Furnace gases are produced in different types of furnace during the production of metals. The principal metal is steel production. Throughout the steel production large volumes of different types of gasses are produced. The process would start with coke oven gas, blast furnace gas for the production of basic iron, and converter gas or Basic Oxygen Steel (BOS) gas from the conversion of basic iron to steel.
High levels of power requirement and rising energy costs present a major challenge to the metallurgical industry. Some furnace gases created as a ‘free’ by-product during production processes serve as an attractive fuel for power generation. In addition to the economic benefit, using these gases reduces industrial CO2 emissions and reduces dependence on fossil fuel resources.
Coke Oven Gas
Coke oven gas forms as a by-product when producing coke. Lignite or black coal are heated in a coke oven. At 1000-1400ºC the pyrolysis distillation process starts under the absence of oxygen. There are different processes available, with or without oxygen and with fresh water injection use to increase the gas quality.
The gas is made up of major compounds hydrogen (50-60%), methane (15-50%), a small percentage of carbon monoxide, carbon and nitrogen. With a calorific value between 4,4 – 5 kWh/m³, Coke Gas is considered a high value fuel for power production within the MWM range of reciprocating generating sets.
The leading Italian coking factory Italiana Coke SpA produces about 500,000 tons of coke per year, and generates over 25MW of power using four MWM TCG 2032 v16 generating sets.
Benefits of using Coke Gas
- Use of gases that are available at no additional costs
- Reducing energy consumption of the pyrolysis process (coke production)
- Reduction of greenhouse gas emissions, especially methane
- Saving money, because of significant lower energy demand
- In addition to power generation, heat or coldness production is also possible and can enhance the overall efficiency of the plant even further
Blast Furnace Gas
Blast furnace gas is a by-product of blast furnace operations where iron ore is reduced with coke into basic (pig) iron. Significant volumes can be produced but it has a very low calorific value of around 0.9 kWh/Nm3, which on its own is not high enough to fuel a gas engine. However, within an integrated steel works there is the possibility to blend this gas with the other gases from steel manufacturing process to produce a useable gas for power generation.
Converter or BOS Gas
Converter gas is created from pig iron during the steel production process. The conversion initially is to remove carbon from the pig iron. The two main steel making processes are air or more commonly oxygen injection (Linz-Donawitz (LD) process), or electric arc furnace. With oxygen injection the process produces sufficient heat itself to keep the metal molten, by lowering the carbon content. Electric arc furnace provides additional heat to the process. The Converter gas produced has a higher calorific value than BOS gas and consists mainly of carbon monoxide (~65%) and carbon dioxide (~15%) and Nitrogen (~15%). It can be used directly with for power generation but may benefit from addition of higher caloric value gasses.