Introduction

Many industrial continuous processes produce large amounts of hot waste gases. Genera­tion of steam or power from these waste gases has been practiced for a long time. The waste gases can be at high, medium, or low temperature at —1000, 500, or 300°C, respectively. The gases can be clean or dust-laden, erosive, and even corrosive. Gases with meaningful calo­rific values (CV) are burnt with or without an additional support fuel. Blast furnace gas (BFG) and coke oven gas (COG) fall in this category. Several waste gases produced at high temperatures or in large volumes that contain considerable heat but no combustibles need only to be cooled (and at times cleaned) before release into the atmosphere. Sponge iron kiln waste gases fall in this category.

The devices that cool the gases and produce steam are generally called waste heat boil­ers. There may or may not be supplementary fuel firing, just as there may or may not be a need to clean the waste gases. The two types are:

1. Heat recovery steam generators (HRSGs) in power plants

2. Waste heat recovery boilers (WHRBs) in process industries

• Gas turbines (GTs) exhaust large amounts of clean, medium hot gases used in boil­ers, usually called HRSGs or turbine exhaust gas (TEG) boilers.

• In metallurgical, cement, and similar plants, large amounts of dusty hot gases pro­duced are cleaned and cooled and steam is produced in boilers generally known as WHRBs.