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TRANSCRIPT
Optimization ofAdvancedBiofuelProductionviaFischer-TropschSynthesis
Umesh Pandey1, Koteswara R. Putta1, Ljubisa Gavrilovic1, Kumar R Rout2, Erling Rytter1, Edd A. Blekkan1, ∗Magne Hillestad1
1 Department of Chemical Engineering, NTNU, Sem Saelands Vei 4,7491, Trondheim2 SINTEF Industry, Trondheim
Problem Description
Model Description
Fischer-Tropsch reactions
Paraffin polymerization
CO + U1(α1)H2
r1−−→ H2O + ν1(α1)CH4 + ν2(α1)C2H6 +
ν3(α1)C3H8 + ν4(α1)C4H10 +
ν[5,∞](α1)Cp5+
Olefins polymerization
CO + U2(α2)H2
r2−−→ H2O + ν1(α2)CH4 + ν2(α2)C2H4 +
ν3(α2)C3H6 + ν4(α2)C4H8 +
ν[5,∞](α2)Co5+
• Kinetic model developed by Todic et al. used for mod-eling application.
• A new kinetic model will be proposed and used for fur-ther design application.
The design model
[γI− uMσJ̃]dx
dξ= σuAR̃(x) + uFK(xF − x)− uHE(x− xw)
dγ
dξ= uF − uS
ξ is the dimensionless PATH VARIABLE, ( VVt)
γ is the dimensionless mass flow rate, (W/W0)
x = [wC , θ], θ =T−TrefTref
R(x) is the reaction rate vector in mass basis
σ residence time or space time, (VR/W0)
J̃ is the partial derivative of component reactions
K is a diagonal matrix, K = diag(1, 1, ...,Cp,FCp
)
E is a diagonal matrix of reaction enthalpies
Path Optimizationmax
[σ,u]∈UJ
s.t.dz
dξ= f(z,u), z = [x, γ], z(0) = z0
h(z, u) 6 0
Design variables (u)
FT volume distribution ∆VV
Hydrogen feed distribution uFCoolant temperatures TcCatalyst activity/ dilution uAMixing structure uM
• Optimization solver: MultiStart, global optimizationsolver in MATLAB
• Constraint: Treactor < 230◦
• Vtotal,bed = σ × W0, same for three different reactorsystems
Flow Profiles at Optimal production of Liquid Hydrocarbons (C5+)
Figure 2: Mass fraction, component reaction rate, temperature and H2:CO profiles for single stage (left), two-stage (middle)
and three-stage(right) reactor systems at optimal production of C5+.
Key Findings
Characteristics 1-stage 2-stage 3-stage
CO conversion 74.97% 86.86% 94.60%
Total C5+ production 41117 kg/h 49027 kg/h 53228 kg/h
Extra H2 feed requirement 10379 kg/H 9847 kg/h 10164kg/h
Reactor types Stage-1: PFR Stage-1,2: PFR Stage-1: CSTRStage-2,3: PFR
NPFR (φ = 5cm and L = 8m ) Stage-1: 14170 Stage-1: 8237 Stage-1: —-Stage-2: 5933 Stage-2,3: 2947 and 6273
Cooling temperature Stage-1: 214.7◦C Stage-1: 213.2◦C Stage-1: 213.1◦CStage-2: 214.8◦C Stage-2,3: 234.9◦C, 215.2◦C
Reaction Stoichiometry (φ = ν/2.1) Stage-1: φ < 1 Stage-1: φ < 1 Stage-1,2: φ < 1Stage-2: φ > 1 Stage-3: φ > 1
Conclusion• 29.5% improvement in C5+ production between opti-
mal single stage to 3-stage reactor system.
• Understoichiometric mode of operation for initialstages and overstoichiometric mode for the final stage.
• H2/CO ratio suitable for the bio-syngas (φfeed =1
2.1 << 1) with integration for extra H2 supply.
• Three stage system has highest extra H2 feed to theproduction ratio and corresponds to optimal multi-stage reactor system.
• Results are applicable for conceptual biomass to liquidplant design.
References
[1] Magne Hillestad. Systematic staging in chemical reac-tor design. Chemical Engineering Science, 65(10):3301–3312, 2010.
[2] Branislav Todic, Wenping Ma, Gary Jacobs, Burtron H.Davis, and Dragomir B. Bukur. CO-insertion mechanismbased kinetic model of the Fischer–Tropsch synthesis re-action over Re-promoted Co catalyst. Catalysis Today,228:32–39, jun 2014.
[3] Magne Hillestad. Modeling the Fischer-Tropsch ProductDistribution and Model Implementation. Chemical Prod-uct and Process Modeling, 10(3):147–159, 2015.
[4] Dongsheng Wen and Yulong Ding. Heat transfer of gasflow through a packed bed. Chemical Engineering Sci-ence, 61(11):3532–3542, 2006.
[5] Zsolt Ugray, Leon Lasdon, John Plummer, Fred Glover,James Kelly, and Rafael Martí. Scatter search and localnlp solvers: A multistart framework for global optimiza-tion. INFORMS Journal on Computing, 19(3):328–340,2007.
Optimization Superstructure
Figure 1: A multistage superstructure considered for product optimization basedon path optimization concepts.
Feed characteristics:
• H2/CO ratio: 1:1
• Feed pressure and tempera-ture: 20 bar and 210◦C.
• Flow rate: 133550 kg/h
Process characteristics:
• A fixed bed Reactor, threephase separation, heat ex-changers and mixing units ineach stage
• Main feed to each stage is at210◦C and 20 bar
• Bulk catalyst density: 200kg/m3
• Alternative paths to choose be-tween one big reactor or twoseparate reactor with recycles