• David Egede Fich
  • Mark Burgdorf Herskind
4. term, Energy Engineering, Master (Master Programme)
This project is an investigation of the feasability of integrating a CCS unit at the pulverised coal fired unit 3 at Nordjyllandsværket. The project has been made in cooperation with the plants owner, Vattenfall. Vattenfall has a vision of being a low emission energy producer, and are investing in a multitude of technologies to decrease their carbon footprint. Part of this effort is decreasing CO2 emissions from their existing fossil fuelled power plant fleet. One of the investigated approaches is to implement CCS systems in their plants. To gain experience in this field, Vattenfall is working with a number of the foremost companies in the world, as well as having their own engineers working to integrate a CCS unit at NJV Unit 3. Nordjyllandsværket has been chosen as the test site for this project, as the plant is one of the most efficient power plants in the world today, thus the CO2/MW rate is very low, resulting in a lower relative cost of capture. The scope of this project has been to gather the necessary information on the state of the art, and evaluate the different technologies for potentials, create simplified models of the steam cycle and the CCS unit, and obtaining a feasible integration proposal. The information gathering has been done through the available litterature on the subject, including books, articles, and the internet, but even more through participation in the 8th Annual Conference of Carbon Capture and Sequestration in Pittsburgh, USA. This effort has resulted in a chapter describing the most promising technologies in terms of state of maturity. Furthermore the chapter tries to give a short introduction to how a given capture method works and how it affects the layout of a power plant. The conclusion of this chapter is, that even though Vattenfall is focused on a MEA based capture unit, which still is the only technology at a maturity level suitable for full scale integration, other solvents and technologies yields great potentials. The models has been written in Engineering Equation Solver (EES). The modelling of the steam cycle has been an effort of creating a model as simple as possible, while still maintaining a sufficient level of accuracy both in full load and partial loads. Since a unit like NJV3 is a very complex unit, including 10 feed water heat exchangers, 9 turbines, district heating, and double steam reheating, building a simple model is still a very tedious work, resulting in a very complex set of equations. As EES, as most other iterative solvers, is based on Newton-Raphson iteration, limits and guesses for the variables of the system is of high importance for a succesfull convergence. For a system of high complexity with only limited data available, guesses can be hard or even impossible to provide, thus hindering the convergence of the system. Despite this, the steam cycle converges at all load cases and predicts model behaviour with a high degree of precision. The CCS unit has been build on basis of information given by Jens Møller Andersen (Vattenfall). The information given only covers the full load case. Due to this, the model of the CCS is only valid for a full load simulation, and can not be expected to depict the system at other loads. The integration phase of the project holds an analysis of the steam cycle. As the CCS unit needs a certain amount of heat at a given temperature, there are limitations as to where in the steam cycle the heat can be extracted. The purpose of the analysis is to extract steam three different places in the steam cycle while monitoring the energy penalty imposed on the system. The analysis yields a stream most suitable for extraction, while also revealing model vulnerabilities to extraction at certain points, as a result of insufficient guess values. On basis of the results of the analysis, the CCS unit is integrated into the steam cycle model, yielding a small loss in electricity production and a substantial loss in district heat production. While these results seem perfectly in order, the cost penalty on the system is far to high for a economically viable plant. Hence, further integration is needed in order to optimize plant performance. The approach of this work has been to utilize the waste heat, as a CCS unit of the type modelled for this project has a quite substantial waste heat, amounting to 309 MW. As this waste heat is of low temperature, it can not be used, as is, to increase the efficiency of the plant. The proposal of this project is to increase the quality of the heat by implementing a set of heat pumps. A heat pump is a system enabling transfer of heat from a low temperature to a high temperature reservoir, by utilizing that the saturation temperature of fluid changes with pressure. A crude heat pump model has been built in EES and implemented into the joined model. By using these simple models it is possible to recouperate a total of 195.33 MWof heat. The pressure difference of a heat pump is maintained by a pump. For the heat pumps of this project, the total energy required by the heat pumps amounts to 34.35 MW. Thus the loss in district heating output is minimized on expence of electric output. In conclusion, the models of the project reasonably models the expected performance of Nordjyllandsværket Unit 3, and displays a feasible performance when integrating a CCS unit and a set of heat pumps. As expected, the unit will impose a severe cost penalty to the plant, but the integration attempt of this project reveals that a well designed integration can minimize the actual penalty of integration.
Publication date2009
Number of pages132
Publishing institutionAalborg Universitet, Institut for Energiteknik
ID: 17636127