Construction of a Coke Oven Battery
Introduction
Coke oven plants in SAIL steel plants are due for rebuilding and presently many batteries in various plants are under rebuilding. In order to successfully complete the rebuilding of batteries, lot of concerted effort is required from engineers of all disciplines. The experience of Russian engineers for construction of green field Battery No. 4 at Bhilai Steel Plant has been described in this paper and can be used as a guideline for building new batteries as well as rebuilding of batteries.
For green field battery, the first job is making available clear levelled site for the battery and proceed for the civil work like excavation laying of lean concrete and reinforcement for laying raft concrete. If piling work is necessary, it should be done. The approximate volume of work involved is given below:
Sl. No. / Item / Quantity1 / Earth Work / 17,000 m3
2 / Concrete / 10,000 m3
3 / Refractory / 14000 t
4 / Structure / 1100 t
5 / Equipment / 2000 t
During rebuilding or construction of new coke oven battery, all jobs have to be done under difficult working conditions with adequate safety precautions and in a coordinated manner with the operation department.
Two reinforced concrete buttress walls have to be constructed at each end of the battery. These buttresses keep the battery in position in the longitudinal direction during heating and operation
Temporary Oven protection roof
The main refractory work in the battery is done in the temporary construction shed. This shed is necessary as any exposure to rain will damage the silica bricks used in the construction of the battery simultaneously with the work of waste heat flues, erection of construction shed is taken up. The size of the shed is generally 80m X 20m X 13m in height. There about 18-20 bays with column at about 5m distance. The total weight of the structure is about 250 tonnes. The erection of this shed poses considerable difficulties owing to the movement of quenching car containing hot coke. Many working platforms are erected for enabling refractory erection. Corrugated GI sheets are used for the roof and side cladding of the shed with provision for ventilation. The construction of the shed is completed in about 3 month’s time.
Coke Oven Battery
The overall output of the battery is about 0.5 mt of coke per year depending on the design. Most of the coke oven batteries are of Girprokoks design with a coking time of 16-18 hrs. With a small change in the temperature regime of the battery, it is possible to reduce the coking time to 16 hrs. thereby increasing the output. Giprokoks design batteries are in operation with 14 hrs. coking time giving higher output.
Refractories
Refractories are required for the construction of the coke oven battery. About 550 shapes of refractory are required in the following zones of the battery.
Heating flues & Regenerator, Vertical flues, Flue covers, Oven covers, waste heat flues, Insulating bricks, light weight bricks, high grog bricks, door lining, armour lining, regenerator shield lining, fire clay mortar, silica mortar, insulation mortar. The approximate quantity of refractory bricks including all shapes is about 14,000 t which includes both silica and fireclay.
The construction of refractory is carried out zone-wise.
Anchoring of Oven Brick Work
The refractory work of the battery is anchored from outside to guard against any damage.
The reinforcement of the brickwork consists of cast iron armours covering the heating walls from both pusher and coke sides and huge anchor columns of steel pressing the armours to the brick work and fitting closely to the face of the dividing wall of the regenerators. The columns are braced together with tie rods of 50 mm dia. one in the concrete basement of the battery and two in the top portion of the battery brick work.
Mortars
About 1200 tons of mortar of different types is used corresponding to the requirements of bonding of the particular class of bricks with admixtures of other materials like sulphited cellulose extract, high alumina cement etc. to secure special properties and give the required strength of bond.
Fire clay mortar: Used for bus flues and regenerators and ovens cover
Silica mortar: Low temperature (100-1350 deg C) – used for regenerators
Average temperature (1350-1500 deg C) – used for all other zones of the battery
Insulation mortar: Used for all insulation work in all the zones
The mortars are prepared in different mortar mixers to the required consistency
CI Fittings
The construction of the battery involves about 50 tons of CI Fittings as mentioned below, which have to be placed in the refractory masonry as the work proceeds
Bushing and collars 10 tons
Top sight hole for the vertical flues 20 tons
Sight holes into the regenerators 2 tons
Charging hole frame with covers 20 tons
All the above material are HR castings having about 8% chromium
Temporary Heating System
For heating up of the battery, temporary heating system comprising of ovens built with fireclay bricks both on pusher side and coke side is erected. These ovens have checker work and also ports for introduction of gas burners. The volume of work is about 400 tons. After heating up of the battery up to 800 deg C this temporary heating system is dismantled and removed from the battery.
Chimney
The gases from the waste heat flues are led to a chimney through a common flue. This chimney is 100 m high and has the shape of a truncated cone with top and bottom diameter of about 3.4 m and 8.2 m respectively. The thickness of the chimney wall varies from 300 mm at the bottom to 160mm at the top. At 10 m intervals continuous ring brackets are provided on the inside to support the refractory lining.
Erection of Mechanical Equipment
The erection of mechanical equipment for coke oven battery consists of the following:
I. Battery
Flash plates
Bottom tie rods
Top tie rods
Buckstays
Doors & Door frames
BF & CO gas piping for permanent heating
Air and gas valves
Reversing mechanism
Hydraulic mains with platforms and pipelines
Stand pipes, Goose necks with valves
Charging hole covers and frames
Technological piping for steam, water, compressed air, condensate lines etc.
Cross over gas mains with platforms etc.
Temporary heating system
II. Machines
Electric Loco
Quenching Car
Pusher Car
Charging Car
Door Extractor
In Coke Oven especially, the physical placement of equipment on prepared foundation and alignment does not complete the erection. This is mainly because the equipment and structures are erected at the ambient temperature whereas the working temperature is considerably higher and as the battery is heated up to the working temperature, the equipment and erected structures have to be regulated. The critical temperature to which the ovens are heated is 1000 deg C and in order to avoid undue stress on the equipment and structures, these are regulated day-to-day as the heating is in progress. The regulation is the most time consuming and important element in any coke oven battery erection.
Temporary works in the battery erection
The refractory work of the battery is done under the protective covering of a temporary shed. This shed is utilized as a supporting structure for many of the temporary works required for the equipment erection. Two mono-rails are supported on the trusses along the entire length of the shed on either side of the battery. With the help of telphers erected on these mono-rails, the equipment coming on the side walls of the battery and the top of the battery are lifted and placed in position. With the columns on the temporary shed as a support, cantilever platforms at 3 different levels on either face of the battery are erected for erection of mechanical equipment at respective levels. 2 temporary railway tracks of 1 meter gauge are laid on either side of the battery along its entire length. With the help of trolleys on these lines, the equipment required to be erected on the side walls of the battery are moved into position, lifted by the telpher and erected at various levels. After the equipment erection on the side wall is completed, the same railway track is shifted to the battery top and laid along the entire length of the battery and with the help of this temporary railway track and trolleys, equipment for the hydraulic mains, ammonia liquor line etc. are moved into position.
As all the equipment to be erected in the battery comes into direct or indirect contact with the refractory work of the battery which is liable to be damaged, extreme care is taken to protect the refractory edges from damage by placing across them pre-prepared protective wooden covers wherever erection is in progress.
The buckstays are held in position by the bottom tie rod already erected and the top tie rod. The buckstays are also supported at intermediate points to the battery by means of spring loaded fixtures. The buck stays support the flush plates in position. The alignment of the buckstays is done by spring loaded holdings at the top and bottom tie rods and intermediate positions. After the buckstays erection has progressed for 5 to 6 ovens, the door frame erection is started. The door frames are bolted down to flush plates already erecte with the help of tee bots inserted into slots in the flush plates. Between flush plate and the door frame 2 layers of glass fibre ropes are inserted. After the top plastering is done, the dismantling of the temporary shed is taken up and permanent alignment of hydraulic mains is done together with the working platforms on the top of the hydraulic mains. As and when the ovens are declared ready after attaining the critical temperature and completion of regulation of various equipment, the battery is switched over from temporary heating system to permanent heating system with CO gas. Continuous regulation of buckstays is to be done to prevent undue stress being developed and local buckling due to rise in temperature and expansion of refractory brick work.
Other equipment mainly consists of material handling systems, repair facilities, power supply systems, data acquiring, control and automation related subsystems which are also erected progressively along with mechanical equipment and commissioned along with battery.
Conclusion
The successful construction and commissioning of a coke oven battery requires a considerable amount of coordinated effort and excellent team work by experienced engineers and project executing agencies at all levels.
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