INDUSTRIAL AND ENGINEERING CHEMISTRY
2178
reported are the best' values available a t this time for use in safety work a t 1 at,mospherepressure. These data also may be used for other purposes. Thus, plots of the spontaneous ignition temperature against the time lag before ignition (Figure 3) may be used to determine the maximum time during Tvhich a combuitible-air mixture at a specified pressure may be held safely a t a particular temperature. Similar data have been obtained by Mullins for floIving hydrocarbon-air mixtures a t elevat'ed temperatures ( 7 ) . These data also may be used to obtain approximate activation energies for the oxidation of the combustibles tested ( 7 ) . The statistical interpretation of the Arrhenius equat,ion ( 2 ) indicates that the rate of a collisional reaction ib proportional to exp ( - E / R T ) where E is the activation energy. As the rate of reaction is inversely proportional to the time of reaction, the time of reaction should be related t o the energy of activation as follows (7): In
T
Accordingly, a plot' of In
=
constant
E + Ri'
7-
1
should give a straight, line T with a slope equal t o EIR. The data used to plot Figure 3 have been replotted in Figure 9 to show the straight lines that result from this type of plot. These graphs indicate that the activation energy for heptane-air ignitions a t 1 atmosphere pressure in a borosilicate glass container decreases from 31 kcal. per mole over the temperature range 222" to 233" C. to 18 lrcal. per mole over the temperature range 233" to 333" C. Similarly, the activation energy for decane-air ignitions a t 1 atmosphere presaure 7
against
-
Vol. 46, No. 10
decreases from 47 kcal. per mole over the temperaturerange209" tu 223" C. to 34 kcal. per mole over the temperature range 223" to 2-51' C. These activation energy calculations do not take into account the time required to vaporize the fuel which is probablj- negligible for temperatures near the minimum spontaneous ignition temperature that involve long time lags; these are the temperatures that yield 31 and 47 kcal. per mole for nheptane and n-decane, respectively, in these examples. LITERATURE CITED
Frank. C. E., Blackham, A. U., and Smarts, D. E., ISD.E s n . CIIEIU., 45, 1753-9 (1953). Hinshelwood, C . S . , "Kinetics of Chemical Changc," Oxford University Press, Sew York, 1940. Jones, G. W..Zabetakis, h l . G., and associates, Wright .Air Development Center, Tech. Rept. 52-35 (-1rmed Serv. Tech. Information Anencv. Cataloe: KO. AD 5805). 1952. Jost, W., 'Explo3ion and Combustion Processes in Gases." 3IcGraw-Hill, S e w York, 1946. Lorell. W. G., Campbell, J. 11.and Boyd. T. h.,IVD. EN(.. CHEM., 26, 1105-8 (1934). lIulcahy, AI, F. R.. Trans. Faradal/ Soc., 45, 537-41 (1949). Mullins. B. P.. P a d , 32, 211-52, 327-79. 451--91 (1953). National Fire Protection Assoc., 60 Batterymarch St.. Boston, Xational Fire Codes, 1, 1951. Scott, G. S., Jones. G. W., and Scott, F.E . . d n a l . Cheni., 20 (1948). I
"
~
Walsh. A . D., Trans. Faraday Soc., 42, 269-83 (1946); 43,
297-313 (1947). Zabetakis, AI. G.. Scott, G. S..and Jones. G . W.,G S.Bur. lIines, Rept. Invest. 4824, 1951. RECEIVEDfor review April 14, 1954. ACCEPTEDJune 23, 1924. This research waa supported in part by the 4 i r Research and Development Command under Contracts (33-038)50-1293-E and AF 18(600)-151.
Measuring istillate Fuels G . I. WORKALL Research Department, Standard Oil Co. (Indiana), Whiting,Ind.
€B
U R S I N G quality of a distillate fuel oil is judged by the amount of soot or coke deposits formed in oil b u r n m used in the home. Home burners vary widely in tendency to form deposits, but all burners rate fuels in essentially the Fame order of quality. It is of interest t o petroleum refiners, therefore, to be able to measure the burning quality of fuel oils in order to ensure customer satisfaction. Several laboratory met,hods have been used for evaluating burning quality. St,udies of burner deposits and of flue gas soot have been report,ed ( 6 . 9). and combustion indexes relating to burning qualit? have been propnsed (2, 7 ) . However, all of t,he reported methods are based on oils differing widely in physical properties. h t t e m p u to confirm the methods by application to closely relat,ed fuels have failed. X more sensitive burner teat is needed that can differentiate between fuels of almost identical gravity and boiling point. Precise data on burner deposits might then offer a firm basis with Tvhich simpler meaaarements of fuel qualit,y could be correlated. Burners for evaluating distillate fuel oils should be comparable to the home burners for il-hich the oils are intended. L I o s t commercial burners are of two types-atomizing or vaporizing. Atomizing burners usually spray fuel from a nozzle, whereas vapoiizing burners evapoi-ate fuel from a pool of hot oil by heat
of combustion. Atomizing burners form only a sootmydeposit on the int,erior heat, exchange surfaces; vaporizing burners form a greater amount of sooty deposits, and, in addition, a cokelike deposit on the vaporizing surface. For laboratory- purposes the vaporizing burner is desirable because both types of deposits can be studied in one test of short duration. The pot burner is the most common of the vaporizing type and has been used in previous burner studies ( 1 , 3, 9). Briefly, the burner consists of a vertical combust,ion e;-linder surrounded by a rectangular metal shield. The lower part of the cylinder houses a perforat,ed pot xhere oil vapors and air are mixed. Figure 1 IS a schematic diagram of a typical pot used in conimercial burners. When the burner operates, oil vapors rise from the pool of oil on the pot bottom, meet, air drawn through the holes in the side, and burn. The hot gases rise upward through the combustion chamber and out the stack. Sooty deposits, caused by incomplete combustion, form on the pot side and in the upper regions of the burner and reduce heat transfer to t,lie surrounding space. Cokelike deposits, caused by cracking or condensation reactions in the pool of vaporizing oil, form on the pot bottom and tend to clog the oil inlet,. Because both types of deposits form rapidly with cracked fuel oils, maight-run fuels are generally used.
October 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
Laboratory fuel studies in burners usually consist of 0 0 0 0 0 burning a measured amount of oil, cleaning the burner, and weighing the removed deposits. ?\Ia n u f a c t u r e d commercial burners do not give repeatable results and are difficult to clean. However, repeatability can be immoved bv better control Figure 1. Typical Pot for of air and oil rates and by D e t e r m iQuality ning Burning eliminating air leaks around the door or in the stack. Access for cleaning is made only through the door in the side of the combustion chamber, but this chamber can be modified to allow easier cleaning. Although these changes can be made in any conventional burner, building a new one is probably simpler. iWODIFIED POT BURRER
A% pot burner of modified design has been built and used in laboratory studies of fuel quality. Figure 2 is a schematic diagram of the modified pot burner. It consists of three main sections, pot, combustion chamber, and stack. The pot section comprises a pot 10 inches in diameter and 8 inches deep welded into a surrounding air chamber. Entrances for air and oil lines and thermocouples are provided. The combustion chamber is a hollow cylinder to which a 11/2-inchpipe nipple is welded a t the top, The stack section includes openings for a thermocouple and a tube for sampling the flue gas. In operation, the burner is surrounded by a protective shield.
2179
metered to the burner with a gear pump. Conventional burners use a float-controlled valve that regulates gravity flow; variations in flow can occur if even a small amount of foreign material gets into the valve. The modifications built into the test burner result in precise control without material change in the conventional design. Work involved in cleaning and operating the burner has been reduced to a minimum. OPERATION OF TEST BURYER
Testing for fuel differences requires the use of identical air rates and oil rates for all fuels. The rates used determine the amount of deposits formed by a given fuel but do not affect the relative amounts formed by different fuels. RaJes chosen for the test were 5.3 cubic feet (150 liters) of air per minute and 1 pint (473 ml.) of oil per hour. They correspond to low draft, low oil rate operation of conventional burners and yield the most deposits for the amount of oil burned. The standard test requires 2.5 gallons of oil. Burning time is 20 hours. The test can be extended by burning more oil to magnify small differences between fuels. ilt the beginning of a test, the air valve is opened and the oil pump is started. The oil is lighted by lowering a taper to the pot bottom through the pipe nipple a t the top of the combustion chamber. The burner operates u n a t t e n d e d until the oil supply is exhausted. The Figure 3. Modified Pot pot section is then removed Burner for cleaning, and the bottom and side deposits are separately scraped off and weighed. After the combustion chamber has been cleaned with a vacuum sweeper, the burner is reassembled. FUEL EVALUATION
Figure 2. Modified Pot Burner
Figure 3 is a picture of the burner. Main parts are made of 16-gage steel and are welded a t the joints. Three supporting legs are Telded to the side of the combustion chamber. The flanged pot section is connected to the chamber with an asbestos gasket and twelve C-clamps. It can be easily disconnected for careful cleaning and collection of deposits. Auxiliary equipment includes a flue gas exhaust system and apparatus for controlling the flow of air and oil. Air is forced into the burner under a closely regulated pressure of 0.5 pound per square inch. The air flow is measure? by pressure drop across an orifice in the 1-inch supply line. This system controls air supply much more closely than the butterfly dampers used with the conventional induced-draft system. Fuel oil is
The weights of side and bottom deposits formed during the standard 2.5-gallon test are the criteria of burning quality used for all fuels. The significance of this test has been established by correlation with field tests in 12 conventional pot burners being used to heat homes. Two straight-run fuels, similar in gravity and boiling range but different in crude oil origin, were supplied to the burners. Properties of the fuels are shown in Table I. Duplicate tests covering 24 weeks showed total deposit differences of 38 and 49%. The 2.5-gallon laboratory teets showed a 43y0 difference. Total deposit results were obtained in the field tests because time limitations did not allow accurate separation of side and bottom deposits.
O R FIELD TESTFUELS TABLE I. PROPERTIES
Gravity, API AST.M Distillation, Initial 10% 50% 90%
Maximum
F.
Poor 41 .Q
Good 42.2
INDUSTRIAL AND ENGINEERING CHEMISTRY
2180
Formation of side and bottom deposits in the modified burner has been studied with five widely different fuels-a kerosine, two KO.1 fuel oils, a No. 2 fuel oil. and a catalytically cracked oil. S o . 1 oih, supplied mainly for vaporizing burners, are straight-run oils with a maximum boiling point higher than kerosine. No. 2 oils, normally supplied for atomizing burners, are blends of cracked and straight-run oils Properties of the five fuel5 are shown in Table 11.
200-
Vol. 46, No. 10
for the other three fuels. The two KO,1 fuels are more clearly differentiated than by side deposits. Other studies with many No. 1 fuel oils show no relation between the amounts of bot.toni aiid side deposits formed. Bottom deposits cannot be predictctl from known fuel properties, but side deposits can be estimated from boiling range and aromatic content. The data on side and bottom deposits a t various galloriagcs show the advantages and limitations of the 2.5-gallon test. I t can distinguish betrreen most fuels but should be extended in cases M-here deposit differences approach the precision limits of t,he burner. Precision of the 2.5-gallon test has been determined from results of 15 separate tests made with the same straight-run fuel over it period of time. Stat,istical analysi. showed that %yo of all t,ests made with this fuel should form side deposits weighing n-it,hin 2.470 of the mean of the 15 tests. Similarly, for bottom deposits, the 05% confidence liniit,s were h6.473 of the mean of the test,s. Greater accuracy than this is seldom required for evaluating fuels. CONTRIBUTION OF HYDROCARRON TYPES
'// 2
0
4
I 8
6
10
12
14
16
O I L BURNED, GALLONS
Figure 4.
UraTVity, API .ISTll Distillation,
Formation of Side Deposits
Kerosine 43,4
-.xo~??!L A B 4L2
12.2
So. 2
Oil 37.0
The significance and precision of results obtained with only 2.5 gallons of oil justify studies with individual hydrocarbon types that are too expensive for use in large quantities. One such studv determined the relative effect on deposits of monoand bicyclic aromatic compounds. Both types of hydrocarbons are present in No. 1 and No. 2 fuel oils and contribute to deposit formation. The three blending stocks used in the st,udy were H. paraffinic heavy alkylate, a monocyclic heavy hydroformatme, and Eastman 1-methylnaphthalene. The properties and com-
Catalytically Cracked Oil 30.9
50
336,
380 427 474 520 0.10
334 376 4.12 522 5613 0 la
320 356
11.5 510 368 0.53
330
376 470 595 655 0.04
383 419 461 516 89G 1.04
1
I
F. vi
a
c
o l
40-
30-
0
w 0
20-
Figure 4 shows the formatioil of sick deposits by the five fuels. The four lower curves rise almost, linearly; greater deposit differences occur with increasing amounts of oil burned. The t,wo S o . 1 oils show a marked difference in burning quality despite identical gravities and similar distillation patterns. The curve for catalytically cracked oil differs from the other four; it,s change in slope indicates t,hat8the accumulation of side deposits slows down after about 3 gallons of oil is burned. The cause is an increasing carry-out of soot, from the pot after a certain thickness of deposits has collected on t"ne sides. Soot density methods of furl evaluation are used in many laboratories because of simplicity. Side deposits correlate with soot, densit,y measurements macle of flue gases from the five fuels. Kerosine 3
s o . 1 011s
A 4
B 4
s o 011
5
2
KER~SINE
,-
O I L BURNED, GALLONS
Figure 5 ,
Formation of Bottom Deposits
Catalytically Cracked Oil 7
The numbers are averages of many tests and indicate the relative blitckriess of a filter paper t,hrough which a standard volume of flue gas has been drax-n; on this arbitrary scale, 0 is white and 9 is black. hlthough the test rates the fuels in the same order as do side deposits, it does not dist,inguish between the two Xo. 1 fuel oils. Moreover, individual soot tests varied by several units for the same fuel. The weight of bottom deposits is alwap less than that' of eide deposits at any given t,ime. Figure 5 shows the rate of forming bott,om deposits by the five fuels. Bottom deposits remain low for kerosine and one of t,lw So. 1 fuels, but increase
0
5 IO I5 PER CENT HYDROFORMATE
20
Figure 6. Relation of Side Deposits to Fuel Coniposition
October 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
position of these stocks are shown in Table 111. Sixteen blends of the three components were tested in duplicate. Blend compositions ranged from 72.5 to 100% alkylate, 0 to 20% hydroformate, and 0 to 7.5% methylnaphthalene. These percentages by volume were chosen to bracket the normal distribution of these hydrocarbon types in most straight-run fuels.
TABLE111.
PROPERTIES
COMPOSlTION
AND
OF
STOCKS
Heavy Alkylate Gravity, O API ASTM Distillation, Initial
52.3
28.8
350 370 388 482 660 0 05 1 4295 103.3
298 314 329 356 400 0 01 1.5065 184.0
F.
O
LO%
00% EZimurn Sulfur 5% Refradtive index, nz2 Specific dispersion
Heavy Hydroformate
relate deposit formation to pure hydrocarbons and sulfur compounds. RELATION OF SMOKE POINT
Smoke point is the height of a wick-fed flame in a standard lamp under conditions of incipient smoking. The test was first used in about 1930 to relate the quality of kerosines used in lamps, and has since been refined. I t has been related to the moleouler BLENDING structure of pure compounds ( 4 ) and is gaining acceptance as a measure of jet fuel quality. KO data relating it to burner deposits have been published. MethylFigure 8 shows a straight-line correlation of smoke point with naphthalene the logarithm of side deposit weight. The fuels represented in6.6 clude all classes of distillate fuels. Smoke point data were ob451 tained RTith a Factor lamp (8) which has greater sensitivity over 456 458 a broad range of fuels than the more widely used Institute of 460 486 Petroleum lamp (10). 1.22 1.6130 282.0
.\..
100
C A T ~ L Y T I C A L L YC R A C ~ E OO I L S
Approx. Composition", 3 '%
6l
Cs paraffins C1z paraffins
it
CMparaffins
2181
Heavy Alkylate
Heavier paraffins 5J Ci aromatics Ca-Clo aromatics Heavy Hydroformate Heavier aromatics Naphthalenes 4 1-Methylnaphthalene 2-Methylnaphthalene 29 Unknown Determined b y true-boiling-point distillation, infrared absorption, and ultraviolet absorption.
7
-
50 40-
I
2 5
30-
e
20-
Y E
4
10-
i
l
4
-
v i -
c
P
54EXPERIMENTAL OIL5
The amount of side deposits ranged from 2 grams for 100% alkylate to about 28 grams for a blend containing 20% hydroformate and 7.5% methylnaphthalene. Deposits were additive for both components; the methylnaphthalene formed about 1.3 grams for each per cent and the hydroformate about 0.75 gram. Bicyclic aromatics appear to be about twice as active as monocyclic aromatics in side deposit formation. Figure 6 is a three-dimensional plot showing the average deposit results as a function of the per cent of mono- and bicyclic stocks in the blends. The deposit data appear to define a plane.
'
\.I
1
i
SMOKE POINT, MM
Figure 8.
Correlation of S m o k e Point with Side Deposits
As would be expected, smoke point does not correlate with bottom deposits. Accepted combustion indexes, such as carbonhydrogen ratio, diesel index, and burning index, also show a correlation with side deposit weight for distillate fuels. The smoke point correlation, however, is closer. Although the smoke point and side deposit data are in good general agreement, deviations occur that cannot be explained by experimental error. The flame of the lamp is affected by small variations in such fuel properties as surface tension and viscosity (6). These minor changes in fuel properties can alter the lamp reading sufficiently to obscure the small differences in burning quality shown by the burner for some No. 1 fuels. Despite this limitation, smoke point is useful for predicting one facet of burning quality-side deposits-where close differentiation of fuels is not required, CONCLUSION
0
5
10
15
20
PER CENT HYDROFORMATE
Figure 7. Relation of Bottom Deposits to Fuel Composition
Figure 7 is a similar plot for the bottom deposits. I n this instance, interaction between components or impurities produced a curved surface that bends along both the hydroformate and the methylnaphthalene axis. Further work is being done to
Burning quality of distillate fuels in domestic oil burners can best be fully determined in terms of side and bottom carbon deposits in a vaporizing pot burner. Side deposits are closely related to fuel composition and can often be predicted by smoke point. Bottom deposits are not as well understood; further knowledge can best be obtained by continued studies of these deposits in a closely controlled pot burner. ACKNOWLEDGMENT
The author is indebted to K. F. Richards for assistance in the experimental work.
INDUSTRIAL AND ENGINEERING CHEMISTRY
2182
Vol. 46, No. 10
(7) Reid, J. C., and Hersberger, A. B., A S T M Bull., 145, 7 7 ,
LITERATURE CITED
(1) Burkhardt, C. H., Fueloil d Oil Heat, 7 , 50,12, 58 (1949). (2) cauley, s, p,, and ~ ~E. B.,oil i &s J~, , 45, so, ~ 10, 166 ~
(1946).
(3) Cauley, S. P., and Linden, H. R., Ibid., 45, S o . 12, 80 (1946).
(4)Hunt, R. A., IKD. EKG.CHEM.,45, 602 (1953). (5) Kewleu, J.. and Jackson, J. S..J . Inst. PetroZeum Technol., 13, 364-(1927). (6) Lochlin, D. TV,,and Parmalee, G. V., Heafing. Piping, Air Conditioning, 22, No. 12, 121 (1950).
(1947). ~(8) Terry, , J. B., and Field, E., 1x1,EM. CHEN., 8, 293 (1936). (9) Western Petroleum Refiners ;ISJOC.. Tulsa, Okla., “Burner Oils-Report of Research Project,” 1945. (10) Woodrow, W.A , , World Petroleum Congr., Proc., 1st Congr., London, 1933, Vol. 11, p , 7 3 2 . RECEIVED for review January 27, 1954. ACCEPTEDM R 24, ~ 1954. Presented before the Division of PetroleJm Chemistry a t the 125th Meeting of the AMIEXICAK CHEXICALSOCIETY, Kanaas City, Mo.
Prediction of ASTM End Points of Blended Light Petroleum Products MAURICE E. STASLEY AND GWENDOLYX D. PINGREY The Texas Co.,P o r t rlrthur, Ten.
ETROLEUM refinery designers and operating engineers are frequently called upon to estimate the XSThI distillation curves of mixtures of stocks. I n the past, such predictions have relied heavily upon the experience and judgment of the estimator, and there has been no satisfactory method for predicting the results of blends of widely dissimilar stocks. The increasing consumption of fuels over the past severa.1 years has made it imperative to blend closer and closer to limiting volatility specifications in order to obtain masimum production. At the same time, the development of new processes such as alkylaiion and catalytic cracking has made new stocks available for use which have such imrrow boiling ranges that they considerably complicat,e blending predictions. Therefore, the need for more precise met,hods for estimating distillation points has inweased steadily over the past several years. The effect of natural gasoline on the ASTRI distillation curve of gasoline blends is discussed by S a s h and Howes ( 4 )who present a summary of work done by Zublin ( 6 ) and by Alden and Blair ( 1 ) . The correlations of these authors are somewhat limited in their applicability to modern refinery calculations. However, a method presented by Haskell and Beavon ( 3 )appears applicable for estimating the 10% points of most refinery blends containing natural gasoline, butane fractions, and pentane fractions. Kelson (6) states that the boiling range of naphtha-natural gasoline blends can be estimated by averaging the material boiling up t’o a given temperature in the ratio of the quantity of each blending agent used. Although this method is suggested only for naphthanatural gasoline blends, it has found wide usage for many gasoline blending problems and is thought to be generally applicable for the mid-range of gasoline blends provided the components do not differ too widely in distillation characteristics. This paper presents a method for predicting the ASTRI. end points of blends of light petroleum products when only the composition of the blends and the ASTLI distillations of t’he component stocks are known. This method appears to be sufficiently accurate for most refinery calculations and is applicable to stocks varying in distillation characteristics from butane and pentane through full range naphthas and narrow boiling range products to kerosine. EXPERIMENTAL PROCEDURE
The development of a blending correlation requires a large amount of accurate data on a representat’ive portion of the many combinations of stocks that may be encountered in refinery operation. Therefore, R survey was made in a large re-
finery to determine how many tjpes of stoclre were manufactured. On the basis of this survev, the thirteen stocks shown in Table I were chosen t o represent the various fractions that might be encountered in refinery calculations. Butanes and pentanes were considered sepaiately, as discussed later. The list included wide boiling range fractions such as thermal cracked gasoline (G), narroF boiling range fractions such as Stoddard Solvent ( P ) , stocks that have a long “tail” such as light catalytic cracked gaqoline (E),and stocks iyith short “tails” such as aviation straight run gasoline ( A ) . “Tail” is used t o desciibe the final portion of an ASTM distillation Curve where the temperature normally iises much more rapidly than it doe> during the midportion of the curve. The stocks ranged from low boiling aviation gasoline fractions through motor gasoline and special solvent fractions to stocks which might be uwd in kerosine and jet fuel manufacture. From these thirteen stocka, 108 blends were prepared and
420
280
t
‘
I
20
I 40
I 60
I 80
r 100
% HIGH END POINT COMPONEP1T
Figure 1. Typical End Point-Composition Curves
