Clinker Making

Clinker is produced by sintering limestone (calcium carbonate) and clay (alumino-silicate) at elevated temperatures. The production of clinker involves the feeding of the raw meal into the kiln, where first the calcination of calcium carbonate takes place and then the resulting calcium oxide is burned at high temperatures together with silica, alumina and ferrous oxide to form clinker. 

Clinker making is responsible for 90% of the total energy consumption in cement plants.  In modern plants, hot exhaust gases are used for pre-calcination, for pre-heating the raw meal and may also be used for additional energy recovery, thereby helping to reduce energy consumption. 

Clinker MakingSchematic

Clinker MakingTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Cement Suspension Preheater Calcining Technology with High Solid-Gas Ratio

Chinese Flag Heat energy consumption for clinker making can be reduced below 2.85 GJ/t-clinker. Savings of 14.3 kg of standard coal per ton of clinker can be realized (NDRC, 2011. p.37)

Chinese Flag In a Chinese plant with 2500 tpd capacity, the installation of this technology reduced annual energy consumption by 571.5 TJ (19 500 tce) (NDRC, 2011. p.37)

Chinese Flag In a Chinese plant with 3000 tpd capacity, the installation of this technology reduced annual energy consumption by 633 TJ (21 600 tce) (NDRC, 2011. p.37)

N/A

Chinese Flag Installation of this technology in a Chinese plant with 2500 tpd capacity required an investment of 35 million RMB, and took one year to complete. The economic benefits of saved energy was about 34.5 million RMB, resulting in a payback time of around 1 year (NDRC, 2011. p.37)

Chinese Flag Installation of this technology in a Chinese plant with 3000 tpd capacity required an investment of 35 million RMB, and took one year to complete. The economic benefits of saved energy was about 37.2 million RMB, resulting in a payback time of 10 months (NDRC, 2011. p.37)

Commercial
Waste Heat Recovery for Power Generation

Typically, 8–22 kWh/t-clinker can be produced without changes to kiln operation. Generation up 45 kWh/t clinker is possible by modifying kiln operations (e.g. less cyclone stages or by-passing upper stage(s) (CSI/ECRA, 2009. p. 31)

Chinese flag In China, production potential is reported to be around 24-32 kWh/t-clinker using domestic technology and 28-36 kWh/t-clinker using foreign technogly.  39 kWh/t-clinker is achieved in a Chinese plant using Japanese technology

Japanese flag Japanese technologies are reported to be able to produce 45 kWh/t clinker. 

Indian flag The potential for Indian plants are reported to be 20-24 kWh/t clinker.  

Chinese Flag 48.5 GWh/y of net electricity production was projected for a 8 MW WHR unit installed at a 4500 tpd plant in China (UNFCC, 2008).

Indian flag The 8 MW power plant installed by the Indian Cements Ltd. (for their 4500 tpd plant) has been reported to reduce the CO2 emissions by 45 000 tons per year (PCA, 2008). 

Chinese Flag With the installation of a 9 MW WHR plant to a plant with 5000 tpd capacity, annual CO2 emission reductions in excess of 52 000 ton year is planned (UNFCC, 2007)

Chinese Flag 41 000 t CO2/y reduction is expected with the installation of an 8 MW waste heat recovery unit in a 4500 tpd plant in China. 

For a plant with 2 millon t-clinker/y capacity, installation costs are estimated to be between € 15-25 million. Operational costs are estimated to decrease by €0.3–1.2/t-clinker (CSI/ECRA, 2009. p.32).

Chinese flag Investment per kW are estimated to be about 6000-10000 RMB (US $ 940 - 1570) for Chinese technology and 16,000 - 22 000 RMB (US $2500 to 3400) for foreign technology for China.  Estimated payback periods are usually less than 3 years.  

Chinese flag For China it was estimated that  for a 2000 ton per day (730,000 annual ton) kiln capacity, about 20 kWh/t clinker of electricity could be generated for an investment of 20 to 30 million RMB (US $ 3.1 to 4.7 million).

Indian flag For India, investment costs are given to be around $2.25 million per MW capacity. Indian Cements Ltd. has put up an up to 8 MW power plant using Japanese technology for its 4500 tpd plant for a total investment of US $ 18.7 million (PCA, 2008).  

Chinese Flag The installation cost of the 8 MW WHR unit in a 4500 tpd plant in China is reported to be RMB 58.8 million. The project is reported to have an IRR of 6.65% (the IRR value is stated to be 17.08% with carbon credits) [2008 values]. (UNFCC, 2008)

Commercial
Process Control and Optimization in Clinker Making

Savings vary between 2.5 to 10% and typical values are estimated to be 2.5 to 5%.

Chinese flagFor modern dry kilns with capacities more than 2500 tpd, savings are reported to reach 0.29 GJ/t-clinker (NDRC, 2012. p.66)

Chinese flagIn a 4500 tpd Chinese plant, annual energy consumption was reduced by 395.6 TJ (13500 tce) with the installation of a process control and optimization system (NDRC, 2012. p. 66)

Chinese flagIn a 4000 tpd Chinese plant, annual energy consumption was reduced by 351.7 TJ (12000 tce) with the installation of a process control and optimization system (NDRC, 2012. p. 66)

The costs of process control optimization measures/techniques vary widely and can be up to $6.8 million [1€=$1.35 US] 
The economics of advanced process control systems are very good and estimated payback periods can be as short as 3 months. In general, estimated payback period is less than 2 years.

Chinese flagIn a 4500 tpd Chinese plant, installation of a process control and optimization system required an investment of 980 thousand RMB, and took one month. The system provided annual savings of 8 million RMB, resulting in a payback time of 2 months (NDRC, 2012. p. 66).

Chinese flagIn a 4000 tpd Chinese plant, installation of a process control and optimization system required an investment of 990 thousand RMB, and took one month. The system provided annual savings of & million RMB, resulting in a payback time of 1.5 months (NDRC, 2012. p. 66).

Commercial
Combustion System Improvements

Specific fuel savings up to 8% have been realised in plants using Gyro-Therm technology.  

Another technique developed in the UK for flame control resulted in fuel savings of 2 to 10% depending on the kiln type.

The payback times for Gyro-Therm technology is expected to be less than one year. 

Costs are estimated to be around $1.0/annual ton clinker capacity, with estimated payback periods of 2-3 years.

Commercial
Dry Kilns with Multistage Pre-heaters and Pre-calcination

Fuel savings up to 3.0 GJ/t-clinker can be realized. Electricity consumption can increase by around 9 kWh/ton clinker.

In a case in UK, two wet process kilns with a total heat requirement of 5.65 GJ/t-clinker were replaced with a single pre-heater/pre-calciner kiln resulting in energy saving of 36% (down to 3.5 GJ/t-clinker).

Emission reductions are estimated to be:

Chinese flag 284 kg CO2/t-clinker in Chinese context.

Indian flag 297 kg CO2/t-clinker in Indian context

US flag 233 kg CO2/t-clinker in the United States.

Commercial
Conversion of Long Dry Kilns to Preheater/Precalciner Kilns

Up to 1.4 GJ/t-clinker can be saved.

For every ton of clinker, following amounts of CO2 reductions are estimated: 

Chinese Flag

 132.4 kg in Chinese context;

Indian flag 138.5 kg in Indian context;

US flag 108.8 kg in the United States.

Upgrading costs are reported to be between US $8.6 to $29 per annual ton of clinker capacity.  

Commercial
Kiln Shell Heat Loss Reduction

Fuel consumption is estimated be reduced by around 0.12 to 0.4 GJ/t of clinker. 

 in China, switching to better refractories may reduce CO2 emissions by 11 to 38 kg per ton of clinker. 

Switching to higher quality refractories may cost around US $0.25/annual tonne clinker capacity. Estimated payback period is approximately 1 years.

Commercial
Addition of Pre-Calcination to Kilns with Preheaters

In an Italian plant, the conversion reduced specific fuel consumption from 3.6 to 3.1-3.2 GJ/t clinker, resulting in savings of 11 to 14%, and enabled a capacity increase of 80 to 100% (from 1100 tpd to 2000 to 2200 tpd). 

Chinese flag For Chinese context, this option holds the potential to reduce CO2 emissions by 38 to 47 kg for every ton of clinker produced. 

Investments in the range of US $9.4-28 per annual ton clinker may be required. Payback times are usually less than 5 years.  

Indian flag In India, the payback times are reported to be less than 3 years. 

Commercial
Replacing Vertical Shaft Kilns

Savings up to 2.4 GJ/t clinker can be obtained. 

Indian flag Savings of  1.6-2.0 GJ/t clinker are reported from India depending on pre-heater/pre-calcination system configuration

Chinese flag In China, CO2 emissions can be reduced by 227 kg/t clinker by converting VSKs to pre-heater/pre-calciner kilns.  

Costs of such conversions can be between US $28-41 per annual ton of clinker production. 

Commercial
Low Pressure Drop Cyclones for Suspension Preheaters

Power savings in the range of  0.7-4.4 kWh/t clinker  depending upon feasibility of cyclone  modification and  fan efficiency. 

Indian flag In India, average savings are reported to be 1.5 kWh/t clinker. 

Chinese flag Use of this option may reduce CO2 emissions by 0.5 to 3.5 kg per ton of clinker produced. 

indian flag Based on the average savings of 1.5 kWh/t clinker, use of this technology reduces CO2 emissions by 1.2 kg per ton of clinker produced. 

The cost of a low-pressure drop cyclone system is assumed to be US $3 per annual ton clinker capacity.  Installation of the cyclones can be expensive, since it may often entail the rebuilding or the modification of the preheater tower, and the costs are very site specific. 

Commercial
Additional Preheater Cyclone Stages

Moving from 4 stage to 5 stage, or from 5 stage to 6 stage can reduce the specific heat energy consumption between 0.08 to 0.1 GJ/t clinker

Indian flag In India reductions between 0.06 to 0.1 GJ/t clinker are reported.  

Chinese flag CO2 emissions can be reduced by 7.6 – 9.5 kg/t-clinker.

Indian flag  CO2 emissions can be reduced by 7.9 – 9.9 kg/t-clinker.

Commercial
High Efficiency Fans for Preheaters

0.7 kWh of electricity can be saved for each ton of clinker produced. 

Indian flag In India savings in the range of 0.3-.0.5  kWh/ton clinker are reported depending on generation of existing fan. 

CO2 emissions can be reduced by: 

Chinese flag 0.55 kg CO2/t-clinker

indian flag 0.57 kg CO2/t-clinker

Capital costs of US $0.01 per annual ton of clinker capacity are reported. 

Commercial
Bucket Elevators for Kiln Feed

Following savings in electricity consumption are reported in literature: 

  • 2.26 kWh/t-clinker (UNFCC)
  • 2.5 kWh/t-portland cement (US-EPA)

Indian Flag In India savings in the range of 1.0-1.3 kWh/t of clinker are reported. 

Following cost informatin is provided in the literature: 

  • US $0.23 per annual ton clinker capacity (UNFCC)
  • US $3.43 per annual ton portland cement capacity (US-EPA)

Indian flag In India Installation costs of this technology is reported to be US $4000-5000 per meter. 

US-EPA reports a US $0.17/ton-portland cement reduction in operating costs. 

Commercial
Fluidized Bed Advanced Cement Kiln System

Thermal energy use can be decreased by around 0.4 GJ/t-clinker (NEDO, 2006), while the electricity consumption increases by around 9 kWh/t-clinker (ECRA, 2009)

20% more heat can be recovered in the cooling system, as compared to conventional methods (APP, 2009)

CO2 reductions in the range of 10% can be realized (NEDO, 2006). 

Demonstration
Efficient kiln drives

0.5 – 1% reduction in electricity use of the kiln drive can be achieved  by replacing a DC motor with AC motor.

Using high-efficiency motors to replace older motors, or instead of re-winding old motors, may reduce power costs by 2 to 8%. 

Electricity savings are  0.55-3.9 kWh/t clinker 

The capital cost for single pinion drive with an air clutch and a synchronous motor is around 6% higher than standard kiln drive.

Commercial
Improved Burnability Using Mineralizers

Based on the modelling results, thermal energy consumption can be reduced by between 0.05 to 018 GJ/t clinker. 

CO2 emissions can be reduced by 4 to 16 kg per ton of clinker

Additional costs of mineralizers has to be considered and may outweigh the fuel cost savings.  Espeically CaF2, which is commonly used, is an expensive material.  Use mineral wastes containing flourides can be economically viable, however, such materials have a limited availability. 

Commercial
Alkali Bleed (alkali by-pass) SystemsCommercial
Oxygen enrichment technology

Thermal energy use can be decreased by 0.1 - 0.2 GJ/t clinker but electricity use increases by 10 - 35 kWh/t clinker

While this technology may reduce direct CO2 emissions by 10 to 20 kg per ton of clinker due to reduced fuel consumption, the indirect emissions are estimated to rise by 15 to 25 kg/t clinker due to increased electricity use. 

Demonstration
Using modern multi-channel burners

Depending on the secondary air temperature, reduction of the primary air ratio by 5-10% will lead to a fuel energy saving of 0.05-0.08 GJ/t-clinker at conventional kilns and about half of this at precalciner kilns. The electrical energy demand will remain almost unchanged as the higher consumption for control fittings and air delivery channels can be offset by the reduction of the primary air.

Chinese flagFour channel pulverized coal injection burner is expected to reduce primary air usage by 4% and reduce kiln energy consumption by 0.020 GJ/t-clinker (NDRC, 2009. p.44).

Chinese flagBy replacing the existing burner in a 2500 tpd kiln with a four channel pulverized coal injection burner and making necessary adjustments in their fan, Hunan Yintaishan Cement Co. Ltd. reduced its annual energy consumption by 16.2 TJ (553 tce) (NDRC, 2009. p. 45)

Chinese flagBy retrofitting a more efficient burner in a 2500 tpd kiln, Ningxia Qingtongxia Cement Co. Ltd., reduced its energy consumption by 17 TJ/y (583 tce/y) (NDRC, 2009. p. 45)

Chinese flagBy retrofitting a more efficient burner in a 5500 tpd kiln, Hebei Yanzhao Cement Co. Ltd., reduced its energy consumption by 35.7 TJ/y (1218 tce/y) (NDRC, 2009. p. 45)

Chinese flagFour channel pulverized coal injection burner is expected to reduce NOx emissions by 41% (NDRC, 2009. p.44).

Chinese flag In Hunan Yintaishan Cement Co. Ltd., retrofitting a four channel pulverized coal injection burner and making necessary fan adjustments in a 2500 tpd kiln took three days and costed 0.5 million RMB. The retrofit provides annual savings of 0.44 million RMB and had a payback time of 1.1 years (NDRC, 2009. p.45).

Chinese flag In Ningxia Qingtongxia Cement Co. Ltd., retrofitting a new burner in a 2500 tpd kiln took one month and costed 0.47 million RMB. The retrofit provides annual savings of 0.47 million RMB and had a payback time of 1.2 years (NDRC, 2009. p.45).

Chinese flag In Hebei Yanzhao Cement Co. Ltd., retrofitting a new burner in a 5500 tpd kiln took three days and costed 0.6 million RMB. The retrofit provides annual savings of 0.83 million RMB and had a payback time of 9 months (NDRC, 2009. p.45).

Commercial
Stabilization of Kiln Coating

Radiation heat losses will be reduced leading to energy savings. 

Commercial
Indirect firing

Assuming a reduction of excess air between 20% and 30%, indirect firing may lead to fuel savings of  0.015 -0.022 GJ/t  clinker. 

The advantages of improved combustion conditions will lead to a longer lifetime of the kiln refractories and reduced Nox emissions. These co-benefits may result in larger cost savings than the energy savings alone.

US $5 million for an annual production capacity of 680,000 ton clinker, or US $7.4/t annual clinker capacity.

Commercial