Construction of the acid dilution tank
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It is now necessary to construct an acid dilution tank with dimensions of DIA6m x 6.5m, to dilute 98% concentrated sulfuric acid to 30%, after which the solution flows automatically into a buffer tank; from there, it is pumped to a heat exchanger using a dilute acid pump for cooling. Regarding the construction of this dilution tank, as I lack experience in this area, I would appreciate your advice: (1) What material should be used for the tank body? From what I’ve found, stainless steel is not resistant to corrosion by sulfuric acid at moderate concentrations; therefore, I am considering using a structure with carbon steel as the base and epoxy fiberglass as the lining. Since there is only liquid-to-liquid contact between sulfuric acid and water inside the tank, the stress on the tank walls should be less than that caused by solid slurries. Is it then unnecessary to use acid-resistant tiles on the inner walls? The dilution process releases a large amount of heat, raising the temperature of the solution to over 80 degrees. By using a method of cooling part of the acid before reuse, it is possible to keep the acid temperature around 70 degrees – a level to determine whether epoxy fiberglass can withstand. Also, is it necessary to add turbulence plates in this mixing tank? If so, will it affect the quality of the lining? Can turbulence plates also be made by lining carbon steel with fiberglass? (2) The takeover issue. The connections on the acid dilution tank include an inlet pipe for concentrated sulfuric acid, an inlet pipe for waste diluted acid (with a concentration of around 6%), an inlet pipe for the cooled diluted acid, an inlet pipe for fresh water, a thermometer connection, and a density meter connection. The overflow port (dilute acid outlet) is located 500 mm below the top cover. High-silicon stainless steel (XDS) pipes are used for transporting concentrated sulfuric acid, while pipes lined with reinforced polypropylene (FRPP) are used for transporting waste dilute acid. Pipes lined with PTFE are employed for transporting dilute acid after cooling, and carbon steel pipes are used for fresh water. Due to the acidic environment in the acid dilution tank, it is necessary to determine whether the material of the corresponding connection pipes needs to be changed, what material would be suitable, as well as the interface sleeves for the instruments. Since the dilute acid outlet is an overflow at the top, it is necessary to determine whether the inlet nozzles need to extend below the liquid surface to ensure proper mixing, how far they should extend, what type of structure the end of these nozzles should have, and what kind of anti-corrosion measures should be applied to the outer walls of the extended sections. I earnestly ask for your guidance; thank you.
It is recommended to use glass-lined steel for the tank, which has already been applied in our company. The material used for the takeover is UPVC, or rigid polyvinyl chloride.
The removal of the heat of dilution of concentrated acids must be taken into account; discussions on this topic regarding the dilution of concentrated acids have already taken place in this section. If the volume is small, a glass-lined reactor can be used; for larger volumes, things become more complicated. This post was last edited by in the blink of an eye on 2007-12-27 21:13]
It can be considered that the following process could be simplified by using a vertical graphite heat exchanger to combine acid mixing, dilution, and cooling in one step (graphite acid mixers are generally available from manufacturers of graphite heat exchangers such as Nantong Sansheng). The diluted acid, once it has been properly diluted, flows automatically into a small pump tank and is then pumped into a storage tank using an acid pump. The advantage of this approach is that it allows the heat from the diluted acid to be removed first, thereby reducing the difficulty of corrosion protection for the subsequent equipment.
Vertical graphite heat exchangers require significant investment and are prone to cracking and acid leakage. In the past, our factory used them for producing ordinary calcium carbonate; for diluting small amounts of concentrated acid, a glass-lined tank with a jacket was sufficient – cooling water was used inside the jacket, and an agitator was installed within the tank, so no additional heat exchanger was needed. The piping connections can be arranged as required.
Epoxy coating on such a large groove might be quite difficult!