A Lancashire boiler is horizontal, fire tube, internal fired, natural circulation type boiler. There are two fire tubes. The fuel is burnt on the grate and hot flue gas is produced. The flue gas moves along the furnace tubes and is deflected up by fire bridge. As soon as the flue gas reaches the back of main flue gas tubes, it deflects downwards and travels through the bottom flue gas tube as shown by arrows in Figure 4.13. The bottom flue is just below the water shell and heats the lower portion of the shell. After travelling from back to front, the flue gas bifurcates into separate paths in the side flues as shown by arrows in sectional side view. Now, it travels from front to back in side flue and heats the side of the water shell. These two streams of flue gas meet again in the main flue passing; through damper they are discharged to atmosphere through the chimney.
Figure 4.13 Lancashire Boiler
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