As (Fe2O3). The next stage is grinding clinker with

As describe of Fig. 1.6 cement production is
combining with multistage process that linked with several activities (Saidur
et al., 2011 and Kaantee et al., 2004). Clinker is the main ingredient of the
cement and clinker is produced from limestone and some additives, which are
crushed, homogenized and fed into a rotary kiln. For clinker burning process
material temperature needs to be 14500C (Aranda et al., 2013), which
is needed to form the new compounds. Clinker is mainly consist with calcium
(Ca), silica (SiO2), aluminium (Al), and iron oxides (Fe2O3).
The next stage is grinding clinker with gypsum and other materials such as
slag, ?y ash, pozzolans, or residues from other industries such as steel
production materials (Bernardo et al., 2007). All constituents are ground
leading to a fine and homogenous powder called cement.

Figure 1.6 Flow diagram of the cement manufacturing
process, including the points of energy consumption and emissions.

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Emission

Energy

 

1.2.3       
Energy
consumption in the cement manufacturing process

According to Fig. 1.6 energy is an influential
feature of the cement manufacturing process and it’s involving in every stage
of the process. According to Hendriks er al., 2002 and Zeman and Lackner, 2008
approximately 1750 MJ of thermal energy consumptive for production of 1 tone
Portland cement clinker, and this value has been gained from a theoretical
period of opinion.  Though, Szabo et al,.
2003 emphasizes that energy requirement is depending on the technology that is used
by manufacturing plant and especially kiln technology will directly effect the
final energy value.

There are two types of cement manufacturing process
such as dry process and wet process. Nevertheless, Table 1.4 emphasize dry
manufacturing process leading energy saving process with compared to wet
production process (Szabo et al., 2003 and Damtoft et al., 2008). Because in
wet process the raw material is fed into kiln as a slurry, therefore more
energy needs for the water evaporation process. This resulted to consumptive of
more energy. As well as using of pre heaters and calciners will effected to
energy savings (Taylor et al., 206)

Table 1.4 Ranges in the thermal
energy consumption and quanti?cation of the fuel-derived CO2
released (from traditional fuels) per ton of clinker depending on the type of
kiln technology. (Source: Szabo et al., 2003 and Damtoft et al., 2008)

Kiln
technology

MJ/t
of clinker

kg
fuel-derived CO2/kg of clinker

Dry rotary kiln with pre-heater
and pre-calciner

3000–4000

0.31–0.38

Dry rotary
kiln with pre-heater

3100–4200

 

Dry long rotary kiln

Up to 5000

0.4–0.6

Semi-dry rotary kiln

3400–4000

 

Wet rotary kiln

5000–7500

 

Shaft kiln

3100–6500 and higher

No data found

 

1.2.4       
CO2
emissions from the cement industry

There are two main sources of CO2 emissions
to the environment in the cement industry, such as, energy used for the fuel
combustion for burning the clinker and running the pre-heaters and other
operations. The next source is the natural release of CO2 in the
production of clinker process under inordinate heat (Ali et al., 2011, Kim et
al., 2002, Hendriks et al., 2002 and Taylor et al., 2006)

However, according to the cement sustainability
initiative 2002, there are other petty sources that should also be counted when
focusing on the sustainable cement production. Quarrying of raw materials and
their transportation, grinding, and packing are contributing to the CO2
releasing into the environment in subordinate level (Habert et al., 2010)

Figure 1.7
Simpli?ed cement manufacturing process and associated CO2 emission
sources, and their relative magnitudes (denoted by the widths of the arrows)
(Source: Habert et al., 2010)

 

The raw material calcination process and cement
production

The
calcination process can be declared as following reaction (Stefanovic et al.,
2010).

XCO3 + Heat              XO + CO2

In this reaction X usually denoted as Ca and Mg.
Therefore, the MgCO3 and CaCO3 are converted into CaO or
MgO, these are the main component of clinker. In the CaCO3 burning process huge
quantities of CO2 given off into the surroundings. This amount of CO2
directly proportional to the CaO quantity of the clinker. Roughly 65% of the
clinker is consisted with CaO or MgO (Van Oss et al., 2003). Furthermore,
quantity of CO2 emissions in cement production process depends on
some other factor related to clinker/cement ratio, which is varied from 0.50 to
0.95. Thinning of this ratio desired to mitigate the emission per ton of
cement. Considering of these statuses, an average of 0.50 – 0.53 kg of CO2
is produced per kg clinker (Hendriks et al., 2002 and Van Oss et al., 2003).