Improving the effectiveness and profitability of thermal conversion of biomass
Saari, Jussi (2017-12-08)
Väitöskirja
Saari, Jussi
08.12.2017
Lappeenranta University of Technology
Acta Universitatis Lappeenrantaensis
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-335-177-6
https://urn.fi/URN:ISBN:978-952-335-177-6
Tiivistelmä
Sustainably produced and efficiently used biomass has many advantages as an energy source. It provides an opportunity for reducing greenhouse gas emissions by replacing fossil fuels, and is typically also a local energy source. When used for combined heat and power (CHP) production, biomass can provide a dependable source of renewable energy at high efficiency. There are also drawbacks for CHP production and the use of biomass as a fuel, however. Untreated wood is an unstable fuel of uneven quality and low energy density, which limits its potential for fossil fuel replacement. In the current economic environment of relatively low and volatile electricity prices, CHP plants are also a risky investment at best.
This work investigates the possibilities of improving the profitability and effectiveness of small-scale Nordic wood-fired CHP plants through two different approaches. Integration with mild thermochemical conversion processes is studied to find the best integration concepts, and to learn whether such an integrated plant would be superior in its economic and technical performance to stand-alone CHP and biomass conversion plants. Process simulation software was used to investigate the operation and technical performance of the different plants. It was found that while there is little potential to improve energy efficiency, integration can still improve the profitability of the plant. This is achieved mainly through reductions in investment costs, and by increasing the annual operating time of the CHP plant through the introduction of an additional heat consumer that enables the plant to run when the district heat load alone would be less than the plant minimum load.
The second focus of the study is improving the profitability by component design optimization, namely the condenser of a pure CHP plant. Condenser heat transfer and mechanical sizing models were developed in MATLAB environment, and optimization was carried out at different electricity prices. Metaheuristic optimization algorithms were used for the optimization. It was found that while the profitability of the plant depends heavily on the price of electricity, the optimal performance required of the condenser, as well as its design, are affected only slightly by the electricity price at moderate to high price levels. The optimization did not consider the possibility of varying the plant operating strategies, which limits the practical applicability of the results at low electricity price scenarios.
In an effort to reduce the computation time required for the condenser optimization, a novel way of combining two existing metaheuristic optimization methods was shown to perform better than the other tested algorithms, including either of the two on which the new hybrid method was based on. Further testing with other problems is needed to determine if this hybridization is a generally well-performing algorithm, or is merely particularly well suited for the condenser optimization on which it was implemented in this thesis.
Some topics for future research are identified. The economic and operational analysis of the process integration studies was performed only on a small CHP plant, integrated with a comparatively large-scale biomass conversion plant. A larger CHP plant would offer more options for both heat sinks and heat sources as well as operational flexibility, and could yield different results. The optimization of the condenser could be more flexible, allowing varying the plant operation. This could produce more valuable and realistic results on optimal condenser sizing for low electricity price scenarios.
This work investigates the possibilities of improving the profitability and effectiveness of small-scale Nordic wood-fired CHP plants through two different approaches. Integration with mild thermochemical conversion processes is studied to find the best integration concepts, and to learn whether such an integrated plant would be superior in its economic and technical performance to stand-alone CHP and biomass conversion plants. Process simulation software was used to investigate the operation and technical performance of the different plants. It was found that while there is little potential to improve energy efficiency, integration can still improve the profitability of the plant. This is achieved mainly through reductions in investment costs, and by increasing the annual operating time of the CHP plant through the introduction of an additional heat consumer that enables the plant to run when the district heat load alone would be less than the plant minimum load.
The second focus of the study is improving the profitability by component design optimization, namely the condenser of a pure CHP plant. Condenser heat transfer and mechanical sizing models were developed in MATLAB environment, and optimization was carried out at different electricity prices. Metaheuristic optimization algorithms were used for the optimization. It was found that while the profitability of the plant depends heavily on the price of electricity, the optimal performance required of the condenser, as well as its design, are affected only slightly by the electricity price at moderate to high price levels. The optimization did not consider the possibility of varying the plant operating strategies, which limits the practical applicability of the results at low electricity price scenarios.
In an effort to reduce the computation time required for the condenser optimization, a novel way of combining two existing metaheuristic optimization methods was shown to perform better than the other tested algorithms, including either of the two on which the new hybrid method was based on. Further testing with other problems is needed to determine if this hybridization is a generally well-performing algorithm, or is merely particularly well suited for the condenser optimization on which it was implemented in this thesis.
Some topics for future research are identified. The economic and operational analysis of the process integration studies was performed only on a small CHP plant, integrated with a comparatively large-scale biomass conversion plant. A larger CHP plant would offer more options for both heat sinks and heat sources as well as operational flexibility, and could yield different results. The optimization of the condenser could be more flexible, allowing varying the plant operation. This could produce more valuable and realistic results on optimal condenser sizing for low electricity price scenarios.
Kokoelmat
- Väitöskirjat [1037]