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.

Wood Pellet Production: With a Rotary Dryer or Belt Dryer?

Air quality is an important factor in environmental health. The better the air quality, the better the environmental quality. Maintaining clean air quality is sometimes not something that is easy and cheap, especially for industry players. The higher the air quality standard used, the greater the effort and cost incurred.

In the wood pellet industry as an example, especially in the use of dryer. Almost all wood pellet industries in Asia use rotary dryer and almost none use belt dryer. Meanwhile, in Europe belt dryers are widely used because of lower emission than rotary dryers. In addition, belt dryers also have higher efficiency and can work at lower temperatures than rotary dryers. With a number of these advantages, however, belt dryer are also more expensive compared with rotary dryer.

Basically, rotary dryer can also have good performance, especially in terms of emissions if they are designed and operated properly. The use of high-efficiency dust collectors such as cyclones and bag filters can achieve high emission quality standards. However, the higher the efficiency of the dust collector, the higher the power required.

So the choice used actually depends on the expected air emission target. Europe and US/Canada generally have higher air quality standards than countries in Asia. This makes the emission aspect an important concern for them. Meanwhile, in terms of wood pellet production, the priority aspect is efficiency, so that with good performance the dryer can produce dry wood powder product that are suitable for feeding into pelletiser. The quality of the wood pellets as the final result is also very dependent on the quality of the dry powder product from the dryer. Meanwhile, in terms of safety, the high concentration of dust particles so that they can accumulate in a number of places in the wood pellet factory also has a greater potential for fires to occur.

Wood Pellet Export Opportunities
The lack of supply of wood pellets in Europe due to the Russia-Ukraine war caused wood pellet producers from Southeast Asia and North America to try to seize this opportunity. Production of wood pellets from Russia is estimated at around 3 million tonnes/year which previously filled the European market is now banned, so as a result of this ban the stocks of wood pellets in Europe have decreased drastically. The large demand and lack of supply will naturally push up prices, especially when coupled with increases in other energy commodities, so that the price of wood pellets continues to increase. In fact, because of the high price of wood pellets in Europe, wood pellets from Vietnam, which previously planned to be exported to Japan, were diverted to Europe.

It is also predicted that this uncertain condition will not recover in a short time. In 2021 Europe leads the production of wood pellets with production reaching nearly 20 million tons or around 48% of global production, while consumption of wood pellets reaches 24.5 million tons. Meanwhile, according to Hawkin Wright's data for 2020-2021, the growth in global demand for wood pellets has reached 18.4%, while supply or production growth is only 8.4%. Indonesia should have a great opportunity to become a major wood pellet player with its potential. The wood pellet production can be exported to Europe to cover the shortage of supply and in general to meet global demand.