| OCR Text |
Show Coal sized -16t3mm (Table 1 shows the typical proximate and ultimate analyses) was supplied from a sealed hopper and fed via a screw feeder into the combustor. The coal entered 42cm above the distributor. Derbysh ire 1 imestone (mean size 2, 2mm) was used as the sorbent and fed prematically to the bed. Table 2 shows the chemical and size analyses of the limestone. The bed temperature was controlled by an adjustable heat exchanger coi 1 immersed in the bed. Exhaust gases were ducted to a cyclone where carryover was removed and co 11 ected in an ash bi n. An overhead propane burner was used to preheat the bed during start-up of the combustor. Experimental and Gas Monitoring Facilities The temperature of bed, freeboard and exhaust gases were continuously monitored by Chromel Alumel thermocouples located throughout the combustor, as shown in Figure 1. The axial temperature profile in the freeboard was monitored by a vertical temperature probe. The thermocouple outputs were displayed on a direct reading digital temperature indicator. The coal feeder was always calibrated at the start of each run. Water-cooled stainless steel sample probes were used to draw the combust i on gas samples to i nfrared analyzers for the determi nat i on of CO and CO2 and to a paramagnet i c analyzer for detect i on of °2 , An uncoo 1 ed sampling probe, located at the cyclone exit was used for t~e determination of S02 (by infrared analyzer) in the flue gases. The tips of all sampling probes were plugged with quartz-wool to prefilter the sample gas stream. EXPERIMENTAL PROCEDURE The bed was preheated by the propane burner with the cooling coil raised clear of the bed and fluidizing air flow rate set at the lowest practicable level to minimise heating time. The bed was preheated by the propane burner wi th the cool i ng coi 1 raised clear of the bed and fluidizing air flow rate set at the lowest practicable level to minimise heating time. Coal feeding was started when bed temperature reached at 550 C. When the bed temperature had reached 800 C, the required coal feed rate was set, the propane burner was switched off and the fluidizing air set to the required level. The overall total velocity was 1.5 m/s. For staged condition various proportions of the total air flow were diverted to the secondary air injector. The coal feed was adjusted to the des i red excess air 1 eve 1 . The bed temperature was maintained at 850 C by adjustable cool ing coil. Stable conditions were reached within 1 hour of the commencement of full coal feeding. Values of O~, CO, CO2 and S02 were recorded continuously during the experimental run. At the enCt of ttle run the bed materi a 1 was removed and co 11 ected for analysis. Fresh bed material was used for each run. (3) |
