“Hold on to your hard hat!” Our tour guide’s warning comes just as a heavy gust hits us from below. We’re dropping at a speed of eight metres a second down the pitch-black Franken shaft in a salt mine in southwestern Germany. The cage is normally used to carry as much as 18 tonnes of salt from the mine to the surface. Some 200 metres below ground level we stop. Ahead of us is a maze of tunnels with passages as wide as freeways, 700 kilometres in all, some of them stretching beneath the town of Heilbronn, population 120,000, just north of Stuttgart.This is where Südwestdeutsche Salzwerke runs Western Europe’s largest salt mine. Established in 1885, it holds guaranteed reserves for at least another 40 years of excavation.

Salt, sometimes dubbed “white gold,” has been one of the world’s most essential commodities for centuries and has made fortunes as well as started wars. Here in Heilbronn, where the horizontal salt deposits are up to 40 metres thick, the mine is focused primarily on industrial salt used in the chemicals industry, with end products ranging from plastic cups to mobile phones and road de-icing salt. The car we are riding in is completely covered with salt. It’s a bumpy road through the dark tunnels to where the two Sandvik continuous miners are working. We regularly pass by chambers 10 to 12 metres high blasted into the salt deposits, where conventional excavation is taking place by drilling and blasting.

After a five-kilometre drive we reach our destination, where we can make out the shape of a Sandvik MB770 bolter miner. The machine is the world’s largest machine of its kind, 13 metres long, 4.7 metres high and weighing 125 tonnes – almost the size of a small house. A 400 kW electric motor, making 32 rpm, runs the cutter drum vertically and scrapes the mineral out of the face. The mineral is then collected and transported out automatically by the machine’s conveyor system. Two trucks, capable of carrying 30 tonnes each, work in shifts to load the material onto the conveyor belt at the mouth of the section. The rock salt is then screened before it is hauled out of the mine. With that kind of continuous cutting machine, a crusher is no longer necessary.

“The machine is fantastic,” says machine operator Ernst Scheiterbauer. “On average, we’re moving 25 metres each shift.” He’s managing and overseeing the process with a radio remote control unit strapped around his waist. No more than four people handle the excavation section. Besides the operator, there are two truck drivers and a fourth person helping out with whatever is needed.

Half of the Heilbronn mine is still excavated the conventional way. Large jumbos drill holes up to seven metres deep that are prepped with explosives. Each blast tears down between 300 and 1,000 tonnes of salt.

Nowadays, personnel perform three detonation periods a day, one for each mining area. After each discharge the area has to be cleared out for four hours while the poisonous gases are dissolved. Detonations are prohibited after 10 p.m., and new regulations regarding the safety procedures are expected from the EU. The rapid exploitation of the mine is also closing in on new and crowded housing areas in this fast-growing industrial region.

“Studies performed frequently show that the blasts don’t cause any damage above ground,” says the mine’s manager, Dr. Gerd Bohnenberger. “But some people have expressed annoyance. That is why we started considering alternative techniques.”

As a board member of Südwestdeutsche Salzwerke, Dr. Bohnenberger contacted the mining experts at the Institute of Technology, RWTH, in Aachen. They evaluated the various options and recommended getting into continuous mining, a well-regarded method for coal mines, especially in North America and South Africa. Südwestdeutsche Salzwerke decided to go with an MB770 (then Alpine Bolter Miner ABM30-CM). The machine had never before been used in salt mines, and no one could say for sure how it would perform other than in theory. It was still considered an experiment in 2006 when the machine was taken down into the mine. Months of adjustment came.

“The only experience we had with drum miners was from coal, which is completely different from salt,” says Franz Feuchter, field service manager underground mining for Sandvik Mining and Construction in Germany. “Salt is tough and requires stronger equipment. We knew that from day one, while other things we had to figure out along the way.”

Feuchter is still strongly committed to the project. Since the beginning in May 2006, he has travelled to Heilbronn once or twice a month to talk to the operators, survey the performance of the machine and supply Sandvik’s design department with fruitful information. Wolfgang Rüther, the production manager at Südwestdeutsche Salzwerke, frequently meets with Feuchter in status briefings. Of the partnership with Sandvik he says, “They have invested a lot of their knowledge in order to make this work.” The standard manual steering has been replaced by a system for automated cutting as well as the vibration-sensitive transformer and the cutting drum, he says.

“It has been a continuous optimization process which has brought us a massive reduction in non-operational hours as well as heavily improved production volume,” Dr. Bohnenberger says. Production using this method increased from 40,000 tonnes a month in 2007 to 60,000 tonnes a month one year later. By the end of 2008, it reached a staggering 95,000 tonnes a month. It’s been an extremely successful technology upgrade, he says, in regard to both the technology and the production costs.

Hence, in 2007, the company decided to acquire another continuous miner, again an MB770. Experience gathered from the first unit, and the already trained personnel, made it possible to get the machine running in only a month after delivery in November 2008. Since then the mine has reached 110,000 tonnes a month using continuous mining, and costs are constantly dropping.
“Compared to drilling and blasting, our costs are down more than 10 percent per tonne,” Wolfgang Rüther says.

The market for salt – industrial as well as road salt – is characterized by overcapacity and killing competition. Pursuing cost-efficient solutions is a necessity for survival.

“Salt for industrial and de-icing purposes is generally a mass product,” Rüther says. “The things that matter are price, quality and fast and flexible shipping.”

Although just half of Südwestdeutsche Salzwerke’s excavation process has been switched to continuous mining so far, the plan is to keep expanding in that area, with another machine to be implemented in 2011.

“Long-term, we’re most likely going to be solely on this new technology,” Dr. Bohnenberger says. “Blasting is only going to be necessary in order to handle extreme peaks in demand.”

All in all, five continuous miners will then be running pretty much the entire excavation in Western Europe’s largest salt mine.