Linde's smart solution makes Stockholm's metro construction greener

Linde's SOLVOCARB® technology – a system that uses carbon dioxide gas to neutralize alkaline water – is helping Subterra in the construction of the Järfälla tunnel. The product is extracted from residual products from bioethanol production. "Using the carbon dioxide from there saves us hundreds of thousands of tonnes of carbon dioxide emissions every year," says Eva Ålander, Application Expert for Water Treatment at Linde.

The construction industry has many challenges when it comes to the environment and sustainability. Subterra is in the middle of constructing a tunnel for the Stockholm metro's blue line to Barkarby and has turned to Linde for help with high alkaline pH levels in tunnel water. This results when groundwater and process water are mixed with cement. If the alkaline is not neutralized, it can disturb the chemical balance out in nature or in a sewage treatment plant, which in the long run can lead to microorganisms and other species in the ecosystem being damaged and even wiped out. Linde's complete solution neutralizes the alkaline water with the help of carbon dioxide.

Safe and easy handling

The technology is called SOLVOCARB ^® and it is a system for automatic dosing and efficient dissolution of carbon dioxide gas in water to neutralize alkaline.
“Carbon dioxide dissolved in water forms a weak acid. Compared to strong mineral acids, this means less corrosion, safe and easy handling, as well as more stable and more precise pH adjustments. In addition, no undesirable substances are added, such as sulphate and chloride ions. The technology has been around for many decades and is well proven,” says Eva Ålander.

Reduced carbon dioxide emissions

Subterra previously used a different type of acid to adjust the pH of its wastewater, but handling it entailed hazard risks for personnel and it was difficult to get good dosing.

“We instead chose to test carbon dioxide to reduce the risks of handling for our personnel, and also so that we get help with a simpler dosage regulated by the pH level in the water,” says Camilla Isgren, Environmental and Sustainability Coordinator at Subterra. “The fact that carbon dioxide is also a residual product that can be reused instead of being wasted is also a real plus.”

Linde's carbon dioxide is a by-product from bioethanol production.

“Capturing carbon dioxide saves us hundreds of thousands of tons of carbon dioxide emissions every year,” says Eva Ålander.

Sustainability was very important when Subterra chose Linde’s solution.

“In our sustainability efforts, we work with a resource management plan where we have documented how we plan and implement resource-efficient solutions to limit our climate impact. For example, in this plan we have noted the fact that the carbon dioxide we use is a residual product from the ethanol factory in Norrköping,” says Camilla Isgren.

Facts: SOLVOCARB®

SOLVOCARB®-technology is used for pH control of process and wastewater in many industries such as the food, textile, and chemical industries as well as in the pulp and paper industry. It can also increase alkalinity and remineralize in the production of drinking water.

Advantages of carbon dioxide:

Stable and accurate pH adjustment
Reduced risk of equipment corrosion
Eliminates the need for storage and handling of dangerous mineral acids

Faster and more sustainable process

Cement production alone accounts for seven percent of global carbon dioxide emissions. By capturing and developing solutions with carbon dioxide, Linde can help the concrete industry become more sustainable and environmentally friendly. In addition to neutralizing the alkaline water that arises when using cement, for example in tunnel, road and bridge construction, carbon dioxide can also be injected during the actual concrete casting.

“It enables a faster manufacturing process, but it also means a reduced carbon dioxide footprint when the carbon dioxide is bound into the concrete,” says Eva Ålander.