Epsilon Archive for Student Projects

Abstract

To achieve the requirements to decrease emissions of greenhouse gases by 20 % by 2020, Sweden
needs to increase its use of bioenergy. In doing so it seems natural that those who already have
access to large amounts of biofuels in the form of by-products such as straw, wood chips and
digestible materials take advantage of these assets locally. By combining production of heat with
power production at the farm it may be possible to not only reduce the direct use of fossil fuel for
heating but also reduce energy costs.

The purpose was to simulate different cases of using a small scale biofueled combined heat and
power plant for farm-based systems. A MatLab-model was developed and used to draw conclusions
about the costs for production of heat and electricity with different conversion technologies.

The model uses climate data to simulate the variations in heat energy demand on a day-to-day basis.
The given heat demand is the base of the simulation and from this the possible electric output is
calculated. This study has focused on the impact of the following properties: electric-, heat- and
total efficiency, fuel, fuel price and specific fuel requirements. The studied cases cover applications
with a heat demand from 70 kW to around 400 kW.

In this thesis two case studies has been conducted. The first was a study of a plant with a maximum
heat power of 70 kW and fueled with straw. The interesting heat engine is in these case was a
Stirling engine. After simulations some conclusions could be drawn that suggested that it may be
hard to find a Stirling engine that is cheap enough to motivate investment. The second case study
was carried out on a dry fermentation plant in the south of Sweden, as substrate algae would be
used. After production all biogas should be used as fuel for a micro turbine or for an Otto-engine.
Even in these case the result suggested that it would be hard to motivate an investment.