Polysius

As one of the world's leading engineering companies on the plant-making sector, Polysius possesses the comprehensive knowledge required for planning and building complete silo systems that combine innovative designs with proven technology. Polysius offers two (2) types of silo: the multiflow silo and the tangential blending silo.

Both multiflow and tangential silo systems operate in accordance with well-proven blending processes:

Silo filling by means of a distributing system which is specially adapted to the flow characteristics of the material
Blending of the horizontal layers of raw meal with their different chemical contents. This is effected by rapid filling of the central chamber, causing a strong vertical flow of material which cuts through all the horizontal layers
Continuous turbulence mixing of the contents of the central chamber and continuous extraction of the material from the silo

		High production capacity coupled with low capital cost and operating expenses head the list of demands placed on the cement clinker manufacturing process. Apart from the rotary kiln, modern kiln lines include a multi-stage cyclone preheater and a calciner with tertiary air duct. The heat produced by the burning process in the rotary kiln and calciner is utilized for preheating the raw material. Preheating and extensive precalcining of the raw material shorten the burning process. The high degree of heat utilization reduces the fuel consumption and the capital cost for the rotary kiln.
Dopol 90 Dual-String 5-stage Preheater Tower 2 min or less download at 56k		Also, the calciner can be used for burning cheap fuels and secondary materials. This positively influences the emissions of NOx and CO, an aspect of increasing significance. Thus, the calciner is a crucial system component for the operating economy and environmental compatibility of the plant.

The raw meal fed into the preheater is progressively heated in the various cyclone stages by the exhaust gas from the rotary kiln.

After entering the system through the gas ducts between the top two cyclone stages, the raw meal mixes with the gas flowing upward through the preheater and is carried into the topmost cyclone stage. It consists of one or more meal collection cyclones, depending on the production capacity of the plant. Here, the meal is separated centrifugically from the gas, leaves the system through the exhaust gas duct, and cleaned in an electrostatic precipitator.

The heated raw meal passes through meal chutes with integrated double flap valves into the next lower cyclone stage, where the process is repeated. Due to heat transfer from gas to material, the raw meal temperature increases from stage to stage, while that of the counter flowing kiln exhaust gas progressively decreases on its way to the topmost cyclone stage. For instance, in a 5-stage DOPOL® 90 the gas enters the preheater at around 1,000° C. It leaves the preheater at about 320° C. After passing through the lowest cyclone stage, the preheated raw meal enters the rotary kiln at a temperature of approximately 800° C, ready for the subsequent burning process.

The number of cyclone stages is adapted to the individual application. As a rule, the factor dictating whether it should be a 3,4,5 or 6 stage preheater is the moisture content of the raw materials and fuels which have to be dried by the heat remaining in the exhaust gas. The refractory lining of the cyclones and gas ducts keeps radiant losses below 2% of the heat consumption, which is a very low value.

Since the DOPOL® 90 is specially designed to produce an optimum flow pattern, the pressure drop of the preheater is low, which minimizes the electrical power requirement of the exhaust gas fan. The high collection efficiency of the cyclones ensures that the dust content of the exhaust gas is minimal.

Advantages of the DOPOL® 90 include:

Minimized energy requirement due to high heat recuperation and low pressure drop
High efficiency and low heat consumption due to high collection efficiency of the cyclones and uniform distribution of the meal over the cross section of the ducts
High availability due to proven and reliable design and execution