How does sulfuric acid decompose phosphate rock to produce phosphoric acid maintain a high enough concentration in the reaction system

In the reaction of anhydrous sulfuric acid to decompose phosphate rock to produce phosphoric acid, sulfate is easy to form calcium sulfate to prevent the reaction, and phosphoric acid is more favorable to the decomposition of phosphate rock than sulfuric acid. In order to maintain a high enough phosphoric acid concentration in the reaction system, a large amount of repulsing and intense agitation are generally used. Such a reactor, which circulates a large number of reaction products to achieve mixing, may also be considered to achieve full mixing as long as the amount of circulation is sufficiently high. Usually when the amount of circulation reaches more than 25 times, it can be treated by full mixed flow.

The reaction parameters in the steady-state full-mixed flow reactor do not change with time and space, and the discharged reaction material has the same concentration and temperature as the material in the reactor. In the actual reactor, the fluid flow more or less deviates from the ideal condition of complete mixing. When the inlet pipe and outlet pipe are close, there will be short circuit phenomenon, part of the inlet reactants almost have no time to react out of the reactor.

At the corners of the reactor, the boundary layer flows will form a stagflation zone, which is often called a dead zone. It is difficult for the fluids in the dead zone to exchange material and energy with the fully mixed fluid body. The scale-up design of CSTR requires consideration of non-ideal characteristics such as short-circuit fluid volume and dead zone volume, although the ideal case of full mixing can be used as its basic characteristics. The actual operation state of the reactor is always between these typical reactors, and the reaction state is more complex. Semi-continuous operation is a combination of batch and continuous reactors. The spatial distribution should be considered as well as the time variation of the reaction parameters. For a multiphase reactor, the flow state of different phases is very different. For example, in some fine chemical hydrogenation reactions, the liquid phase reactants are added to the reaction tank in one go, and the hydrogen bubble is passed through the liquid phase reactants. In this case, the flow of hydrogen can be regarded as a continuous flow of flat thrust flow, while the liquid phase can be calculated as a batch reactor.