Slagging temperature indicators

The temperature at which ash particles change from a liquid to a solid. A high ash fusion temperature indicates that the ash particle will quickly change to a solid after burning and is less likely to adhere to a boiler fireside surface (as slag). 

The following is a brief survey of the methods adopted for slagging assessment. Temperature indicators... 

A number of indicators have been devised, based on the effects of temperature on the ash produced from the coal under carefully controlled conditions. The temperature indices are an attempt to assess, under standard conditions, the temperature at which the solid ash becomes soft and fluid thereby giving an indication of the temperature at which slagging is likely to occur. The major standards that are used for these tests are, in no particular order ... 

Temperature indices are useful but limited in application as discussed earlier in this section. Until improved methods of assessment become available predictions based on chemical composition are likely to yield the most useful data. Tables 16.4 and 16.5 probably provide the most reliable indication of slagging propensity along with the base to acid ratio... 

Because of the broad similarity to coal, tests to assess the potential for fouling (and/or slagging) have been based on those developed for coal, for instance the temperature indicators described in Section 16.3.2.1 Dabron and Rampling [1988] have given some ash fusion data for refuse derived fuel from three different UK incinerators and compared them with a coal as presented in Table 16.16. 

Real MHD Channel Slag (Ki). Detailed TMS and KMS studies were made of vapor transport over a high liquidus temperature (a. 1700 K) potassium-enriched coal slag with initial composition as indicated in Table II. This slag sample was obtained by combustion of Illinois No. 6 coal with additional potassium added to the combustor [see ( )[. Note that this slag composition lies between those of the "Eastern" and "Western" coal-types. 

Can one explain this importance of the slag Measurements of conductance as a function of temperature and of transport number indicate that the slag is an ionic conductor (liquid electrolyte). In the metal-slag interface, one has the classic situation (Fig. 5.81) of a metal (i.e., iron) in contact with an electrolyte (i.e., the molten oxide electrolyte, slag), with all the attendant possibilities of corrosion of the metal. Corrosion of metals is usually a wasteful process, but here the current-balancing partial electrodic reactions that make up a corrosion situation are indeed the very factors that control the equilibrium of various components (e.g., S ) between slag and metal and hence the properties of the metal, which depend greatly on its trace impurities. For example,... 

Fig. 3 shows the effect of using the new system on the outlet temperature of the packed bed. For this experiment the reactor was started as usual (no gas withdrawal), after 6 cycles, gas withdrawal via the slag tap was started. It was observed that the maximum outlet temperature (at the end of a cycle) decreases to an acceptable level of about 75 °C. This decrease in maximum outlet tenq)eTatuie indicates that cooling of the bed is now faster than reheating of the beds. 

Hot phosphoric acid has been successfully used to digest ion-based alloys when HCl would have volatilized specific trace constituents. Phosphoric acid can also digest a wide range of aluminium slags, iron ores, chromium and alkali metals. The temperature and pressure profiles for H,POj indicate that temperatures of 240°C can be attained with just 3 atm. Because of its low vapour pressure, relatively high temperatures can be reached without disrupting the digestion. 

The results of practical tests with glasses and slags indicate that with porous refractories melt infiltration takes place which may change the mineralogical (phase) composition in zones even quite distant from the interface. If the melt penetrates to points of lower temperature, reactions with the melt may create new minerals, in the form of quite distinct zones parallel to the surface. The infiltration can be effected not only through pores but also by faster dissolution of the finer bond between the Coarser grog grains. Such a transformed surface layer may cause faster destruction. 

To further investigate the characteristics of the slags, plots of the logarithm of viscosity versus temperature were made. These indicated straight lines or two line segments. For slags with a sudden increase in viscosity at lower temperatures, two segments were observed. Shear rates were not varied and the various types of non-Newtonian behavior were not explored. A related study indicated pseudoplastic behavior for this type of material (9 ). 

T,K) are shown in Figure 4 and Table V for this investigation on Kilauea Iki basalt, for the work of Shaw on Halemaumau basalt (10,13) and for Corey s report on Coal Slag X (1 ). The Kilauea Iki data show a sharp increase in slope at 1170 C as indicated by the limiting straight lines above and below this temperature. 

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