First a number: The world uses around three billion tons of cement a year – and rising. And now a question: Do you know how this gray powder, that holds together bridges, roads, tunnels and buildings, is made?

“Dig, grind, heat and grind again,” is how Dr. Dietmar Schulz sums up the complex production process. The 50-year-old works as an engineer for ThyssenKrupp Polysius, one of the world’s leading companies in cement plant construction. In an interview held at the research laboratory in Neubeckum, Schulz explains why so much energy is needed in cement production, how much expertise goes into the design of ThyssenKrupp Polysius cement plants and how the company has developed a process to run cement kilns on 100 percent substitute fuels.

Cement is the material our modern world is built of. What is the recipe for making it?
Dr. Schulz: The basic ingredients are limestone, clay, sand and iron ore. But there’s no universally valid recipe for mixing them. These are natural raw materials, whose composition can vary depending on geography. Limestone in China is not exactly the same as limestone in Spain. The challenge is to tailor the manufacturing process to the local raw materials situation, because cement is an internationally standardized building material and is subject to strict quality rules.

So that also means that no two cement plants are the same. But what comes out at the end is largely the same everywhere. Yes, you can rely on cement. After all you have to be sure that a dam or a bridge will really last. To guarantee high quality you need lots of experience. We’ve been in the business for over 150 years and today we offer our customers the whole chain from a single source. It begins with exploring the quarry and ends with turnkey handover of the plant.

“Cement is regarded as an indicator of advancing economic development in the emerging nations.”

After the rock has been quarried and the right mixture has been established – what is the next step in production?
The rock mix is crushed and ground into what’s called raw meal. This is heated to 800 to 900 degrees in the “calciner” to allow the CO₂ to escape. Then the natural minerals are destroyed at 1,400 to 1,500 degrees in the “rotary kiln”. A new mineralogical structure is produced. The material melts in part and sinters into small lumps or “clinkers”. These are cooled and then ground together with gypsum to give Portland cement.

Are these good times for cement?
Cement is the biggest-selling building material today. And it’s regarded as an indicator of advancing economic development in the emerging nations. China alone uses around 50 percent of global cement production, and in India and Brazil, too, demand is rising disproportionately.

So cement is being used to build the future. Is it an infinitely available building material?
Its production requires a very large amount of energy, and energy resources are finite. Then there’s the environmental aspect: The CO₂ emissions of cement plants are very high. The classic fuels for the kilns are coal, gas and oil – and they are becoming increasingly scarce. ThyssenKrupp Polysius was quick to recognize this and focus on the use of substitute fuels. We set up the joint venture “Vecoplan FuelTrack” to accelerate this process.

Which substitute fuels can be used?
The kilns can burn waste oils, solvents and plastics, as well as biogenic materials such as sewage sludge, paper and wood. Thanks to the latest technology, 60 percent of primary fuels are substituted in Germany today, and in the rest of Europe it’s 20 percent. ThyssenKrupp Polysius can already build plants that run on 100 percent substitute fuels. A medium-size plant saves 165,000 tons of coal a year through the use of recycled materials.

Can the kilns be switched easily to alternative fuels? This is another area where our expertise is in demand. The joint venture I just mentioned is driving forward our AFR strategy for “Alternative Fuels and Raw Materials”. We’ve already received orders worth millions for this technology. In the past we were only able to use specially treated and comparatively expensive substitute materials. Now, under AFR, we have developed machines that prepare the waste thermally and allow us to burn pieces 250 to 300 millimeters in size, making production even more cost-efficient.

What is the benefit for the environment?
When waste is disposed of in conventional incinerators, residues are left over that have to go to landfill. But when waste is used in our plants, the pollutants are permanently incorporated in the cement clinker – a beneficial side effect! The other big issue is CO₂ emissions. A cement plant using a high proportion of biogenic substitute fuels requires far fewer emission allowances. That’s good for the cost structure and it’s also good for the environment.

What will the cement plant of the future look like?
One long-term goal is to one day replace limestone with a different material, because around 60 percent of the CO₂ emissions come from the limestone. It would be fantastic if we could find an alternative raw material. We’re working on it.

Surface coal mining is often extremely heavy-duty work carried out with extremely heavy-duty machinery. After the top rock cover is blasted away, giant excavators systematically remove the coal seams. Across the world, ever new and ever larger deposits are being developed. Demand for coal is rising rapidly – in part due to the growing raw materials needs of the emerging economies.

So it’s all the more important that mining techniques become more efficient and save on resources. The potential for savings is huge: Hundreds of heavy-duty trucks, each carrying up to 350 tons, are in operation every day transporting the coal to often distant crushers where it is broken down for further processing. For mine operators this is a mammoth logistical exercise. Added to the high fuel costs there are also the costs of wear parts such as the four-meter-diameter tires that have to be replaced every year. One set can cost as much as 300,000 euros.

To make the process more efficient, the experts from ThyssenKrupp are now taking the crushers directly to the face: There, the fully mobile crawler-mounted machines are loaded with meter-size blocks of coal by an excavator. The crushed raw material is then transported away on a shiftable conveyor belt system. Now, instead of hundreds of truck drivers, only three to four specialists are needed to operate the electrically powered crusher/belt system. This reduces operating costs enormously and cuts CO₂ emissions by up to 150,000 tons per year. And instead of keeping stocks of many different truck spares, operators can rely on low-cost, standardized spare parts for the crusher/belt system.

The first of these crusher plants went into operation in the YiminHe surface coal mine in Inner Mongolia in 2007 and has already proved itself under extreme climatic conditions: The system operates with a rated capacity of 3,000 tons per hour even at minus 40 degrees. Four further systems for the Chinese market and two systems for a pilot project in Brazil are under construction, and an order for three further systems was received from China in 2011. The systems have a rated capacity of up to 10,000 tons per hour.