Coke oven gas is a fuel gas consisting of hydrogen, methane and carbon monoxide. The gas is a side-product when producing metallurgical coke. The gas is produced by heating coal with a high bitumen content in a reducing atmosphere. The resulting off gas is filtered to remove dust, tar and oil and other impurities and then used as fuel gas. H2S is measured after the scrubber (process control) and O2 for process control to measure the amount of excess air added.