Use of Alternative Fuels

Conventional fuels like hard coal and lignite that are commonly used fuels in cement production have high specific CO2 emission values (Hard coal: ~95 kg CO2/GJ; Lignite: ~98 kg CO2/GJ). Consequently, substituting these with other fuels  having lower specific emssion values (e.g. fuel oil or natural gas) or with other sources that can satisfy the thermal demand of the processes is an effective way of reducing CO2 emissons. Table below provides an overview of alternative fuels that can be used in Cement kilns. 

Alternative Fuels for Cement Kilns (Kääntee et al., 2002)
Phase of Fuels Possible streams
Liquid alternatives Tar, chemical wastes, distillation residues, waste solvents, used oils, wax suspensions, petrochemical waste, asphalt slurry, paint waste, oil sludge.
Solid state alternatives Petroleum coke (“petcoke”), paper waste, rubber residues, pulp sludge, used tires, battery cases, plastics residues, wood waste, domestic refuse, rice chaff, refuse derived fuel, nut shells, oil-bearing soils, sewage sludge.
Gaseous alternatives Landfill gas, pyrolysis gas

Principally, in cement kilns conventional fossil fuels can be substituted up to 100% by alternative fuels. Nevertheless, there are certain technical limitations like the calorific value, the moisture content, and the content of side products like trace elements or chlorine. The calorific value of most organic material is comparatively low (10 – 18 GJ/t). For the main firing of the cement kiln an average calorific value of at least 20-22 GJ/t is required, meaning that high calorific alternative fuels are mostly used in the main firing.

In some European countries the average substitution rate reaches more than 50% for the industry sector and up to 80% as yearly average for single cement plants. Biomass share in pretreated industrial or domestic wastes can come up to 30 or 50%. Pure biomass waste fuels used in the cement industry today are mainly animal meal, waste wood, sawdust and sewage sludge. 

While the use of alternative fuels contribute to reductions in CO2 emissions, they do not reduce the actual energy demand.  On the contrary, both the thermal and electrical energy demand may increase by 0-0.3 GJ/t-clinker and 0-3 kWh/t-clinker, respectively, due to the use of alternative fuels.  

Use of Alternative FuelsTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Refuse Derived Fuel (RDF) Co-processing

For every ton of RDF, fossil fuels corresponding to 15 to 19 GJ can be saved. 

For every ton of RDF, following amounts of CO2 reductions can be realized due to avoided coal burning:

Chinese flag 1.42 – 1.80 ton

Indian flag 1.48 – 1.88 ton

US flag 1.17 – 1.48 ton

Japanese flag In Japan, installation costs for facilities to process 10 t/d of RDF were reported to be approximately US $650 thousand (1US$=¥110). 

The economics of RDF usage can be significantly influenced by the availability and level of gate fees. 

Commercial
Used Tyres as FuelFor every ton of waste tyres used, fossil fuels corresponding to 25 to 29 GJ can be saved.In Japan, a system that aligns the tyres and feeds them at a constant rate to the kiln, or to another furnace, with a capacity of 10 000 t/y was installed at a cost of US $2.7 million (1 US$ = ¥110). Commercial
Waste Oil and Oil Sludge as Fuel

For every ton of waste oils used, fossil fuels corresponding to about 21.6 GJ can be saved. 

For every ton of waste oils used, following amounts of CO2 can be saved due to avoided coal use: 

Chinese flag 2.04 ton

Indian flag 2.14 ton

US flag 1.68 ton

In Japan, installation costs for storage and processing facilities for about 10,000 t/y costed about US $730  thousand (1US$=¥110)

Commercial
Use of Waste Plastics as Fuel

Depending on its exact composition,  for every ton of plastic waste used, fossil fuels corresponding to 17 to 42 GJ can be saved.

Due to high variations of different plastics, many of which are derived from fossil resource, estimations of CO2 emissions are hard to generalize.

In Japan, a system to process and feed 10 000 t/y of plastics was installed at a cost of US $3.6 million (1US$=¥110)

Commercial

Use of Alternative Fuels Publications

Development of State of the Art Techniques in Cement Manufacturing: Trying to Look Ahead

The report represents the independent research efforts of the European Cement Research Academy (ECRA) to identify, describe and evaluate technologies which may contribute to increase energy efficiency and to reduce greenhouse gas emissions from global cement production today as well as in the medium and long-term future. 

Page Number: 

42-43

Use of Alternative Fuels Tools

Sewage Sludge Use in Cement Companies as an Energy Source (SUCCESS) Tool

Chinese Flag This Excel-based tool serves to assist decision makers in implementing sludge-end-use-in-cement schemes with optimal economic and environmental outcomes. The environmental and economic costs and benefits associated with burning sewage sludge in cement kilns will vary based on the energy content of the sludge (lower heating value) and the transportation distance between the wastewater treatment plant and proposed cement plant.

Use of Alternative Fuels Conference Papers