About three years ago, Svegro exchanged fossil oil for bio-oil to heat 80 percent of the area in its greenhouses on Färingsö in Ekerö municipality. It was the first step towards fossil-free warming. Now Svegro has moved on to 100 percent bioenergy for heating and at the same time changed from bio-oil to pellets to reduce energy costs.
Svegro grows lettuce and fresh herbs in 50,000 square meters of greenhouses and has a heat demand of 7.5 GWh per year. Now Svegro has made one of its largest investments, a new energy center. There are several reasons why the investment has been made this year.
- We wanted to replace the last part of fossil oil for heating. Previously, we did not have the capacity to connect all greenhouses to our bio-oil-heated heating plant. What we are doing now is the right step in our sustainability work. We can state that even the last square meters in our greenhouses will be heated with fossil-free energy, says Kristin Orrestig, production manager at Svegro.
Fewer disruptions and lower cost
Last winter, Svegro had operational disruptions in its energy plant and did not want to risk another winter with disruptions. It was urgent to build a new heating plant.
It will also be lower costs for us with pellets instead of bio-oil when we count the depreciation for the investment. But above all, it feels very good to get rid of the last part of fossil fuels, says Kristin Orrestig.
Short schedule
In March this year, the decision was made to invest and after evaluating the tender, AKJ Energiteknik was chosen as the supplier.
- This is one of the largest projects that Svegro has done. Great efforts have also been needed from the staff as the project would be completed in a short time, says Kristin Orrestig. The climate step has provided support for the culvert and the conversion from airborne oil heating to waterborne bioheating.
Two boilers
The new power plant was started in early December and consists of two boilers, a smaller boiler with an output of 1.5 MW and a larger one of 3 MW.
- We chose two boilers to be able to drive with low power during the summer with the smaller boiler. The larger boiler starts up during the winter. The maximum heat output requirement in greenhouses is 7.5 MW. It occurs when the lighting in the greenhouses is turned off and it is cold outside. To cope with the difference, we use four accumulator tanks, says Karl-Gustaf Järn, technical manager at Svegro.
Recycled thoughts
Both the four accumulator tanks and the pellet storage, which consists of two silos, come from Spendrup's closed brewery in Vårby.
- In the true spirit of sustainability, we have taken advantage of recycled thoughts instead of creating new ones . These are stainless steel tanks that we have transported here by boat, rebuilt on site and adapted for the purpose. Large parts of the boiler house have also been dismantled in Vårby and rebuilt. The accumulator tanks hold a total of 600 cubic meters. The pellet storage consists of two pellet silos, one for each boiler, each silo holds 186 cubic meters, Karl- Gustaf Järn explains .
Heat with high temperature
Svegro investigated several heating solutions, such as with heat pumps.
- But we have a system for water-borne heat that requires a high temperature, so the heat pump solution fell away. We chose pellets because we wanted as fully automated a plant as possible. The plant is managed by staff from Svegro and sooting, ash discharge and electric ignition takes place automatically, says Karl-Gustaf Järn.
Challenges
AKJ Energiteknik has made lots of calculations on different solutions, including different numbers of boilers and different sizes, to find the best solution.
- The big challenge is to handle the rapid load variations that occur in greenhouses and the rapid temperature changes that occur when the lights go out. It is an advanced facility technically with systems around the boiler to handle the load variations including control of the accumulators and water flows and more. The boilers are built with AKJ's combustion system for dry fuels with, among other things, water-cooled movable grate. It is fun that Svegro has decided on such a large investment and is really carrying out a conversion that provides fossil-free heating at a lower energy cost, says Gustav Jansson, CEO of AKJ Energiteknik.
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