Bild IAB Weimar Rotary Kiln

Calcination of mineral raw materials

Calcination in production

Industrial calcination is generally associated with the deacidification of limestone to produce clinker for industrial cement production. However, this process is associated with a significant release of CO2 emissions, mainly due to the raw material. Furthermore, many other primary and secondary raw materials can be calcined by a thermal process but the associated CO2 emissions are significantly lower.

Important examples of this are the so-called calcined clays, which may already be used as clinker substitute or concrete additive in many European countries. Thermal processing of such clayey primary and/or secondary raw materials results in the formation of individual surface charges or a change in the cation exchange capacity of the clay particles. This leads to the de-velopment of specific characteristics of the calcined products. In the temperature range be-tween 600 and 850 °C, metakaolin or metatone with pozzolanic characteristics are formed.

Basics of a successful calcination of your products

Image Rotary kiln in the recycling pilot plant of the IAB WeimarImage Rotary kiln and hydrothermal furnace at IAB WeimarImage Plant for thermal afterburning and flue gas desulfurization at IAB Weimar

 

 

 

 

The IAB - Weimar Institute of Applied Construction Research deals with the calcination and thermal processing of primary raw materials within the context of its research and develop-ment activities for more than 25 years. These primary raw materials include stones and soil as well as industrial limestone, marl and dolomitic stone, gypsum or anhydrite stones, clays and loams. The infrastructure at the Weimar Institute enables the examination of calcination in small-scale as well as semi-technical scale. For this purpose, an industrial rotary kiln with downstream thermal afterburning, gas measurement analytics and flue gas desulphurisation system is available.

Due to the increasing demands on the recycling economy of the construction industry, the calcination of secondary raw materials in particular has become the focus of attention. In co-operation with several industrial partners, we provide clients support in the realization of their visions.Due to the increasing demands on the recycling economy of the construction industry, the calcination of secondary raw materials in particular has become the focus of attention. In co-operation with several industrial partners, we provide clients support in the realization of their visions.

Sequences of different processes in production

Image Filling of a muffle furnace at IAB Weimar Image Specimen Vessels for Chapelle TestImage Calcined clays in vessels

The small-scale examinations include the preparation and packing of the raw materials, the determination of the optimal burning parameters as well as the verification of the achieved product characteristics. With a developed at IAB and patented hydrothermal calcination pro-cess, it is possible to simulate oxidizing or reducing calcination conditions using synthesis gas and can be used for the calcination of raw materials. The assessment of the surface activity of calcined raw materials or their reaction potential (pozzolanicity) is carried out by fixing calci-um hydroxide ions in aqueous solution (Chapelle test following NF P 18-513, Annex A) as well as by the determination of the surface charge (zeta potential). The product characteristics for the use as clinker substitute and in cement-bound building materials can be determined by conventional mortar tests according to DIN EN 196-1. If required, examinations of concretes will also carried out using various mixing methods.
The results obtained within laboratory tests have to be scaled for industrial implementation. This can be carried out in a rotary kiln. Such a kiln is available at IAB. The influence of both an oxidizing (λ > 1) as well as a reducing (λ < 1) burning atmosphere on the product character-istics can be examined with this technical equipment. The downstream thermal afterburning and the flue gas desulphurisation system enable the simulation of a fully integrated production chain on pilot scale and the determination of essential characteristic values. Sensors measure the emissions of the most important process gases. Particulate pollutants and pollutants as chlorides, fluorides and sulphates are filtered out by an integrated large filter. This process is carried out by means of dry absorption in accordance with the German Federal Immission Control Law (BImSchG). The rotary kiln is operated with material throughputs in the range of 50 to 150 kg/h, depending on the grain size of the feed material, the rotational speed and the angle of inclination of the rotary kiln. The grain size of the feed material should not be less than 2 mm.

Calcination documentation

The price of CO2 certificates issued to produce one ton of CO2 or other greenhouse gases within the European Emissions Trading System (EU-ETS) knows only one direction: up. Due to this ongoing development, production processes are already converted to sustainable pro-duction technologies in a very short time, especially those in the energy sector and in steel production. Several secondary raw materials that are currently used as clinker substitutes in the cement production or as concrete additives in the production of concretes become inappli-cable. This applies in particular to fly ashes, granulated slags and FGD gypsum. This gap can be filled by calcining clayey primary and secondary raw materials.The price of CO2 certificates issued to produce one ton of CO2 or other greenhouse gases within the European Emissions Trading System (EU-ETS) knows only one direction: up. Due to this ongoing development, production processes are already converted to sustainable pro-duction technologies in a very short time, especially those in the energy sector and in steel production. Several secondary raw materials that are currently used as clinker substitutes in the cement production or as concrete additives in the production of concretes become inappli-cable. This applies in particular to fly ashes, granulated slags and FGD gypsum. This gap can be filled by calcining clayey primary and secondary raw materials.
Scientific work and services carried out at IAB are already showing that the pozzolanic reac-tion potential of aluminosilicate by-products and side products can be significantly increased by moderate thermal treatment. For the production of clinker substitutes and concrete addi-tives, in the future brick clays will increasingly be used as alternatives to kaolin and clayey RC gravel wash residues or diatomaceous earth (Kieselguhr).Scientific work and services carried out at IAB are already showing that the pozzolanic reac-tion potential of aluminosilicate by-products and side products can be significantly increased by moderate thermal treatment. For the production of clinker substitutes and concrete addi-tives, in the future brick clays will increasingly be used as alternatives to kaolin and clayey RC gravel wash residues or diatomaceous earth (Kieselguhr).
In this context, calcination refers to the thermal processing of clayey raw materials. This oc-curs in the temperature range between 400 °C and 1100 °C. The production of metakaolin respectively metaton occurs in the temperature range from 600 °C to 850 °C. Under industrial circumstances, calcination is carried out in a modified rotary kiln, tunnel kiln or flash calciner.In this context, calcination refers to the thermal processing of clayey raw materials. This oc-curs in the temperature range between 400 °C and 1100 °C. The production of metakaolin respectively metaton occurs in the temperature range from 600 °C to 850 °C. Under industrial circumstances, calcination is carried out in a modified rotary kiln, tunnel kiln or flash calciner.

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