There is a leak in the tubes of the waste heat boiler, and the cause remains unknown to this day
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Dear all**, let me first introduce the equipment. The waste heat boiler here is essentially a simple U-shaped heat exchange vessel; there is no gas-liquid separation device on the shell side. The reaction products – aniline, hydrogen, and water – flow through the tube side, while boiler water flows on the shell side. This setup generates 10 kilograms of saturated steam, which is directly fed into the steam distribution network. The oxygen content in the boiler water quality is generally kept below 10 PPB. An ammonia addition device is installed at the water inlet of the steam drum; the ammonia solution is diluted with PW water, keeping the pH of the incoming water around 9. The pH of the wastewater remains around 8, and samples of this wastewater often turn yellow, indicating that tube corrosion is still ongoing. I have two questions: 1. When the drum liquid level is controlled at 50%, half of the tubes are above the boiler water level. Is there any equipment or similar design that addresses this? 2. The amount of chemical added by the dosing device is very small, usually around 300 kg; this water has not passed through the deaerator. With a boiler make-up water volume of 30 tons, could this have an impact on the boiler? 3. Ammonia water is added to adjust the pH – will it evaporate in the drum, resulting in a low pH level of the water inside the boiler? I’m checking the relevant standards; the pH of water in boilers should be between 10 and 12. Do you also use ammonia to adjust the pH when adding chemicals? Are there better chemicals to replace ammonia? 4. Where are the locations for adding chemicals? The deaerator, or the feed water pump inlet?
The pipes should not be above the water surface, and ammonia should certainly not be added to the water; the required quality standard for boiler water is no more than 0.03
The problem might lie in what is exposed above the boiler water level, as well as the addition of ammonia.
1. Have never seen it, nor have I heard of it. Possible process requirements. 2. Oxygen must be removed from both return water and newly added water. 3. Ammonia and water are mixed in a 1:1 ratio. Evaporation is inevitable; it’s absolute, though it occurs relatively rarely and has little impact on pH. 4. Add deoxidizer at the deaerator outlet, ammonia before the feed water pump, and sodium hydrogen phosphate in the steam drum.
Judging from the poster’s question, they seem to be a process technician; however, based on the content of the question, they appear to be a beginner. Judging from the image, the degree of corrosion in these tubes indicates serious problems in the manufacturing process. Articles 2, 3, and 4 are not related to the engineering field, so I am unable to answer your question. Firstly, for boilers, it is a serious violation of operating procedures for the heat exchange tubes to extend above the liquid level. Tubes that are above the liquid level mean dry burning, which causes significant damage to the tubes; in severe cases, it can even lead to the tubes exploding.
Shouldn’t boiler make-up water be deoxygenated?
Power plant boilers also use ammonia to adjust the pH of the feedwater; this is a highly mature technology
This is what we commonly call a submarine-type evaporator; all the tubes must be submerged in water, otherwise it will overheat. There is one exception: in this type, the heat medium enters at the lower part of the U-tube, and by the time it reaches the upper part, its temperature has already dropped to the desired level. For chemical addition, we generally use phosphates, adding them directly to the steam drum and then carrying out blowdown.
Yes, our operating conditions might indeed represent the exception case you mentioned. The temperature of saturated steam at 10 seconds is 184°C, and the temperature of the material after passing through the heat exchanger is also 184°C. Is there any documentation where the design details for such exceptional cases can be found? Or have there been such examples before?
Actually, you can switch to a fire-tube boiler. This will be better