Modelling of liquid-vapor-solid equilibria in the NH3-CO2-H2O system Maria G. Lioliou, Statoil ASA Introduction • CO2 capture by amines is state-of-the-art technology • Characteristics of a desired technology − Temperature stability over a temperature range − High selectivity for CO2 − Non-corrosive − High cycle life − Low energy regeneration (stripping) − Rapid kinetics for scrubbing and stripping • Can ammonia processes challenge amines with respect to − energy requirements − reduced environmental impact 2- Photo: Marit Hommedal, Statoil Ammonia for CO2 capture • Used in De-NOx processes & to remove SO2 and HCl • Low environmental impact • Several approaches on the thermodynamics − Edwards (1978), Pawlikowski (1982), Bieling (1989), Kurz (1995), Krop (1999) • Tool to predict phase behavior, mass & energy balances 3- Components & equilibrium reactions Vapour Aqueous CH 4 , N 2 , O2 , Ar CO2 NH 3 H 2O CO2 NH 3 H 2O CO2 + H 2O ↔ H + + HCO3− Soave-Redlich-Kwong EOS for gas fugacities Henry’s law HCO3− ↔ H + + CO32− NH 4+ ↔ H + + NH 3 NH 3 + HCO3− ↔ NH 2COO − + H 2O H 2O ↔ H + + OH − NH 4+ + HCO3− ↔ NH 4 HCO3 ( s ) Solids 4- NH 4 HCO3 ( s ) Pitzer model & equilibrium constants Solubility product Pure solids Thermal model • Heat capacities, standard state enthalpies & entropies were used T H Tf • H 0f + ∫ C p (i ) (T )dt •= 0 − For water: C p ( H 2O= C p, A + C p,B ⋅ T + ) C p ,C ⋅10−5 T 2 − Aqueous & dissolved species: C p (i=) + C p , D ⋅10−6 T 2 C p, A + C p,B ⋅ T + C p ,C T − 200 − Solid(s): treated as particles/species in a water stream − Gas components: C idp= (m) C= C idp (i ) + C pres (i ) p (i ) ∑ x ⋅C i id p (i ) i C idp (i= C p , A + C p , B ⋅ T + C p ,C ⋅ T 2 + C p , D ⋅ T 3 ) 5- residual term: calculated through the EOS Data • Model is based entirely on open literature data • Approximately 3500 experimental data on: − VLE − SLE − heat capacities, enthalpies, entropies • Scattered SLE data • NH4HCO3(s) of primary importance • Other possible salts: (NH4)2CO3 NH4CO2NH4 NH4HCO3-NH4CO2NH2 (NH4)2CO3-NH4HCO3-H2O 6- Model testing – NH3-CO2-H2O system 0.20 80 Temp=20oC ) ( o T=60 Temp=60 C C NH3=0.49752 NH3=0.5078 NH3=1.02846 NH3=0.1288 NH3=1.56242 NH3=2.11016 T=20oC 0.16 0.12 o NH3=0.721 NH3=0.728 NH3=0.966 NH3=1.0285 NH3=1.129 NH3=2.1102 NH3=2.186 NH3=2.658 NH3=3.837 NH3=3.977 NH3=8.14 NH3=11.69 NH3=11.79 60 40 p 20 0.04 0.00 0 0.0 0.3 0.6 0.9 1.2 1.5 1.8 0.0 100 2.5 5.0 7.5 12.5 15.0 80 o Temp=80 C oC T=80 T=100oC Temp=100oC 75 Reliable results at least up to 100oC ) 60 NH3=1.079 NH3=3.12 NH3=9.57 NH3=11.2 NH3=14.19 ( 50 NH3=0.591 NH3=1.087 NH3=2.006 NH3=4.14 NH3=5.93 NH3=9.03 NH3=12.17 25 0 40 20 0 0 2 4 6 8 10 12 0 2 4 6 CO2 concentration (mole/kgH2O) 7- 10.0 p Vapor pressure (bar) 0.08 NH3: 0.5-13 mole/kg H2O CO2: up to 15 mole/kg H2O 8 10 12 Data from: Pexton and Badger (1938), Van Krevelen et al. (1949), Otsuka et al. (1960), Kurz et al. (1995), Verbrugge (1979), Göppert and Maurer (1988), Müller et al. (1988), Pawlikowski et al. (1982), Mezger and Payer (1925) Model testing – NH4HCO3 solubility NH 4+ HCO3− SR = K sp ( NH 4 HCO3 ) Supersaturation, SR 3.0 2.5 SR=1 perfect match SR>1 model predicts too low solubility 2.0 SR<1 model predicts too high solubility 1.5 1.0 0.5 0 20 40 60 80 Temperature (oC) 8- 100 120 Data from: Jänecke (1927), Jänecke (1929) Simulation tool • Excel based process simulator, thermodynamic calculations in dll 9- Application in a generic ammonia process Pure CO2 • Chilled Ammonia Process patented by Eli Gal (2006) Cleaned gas Air cooler • Powerspan’s ECO2® technology • CSIRO’s ammonia PCC • CAER pilot studies (Univ. of Kentucky) Desorber Heat exchanger Absorber Flue gas CO2 rich CO2 lean 10 - Cleaned gas Simulation results Solven t Absorber Flue gas NH3 in cleaned gas CO2 rich 3.5% CO2, G: 10 kg/s, L: 200 kg/s, (NH4)2CO3: 3,4,6 mol/L 30 3.5% CO2, G: 10 kg/s, L: 200 kg/s, (NH4)2CO3: 4 mol/L 20 2400 15 Flue gas temperature 80oC 90oC 120oC 2000 10 5 0 5 10 15 20 25 30 35 o Temperature in absorber ( C) 40 45 Cooling duty of flue gas (kJ/s) NH3 slip (mmole/s) Cooling duty of flue gas Solvent: (NH4)2CO3 3 mol/L 4 mol/L 6 mol/L 25 1600 1200 800 400 0 5 10 15 20 25 30 Temperature in absorber (oC) 11 - 35 40 45 Simulation results Energy needed to heat CO2 rich stream Pure CO2 T(regen): 60, 70, 80, 90oC, T(abs): 12, 20, 35oC 250 T in absorber 15oC 20oC 35oC Desorber CO2 lean Heating duty (kJ/s) 200 150 100 50 0 60 65 70 75 80 85 o Temperature in desorber ( C) 12 - 90 Thank you Modelling of liquid- vapor- solid equilibria in the NH3- CO2- H2O system Maria G. Lioliou TNE RD NEH CCA [email protected], tel: +47 94424249 www.statoil.com 13 - Backup slides 14 - Calculations • Calculate thermodynamic equilibrium and other P-T constants • EOS solved for gas fugacity coefficients • Pitzer solved for aqueous components activity coefficients • Equilibria, mass balances for CO2, NH3, H2O & alkalinity equation • Update EOS and SRK with new values • Typically 3-6 iterations 15 - Parameters & simplifications in Pitzer model • Similar to Bieling et al. (1995) • Theoretically: 36 binary and 120 ternary parameters • Interactions neglected: − H+/[OH-] << NH3/NH4+ and CO2/HCO3-/CO32− CO2 and NH3 cannot coexist − ions of the same sign − ion and a neutral • Ternary parameters: important only at very high concentrations • Same approach for triple interactions 16 - NH3 solubility – Comparison with HYSYS x% NH3 20 kg/s • oC Gas out, ToC 3.0x107 HYSYS 40% NH3 Model 40% NH3 HYSYS 60% NH3 Model 60% NH3 HYSYS 80% NH3 Model 80% NH3 2.5x107 2.0x107 Heat Flow (J/s) 1.5x107 1.0x107 Water 10 kg/s • oC Water: 10 kg/s Gas: 20 kg/s Liquid out, ToC Q 50 5.0x106 0.0 experimental points developed model Peng-Robinson NRTL 40 6 -5.0x10 NH3 solubility -1.0x107 -1.5x107 20 30 40 50 60 70 o Temperature ( C) 30 20 -9.00x105 10 -1.05x106 Heat Flow (J/s) -1.20x106 0 Peng Robinson EOS model developed model Redlich Kwong 6 -1.35x10 0 20 30 40 50 60 70 80 90 100 Temperature (oC) -1.50x106 • Different fluid packages in HYSYS – non ideal behaviour of NH3 in water -1.65x106 -1.80x106 -1.95x106 -2.10x106 10 20 30 40 50 Temperature (oC) 17 - 10 60 70 80 • Solubility of NH3 is calculated and compared to various models
© Copyright 2024 ExpyDoc
