STABILITY OF FURNACE OIL A. B. HERSBERGER, H. C. COWLES, AND B. ZIEBER T h e Atlantic Refining Company, Philadelphia, Penna.
T
metallic copper. During periods HE extensive use of furThe fouling of domestic oil burner systems when fuel oils lie stagnant in nace oil for domestic by unstable furnace oils is discussed. A burner systems, it is probable heating has placed new stability test is described, and data are prethat copper accelerates their demands on quality. The crisented relating this test to results obta:ned deterioration. teria of performance are a clean Solubility analyses of material by circulating oils through the essential burning flame and uninterrupted removed from cotton strainen parts of a gravity-feed burner system; the automatic operation. T o obtain placed in the feed lines of latter results have been found to correlate the latter condition, the oil must domestic installations are shown be free of solid material and with practice. Data on both refined and in Table 11. The alcoholmust be stable in storage in the unrefined oils are included. The stability soluble portion of these sludges consumer's burner system where test is based on the reaction of oils to two was identified as consisting it is in contact with metals largely of soaps formed by the metal pairs, iron-copper and iron-lead, known t o promote sludge formareaction of oil constituents with under controlled conditions. The test was tian. Burners that are particumetals. The sludges containoriginally designed for straight-run oils, larly sensitive t o small amounts ing large percentages of alcoholand its limitations in regard to cracked oils of solids in the oil are the soluble material in general were gravity feed type rather widely are pointed out. the most gelatinous. used in some sections of the eastern United States. Much of the previous work on the stability of fuel oils has been TABLEI. METALLIC CONSTITUENTS IN SLUDGES REMOVED concerned with the heavier grades. Batchelder (1) developed FROM CLOGGED BURNER SYSTEMS a method of predicting the heater-coating tendencies of these Sediment Removed from: oils; Voskuil and Robu (6) and Batchelder and Wellman (2) Metallic Oil storage pointed out the factors involved in blending cracked tars and Constituent tank Strainer Float bowl straight-run oils in order t o prevent the precipitation of asIron Preaent Present Present Present Present Present Zinc phaltenes. Trusty (4), in discussing the problem of producing None Present Present Lead stable furnace oils, outlined several test methods reported in Cadmium None Present None Trace None None Copper we. Hawes and Miller (8) presented a test for determining None Present Present Nickel potential sludge formation in light oils. However, neither of the last two references offers any evidence t o indicate t h a t t h e TABLE11. TYPICAL SOLUBILITY ANALYSEBOF GELATINOUS methods described will predict what happens to the oils in SLUDGE FOUND IN STRAINERS OF FOULED GRAVITY-FEED B~NER practice. SYBTEMB The test presented in this paper was developed primarily for of Material Solublealight distillate furnace 03s and has been in use by this company No. 1 No. 2 No. 3 No. 4 Solvent for approximately three years with excellent results. It is 88' na htha 75.5 92.6 93.7 89.6 D-30a%ohol 22.7 6.8 4.3 1.7 designed for s t r a i g h h u n oils and is not entirely indicative of the Acetone-beneene, 50-50 0.3 0.6 6.7 performance of cracked oils. However, no cracked oils have 1.5 0.0 1.5 3.0 Water been encountered which are stable in practice yet fail to meet the In order of extraction. requirements of the test. 7 %
FOULING OF BURNER SYSTEMS
The use of unstable oils in domestic burner systems results in sludge formation and the corrosion of parts, particularly brass, leading to clogged strainers and valves. In many systems the flow of oil depends on gravity, and since the effective "head" may be as small as one foot, only small amounts of sediment are required t o retard this flow. Both straight-run and cracked oils may show this type of instability. The appearance of sludges removed from fouled burner systems varies from dark viscous materials t o light colored substances of a flocculent or gelatinous nature. Analysis of these sludges showed the presence of metallic constituents, all of which were identified as parts of the burner system (Table I). Zinc is usually found in the sediments where t h e oil may have been in contact with brass parts. Lead, cadmium, and nickel result from t h e corrosion of solder, cadmium-plated parts, and Monel metal. Copper is seldom found in t h e sludges, although many furnace oils discolor and oxidize when allowed t o stand in contact with
STABILITY TEST
From the above sludge analyses, which disclosed the presence of metals, and the soapy gelatinous nature of the sludge, it was considered likely t h a t an indication of fouling of burner parts of furnace oil could be found in a study of the action of these oils in the presence of metals. Such a study waa undertaken along with a n investigation of the sludging of various oils in a circulating system consisting of the essential parts of a typical domestio gravity-feed burner system. As a result of this work a stability test was developed for furnace oil based on the stability of the oil in the presence of two metal pairs-namely, iron-copper and ironlead. A description of the test follows: APPAHATUS. Metal test strips were selected of standard materials. The lead was X 4 X l/~,, inch commercial sheet. The copper strips, a/! x 4 X a / 8 9 inch in size, were cleaned b y pickling in a sulfuric-nitric acid solution for 30 seconds, washing, and dry-
1104
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1943
mg. The piokling heth contained 22 per cent of sulfuric and 12 o m Gent nitric acid bv weieht. If a StriD was not entirely hright after this treatment, t k procedure &repeated. inch cold-finished The iron strips consisted of *I/.X 4 X xteel(colddrawn,S.A.E.XlMO). They wereele?nedbypickling in a 40-54 per cent (by wei ht) solution of sulfuric acid until the surface scale was remove%. All surfaeea of the strip were scrubbed with R brysh, washed free of acid with water, and immediately dried with seetone. New atandwd 4aunee oil sample bottles were used. They were supplied wit,h a neoprene stopper secured by about 8 inches of No. 18 gage copper wire. Corks im regnated with B msterial to close the pores may be substituted the neoprene sto pers Oxygen was aupplied from a cylinder equipped with refueing valve. The oxy en delivery tube was glass, 6-6 mm. inside dimeter with outkt reduoed to 1 mm. i. d. The oxygen gas was bled into the sample throu h a glass tuba ahout 5 or 0 mm. in diameter with the outlet re%uueed to 1 mm. dinmetor. Other equipment used were an oven thermostatically regulated within *2' F., an anslytied balance sensitive to 0.1 mg., several Coors No. 4 Gooch crucibles, a desiccator, and crucible tongs. PROCEOWRS. The method con3isted of determining the amount of sludee formed hv the oil in the Dresence of fa) iron and CODDer and of"(b) iron and lend under test condition$. Duplicate i&ts were run for each of the two metd combiostions. Fifty milliliten of the furnace oil are introduced into eltoh of two 4ounce bottles, sfter tiltering through a No. 42 Whatmso filter pa r To one bottle i s added B ieee of iron and ofco and to t% bther B piece of iron and n?lsad. Oxy en is bnh% ! thmu h the oil a t the rate of 3w cc. per minute for 5 minutes. Each h e is stoppered immedistely on withdrawal of the oxygen delivery tubesso that nooxygenabove the oil islost, and theatop per is securely wired in. The samples are placed in an oven maintained a t 210" F. * 2" for 4 dam, after which they are removed and cooled. The metal strip a& withdrawn. Any sludge adheri m t o thestrimiisreturnedtotheoilinthebottlewiththeaidofa
8,
A correlation between the etability test and the parformsnoe of the oils in the circulating systems WBS established from data obtained by circulating oils through the essentid parts of B typical gravity-feed burner system and determining the extent of currosion ofthe parts and the amount of sludge deposited (Figure l). This lahoratory ciroulating system consisted of an elevated ohsrge container, 1, from which oil flowed into 15 feet of o a p p r tubing, 0, then into B f l a t bowl nspemhly, 3, 4, m d fmm there to
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LL receiver, 9. from which theailoould h e periodionlly forced by lowpressure sir into the charge container. T w o weighed hrass test pieces were placed in eeeh float howl for corrosion determination. The cop er tubin (feef line) an4 f l o a t bowl assembly were oainted black and heated by an infrared lamp, 2, so s d i u s t e d as t o produce oil tempereture of 140' F. measured st the float bowl outlet. 5. A iest run in this system was made 8s fallows: 10 &lous of oil to he tested were tilted through a funnel containing P. wnd of absorhent cotton, charged to the syystem, and circulated for 5 days at 140" F. and then for 2 days at mom temperature. This cycle was repeated on the mme hatch of oil. At the end of the second week t h e charge was drained from the system without disturbing the oil in the float howl end a fresh ICallon batch of &e test oil wss char ed This ,coni I O gallons of oil was circulated throuah the system for two oydes, the o ra tioo hein i z t i : oal with t%atused on the first 10. Figure 1. Gravity-Fecd Circulating gallon portion. Systems for Accelerated Stability The total time r e Tests on Furnace O S a quired to make B test was 28 days. The rate of oil flow through the ayatem wasmaintsined st 12-15 oe. per minute; 10 e e . o f w a t e r were added to the system weekly. The oil in the reoeiver was forced bilok into the charge container once each day. and the whole charge itated by hand stirring for about 6 minutes. The rate of ,4k flow through the s stem was checked twice dsil and B record kept of sny notieeahfe tendency for the valves to Loome clogged. At the end of the 28-dav ooeretine oeriod. the followin= infar-
medium iurnrrue oil (rehaad1
9
brass piece8, and (c) the dog 'ng ofvalves and st&iner retarding $be rate of oil flow through ti% syslem.
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
Vol. 35, No. 10
Figure 2. Sediment in Eloar Bowls of GravityF e d Cireulating Systems after Operating on Medium Furnaoe Oils under Test Conditions
The accurtluiated nediareat in the float buriwa, removed with the oil by II motion Bssk, the bowl beingwashedwith clean furnace oil. The amount of sediment W&J then determined by centrifuging a t 2500 r. p. m. in B 100-ce. pear-shaped A. S. T.M. oentrifu e tube for 5 minutes. If thevolumeofoil exceede$l00cc., a. portion of the oil-sediment mixture w&s centrifuged and the clear oil decanted; then the remainder of the mixture was added to the aediment in the centrifuge tube and the total volume of sediment determined. The b r a s pieces pleoed in the float bowl for corrosiorr determination were washed with aoetone and slcohol, dried, and weighed. This laboratory arrangement of part8 of & burner system snd the teat method used was considered an sdequate Rubstitution for an aotual domestic installation since the type of corrosion found and the nature of the sediment deposited in the floet.bowh were similar to those observed in eustomer installations. U1SCUSSION OF RESULTS
Oila that formed large amounts of sludge i n the stabiiity test w e n fuund to corrode parts of the circutatiog system and to deposit sediment in the float bowl sssembly. Frequently the flow of oil through the system WIW retarded as a result of accumulation of sediment in the valves. OLk that formed only small a.mount8 of sludge in the stability test did not deposit notioesble mounts of sludge in the circulating system or corrode paria. and the rate of flow of oil through the #ysisni remained relatively uniform.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Odober, 1943
F b u n 3. Corrosion of Brass Floats in Cuntaet with Furnace We in Float Bowls
1107
pointed out; the amount of sludge iumied in tlie individual iron-oopper and iron-lead tests must be oomidered. Table IV gives the results obtained on a variety of o h in both the eirculsting system and the atability test. Some m w straightm oils (run 10) are sufficiently stable. The oils labeled "fefined" were unstable to the stability test prior to refining. The proper refining method een be selected on the basis of the stability tent of the raw oil. The fsot that an oil has been refined does not necebsarily mean that it is stable. Run 26 is ED exsmple, and this ia olearly pointed out by the stability test. Table IV also shows five runs made on blends of atmight-run and cracked oils. Theae blends contained up to 50 p r Cent of cracked oil. In general, the stability test waa indicative of their performance in the circulating systems. However, ND 28 which waa quite stable to the stsbility tent was unsatisfsetory in t h e circulating system. No crsoked oil or blend of cracked and straight-run oils hsve been found whioh ape unstable to the stability t a t but stsble in the oirculating systems. The failure of the stability test to rate all crsoked oils properly ia nppmntly due to formation in service of B varnishlike film (gum precipitation) on valves and strainers that is not picked up by the test. Where cracked oils are m d extensively, the stability tset probsbly should be supplemented by a form of potentid gum test.
g.F i g ~ r e2 show four Hod boala of ~ y s t e mafter operation on oih of various degrees of stability. During run 12 B minimum m o u n t of sludge deposited and there was little evidence of cormsion. There WBB uniform !low of oil during the zgday test. In nuis 11, 13, and 14 there waa greater sludge deposition and nonuniform Row of oil. In NDB 11 and 14 there was considerable corrosion. Figure 3 shows the condition of the brass 0oet.s used in m a 12 and 11, the latter being corroded. Corrosion sometimes is in the form of B b h k layer (probably B oopper sulfide) over the brass pa& rather than an etching effect. This pictorial evidence of one ssti&ctory oil (run 12) and three unsstidaotors oils (runs 11,13, and 14) is supported by the data in Tnble IV. These mults represent four types of oil based on their reaction to the rtsbility test. Run 12 had low iroe-copper and iron-led va1u:a. Run 11had high values in both testa. Run 13 hud low iron-eopper but high imn-lead vslueu. Run 14 WM the opposite, high iron-copper but low iron-lead values. These dsta show definitely that neither of the individual tests adequately predicts the atability of furnace oil and that a combinetion of tests is required, eaoh having its rniiximum value. To arrive at these meximum values, the data from the hbomtory circulating systems and the stability test were oorrelated and the limits selected were 15 mg. of sludge in 50 eo. of oil for the iron-copper tmt and 45 mg. of sludge in 50 cc. of oil for the iron-lead test. To avoid being too near the maximum value in both tests, the Bum of the two values should not exceed 55 mg.-for example:
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TOTP.L 9u)ooE IN STABIITY TEST
Figure 4. Helation of Total Sludge Formed in Stability Test to Sludge Formed in Float B o w l of Cimulatine Systems
The stability teat presented here has been in w e by this company far the paYt three yean5.a B means of omtrolling the quality of its domestic furnaoe oil and the refining operations related to its production. Since its we, trouble experienwd by consumers from fouled burner systems hss been reduced to a negligible amount. ACKNOWLEDGMENT
The author3 take this opportunity of expressing their iodeb?bt*?dS. W. Ferris who directed the work, to H. M. Hanoook, K. G. Krech, and J. J. Mulvey for helpful discussion, and to G. E. Irwin whose mistance wy&linvaluable in correlating laboretory experimental work with resulte obtained in practice. ness to
Un*rti.faat"ry
WTERATURE CITED
Una.tiafPctory
(I) Batchelder, A. H.. Refnei NaIlrrol &dim AUT.,15. 4 8 5 4 0 (1936). (2) Batohelder. A. H., and Wellman, H. B., 16% 17. 280-2 (ISSSj. (3) Hawes, R. J.. and Miller, F. M.,
[email protected]&. 33, 1318.-20
Phlaea
That n general relation eniat~between the total sludge formed in the stability test and the volume of sludge deposited in the float bowls of the eimulating systems is evident in Figure 4. Flost bowl sludges of 0.1 co. and higher correspond to high values in the stability test. However, the total sludge formed in the stability test is not sufioient M judge an oil, BS hss already been
(1941).
Tw&, A . W.,Refiner Nolurol Gaolinc MJ,., 20. 71-3 (1941). (5) Yoskuii. J.. and Rob", I.. d . InaL. Petroleum Tech., 24, 181-206 (4)
(1938).
Pmsrxrm before $lie Division of Petroleum Chemistry (rt the 106th Meeting of the Arraicm C m m r c u Socrerr. Detroit. Mich.
