24
Technology Roadmap
Low-Carbon Transition in the Cement Industry
A theoretical minimum energy requirement of
1.85-2.80 GJ/t clinker is defined by chemical and
mineralogical reactions and drying needs, which
vary depending on the moisture content of the raw
materials (ECRA and CSI, 2017).
Long-dry-process kilns can be retrofitted to
incorporate a precalciner and multistage preheater
19
to dry and precalcine raw materials with recovered
process excess heat before they enter the kiln.
Different strategies can be implemented to improve
the thermal
energy intensity of clinker, beyond
operating state-of-the-art kiln technology. These
include increasing the burnability of raw materials
by adding substances called mineralisers, which
lower the viscosity and the temperature at which
clinker melt begins to form. Operating the kiln
with oxygen-enriched air can lead to up to 5%
thermal energy savings (ECRA and CSI, 2017). In
comparison with
planetary and rotary coolers, grate
clinker coolers enable greater EHR from hot clinker,
which can be used for drying of raw materials
when integrated with a precalciner (equivalent to
0.1-0.3 GJ/t clinker energy savings) or for enabling
electricity generation (ECRA and CSI, 2017).
Some of these strategies have an impact on the
electricity intensity of cement due to side effects.
For instance, the addition of mineralisers may
worsen the grindability of clinker.
Other strategies,
such as installing a precalciner, increasing the stages
of the preheater or upgrading the clinker cooler,
involve additional electricity needs to operate
the new or upgraded equipment. These could be
offset in specific terms, as many of these measures
increase the clinker production capacity.
Electricity in cement production
is used for cement
grinding (31-44%), raw material grinding (26%),
fuel grinding (3-7%) and clinker production
(28-29%), with solid fuel grinding, cement loading
and packaging accounting for the remainder
(ECRA and CSI, 2017; Madlool et al., 2011). The
use of efficient grinding and milling technologies
decreases the global electricity intensity of cement
by 14% by 2050 compared to 2014 in the 2DS.
The state-of-the-art grinding technologies
considered in the analysis are high-pressure grinding
rolls and vertical roller mills. These can theoretically
19. An additional cyclone stage in a multistage preheater can result
in a thermal energy intensity reduction of 0.08-0.10 GJ/t clinker.
However, this is only possible if the raw material moisture
content is below that which the
preheater design considered,
and if there are no dimensional constraints on the site (ECRA
and CSI, 2017).
provide up to 50% (high-pressure grinding rolls)
and 70% (vertical roller mills) electricity savings
compared to the current widely used ball mills
(ECRA and CSI, 2017). Electricity demand for cement
grinding is highly dependent on product quality
requirements. The higher the strength class needed,
the finer the cement needs to be ground. Therefore,
in-field achievable electricity savings from installing
an efficient grinding technology rely on product
fineness requirements. Other electricity saving
strategies include cross-cutting measures such as
upgraded cement process
controls and the use of
variable speed drives to run mechanical equipment
across the site (e.g. grinding machines, fans, solid
matter transport or kiln rotation).
Energy efficiency improvements are offset by
additional energy requirements related to the use
of other carbon mitigation levers. For instance, a
greater use of alternative fuels (from 6% to 30%
globally by 2050 in the 2DS), typically with lower
calorific content, results in an increased specific
thermal energy demand of clinker (an
additional
0.11 GJ/t clinker globally by 2050 in the 2DS).
The reduction of the clinker to cement ratio can
also incur an additional energy demand, such
as the need to calcine raw clays used as cement
constituents. This is estimated to result in almost an
additional 0.35 GJ/t clinker produced by 2050 in the
2DS globally, or around 11% of the global average
thermal energy intensity
of clinker in that year
(Figure 8).
The integration of carbon capture
20
equipment
in cement plants
21
in the 2DS similarly leads to
additional electricity demand and thermal energy
use, with thermal energy use being specific
to post-combustion capture technologies to
regenerate the saturated sorbent. For instance,
capturing CO
2
from cement plants in the 2DS
globally results in an additional 15-19 kWh/t cement
or 19-24% of the electricity
intensity of cement
production considering only efficiency gains by
2050. Environmental regulations to lower dust and
emissions of nitrogen oxides and sulphur dioxide also
lead to higher cement-specific electricity demand
levels, as additional electricity is required to operate
emissions avoidance or abatement equipment.
20. See the section below discussing carbon capture technologies
for details of the technologies.
21. The 2DS vision considers CO
2
emissions capture starting
commercial-scale deployment in 2030.
