Calcination and Mineral Processing
Calcination is a process that involves heating a substance, typically a solid material, at high temperature with limited supply of air or oxygen. The purpose of calcination is to remove volatile components and drive off impurities or to transform the material into a more desirable form for further processing.
One of the most common processes is the manufacture of Portland cement where limestone (CaCO3
) is fed into a large rotating kiln with clay. Hot air generated from coal, pet-coke or natural gas-fired burners raises the temperature to produce quicklime (CaO) which fuses minerals with the clay and cools down into clinker: pale, grayish nodules that are ground to make cement powder. In the process, large amounts of CO2
made up by a series of cyclones is used to pre-heat limestone, clay and sand before these raw materials enter the rotary kiln. This process helps to reduce the amount of energy required to operate the kiln, as well as the amount of fuel needed to achieve the desired temperature.
A clinker cooler
cools and solidifies the hot clinker discharged from the rotary kiln, to facilitate handling and storage of the material.
Both processes need dedusting
before the hot gases are released to the stack or are used for heat recovery
Pre-heater dedusting for energy recovery
There is usually a large concentration of fines escaping with the last cyclone gas outlet of the pre-heater, typically composed of small particles of raw material and fly ash (D50~2.5mm).
In new generation cement plants, the hot gases are used for heat recovery, such as heating a mill for the grinding of pet coke, heating a limestone dryer
or to enable heat recovery in exchangers or recovery boilers.
include high efficiency cyclones
to heavily reduce the concentration of fines before petcoke mills
, low pressure drop process cyclones for limestone dryers and pre-separator cyclones
for heat recovery.
Clinker cooler dedusting
The particles carried over in the exhaust gases of the clinker cooler are very abrasive due to their chemical composition and physical properties. The hardness of clinker particles, combined with their irregular shape, surface texture and large size (D50>100mm), can cause them to wear down equipment and machinery, such as high exchangers, waste recovery boilers and end stage bag filters.
include abrasive resistant cyclones with low pressure drop
to heavily reduce the concentration of clinker particles, thereby enabling energy recovery and increasing the lifetime of bag filters.
New materials to partially replace clinker
(or metakaolin) can play a role in cement manufacturing by partially replacing clinker and thereby contribute to a reduction in CO2
emissions. When used in combination with other supplementary cementitious materials, such as fly ash or slag, calcined clay can help to reduce the overall clinker content of cement while maintaining or improving its mechanical and durability properties. As in other calcination processes, calcined clay is manufactured in kilns by heating natural clay materials to high temperatures (though lower than those of clinker) typically in the range of 650-800°C, to drive off water and other volatile components.
include high efficiency cyclones to separate clay particles after kilns and flash dryers / calciners
upstream of final stage dedusters such as wet scrubbers.
CALCINATION OF MAGNESIUM OXIDE
Magnesium oxide (MgO)
has a wide range of applications due to its unique properties, such as high melting point, high thermal conductivity, high electrical resistivity, and good chemical stability. Applications include construction materials (MgO can be a binder to the construction of cement), refractory materials, fertilizer use and others.
MgO is also obtained by a calcination process similar to that of quicklime. In this case, magnesium carbonate (MgCO3
) is decomposed into MgO and CO2
include cost efficient and abrasive resistant last stage cyclones in the pre-heater tower
to greatly reduce concentration before baghouses.
CALCINATION DOLOMITIC LIME
Dolomitic lime is obtained by calcinating dolomite in a furnace or kiln with a high degree of limestone and magnesium CaMg(CO3)2, obtaining CaO°MgO. Applications include the steel industry, refractory materials, glass and agriculture.
Client needs for dedusting are very similar to those of Magnesium Oxide and include abrasive resistant cost-efficient cyclones to reduce concentration before baghouses.
CALCINATION OF CALCIUM ALUMINATE
Calcium aluminate (CaAl2O4) is a compound made up of calcium oxide (CaO) and aluminum oxide (Al2O3). One of the main applications of calcium aluminate is as a raw material in the production of refractory materials. Calcium aluminate can also be used as a binder in the manufacture of high-performance cement. which has superior strength, durability, and resistance to chemical attack compared to traditional concrete.
Calcium aluminate can assume a vitrified fiber form,
similar to rock wool which is very demanding to end stage dedusters, such as bag filters, causing frequent clogging. ACS solutions
include cost efficient cyclones to increase the collection of fibers
and reduce maintenance
to the bag house.