Tube leaks, reboilers

That is, carbonic acid, will be formed. Carbonic acid is quite corrosive to carbon steel. Reboiler tube leaks, associated with steam-side corrosion, are almost certainly due to carbonic acid attack. 

Water in reflux tends to get trapped in the tower, if the tower-bottom temperature is above the boiling point of water, at the tower s operating pressure. The water trickles down the tower and revaporizes off of the hot reboiler tubes. As the water may be saturated with corrosive salts and gases, reboiler tube corrosion can be rapid. In almost every petroleum refinery service, refluxing water is a quick route to reboiler tube leaks. 

I cut the debutanizer pressure back to 100 psig and immediately the flooding in the main fractionator subsided. The operators then closed the inlet block valve to the hot-oil side of the reboiler and opened up a drain. Naphtha poured out instead of gas oil. This showed that the debutanizer reboiler had a tube leak. 

Obtain a clear, factual definition of the symptoms. A poor definition of symptoms is one of the most common troubleshooting pit-falls. In the debutanizer case history above, the following definitions were used by different people to describe the symptoms of a reboiler tube leak problem ... 

Tube leaks may occur in the reboiler, condenser, preheater, precooler, or any other heat exchanger linked with the column. Several experiences where leakage caused poor performance have been reported (71, 238, 239). The effect of a leaking heat exchanger tube depends on the magnitude, the direction, and the location of the leak. 

Effects of heat exchanger tube leaks into the column include off-spec products and/or undesirable chemical reactions. In some cases, this reaction may lead to rapid corrosion or plugging. It is important to realize that material leaking at the condenser or at an intermediate exchanger may travel to the column base and decompose there. In one vacuum column, water leaking at the condenser reached the reboiler and caused a pressure surge and tray damage (358). 

Effects of heat exchanger tube leaks out of the column include inability to maintain column pressiure, erratic performance of reboiler or condenser, and erratic performance in other units because of contamination of the heat transfer medium. One classic experience (239) of an extremely sick column performance caused by a leaking reboiler was described in Sec. 1.2. 

If none of these steps has identified the problem, it is likely there is a regenerator reboiler tube leak. When the regenerator has one reboiler, it cannot be taken off-line for leak testing. In this case, inject a small quantity of a tracer chemical into the steam supply. Then check the regenerator bottoms by chemical analysis for the tracer. Sulfur hexafluoride or lithium bromide can be used." ... 

He noted that the reboiler duly was partially restored when the vent on the top of the channel head (i.e., the steam side) was cracked open. He checked the vented steam with a gas test meter and found that it contained several percent hydrocarbons. Concluding that the reboiler had developed a tube leak, he advised management to shut down the tower to repair the reboiler. 

Low tray efficiency High tray AP Reboiler tube leaks Corrosion to tower shell Dew-point calculation for overhead... 

Most of my experience with this subject is a loss in reboiler duty (over one day) due to a tube leak, or the more gradual loss of reboiler duty (over one month) due to CO accumulation in the channel head. Regardless, to alleviate the loss of reboiler duty, vent the channel head just belozv the bottom channel head pass partition baffle. 

Solvent contaminated] carryover from upstream equipment example oil from compressor brines, corrosion inhibitors, sand, [corrosion products, see Section 1.3] /oxygen leaks into storage tank/inadequate corrosion control, example low pH causing corrosion/degradation via overheating, ex hot spots in reboiler tubes or fire tubes/ineffective filters/ineffective cleaning before startup/for amine absorbers corrosion products/FeS/chemicals used to treat well. 

Low boilup rate and decrease in steam pressure steam trap blowing, see Section 5.1. Low boilup rate, pressure increase in reboiler and surges ]foaming] /inerts/leaks/ undersized reboUer/diameter of vent line too small/top tubes not covered with liquid/high liquid level that floods the vapor disengagement space/inlet feed maldistribution/inadequate vapor disengagement. 

The preheater had several leaking tubes. Liquid hydrocarbon had backed into the exhaust steam header through these damaged tubes and flashed to a vapor. The light hydrocarbons flowed into the depropanizer reboiler along with the low-pressure steam. The propane and butane were, of course, much too volatile to condense. They filled up the reboiler tubes and thus reduced the ability of the reboiler to transfer heat between the condensing exhaust steam and the depropanizer. 

One of the questions that 1 am often asked is what can be done to mitigate reboiler tube failures in sour water strippers and the consequent steam leaks into the stripped sour water ... 

If the steam is at higher pressure than the process (which is frequently the case) and if one of the reboiler tubes develops a leak, steam will enter the process and flow up the distillation column. Given that the water has a much lower molecular weight than most chemicals that are being distilled, the volumetric flow of gas up the column can be so large that the trays or packing in the column are lifted up off their supports and seriously damaged. 

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