Civil Engineering Reference
In-Depth Information
2010). a critical review on energy use and savings in the cement industries
can be found in Madlool et al. (2011), but the factors involved to further
reduce this demand are plant-specific, which will involve large investment.
as moisture content of the raw materials determines the heat consumption
(bauer and Hoenig, 2010; Klein and Hoenig, 2006), the main driver to
reduce energy consumption on a global average is the kiln size, which is,
in most cases, not applicable for existing installations. an increase in the
cement plant capacity could still enhance the productivity and therefore the
efficiency of cement plants. However, cement plant capacities will remain
in the typical range of between 1.5 and 2.5 million t/yr, resulting in typical
single clinker production lines between 4000 and 7000 t/day and very large
cement and clinker lines of 10,000 or even 12,000 t/d will generally be the
exception (Nobis, 2009).
As the change in cement kiln size or capacity is difficult, waste heat
recovery may play an important role. Actually 30-45 kW h/t of clinker is
becoming feasible for recovered energy and the waste heat utilization industry
itself is developing technologies to widen the potential for energy recovery.
Depending on the volume and temperature level of waste heat, a range of
specific technologies can be applied. A large quantity of low temperature waste
heat (below 350 °C), approximately 30% of the total heat consumption of the
system, is still not recovered. Several different low temperature waste heat
power generation technologies for cement production have been developed
including the steam rankin cycle with three main patterns: single and dual
pressure or flash steam generation system (Jintao et al., 2009).
1.4.3 Carbon capture and storage
The use of pure oxygen instead of air can in theory result in a very significant
improvement in thermal efficiency, because it reduces the volume of the
exhaust gases (and their associated heat losses) by a factor of about 3. It
also leads to exhaust gases that are essentially a simple mixture of CO
2
and water vapor, which could then easily be separated by condensation, the
resulting pure CO
2
then being readily transportable or directly injectable
into underground aquifers or other such potential disposal sinks. this type
of approach is currently under consideration by the electric power generating
industries for a new generation of coal burning power plants, and the cement
industry could in theory try to apply the same approach. However, the electrical
energy required to produce pure oxygen from air with current technology
is about 420 kW h/t-O
2
(eCra, 2009). If we consider that the minimum O
2
requirement is 1 mol per mol of exhaust CO
2
, this energy already represents
10-15% of the energy needed to produce clinker. Based on this, oxygen
enrichment would not actually save a lot of energy or CO
2
generation in
cement manufacture. this situation will evidently improve as the primary
