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Replacement of the bell-less top gearbox at Baotou Steel’s No4 blast furnace with a modern hydraulic distributor Following years of unreliable operational and maintenance performance with conventional blast furnace bell-less top gearboxes, Baotou Steel designed and built its own, based on a hydraulic principle. This was successful and now all six furnaces are equipped with this design. Retro-fitting is straightforward.

Baotou Steel Works is a fully integrated steel producer in Inner Mongolia located approximately 600km west

of Beijing, China, which produces approximately 10Mt/yr of steel. The main products are steel rods, beams, columns, plate, heavy tracks for high-speed train systems, square and seamless pipe. Baotou Steel operates six blast furnaces.

REASON FOR CHANGING THE BELL-LESS TOP GEARBOX In 1995 Baotou Steel installed a conventional bell-less top on its No4 blast furnace. After experiencing operational and maintenance issues with the conventional planetary gearbox, Baotou decided to develop a more reliable system based on the use of hydraulic technology, which was installed in 2000 on the newly built No1 blast furnace.

In 2003, after rotational problems with the conventional gearbox that ultimately led to bearing failure on No4 blast furnace, Baotou replaced the gearbox with a second conventional-style gearbox. The second gearbox operated for approximately one year, and once again failed due to bearing problems. Senior management at Baotou decided to replace the conventional electro-mechanical gearbox, including the distribution chute, with its own hydraulic distributor design similar to the one installed on No1 blast furnace, and for which the company holds three patents.

DESIGN REQUIREMENTSThe new hydraulic distributor (see Figure 1) was designed to meet or exceed the capabilities of the existing conventional gearbox. Design requirement criteria included: ` Repeatability in establishing chute positions for

charging ring locations ` Revolution speed

Authors: Han JianJun, Zhang WeiDong, Donald Howell, Robert A D’Arrigo, Johan van Ikelen and Geert-Jan GravemakerBaotou Steel, Woodings, Corus and Danieli Corus

Raw MateRials and iRonMaking

` Reduced maintenance costs through reduced complexity of components

` Improved reliability through redundancy ` Provided the ability to withstand top temperatures and

pressures, both under normal blast furnace operations and during excursions

The distribution chute and the cradle design allow the chute to be exchanged without needing to open or enter the hydraulic distributor case. The chute change door on a

r Fig 1 Hydraulic distributor design

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to provide easy access and maintenance to the cylinders. Connecting rods link the hydraulic cylinders to an inner ring inside the distributor casing. The inner ring moves in an up and down motion as the hydraulic cylinders extend and retract. This inner ring is then connected to an actuator ring assembly through a connection using an X-style roller slewing bearing. The bearing connection is designed to allow the actuator ring to rotate in a continuous 360-degree motion and move up and down based on the movements of the inner ring. The actuator ring is then connected to two pivoting crankshafts by a robust link-arm design. The link-arms force the crankshafts to pivot as the actuator ring moves. This link-arm to crankshaft connection transfers the vertical motion into a horizontal rotation motion that in turn tilts the distribution chute up and down. The crankshafts pivot on a set of bushings located in the trunnion. The other end of the crankshafts are connected to the distribution chute cradle using a spline connection. The distribution chute is connected to the distribution chute cradle and as the crankshafts rotate, the distribution chute cradle tilts the distribution chute.

Chute rotation is achieved with a 10hp variable frequency drive motor which is coupled to a vertical gear reducer that rotates a drive pinion. The motor and reducer assembly are located outside and on top of the distributor case to provide for easy maintenance. The drive pinion rotation movement is transferred to the distribution chute through the following connections: The drive pinion rotates an externally geared X-style roller slewing bearing. The trunnion is bolted to the rotation slewing bearing and the trunnion then rotates the crank shafts. As mentioned above these are connected to the distribution chute cradle which connects with the distribution chute.

This design meets the redundancy requirements by designing repetition into both the tilt and rotation motions.

the blast furnace is the only portal opening required to exchange the chute. In addition, the cooling system was designed to utilise once-through untreated cooling water instead of closed loop cooling, which would increase the capital and operating cost of the system.

The scope of work for the conversion included the removal and re-design of the lower cone section below the bifurcated chute, the expansion joint and internal liners, the goggle valve, and the conventional gearbox. The new water discharge lines were designed to be located above the furnace top flange to avoid making penetrations in the furnace shell. The furnace top flange and chute change door were removed and re-designed to accommodate the different height of the new design, thus the elevation of the furnace top flange was lowered by 230mm. Everything above the lower cone section of bifurcated chute remained the same (see Figure 2).

The benefits of hydraulic systems in other equipment applications, namely, reliability, repeatability and low maintenance cost, played a major role in this decision. In comparison to a conventional gearbox design that utilises complex mechanical gearing and mechanical brakes to control the distribution chute angle, the hydraulic distributor design is simplified by hydraulic cylinders and a main bull gear to achieve the chute manipulations required for modern blast furnace burden charges. Another recognised benefit when comparing electro-mechanical chute movements to a hydraulically controlled system, is the increased speed and repeatable accuracy to locate the distribution chute with the hydraulic control system.

The hydraulic distributor uses two types of motion to control the distribution chute, tilt and rotation. The tilt motion is achieved by utilising hydraulic cylinders to precisely locate and hold the chute position. The cylinders are mounted on top and outside of the distributor case

r Fig 3 Hydraulic distributor water cooling diagramr Fig 2 Equipment comparison before and after

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a

The distribution chute tilt will operate even if one hydraulic cylinder fails. A cylinder can also be easily replaced because the cylinder and its connections are mounted outside the distributor casing. The distribution chute rotation redundancy is achieved by the installation of a complete spare drive assembly which is mounted on the outside of the distributor case. This back-up drive can quickly be activated should the main drive fail. The conventional gearbox design does not provide these redundancy features.

The cooling system (see Figure 3) was designed to utilise once-through untreated cooling water instead of closed loop cooling which would increase the capital and operating

cost of the system. The cooling water is pumped into an enclosed trough located inside the top of the distributor which then discharges into a shower ring-pipe below the trough. The shower ring-pipe has several holes in it which are positioned to directly spray the cooling water onto the feeder spout housing. The water cascades down to the top of the trunnion and collects in a containment area on the trunnion top surface until it builds up in a shallow pool. The water then falls over a ring dam and cascades down the trunnion and is collected in a stationary trough located at the bottom of the distributor. A paddle system connected to the rotating trunnion is continually rotating to prevent

r Fig 4 Construction photographs: a) Chute door and frame removed, b) Cutting top flange, c) Removing top flange, d) Preparing to install chute door and frame, e) New hydraulic distributor being hoisted, and f) Installing hydraulic distributor and lower cone section of bifurcated chute

e f

c d

a b

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instrumentation lines were connected to the associated equipment. After all equipment was installed, the furnace was leak tested. All systems were tested during the cold and hot commissioning and the furnace was restarted 72 hours after construction began (see Figure 5).

RESULTSFrom a process observation, the learning curve for the operators was minimal due to the similar characteristics of the burden material falling curves. The hydraulic distributor is easy to maintain, yet very robust in design. The principal process features are similar to a conventional bell-less chute distributor (ie, upward and downward spirals, ring charging and point charging). The chute revolution is 8RPM and the tilting speed is 1.5 degrees per second. The system can operate in two modes: weight based and time based.

The hydraulic distributor has been proven to withstand high top gas temperature excursions of >1,000°C without any damage and provides more accurate control of the chute position, allowing improvement potential of burden distribution and thus higher productivity. The operating philosophy for a centre working furnace is easily accomplished. With the continuous requirement to lower blast furnace coke rates, burden

sediment from settling out of the water and building an insulating layer of debris in the bottom of the distributor. In addition, nitrogen is injected into the distributor case to provide a slightly higher pressure than the blast furnace top pressure. This positive pressure prevents dirty blast furnace gas from entering the distributor and, in order to provide additional heat protection, a refractory lining is applied to the all surfaces exposed to the inside of the blast furnace.

CONSTRUCTION A selection of photographs during construction are shown in Figures 4a-f. In September 2005, No4 blast furnace was stopped. The burden was capped and the demolition began, including the removal of the lower cone section of the bifurcated chute, the expansion joint, the goggle valve, the conventional gearbox and the chute change door. The furnace top flange was removed and the upper section of the furnace dome and chute change door was cut and removed to accommodate the new elevation of the top flange.

The new furnace top flange and chute change door were installed on the furnace dome, then the hydraulic distributor, goggle valve, expansion joint and lower cone section of the bifurcated chute were installed. The new hydraulic lines were connected to the cylinders, and the water supply, discharge pipes and lubrication system connected. The electric and

r Fig 5 Construction schedule

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SUMMARYDuring the planned outage in September 2005, the successful conversion of a conventional bell-less top to a hydraulic distributor was achieved on No4 blast furnace gearbox at Baotou Steel. The project was performed safely, ahead of schedule and on budget. All equipment design and operational requirements were achieved and proven through several years of operation at Baotou. Since the conversion to the hydraulic distributor, the furnace has operated without process concerns or equipment issues. Now all six blast furnaces at Baotou are equipped with hydraulic distributors, including No1, the newest one, which was commissioned in 2006 with the technology.

The productivity rate of No6 blast furnace is 2.7tHM/m3/24hr (8.4tHM/100ft3/24hr) with a pulverised coal injection rate of 150kg/tHM. This world class performance is a direct result of the advanced technological design of the hydraulic distributor. MS

Han JianJun is Director of Iron Making Plant and Zhang WeiDong is Deputy Section Head of Equipment Section of Iron Making Plant, both at Baotou Steel (Group) Co Ltd. Donald Howell is Vice President Operations and Robert A D’Arrigo is Vice President Sales, both at Woodings Industrial Corporation. Johan van Ikelen is Maintenance Manager Special Projects at Corus IJmuiden, The Netherlands and Geert-Jan Gravemaker is Consultant Iron Making with Danieli Corus BV, IJmuiden, The Netherlands.

CONTACT: Edo.Engel@danieli-corus.com

distribution plays an important role in accomplishing steady PCI levels of 150kg/tHM, at productivity levels of 2.7tHM/m3WV/24hr.

Table 1 indicates operating data for Baotou Steel’s blast furnaces. Note: all blast furnaces now operate with a hydraulic distributor.

SECOND GENERATION HYDRAULIC DISTRIBUTOR DESIGNIn 2006, Woodings Industrial Corporation, Mars, PA, USA, bought the ownership of all rights to this technology, with the exception of use on mainland China. Woodings, in cooperation with Baotou, developed the second generation design of the hydraulic distributor. The main design criteria called for the direct interchangeability of the distributor with a conventional gearbox. The design now maintains the same distance between the furnace top flange and the lower flange of the isolation goggle plate, therefore, changes to the equipment above the isolation goggle plate are not required. The furnace top flange can also remain in place and all bolt patterns are matched. This greatly reduces the outage time for installation.

Another important design requirement included holding all critical dimensions and elevations related to the position of the distribution chute. This is done to maintain material falling curves and avoid any changes to existing burden charging models currently in place on operating blast furnaces. The cooling system for the conventional gearbox can be adapted to meet the hydraulic distributor requirements with minimal change.

BF BF BF BF BF BF No1 No2 No3 No4 No5 No6Working volume (m3) 2,200 1,780 2,200 2,200 1,500 2,500Furnace top equipment Hydraulic Hydraulic Hydraulic Hydraulic Hydraulic Hydraulic distributor distributor distributor distributor distributor distributorTop charging skip skip skip conveyor skip conveyorHoppers 2 2 2 2 2 2Top pressure (bar) 2.5 2.5 2.5 2.5 2.5 2.5Blowing rate (m3/min) 4,000- 3,400- 4,000- 4,000- 2,900- 4,800- 4,500 3,500 4,200 4,200 3,000 5,200Hot blast temperature (°C) 1,150 1,150 1,150 1,150 1,150 1,230Moisture (%) 20 20 20 20 20 1Oxygen (%) 2.2 2.2 2.2 2.2 2.2 2.5Blast pressure (bar) 3.5-4.0 3.5-4.0 3.5-4.0 3.5-4.0 3.5-4.0 3.5-4.0Coal injection (kg/tHM) 111 101 123 125 137 150Coke rate (kg/tHM) 468 452 444 416 429 350Ferrous charge: Pellets (%) 18.7 19.4 18.7 19.2 18.7 17.5 Sinter (%) 81.3 80.6 81.3 80.8 81.3 77.5 Raw ore (%) 0 0 0 0 0 5Iron production: tHM/day 4,100 3,400 4,550 4,600 3,150 5,894Average furnace availability (%) 98.50 98.50 98.50 98.50 98.50 99.73

r Table 1 Blast furnace operating data at Baotou Steel

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