This plant has quite a history, stretching back to 1938.
A biomass power generation system using wood chips as fuel was introduced in 2009.
Believe it or not, I studied some architecture at high school. Although my dabbling in architecture is long past, my affinity with cement may be a legacy of my youthful studies. Indispensable for roads, railways and all sorts of other infrastructure, cement is actually a very environmentally friendly material. I visited the Tochigi Plant of Sumitomo Osaka Cement to find out what cement making is all about.
The principal raw material of cement is limestone. Kuzuu in Sano City where Tochigi Plant is located has long been known for its rich limestone deposits, which have been quarried since the Edo period. Indeed, limestone from Kuzuu was used for repairing Edo Castle. With a feeling of nostalgia induced by all this history, I arrived at our first destination: Karasawa Mine. At the mine, where limestone has been quarried for some 80 years, production is currently running at about 3 million tons per year.
At the entrance of the mine is a gigantic 90-ton dump truck. Its massive tires are 2.7 meters in diameter. Encountering this behemoth at the start of the tour fuels my excitement. The terraced slopes are typical of an opencast mine. Quarrying using the bench-cut method results in this memorable topography. Look back on the way to the top of the hill for a panorama reminiscent of Machu Picchu. What a spectacular view!
But our main purpose in visiting the mine is not just run-of-the-mill sightseeing. We are here to experience blasting, the highlight of activity at the mine. Dynamite loosens up more than 10,000 tons of limestone in a split second. Blasting is done at Karasawa Mine once a day, always at 11:50 a.m. The clock is ticking. I hold my breath... Bang! There is an almighty rumbling and trembling. At that moment, there is a tremendous upheaval in the bedrock in the direction I was told to look. It collapses like a mountain of sand. But as I approach, it is evident that these are not grains of sand but rocks, many too large for me to shift even if I summon all my strength to the task. Step by step, these rocks will be crushed into smaller pieces until the largest are no more than 90 millimeters in diameter. Then they are transported to the plant.
The rocks are whisked to the plant by the Capsule Liner, which is unique to this mine. Compressed air is used to propel capsules containing limestone at 32 kilometers per hour through a 3-kilometer pipeline to the plant at a rate of 300 tons of limestone per hour. I imagine small trucks running through the pipeline. It looks like something from science fiction. In fact, the system was originally conceived and designed in the Soviet Union.
Following the Capsule Liner, most of which is buried underground, we arrive at the plant. “What’s good about cement production is that the waste can be used as raw materials and fuel. So, recycling is almost 100% within the plant,” explains Mr. Yasufumi Adachi, our guide.
In addition, the Tochigi Plant has a biomass power generation system, with wood chips derived from waste building materials accounting for 90% of its fuel. All the electricity used by the plant is generated by environmentally friendly means. At the Tochigi Plant some 700 kilograms of recycled resources are used in the production of each ton of cement. This is one of the highest recycling ratios in Japan, where 471 kilograms is the average for cement plants.
The raw materials for cement are limestone, which accounts for 70% of the total, with calcium, silicon, aluminum, iron, etc. accounting for the other 30%. Waste building materials and byproducts of other industrial processes are the sources of most of this 30%.
The temperature inside the kiln for producing clinker (intermediate product) by sintering is about 1,450℃. High-temperature sintering decomposes toxic substances, thus minimizing emissions of toxic substances.
To prevent cement solidifying too fast, plaster is added to clinker before grinding in the finishing process.
The enthusiasm for recycling is palpable throughout the plant. An eye-catching piece of kit is the rotary kiln, 4.1 meters in diameter and 62 meters long. Clinker, an intermediate product in the manufacture of cement, is produced in the kiln by sintering at high temperature. Sintering at 1,450℃ detoxifies dioxin contained in waste. The temperature of the kiln surface is around 400 - 500℃. Believe me, you can feel the heat if you approach the kiln.
The kiln is installed with a slight inclination so the raw materials shift inside it during sintering. Finally, clinker reaches the cooling process where its rapid cooling generates ultra-hightemperature air.
“This air is transported to the kiln’s preheater where all its energy is put to good use,” says Mr. Adachi. The waste-combating mottainai spirit is impressive.
Various facilities and processes are orchestrated into a smoothly functioning productive symphony that has an irresistible attraction for anyone with a taste for big industrial plant. Included in the itinerary of a Hato Bus sightseeing tour for a while in 2018, the plant was a popular attraction. Considering its impressive environmental credentials, I hope cement will continue to sustain our way of life far into the future.
Excited at the prospect of witnessing the blasting, which is something never encountered in the course of everyday life, we all headed for the site with Mr. Tsuboi.
Karasawa Mine was enveloped in silence. Massive machines were neatly lined up as though to welcome us. The equipment was even bigger than we had imagined. A member of the Sumitomo Osaka Cement staff told us, “At the biggest mines, you will find machines operating that are at least twice the size of the ones you see here!” Our jaws dropped and our expectations mounted as we were conducted round the mine. It was a strange new world to us.
The blasting proceeded as Mr. Tsuboi describes in his article. As we approached the shattered bedrock in the aftermath of the blasting, we were surprised by the sheer size of the fragments. As though performing in some expertly choreographed gigantic ballet, massive dump trucks moved back and forth transporting the rocks.
It was no surprise to learn that a sightseeing tour including a visit to Karasawa Mine had been a big hit with the general public. At the mine with its tremendous scale, we had the strange feeling that we were visitors to another world.
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