NOVEMBER, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
Literature Cited Altschuler and Graves, Refiner Natural Gasoline i!4frs9 16, 272 (1937). Baroni, Attiaccad. Lincei, 11, 905 (1930); 14, 28 (1931). Birch and Stansfield, IND.EKG.CHEM.,28, 668 (1936). Dryer, Morrell, Egloff, and Lowry, Ibid., 27, 15 (1935). Egloff and Morrell, Refiner Natural Gasoline Mfr., 2, No. 7, 5 (1923). (6) O t t and Reid, ISD. ENG.CHEM.,22, 878 (1930). (7) Ibid., 22, 884 (1930). (8) Reid, private communication.’
1279
Schulta and Buell, Natl. Petroleum News, 27, No. 41, 25 (1935). Schulta and Buell, Oil Gas S.,36, No. 28, b6 (1937). Schultz and Buell, Refiner Natural GasoZine.Mfr., 16, 268 (1937). Universal Oil Products Co., “Laboratory Test Methods for Petroleum and I t s Products,” Chicago, May, 1937. (13) Wirth and Strong, IND. ENO.CHEM.,Anal. Ed., 8 , No. 5, 344 (1936). (9) (10) (11) (12)
RECEIVEDJune 13, 1938. Presented before the Division of Petroleum Chemistry ah the 95th Meeting of the American Chemical Society, Dallas, Texas, April 18 t o 22, 1938.
DESCALING STEAM TURBINES A
SMALL oil company in vided the cost would be low. northwest Louisiana had Sections of the blades of the I-L been operating its field abandoned turbine rotor were repumps and refinery units by elecmoved and treated with various trical power which it generated strengths and temperatures (up by two multistage steam turto the boiling point) of hydrobines, each of which originally chloric acid. The acid was the generated 350 horsepower when same as that which was being JOHN B. ENTRIKIN driven a t 3500 r. P. The used in the area for acidizing oil Centenary College of Louisiana, Shreveport, La. steam was moduced in four 250wells. Accordinn to the makers. horsepower boilers which were it was inhibited-with less than rated a t 200 pounds and were operated a t 185 pounds per square one per cent of certain organic chemica1s.l The results of these inch. The raw water was untreated for the most part. Octests indicated that about one-fourth of the scale was silica and casionally it had been haphazardly treated with alum. No inthe rest carbonates. No representative sample of scale was ternal boiler treatment had been used, and the blowdown obtained and analyzed completely. Even the boiling conpractice was irregular. After several years of such operating centrated inhibited acid did not seem to damage the brass conditions, the turbines became so badly clogged with scale blades or the iron rotor, whereas the scale either dissolved that the steam was by-passing the first two stages entirelyland or was entirely loosened from the blades by much lower conthe operating efficiency had dropped to less than 50 per cent centrations of the acid. It was therefore decided to acidize of the rating. This made it necessary to shut down the plant the two turbines which were to be descaled. The design of until some means of obtaining more power could be arranged. the turbine shell prevented simply filling the shell with hot The company executives contacted the sellers of the turbines inhibited acid and soaking it. Since the treatments were who suggested that the turbines be descaled by handscraping. admittedly experiments, and with the consent of the owners The cost of such a method seemed too high in comparison it was decided to pump the inhibited acid into the turbine with the cost of new turbines, when the age of the old turwith sufficient steam to keep the rotor turning a t about bines was considered. half speed. Since all concentrations had been tried on the At this stage the authar was asked to advise the manageabandoned rotor without harm to the metal parts, no atment. Inspection of the plant revealed that there was a tempt was made to control the dilution of the acid with steam, third turbine rotor which had been scaled and abandoned except that about 2 gallons of acid were admitted per hour. some years previously. Examination of the scale on this Ten gallons of acid were used on the first turbine to be turbine showed that it contained about 25 per cent silica. treated. About every 15 minutes heads of very wet steam Office records were incomplete as regards the analyses of the were sent through the turbine in the hope that any loosened feed water and boiler water during previous operations, but scale that had not dissolved might thus be dislodged. the following data, given in parts per million, were recorded When the shell of the turbine was opened, about one-third and should be average for the years during which the scale of the scale had been completely removed and the remainder had been forming: was softened. Attempts to dislodge the remaining scale with high-pressure water hose failed. The second turbine R a w Water Boiler Water was then treated in the same way, except that 50 gallons of Silica 10.3 10.3 the inhibited acid were used during 8 hours of steaming. Ca(HC0a)z 72.0 .... Mg(HC0s)n Again it was found that a considerable part of the scale be25.0 .... NaHC03 609.0 .... tween the small blades had been softened but not dislodged NanSOa 37.6 2394.0 NaCl 950.7 13609.0 by the acid treatment. Again, water failed to remove the NaOH .... 3312.3 Fa&% scale. There had been no appreciable effect on the metals .... 3007.9 NZU3 9.1 .... of the turbine by the acid. All the rust had been removed, Total solids 1527.0 .... Hardness (soap) 61.6 as well as all of the scale from the shell. Phenol hthalein alkalinity 13,7 5557.6 MethyPorange alkalinity 424.1 6976.8 Both turbine rotors were then treated with sandblasting PH 8.9 machines, using 40-mesh hard sand under 125 pounds per square inch pressure. The actual blasting time was about Because of the age and condition of the turbines, the man1 Grebe, J. J., and Sanford, R. T. ( t o D a w Chemical G o . ) , U. S. Patent agement was willing to try novel methods of descaling, pro1377,604 (Sept. 13, 1932).
An Experience with Inhibited Acid
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INDUSTRIAL AND ENGINEERING CHEMISTRY
3 hours for each turbine rotor. No erosion of either the brass blades or the iron rotor was noticed, but the softened scale was entirely removed. Although i t is possible that the sandblasting would have removed the scale without acidization, it is certain that the softened condition of the scale made its removal much easier. When the turbines were again put to work, they delivered their full rated capacity instead of the half efficiency which they had showed in the scaled condition. The oil company management then secured the services of a feed-water treating company to keep the water in condition. Their recommendations included,the addition of 2.5 pounds of sulfuric acid per 1000 gallons of water, so as to bring the total alkalinity below 200 p. p. m. A continuous blowdown system was installed, and the condensate was checked by conductivity methods until the plant was producing nearly
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VOL. 30, NO. 11
solid-free steam. After more than a year of operation in accordance with these recommendations, an inspection of the turbines showed them to be practically scale-free.
Conclusions Inhibited hydrochloric acid, as used for acidifying oil wells, may be employed on steam turbines without damage to the metal parts. The experiences of the author lead him to believe that if the scale in a turbine is nearly silica-free, acidizing will clean the turbine satisfactorily. In a carbonaceous scale containing as much as one-fourth silica, acidiaing alone is not sufficient. The acid will soften the scale, however, if i t contains carbonates and will make it easier to remove by sandblasting. RECEIVED May 2, 1938.
Calculations of the Void
Volume in W o o d
ALFRED J. STAMM U. S. Forest Products Laboratory, Madison, Wis.
eral, used 1.56 as an average value which they have taken from the old measurements of Sachs (6) and Hartig (3). This value, however, seems a little high in the light of more recent measurements (3,8). . The fractional part of the total volume of wood that is made up of voids, V,, can be calculated from the general formula :
C
ALCULATIOKS of the void volume of wood in seasoning, preserving, and other treating studies have been made in the past, using values for the specific gravity of wood substance obtained from water or aqueous solition displacement measurements. These values can be satisfactorily used when the moisture content of the wood is a t the fiber saturation point1 or above, but lead to false ‘kesults at lower moisture content values. The apparent specific gravity of wood substance determined in water should not be used in conjunction with the dry weight-dry volume specific gravity as Kollmann (6) did if accurate results are desired. The reason is that water displacement does not give a true measure of the specific gravity of wood substance, owing t o the fact that water is so strongly adsorbed within the wood structure that it becomes compressed on the wood surface (8, 9). Measurements of the specific gravity of wood substance in aqueous systems will thus be too high. Helium displacement measurements, on the other -hand, give what appears t o be a true measure of the specific gravity of wood substance (9) ; the latter is nonadsorbed ( I , 4), and the molecules are sufficiently small t o penetrate the void volume completely. The recently obtained helium displacement value for the specific gravity of white spruce wood substance, 1.46, will be used in the following calculations, as well as the apparent specific gravity of white spruce wood substance, 1.53, obtained from water displacement measurements (9). The specific gravity of wood substance varies slightly with variations in the species of wood. Stamm (8) obtained values for the apparent specific gravity of wood substance varying frwn 1.51 t o 1.55 for nine different species from water displacement measurement. Dunlap (2) obtained values vprying from 1.50 to 1.56 for seven species from aqueous salt solution displacements. The average of these, 1.53, is identical with the above white spruce value and is recommended for use in general calculations where the apparent specific gravity of wood substance is applicable. European investigators have, in gen1 The moisture content at which the cell walls are saturated but no free water exists, in the grosser capillary structure, which, for most woods, is approximately 30 per cent by weight of the dry wood.
v, = 1 - g
,
(i + m”+ y ) Pa
A general equation is given for the calculation of the fractional void volume of wood at any moisture content from the specific gravity of the woodl the true specific gravity of wood substance (average value 1.46), and the specific gravity of the adsorbed water. At moisture content values corresponding to the fiber saturation point and above, the generally used equation involving the apparent specific gravity of wood substance obtained by water displacement (average value 1.53) can be employed: but this equation gives false results below the fiber saturation point. The values for the fractional void volume vary almost linearly with the moisture content below as well as above the fiber saturation point, but the two portions of the curve have different slopes.
