September, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
combustion evaporation a t high efficiency and without the difficulty attached to heat transfer through tubes. The stoichiometric calculations of run 4 check well, but those of run 5 do not show as good agreement; errors in gas analysis can readily cause all these calculations to show discrepancies. Fused silica is not a satisfactory refractory material as it devitrifies a t about 1200" C., and the temperature within the combustion chamber is practically equal to the theoretical flame temperature of the gas, or about 2000" C. Thus the temperature of the refractory walls is a t least 1400" to 1700" C., depending on the operating conditions. The metal grid over the end of the burner is slowlv burned awav bv the hot gases passing through, but it can "easily be repiacei. With
987
these exceptions there has been no noticeable deterioration of the burner or evaporator parts, even when normally corrosive solutions were evaporated. ACRNOWLEDGMENT The writers wish to thank W. L. Beuschlein for his helpful suggestions and interest in this work. LITERATURE CITED (1) (2) (3) (4)
Eastman, Bur. Mines, Tech. Paper 445 (1929). Hammond, J. Inst. Fuel, 3, 303 (1930). Kobe and Hauge, Power, 77, 402 (1933). Swindin, Trans. Inst. Chem. Eng. (London), 5, 132 (1927).
RECEIVBD February 15.1933.
11. Sulfite Waste Liquor
T
ized liquor in an evaporator with H E p r o b l e m of sulfite Unneutralized sulfite waste liquor has been heating rings, which gave natural waste liquor disposal or successfully evaporated by submerged combustion circulation. The cylindrical surutilization has been atwithout the dificulties encountered by the usual faces of t h e h e a t i n g r i n g s are tacked from many standpoints tube type evaporators. The evaporation gives mechanically cleaned of scale by but still seeks an economical solua product containing 63.4 per cent solids, with a scraper continuously operating tion. The industry realizes that between the rings. The Paulson approximately 50 per cent of the a thermal recovery in the process of approximethod (S) employs a doublepulp wood is being disposed of in mately 94 per cent. Higher concentrations of effect, stainless-steel evaporator, an uneconomical manner. This solids can be obtained. o p e r a t e d under a pressure of waste has attracted much attenI n order to form a thermal cycle in recovery, 180 pounds per square inch in tion and its utilization has been evaporation, and combustion of the sulfite waste the first effect and 130 pounds the subject of many patents. A per square inch in the s e c o n d review of these p r o p o s a l s by liquor, the present p u l p mill practice must be effect. The pressure operation Benson ( S , 4 ) shows that the machanged to give a waste liquor of over 12 per cent prevents foaming and allows the terial used is not the dilute waste solids. Below this concentration the evaporation steam from the second effect to liquor of the mill but is a conwill require more heat than is recovered by the be utilized for pulp cooking. The centrate which contains from 50 combustion of the solid residue. concentrated liquor from the first to 90 per cent solids. The prepaeffect is burned in a W a g n e r ration of this concentrate calls The application of the principles of subfurnace for the p r o d u c t i o n of for an evaporation process. merged combustion offers a technical and ecos t e a m to heat the first effect. Sulfite waste liquor has been nomic solution to the problem of sulfite waste This arrangement is equivalent a p o 11u t i o n nuisance because 1iquor d isposul. to the installation of a new and no u t i l i z a t i o n has been made on a scale large enough to conexpensive steam-generation syssume the entire s u p d y of waste liquor. The result is that tem in plants already possessing adequate steam plants. disposal by dumping in the nearest body of water has been Kuhles (8) has described a plant in which the waste liquor is the common practice. This has not gone on without objec- first evaporated in multi-effect evaporators from 10-12 per tion from neighboring cities or industries who have forced the cent solids to 40-50 per cent solids, then spray-dried to 5-8 mills to use a less objectionable method of disposal. The per cent moisture. This dried residue is a fine powder which usual method has been concentration and combustion of the can be burned in a powdered coal burner. organic solids. Since a concentration to a t least 50 per cent Despite the numerous systems proposed and described as solids is necessary previous to combustion, an evaporation operating successfully, it is also known that some such plants process is usually employed. have failed ( I ) , and that others do not continuously operate with the freedom from difficulty that their sponsors have deEVAPORATION OF SULFITEWASTELIQUOR scribed. With hopes of overcoming these difficulties the The evaporation of sulfite waste liquor in tube evaporators concentration of sulfite waste liquor by submerged combustion has been the subject of considerable research and has been has been attempted on an experimental scale ( 5 ) . employed on a commercial scale. The difficulties in the evapoSUBMERGED COMBUSTION EVAPORATION ration have been pointed out by Badger ( 2 ) and by Miller (9). These are: (1) the extreme viscosity of the solution, The concentration of sulfite waste liquor by submerged (2) the serious scale-forming tendencies of the liquor, (3) the combustion eliminates many of the difficulties inherent in the corrosive nature of the unneutralized liquor, (4) excessive tube evaporator. As previously pointed out ( 7 ) , whenever foaming, and (5) the escape of volatile substances causing heat is transferred through a metal wall, corrosion and scale trouble in condensing. formation take place. With a submerged combustion burner Badger (2) carried out his work on neutralized liquor to the heat transfer is directly between the hot gases and the avoid corrosion difficulties. Forced circulation was neces- liquid so that the formation of solid calcium sulfate at the sary with the viscous solution, and high values of the heat interface now merely results in its precipitation in the liquid. transfer coefficients were obtained in this way. No scale de- The body of the evaporator is a t the same temperature as the posit was found on the nickel tubes. Miller (9) used neutral- liquid, and, since it is not externally heated, corrosion is
I S D U S T R I A L A S D E N G I N E E R I S G C H E 11 I S T R Y
988
slight or may be resisted by alloys or ceramic ware. These numerous advantages of submerged combustion make it appear to be a promising method of attack on this problem.
EXPERIMENTAL PROCEDURE The equipment used for submerged combustion evaporation has been described in Part I (6). SULFITE WASTELIQUOR. Waste liquor from the pulping of hemlock was drawn directly from the digestor before it was blown. Analysis showed the following composition: Sp. gr. Free acid, Total acid, %
Total solids, yo Ash in solids, % Heating value of dry solids, B. t . u./lb.
1.059 0.4 0.6
OPERATION. The evaporator was charged with unneutralieed sulfite waste liquor and the lighted burner submerged in the liquid. When the temperature of the liquid had come to a constant boiling point, the data for the runs were taken. Evaporation took place with no difficulty. Despite the fact that gas was being introduced into the liquid, no foaming occurred. The free sulfur dioxide in the liquor was evolved a t the beginning of the run.I S o scale was found in the evaporator or on the burner itself. A small amount of carbonized material was found adhering to the metal grid near the openings for the hot gases, though the amount of material did not build up enough to interfere with the operation of the burner. From the initial weight of the evaporator and the loss in weight as evaporation occurred, the approximate concentration of solids could be calculated. Two runs (6 and 7 ) were made using the 12.1 per cent liquor in which the solids content was increased to approximately 33 per cent. The product from these two runs was then mixed and concentrated to 63.4 per cent solids. Further concentration could not be carried out in this run, as the depth of liquid in the evaporator became too low for operation of the burner in the liquid. Higher concentrations of solids could have been reached had larger amounts of sulfite liquor been concentrated in runs 6 and 7 . The data for all runs are given in Table I. TABLEI.
EXPERIMEYT.%L
Run 6 217 Time of run, min. 758 Barometer mm. H g 6 Static p r e s k r e of gas, i n c h y Hg Temp. of gas entering,
c.
, O D ,
02
N? Fuel gas analysis, %: CO? Illuminants ( C ~ H G ) O?
co
Hz CHI C2Hs N? Fuel gas. B. t.
U./CU.
ft.
DATA 7
200 766 6
8 6.5
22.8 (i3) 3.79 7.48 25 (77) ,4.25 12.1 41.75
33 63.4 30
89 (192.2) 88.3 (191)
89 2 (192 6) 88 3 (191)
8 9 . 5 (193.1) 9 1 . 1 (196)
11.8 1.5 86.7
12 1 1 6 86 3
12.1 1.6 86.3
~
5.4 i. 1 0.3 11.4 27.0 20.2 0.7 27 9 505
.
I
22.8 (73)
s.62 8
.33
?5
(77)
55
..
The data from Table I have been calculated to give a water and heat balance as previously shown f6). The calculated results are given in Table 11. THERMAL CYCLE
The present mill practice of blo\Ting the digestor and Jvashing the entire blow from the pit is satisfactory Rhen the waste 1
T h e evolution a n d recovery of sulfur dloxide
1s
TABLE 11. Run Time a t equilibrium, min. HzO output (weighed), Ib. Gas used, cu. ft. Ratio air t o gas Excesa air, % Hz in gas used, mole 1 2 0 calcd. bv 0 2 balance.
nou b a n g studied further.
CALCVLATED
RESULTS
A
150 35.0 84.7 5.22
7
Q
160 39.75 90.3 5.03
120 28.75 67.2 5.03
45,602
33,936
0 199
Heating value of gas used 42,774 Sensible heat in gas and air above 60' F. 125
-
H e a t input
42,899
130
96
45,;32
34,032
39,031
28,218
3,751 1,191 0
2,787 853 35
43,973 1,759
31,893 2,139
42,899
45,732
34.032
91.0 80.1 84.3
96.2 85.4 89.5
93.8 82.9 86.3
Heat of vaporization of H i 0 evapo34,374 rated Heat of vaporization of HzO from combustion 3,516 Sensible heat in gases above 60' F. 1,151 superheat of H i 0 vapor 0
__
Thermal recovery 39,041 Radiation a n d unaccounted for losses 3,858
__
I _
H e a t output Efficiency, %: T herinal Evaporation Over-all
lye may consider the heating value of the dry solids to be 9150 B. t. u. per pound, the over-all efficiency 85 per cent, the temperature of the feed liquor 70" F., and evaporation to occur a t 192" F. with a heat of vaporization of 982 B. t. u. per pound. The sludge of maximum dilution which will give a thermal cycle for the process is calculated. Ib. solids in 100 Ib. waste liquor (100 S)(1104) = (0.85)(9150) S = 12.5 Ib. solids
S
130 766
22.8 (73) 3.93 7.82 24 (75.2) 75.5 12.1 33 46.0
?2
liquor is to be run directly into a body of m-ater. If evaporation of the waste liquor is t o be employed the practice of dilution must be abandoned, It is possible to withdraw most of the waste liquor from the blow pit, thus securing a liquor containing from 10 to 12 per cent solids, instead of about 3 per cent as given a t present. Since concentrated waste liquor containing over 50 per cent solids can be used as a fuel, either alone or mixed with fuel oil, a certain amount of the heat employed in the evaporation can be recovered by the combustion of the concentrate. Thus a thermal cycle can be formed.
12.1 13.5 9150
Vol. 25, No. 9
=
-
Thus if the mill wishes to regain the amount of heat equal to that used in the evaporation, it is necessary that liquor be recovered from the blow pit which has 12.5 per cent solids. Since this concentration of solids is a t the upper limit of the usual 10 to 12 per cent solids in the liquor from the digestor, it is apparent that it mill not usually be possible to regain all of the heat used in the evaporation process.
DISCUSSION OF RESULTS The huccessful application of submerged combustion evaporation to the concentration of sulfite waste liquor has shown that this method surmounts the difficulties which confront the other evaporation processes. Scale formation, corrosion, foaming. and forced circulation present special problems not yet encrely solved in present practice. Submerged combustion evaporation successfully eliminates such problems. Although such an evaporation system does not have the evaporator economy of a multiple-effect system, its numerous other advantages make it worthy of consideration. The principles of submerged combustion can be applied in a different apparatus using cheaper fuel, and the result can well be a piece of equipment \\,hi& is both technically and economically superior to present practice.
IN D US TR I A L A N D EN G I N E E R I N G C H E M I STR 1
September, 1933
LITERATURE CITED (1) Allen, Chem. & Met. Eng., 32, 928 (1925). (2) Badger, IND.EBG. CHEM.,19, 677 (1927). (3) Benson, “Chemical Utilization of Wood,” Rept. Xatl. Comm. Food Utilization, Dept. Commerce, 1932. (4) Benson, Pacific Pulp Paper Znd., 6 , 30.13, 19 (1932): Paper Trade J , 95, KO.20, 31 (1932).
983
Kobe, Paper Trade J.,95, S o . 3, 33 (1932). Kobe, Conrad, and Jackson, IND. ENG.CHEM.,25, 984 (1933). Kobe and Hauge, Power, 77, 402 (1933). Kuhles, Ibid., 72, 468 (1930). (9) Miller, Can. Chem M e t . , 14, 19 (1930). (5) (6) (7) (8)
RECEIVED February 21, 1933.
Efficiencies of Tar Oil Components as Preservative for Timber F. H. RHODESAND IRAERICKSON,Cornell University, Ithaca, 3. Y.
I
S THE determination of the fungicidal powers of creosote
oil fractions by the wood pulp method of Rhodes and Gardner, the use of pine pulp gives results consistent with those obtained when Norway spruce pulp is used. No one compound in coal-tar creosote oil is primarily responsible for its preservative power, although diphenyl appears to be slightly more toxic to fungi than any other single compound. The fractions from water-gas tar oil are much les- effective as preservatives than are those from coal-tar creosote oil. The chlorine derivatives of phenol and creosols and of naphthalene are more toxic to fungi than are the compounds from which they are obtained. This investigation is essentially a continuation of that of Rhodes and Gardner ( 2 ) . I n this earlier work a method was devised for measuring the fungicidal powers of wood preservatives by determining the minimum concentration of preservative required to prevent the growth of Fornes annosus in mechanical wood pulp. The conditions in this test resemble, in many respects, those under which the preservatives are actually used, so that the experimental results should be indicative of the results that may be expected in service. This method of testing was used in the present investigation also. A possible criticism of the original method of Rhodes and Gardner is that the test material was mechanical wood pulp from Norway spruce, which is not commonly used for structural purposes. To determine whether or not the apparent efficiency of the preservative varies with the specific type of wood pulp used, parallel tests were made with careosote oil fractions as the preservatives, using Xorway spruce and mechanical pine pulps. The mechanical pine pulp was obtained through the courtesy of the Forest Products I abmatory, Madison, Wis. The results were as follows: -LIMITING
OIL FRACTION
CONCENTRATIONSO--
S O R W A Y SPRUCE PULP
A
B
A
B
%
%
%
%
0 s 1 0 0 6 0 8 0.6 0 8 0 6 0 8 9 0 6 0.8 0 6 O S a A , maximum concentration a t which any g r o a t h of F annosus occurs, B, minimum concentration at which no growth of F annosus ,occurs
5 7
It appears that within the limit of experimental error the results of the test do not depend upon the specific type of pulp used. Several investigators in this field have made comparisons of the relative efficiencies of preservatives by determining the concentrations of the various preservative substances that are required to inhibit the growth of the wood-destroying fungi in a malt-agar medium, or the concentration required to kill the fungi in such medium. One such method has been described by Schmitz and others ( 3 ) . This method is a
convenient one, although the conditions of the test differ so markedly from those of actual service that, in some cases at least, the results inay not be directly comparable with those that may be expected in practice. A series of fractions from coal-tar creosote oil was tested by the methods of Schmitz and of Rhodes and Gardner. The results were as follows: KILLINGCOSCESTRI T I O A N e t h o d of Rhodes hlethod of Schmitz % by uezght o/ Load p u l p o/ agar medium 0.9 0.03 0.7 0.03 0.55 0.03 0.7 0.03 0.03 0.1) 0.7 0.03 0.9 0.05 1.3 0.05 0.08 0.15 0.9 0.05
F R ~ C T I O N and Gardner yo by u e t g h t 1 2
3 4 5
6
;
9 10 ,\I ixt ure
R~TIO 30:l 23:l 18:l 23:l 30:l 23:l 18:l 26:l 21:l 18: 1 18: 1
:.s
These results show that in the comparison of the preservative efficiencies of variouh fractions from coal-tar creosote oil the two methods give reasonably consistent results, although quantitatively the concentration required to kill Fomes annosus in an agar medium is much lower than that to prevent the growth of this organism in wood. COAL-TARCOhTPOUNDS The matetial used in this series of tests was prepared from a typical coal-tar creosote oil that showed the following analysis: PERCENTDISTIL LED^
TEMP.R A N G E
(BY
c.
WEIGAT)
0-2’10 1.2 14.3 235-270 20.8 270-3 15 20.5 3 15-355 20.2 Residue 21.0 Limpid point, C 27 Sp. gr. (38/15.5j C.’ 1.065 T a r acids, % 11.6 T a r bases. 5% 5.9 Bulb distillation by:l S T hl method D246-27T 2 10-235
Several gallons of this material were freed from tar acids and bases by repeated alternate extraction with a 10 per cent solution of sodium hydroxide and a 30 per cent solution of sulfuric acid. Two liters of the resulting “dead oil” were distilled from an iron still provided with a Hempel fractionating column, and the distillate was collected in ten approximately equal fractions, as follows: FRhCTIOs
1
2
3 4
DISTN TEMP “C 184-210 210-225 225-240 240-260
Fn4crros 5 6
7
DIJTN. TEMP.
c.
260-290 290-300 300-310
DISTN.
FRICTION TEMP.
oc
S 9
10
310-320 320-340 340-385
