Civil Engineering Reference
In-Depth Information
for single cement plants. As fuel-related CO
2
emissions are about 40% of
total emissions from cement manufacture, the CO
2
reduction potential from
alternative fuel use can be significant.
although, technically, cement kilns could use up to 100% of alternative
fuels, there are some practical limitations. the physical and chemical properties
of most alternative fuels differ significantly from those of conventional fuels.
While some (such as meat-and-bone meal) can be easily used by the cement
industry, many others can cause technical challenges. these are related to, for
example, low calorific value, high moisture content, or high concentration of
chlorine or other trace substances. For example, volatile metals (e.g., mercury,
cadmium, thallium) must be managed carefully, and proper removal of CKD
from the system is necessary. This means pre-treatment is often needed to
ensure a more uniform composition and optimum combustion. However,
the achievement of higher substitution rates has stronger political and legal
barriers than technical ones:
∑ Waste management legislation significantly impacts availability: higher
fuel substitution only takes place if local or regional waste legislation
restricts land-filling or dedicated incineration, and allows controlled
waste collection and treatment of alternative fuels.
∑ Local waste collection networks must be adequate.
∑ alternative fuel costs are likely to increase with high CO
2
costs. It may
then become increasingly difficult for the cement industry to source
significant quantities of biomass at acceptable prices.
∑ The level of social acceptance of co-processing waste fuels in cement
plants can strongly affect local uptake. People are often concerned about
harmful emissions from co-processing, even though emissions levels
from well-managed cement plants are lower with alternative fuel use
(rovira et al., 2010). In addition, alternative fuel use has the potential to
increase thermal energy consumption, for example when pre-treatment
is required as outlined above.
Alternative cementitious materials
another option to reduce the environmental impact of cement production
is to reduce the amount of clinker in the cement. this option allows a cost
reduction in the cement manufacturing process by saving burning costs and
is a highly efficient CO
2
reduction way. the next chapters will describe the
different materials that can be used to develop these low clinker cements. In
this section we will discuss the question associated with the environmental
evaluation of these alternative cementitious materials. according to ISO
standards, when a production system produces more than one product, it
is necessary to attribute an environmental burden to each product. this is
