20 BULLETIN 572, U. S. DEPARTMENT OF AGRICULTURE. 



entering the treaters are cooled by radiation in the flues to the 

 desired temperature for the precipitation of the dust. 



Several precipitating installations are also in operation at plants con- 

 trolled by the Universal Portland Cement Co., but as indicated in Table 

 I the dust from these plants is too low grade to be of value as a source 

 of potash. The dust collected in the treaters at these plants, there- 

 fore, is returned to the kilns automatically, for use as cement material. 



In the precipitating system recently installed at the Cement on 

 plant of the Alpha Portland Cement Co., the gases from the kihis 

 are passed successively through a boiler and economizer system 

 before entering the treaters. In this way the waste heat of the gases 

 is utilized for the generation of power by steam turbines. In this 

 installation, as well as in the multiple-pipe treaters already referred 

 to, an artificial draft produced by a fan placed beyond the treater 

 system replaces the natural draft originally given by the flue stacks. 



The advantages claimed for installations of the kind last mentioned 

 are as follows: (1) The abatement of the' dust nuisance is effect- 

 ively secured; (2) material is recovered suitable as a source of 

 potash or cement material or of both when separation of the potash 

 is brought about; (3) a greater efficiency in the burning of the cement 

 is secured owing to better possible regulation of the draft through 

 the kilns, with resultant economy in the amount of fuel required; and 

 (4) utilization of the waste heat of the gases from the kilns. 



In the plant of the California Portland Cement Co. use is made of 

 the Fleming patent dust-collecting system. 1 This system has been 

 in operation since 1912, and it is claimed that this method of collecting 

 the dust is not only efficient but it is also more than self-supporting, 

 there being a saving to the companv in the dust collected, a larger 

 output per barrel of oil used for fuel, and fewer shutdowns than before 

 the Fleming system was installed. 



The draft for the kilns is produced by fans sucking at the end of 

 separate flues. Instead of discharging the gases into the atmosphere, 

 these fans blow the dust and fumes into a large dry dust-settling 

 chamber, where the velocity of the gases is reduced 90 to 95 per cent 

 and about two-thirds of the dust is deposited. The gases carrying 

 the extremely fine dust which does not settle then go to wet washing 

 chambers, where they are forced up and down several times through 

 a system of seven baffle sections in each of which are sprays of water 

 for capturing the remaining dust. In both the wet and dry chambers 

 means are provided for removing the collected dust to the cement 

 kilns. The same water being repeatedly used in the wet baffle cham- 

 bers, it soon becomes charged with soluble salts, principally in the form 

 of sulphur compounds of potassium, sodium, and calcium. When 

 more than one-half pound per cubic foot is found some of the solution 

 is removed and replaced by fresh water in order not to cause trouble 



i Hanna, W. C, Metallurgical and Chemical Engineering 13, 609 (1915). 



