Advanced Modeling of Gasifiers

Transcription

1 Advanced Modeling of Gasifiers Gasification Process Modeling Using Computational Fluid Dynamics (CFD) John B. Roucis, GE Energy J. M. Kline, ChevronTexaco J.D. Smith, The CD adapco Group Gasification Technologies Conference October 6, 2004 Washington, D.C.

2 Topics Reactor modeling motivation and goals. Two natural gas gasifier models: 1. Equilibrium chemistry model results. 2. Finite rate chemistry (kinetics) results. Comparisons and applications. Summary and open discussion.

3 Gasifier Modeling & Experimental Team (L-R): Michael Kline (ChevronTexaco), John Roucis (GE Energy), Joseph Smith (CD-adapco), and GE s Gasification R&D Team

4 Program Motivation and Goals

5 Program Motivation and Goals Develop advanced fundamental models of gasifiers to: Provide advanced tools for improved design and scale-up. Improve plant operability. Improve contingency planning prior to running plant tests. Reduce development and troubleshooting costs.

6 What is CFD? CFD Computational Fluid Dynamics Computer solution of mass, momentum, & energy equations, and can include chemical reaction. Advanced software now available commercially. Utilizes enormous computing power readily available today. Industrial applications: turbines, combustion units, aerospace. Models are approximations.they re only as useful as they accurately reflect the real system.

7 Plan of Attack Leveraged approach: - CDa-acces (CD adapco Group): CFD software with advanced kinetics capability Dr. Joseph Smith - Reaction Design: kinetics software. Pilot gasifier (Research Gasifier Unit): - Models are only as good as the data they re calibrated to. - Generated basic data in pilot unit by conducting modeling experimental program.

8 Model System Natural Gas Gasification (or Partial Oxidation )

9 Natural Gas Gasification Is applied industrially for H 2 and CO production. Provides the simplest chemical system as departure point for modeling: CH 4 + O 2 CO + H 2 + (H 2 O + CO 2 + CH 4 ) Provides opening opportunity to implement full reaction kinetics vs. equilibrium only CFD calcs.

10 Two Types of Reaction Models Were Developed

11 Equilibrium Chemistry Model w/ Mixing Only - Simplest model, computationally. - Local instantaneous chemical equilibrium assumed. - Local species concentration is controlled by mixing rate. - Probability density function controls the mixing rate. - Useful for e.g. heat transfer calculations. Kinetics Model w/ Finite Rate Chemistry - Greater complexity, but can give greater accuracy. - Significant computing power/advanced software required. - Transient model combines kinetic reactions with turbulent mixing. - Useful for e.g. evaluating new injector design, reactor geometries, and predicting carbon conversion.

12 Results

13 Equilibrium Model: Contours of Axial Velocity in Pilot Gasifier, Steady state simulation Recirculation zone Plug flow zone Natural gas Oxygen High velocity zone, exit injector Flow direction High (+) V -0 - High (-) V = reverse axial flow

14 Equilibrium Model: Velocity Vectors in Gasifier Dome, Steady-state Dome High V Recirculation zone Low V Natural gas Oxygen Injector Axial flow zone

15 Finite Rate Chemistry Model Results. the Kinetics Model

16 Kinetics Model: Animation of Transient Gasifier Temperature t = 0 to t = 5.9 sec (~ 1.5 res. time) s O2 Natural gas 1.0 s 4.3 s 5.9 s High T Low T Flow direction

17 Kinetics Model: Animation of Transient Velocity Profile t = 0 to t = 5.9 sec (~ 1.5 res. time) 0.04 s High Velocity O2 Natural gas 1.0 s 4.3 s 5.9 s Low Velocity Flow direction

18 Comparison of Flame Shapes for Kinetics vs. Equilibrium Models

19 The Models Predict Different Flame Shapes. Top of gasifier Injector: O2 + Natural Gas Kinetics Model Equilibrium Model Flame begins after Induction region Flame starts as soon as O2 and Natural Gas mix Flame penetrates further into reactor Peak T is higher T max T min Direction of Flow

20 Summary Equilibrium and kinetics based models were developed and compared: - Kinetics Model results represent first simulation of a gasifier, with full reaction kinetics. - Including kinetics allows: - More accurate prediction of e.g. flame shape. - Application to injector design, reaction chamber design, etc. - With computing power and advanced software available today, we can begin to do fully transient simulations including kinetics. - Transient modeling shows potential for analysis of startup and upset procedures. Successful modeling provides advanced tools for more accurate gasifier design, trouble shooting, and advanced technologies.