Low Temperature Dry Injection

With commercial hydrated limes (BET surface area about 15 m /g), and under optimum conditions, the high temperature injection process can remove 50 to 65 % of the sulfur dioxide, using a Ca to S stoichiometric ratio of 2.0, and given a residence time of about 500milli seconds at above 850 °C [29.5]. 

A pilot plant investigation [29.5] showed that the efficiency of desulfurisation depended on the fuel, burner operation and injection mode, but not on the surface area of the hydrated lime. However, a strong correlation was found between the development of internal surface area during calcination and sulfation, and the capture of sulfur. 

It should be noted that quicklime is not favoured for this desulfurisation technique, presumably because of  

Improved absorbents have been developed — see section 20.6, which describes the production of hydrated limes with high specific surface areas. [29.6] mentions a calcium lignosulfonate-modified hydrated lime for the high temperature injection process (presumably a high surface area hydrate). 

The principle advantages of this technique are that it requires relatively little capital expenditure and can readily be retro-fitted. However, it has relatively high absorbent costs and is only suitable where partial desulfurisation is required. 

---