Gas detection for the steel industry
Regarded by many as providing the backbone to modern society, the steel industry is one which continues to evolve. Whether it is geographic shifts in demand or production, or challenges brought by energy or raw material costs, companies continue to develop their processes and facilities to meet them. Alongside these changes companies have also realised the requirement to minimise downtime due to unplanned maintenance and protect workers from exposure to toxic or flammable gas hazards.
Supporting these initiatives, Crowcon and its network of trained and experienced distributors has provided gas detection equipment to most of the major steel companies around the world.
The main gas hazards faced by these and other clients in the steel industry are from toxic gases such as carbon monoxide, ammonia and sulphur dioxide; from oxygen deficiency or enrichment; or from flammable gases such as hydrogen. Useful information on these is provided below.
The main process areas in steel production, explained in more detail below, are:
- The basic oxygen steel (BOS) process
- Secondary steel and concast
- Coke ovens
- Sinter production
- Iron production
Coke Oven Process
Coal is transformed into coke by an intense heating process, during which a mixture of high levels of the toxic and/or flammable gases carbon monoxide and hydrogen is produced. This gas mixture is used as fuel in other parts of the plant once other valuable but potentially harmful by-products such as ammonia, naphthalene and benzol have been removed and collected. The coke is cooled and passed to the blast furnace.
At the sinter plant, iron ore is crushed and blended, then mixed with limestone, coke, coal dust and water. A conveyor grate carries the mixture under a hood where a gas flame ignites the coke. This creates enough heat to melt the outside of the particles of material and create an iron rich clinker called sinter, which is sized and passed to the blast furnace. Gas hazards in sinter plants include unburned gas from burner flame-outs and oxygen depletion due to combustion.
Using coke as a fuel, very high temperatures are obtained by forcing hot air into a blast furnace (see diagram). As well as iron ore and coke, limestone is added to help separate impurities called gangule from the molten iron by combining with them to form a liquid slag that can be skimmed from its surface. A blast furnace produces a great deal of hot, dusty, toxic and flammable gas consisting of carbon monoxide with some hydrogen - the dust is removed and the clean gas stored for re-use.
Basic Oxygen Steel (BOS) Plant
Iron is converted into steel by removing impurities, most commonly via the Basic Oxygen Steel (BOS) process. Molten iron (‘hot metal’) is poured into an egg shaped steelmaking converter mounted on pivots so that it can be rotated. A long water-cooled ‘lance’ is lowered into the converter and pure oxygen blown through it. The oxygen combines with carbon and other elements eliminating some impurities while added lime reacts with others to form a slag. The carbon leaves the converter as carbon monoxide gas, which is cleaned and reused as a fuel or burned off. Nitrogen and argon may then be added for further refining before the steel is passed for secondary steel making or continuous casting. Gas hazards therefore include those associated with enriched oxygen, carbon monoxide and the oxygen depleting effects of nitrogen and argon.
Secondary Steel and Concast
The steel is given one or more extra treatments depending on the grade of steel required. These stages include ladle stirring with argon or nitrogen and vacuum degassing. These processes reduce unwanted gases such as those of sulphur and carbon to very low levels.
The steel is passed to a concast machine where it is fed into water-cooled moulds to solidify. When solid, it is cut into slabs and passed to the hot mill for re-heating to 1,300°C. Once re-heated it is rolled into strips. These processes present hazards of oxygen depletion, toxic sulphur or carbon derived gases and flammable risks from reheat burner flame-outs.
Such very harsh environments necessitate rugged and reliable protection - Crowcon’s advanced technologies deliver a range of products suited to this task. For example, robust carbon monoxide (CO) sensors can withstand temporary exposure to very high gas levels, ensuring long-term operation of fixed and portable detectors. Similarly, Crowcon’s fixed-point gas detectors and control systems are easy to use and integrate into existing control systems on older plants.
Robust design and ease of use applies equally to Crowcon portables. Led by Gasman and Tetra 3; enhanced by special dust filters and high resistance to RFI (Radio Frequency Interference) fields from Electric Arc Furnaces (often on-site for reheating scrap metal), Crowcon single and multigas detectors are trusted by steel industry users around the world.
Crowcon’s steel industry products and services are supported around the globe by its regional support centres and a mature network of experienced distributors.