Effects of Sorbent Injection on Participate Properties: Part I. Low-Temperature Sorbent Injection

Abstract

This article is the first of a two-part series dealing with the effects of sorbent injection processes on particulate properties. Part I reviews the effects on particulate properties of low-temperature sorbent injection processes (those processes that treat flue gas at temperatures near 300 °F). Part II reviews the effects on particulate properties of high-temperature sorbent injection processes (those processes that involve sorbent injection into the combustion or economizer sections of a boiler). In this article, we review what is currently known about the effects of the low-temperature sorbent injection processes on electrical resistivity, particulate mass loading, particulate size distribution, particulate morphology and cohesivity.

Mixtures of ash and sorbent produced by low-temperature sorbent injection processes are typically less cohesive than most types of fly ash. At temperatures within 30 °F of the water dew point, the combination of low cohesivity and low electrical resistivity of the ash and sorbent mixtures can cause electrical reentrainment in electrostatic precipitators. Deliquescent additives such as calcium chloride cause the water to be retained on the particle surface, thereby increasing cohesivity.

Sorbent injection has been reported to increase the particulate mass loading by a factor of 1.8 to 10, depending upon the reagent ratio and the coal sulfur content. Conventional and in-duct spray drying processes tend to shift the particle size distribution toward larger particles, while dry injection processes tend to shift the particle size distribution toward smaller particles.