Heat Recovery Steam Generators
Continuously increasing local and foreign demand for Heat Recovery Steam Generators triggered the establishment within Hari Machines Ltd. of a dedicated design office dealing with designing and offering of Heat Recovery Steam Generators for the systems recovering heat from exhaust flue | gases leaving DRI | Sponge Iron Kilns, Blast Furnace Gas and Coke Oven Batteries.
Currently, one of the most developed solutions for Sponge Iron waste flue gases consists of units operating in an arrangement:

• Kiln Flue Gas
• Heat Recovery Steam Generator
• Steam Turbine

 
The challenges in the design of these boiler
• The design has to consider the high dust loading in the flue gases leaving DRI/Sponge iron kilns and its abrasive nature.
• Erratic fluctuations in the Temperature and Volume of the flue gases.
• Since the campaign life of Kilns varies, the boiler is subjected to thermal shock during start up.
• Flue gas feeding to the boiler is dependent on Kiln operation and quantity cannot be controlled.
The boiler system design has to consider these aspects for safety and optimum running cost of Boiler.
Boilers utilizing waste heat contained in the exhaust gases coming from the DRI Kilns, Blast Furnace and Coke Oven are called Heat Recovery Steam Generators (HRSG).
Heat Recovery Steam Generators may be manufactured as units without a supplementary firing, and in this type of boiler, only the heat contained in the exhaust flue gases is recovered, or as so called fired boilers, where a burner (or burners) supplying additional heat are installed in the boiler inlet duct.
Main features
• Large amount of gas compared with the amount of generated steam
• Low pressure drop on gas side of the boiler
• Large percentage of heating surfaces made of finned tubes
• Light and leak proof construction
• Modular structure and high integration level of boiler components
• High reliability
The use of finned tubes for heat exchange surfaces is necessary because of considerably lower temperature differential between gas and water/steam side in comparison with conventional boilers. Low temperature differential may also affect operating conditions. The slight change of evaporator pressure results in considerable change in the amount of steam generated thus creates a danger of not achieving the required boiler steaming capacity or a specified steam temperature. This shows the importance of precise thermal calculations and an importance of the heat transfer surface selection.