GULF OF MEXICO 



155 



ment. Sea water, which contains 69 parts per 

 milHon bromine, is carefully screened to remove 

 debris, seaweed, and fish and is continuously 

 pumped to the top of a "blowing out tower," 

 a brick structure packed with wood grids. On its 

 way to the top of the tower it receives chemical 

 additives which convert the nonvolatile bromide 

 of the water to relatively volatile free bromine. 

 The first additive is dilute sulphuric acid which 

 is automatically controlled to reduce the pH of 

 the sea water from 7.8 to 3.5 and thus suppress 

 the hydrolysis of the free halides. The second 

 additive is chlorine gas. This is injected in an 

 amount slightly in excess of the equivalent bro- 

 mide, converting it to free bromine. At the top 

 of the blowing out tower the treated brine is 

 distributed evenly over the upper layers of wood 

 packing and trickles downward through the pack- 

 ing to outlet ports about 40 feet below. As it 

 slowly moves down, a current of ah- is drawn into 

 the bottom of the tower by fans at the end of the 

 system; it passes up through openings in the grids 

 and blows the free bromine out of the treated sea 

 water. The latter now passes back to the ocean 

 at some distance from the intake, little changed 

 except for its bromine content. 



The bromine-laden air from the top of the blow- 

 ing out tower next passes to the soda ash absorption 

 tower. This consists of nine spray chambers in 

 series, each chamber having its own separate 

 recycle system for spraying alkaline absorption 

 liquor. Here nozzles at the top of each chamber 

 spray a dilute soda ash solution into the air stream. 

 The sodium carbonate reacts with the bromine 

 and puts it into solution as a mixture of sodium 

 bromide and sodium bromate. Continued re- 

 circulation of the alkaline solution builds up the 

 concentration of bromide-bromate, and at regular 

 intervals the solution of highest concentration 

 from the chamber adjacent to the blowing out 

 tower is pumped to a storage tank. The charges 

 of partially brominated alkaline solution in the 

 other chambers are eacii pumped forward one 

 step, and when the solution in the weak end of 

 the system has been forwarded the last chamber 

 is recharged with a fresh 5 percent soda ash 

 solution. 



By means of this batch-countercurrent recir- 

 culation a solution is obtained which is nearly 

 eight-hundred-fold more concentrated in bromine 

 than the original sea water. 



Tli(> production of pure liquid bromine from the 

 sodium bromitle-sodium bromate solution is ac- 

 complished by a second operation. The solution, 

 which has a slight residual alkalinity, is pumped 

 over a brick-lined scrubber tower where it serves 

 to absorb bromine from the condenser vents. 

 A small amount of steam is added to the bottom of 

 the tower to preheat the liquor for the stripping 

 step. A controlled excess of 60° Be sulphuric acid 

 is then mixed with the liquor, and the reaction 

 between sodium bromide and sodium bromate in 

 the acidic solution produces free bromine. The 

 mixture passes to a continuous steam-stripping 

 column of acidproof construction. The bromine 

 is distilled off and together with excess steam is 

 liquefied in ceramic or glass condensers. The 

 immiscible water layer saturated with bromine is 

 returned to the stripping column. The bromine is 

 purified by distillation, yielding elemental liquid 

 bromine having a purity of 99.7 percent plus. 

 The slightly acid stripping column effluent is added 

 to the incoming sea water to utilize its relatively 

 small acid content. 



The second bromine process, known as the 

 "acid process" or "SO2 process," was developed in 

 1937 and has been used in all bromine-from-sea- 

 water plants built in the United States since that 

 date. In this method the acidification, chlorina- 

 tion, and blowing out of the sea water are carried 

 out essentially the same as before. Into the 

 bromine-laden air from the blowing out tower is 

 injected a carefully controlled flow of dilute SO2 

 gas prepared by burning sulphur in a conventional 

 type burner and cooling the 10-12 percent S02 

 so obtained. The two gas streams are thoroughly 

 mixed by passing through a system of carefully 

 designed baffles, whereupon the bromine reacts 

 with the slight excess of SO2 in the presence of 

 water vapor to give a mixture of hydrobromic and 

 sulphuric acids in the form of a fine acid mist. 

 Tlie acids are readily scrubbed from the air 

 stream by fresh water in an absorption tower. 

 The resultant acid solution has a bromide content 

 of approximately 7 percent, or 70,000 parts per 

 million. This step thus accomplishes a one- 

 thousandfold concentration of the original bromine 

 of the sea water. 



The bromine is removed from the strong acid 

 solution by a method very similar to that em- 

 ployed in the "alkaline process." The acid 

 liquor is pumped over a packed column where it 



