Fundamental Studies Concerning Calcium-Based Sorbents

Abstract

Sorbent preparation techniques used today have generally been adapted from techniques traditionally used by the lime industry. Traditional “dry” hydration and slaking processes have been optimized to produce materials intended for use in the building industry. These preparation techniques should be examined with an eye to optimization of properties important to the SO₂ capture process.

The study of calcium-based sorbents for sulfur dioxide capture is complicated by two factors: (1) little is known about the chemical mechanisms by which the “standard” sorbent preparation and enhancement techniques work, and (2) a sorbent preparation technique that produces a calcium-based sorbent that enjoys enhanced calcium utilization in one regime of operation [flame zone (>2400°F), in-furnace (1600–2400°F), economizer (800–1100°F), after air preheater (<350°F)] may not produce a sorbent that enjoys enhanced calcium utilization in the other reaction zones. Again, an in-depth understanding of the mechanism of sorbent enhancement is necessary if a systematic approach to sorbent development is to be used.

The long-term goals of the experimental program that resulted in this report were (1) defining the effects of slaking conditions on the properties of calcium-based sorbents, (2) determining how the parent limestone properties and preparation techniques interact to define the SO₂ capture properties of calcium-based sorbents, and (3) elucidating the mechanism(s) relating to the activity of various dry sorbent additives.

This chapter documents (1) the collection, production, and characterization of a series of limestone/hydrated lime/quicklime samples representing a range of Ohio limestone products, (2) an investigation of the importance of lime solubility enhancement in the evolution of surface area during the slaking process, and (3) a model/paper study of the effects of chemical additives on the performance in spray drying and in-duct injection processes.