EESAC SAS

Modelled fate of sulphur and chlorine
in rotary lime kilns | Part I: Chemical equilibria prevailing
in the kilns

All authors

1 Decomposition yield of CaSO₄ at different temperatures and different CO levels

2 Fluid inclusions inside a limestone matrix detected with a scanning electron microscope (SEM)

3 Decomposition yield of CaCl₂ at different temperatures and SO₂ levels

4 HCl formation rate from the thermal decomposition of MgCl₂

5 Sulphur concentrations in the cross section of a 50 mm lime pebble

6 HCl capture by CaO or CaCO₃ at different temperatures according to [7]

7 Sulphur and chlorine loops in a rotary lime kiln with shaft preheater

8 Continuous emission monitoring of the CO, SO₂ and HCl emissions of a lime rotary kiln

9 Vapour pressures of different salts found in lime kilns as a function of the temperature

10 KCl formation yield from K₂SO₄

11 Potassium chloride loop in a lime rotary kiln with shaft preheater

12 Typical relationship between chloride and potassium contents in the LKD of different types of rotary kilns

Investigations performed to predict the SO₂ and HCl emissions of rotary kilns have shown that Investigation performed to predict the SO₂ and HCI emissions of rotary kilns have shown that the chemical reactions needed to assess these emissions also enable quantification of the generation rate of build-ups in the preheating zone of these kilns. As anticipated by the theory and confirmed by industrial tests, sulphur and chlorine loops were found. The chlorine loop is closely interconnected to the sulphur loop that is itself influenced by the process conditions prevailing in the kilns. The quantification of the thus resulting emissions and generation of build-ups requires a precise assessment of all reactions involving sulphur and chlorine. However the first results of the modelling showed only a fair agreement between calculations and monitoring results. Further investigations were therefore carried out. Accordingly it was found that potassium plays a key role in the chemical reactions occurring in rotary lime kilns. The inclusion of this element in the modelling enabled a significant increase in the accuracy of the prediction. This paper presents the chemical reactions used in the model.

1 Introduction

The lime industry is using rotary kilns especially for the flexibility of this production tool. The energy efficiency of rotary kilns was along the time improved, especially with the development of shaft or vertical preheaters.

Practical experience shows that operators of rotary lime kilns face several challenges:

Rotary kilns equipped with vertical preheaters have to be frequently stopped since the preheaters are clogging for reasons that were until now unexplored and often considered as unavoidable. These stops trigger operational costs (cooling down of the kiln, cleaning of the...