Developments in Blast Furnace Salamander Tapping
(Johan van Ikelen, Edwin van den Haak, Jan de Pagter, Frank Kerkhoven, Luc Bol Tata Steel IJmuiden, Blast Furnace Department PO Box 10.000, 1970 CA IJmuiden, Netherlands. Presented this document at the ECIC conference in Dusseldorf in June 2011.)
Blast furnace iron making
Life extension of blast furnaces
Over the past 10 years, five salamanders have been tapped at Tata Steel Europe IJmuiden’s BF6 and BF7. The techniques involved gradually changed over the years. By using a remote drilling technique, a more safe salamander tapping procedure was developed. The safety risks related to personnel working in a narrow space are avoided. In this method the drilling machine is positioned away from the furnace, even behind the salamander bed. Workforce close to the salamander taphole during drilling, is in this method no longer required. Apart from the much safer working conditions, there also is no longer the need to break away parts of the casthouse floor to create working space for personnel. Subsequently, the cast house can stay in operation until a much later stage. The drilling angle and drill diameter changed from almost horizontal with a small drill bit, to more steeply upwards with a larger diameter bit. The angle at which the runner is connected to the salamander tap spout consequently also became steeper over the years. A sand bed composed out of steel slag is created with excess capacity to collect the liquid salamander in a so-called ice-cube array. The large capacity allows for the use of a large diameter drill hammer and bit. In combination with the steep drilling angle (and hence higher Ferro static pressure) this results in a quick release of the salamander iron from the furnace hearth.
Salamander tapping of a blast furnace is the final tap after the furnace is blown down in order to drain the last liquid iron from the furnace hearth. Because of its rare occurrence a salamander tap represents for most companies a special job which requires a lot of preparation.
The salamander tap will be made at preferably the lowest level where liquid iron can be expected in the blast furnace hearth.
Given the construction of a blast furnace and its casthouse, in most cases the salamander taphole must be positioned somewhere close under the casthouse floor in a difficult to reach area, full with piping, cables, etc.
These difficult to access areas may also be dangerous areas for the people who are drilling or lancing the salamander, this because of insufficient or poorly accessible escapes routes.
This difficult situation is also present at the blast furnaces of Tata Steel IJmuiden.
In the past in IJmuiden the salamander tap was always organized with the intention to yield as much as possible liquid iron, to use it as hot metal for the BOS plant.
For that reason it was tried to catch the liquid salamander in a torpedo ladle, which led to the construction of salamander runners under almost flat angles, close under the casthouse floors.
Due to the rare occurrence the salamander taps in the past were not thoroughly engineered, they represented more or less a piece of improvisation, with experience from the last salamander tap in the lead and the outcome of the exercise was partly the result of empiric and gut feelings, rather than from systematic approach.
Also environmental effects such as big brown clouds were normal at a salamander tap.
Challenge to improve salamander tapping
The increasing emphasis on safety and environment became the drive to improve step by step the process of salamander tapping. While draining as much liquid iron from the hearth as possible still being the major goal, other issues became more and more important:
- Location of the salamander taphole
- Environmental aspects of salamander tapping
- Tapping the maximum of liquid salamander iron
The first problem to solve was finding the best position of the salamander taphole.
In the older days the exact position of the salamander was unknown, due to a lack of information on the blast furnace hearth interior and thus on the position of the wear line.
Without any or insufficient data from thermocouples it was difficult to determine the optimal position to drill or lance the salamander taphole.
Professional experience was leading in order to determine the drill location and angle to hit the salamander. More than once a number of holes had to be drilled and lanced before the salamander was hit and started to tap.
With modern blast furnace hearths being more and more equipped with dense thermocouple grids, thermal calculation of the position of the wear line, and hence of the salamander position, become possible.
The thermocouple grid of BF#7 in IJmuiden. The vertical rows of the thermocouples are installed in a much denser pattern than in previous campaigns.
Densifying the thermocouple grid improves the calculation accuracy, so that guessing where the salamander may be hit, is now replaced by knowing where the drill hits the wear line and, hence, from where we may expect hot metal.
An additional advantage of a more precise location is the possibility to improve the engineering of the setting round the salamander tapping.
The improvised salamander tapping in the past not only resulted in a lot of sparkling iron, but also in large clouds of smoke, conspicuously watched by the local authorities.
With growing attention for the environmental aspects, these dark clouds became more and more unwanted.
The improved estimation of the wear line position allowed for more detailed engineering of the salamander tapping.
Over the time, step by step improvements of the dedusting facilities at the salamander taphole were introduced.
Temporary exhaust hoods and duct work were engineered and constructed, sometimes even made from scaffold materials and connected to the existing dedusting system, in order to make a salamander tap not more polluting then a regular tap. The enormous clouds of red smoke in the past, which hampers also the view on the tap, have now largely disappeared.
In the past, salamanders were tapped after the blow down and after the blast furnace were completely off blast. As a result the salamander had only its own erro static?pressure as the driving force to come out of the furnace. Preferably one tapped as much liquid iron as possible, because the removal of a solidified salamander costs many days, with additional risks of damaging the blast furnace, due to the use of explosives.
Not drilling the salamander taphole completely through into the liquid and lancing the last part, results in an undefined taphole diameter and sometimes in slowly running casts. These slowly running casts may also be retarded by a decreased hot metal temperature of the salamander, caused by the effect of the hearth cooling system during the waiting time between the end of the blow-down and of the start salamander tap.
The doubt of whether all hot metal was completely drained from the furnace hearth, led to attempts to increase the drainage.
It was tried to keep some blast pressure on the furnace as an additional driving force to drain out more liquid. These attempts however were never very successful: usually the time to open the salamander tap was much longer then the time that the blast pressure was still on the furnace. More precisely: the blow down of the furnace was completed well finished before the opening of the salamander taphole.
Reducing or shutting off the hearth cooling was never considered, mostly due to the necessity to keep the hearth refractory and steel shell in good condition.
Another important drive to improve the salamander tapping was to eliminate safety risks. With the increasing emphasis on safety, the desire developed to tap a salamander without the need of having people directly nearby the salamander taphole. Salamander tapholes, however, in most cases are situated in a difficult to reach and confined areas, with difficult escape routes, inherent to their position directly under the casthouse floor.
The salamander hot metal was originally led to the torpedo ladles with runners shelled by dam-plates.
This allowed for a controlled filling of up to three small torpedo ladles, as here is no possibility to switch back to a ladle position upstream.
A tilting runner made it possible in 2000 to exchange an unlimited amount of ladles, but its disadvantage was the extra height required, lowering the salamander drill angle. The use of the tilting runner required a bended long runner to get a cross-flow in the centre of the tilting runner and the tilting runner had to be actuated.
In the same period, a dedicated salamander taphole drill was engineered. That was a regular pneumatic casthouse drill, which was mounted in a position under the floor, first manually controlled, like at the salamander tap of BF#7 in 2000.
To facilitate the installation and control of the tilting runner and the drill, it was required to break away a part of the casthouse floor. The actuator of the tilting runner was installed on casthouse floor level with view on the torpedo ladle. The opening of the
casthouse floor was a first step to improve the accessibility of the salamander taphole area. It was on the other hand also the start of increasing costs. Platforms were improved; drill machines professionalized and the numbers of access and escape routes increased but still people had to work directly under the casthouse floor and even with extra stairs it remained a difficult to reach and narrowly spaced area.
The flat angled and bended runner increased the risk of spilling hot metal. At the BF#7 2000 salamander the tapping speed suddenly doubled, resulting in a big overflow just in that bend. This in turn led to the fixation of a torpedo ladle in a pool of hot metal over the railway tracks.
During this incident the view on the torpedo ladles had completely vanished due to big dust clouds coming through the opening in the casthouse floor. As a consequence control of the tilting runner in order to shift from to ladle was impossible.
For 2002 partial reline of BF#6, engineering was prepared for a salamander cast in a pit of steel slag. Operations department however, preferred again a main salamander tap in torpedo ladles with the use of a tilting runner.
To check whether or not the furnace was complete drained from liquid iron, a secondary safety salamander tap was engineered at south side to be collected in a steel slag pit. This was our first attempt to tap a salamander in a pit instead of in a torpedo ladle.
After a slow running main salamander at the north side into the torpedo ladles, the south salamander tap in the steel slag pit yielded only a symbolical amount of 7 tons of hot metal.
The BF#6 2002 salamander was the last one tapped in torpedo ladles. The specially built large temporary platform and a remotely controlled drilling machine under the casthouse floor rendered the 2002 salamander tap the most expensive ever.
In 2005 we were informed that at SSAB Lulea salamanders were tapped, using a drilling machine positioned at more then 30 m distance from the salamander taphole, operated by Norrfjarden Brunnsborningar. This specialized company drills on a daily basis the Swedish rocks to find drinking water and thermal water for household heating.
With their pneumatic equipment they are able to cover all drill angles from vertical to horizontal. In the horizontal mode and with a slightly flexible air pipe they could drill the salamander at safe distances from behind the sand pit. When the salamander tap was running, the drill air pipe was cut off with an oxygen cutter and the drilling machine was driven backwards from the sandpit, while a front loader restored the outer wall of the sandpit.
An essential difference with the conventional drilling technique is the use of a drill hammer with the drill bit on top, which is mounted on the air pipe. In this array the impact of the hammer is directly given to the drill bit. The air pipe has no other function then only transporting the air from driller to the hammer. The drilling machine itself was used for forward transport of the air pipe and for a slow rotation to improve the removal of the fines crushed by the drill bit. A rack at the driller loaded with pipe segments of 3 meter allows for a quick elongation of the pipe. The hammer may is driven by a maximum of 25 bar of air pressure, provided by a big compressor.
After hitting the hot metal in the hearth, the pipe is cut, hereby disconnecting the driller from the running salamander tap.
With this information in mind, plans were developed for the 2006 intermediate repair of BF#7.
For this hearth repair the maximum amount of liquid had to be tapped to ensure the lowest possible amount of solidified salamander to be removed by the use of explosives.
A main salamander was prepared at the south side of the furnace and a secondary salamander at the north side, both to be tapped in a pit of steel slag.
A big horizontal beam of the BF tower construction, made it necessary to drill under an angle with increasing inclination. That created such high tensions in the steel pipe that the segments cracked and broke during trials. The solution was to use smaller diameter aluminium pipes in the heavily bended zone and to use guidance pipes through which de drill pipe was guided. This guidance was different from the drill method used in Lulea, where the drill rod lay completely free in the sand pit. At some 30 m distance the driller was positioned behind the steel slag pit.
Using nitrogen instead of air, due to fear for damaging the graphite refractory around the salamander taphole, the drill bit and hammer proceeded quickly through the graphite and the skull. Upon hitting the hot metal iron froze around the drillbit. After cutting off the air pipe, only one oxygen lance, pushed through the upwards pointing drill pipe towards the drill hammer, was sufficient to melt a hole in drill hammer and bit.
Both melted quickly away, resulting in a big iron flow that came through the Ø95 mm taphole. The 2006 salamander collected in a pit of steel slag was successful at South. But even with only one hour to ride the driller into the position at North, the secondary tap was a dry run.
One big advantage of drilling with the rock drill was the larger diameter drill bit used. Where with a conventional taphole driller mostly Ø50 mm bits were used, the rock driller had Ø95 mm, but also Ø110 mm was possible.
This more steeply upward drilling combined with a larger diameter taphole, secured that the taphole did not clog and that the furnace was optimally drained from hot metal.
The salamander taphole is repaired by inserting a graphite plug after core drilling the refractory around the taphole.
Due to the collapse of the steel market, it was decided to blow down BF#6 in 2008.
But for that salamander low cost was more important than completely draining the hearth. In order to tap the salamander in a pit of steel slag, a simple runner and a core drill combined with lancing was applied. This was cheap, indeed, but not everyone was satisfied with working conditions then.
In 2009, refractory problems below the North taphole of BF#7 were the trigger to develop the possibility to tap a salamander with only one day preparation time. This demanded to have the equipment for the salamander tap ready for use available on site. On order to facilitate a “one day lead time” to prepare a salamander tap, the North side of BF#7 was chosen for the construction of a permanent salamander spout, with a potential salamander pit made of steel slag above the north ladle tracks.
With prefab runner parts and an easy to transport everything was pre-arranged for the 2010 local hearth repair below the North taphole area. During the preparation, the prefab runner elements were positioned at the railway tracks, to check dimension and connections plus the required erection time. The blast furnace was blown down on two tapholes, South and West, and only when the last torpedo ladle at West was carried away to the BOS shop, the prefab runners could be positioned at the west railway tracks.
This part of the preparation was in line with the goal to be ready anytime to tap a salamander at BF#7 within 24 hours.
The only mismatch was the availability of the drillers. The drilling crew and machine had to travel from North Sweden to IJmuiden by truck, it takes about 48 hours to get them into drilling position.
The use of local drillers, however, is no option, because this drilling technique is not available nearby the Netherlands, also the proper equipment and the special tools can not to be acquired at short notice. These special tools are mostly notable the in-line drill hammers with diameter 95 or 110 mm, of which one needs more then one. This is because a so called”dry drill” implies that the drill hammer and bit are damaged or partly molten when compressed air as pneumatic driver is used.
In our case using nitrogen, which is available at 18bar for the PCI injection, instead of air for the power supply to the driller, it is possible to retract the drill hammer and bit after drilling into the liquid.
Of course the salamander iron froze direct due to the nitrogen purge, but again using one stitch with an oxygen lance, and the clogged taphole opened easily. The result is an easy running and safe opened salamander tap.
- An intensified thermocouple grid improves the calculation accuracy of the wear line
- Drilling at distance with the rock drill technique secures a fast opening of the salamander
- The rock drill bit of minimum 95 mm diameter provides a taphole which may drain the hearth quickly and minimizes the solidified salamander
- Equipping the blast furnace with a fixed salamander taphole spout and having prefab runners available, allows for the shortest possible lead time to tap a salamander in emergency cases
- Upwards drilling under an angle with larger diameter drill bit secures that the salamander taphole will not clog up and that the furnace will be totally drained from all hot metal