Chemical Engineering - Fuels and Combustion - Discussion

Converter Gas, its Characteristics and Safety Requirements.

During the process of steel making in the basic oxygen furnace (BOF), a significant amount of gases, rich in carbon monoxide content, are generated during the blow time at a temperature of 950 degrees C. This gas is termed as converter gas or BOF gas. Converter gas is also known as LD gas. It is a byproduct gas produced during the production of liquid steel in a basic oxygen furnace (converter), where impurities of hot metal are oxidized with oxygen gas. The main constituents of converter gas are carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2), and nitrogen (N2). Composition-wise it is similar to blast furnace gas but with a lesser percentage of nitrogen in it.

Converter gas is dust-laden at the converter's mouth. The dust content is around 100 to 120 g/N cum. The recovered converter gas is cleaned in a venturi scrubber using water, followed by processing in the mist eliminators. The gas is then stored in a gas holder for steady supply cleaned further in the electrostatic precipitators (ESP) and finally fed to the gas distribution system. Wet type of gas cleaning plants can reduce the dust content of the gas to a level of 5 mg/N cum.

The composition of the gas varies from the start to the end of the blow and this is a function of the blow time. In the oxygen-rich phase (air ratio= 1) at the beginning and at the end of the blowing period the primary gas is burned completely and no gas is recovered during this period. During CO rich phase (air ratio less than 1) only partial oxidation takes place and a combustible waste gas is formed containing CO, H2, CO2, and N2. The maximum CO and H2 content in the waste gas corresponding to the minimum air ratio (air ratio 0. 1) is present during the main decarburization period (middle part of the blowing period) and maximum gas is recovered during this phase.

Converter gas typically has a high carbon monoxide content, low combustion speed, and is very harmful. It has got a calorific value which varies in the range of 1600 to 2400 kcal/N Cum of the gas. It is the function of the air ratio. The lower is the air ratio higher is the calorific value since the nitrogen percentage of the gas reduces. A lower air ratio also means a lower specific yield of the gas. The density of converter gas is 0.865 kg/Cum.