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 6: Clinker Substitution in Cement Plants

Substituting clinker with additives or SCM (Supplementary Cementious Material) plays a major role in efforts to reduce CO2 emissions in cement plants. This clinker substitution is ranked second after carbon capture or CCS (Carbon Capture and Storage) in efforts to reduce CO2 emissions or decarbonization in the cement industry. This is because the largest CO2 emissions in cement plants are not from combustion or related to fuel but in the calcination process. CCS technology is still expensive so its implementation still faces many obstacles, but clinker substitution is easier to do, so many cement plants are already doing it. 

In the cement industry, all fuel use and around 60% of electricity use is used for clinker production starting from grinding raw materials, fuel preparation and cement kilns. The higher the clinker to cement ratio, the higher the electricity and fuel used for each ton of cement produced. The clinker to cement ratio can be reduced if less clinker is used in cement production or more additional materials or SCM are added to the clinker. This also means that substituting clinker with SCM can significantly reduce energy use (electricity and fuel) for each ton of cement produced. 

China currently has the lowest clinker to cement ratio in the world, namely 0.58, while a number of areas in other countries have the highest ratio, up to 0.9. It can also be understood that China uses the highest portion of SCM compared to countries in the world. The most commonly used SCMs today are fly ash, ground granulated blast-furnace slag (GGBFS) and ground limestone. Meanwhile, other SCMs such as pozzolan and calcined clay have the potential to be used in the future.

Fly ash comes from by-products or waste from coal-fired power plants. Decarbonization of coal power plants is also continuing to be carried out, namely by cofiring coal with biomass, but this is being done in stages so that fly ash production will still be large for a while. Fly ash from coal-fired power plant waste is very useful in cement production because it reduces the clinker to cement ratio, thereby reducing energy requirements for cement production or in other words reducing the carbon footprint of cement products. Meanwhile, GGBFS comes from iron and steel plant waste. Not all iron and steel plants produce GGBFS waste, this is because it depends on the type of furnace used. Only plants that use blast furnaces - basic oxygen furnaces (BF - BOF) can produce GGBFS, while those that use electric arc furnaces (EAF) cannot. Around 70% of iron and steel plants in the world currently use the BF – BOF process so as to produce quite a lot of GGBFS, even in China more than 90% use this BF – BOF process. Decarbonization in the iron and steel industry is marked by the switch from BF – BOF to EAF which results in the availability of GGBFS. However, the process is running slowly and gradually, so that for a while the amount of GGBFS will be available and can reduce the carbon footprint of cement production.

The use of fly ash in cement production is usually limited to 25-35% for technical performance reasons. Meanwhile, GGBFS can be used in larger portions than fly ash or other SCM. Even European standards allow the use of GGBFS up to 95% but in practice it is lower. Other SCMs commonly used are pozzolan and calcined clay. Pozzolan comes from mining, namely from deposits in nature. Pozzolan requires drying and grinding before being used in cement production. The electricity used for crushing (grinding) pozzolan is also almost the same as crushing clinker. Calcined clay can also be used as a substitute for clinker. The initial use of calcined clay with a higher portion causes a decrease in the compressive strength of the cement product produced. However, further developments using a combination or mixture of calcined clay with limestone powder have the potential to substitute up to 50% clinker without affecting the quality of the cement. Calcined clay is produced from the clay calcination process which requires energy, but the energy required is much less than the energy for clinker production. It is predicted that in 2050 by the IEA (International Energy Agency) / WBCSD (World Business Council for Sustainable Development) cement production with the above combination of materials will reach more than 25% worldwide. 

It turns out that the use of SCM is not only a substitute for clinker in cement production but also in concrete production. The use of SCM in concrete production is also no less than a substitute for clinker, even in the United States SCM is mostly added during concrete production and not during cement production. A study in the United States estimated that only 5% of SCM was added to cement production and around 13% to concrete production. But basically the addition of SCM to both cement production and concrete production has reduced the carbon footprint or is in line with decarbonization. The problem is that the lack of education regarding the benefits of SCM, especially in concrete production, is a barrier to increasing the use of SCM. Other factors such as the availability of SCM, price and its relation to cement and building quality are also similar barriers. The creation of new standards and codes related to increasing the use of blended cement with SCM and concrete production needs to be developed to transform the current market.   

Green Economy in the Cement Industry Part 5 : Increasing Production and Reducing Emissions

Increasing production capacity but simultaneously reducing CO2 emissions (carbon dioxide, the dominant greenhouse gas) sounds contradictory / paradoxical. It is indeed like that in passing. However, with a decarbonization or CO2 removal (CDR) program, efforts to reduce emissions can be done while increasing cement production. How big the target of reducing emissions and increasing cement production will depend on how much decarbonization efforts are made. The greater the reduction in emissions, the more expensive it will usually be. This is why efforts to reduce emissions while increasing production must also be carried out in stages with certain strategies.

Cement plant is an industry that contributes to an increase in CO2 of more than 6% globally. However, there is something unique about this cement industry, namely that most of the CO2 emissions produced do not come from fuel use, but from the calcination process. The percentage of CO2 produced from the calcination process reaches around 60%, while from fuel use it is only around 40%. The fossil fuels commonly used in cement industries are coal and petcoke, both of which are the two fossil fuels that pollute the air the most. In fact, in a number of areas cement plants are the largest coal users. Cement plants close to oil refineries will use more petcoke.

Decarbonization programs or efforts to reduce CO2 emissions that can be carried out in cement plants include increasing energy efficiency, using clinker substitute materials, using alternative/renewable energy, and using CCUS (Carbon Capture Utilization and Storage). With these characteristics, total decarbonization in the cement industry cannot be carried out by using only the best efficiency technology or by simply replacing the fuel. Meanwhile, the use of clinker substitutes and CCUS is very important among other technologies to achieve near-zero emissions in cement production.

The best scenario for increasing production and reducing emissions can be done by using much higher energy efficiency improvements using commercially available technology, using more aggressive fuels to low carbon or even carbon neutral fuels, using higher rates of clinker substitute materials. and adopting a higher portion of commercially available CCUS technologies.

And it's worth noting that all suggested improvements in these best-case scenarios can be achieved by implementing technologies that are already commercially available and most of them should also be cost-effective. As for CCUS, while the technology is commercially available, implementation requires large investments that demand higher financial incentives or carbon prices. However, on the other hand, CCUS has the largest contribution to CO2 reduction, followed by the use of clinker substitutes and the switch to low-carbon or even carbon-neutral fuels. And the use of efficiency-enhancing technology has the smallest contribution to reducing CO2 emissions. This is mainly because process-related emissions from calcination account for around 60% of total CO2 emissions and are not related to energy use.    

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 Part 3

Fly ash is a byproduct or waste of coal power plants. Like slag, fly ash is also an additive or supplement (SCM/supplementary cementious material) in cement production. The difference is that fly ash is very fine so it doesn't need to be refined anymore and can be mixed directly with clinker and gypsum. Every ton of fly ash used prevents about 1 ton of carbon dioxide (CO2) from escaping into the atmosphere. This is in line with the green economy or decarbonization as a climate solution effort for the industry.

Unloading Fly Ash

As the same with slag, the chemical content of fly ash also influences the quality of the cement produced, for example certain regions or countries have requirements for grade 120 alumina in the slag. Cement with a certain quality can be designed with the use of these additives. In the current era, apart from technical factors such as mechanical strength or cement adhesion, microstructure, durability and so on, and economic factors, environmental friendly product factors are also a concern or have their own positive image. Circular economy in the form of utilizing waste from other industries to become raw materials for this industry, also occurs in the cement industry. And basically the cement industry besides being able to process waste is also a waste destroyer. 

Green Economy in the Cement Industry Part 2

A number of cement plants can do production well by using only limestone and clay raw materials. This is because the material has fulfilled all the oxides needed in the manufacture of the clinker. The oxides needed are CaO (C), SiO2 (S), Al2O3 (A) and Fe2O3 (F). Limestone itself usually has a CaO (C) content of around 90% and 5% SiO2 (S). But the facts on the ground are that many cement  plants require additional materials to achieve the desired oxide composition or commonly called corrective materials. A number of these corrective materials are high grade limestone which has a CaO content of above 95% as C oxide correction, then silica sand for S oxide correction, then kaolin or bauxite for A oxide correction and iron ore or pyrite for F oxide correction.

So in general, currently the materials needed for the production of clinker are limestone, clay, silica sand and iron ore. In its development iron ore can be replaced with slag. The content of Fe2O3 (F) slag is lower than iron ore but the price is cheaper. The slag used mainly comes from the iron and steel industry, commonly known as GBFS or GGBFS. Slag is actually also an additive material that can be added with clinker and gypsum so that it becomes a product (slag) cement. In addition to other slag materials such as fly ash which are also commonly used as a additive, these two materials are commonly called cement supplement materials or SCM (supplementary cementious materials). Fly ash which is very fine does not need to be crushed anymore so it can be mixed directly with clinker and gypsum, while slag from iron or steel industry needs to be crushed again into GGBFS before being mixed with clinker and gypsum. For the need for these additives, in addition to physical aspects such as particle size, chemical aspects, namely slag chemistry and fly ash chemistry, are important parameters that need attention.

The use of SCM such as slag and fly ash above, will reduce the use, especially of fossil fuels. This is because SCM is added to clinker and gypsum so it does not require heat energy. Heat energy itself is needed in the manufacture of clinker, namely in the calciner and rotary kiln. 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. This heat energy currently still uses a lot of fossil fuels and is gradually starting to use renewable energy. Energy derived from biomass such as agricultural waste and animal manure is also starting to be used.  

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.