kiln refractory lining. We will understand the various terminologies and engineering concepts used in cement technology with the help of this category.

Further we will go for discussion of clinker cooling and grinding, cement packing and dispatch, pollution control and much more facts about cement technology in our next post in this category of cement technology.

Refractory Lining

The function of refractory lining is as mentioned following

1.      To protect the kiln shell from influence of flame and hot kiln feed.
2.      To reduce heat losses by radiation and convection heat transfer from hot gases to the feed.
3.      Rough surfaces of brickwork promote the super critical motion of the material, so that effective mixing takes place and heat transfer from hot gases to the feed material is improved.

About 10 % of the heat given by the flame and its associated combustion gases is first transmitted to the surface of the refractory lining and from there; it is transferred to the feed material by radiation.
Damage to the lining is liable to cause trouble which may necessitate shutdown of the kiln for repairs.
Thickness of the lining does not depend fully upon kiln diameter. For good coating condition, it may be less by one or two grades.

Kilns’ refractory lining should have the following properties

1.      Mechanical strength
2.      Refractoriness
3.      Withstand thermal shock
4.      Thermal conductivity
5.      Resistance to abrasion and chemical attack

Coating and Ring Formation

The higher the proportion of liquid formed by the feed material in the burning zone, the more readily will the refractory lining pick up a coating. In a coal - fired kiln, the ash from coal will encourage coating formation. In especially unfavorable cases, the ash may become concentrated in the upper part of the kiln and form a so - called ash ring there.

Coating formation takes place in the following ways

1.      Fireclay bricks - Coating is formed by reaction between basic liquid phase and acidic lining at high temperature.
2.      Magnesite / dolomite bricks - No chemical reaction takes place since both brick material and the liquid phase are basic in nature. Hence formation of coating takes place by softening of lining at high temperature and mechanical combination of the liquid phase with softened surface of lining.

Coating in the burning zone protects the refractory lining from wear and improves thermal insulation of the kiln wall. However, under adverse conditions, it may become too thick thereby reducing flow rate of feed and gases or form objectionable rings.

There are various methods for removing such excess features and these are as mentioned here

1.      Removal by manual breaking out with the aid of rods and pneumatic hammers
2.      By melting or spalling off accretions with the flame
3.      By quenching them with low pressure or high pressure water jettings

Do you have any suggestions? Please write in comment box.

We will see other topic i.e. “Clinker cooling and grinding in cement industries” in our next post in the category of Steel and cement technology. 

I am very thankful to Mr. Subrata Bhaumik, Independent cement consultant, for providing such beautiful information and contents about cement technology. 

Mr. Subrata Bhaumik has more than 50 (Fifty) Years (1965 - 2016) of Experience in Cement and other related Industry covering more than 100 assignments in cement plants with capacities ranging from 100 tpd to 10,000 tpd in India and abroad involving visit to 25 countries overseas in connection with work.

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