FACTSage

Solving your coal ash problems

It is now possible to predict, with a large degree of accuracy, all of the solid, liquid and gaseous phases that can be formed in the system Al₂O₃-CaO-FeO-Fe₂O₃-SiO₂ for the conditions encountered in coal utilisation technologies.

Do you have problems related to the mineral matter in coal?

Do you need to:

• Maximise your coal reserves?
• Optimise mine planning and blending operations?
• Avoid slagging and fouling problems?
• Optimise fluxing/blending for slagging gasifier applications?

These are typical problems faced by coal producers and utilities throughout the world. Now there is a tool to assist you in solving these problems - The FACT computer package. FACT is designed to predict the proportions of gas, liquid and solids in multi-component multi-phase systems. The CCSD has invested in developing a world class database related to coal mineral matter transformations for use with the FACT package.

It is now possible to predict, with a large degree of accuracy, all of the solid, liquid and gaseous phases that can be formed at equilibrium in the system Al₂O₃-CaO-FeO-Fe₂O₃-SiO₂ for the conditions encountered in coal utilisation technologies. These include the oxidising conditions found in pf combustion systems and the reducing conditions found in slagging gasifiers; at high temperatures when all mineral residues are molten and low temperatures when the last liquid slag component crystallises.

Predicting AFT

The AFT test is used by the coal industry to assess the relative melting and fusibility of coal ash. It is now possible to use FACT models to assist in the prediction and explanation of variations in AFT’s between different coal ash samples based on the bulk coal ash analysis (XRF) and the coal mineralogy. An example of this type of application is given in Figure A.

Figure A: Correlating ash fusion with liquidus temperature

FACT can predict the liquidus temperatures of the coal ash slags i.e. the temperature at which the ash is completely molten (Figure B), and the proportions of liquid and solid phases and gas composition at any temperature (Figure C, below). This type of information has direct application to slagging and fouling issues.

Figure B: Predicting liquidus temperatures

Blending of coals

When coals are blended to meet user specifications, and to maximise the use of the coal deposit, the melting behaviour of the mineral matter in the blend cannot be predicted by a simple additive rule. Weighted empirical measures, also, do not always provide a simple solution. For example, two different coals have CaO contents of ~0 and ~18 wt% respectively. FACT predicts a low proportion of liquid phase at 1400^oC for each of these coals (Figure C). A 1:1 blend of these coals, however, would result in a much larger proportion of liquid phase at the same temperature (~ 9 wt% CaO). Thus, care needs to be taken when choosing blending ratios.

Figure C: The effect of blending

Predicting Slag Viscosity

Knowing the composition and proportion of the phases present allows the viscosities of slags as a function of bulk composition and temperature to be predicted and therefore, the ash slag flow characteristics can be determined (Figure D).

Figure D: Predicting liquid viscosity

For more information contact:

Prof Terry Wall
Program Leader
University of Newcastle

Dr Eugene Jak
University of Queensland