Salamander Tapping Position by Using an Acousto Ultrasonic Non-Destructive Testing
In iron making dialogue, a salamander is referred to all liquid and solidified materials in the hearth of a blast furnace which cannot be removed through the taphole. Taphole locations are designed in a way that a pool or sump of liquid hot metal remains in the bottom of the hearth. The resulting salamander has multi purposes. Primarily it provides a buffer to retard bottom refractory wear, acts as a thermal reserve to smooth process swings, and can aid in the control of hearth wall wear through preferential liquid flow patterns in the hearth bottom. Over the course of a campaign, the hearth bottom wears and the final salamander size prior to reline is normally substantially larger than the original design.
The hearth is defined as that volume of the furnace bottom that resides below the tuyere level. The entire hearth contains coke which provides support for the burden above and permeability for the flow of accumulated liquids within the hearth (i.e. interstitial spaces between the coke particles). However, the central section, known as the deadman, is an area of densely packed coke through which iron and slag generally cannot penetrate. The coke in the deadman is more degraded than the coke around the hearth periphery due to loading and extended residence time in the furnace. The top boundary of the deadman is defined by a central zone of coke which does not directly feed the raceway. The remaining deadman boundaries are defined by the underside of the raceway boundary and the furnace hearth containment itself. The shape of the deadman is somewhat conical with the apex located at the center above the tuyere zone. That apex section width is determined by the penetration depth of the raceway. The deadman widens towards the hearth bottom to generally encompass nearly the full area of the hearth bottom.
Under normal operations, the deadman can sit on the hearth bottom and prevent any flow below. This can result in preferential peripheral flow of accumulated liquids and will accelerate hearth wall wear over a campaign, potentially reducing the expected furnace campaign life. The well documented elephant’s foot can at least partially be due to this phenomenon. More recently, the design preference for furnaces has been to increase the hearth sump depth and allow for a larger salamander which increases the buoyancy capability of the salamander. In essence, the deadman can be lifted (or floated) to provide increased flow below the deadman to reduce the peripheral flow around the hearth walls, reducing the impact of wall erosion. The salamander has also been known as the “dead-man’s foot”, “furnace bear” or “furnace horse” (see Figure 1).
During the blast furnace blowdown for full or partial relining of a blast furnace, it is desirable to remove the remaining liquids in the hearth rather than allow the salamander to freeze. The removal of the salamander while in the liquid form has a few critical benefits; it significantly reduces the quench time required prior to furnace entry, facilitates the excavation of remaining hearth refractories and residual burden materials, precludes any subsequent need to remove the frozen salamander by blasting which can cause unintentional damage and require extended outage time, and prevents potential damage to the hearth refractories or shell by stresses imposed during blow in by the expanding salamander prior to re-melting.