Energy Technology Centre in Piteå

Modelling, Simulation and Optimisationof a Downflow Entrained-flow Reactor

for Pressurised Black Liquor Gasification

Magnus Marklund, PhD student ETC

Energy Technology Centre in Piteå

Gasification Plant Gasification Reactor

600 mmH: 1886 mm

Energy Technology Centre in Piteå

Objective

The main goal is to develop an advanced process model forthe reactor that can be used for design optimisation ofarbitrary unit sizes.

Energy Technology Centre in Piteå

Main model specifics

• Based on a commercial CFD code

• Simplified atomiser/burner

• Submodels for drying, pyrolysis, and char gasification

• Gas/droplet interactive turbulence model

• Partial combustion of fuel gases

• Inclusion of radiation and conjugate heat transfer

• Submodel for thickness prediction of smelt layer on wall

• Inorganic (smelt) reactions

Energy Technology Centre in Piteå

Methodology

• CFX4 (or FLUENT 6/CFX5)

• Distribution of non interacting discrete droplets

• Droplet conversion by customised user routines

• k- and Reynolds stress turbulence models

• Gas combustion modelled by EDC

• Discrete transfer or Monte Carlo method for thermal

radiation and a coupled model for conjugate heat transfer

• Åbo Academy’s model for wall layer thickness

• Inorganic (smelt) reactions by customised user routines

Energy Technology Centre in Piteå

Plan 01/02

Activities AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUNCFD2: Modified coal combustion model in CFX4 (paper)CFD3: Using EBU, EDC, and PDF for a combustor chamber (paper)CFD4: Including more char gasification reactions in CFD2 (article)EXP1: Determine droplet size and velocity distributions from nozzles (paper)

• CFD4: Possible collaboration with Dr. Fletcher USYD or Åbo Academy• EXP1: Possible founding of a Particle Dynamics Analysis (PDA) device

Energy Technology Centre in Piteå

Modified coal combustion modelNeeded:

• Proximate analysis (Moisture, volatiles, fixed carbon, and ash)

• Ultimate analysis of the volatiles and fixed carbon

• Higher heating value

• Emissivities for droplet and char particle

Devolatilization:

• Moisture and volatiles are released at a rate proportional (Arrhenius) to the remaining volatiles in the droplets

• Droplet swells linearly with released volatiles

Char gasification:

• Only combustion with oxygen

• Controlled by diffusion of oxygen to the droplet surface and the char reactivity

Energy Technology Centre in Piteå

Uncertainties and difficulties

Uncertainties:

• Droplet size and velocity distributions from burner

• Parameters for devolatilization and gasification rates

• Characteristic volatile composition

• Gasification of char

• Boundary conditions for heat transfer

Difficulties:

• Resolving the burner

• Convergence

Energy Technology Centre in Piteå

Simulations

So far...

• 2-dimensional axi-symmetric model

• Burner modelled as a circular inlet

• Simplified mechanistic model (no gas/ droplet interaction)

• CFX4 coal combustion model

• K- turbulence model

• Eddy Dissipation Model (EDM) and Eddy Dissipation Concept (EDC)

…to come

• 2D and 3D models

• More detailed burner (separate inlets for liquor and oxygen)

• Implementation of a more advanced droplet/gas interaction model

• Reynolds stress turbulence model

• Wall smelt layer

Energy Technology Centre in Piteå

First results (simple model)

90º Full-cone 95º Full-cone

Energy Technology Centre in Piteå

Latest results (coal model)

110° full cone spray70° full cone spray

Energy Technology Centre in Piteå

For updated information

www.etcpitea.se/blg

Acknowledged sponsors: