Green Economy in the Cement Industry Part 7: Use of Biomass Fuel Apart from Clinker Substitution in Cement Plants

Cement plants are unique or different compared to processing plants or other industries, namely that the majority of carbon emissions (CO2) are produced not from fuel use but from clinker production. CO2 emissions from clinker production reach 60%, while from fuel use it is only 40%. This indicates that decarbonization efforts in cement plants must prioritize these two things. 

The use of cement additives or SCM (supplementary cementious material) as a substitute for clinker has played a major role in decarbonization in cement plants. The greater the use of SCM or the smaller the clinker to cement ratio, the smaller the carbon emissions in cement production. The use of SCM is generally used in cement production in plants, but there is use of SCM in concrete production, even in a larger portion than in cement production, which is common in the United States.

Cement plants in general are major users of coal with large volumes so they must be gradually reduced as part of decarbonization efforts. Regarding carbon emissions from the use of this fuel, many cement plants use alternative energy such as used tires or RDF from municipal solid waste (MSW). Ideally, the use of renewable fuels will reduce carbon emissions significantly. This is why a number of cement plants have started using biomass fuel such as agricultural waste or wood waste from wood working industries. The greater the portion of renewable fuel used, such as agricultural waste biomass and such wood industry, the lower the carbon emissions produced.

The use of technology to increase fuel efficiency also reduces carbon emissions, such as the use of preheaters and precalciners, because there is savings in fuel use in clinker production. But there are also certain specific conditions, for example the production of type II/V or type V cement (high sulfate resistance) will require more fuel because cement requires clinker with a low C3A (tricalcium aluminate) content, the process of which requires more heat energy.

The analogy to a coal-fired power plant in decarbonization efforts is more or less the same as a cement plant. Coal power plants are industries that produce large carbon emissions, like cement plants. At coal-fired power plants, decarbonization efforts begin by cofiring coal with biomass. The biomass ratio in the cofiring continues to be increased over time. The greater the cofiring ratio or biomass portion, the lower the carbon emissions. At a certain level, the coal power plants will be 100% replaced with biomass (fulfiring).

If efforts to become zero carbon emissions (net zero emissions) in coal power plants can be done by converting the fuel into 100% biomass, then in cement plants it cannot be done simply by replacing the fuel with biomass because the main source of carbon emissions in cement plants is in the clinker production. That is why in cement plants the use of SCM to substitute clinker, the ratio or portion must also be increased. Maximizing biomass fuel use and using SCM also cannot reduce carbon emissions to zero (net zero emissions), because of the calcination process. This is why to achieve net zero emissions in cement plants it is necessary to add CCS (carbon capture and storage) unit.

Ideally, when a coal-fired power plant converts 100% of its fuel to biomass, the carbon emissions are zero (net zero emissions) and if CCS equipment is added, it becomes carbon negative emissions. Meanwhile, in cement plants, the use of optimum SCM and 100% biomass fuel still cannot achieve zero carbon emissions, so CCS equipment needs to be added to capture CO2 from the calcination process to achieve zero carbon and if want to achieve carbon negative emission conditions, CCS is also needed to be used to capture CO2 from burning or using biomass fuel.