Limestone calcination

The calcination of limestone is a simple chemical process:

CaCO₃ + heat = CaO + CO₂

The calcination temperature depends upon several factors. At the atmospheric pressure and with a CO2 concentration of 25%, the dissociation starts at about 810°C. Some components in fact (e.g. NaHCO3 or KHCO3) dissociate at lower temperatures (200-300°C) already in the preheating zone; some other like NaCO3 or K2CO3 dissociate at 800-900°C in the calcining zone, this forming Na2O and K2O which sublime to Na and K vapours at approx. 1200°C.
The ideal calcination process features: gradual preheating with a smooth increase in calcination temperature up to the point at which dissociation is complete, finally cooling down the burnt lime, avoiding as much as possible further retention time in order to prevent possible re-carbonation.

The TSR kilns represent today the best option for high and medium reactivity lime production in terms of:

• lower fuel consumption,
• lower maintenance costs,
• lower emission rates,
• higher quality of the lime.

However experience and a well proven design are the secrets for a successful lime burning project as several factors influence the choice of a lime kiln technology: the available raw material quality, the fuel and the required characteristics of the finished product.

TSR kilns models:

• Cim-RT
• Cim-TD
• Cim-RD
• FinerStone models

Annular kiln Twin-C

Single shaft kiln ABC

Link to the Uses of Lime...

  TSR kiln models
 

The TSR kilns family consists of two main groups:

• «Direct Crossover» featuring a single and short channel placed between the shafts,
• «Radial Crossover» featuring circular channels around the shafts which are then connected in the central part.

The Cimprogetti direct crossover group includes:

• the RT series, with rectangular cross section, which represents the “entry level” among the TSR kilns.
• the TD series, featuring the exclusive semicircular section design, which is the natural technical evolution of the rectangular section, for capacities up to 500 tpd.

The Cimprogetti radial crossover group includes:

• the RD design with its circular cross section, which represents the state-of-the-art in its field and the top of the TSR kilns range.
   

Cim-ReVerSy-TD Kiln
 

The Cim-TD lime kiln features the patented “D-shaped” shaft cross section and is Cimprogetti’s distinguishing mark in TSR kilns.
The simplicity of the rectangular cross section and the performance of the circular cross section are combined to offer excellent value for money performance.
The advanced semi-circular shape of the shaft, the SRT/ULD pressurized limestone charging and distribution and the double deck discharge tables moving in four directions allow very good burning uniformity.
The Cim-TD kiln is mainly targetted at plants with:

• medium and high outputs (300 to 500 tons per day) of burned lime or dolomitic lime or
• smaller capacity kilns where a superior lime quality (res.CO2 <1,5%) is a key requirement.

Moreover, the short interconnecting channel between the shafts allows a design with a reduced requirement for refractory materials and steel structure.
The Cim-TD kiln is also available in the FinerStone configuration.
 

Daily output (tons)

150 to 500

Fuels

gaseous, liquid and pulverised solid fuels

Reactivity of lime

very high to medium

Cim-ReVerSy-RT kiln
 

The Cim-RT is a twin shaft regenerative kiln featuring an improved rectangular cross section.

It is the Cimprogetti entry level design in parallel flow regenerative kilns.

The key technological features of the process are:

• the efficiency of the regenerative calcination technology, proven by innumerable installations around the world;
• the simple cross section and the use of standard refractory linings;
• the option to use all technological innovations developed for the higher performing TD and RD kiln families, namely for the charging and discharging systems.

The Cim-RT is the logical choice for smaller plants and/or specific applications like the mining industry when sound technology and reduced investment are required.
 

Daily output (tons)

from 100 to 300

Fuels

gaseous, liquid and pulverised solid fuels

Reactivity of lime

very high to medium

Cim-ReVerSy-RD kiln
 

To respond to the lime market trend moving towards larger kiln capacities, Cimprogetti has developed the Cim-RD kiln design, featuring a circular cross section.
The Cim-RD kiln represents the state-of-the-art in its field while it retains the well proven design features of the other Cimprogetti TSR kilns, for most of the process sub-systems (combustion and cooling air units, hydraulic power-pack, automation and control system logic, etc).
The kiln is made of two cylindrical parts , the upper cylinder, of smaller diameter, where limestone charging and burning take place, and the larger diameter lower cylinder where lime cooling and the lime discharge are effected.
It features a “free flow” radial channel of adequate cross section, all around the shafts, for an unobstructed hot gas flow from one shaft to the other.
The Cim-RD kiln is also available in the FinerStone configuration.

Daily output (tons)

from 400 to 800

Fuels

gaseous, liquid and pulverised solid fuels

Reactivity of lime

high to very high

Operating principles of
a TSR kiln

The Cimprogetti TSR is a two-shaft vertical kiln which utilizes the regenerative process for lime calcination.
When one shaft operates in the burning mode, the other shaft operates in the regeneration (nonburning) mode.
Each shaft operates for an equal amount of time in the burning and regeneration modes.
There are two distinguishing characteristics of the TSR kiln:

• the parallel flow of hot gases and stone in the burning zone, which allows a mild burning of the limestone without over-burning,
• and the regenerative preheating of all combustion air using the limestone contained in the preheating zone of the kiln (in the non-burning shaft) as a heat accumulator.

The two shafts are alternately loaded from the top, with pre-weighted limestone charges.
The fuel is introduced to only one of the two shafts at a time, at the upper side of the burning zone where the material is still un-calcined and can absorb most of the heat released by the combustion.
The combustion gases travel downwards, in parallel flow with the material and leave the burning shaft through the crossover channel, entering the non-burning shaft travelling upwards in counter flow with the stone.
The off-gases then cross the freshly loaded limestone in the pre-heating zone located in the upper part of the non-burning shaft, where they transfer most of their residual heat, before being vented off at temperatures around 100 C on average.
The heat transferred by the hot gases to the fresh limestone in the non-burning shaft, is then recovered in the next cycle, from the combustion air entering that shaft from the top, when that given shaft will shift to burning mode.
The shifting between burning and non-burning modes is called “inversion” and it takes place at set intervals.
In the lower part of the TSR kiln, the hot lime lumps are progressively cooled down to temperatures below 100 C by means of cooling air introduced from the bottom of both shafts so as to be handled with standard conveying equipment.
 

 TSR process

DVD video on TSR process
can be requested
to our headoffices