Disputas: Udara S.P.R. Arachchige

Graden avlegges ved  Universitetet i Sørøst-Norge (USN), Fakultet for teknologi, naturvitenskap og maritime fag.

Om avhandlingen

This study has focused on process modeling and simulation of CO2 capture with the post combustion chemical absorption process. The carbon capture model is developed and implemented in the Aspen Plus process simulation tool. The required re-boiler energy demand is calculated for both coal and gas fired power plants.

The developed model for the CO2 removal process is validated with a model developed with MATLAB. The simulation results from the Aspen Plus and MATLAB models are compared using the temperature profiles. Both models follow similar patterns for the temperature profiles. Therefore, the developed base case model is validated as a suitable model for the post combustion carbon capture process.

Moreover, MEA and DEA solvents are selected to optimize the CO2 capture process. The same simulation conditions are used to develop the model for CO2 capture process with both solvent. Re-boiler energy requirement is significantly lower for DEA than MEA. Since DEA is less corrosion than MEA, DEA can be recommended as a better solvent for carbon capture plants. The comparison with the single amine model with the same 85% efficiency is performed to understand the benefits of blended amines. The model is developed for MDEA/MEA blended solvent with 4:1 mixing ratio in weight basis. Finally, the model is implemented with optimized parameters to get 85% removal efficiency with a closed system. The blended amine system requires 2937 kJ/kg CO2 for the coal fired plant flue gas capture process according to the present study. This is a significant lower value compared with single amine re-boiler duties.

The most important two factors for selecting packing material are identified as surface area and void fraction. The higher surface area gives the lower solvent requirement and will lead to lower re-boiler duty. Therefore, BX, Flexipac-1Y or Mellapak-350Y can be recommended for coal and gas fired power plant flue gas treating.

The parameters' effects on CO2 removal efficiency, as well as effect on re-boiler duty, are examined. sensitivity analysis was performed for single parameter effect, as well as, multiple parameters effect on the desired output. Both the main effect and interaction effect of the parameters have been studied. The most important parameters (highest influence parameters on re-boiler duty) are lean CO2 loading, absorber diameter and height. Similarly, the correlation between variables were studied for CO2 removal efficiency, which indicate that inlet solvent flow rate, absorber packing height and diameter, absorber pressure and temperature of the solvent stream are positively correlated with CO2 removal efficiency whereas the lean loading and temperature of flue gas are negatively correlated with efficiency.

The implemented model designed for the flue gases is used for coal fired power plant, gas fired power plant, cement plant as well as the aluminium industry. The required re-boiler duty was calculated for every situation. The required re-boiler duties are calculated as 3229, 3306, and 3365 kJ/kg CO2 for 85%, 90% and 95% removal efficiencies, respectively for the cement industry. The specific thermal energy demand, as well as the false air factor of the kiln system, were varied in order to determine the effect on CO2 capture plant performance, such as the solvent regeneration energy demand. The simulations showed that a variation in specific thermal energy demand of the kiln process within a relatively wide range, applicable to real cement kiln systems, does not give a substantial impact on the operation of the CO2 capture plant. However, increasing the false air ingress in the kiln system pre-heater from 25 to 70 % results in a 4 % increase in the re-boiler duty. The amount of energy available in the cement kiln exhaust gas is calculated as around 18MW. This will cover 18% of the total energy requirement in the stripper regeneration process.

Four different CO2 concentrations, 3, 4, 7 and 10 vol%, in the flue gas from the aluminium production are considered for the simulation study. The re-generation energy in the stripping process is in the range of 3.0 - 3.5 MJ/kg CO2 for 85% removal efficiency and 3.2 - 3.5 MJ/kg CO2 for 90% removal efficiency and 3.4 - 3.6 MJ/kg CO2 for 95% removal efficiency.

The experiments were performed to check the viscosities of monoethanolamine (MEA), Diethanolamine (DEA) and Methyldiethanolamine (MDEA). The concentration of the amine is varied from (10-100) wt% and the temperature also varied from (293.15-423.15) K. The viscosities of MDEA+MEA+H2O mixtures for different concentrations have been analyzed for temperature range from 293.15 to 413.15 K.

The total amine strength in the solution is maintained at 0.2, 0.3 and 0.4 mass basis. Temperature range 293.15 to 303.15 K is performed with cooling system to achieve the lower stable temperatures during the experiment. The dynamic viscosity of partially carbonated MEA solution was measured for the temperature range (20 to 150)°C for mass fraction (10 to 50)% and CO2 loading (0.1 to 0.5) mol CO2/mol MEA.