Carbonic acid baffle

Figure 8.6 Venting below the pass partition baffle stops carbonic acid corrosion.

The reaction tank (Figure 11.14) is constructed of rubber-coated steel or concrete and is lined with carbon bricks. Baffles are fitted onto the walls to prevent the slurry from rotating bodily as a single mass inside the tank The cover of the reactor is constructed of polyester or ebonite-coated panels. The phosphate rock is fed by a special duct within a cylindrical shroud at one or two points, according to the size of the tank, and into the turbulence zone of the central agitator on the opposite side to the gas extraction hood. The sulfuric acid is introduced into one, or several, independent discs fixed to the drive shafts of some of the surface coolers. The proprietary equipment distributes the acid so evenly over the entire surface of the tank that 98% acid can be introduced directly without prior dilution. There is no risk of local sulfuric acid concentration excess or temperature peaks, which can adversely affect the crystallization. 

Accupfiulations of non-condensables in the channel head will also retard the condensation rate of steam and lead to a loss in reboiler duty. Typically, CO2 contained in the steam supply collects below the bottom channel head-pass partition baffle. If left to accumulate, the CO2 will dissolve in the steam condensate and form corrosive carbonic acid. 

If CO is not vented off from valve B, then it will begin to dissolve in the condensate to form H CO (carbonic acid). This acid causes tube failures due to acidic corrosion. Venting gas below the pass partition baffle will stop this corrosion, according to the Shell expert. I don t have any personal experience in stopping CO corrosion with such venting. But it seems to make good engineering sense to me. 

The unit has virtually the same flow sheet (see Fig. 2) as that of methanol carbonylation to acetic acid (qv). Any water present in the methyl acetate feed is destroyed by recycle anhydride. Water impairs the catalyst. Carbonylation occurs in a sparged reactor, fitted with baffles to diminish entrainment of the catalyst-rich Hquid. Carbon monoxide is introduced at about 15—18 MPa from centrifugal, multistage compressors. Gaseous dimethyl ether from the reactor is recycled with the CO and occasional injections of methyl iodide and methyl acetate may be introduced. Near the end of the life of a catalyst charge, additional rhodium chloride, with or without a ligand, can be put into the system to increase anhydride production based on net noble metal introduced. The reaction is exothermic, thus no heat need be added and surplus heat can be recovered as low pressure steam. 

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