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.      

Green Economy in the Cement Industry Part 4

The cement plants apart from being an industry that utilizes or processes waste such as slag and fly ash so that a circular economy pattern is formed, is also an industry that destroys waste by using it as fuel. RDF (Refuse Derived Fuel) from municipal solid waste (MSW) is an alternative energy source that is widely used by the cement industry, especially in the manufacture of clinker. In addition to helping overcome environmental problems in the form of environmental pollution from city waste, the use of RDF  also helps reduce carbon emissions or is part of the effort to decarbonize. Related to addressing environmental problems, alternative fuels such as used tires which are chopped into tire chips and plastic are also often used. In addition to these alternative fuels, biomass waste such as agricultural waste and livestock waste are also being used. The biomass waste is 100% renewable fuel, so it is more compatible and environmentally friendly. The use of agricultural waste such as rice husk and camel manure is an example of the use of this biomass waste, for more details, read here.

By operating at high temperatures, the cement plant can function as an effective waste destroyer. In this regard, a DRE (Destruction Removal Efficiency) test is required which must meet a very high score or nearly 100% (99.9999%) to be able to carry out the waste destruction activity. The failure to reach this value is due to the insufficiently high temperature, so the consequence is that not all facilities in the cement plant are able to destroy or burn the waste, only burners in kilns that operate above 1200 degrees Celsius can do it, which technically is waste or alternative fuel also has its own feeding point.

Apart from the power failure, cement plant operations can stop due to blocking. The blocking clogs the cyclone on the preheater and calciner. The main cause of blocking occurs is due to the sulfur content, especially from coal and petcoke or alternative fuels that have a high sulfur content such as tires (tyre chips, the sulfur then reacts with the alkali to form compounds that easily stick to the walls of the cyclone or even the kiln. This means that the percentage of sulfur needs to be limited. And the second cause of blocking is chlorine, which also reacts with alkali so it easily sticks to the walls of the equipment, but the difference is blocking because chlorine occurs at a lower temperature, so it sticks to the top of the cyclone. This means that the percentage of chlorine also needs to be limited.

Based on the conditions mentioned above, the use of alternative fuels, especially from renewable materials, is important, moreover, renewable fuels such as biomass have very low sulfur content, as well as chlorine, but certain alternative fuels must be calculated carefully, especially sulfur and chlorine content. , so no blocking occurs. Meanwhile, fossil fuels such as coal and petcoke apart from being cons of decarbonization efforts also turn out to be the main cause of blocking. This means that the use of fossil fuels must be further reduced.  

Green Economy in the Cement Industry

The trend of decarbonization, including the low carbon economy, has penetrated various sectors, including the cement industry. Cement is the most common human-made product in the world, consuming about 0.5 tons per person per year. The cement industry is also a significant contributor to greenhouse gases, reaching 21% (IPCC 2014), with these conditions making it one of the biggest contributors to climate change. And because the cement industry has a history as a major contributor to these greenhouse gas emissions, there are opportunities today to reduce emissions significantly through increasing efficiency and innovation in the industry.

Increasing energy efficiency in cement production will reduce the resulting carbon emissions. Even in the cement industry, the use of energy is also slowly starting to be used as renewable energy or alternative energy, including the use of RDF from municipal waste or household waste, which more or less reduces environmental pollution. While in the production aspect the use of additional materials originating from other industrial waste (circular economy) such as slag and fly ash or SCM (supplementary cementious materials) has also been widely used. The addition of these materials depends on the type of cement to be made and aims to reduce the use of clinker because clinker production requires high costs and produces CO2 gas as a result of calcination. For example, the manufacture of slag cement produces 38% less CO2 emissions than the process for the production of portland cement because less limestone is burned for the production of slag cement than is required for Portland cement. In addition, a number of countries also support the production and use of slag cement in order to support environmentally friendly products. The things above also indicate concern for the environment and sustainability is increasing.

In the cement industry, about 50% of emissions come from the calcination process itself, 40% from fuel for heating the kiln, and the remaining 10% from grinding and transport. Inside the calciner, a calcination process occurs, namely the decomposition of CaCO3 into CaO and CO2 and a little MgCO3 into MgO and CO2. Because the calcination reaction is endothermic, high heat is required, so it is equipped with a burner for burning coal utilizing tertiary air from the cooler and hot gas from the kiln. The release of CO2 due to the reaction in the calciner is a crucial environmental issue in the cement industry, the volume of CO2 gas from calcination is much greater than CO2 from burning fuel (coal) or 50% to 40%.

Various types of cement with different qualities often require specific SCM qualities as well. Under these conditions the review is not only general specifications but down to the chemistry of the material. For example slag from a steel plant or Granulated Blast Furnace Slag (GBFS) with a certain chemical content or fly ash but with a low alkaline content or slag from a nickel smelter not suitable for certain types of cement and so on. To obtain specific SCM such as slag and fly ash is closely related to the particular source of slag and fly ash, although in some cases it is possible to add certain materials to obtain the desired chemical composition.

And in the cement industry, emissions are not easily reduced. Emissions from processes cannot be reduced by optimizing or using only renewable energy or alternative energy. In the cement industry, when following the scenarios developed by the International Energy Agency (IEA) or the Intergovernmental Panel on Climate Change (IPCC), it is clear that to reach the limit of 2 C or even 1.5 C, cabon capture and storage / carbon capture and utilization (CCS / CCU) is needed. However, more is needed if the industry is to meet the ambitious goals set by the Paris agreement. The cement industry is particularly challenged by this target because carbon is generated by the energy used in the process and the calcination process itself. Even if energy-based emissions could be eliminated by switching to carbon-neutral fuels, those calcination process emissions would still be present and would require a carbon capture unit (CCS/CCU).

Europe has become a research center for carbon capture and storage (CCS) and carbon capture and utilization (CCU). From a number of carbon capture technologies, amine-based absorption (organic compounds and functional groups whose contents consist of lone-paired nitrogen atoms) is the most advanced carbon capture technology and has been implemented on a commercial scale. Carbon capture technology seems to play an important role in fighting climate change, especially in the cement industry.