DEVELOPMENTS IN CLEANING COKE OVEN DOORS Paul H. Donnan Jetin Sullair Inc. 5131 N.E. Union Avenue Portland, OR 97211 SUMMARY This paper will report on the work carried out over the last eight years on cleaning coke oven doors by using high pressure water jets. On a coking plant the doors are regularly removed to enable the re-charging process to take place. The doors have to be cleaned within one and a half minutes during the "pushing cycle". Buildup of hard carbonaceous, bitumastic layers on the doors and seals prevent easy removal and replacement. Additional benefits of clean door seals are the prevention of polluting the surrounding area, and a lessening of health hazard to the coke oven operators. Investigation into optimizing the cleaning operation will be reported. INTRODUCTION Coke is used in the iron making processes and to make the coke, coal is baked in ovens for about 18 hours. The gases released from the coal are used for firing the steel furnaces. There are many by-products, such as tar, benzine and the residue coke is discharged, and cooled, prior to being fed into the hungry blast furnaces, as required, for the steel making processes. The ovens used for coke making are up to 10 meters high, 0.5 meters wide and 30 meters deep. In a large coking plant there are several batteries and each battery comprises 50 ovens (see figure 1). The charge of coal is fed into the top of the ovens and after cooking for about 18 hours, vertical doors placed at each end of the oven are removed, the red hot coke is pushed through into specially built railway trucks. The coke is then cooled and then fed by conveyors directly to the blast furnaces. After the coke has been pushed through, the two doors are replaced. There has been an increasing problem with existing coking plants where the doors have suffered from fouling with tar deposits from the coal. During the 'cooking process', bitumen separates out mainly on the bottom of the oven and if there are any gaps in the door seal, coal tar oozes out of the door. One can imagine that with high narrow doors making a metal to metal seal is quite difficult if not impossible. Distortion of the doors is inevitable due to high temperatures in the oven. The doors are held onto the oven with two latching catches; as these are turned from the vertical to the horizontal, the latch tightens onto the door jamb, pushing it towards the oven. At times, it is impossible to get the door back onto the oven because of a buildup of bitumen on the faces, thus a spare door has to be collected from the end of
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the battery and placed onto the open oven. This disruption wastes time and the target of pushing at least 6 ovens per hour falls quickly behind. On the side of the oven where the coke is deposited into the railway trucks, the door extracting machine is known as the 'Coke Guide' (see figure 7.) The coke guide removes the door, it moves along, positions the guide at the open oven and when the coke is pushed through, it prevents the red hot coke from falling onto the bench or walkway around the oven. On the other side of the oven, the door extracting machine is very different and is known as a 'pusher' (see figure 1.) It is large enough in size to carry a large ram up to 30 meters long, the ram face being the size of the oven. The pusher removes the door and then lines up the ram which then pushes all red hot coal through the oven and out of the other side. THE ENVIRONMENT Leaky doors allow coal gas and sulphurous fumes to escape to the surrounding countryside. When coal gas escapes from a leaky door, usually the gases ignite, causing a flame on the outside of the oven. These flames allow local overheating of the outside skin of the door and door jamb and this uneven heating can cause distortion. So, in addition to the buildup of carbonaceous deposits on the door and the door jamb, a distorted door presents an even greater problem in making a good seal. So the benefits of clean doors which are well sealed are many and are listed below, but not necessarily in order of their importance: 1. The operators have an improved working environment in that there is a reduction of obnoxious and potentially dangerous fumes. 2. The surrounding countryside is protected from pollution thus keeping EPA satisfied. 3. The doors can be removed and replaced as required and do not hold up the production of coke. 4. The doors are sealed against the ingress of air into the oven. 5. The oven temperatures can be stablized at the required temperature, therefore less energy is used. 6. A reduction of distortion due to flaming gases, which would overheat the doors and frames. 7. A reduction in the burning or wearing of the doors, seals and frames. TASKS TO BE CARRIED OUT The only time that is available for cleaning the coke oven doors is during the pushing cycle. The time allowed here is about 1 minute. Hitherto mechanical means have been tried by using hand-held scrapers, but with the size of the door and the time available, only one small part could easily be cleaned by an operator. This is sufficient in places such as India, where labor is cheap and their ancient coke ovens are only 3 meters high, but, of course, modern oven doors are up to 7 meters high and are impossible to hand scrape. This led to the development of a tracing motion which contained a large number of spring-loaded scrapers. This tracing motion was positioned up to the door which had been taken off. Pressure was then applied to the scrapers and the scrapers were propelled around the door seal with a hydraulic chain drive conveyor. This system allowed buildup of tar on the scrapers; lumps of tar fell onto the chair drive, jamming up the system, 159
causing chain breakages and the scraper jumped over hard deposits. This led the maintenance and operating staff to look for an alternative method of cleaning doors. The first approach of the idea of using a water jet was rejected on the grounds that the water would cause thermal shock to the door which has a ceramic insulation cladding attached to it. It was also thought that the cold water jetting would cause further distortion to the metal seal. Early trials with hand-held lance showed that if the water was directed at the seal and not the door plug (the ceramic insulation), then thermal shock cracking did not take place. It was concluded that the amount of water used in high pressure water jetting was dispersed in evaporation before sufficient heat loss of the door plug occurred. Trials were carried out to establish the cleaning rates and other information such as stand-off distance, water jet pressure, volume of water, effective spray patteren, velocity of traverse of water jet, etc. , etc. Initial ideas also included the use of a double water jet so that the door seal was cleaned twice in the one cycle. The object was to replace the scrapers with a lance carrier. There was also the problem of hose pipe snagging. With high pressure water jetting, the hose pipe remains in a fairly still condition and therefore, if there was to be a rotation of the water jet lance around the door seal avoiding the sprocket wheels and chains, then hose pipe trials had to be carried out. The possibility of a water jet lance with three nozzles attached to it was considered against a single jet of high pressure water with a greater stand-off distance. The next problem to tackle was the fact that it was found that a new or recently completely cleaned door could be kept clear if a water jet cycle was carried out at every door removal. Whereas doors which were already encrusted with hard bituminous deposits had to have a more intense cleaning operation carried out on them until bare metal was achieved. Always remembering that the time allowed for the door cleaning cycle had to not interfere with the 'pushing time'. One idea was to water jet the seals at 10,150 PSI for one traverse of the periphery, knowing that it would not completely clean the door. After three cleaning operations, the door seal should then be down to bare metal. After this, the cleanliness could be maintained with a single pass carried out at a lower pressure - say 4,350 PSI. The methods that were considered for changing the pressure of water jets are listed as follows: 1. The high pressure water is supplied by a triplex plunger pump, and the size of the plungers could be increased or decreased to give higher or lower volume of water by changing the size of the plungers. 2. The nozzle could be changed in the cleaning head to increase or decrease the orifice size. 3. One could vary the number of nozzles in the cleaning head. 4. The pressure could be changed by re-setting the unloading valve which has the effect of matching the jetting nozzles with the pump plungers used. The unloader is an adjustable spring-loaded annular orifice which can be increased or decreased to achieve any pressure desired. This could be wasteful of power in dumping water not
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required, and although it is convenient in other water jetting situations, in a fixed installation this is not always found to be desirable. 5. The speed of the pump could be increased or decreased with a variable speed motor, thus increasing or decreasing the volume of water. Eventually, the last solution was used, but as only two pressures were required, then a double wound stator was used and it was found that without changing the nozzles, simply by changing a connection on the motor winding, that the motor would rotate at either 1450 rev/min or 960 rev/min. The pressure being approximately inversely proportional to the flow, therefore, the higher speed rotation of the pump gave 10,005 PSI and lower rotational speed of the pump gave a pressure of 6,525 PSI. This simplified the operation of the speed changes or pressure changes for the operator. He could merely move a lever on the starter which was indicated 'high pressure' or 'low pressure'. So, as a door was removed, it was examined and the pump started at the required speed. Eventually, after the ovens had been used for about 3 times and all doors were kept clean by the lower pressure of 6,525 PSI, this saved pump power, use of water, pump wear, gland wear, nozzle wear and was generally thought to be the most efficient way of using the jet cleaning system. DESIGN SOLUTIONS The first cleaning machines were to be used on the coke side which generally has a more difficult problem with door sealing, as the hot coke is passed through this side of the oven. The coke guide machine is fairly small as it merely has the door extracting facility; a separate trolley car is towed behind the door extractor, which is quite a simple openwork structure. There was difficulty to find space to accommodate quite a large pump, 125 hp unit and a 400 gallon tank. The size of the tank was determined by the number of cleaning operations or pushing cycles required per shift and in order not to interrupt the flow of coke pushing, it was planned that the tank would be filled at the beginning of each shift. The tank was placed as high as possible in the coke guide machine to give a positive head to the triplex plunger pump, low level alarm and shutdown facility ensured that low level of the tank would either stop or inhibit the starting of the pump, this protected the pump from dry running. High pressure water is fed through a pulsation damper and a high pressure hose to the nozzle cleaning lance. Special attention had to be paid to the gland of the pump to ensure that the coal dust and ash dust which penetrates every corner of the door extracting machines did not affect the plunger seals and crankcase oil seals (see figure 6.) The tracing motion which originally carried the scrapers had to be redesigned to take the water jetting lance. The first design of the tracing motion carried two cleaning lances each on cleaning one half of the track around the periphery of the door seal. Eventually, this was replaced by one single lance, which rotated completely around the periphery of the door seal. OPERATING EXPERIENCES & CHANGES TO DATE Early use of the door cleaner in production had some problems with the lance becoming bent due to the buildup of tar on the door plug. This led to refinements on the hydraulic drive of the tracing motion. A relief valve was fitted so that if an obstruction
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was encountered, then the rotation would stop, giving a stall situation. After running the first machine for 15 months, it was then decided to install a water jet cleaner on the pushing side. The problems of installation were much simpler as the pushing machine is very large having to accommodate the hydraulic ram and there is much more space available for the water tank and the high pressure pump. Although this side of the coke ovens is a good deal cleaner than the coke guide side, provision was made for protecting the pump unit from coal and ash debris (see figure 6.) In order to prevent the buildup of tar on the brick retaining surface (see figure 4), it was decided to attempt to clean from the knife edge seal back to the edge to the brick retaining piece. This necessitated a re-design of the nozzle lance assembly. It was decided in order to obtain maximum coverage and maintain effective cleaning to fit a 3 nozzle design lance with accurately spaced nozzles with a stand off of approximately 160 mm. This in practice worked extremely well, however, the tar deposits were still adhering to the refractory and causing the lance to bend. In order to overcome this problem, we decided to approach the coke oven engineers with a further design of lance with different nozzle orifice areas which would effectively lower the pump pressure in order that we might clean the refractory without damaging same. The refractory cleaning lance would be fitted to the carriage assembly when the buildup was becoming too great and endangering the main lance. The formation of tar deposit under normal operating conditions can take up to eight weeks to form so therefore this refractory cleaning lance could be scheduled into the planned maintenance requirements on a monthly basis. In practice, initial worries about cracking the brickwork were soon dispelled as the lance was found to work perfectly and completely eliminated the problem of the lances bending. With the onset of automation in coke oven plants, it was requested that we design a fully automatic pushbutton system so that the door cleaning can be carried out completely from the coke car drive cabin. The only power sources available to us were electrical and hydraulic supplies. It was decided after due consideration and also the cost case to use hydraulics to actuate our diverter valve (see figure 10.) Variable orifice solenoid controlled hydraulic valves were already in existence on the coke cars since they were used for driving the old type coke oven door seal scraper unit but were made redundant when water jetting systems were fitted. In order to eliminate the unloader valve, it was decided to incorporate in the body of the diverter valve a needle valve which would be used to regulate the pressure and compensate for any nozzle wear, etc. (see figure 10.) In doing this cost reductions were made to the overall system, simplicity was added and the operational problems of adjusting the unloader valve, etc. were removed. Also by fitting the hydraulically operated diverter valve, we, to a very large extent, eliminated the tampering and deliberate abuse of the manually operated dump valve which existed in the original system. As has been stated previously, the bottom sides of the door are a lot more contaminated with the tar deposits than the top end, therefore with an automatic sequence control unit we would be able to decide at the touch of a button whether a single pass at the bottom of the door was sufficient or if not a double pass could be instigated so that only the most heavily contaminated areas at the bottom of the door were cleaned twice. This particular development has greatly enhanced the overall efficiency of the total cleaning system.
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Throughout the development of the systems, problems existed which were not immediately solvable since no equipment was available on the market. The problems were: 1. The hoses becoming caught in the cleaner frame. 2. The swivel couplings burst because of the high radial and axial loads they encountered and also dirt and acid ingress to the vital parts such as seals and bearing areas, etc. A decision was made to design a swivel coupling which would overcome all these problems and would, through necessity, incorporate the following features: 1. 2. 3. 4. 5.
Low breakaway torque, low dynamic friction. Rugged design with robust bearings. Would withstand the high operating pressure and intermittent high temperatures. Very fast seal replacement in the vent of seal failures. Would be resistant to acid attack and dirt ingress.
Prototypes of the swivel design were made and fitted to a coke oven plant on June 21st, 1982. So far these swivels have performed very satisfactorily and have had, to date, no seal failures or failures of any kind. They have completely eliminated the problem of the hoses kicking out sideways when the lance turns a corner, thus preventing the hoses from getting caught in the cleaner frame. The swivel couplings (see figure 9) are made of stainless steel and incorporate a large heavy duty roller bearing carrying the main shaft and a large heavy duty roller thrust race which carries thrusts developed by the high operating pressures. The swivel is fitted with a very high specification, low friction, pre-stressed seal, which is supported by an anti-extrusion ring. Many of these swivels have been made to date and so far not one has failed in any way. Since the swivel design has quite a large outside diameter, it was decided to bore out the carriage and fit clamps to accept the new design of swivel so that it was rigidly supported. Screwed directly into the swivel are the lances for cleaning the seals. FINANCIAL ASSESSMENT The installation of the water jet door cleaner will reduce the number of ovens lost due to the inability to latch doors after pushing because of their dirty condition. The number of ovens lost before the water jet cleaner became operational was 30 per month. This has now been reduced to 10. A saving of 20 ovens a month was made and this will increase the coke output by 4,080 tons per annum, assuming a wet coke output of 17 tons per oven. There are other expected savings, but these cannot be evaluated: (A) Reduction in maintenance costs because of the reduced oven door jamb and refractory damage due to firing around ovens caused by overheating and distortion. (B) Slight increase in gas (by-product) production because it is recovered and not burned around the door seals. Total savings are unaccountable here. But nonetheless, there are some savings. 20 ovens per month X 12 = 240 ovens per year 17 X 240=4,080 tons 4,080 tons X $75=$306,000 per year
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(C) Capital Expenditure: Material i.e. Pump unit Tracing Motion, tank etc. $112,210 Installation $ 32,060 Total $144,270 The payback time is less than six months as this is the first machine on the battery. The second machine on the pusher or cooler side has a longer payback period, say 12 months as the problems of fouling are not so great and the saving returns are less. CONCLUSIONS High pressure water jetting has proved to be a practical facility which assists the production of coke. It improves the environment of the plant coke operators and reduces the atmospheric pollution. The cleaning of doors is completed within the pushing cycle via a machine which is uncomplicated and reliable. Clean doors vastly improve door extraction and maintenance downtime on door machines has been reduced. Gas emissions have been cut down to a bare minimum, thus preventing open door fires which lead to oven door and jamb damage. There is more gas available for by-products recovery. Due to the elimination of door extraction and replacement problems, machine availability has been greatly improved. Also since the water jet cleaners have no mechanical contact with the door or plug, the machines do not cause any seal or plug damage; this has in turn reduced the maintenance requirement of the door seals. As can be seen, water jetting has assisted greatly in every coke oven manager's aims which are high production coupled with lowest possible running costs. REFERENCES 1. Graham, R.J., 1979 The Development of High Pressure Water Jet Equipment for the Cleaning of Coke Oven Doors, C.O.M.A. Northern Section, U.K. 2. Odds, D.J.H., 1982 Cleaning Coke Oven Doors 6th International Symposium on Jet Cutting Technology, University of Surrey, U.K.
Figure 1. Coke oven battery seen from Figure 2. View of bottom of door with tar Pusher side. Deposit hanging from seal.
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Figure 3. Tracing motion lance carrier.
Figure 5. Coke oven door – tracing motion unit.
Figure 7. Jetting lance with single nozzle in operation.
Figure 4. Section thru coke oven door.
Figure 6. Water jetting unit in its normal environment.
Figure 8. Cleaned up battery 12 months after installation of waterjetting equipment,
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Figure 9. Swivel coupling
Figure 10. Hydraulically operated diverter valve.
Figure 11. System layout.
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DISCUSSION NAME COMPANY:
R. Pootmans Indescor
QUESTI ON: "Is there not a problem in using multiple jets for cleaning the knife edge, the gas chamber, etc.? The reason for this is that Indescor holds USA patents for cleaning coke oven doors with multiple jets. British Steel gave us assurances that in trying to develop their own door cleaner, they would use single jets only." ANSWER: I do not believe there to be any problem in using multiple jets. I am reliably advised that the Indescor U. S patent requires jets oriented in different directions. The British Steel Corporation arrangement provided most satisfactory operation, either with single jets or with a plurarity of jets oriented in a common direction. I have no knowledge of the assurance mentioned.
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