High Temperature Dry Injection

In this technique, hydrated lime is fluidised in air and injected into the boiler or kiln at temperatures in excess of 850 °C. A system designed for injecting hydrated lime is described in [29.1]. The hydrated lime decomposes within 30milliseconds [29.5] to a porous and extremely reactive form of quicklime. 

In the presence of excess oxygen (and in the absence of carbon monoxide), the quicklime reacts with oxides of sulfur at temperatures below 1200 °C to form calcium sulfate. The quicklime also reacts with any HCl or HF present. 

Early work, in which hydrated lime was injected into the firing end of the boiler, gave low SO2 removal and poor utilisation of absorbent. It now appears that this was due to over-burning of the quicklime. More recent research shows that the temperature at the point of injection should be below 1200 °C and above 850 °C, with an optimum range of loioo to 1100 °C [29.5]. 

The reaction products, together with ash from the combustion process, are removed in a dust collector and disposed to landhll sites. As with the dust from the low temperature injection process, the lime content can be used to solidify other wastes (see also section 29.8). 

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Calcium silicate - board 29.4 High-temperature dry injection... 

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