Evaluating IGCC Slags

Coal gasification is at the heart of the integrated gasification combined cycle (IGCC) power generation process. Slag tapping difficulties and limestone flux requirements associated with high ash fusion temperature coals are considered the principal challenges to the economic use of Australian coals in slagging gasifiers.

Coal gasification is at the heart of the integrated gasification combined cycle (IGCC) power generation process. Slag tapping difficulties and limestone flux requirements associated with high ash fusion temperature coals are considered the principal challenges to the economic use of Australian coals in slagging gasifiers. CSIRO Energy Technology and the CCSD have been evaluating the suitability of Australian bituminous coals for use in entrained-flow slagging gasifiers. Services to the coal and power industries can now be offered in the areas of slag viscosity measurement and determination of limestone or other fluxing requirements.

Figure 1: Viscometer apparatus

Within the CCSD, CSIRO and Pacific Power have worked to provide viscosity data and models for evaluation of prospective coals. This has resulted in:

• development of accurate viscosity models for predictive purposes.
• establishment of the fluxing requirements for a range of Australian coals.
• the demonstration of the advantages of coal blending for reducing fluxing needs, and
• the development of a coal value model for predicting the optimum balance between gasification temperature and amount of limestone flux required for slag flow on an economic basis.

Coal value modelling has shown significant differences between various types of gasifiers (Texaco, Shell, MHI). Results indicate that for some cases it is more economically feasible to increase operating temperatures, rather than to add more flux, in order to obtain the proper slag flows.

Coal blending is advantageous for reducing or eliminating the need to add a flux at the plant, and for avoidance of blockages in the tap hole due to slag crystallisation. A low ash fusion coal can provide the flux for a high ash fusion coal and the high SiO₂ / Al₂O₃ ratio typical of many Australian coals is used to reduce the temperature of critical viscosity, which affects slag flow characteristics.

The procedures developed and the experience gained from the work described above, is now available on a consulting or contract basis to the coal and power industries. Facilities and services available include:

• an extensive slag viscosity data bank for the full range of Australian bituminous coals.
• empirical models for slag viscosity prediction over the range of temperatures of interest for continuous slag tapping.
• procedures for the estimation of flux requirements.
• established facilities and procedures for slag viscosity measurements using a high temperature rotational viscometer at temperatures up to 1650^oC.

For more information contact:

Dr David Harris
CSIRO DET

Prof Peter C. Hayes
Director, PYROSEARCH
University of Queensland
[ www ]: http://pyrosearch.minmet.uq.edu.au