The burden is usually distributed so that the gas flows through the centre of the blast furnace. This will cool the soup rapidly – and the same thing can happen in a furnace. Imagine you’ve just made a hot bowl of soup and then you drop an ice cube in it. Worst case scenario is that the scab can break off and fall into the molten iron below which can rapidly cool the iron and cause it to solidify. However, when a large scab forms, this distorts the path the gas takes and can reduce the amount of reactions happening. The ideal blast furnace burden should have a large cross-sectional area for the carbon monoxide gas to do its magic and react with the raw materials. A high lime chemistry increases the melting point of the slag, which can mix with the excess fines to form a sticky mixture which can adhere to the furnace wall. There are a few main causes for scab build-up – excess sinter fines within the furnace (which is sinter smaller than -5mm) and a high lime chemistry of the slag (which is the by-product of the ironmaking process). The same goes for alkali build-up in a blast furnace – a little is great for protecting the furnace refractory bricks from premature wear, however a large build-up can cause significant issues. Imagine an actual scab which forms when you’ve hurt yourself – it’s there to protect you. Alkalis naturally cycle within the blast furnace as they are present in the raw materials charged into the furnace and to some extent are good for the furnace. Scabs, also known as scaffolds, are alkali build-ups within the furnace which adhere themselves to the furnace wall. On to the main event – what are alkali scabs? The molten iron works its way to the bottom of the furnace where it is tapped out and transported to the steelmaking plant. This hot blast reacts with coal that’s injected through the tuyeres to produce carbon monoxide gas, which travels up the furnace and reacts with the raw materials to produce molten iron. Hot blast at temperatures around 1100 degrees is injected through the bottom of the furnace through copper nozzles called tuyeres. The burden slowly descends as the chemical reactions occur within the furnace. These layers make up what is called a burden. These are charged in specific layers – a ferrous layer of iron ore and sinter and then a coke layer which is a fuel. Raw materials including iron ore, sinter and coke are charged into the top of the furnace. Personally, I think they are named after women as, like me, they can be very temperamental at times and they definitely have different personalities. There are four blast furnaces at British Steel – known as the four queens of ironmaking. So what actually is a blast furnace? In scientific terms it’s a counter current thermal reactor, but in layman’s terms it’s a smelting furnace which produces molten iron. Throughout my apprenticeship, I had the opportunity to rotate my placements around different plant areas and this helped me discover my passion – ironmaking at the blast furnaces. I started my career at British Steel in September 2015 as a technical apprentice. Lucy Smith Technical Degree Apprentice - Blast Furnaces
0 kommentar(er)
