The aim of this project is to study the viability of a 1MW waste heat power plant. There is a
lot of waste heat available in the port of Rotterdam and it is usually released into the
environment. Alternatively, it is used for a District Heating network. If we can manage to
produce electricity (with profits), we then have a CO2-free power plant.
The design conditions are: a hot source of 100ºC temperature and the ocean as cold source.
The temperatures of the ocean change throughout the year so we will use 2 models: one for
summer and the other for winter.
The two most suitable technologies are Rankine cycle (using organic fluids) and the Kalina
cycle. The first is also called Organic Rankine Cycle (ORC) and it uses organic fluids with
lower boiling points (compared to water) which is appropriate for this application.
The working fluid for the Kalina cycle is a water/ammonia mixture and this is the key to its
superior performance: its adjustable boiling point allows for a better exchange of heat, both in
the condenser and the heat exchanger.
Regarding the ORC working fluids, we were left with three potential candidates after
eliminating the compounds with non-suitable boiling points and the candidates that can
damage the environment. The three candidates were R123, isopentane and pentane, in
decreasing order of efficiency. However, we chose the second best (isopentane) because it
contributes 7 times less to global warming.
We achieved similar results with the thermodynamic analysis: less than 10% thermal
efficiency and around 35% exergetic efficiency. It is important to use the concept of exergy
because it allows us to compare magnitudes of different quality: electricity is first-grade
energy while heat is second-grade energy.
The economic methodology that was used was estimation from prior projects or other
studies. Both ORC and Kalina systems achieved similar results: 6% IRR and around 200 k€
of NPV. The analysis was performed using 85 €/MWh as the price of electricity but we also
found that we could sell it cheaper, up to 82 €/MWh. The idea of selling electricity close to
the generation site is aligned with a decentralized generation strategy that seems to be the
trend for the future.
In conclusion, this project is profitable and it would save around 2500 tons of CO2 per year.
