Numerical simulations of particle deposition on super-

heatersA fundamental study

Oslo, 2010.02.16Nils Erland L. Haugen

Introduction

• Main focus: Particle inertial impaction– No thermophoresis, eddy diffusion or

Brownian motions

• This work has been done under the NextGenBioWaste project

Simulations

• Direct Numerical Simulations (DNS) are used– No modeling– No filtering– All space and time scales are resolved

• Including the thin but important boundary layer around the cylinder

• The Pencil-Code• 128 CPUs

The Stokes number

D

udSt

f

p

f

p

9

2

viscosityKinematic :

itymean veloc Fluid :

diameterCylinder :

diameter Particle :

density Fluid :

density Particle :

u

D

d

f

p

Particle impaction (0.01<St<0.3)Re=20 Re=420 Re=6600

Front side impaction efficiency

Front side impaction efficiency

Classical impaction

Boun

dary

sto

ppin

g

Boundary interception

Back side impaction

GKS (MSWI in Schweinfurt, Germany)

1685

mm 733

/sm 10

C600

m/s 5

24-

v

ud

d

T

u

Re

.

Super heater fluid specifications:

GKS particle impactionRe=20 Re=420 Re=1685

Impaction efficiency as function of particle diameter

Three ordersof magnitude

Impaction rate

Particle mass densitypr. bin (independent of bin size)

Conclusion

• DNS is required in order to resolve the important boundary layer

• Both the front and the back side impaction depends strongly on Reynolds number

• The total mass impaction rate at the super-heater of the GKS plant is totally dominated by particles larger than ~30 microns

Turbulence

Single cylinder vorticityRe=20 Re=420 Re=6600

Particle impaction (0.4<St<40)Re=20 Re=420 Re=6600

Alternative to the Stokes number

f

pSt