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Show -8- future programmes, should be the basis for the development of a simple mathemetical model with which to predict the performance of air staged combustion burners with coals of varying rank. DIRECT SULPHUR CAPTURE IN FLAMES BY CALCIUM BASED SORBENTS The majority of the work executed in this field by the IFRF since 1980~1 67; X 8 and 9 ] has concerned semi-industrial scale trials with swirling and parallel flow burners. A number of high volatile bituminous coals have been fired and work has been done also with a sub-bituminous coal. To a lesser extent, work has also been done with heavy petroleum residuals [ 10 ]. During these investigations, various sorbents have been tested including the two principal varieties, calcium hydroxide and calcium carbonate. In brief, the common trend identified, as shown in figure 7, is that relatively high sulphur capture efficiencies of up to 80% can be attained at a Ca/S ratio of 2, in optimum conditions. In order to achieve these results it has been found that the main, controlling factor is the time/temperature history experienced by the sorbent particle. In order to achieve high efficiences, it is important that the particles are not exposed to temperatures higher than circa o 1250 C but they should nevertheless be injected into a region where o they will experience a sufficiently high temperature - circa 1000 C - to promote rapid calcination. Further on the basis of some preliminary fundamental studies [ 11 ], indications are that it is necessary to provide a sufficiently long residence time (circa 600 ms) within this "temperature window" to allow sorbent sulphation to attain its maximum potential level. Another important fact noted was that consistently, Ca(OH) performed significantly better then CaCO , normally by a factor of |