PRESSURE boilers (> 80 bar) are universally used as they offer the following advantages:The efficiency and the capacity of the plant can be increased as a reduced quantity of steam is required for the same power generation if high-pressure steam is used.The forced circulation of water through boiler tubes provides freedom in the arrangement of furnace and water walls, in addition to the reduction in the heat exchange area.The tendency of scale formation is reduced due to the high velocity of the water.The danger of OVERHEATING is reduced as all the parts are uniformly heated.The differential expansion is reduced due to uniform temperature and THUS reduces the possibility of gas and air leakages.Fire-tube boilers are low-pressure boilers, while water-tube boilers are high-pressure boilers.Types of high-pressure boilersLa-Mont BoilerBenson BoilerLoeffler BoilerVelox BoilerCornish BoilerBabcock and Wilcox Boiler.Fire-Tube BoilerWater-Tube BoilerIn this boiler, the hot flue gases are present inside the tubes and water surrounds themIn this boiler, the water is present inside the tubes and the hot flue gases surround themThey are low-pressure boilers. The operating pressure is about 25 barThey are high-pressure boilers and the operating pressure is about 250 barThe rate of steam generation and quality of steam is very low, THEREFORE, not suitable for high power generationThe rate of steam generation and quality of steam is better and suitable for power generationIt requires more floor area for a given outputIt requires less floor area for a given outputThe overall efficiency of this boiler is up to 75%The overall efficiency is up to 90% with the economizerWater doesn’t circulate in a definite directionWater circulates in a well-defined direction