Document ymgKGxeBOJr0p57NMa8e9M1Nn

FILE NAME: ZK/L DATE: DOC#: BO/L DOCUMENT DESCRIPTION: d:Z }S.M.E ANNUAL MEETIN i.;.. s Annual Meeting of the American Society maintain the silica in the boiler water under 12 ppm, but cal Engineers, with a total registration of frequent blowing down of high-pressure boilen; is not ...-were2500 was held at the Hotel Astor, New York, DecelPber 2 to 6. The program included forty.five tech aieitteSSioDS of which a substantial number dealt directly liidlRd:ly with the production of power. Among papers on silica removal from i'eedwater, beds; ~ design and circulation, fnrnaces, boiler casings, lfam fuel flwd temperature of ash, steam piping, -demer tubes, flue dust recovery, turbine lubrication looked upon with favor by the operators. The use of internal chemical treatment for silica has been given some consideration, but as yet has not proved very satisfactoiy, because of the necessity for very close supervision and control of several variables. Finally, a knowledge of the COD1bination and fann in which silica occurs ismost important as it throws light on tlie physical conditions which play a part in the formation 1114 matine power plants. Digests of some of these pa- of scale. While chemical analysis of boiler sea.le will pen and their discussiOJIS follow: ooow the total silica present, this 111ay exist in as many as five dilferent forms. all of which have different physical Methods of Silica Removal properties. However, the more recent employtDent of the .X-ray dlifraction D1ethod of analysis of scale has Rmlova1 of silica from boiler waters formed the subject of &Re papers at the Monday evening session on "Boiler Feed.water Studies," D1ade it possible to identify compounds which from previous knowledge enabl~ one to detenlline the temperature at which they could have been fanned, ever;Bamid Fanner, Chief Chemist of the Philadelphia Blcic:t:ric Company, in a paper on "Silica in High-Pres- An [mprt10ed Magnesia Process aare :Boiler Waters," observed that, in general, silica "Silica Removal by an Improved Magnesia Process" . had not given serious trouble at steam pressures below was the title of the second paper of the session, by H. L. 80I) lb.,. or else could be effectively controlled. How- Tiger, vice president of The Perm11tit Company. This 'with high steam pressures around 1200 lb, and process involves the combined use of ionic magnesium perticularly with high rates of heat input, there been many tube failures in which silica appears to have have and sludges containing undissolved magnesium compounds in which a modified Spaulding Precipitator- is plaved a significant part. . ~ployed to afford extended and intimate rontact be- 'ias been suggested that in some cases high rates of tween the water and the sludge. This equipment per- n ...,,oration have disturbed the circulation and ~ted mits the usual lime-soda reactions to take place at the ill ttanation in =tain tubes, thus permitting deposition same time as silica removal and, by the addition of a of soluble salts, inclu\ung silica, on the dry areas. When coagulant, simultaneous turbidity removal can be ac- these areas are again wetted the soluble salts are dis- complished. The source of magnesium is low-cost aolved, bnt during ,the dry period the silica may have dolomitic, lime. undergone a change in stn.tcture and ceased to be soluble. Summarizing the extensive research study of various With repetition of such cycles the silica deposit will build means of silica removal, as detailed in the paper, the ap and cause overheating of the tube with resulting ulti author ofi'ered the following conclusions: mate failure. Sonie such failures have been manifested by blistering. (a) For any given set of conditions ionic magnesium In other cases, instead of a blister, a small hole sur precipitated as Mg{OH)1 is most efficient, but rounded by hard silica scale bas been noted. Some have undissolved magnesium. conipounds of proper lit_tributed this type of failure prlmarily to starvation quality (fine particle size, etc.) also give satis- wath accoaipanying silica deposits and ultimate failure ~ to miall pieces of this scale breaking away and the factory results when favorable conditions of sludge concentration and agitation are main exposed metal trying to absorb too much heat. tained. Eve.n with good condensate feedwater, assuming the (b) The efficiency of removing silica by pteeipitating to~_solids to be 1 ppm, the water may c:ontain 0,l ppm of silica. While this may seem insignificant, many pra- ent-da.y high-ptesSUre boilers evaporate their own vol- ionic magnesium or by undissolved magnesium compo11.11ds inctca11e11 with temperature, but the application of other facton disclosed makes it zer-torsor llllle of water five times in one hour, which represents 12 PPUi silica in the boiler at the end of 24 hr. Many set this figure as the limit and resort to blowing '11D When this figure is approached. haPlsm.ts operating with high makt!Up, not evaporated, :ve.to ffiiOrt touternaI chemical treatment for removal possi"ble to obtain satisfactory result:s at low temperatures. Slight pre-warming of the water to about 30 or 40 C (86 to 1~ F) reduces the amount of magnesium required to obtain the desittd result. Wa.ste heat may be used for this purpose. !,tof lilica. The JnScnt effectiveness of such treatment, in 'J.thor'a opinion, appears to have a limitation of Thia 2 ppm of silica ~dual remaining in the water. ~ necessitate continuous blowdo:wn in order to (c) The efficieicy incRases with the concentration of . the magnesium-containing sludge in contact with the water. (cf) Increasing the time of contact with the sludge 0 0 ~-~ uaTI o:N--I>ooomJ,e 1940 :a