The present invention provides a heat recovery steam generator (HRSG) which introduces high temperature air generated from a cooler of a sintering factory to improve water circulation performance and maintenance convenience of the HRSG for producing steam and hot water, and provide effects of protecting a tube of high and low pressure economizers and extending a life of equipment. According to the present invention, the HRSG is formed by assembling upper, middle, and lower bodies. Flanges attached to each partition of the upper, middle, and lower bodies are coupled to each other by a bolt to be integrated. The upper and middle bodies, and the middle and lower bodies are connected by a tube to collect heat from the high temperature air flowing through a cooler, such that the HRSG generates the steam and the hot water. The upper, middle, and lower bodies are longitudinally divided into three pieces, so all nine blocks are formed. A sleeve is inserted into a tube hole of a casing an end part of the tube penetrates the sleeve without welding, such that an evaporator allows thermal expansion. A header end pipe of the high and low economizers is made of a low alloy material, and thus flow accelerated corrosion is prevented.
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