Coal supplied to coke oven batteries is most economically brought in freighters that, even in the mid 1970’s, were unloading coal at over 5,000 tons per hour. As, by choice, they bring different kinds of coals, they are first stored in separate piles from where they are eventually collected, blended and sized. (Even the particular underground stream from which the coal is mined can influence the final quality and economics.) It is very desirable to do extensive research and testing to obtain the most desired mixture. The steel plant owners often invest and pay particular attention to this research and lab work to determine which mixture and size gives them the most desirable results. For the volumes and economies, all this makes sense.
In this modern competitive market, one cannot afford to investigate just the high volume, high cost items. One needs to trickle down a similar approach to many of the other aspects that ultimately affect the bottom line. One such item may be the gooseneck or stand pipe elbow which, in most, if not all cases, ends up being one of the “consumable” items in a coke oven battery.
In the “early years” when 4 m (high) batteries were very common, the goosenecks were simple in design. Environmental aspects, if considered hardly at all, were not nearly at the forefront, or strictly applied, etc. They are today. Those goosenecks were mostly cast, often cracked in time, deteriorated from corrosion/erosion, and were basically not repairable. (As one welder once commented “I can weld and join anything but (in use or used) goosenecks”).
There were, and still are, fabricated goosenecks but, generally speaking, they have a much shorter life span than the cast ones, as well as presenting several other shortcomings which cast ones can more easily overcome.
Perhaps it is necessary to note that, when we talk about standpipe elbows, we may be referring to a one single piece elbow (main body) as someone may visualize, or actually an assembly (that consists of many cast/fabricated, manufactured, machined and assembled pieces). Oncehaving been installed on top of the stand pipe, the assembly provides passage for the oven air, vertically to atmosphere, while closed from the collector main orfor the coke oven gas to pass (semi) horizontally to a gas collection system (collector main) while closed from the atmosphere. The units serve several other necessary functions as well, in the process of conversion of coal mixture to metallurgical coke.
When it becomes necessary to replace the elbow, it is usually and primarily due to the failure of the main body. The whole assembly is replacedat that time, with a spare pre-assembled, complete unit. Since every battery usually has several complete spare assemblies, the major impact at that time ends up being the potential disruption to the operations (which generally “never” shuts down totally during the life of the battery), safety and environmental concerns, as well as the cost of machines, various labor groups, etc. which are required to complete the task.
Perhaps it would be fair to assume that, as the spare units are being depleted, someone in the organization initiates an order to obtain more of the “same”. That may involve mostly the purchase of more elbow bodies with the idea of reusing many, or most, of the other components or obtaining complete, new assemblies while scrapping the complete old assembly. Very few of the present plants seem to be equipped to actually look at and try to improve the original design as it usually would involve a multi disciplined team with very specialized knowledge. As the plants with more than one battery may be using both, fabricated and cast elbow bodies, they would quickly recognize that the cast units do not only last longer, but offer numerous other benefits as well. In such cases they may initiate a conversion which could cost quite a bit initially, if processed through specialized design groups. A more cost effective alternative usually would be to have a foundry/fabrication supplier having staff with steel plant, foundry process, pattern making, machining, metallurgical, structural and engineering expertise under “one roof”. They usually can pool the in-house-knowledge and come up with appropriate conversions or improvements to existing castings with very low initial cost.
The fabricated bodies generally end up consisting of “off the shelf” plate and thus somewhat limited to the metallurgical choices. They usually end up not contributing to smooth flow patterns of, what at that stage of operation, could be considered as “dirty”, chemically active, hot gasses while also being exposed to much cooler ambient air conditions at another part of the oven cycle; thus generating internal stress points and collection points for deposits that are very difficult to keep clean, especially with taller, modern ovens which rely almost exclusively on mechanized cleaning.
With the cast bodies, the metallurgical selection could almost be considered infinitely larger as the casting floor and the on- site metallurgist can dictate the exact metallurgy for the uniquely controlled, smaller heats from which the casting is poured. Furthermore, the experience in preparing the mould, the design for internal flows of the liquid metal, the strictly controlled pouring temperatures, etc., etc., all tie into the very precise, individual control and documentation of each casting (to allow even more subsequently improved results as and when so desired). The sharp corners/stress and deposit points can and are very easily eliminated by appropriately designing and development of the pattern. Metal is placed basically where needed, and contoured for smoother gas flow patterns and easier cleaning.
Current requirements may not be just to simply improve the “life” of the elbow, but also to perhaps modify the design for easier assembly/disassembly, better sealing method, etc.
The original design may have called for clearances between mechanical, machined components that were very suitable when all was of new. However, after being exposed to the severe conditions that the goosenecks are exposed to during, even the “normal” operating conditions, those tolerance specifications may be too “tight” and extend the required disassembly/re-assembly times when using many of the previously in-service components. Thus they can be modified without negative impact during the normal operating cycle of the oven.
One of the latest conversions for sealing is to convert from mechanical, spring loaded lids to those utilizing a water seal. In such cases the gooseneck design may require a heavier and altered configuration as the water seal will need to be horizontal while this is not the case for the mechanical seal. Also, depending on type of joints in and around the stand pipe, it may require altered collector main support due to the potentially added side loading of the collector main. Obviously there are other considerations as well.
The bottom line for the bottom line should be that one does not have to live with the original design but, in the spirit of continued improvement, one should seek continued improvement, even if one needs to seek outside help.
Experienced foundry-fabricators such as Wabi Iron & Steel Corp. can provide customized solutions in converting fabricated goosenecks and other steel plant components into quality longer lasting cast pieces.