INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1941
111
TABLEV. COMPARISON OF THE REFINING CHARACTERISTICS OF ACTIVATEDBAUXITE AND BONECHAR
. -Unfiltered Activated
-
Filtrate Composition -
Dry Basis Polarization, % Invert sugar, % Ash % Undetermined, % Color, %
WH
Increase in polarization yo decrease in: Invert sugar Ash Undetermined Color
Unfiltered Activated wash suup bauxite 75.87 81.27 10.39 9.04 6.83 3.93 6.91 5.76 29.3 5.6
6.3
...
... ... ... ...
6.6 5.4
13.0 42.5 16.6
81.2
Bone char 77.42 10.30 5.68 6.60 6.1 6.5
1.6 3.38
16.9 4.3 79.2
c
h
Unfiltered Activated wash sirup bauxite 83.68 87.76 5.30 4.62
Bone char 85.78
6.89
4.13 19.3
4.92
4.84 3.42 5.96
7.0
6.7
0.7
...
2.70 4.0
... ... ... ...
liquor 97.83 0.54
4.0
0.20 1.43 82.0
4.1
2.1
...
13.0
8.8 17.1
34.7 28.0 79.3
crease in ash content produced by activated bauxite is a t least twice that accomplished by char. The color removal efficiencies of the two adsorbents are approximately equivalent. The bauxite filtrates from SOlUtiOnS of intermediate and low purity are rich amber in color and yield exceptionally high-grade soft sugars. The filtrates from bone char tend to show a higher p H than those from bauxite. The difference is small with low-purity solutions and in some cases iS in favor of the latter adsorbent, but with sugar liquors bauxite invariably produces the lower pH.
Acknowledgment The author takes pleasure in expressing his appreciation for E. the assistance and Suggestions of his colleagues,esPeciab' Neunherz, 0. T. Aepli, A. P. Allegrini, and J. B. Sanborn.
13.4
79.3
6.7
... ... .. . ...
bauxite 99.07 0.36 0.03 0.55
Bone char 98.77 0.47 0.12 0.64
6.4
7.1
2.5
1.24 32.8 87.0 62.0 97.0
2.8
0.9 11.9 38.5 55.2 96.6
Once-filtered Activated liquor bauxite 98.41 99.09
0.70 0.16
0.73 1.5 6.9
... ... ... ... ...
0.41
0.05 0.45 1.1 6.7
Bone char 98.74
0.64 0.10 0.62 1.2 7.1
0.7
0.3
4.1 66.2 39.2 96.1
2.2 36.9
16.2 95.9
Literature Cited (1) Devos, Bull. assoc. chim. sum-. dist., 46,292-301 (1929). (2) Hardy, I ~sugar ~J.,35,~64-9 (1933). ~ . (3) Hood, Clark, and Clark, U. 8. Patent 1,452,739(April 24,1933). (4) Hubbell and Ferguson, Oil Gas J.,37, 135-9 (1938). ( 5 ) Hubbell and Fewuson, Refiner Natural Gasoline Mfr., 17, 104-8 (1938). (6) Hfittig and peter,Ko~lo&Z., s4, 140-7 (1931). (7) La Lande (to Porocel Corp.), u. S. Patent 2,211,727(Aug. 13. 1940). (8) Marx, 2.physik. Chem., B23,33-67 (1933). (9) Mead, Econ. Ceol., 10,28-54 (1916). (10) Schulze and Alden, Refiner, 18,96 (1934). (11) Strange and Kane, Brit. Patent 500,880 (Feb. 16,1939). (12) Young and Hartman, Proc. Indiana Acad. Sei., 48,79-86 (1939). before the Division of Sugar Chemistry and Technology a t the 100th Meeting of the American Chemical Society, Detroit, Mich.
PRESENTED
Design of Industrial Exhaust Systems J
L. P. HATCH, Tennessee Valley Authority, Wilson Darn,Ala.
I
N THE design of industrial exhaust systems certain basic
principles of air flow are often overlooked, and not infrequently rule-of-thumb methods are employed. I n many cases, moreover, since the resistance t o air flow is usually low in terms of water gage, significant discrepancies between design and performance values are given only minor consideration. Such methods are not in accord with sound engineering principles. The resistances in pipes and fittings are sufficiently well established to be used with confidence in most designs. Hood losses are perhaps not so well known, but reasonably accurate estimates of such losses usually can be made in the light of experience and from comparison with known characteristics of other hoods.
Calculations Based on Velocity Head Resistances in various parts of exhaust systems, including pipe friction, can be predicted in terms of velocity head, V2/2g, and the design of an entire system, therefore, can be completed without introducing resistances in terms of pressure gage. Since for any given system the velocities in all branches and main sections are related t o the velocity in any one branch, through the velocity heads, a flow picture of the sys-
tem is obtainable in terms of one velocity which may be varied a t will to meet the minimum requirements. The sizes of branch lines are first calculated in accordance with the estimated quantity of air necessary for each hood and, in the case of dusts, the required transporting velocity for the material in question. However, recalculation of the sizes of certain branch pipes is usually desirable in the interests of balanced design and economy. With the velocity head method, the degree of change is readily suggested in the calculations of flow, and trial-and-error computations are minimized. The branch losses may be entered in a table, such as Table I, which presents the essential information in convenient form and gives a flow picture of a n entire system. With this information in hand more accurate estimates of the branch sizes may be made before the actual calculations are begun. Although the accuracy of the resistance values in Table I has no real bearing on the method of incorporating the resistances in a balanced design, the values are believed t o be reliable for practical designs in accordance with information from well-known sources ( I , $ , 3). The values in one column only (pipe friction) are subject t o change with pipe size and are readily obtained from a chart such as Figure 1, showing
INDUSTRIAL A N D ENGINEERING CHEMISTRY
112
Use of Dampers or Adjustable Gates
the length of pipe, in diameters, which would introduce friction losses equivalent to one velocity head, V2/2g. The results as given in Figure 1are expressed as a coefficient, C, the value of which has been found (3) t o vary closely with velocity to the I/, power and with diameter to the 2/r power for a given quality of pipe surface. T h e coefficient is essentially a friction factor to be used, if desired, in the following well-known pipe flow equation:
where h = resistance I = length f = friction factor
Original calculations commonly show the velocities in branches nearest the source of suction to be substantially higher than the required velocity with correspondingly large volumes of flow. Obviously, the size of such branches should be decreased or artificial resistance added if unnecessary waste of power is to be avoided. A method commonly used is to provide for dampers or other adjustable gates in branch lines and to design main ducts simply from the cumulative area of upstream branches. The use of adjustable gates for balancing air flows is to be discouraged, however, for a number of reasons, some of which are as follows:
d = diameter
V
= g =
Vol. 33, No. 1
velocity acceleration due t o gravity
1. Gates are not necessary in many systems since a given distribution of flow can be ensured within reasonable limits throuzh careful design. 2. The adjustments of gates for efficient operation is not always a simple procedure since a change in the resistance in one part of a system will influence the flow in all other parts. 3. Even though gates are set properly and a system is operating as originally planned with respect t o the distribution of flow, there is usually good reason to expect that sooner or later the gates will be moved by accident or in the course of plant repairs and alterations. As a result, the air flow in a system might easily be thrown out of balance to the extent that the over-all efficiency, particularly in the removal of atmospheric pollution, would be seriously impaired. Moreover, when handling particulate material, even temporary reductions in velocity are to be avoided since the removal of accumulations of material in ducts usually requires velocities greatly in excess of the normal transporting velocities. 4. Resistance gates are subject to rapid wear from abrasive dusts. Y
-4
50001 f 6o00
4000
3000 a c W
5
lz
0.
n. W
-
0.
t:
t 3 0
IO00
1'
I n the foregoing discussion i t is not intended that emphasis
FIGURE 1. FRICTION F a c r o R c, OR NUMBER OF DIAMETERS be placed upon small fluctuations in air flow distribution since PER VELOCITY HEAD,FOR CIRCULAR PIPE the limits of tolerance are relatively wide and the available
information upon which designs are based is by no means exact. There is little reason, however, why the limits of tolerance should not be held within reasonable bounds, although i t is said to be not uncommon to find air flows in exhaust systems deviating widely from economical design values. The basis for such discrepancies is probably inherent in the designs b u t the immediate fault often lies in improper setting of gates. Why, then, is i t not good practice to design exhaust systems on as sound a basis as is practicable, if for no other reason than to eliminate the need for adjustable gates and to avoid the haphazard operation which often results?
Figure 1 is based on a value of C = 50 for a velocity of 2000 feet per minute and a diameter of 24 inches (galvanized swedged pipe used for ordinary heating and ventilating ducts). The base value, CB would, however, vary with the nature of the pipe surface; the approximate values are said t o be as follows : CB
=
60 for perfectly smooth pipe
= 50 for average heating and ventilating ducts = 45 for somewhat rough ipe = 40 for rough conduits (tiye, brick, or concrete)
Design of Exhaust Systems without Gates
Values of C from Figure 1 would be corrected b y multiplying b y the factor C ~ / 5 0 . I n many designs pipe friction is estimated t o be only a small portion of the total resistance in certain branches, in which cases the over-all effect of minor changes in pipe size are negligible. The tabulation of losses wholly in terms of velocity heads permits the designer to evaluate the effect of changing the velocities and pipe sizes with little additional calculation.
Consider the exhaust system shown in Figure 2. The minimum velocity is 3000 feet per minute, and the required air volumes are as follows: hood A , 600 cubic feet per minute; hood B, 800; hood C, 800; and hood D, 600. With an estimate of branch sizes based on the above information, the branch losses may be itemized and entered in Table I. All losses are stated in terms of velocity head, and from these one may determine roughly which branch velocity is the lowest. This information is not essential at first but isdesirablc in order that the TABLE I. RESISTANCE CHAR.4CTERISTICS OF EXHAUST SYSTEM IN FIGURE 2 main pipe sections may be de," ,. Estimated Resistances in Velocity Heads, V / 2 g Decrion signed t o operate with the VeTransiPipe Pipe Branch Total Area, Diam Length Hood looity Bends tion stated minimum velocity withNo. inche; Feet Diam. loss head 90° 45O section friction entrance loss Sq. Ft. out unnecessary trial-and-error AE 6 25 50 0.30 1.0 0.24 0.12 . . . 50/35 = 1 . 4 3 0 . 2 0 3 . 2 9 0 . 1 9 6 computation. BE 7 30 51 0.30 1.0 0.24 0.20 51/37 = 1 . 3 8 . . . 3 . 1 2 0.267 CFa 7 16 27 0.30 1.0 . d 12 . . . 27/37 = 0 . 7 3 0.20 2 . 3 5 0.267 I n the following computaDQQ 6 19 38 0.30 1 0 , . 0 12 .. 38/35 = 1 . 0 8 0.20 2.70 0.196 EF 9 36 ... ... . , . . , . 0 . 1 8 48/40 = 1 . 2 0 1.38 0.442 tions much of the indicated CFb 6 16 % 0.30 1.0 ,,, 0.12 ... 32/37 = 0 . 8 6 d.i'O 2 . 4 8 0.198 accuracy is, of course, unwarPO Ill/$ 40 42 ., , 0 14 42/43 0.98 ... 1.12 0.721 19 46 0.30 i:o ::: o.iz , . . 46/35=1.31 0.20 .136 ranted and has little practical gg 13" 2 0 18 . . . . . . . . , . . . . , . 18/45 = 0 . 4 0 . 02 .. 4903 00.922 significance; i t is brought out a First estimate. b Second estimate. only to emphasize the princi,
,
-
..
January, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
ples involved. Moreover, for practical designs many of the steps shown in the computations are unnecessary. Let H = velocity head, V 2 / 2 g O r H A = VA2/2g and H B = VB2/2g where V A velocity in branch A E V B = velocity in branch B E The suction a t E is common to branches A E and BE; thus the resistance in branch A E equals the resistance in branch BE or, from Table I, 3.12 H B = 3.29 H A or HB = 1 . 0 5 H A and V B = 5BA = 1.03 V A Since V Ais estimated to be the lowest branch velocity, area EF = area A 1.03 X area B E or area EF = 0.196 sq. ft. 1.03 X 0.267 sq. ft. =
+ +
0.471 sq. ft.
113
I n most designs, where a specified minimum velocity is a governing principle, there is usually one branch section which serves as a “key section” for an entire system. By this it i s meant that the resistance in the key section is highest in terms of the one velocity head, and that the otherwise normal flow in all other branches must be restricted if the desired section is to be maintained and economical d. If the key branch happens to be a fairly long section;‘$f relatively small diameter, and a major portion of its resistance is caused by pipe friction, it is often advisable to increase the diameter of the key branch beyond its normal value. As a result the calculated volume of flow in this particular branch will be increased, but a t the same time a reduction in the over-all power consumption may be obtained. &INCH DIAM V = 3 0 0 0 ERM. Q-590 CEM.
5iNCti DIAM. REM. Q - 5 9 0 CLM. V-4320
The velocity
Use 9-inch diameter (area = 0.442 sq. ft.). in EF, then, is calculated to be: 0’471 V A = 1.07 V A VEr = 0.442 then HER = (1.07)* H A = 1.14 H A
+
The pressure loss to F = 3.29 H A 1.38 HEF = 3.29 H A 1.38 X 1.14 H A = 4.86 H A ; thus 2.35 H c = 4.86 H A or H c = 2.07 H A and V C= 1.44 V A(CF = 7 inches)
+
But the diameter of CF (first estimate) is based on 8 velocity of 3000 feet per minute or VAS Therefore, the area of CF should be reduced as follows: 0.267 sq. ft. f 1.44 = 0.185 sq. ft. Use 6-inch diameter (area = 0.196 sq. ft.) : 2.48 H c = 4.86 H A or H c = 1.96 H A and V C = 1.40 V A (CF = 6 inches) area FG = area EF 1.40 area CF = 0.471 8 ft. (1.40 X 0.196 sq. ft.’f = 0.745 sq. f t . where EF = required area as computed above Use 11.5-inch diameter (area = 0.721 sq. ft.):
. +
+
7-INCH DIAM. V = 3 0 9 0 RRM. 9’825 CLM.
6-INCH DIAM. V:4200 RRM 9 - 8 2 5 CRM.
FIGURE 2. EXHAUST SYSTEM I n other words, a reduction in resistance in the key branchis reflected by a n equal reduction in the over-all resistance for the system as a whole, while a n increase in flow in the key branch is confined to that branch alone. The net result depends entirely upon which one of these two increments exerts the greater influence upon the product of flow and resistancei. e., the power consumption.
Hood Suction
High Resistances in Certain Branch Sections
Static suction at the throat of an exhaust hood is a measure of the rate of air flow into that particular hood, as is true of any other orifice, but it is by no means an independent measure of hood operating efficiency. I n other words, the static suction exerts a definite influence upon the velocity of air currents within a n exhaust hood and, therefore, in the vicinity of the hood opening, but i t does not govern the over-all efficiency of the hood. Obviously, this is because the required extent of the zone of influence must also be considered. Furthermore, static suction is dependent upon factors whicb may vary considerably for hoods of different design even though the flow remains constant; thus, i t should not be regarded as a uniform design requirement. The important consideration must be that the volume of flow into a given hood is adequate to create local air currents of sufficient velocity to prevent the escape of dusts, fumes, or other air-borne contaminants. If such a volume is provided, the static suction, like any other power factor, should be held a t a practicable minimum for economical design.
Application of the above principles of design is by no means limited to straightforward computations as set forth in this article. On the contrary, they are helpful in laying out systems in which relatively high resistances in certain branch sections play a prominent part. I n such cases it is especially important that the design be given careful consideration if unnecessary power consumption is to be avoided.
(1) Alden, J. L., “Design of Industrial Exhaust Systems”, 1st ed., pp. 83-106, New York, Industrial Press, 1939. (2) Am. Blower Corp., “Air Conditioning and Engineering”, 1st ed., pp. 24-6, 36-7 (1936). (3) Am. SOC. Heating Ventilating Engrs., “The Guide”, 15th ed.. pp.364-7 (1937).
velocity in FG = E 5 V A = 1.03 V A 0.721 HFQ = (1.03)2 H A = 1.06 H A loss t o G = loss to F 1.06 HFQ = 4.86 H A 1.06 X 1.12 H A = 6.05 H A
+
+
The calculations for sections DG and G H are made in a similar manner. By way of comparison, it is interesting to note the distribution of flow to be expected if the system shown in Figure 1 were designed according to the cumulative area of branches. It is assumed that resistance gates either are not provided a t all or are not used effectively. Branches CF and DG would be 7- and 6-inch diameters as originally estimated, and the calculated flows would be 1150 as compared to 800, and 880 as compared to 600 cubic feet per minute, respectively.
Literature Cited
114
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 33, No. 1
LE CHIMISTE By Frans van Mieris (1635-1681)
WEstart the new year with a reproduction of a work by another painter who has appeared previously in the Berolzheimer series of Alchemical and Historical Reproductions [see No. 37, INDUSTRIAL AND EKCINEERING CHEXISTRY, 26, 112 (1934)]. The original of this painting, No. 121 in the series, wa8 owned by the Duc d’orleans. It was painted on wood and was 13 by 18 inches in size. The present location of the original is not known. Our reproduction was made from an engraving of the painting, done by the famous etcher and engraver, Carl Guttenberg. It should be noted that this is one of the few paintings of this type and age which does not have a salamander or its equivalent suspended from the ceiling to mystify the clients and other visitors and possibly, to act as a talisman. Nor is there any still among the few pieces of laboratory equipment. D. D. BEROLZHEIMER 50 East 41st Street New York, N. Y.
BEROLZHEIMER ALCHEMICAL AND HISTORICAL REPRODUCTIONS
THESE prints of famous paintings and engravings were started in the August, 1931, issue, and appear monthly thereafter in our volumes for the subsequent years. Orders for photographic prints 8 by 10 inches a t $1.50, and 16 by 20 inches a t $4,specifying the numbers here indicated and titles as given, should be sent with advance payment to D. D. Berolzheimer, 50 East 41st St., New York, N. Y. These photographs are not carried in stock, but are ordered only on receipt of remittance. Purchase of these photographs does not confer any rights of publication of these reproductions. Special arrangements must be made with Mr. Berolzheimer to obtain such rights. Prints and enlargements can be supplied in black and white only; velvet, matt, or glossy finish. Prints in color cannot be supplied, nor of any size smaller than 8 by 10 inches. An additional reproduction will be published each month. The list of the first 96 reproductions is in our January, 1939, issue, page 124. The list of. reproductions published during 1939 and 1940 follows. The figures in parentheses following the name of the artist denote the pages on which the respective reproductions will be found. 97. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108.
1939 The Alchymist, Teniers (87) Recovery of Olive Oil, Stradano (189) L’Incantation, Raps (338) Der Scheidekuenstler in seiner Werkstatt, Bega (381) The Pharmacist, Bega (617) Sugar Manufacture, Stradano (744) The Alchemist, Tantot (865) Medieval Distilling (971) Alchemie, Van Hofe (1111) L’Alembic, Bonvin (1217) King Frederick William I in the Laboratory, Borckmann (1406) New Discoveries in Pneumaticks, Gillray (1454)
1940 109. 110. 111. 112. 113. 114. 115. 116. 117. 118. 119. 120.
Chemical Patriotic Envelope (134) L’Alchemist, Wijck (267) Le Docteur Alchimiste, Teniers (345) The Alchemist, Dietrich (586) The Alchemist, Cimino (701) The Alchemist, Miller (801) The Chimiologist, Artist Unknown (980) The Alchemist, Teniers (1147) The Apothecary, Artist Unknown (1256) Alchemistic Laboratory, Schgufelein (1398) Kalbfleisch’s Alchemist, Artist Unknown (1473) Philatelic hlchemist, Artist Unknown (1625)
