Rapid Assessment of Ash Agglomeration

Using Electrical Conductivity

R. W. Rice, Ph.DFellow, SWST; Fellow, IAWS

Evan Chatmas, MSThe University of Maine, Orono, Maine,

525 C 1025 C

Increasing Complaints about Sinter, Slag and

Clinkers in Biomass Burner/boiler Systems

Pellets Made of Pure Softwood and

Mixed Hardwood/Softwood

The Effect of Temperature

300-550C

>830C

450x350x

Location

Sinter, Slag and Clinker Formation

Large particles containing

Ca, Si, Mg, Mn, K, Al,

Vapors

Aerosols and fine

particulates, mostly

C, K, Na, Si, some

Ca

Na, K, S, Cl, SOx and

SO2, CO, CO2 heavy

metals

KCl, K2SO4, Na

compounds Melting and Condensation

“Stickiness”

Nucleation

and

Condensation

“Stickiness”

Bottom Ash-

Agglomeration or sinter or

slag

Fly Ash -

Agglomeration or

sinter or foulingSOx and SO2, CO,

CO2 etc

Chemistry

Element

Al

Ca

Cu

Fe

K

Mg

Mn

Na

P

Zn

Si

Oxide

Al2O3CaO

CuO

FeO

K2O

MgO

MnO

Na2O

P2O5ZnO

SiO2

European V Northeastern US~500C

Source Al2O3 CaO Fe2O3 K2O MgO MnO Na2O P2O5 SO3 SiO2

EU 6.76 28.9 5.12 13.2 5.4 2.77 1.42 2.64 2.67 31.6

US 3.63 33.1 2.68 16.34 6.78 2.34 2.05 3.52 2.65 18.67

EU Data extracted from Vassilev, 2010, US data from clean wood pellets, hardwood and softwood mixture

US >EU US < EU

Ca Al

K Fe

Mg Mn

Na Si

P

S

Fly Ash Collection-ESP

Mixed Hardwood

and Softwood

Softwood

Particle Diameters (μm)

Collection

Temperature (ºC):525 1025

Average Particle Size

Increase (%)

Softwood 2.07 3.15 52.2

Mixed

Hardwood/Softwd1.89 2.67 41.3

Malvern morphologi G3

Resistivity Measurements

1.4mPa

Softwood

Mixed Hardwood-Softwood

Comparison of Resistivity; Median Values

Conclusions

• Resistivity is a rapid and easy method to

assess the degree of sinter and

agglomeration in wood pellet ash

• Changes in agglomeration are much greater

between and 825°C and 1025°C than

between 525°C and 825°C

• The resistivity increases with temperature

increases are due to both chemistry changes

and particle boundary contact area changes.

Acknowledgements

• USDA-Wood Utilization Research Grant

• Corinth Wood Pellets LLC

• Maine Woods Pellets Inc

• Technical University of Zwolen; particularly Ratislav Lagana

• Unexpected new friends:

Thank You