Gas preheating temperature
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The reason for preheating coke oven gas is simple: it is to prevent tar, naphthalene, and other substances in the gas from condensing and blocking the pipes. The preheating temperature specified in many books and operating procedures I’ve seen is 45–50°C. Why is this? What negative consequences might arise if the preheating temperature is increased further (e.g., to 70°C)?
We discussed this issue some time ago. When I was asked about it recently, I really didn’t know the answer. A senior from Hebei University of Science and Technology told me that when the temperature rises, substances such as naphthalene, hydrogen sulfide, and other components present in tar break down to form gaseous substances; these then cause carbon particles, elemental sulfur, and naphthalene to be released, which in turn block the pipes! ~:)
What was said upstairs makes sense. I don’t understand it myself, but if 45–50°C is sufficient, then why go up to 70°C? Right?
Reply to 2# penti: I was wondering, what is the temperature on the 2nd floor? Will the naphthalene, hydrogen sulfide, and other substances that make up those medium-viscosity gases separate into carbon particles, elemental sulfur, and naphthalene? Isn’t elemental naphthalene a gas at high temperatures? Why is the pipe still blocked? Besides, wouldn’t the temperature be even higher once the gas enters the pipe bricks? In tube bricks, 700 or 800 degrees should be fine, right?
Reply to 3# Liu Qinfen: You have too little experience and still don’t understand what I mean. My opinion is that preheating to 45–50 degrees is sufficient, but our manager here requires a higher temperature for preheating, and I am looking for reasons to argue against that.
It can easily clog pipes, especially when the tar content is high, as the tar dries and solidifies instantly.
40–50 degrees falls within the normal range; it’s best to keep the temperature around 50–65 degrees, and it should not exceed 70 degrees, as this can cause gum-like deposits to form in your preheaters. For more details, refer to the advice given by the teacher on the second floor!
Instead of using bricks to block the pipes, it will be the gas pipes in your branch lines that get blocked. If preheating to 70 degrees, it won’t take more than a year before there’s a resistance difference of over 2,000 units in all the gas branch lines, along with various temperature differences in the main flue ~
Preheating the gas to 45–50 degrees Celsius is sufficient to prevent the deposition and condensation of tar and similar substances; going any higher is unnecessary. One side effect is that it affects the absolute flow rate and causes fluctuations in the furnace temperature. I haven’t experienced this in practice, but if the temperature is maintained at 60–70 degrees for an extended period, the resistance associated with using the control valves increases within 10 days. It becomes difficult to operate these valves, to the point where even large wrenches can’t turn them.
Bro, we need people to go to the basement, right? The gas pipes aren’t insulated, are they? With a preheating temperature of 70 degrees, how can you expect the guys in charge of adjusting the settings and operating the switches to survive?
There is always a matter of balance involved; a temperature of around 50 degrees is sufficient to prevent tar and naphthalene in the gas from condensing. Going any higher not only wastes steam but also deteriorates the operating conditions, and it may even cause the tar-like substances to solidify, which is not worth it.