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In 1929 Fred Clements, General Manager of the Park Gate Iron and Steel Co, Rotherham, published a massive work on Blast Furnace Practice. He cited many examples from all over the globe including his own Park Gate works. He described some details from the Carnforth works.
Blowing out lines
Blowing out lines
No 1a furnace 209,000 tons of haematite iron on this lining which involved 702,000 tonnes of solid materials. The analysis of the iron is as follows:
Silicon 1.5 to 4%
Phosphorus 0.018 to 0.02%
Sulphur 0.005 to 0.02%
Manganese 0.3 to 0.75%
Blowing out lines are a representation of the remaining refractory lining at the end of the campaign, that is, when the furnace was taken out of service and "blown out". The length of a campaign was dependent upon many different factors, and in Carnforth's case it is fair to suggest the reasons were frequently driven by market forces rather than worn out linings. Under normal circumstances, when a furnace was at the end of a campaign the refractory lining would be wrecked and replaced with a new lining within the same shell (or stack). Relining could take several weeks or months.
From the shape of the lines, two forces have been at work: Abrasion due to the sand blasting effect of dust charged gases, combined with abrasion due to the descending burden. There were other contributors such as the chemical erosion and the scouring effect of molten iron and slag. One major point of wear is practically on the stock line of the furnace, and is due to the impact of the charge as it drops from the bell.
The refractory lining is represented by the hatched area. It's internal outline would be straight lined when new but became worn in time.
If the refractory wears too thin it could expose the steel shell to dangerous high temperatures.
The Distributor
The Distributor
There are several very important reasons for distributing the burden evenly within the furnace. While iron ore is very dense, limestone is relatively lighter, and the fuel, coke, lighter still. There has to be a consistent mixture of the three so that the coke doesn't collapse and inhibit the free passage of gases through the burden.
The Brownhoist Distributor was built by the Brown Hoisting Machinery company of Cleveland, Ohio, and its function was to lift and distribute single skip loads of material inside the furnace. The drawing represents one from the Ebbw Vale works. The skip discharges in to a funnel shaped hopper with a chute with a flap on the end. The flap closes when the bell opens and restricts the escape of gas. Typically the chute might rotate 94 deg. between each skip so that over time the burden is evenly mixed. As already mentioned, it promoted good gas flow but it also prevented hot spots (or worse) cold spots, and distributed the abrasive impact of the burden falling from the bell on the refractory lining.
The drawing is consistent with the image of the top of the furnace, and it would make sense that the Brownhoist distributor would be integral to the upgrade from manual to mechanical handling.
The stock line (burden level) was monitored by a long metal rod hanging from a cable or chain through the top of the furnace. As the burden dropped the rod would fall and be measured. It was temporarily lifted clear every time the bell opened.
Cooling the Bosh (The base of the furnace where the molten iron and slag collect).
Cooling the Bosh (The base of the furnace where the molten iron and slag collect).
Carnforth employed a method for cooling the bosh consisting of a double spiral arrangement of open troughs down which the cooling water runs. There were some drawbacks with this design since the water is cooler at the top, while the bosh is generally hotter at the bottom. Water was in contact with no more than 20% of the bosh surface area leaving hot spots which could be problematic. There were other problems with corrosion and cleaning and it made running repairs to the bosh more difficult. Open water troughs were preferred to closed pipes because they were more easily monitored (and repaired). Workington had this same system until closure in the 1970s.
Dust Catcher
Dust Catcher
Fred Clements describes the special design of dustcatcher. Gas from the top of the furnace was needed to heat the stoves and to raise steam in the power house but it was laden with dust ad had to be cleaned . All contemporary dustcatchers employed the principle of changing the velocity or direction of gas flow to expel the heavier particles of abrasive dust (like a modern day Vacuum cleaner).
The shell is 16ft dia. and has a 6ft dia. central tube pierced with 580 slots, each with a deflecting baffle, sending the gas downwards. Splitting the flow in to many small streams reduces gas velocity and combined with a sharp change in direction, releases dust particles from the stream.
Below the cone on which the central tube is supported, a large space receives the incoming gas. The finer dust deposited, due to the 580 slots, collects in this open space above the supporting cone, and to facilitate removal, automatic unloading doors are arranged around the bottom of the supporting cone. A counterbalance keeps the doors shut until the volume of dust exceeds it and is discharged. The counterbalanced doors seal any leakage of gas between the upper and lower chambers. The valve at the top of the dustcatcher is constructed as a bell, which, when lowered, rests on the top of the inner tube.
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