Feed heat content, variation

Studies of the incineration of liquid and solid wastes must determine the rates at which hazardous compounds are released into the vapor phase or are transformed in the condensed phase, particularly when the hazardous materials make up a small fraction of the liquid burned. We must be particularly concerned with understanding the effects of the major composition and property variations that might be encountered in waste incinerator operations—for example, fluctuations in heating value and water content, as well as phase separations. Evidence of the importance of variations in waste properties on incinerator performance has been demonstrated by the observation of major smges in emissions from rotary-kiln incinerators as a consequence of the rapid release of volatiles during the feeding of unstable materials into the incinerator. 

Variations in efficiency are caused by differences in feed-water temperature and moisture content of the wood residues. The efficiency could be increased by employing the waste heat from the combustion gases to preheat either the fluidizing air or the boiler feedwater. Waste heat could also be employed to partially dry the fuel. 

A number of different evaporator designs are illustrated in Fig. 8, and the variations based upon these concepts are many. Often, physical properties and materials handling considerations for the feed or the bottom streams (e.g., solids content, viscosity, heat sensitivity) will indicate that one evaporator type will be better suited for the duty than other types. 

The retarding effect of sulphur is a dynamic phenomenon. This means that carbon may be formed at certain conditions in spite of sulphur passivation - although at strongly reduced rates and by a mechanism different from the formation of whisker carbon. Therefore, it was important to develop design criteria to make sure that the kinetic balance is in favour of no carbon formation at all positions in the reformer tube. This work was carried out mainly in the full-size monotube process demonstration plant (Dibbern et al., 1986). The influence of various process parameters (pressure, heat flux, sulphur content in feed, etc) was studied. It was demonstrated that the impact of variations in sulphur content in the feedstream on tube wall temperature and exit gas composition was completely reversible. 

---