Rotary Kilns for Sand: Why Kiln Dried Sand is Better than Crushed One
Keramzite sand is filler with particle size of 0.1 - 5 mm. It is obtained by drying clay fines in rotary kilns, screening of the total mass or by crushing larger pieces of keramzite. Keramzite is environmentally friendly insulation. It is a lightweight porous material obtained by accelerated baking of fusible clays. Keramzite looks like gravel, meaning it consists of pellets mostly round or oval of different sizes, so it is often called keramzite gravel.
Keramzite manufacturing process includes two phenomena: at a sudden thermal shock, clay prepared in a special way swells, thus achieving high porosity of the material, and the outer surface rapidly melts which gives the material sufficiently high strength and resistance to external influences and creates an almost hermetic shell. Therefore, keramzite quality largely depends on the process accuracy. Depending on the clay treatment mode, it is possible to obtain keramzite of different bulk density: from 200 to 400 kg/cu. m. and higher. The lower the substance density, the more porous it is, and therefore it has higher thermal insulation properties. However, it is more difficult to obtain the necessary strength during manufacturing. The material is also characterized by keramzite granules size, which ranges from 2 to 40 mm, and depending on their size is divided into fractions, for example 5-10 mm or 10-20 mm. Based on the size, the products are divided into keramzite gravel, crushed stone and sand.
Thus, keramzite is unique ceramic porous gravel having the following properties:
- lightness and high strength; - excellent heat and sound insulation;
- fire resistance, moisture and frost resistance;
- acid resistance, chemical inertness;
- environmentally friendly natural material;
- high ratio of quality/price.
Analysis of thermal insulation and mechanical properties of keramzite allows using this material in Russian and international markets for thermal insulation of roofs, floors and walls, foundations and basements. When rationally used in construction for insulation, keramzite has proved to reduce heat loss by more than 75%.
Keramzite has been successfully used for manufacturing ultra-light concrete and light keramzite concrete blocks; it is possible to use it for thermal insulation and drainage in embankments of roads laid in water-saturated soils.
One of the applications is hydroponics: creating an optimum microclimate for the plants root system. It is important to mention that keramzite is an ecologically friendly material.
Manufacturing keramzite sand together with keramzite gravel is the most simple and cost efficient. For this, we can use a simplified process of preparing clay raw material based on experience of the following companies: "Leka" (Denmark), "Lohja" (Finland), etc. They transfer the granulation process to a pre-treatment drum. Getting more small granules is achieved through using in-kiln heat exchanger devices in the form of chain curtains or cell type heat exchangers. They also contribute to substantial reduction of the exhaust gas temperature emitted by the kiln, and therefore, the total heat savings when drying keramzite.
The usual process allows producing keramzite sand in small amounts (about 3%) in rotary kilns during drying keramzite gravel that does not meet the demand for it being 25-30% of the total aggregate volume.
The missing amount of the sand fraction may be added by its autonomous production, by crushing cakes or large fractions of keramzite gravel, as well as using industrial wastes (CHP ashes, mixture of ash and slag, etc.).
Kiln dried keramzite sand has a number of advantages compared to crushed sand: rounded grain sizing generally from 0.16 to 5 mm, bulk density of about 500-700 kg/m3. Raw material can be prepared acc. to clay treatment process for semi-dry bricks pressing or by crushing dried clay granules.
Strommashina Samara Plant offers sand drying equipment - SMS 197 kiln complex - a line of specially developed equipment for kiln drying of keramzite gravel. This line is a part of a process line for keramzite production involving plastic method. The complex may be used for heat treatment of other lumpy or granular materials after the relevant research of the process specifications and installation of devices to the unit.