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.
 

CEMENT MANUFACTURING

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 are released.

A pre-heater 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.

ACS solutions 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.
 
ACS solutions 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

Calcined clay (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.
 
ACS solutions 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.

ACS solutions 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.
 

CALCIUM LOOPING

In Calcium looping the sorbent calcium oxide (CaO) reacts with the CO₂ in flue gas of an industrial process (such as cement manufacturing) to form calcium carbonate (CaCO₃). 

CaCO₃ is then broken down to capture the CO₂ and regenerate the CaO for further use.

• The process relies on two reversible chemical reactions: carbonation and calcination.
• During carbonation, the sorbent reacts with the CO₂ in the flue gas to form calcium carbonate (CaCO₃) - > captured with cyclones.
• The CaCO₃ is then fed into a calciner, where it is heated to about 850°C-950°C, causing it to decompose into an almost pure CO₂ gas stream and solid CaO. The CO₂ is removed and further purified, before being sent either for geological storage or onward use. 
• The solid CaO can be sent back for reuse in the process to capture more CO₂.

ACS solutions include high efficiency cyclones for the carbonator and for the calciner to increase the collection of both carbonator and calcined sorbents.