Technology Roadmap Low-Carbon Transition in the Cement Industry

Excess Heat Recovery (EHR)
for power generation
EHR technologies for power generation are not 
widely deployed in the cement sector of many 
countries. EHR for power generation can be 
considered as emerging in global terms, despite EHR 
technologies being known in the sector for a long 
time. However, there are certain countries, such as 
China, India, Japan and Korea, in which domestic 
clinker production capacities are equipped with 
considerable shares of EHR to power, ranging from 
30% to almost 90%. China is the leading country 
in implementing EHR to power technologies in the 
cement sector, with almost 90% of its domestic 
clinker production capacity equipped with such 
technologies. This increased the global share to 
just above 50% in 2014, as a result of the significant 
contribution of China to global cement production 
(60% in 2014).
State-of-the-art dry-process kiln systems already 
include EHR techniques to use part of the thermal 
energy of kiln flue gases. These are used to preheat 
raw materials through a series of cyclones
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before 
entering the kiln. Additionally, the air used to 
cool the clinker can be employed as secondary 
combustion air. Thermal energy can be recovered 
in the dry-clinker-making process, depending 
on the moisture content
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of the raw materials. 
This medium-temperature
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additional recovered 
energy can be used for drying cement constituents 
(e.g. slag) or alternative fuels. The use that is most 
widespread is power generation for onsite use or 
export. Between 8 kWh and 25 kWh
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of electricity 
import savings per tonne of clinker are reported, 
depending on the dry-process kiln configuration 
and the moisture content of the raw materials (ECRA 
and CSI, 2017; Hongyou, 2015; IEA, 2016a).
30. The number of cyclones of a dry rotary kiln is determined 
by the moisture content of the raw materials, so that each 
preheating stage increases the level of thermal recovery (the 
greater the number or stages, the lower the kiln exhaust output 
temperature). Dry kilns are typically equipped with three to six 
stages of cyclones.
31. Moisture content in raw materials can reach levels even greater 
than 10% mass, in which case, the thermal recovery potential 
is significantly reduced due to the need to use most of the 
recoverable excess heat for drying. Typical commercially viable 
EHR arrangements operate with raw materials of a low moisture 
content of 2-6% mass.
32. Medium temperature in this context refers to 200-400°C.
33. Greater electricity generation levels are reported for plants 
with supportive co-firing in the boiler or by modifying the kiln 
preheater arrangement (ECRA and CSI, 2017).

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4. Carbon emissions reduction levers
The cost-competitiveness of EHR technologies 
is highly dependent on local conditions such as 
cement plant arrangement and raw material and 
fuel characteristics, electricity and fuel prices, and 
availability of suitable thermal energy users in the 
locality of the cement plant. Other factors such as 
the policy context can also influence the economics 
of EHR technologies depending on whether 
electricity exports to the grid are possible.
Global clinker capacity equipped with EHR for 
power generation increases to 65-80% by 2050 
in the 2DS. This is because electricity prices are 
increasingly driven by growing electricity demand 
in the 2DS due to greater shares of carbon-free 
power generation finding cost-effective means to 
electrify end-uses. Such EHR to power technologies 
can also provide low-carbon electricity generation 
solutions in areas with unreliable electricity 
supplies. The applicability of EHR to power 
technologies in cement plants operating with 
greater levels of moisture content can improve by 
using organic Rankine cycles (ORCs) and Kalina 
cycles. These operate at lower-temperature levels 
(benefiting from the use of thermal fluids with 
lower boiling temperatures than water) and can 
recover heat from lower-temperature sources than 
standard steam cycles.
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