Slag viscosity

Normally ca 50% of the coal ash is removed from the bottom of the gasifier as a quenched slag. The balance is carried overhead in the gas as droplets which are solidified when the gas is cooled with a water spray. A fluxing agent is added, if required, to the coal to lower the ash fusion temperature and increase the molten slag viscosity. 

The slag viscosity-temperature relationship for completely melted slag is... 

Several simple viscometers have been developed for in plant determinations of slag viscosities they include a Herty viscometer and a Krabiell immersion viscometer. ... 

Measurement and Prediction of Low-Rank Coal Slag Viscosity... 

The slag viscosity apparatus was assembled by Theta Industries, Inc. It includes a Lindberg furnace rated for operation at temperatures up to 2732°F (1500°C). The rotating bob viscometer is a Haake RV-2... 

Figure 1. Representative slag viscosity curves for three western U.S. low-rank coals.

Slag Viscosity/Composition Correlations. Several attempts have been made in the past to define the linear portion of the viscosity/ temperature curve based on the composition of the coal ash. In the mid-1960 s, workers at the British Coal Utilization Research Association (BCURA) developed. two such correlations based on work with British (bituminous) coals, now generally referred to as the Watt-Fereday (4) and S (3) correlations (6). Unfortunately, attempts to apply this correlation to low-rank coal slags, using either ash or slag composition data, have been generally unsuccessful. 

Table II. Analysis of Low-Rank-Coal Slags Produced in Slag Viscosity Tests...

Addition of limestone has been used to reduce slag viscosity in wet bottom coal fired plant and pulverised coal combustion, to facilitate slag and deposit removal. 

---