Is it feasible to neutralize the acidity and alkalinity of high-temperature flue gas?
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A waste gas treatment system is being designed to burn 40–60 kg of organic chlorides per hour. The burning temperature is 850 degrees; after the flue gas is produced, a waste heat boiler is used to generate steam. Generating steam is not the main purpose – it is primarily used to cool the flue gas, thereby facilitating its treatment. The flue gas is intended to be treated using a semi-dry method combined with the injection of sodium carbonate powder, before entering the bag filter. Question: The combustion of chlorides produces dioxins, especially during the flue gas condensation stage (around 300 degrees). I want to spray sodium carbonate or a sodium carbonate solution at 650 degrees, after the boiler output, in order to neutralize hydrogen chloride and prevent the formation of dioxins at 300–400 degrees. Dear experts, is this plan feasible? What new problems will arise? Thank you!
The waste alkali solution incinerator used in industrial installations follows the same principle as what the poster mentioned. From a design perspective, there is nothing wrong with it; however, many details need to be taken into account, such as flue gas temperature control (calculation of water injection volume), the structure of the nozzles, and the design of the residence time. Spraying the solution may not always be feasible, as the solution contains water, and spraying water will lower the flue gas temperature, whereas the process requirements dictate that the flue gas temperature should not be too low. . . . There are many more similar small details. Although the melting point of sodium carbonate is 850°C, the temperature of the spray-dried powder is around 650°C; due to the presence of impurities, sodium carbonate may become molten, leading to various engineering problems such as caking and sticking to the walls. . It is recommended to find an experienced engineering company or design firm to handle the design for you.
Pilot tests have been conducted; are there any actual projects that can serve as a reference?
We approached an engineering company to develop a plan: their proposal was for the flue gas coming out of the waste heat boiler (at 600 degrees) to enter a semi-dry quench tower (with an exit temperature of 180 degrees), after which sodium carbonate powder is sprayed in. I’m a bit worried about the formation of dioxins, so I plan to carry out the process in 2 stages: first, neutralize hydrogen chloride by spraying alkali at 650 degrees, then cool it in a semi-dry quench tower, and finally spray alkali powder once more. Everyone, do you think my worries are unfounded?
The low-temperature reformation temperature for dioxins – you can look it up online; there’s a lot of information available!! With dry and semi-dry methods, the main concern is usually related to chlorine. Find the curves showing temperature and removal efficiency, and calculate the chlorine content in the flue gas after treatment to see if there are any issues. Dioxins are relatively easy to treat!!
Theoretically, there’s no problem; it’s advisable to spray the sodium solution at around 80 degrees. Avoid using a cloth bag for dust removal – it’s not necessary. Just install a demister.
The owner does not want to use the wet method, as the wastewater generated is difficult to treat and contains fluorides
Does hydrogen chloride not react easily with sodium carbonate at high temperatures? I don’t have such a temperature response curve; do you have one?
Another question is: will spraying alkali powder in front of the semi-dry tower cause scaling in the semi-dry quench tower?