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to build with less greenhouse gases

Cement production processes cause the emission of a large amount of greenhouse gases. Is there a way to reduce the resulting pollution?

Hot clinker after leaving the kiln. Image manipulation: Macau500, wikimedia/commons
Hot clinker after leaving the kiln. Image manipulation: Macau500, wikimedia/commons

Abi Moshel | Galileo

"And a man said to his neighbor, ``Let it be made of brick, and it was burned to burn, and the brick became to them stone, and the clay was to them clay" (Genesis XNUMX:XNUMX)

In the story of the attempted construction of the Tower of Babel in the book of Genesis, one of the technological innovations of the ancient world is described: as a substitute for quarrying stones and chipping them for construction purposes, local raw materials can be used, put through a burning process and obtain bricks in a convenient shape for construction. This method has been used for hundreds of years (and is still used today in various parts of the world).

The gluing of these bricks to each other was done using different materials: lime - which is a burnt product of limestone, mortar that contains a muddy mixture of clay and other materials, gypsum and bituminous material. Over the generations, mixtures of these materials with various natural materials were developed with the aim of increasing the strength of the building materials, their water resistance and producing a material with uniform properties.
The raw materials of the construction industry

The main development of construction materials in modern times was done during the last 200 years, in which, among other things, a main construction material was developed - cement (Portland cement), which excels in strength, water resistance and controllable quality.

It is known that the ancient Romans used volcanic ash, a product similar to the main cement used today, Portland cement in terms of the process - roasting clay material and lime at a high temperature.

The difference between the ancient and modern material is in the chemical uniformity: the volcanic ash is not a uniform product and therefore its properties are not controlled. In contrast, modern cement is a product of calcination of limestone and clay at a high temperature. It contains lime, gypsum and various metallic oxides to which coal ash and other additives are added.

Cement is considered one of the most important raw materials in the construction industry today. In most countries of the world there is a local industry for the production of cement, and most of the consumption is done within a short distance of the place of production due to the high costs of transporting the cement and the relatively low price per unit of weight.
Cement production and greenhouse gas emissions

Cement production for construction is one of the industrial processes with an important potential for greenhouse gas emissions. According to current estimates, the cement production process is responsible for approximately 7-5% of the world's carbon dioxide emissions. It is expected that the accelerated economic development in third world countries will lead to a doubling of cement production in the world by 2030.

The main process in the production of cement is roasting at a high temperature (over 1,450 degrees Celsius) of a mixture of raw materials, the main of which are limestone and clay to create clinker, a gray mixture of powder and lumps of various sizes (up to several centimeters in diameter). The clinker is then ground with various additives and marketed as cement.

The emission of carbon dioxide in the production of cement is caused by two reasons: one, because the fuel is burned in the process (usually the fuel used in the cement industry is petroleum coke, which is a heavy residue of the fuel refining processes, and contains a relatively high ratio of carbon per unit of energy). The second, due to the very fact of turning the limestone into lime while emitting carbon dioxide:

CaO + CO2. → CaCO3
Reducing the polluting process

In the production process of one ton of clinker, between 700 and 1,000 kg of carbon dioxide are emitted. The amount depends on the energy efficiency of the combustion process (as will be detailed below), and the amount of fuel from renewable sources that is used (if fuel from renewable sources is used, the source of the carbon dioxide is plant material that previously absorbed it from the atmosphere, and therefore it is considered "neutral" in terms of the addition to the atmosphere ). The emission per ton of cement that is ultimately marketed depends on the amount of clinker in it, and on average stands at 500 to 700 kg of carbon dioxide emitted for each ton of cement produced.

Over the years, various technologies have been developed with the aim of reducing energy consumption, raw material consumption and greenhouse gas emissions from Portland cement production facilities. The first processes for cement production were "wet", and included mixing the raw materials in a wet state. The method ensured a relatively simple mixing of the raw materials to obtain a homogeneous product, but required the use of a lot of energy to dry the raw materials upon entering the furnace.

The most important improvements in the cement production process during the last century were aimed at reducing the amount of energy required to reduce the percentage of moisture in the raw materials. Gradually, a transition was made from a "wet" process, as was the case in the "Nesher" company's plant in the Haifa area, which was established in 1925 and is not active today, to a "semi-wet" process, and then to a "semi-dry" process, such as the "Nesher" plant in the wet industrial zone that was established in 1974. Today, modern factories are being built, where the mixing of the raw materials is done in a "dry" state - like this, for example, in the factory of the "Nesher" company in Ramla. Changing the process from "wet" to "dry" made it possible to save over 50% of the energy consumption in the process.

Since in the cement production process a significant part of the greenhouse gas emission is caused by the decomposition of the limestone, another important improvement to reduce the emission is to replace some of the raw materials and some of the components of the final cement with other materials. One of the main points in this process is the use of coal ash, which is created as waste in coal-fired power plants and is added in several stages.

The coal ash contains a mixture of materials necessary for the clinker production process, therefore a certain amount of coal ash is added to the raw materials put into the kiln. Also, the coal ash is added later to the cement itself and in some types of concrete there is an addition of coal ash as an ingredient in the concrete. The addition of coal ash reduces the need for larger amounts of clinker and therefore contributes to reducing the energy required for the process and reducing the amount of limestone put into the kiln.

Ways to reduce waste

In recent decades, the use of various waste materials with a high energy content has increased as a replacement for part of the fuel from fossil sources used in the cement kilns. In this way, waste materials are used as fuel for the cement production process, materials that would otherwise be landfilled. The waste materials include industrial solvents of various types, high-energy sludges generated in industry, tires, industrial waste and household waste after sorting.

The use of the waste materials as a substitute for fuel is carried out after testing, to ensure that their use does not increase the emission of harsh pollutants from the furnaces. It is usually not possible to fully replace all normal fuel with waste materials, mainly because the energy content of most waste products is relatively low, and does not allow reaching the temperature required for the process. The use of different types of waste reduces the emission of greenhouse gases from the furnaces because the alternative is for the waste to be landfilled and undergo decomposition processes in which carbon dioxide and methane are emitted, which is considered a greenhouse gas with 21 times higher potential for causing the greenhouse effect compared to carbon dioxide.

The technological improvements to reduce energy consumption and reduce greenhouse gases in cement production processes are not expressed in the replacement of fuel and raw materials only. There are many other ways to optimize production processes while further reducing total emissions. One way is to use the heat emitted from the furnace and the hot products coming out of it, to heat the raw materials entering the process (heat recycling). With this method, the amount of energy required to heat the raw materials is reduced even before they enter the furnace, therefore this method allows for a better utilization of the energy. In addition to this, the utilization of the heat of the exhaust gases from the furnace allows for their rapid cooling, a cooling required to reduce the emission of some of the air pollutants in them.

Another direction is the search for an alternative to the traditional production of cement. One of the developments in this field belongs to the Israeli company I-Tec-W Ltd. The company has developed a mixture of materials of biological origin, which includes various enzymes and other substances, and mixing them with different types of soil creates a compact and rigid texture, which allows them to be used as a substitute for cement or road infrastructure. This mixture of materials is called Zym-tec solution (a material invented by the company and defined as a patent in Israel and worldwide). Mixing this material with the soil changes its properties and allows the product obtained to be used for paving or stabilizing roads, sealing liquid reservoirs, canals or waste disposal areas. When the concentrated material is mixed with water as a solution and placed in the soil before pressing, it acts on the fine grain components in the soil and has a strong adhesive action.

Petroleum coke: fuel in the cement industry. Photo: Normanm, wikimedia/commons
Petroleum coke: fuel in the cement industry. Photo: Normanm, wikimedia/commons

The application of the technology in the field of the concrete industry makes it possible to reduce the amount of cement in the concrete mix and replace it with (smaller) amounts of the Zym-Tec material while maintaining the full performance specifications. The new material invented by the I-Tec-W Ltd company has many advantages that are already reflected in the dozens of projects the company is responsible for in Israel and around the world: according to this method, mixing the material with local soil and cementing it together afterwards enables the construction of road infrastructures and the creation of bricks for construction.

The application of this method significantly reduces the greenhouse gas emissions that occur in paving and construction processes, not only due to the reduction in the product manufacturing process itself, but also due to the fact that local material was used for the construction processes and that transportation processes of the construction materials from distant quarrying areas to the construction or paving site were saved. Another advantage of the method is the great shortening of project execution times, which means a reduction in the number of hours of heavy mechanical equipment work, and as a result, a further significant reduction in greenhouse gas emissions.

When you wish to apply the method for the purpose of paving a road or road infrastructure, you must process the local soil, and mix the concentrated material with water and then with the soil in a ratio that varies according to the local soil moisture. In the construction of buildings, you can add a relatively small amount of ordinary cement to increase the strength.

reduce infrastructure costs

A great advantage of the method is in the process of leveling the ground and preparing the infrastructure for road construction. Today, quarrying materials are used in large quantities, transported to the road site from quarries and it is necessary to tighten and stabilize these layers in preparation for the construction of the road. The application of the new material allows the use of the local land for these needs, thereby reducing both the costs of the infrastructure itself and the amount of excess dirt that today needs to be disposed of.

The application of the technology in the field of the concrete industry makes it possible to reduce the amount of cement in the concrete mix and replace it with (smaller) amounts of the Zym-Tec material, while maintaining the full performance specifications. This is a unique and patented solution of the company, which contributes to a considerable reduction of the emitted greenhouse gases. So far, several tens of kilometers of roads have been paved in Israel and around the world and buildings have been built using this method.

for further reading:

Paving roads in Ethiopia with a new method

The writer is a graduate of biology and certified in environmental sciences on behalf of the Hebrew University in Jerusalem. For years he worked in the Ministry of Environmental Protection in areas related to reducing air pollution and preventing the emission of greenhouse gases, among other things as the deputy head of the department and the director of the air quality department. Currently a consultant to the Committee for National Infrastructures and various companies on air quality and climate change issues

The full article was published in Galileo magazine, June 2012

2 תגובות

  1. Now, finally, the pollution per kilometer of paved road will be reduced by 50%, and thus the pressure from bodies concerned with preserving the quality of the environment will decrease. And the possibility of expanding the development of the important road infrastructure will open, by 50.009%.

    Only the naive believe that it is possible to build a stable structure whose building blocks are taken from its foundations.

  2. Peace to my father
    The arrow in the chemical formula you wrote should be reversed, in the written direction the process describes the creation of limestone from CO2 and CaO

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