Waste heat boiler is also called in line boiler. It is normally installed between air preheater and oil preheater in carbon black producing line. It is used for recovering heat of high temperature of carbon black smoke gas (around  700℃-400℃) by producing steam, which could decrease secondary quench water yield and increase heat value of smoke gas.

Waste heat boiler belongs to shell and tube heat exchanger. High temperature flue gas flows through the inner part of tubes, while water flows through the outer part of tubes. The water is boiled in shell body and realizes separation in the gas phase space. It is a kind of nature circulation. Waste heat boiler is composed of smoke inlet device (smoke inlet box), heat exchange section, and steam drum (or without steam drum), smoke outlet device (smoke outlet box), and connecting pipes. According to different forms of installation, waste heat boiler can be divided into vertical boiler and horizontal boiler. Vertical type of waste heat boiler has the steam drum, while the horizontal type has two kinds – with or without steam drum.

Besides carbon black industry, waste heat boiler is also commonly used in petroleum chemical industry, metallurgical industry, mechanical industry, paper-making industry and sludge incineration, etc.