5.1 Introduction

Blending can be defined as "to combine or associate so that the separate constituents or line of demarcation can not be distinguished; to prepare by thoroughly intermingling different varieties or grades; . . . to combine into an integrated whole . . ." ^[1]. In the context of solid fuels, blending involves two or more combustible materials coals, biomass fuels, petroleum cokes to achieve a desired result. As the definition implies, blending is performed to achieve a consistent material. This requires an engineered approach to the process, rather than "a slug of this and a slug of that" and a hope for the best! Fuel blending has become increasingly common in the electric utility industry in recent years and for a variety of reasons. Fuel blending has also become commonplace in process industries such as pulp and paper, cement production, minerals refining, and other economic entities where solid fuels are commonly burned.

The basic principle of fuel blending is that, by combining two or more coals, or coals with other solid fuels, a new fuel is produced. While many parameters reflect the weighted average of the parent fuels (e.g., higher heating value), many other parameters reflect interactions between the fuels and as a consequence do not reflect the weighted average of the parent materials. Devolatilization patterns, total volatile evolution...