GB723108A - Process for the manufacture of naco - Google Patents

Abstract

<PICT:0723108/III/1> Sodium carbonate is manufactured by decomposing sodium bicarbonate in a bed of previously formed sodium carbonate which is fluidized by a rising stream of carbon dioxide, air, or steam, or a mixture thereof, and heated by steam coils in the bed supplied with steam at a saturation pressure of up to 250 pounds per square inch, the coils having a heating area of at least 600 square feet per ton of sodium carbonate made per hour. A temperature of 90 DEG C. equivalent to a steam pressure of 10 pounds per square inch, suffices to initiate the decomposition but a minimum of 150 DEG C., equivalent to 60 pounds per square inch, is required to complete it in normal practice. Two or more beds are preferably employed, the first one operating at a temperature of between 90 and 140 DEG C., and the last one at a higher temperature up to 170 DEG preferably between 140 and 160 DEG C. The rate of flow towards the discharge end of the apparatus is restricted to ensure adequate retention time of the sodium bicarbonate in the bed. The retention time is generally at least 20 minutes and is preferably between 1 and 2 hours. The presence of the coils may provide sufficient restriction, but baffles may also be employed, one or more of which may serve as partitions to divide it into two or more compartments operating with different steam pressures and temperatures. The sodium bicarbonate is preferably intimately mixed with dry sodium bicarbonate to convert it into a free-flowing dry-looking feed before being fed into the fluidized bed. Wet sodium bicarbonate from the ammonia-soda process may be employed and the mixing carried out in a closed system from which any ammonia evolved is recovered. As shown (Fig. 1) a bed 2 of sodium carbonate is fluidized by carbon dioxide from compartment 4 and heated by tubes 6. Wet sodium bicarbonate from the ammonia-soda process is fed to the mixer 8 through feeder 9 and is mixed with dry sodium carbonate conveyed from the bed and from cyclone separator 16 which separates dust from the gases liberated by the bed. A proportion of the cleaned gas, presumably consisting essentially of carbon dioxide, is returned through conduits 17 and 18 and blower 19 to the bed while the remainder passes through conduit 17 to the ammonia/soda process. The rate of flow towards the discharge end 12 of the vessel is restricted to ensure adequate retention time by the use of baffles 11. Dense sodium carbonate may be produced in the apparatus by feeding light sodium carbonate mixed with water instead of sodium bicarbonate. The product may be cooled in a fluidized bed with cooling coils Fig. 2 (not shown).