The diploma thesis deals with design of gas steam boiler with given parameters of steam. Blast furnace and coke oven gas are used as fuel. At the beginning of this work, both co-fired fuels are presented to us, their chemical analysis and stoichiometry are performed. The main part of the diploma thesis deals with the dimensioning of individual heat exchange surfaces such as steam superheaters, evaporators, economizers and air heaters. All heat exchange surfaces meet recommended parameters such as recommended steam rates, flue gas, etc. At the end, the total heat balance of the boiler is performed. Part of the work is also drawing documentation showing the main dimensions of the boiler. It is also indicated the connection of individual heat ...