Additional building for pellet storage at Norrenergi

The energy company Norrenergi wanted to divide a pellet storage into two parts at the district heating plant in Solna Strand. “When we build a separate silo for the feed screw, we will be able to optimize the way the grapple bucket works when handling fuel,” says Mats Birgersson, Norrenergi's Production Project Manager, who continues: “We wanted an appropriate inclination for the screw and a horizontal level in the storage in order to avoid unnecessary wearing of the cables and electrical wires of the grapple, because that could lead to interruptions in the supply.” Norrenergi has built a new line in one of its five boilers. The grapple bucket lifts the pellet and distributes it to various warehouses and fuel silos. The feed screw then transfers the pellet to a rotating hammer mill, which crushes it into powder. The powder is blown into the boiler for district heating. NYAB's task was to pile and reinforce the structure with iron, build a mold for the pellet silo and cast the concrete for the silo with a storage on the other side. The project had a number of issues that require special attention, as the walls must carry the weight of a full fuel storage facility and the personnel must be allowed in to perform maintenance operations. The feed screw was made of stainless steel: the screw servicing is more efficient and the need for maintenance is reduced. The concrete warehouse floor measures 15×10 meters and the walls are 10 meters high.

Fully fossil-free production as the goal

According to Mats Birgersson, the pellet consumption of Solna Strand's district heating plant is 60,000 metric tons per season. “Our goal is to be completely fossil-free, and we are only a fraction away from our goal. Pellets are not only renewable and environmentally friendly, but also the second cheapest of all our heat sources. The cheapest is the waste heat from the waste water from the Bromma water treatment plant, which we transform into district heat and district cold in our heat pumps. Due to our strict environmental requirements, it is important that our partners also meet both the sustainability targets of the Bra Miljöval Ecolabel and the specific needs of our own facilities.”

Success with tight schedule and project coordination

The project schedule was very tight because such a plant cannot be idle for long, especially now that fall and cold weather are approaching. Mats Birgersson says the NYAB site was completed a good week earlier than promised. “It's unusual for projects like this. We had a joint meeting  every week, and NYAB was always available and their people went straight to the point. The cooperation worked very well. You can tell that NYAB wants to do their job well and they give an impression of professionality. It is easy to work with the people of NYAB.  During the project we did our own runs and maintenance at the same time, so it was important that coordination worked. It has been very smooth with NYAB.”

Facts about Norrenergi

Norrenergi provides district heating for its owner municipalities Solna and Sundbyberg as well as the nearby homes of more than 100,000 people. The company also produces and supplies district heat to offices, hospitals, shopping centers and data centers. All heat and cold supplies comply with very strict environmental requirements, and the company has been awarded the Swedish Nature Conservation Society's Bra Miljöval eco-label long ago. In 2015, 99.6% of the energy production was renewable, including transport.

Contents of the project

• concrete, casting and reinforcement work for 10-meter walls designed for single load use
• frames made of stainless steel and protective cladding with stainless steel plates
• installation of an explosion-proof service door and locks in the silo and storage.