Energy losses from a concrete digester : Analysis of concrete digester at Lundsby biogas

Abstract: Digesters at a biogas plant have high temperatures and poor insulation. There is great potential to save energy by improving the construction. This study has two aims. One is to compare the difference between a simple steady-state calculation and a calculation that uses simulated values from Heat2. The second is to develop an improved insulation method at the concrete digester that can be used in future projects. Ten different insulation scenarios have been simulated to understand how to improve the insulation method to develop an idea of where the insulation has the most impact. Then a combined insulation method was created from the scenarios. That combined method was then simulated with 5 different insulation thickness to find the most profitable design. The conclusion was that there is great value in making more advanced calculations for the walls and floor because the energy losses are very excessive using the simplified calculation, especially on surfaces covered in soil. It was proved difficult to calculate the losses for the roof, this was because the assumption that was needed to perform the calculation does not mirror the reality. Due to this, the roof has been neglected in the suggested insulation method. The insulation method proposed provides an energy saving of 58 MW h/year and a discounted payback time of 4, 3 years if the saved energy can be delivered as 90◦C degree hot water into the district heating network.