UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA OPERATION OF ORCHARD HEATERS ROBERT A. KEPNER BULLETIN 643 October, 1940 UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE Introduction 3 Description of heaters operated in field tests 3 Reasons for improving heater management 6 Smokiness of heaters 7 Previous tests on smoke output of heaters 7 Factors affecting smokiness 7 Soot accumulation in lazy-flame and return-stack-gas heaters 10 Effect of soot accumulation on smokiness of heaters 13 Economic considerations of smoke reduction 16 Eesidue in distilling-type heaters 17 Eesidue in lazy-flame heaters 17 Residue in return-stack-gas heaters .17 Disposal of residue 18 Operation of oil-burning heaters 20 Lazy-flame 20 Return-stack-gas 21 Jumbo Cone 23 Exchange model, 7-inch stack 23 Kittle 24 Fugit 24 Coke heaters 25 Lighting and burning-rate characteristics 26 Control of length of burning period 28 Fuel losses 29 Storage and handling of coke 30 Labor requirements 30 Depreciation of heaters 30 Commercial solid-fuel heaters 30 Summary and recommendations 31 OPERATION OF ORCHARD HEATERS1 EOBEET A. KEPNEE3 INTRODUCTION During the winters of 1937-38, 1938-39, and 1939-40, orchard heating was studied comprehensively in the field at the Citrus Experiment Sta- tion at Riverside. Though the studies could not cover all types of heaters now in use, they yielded much information on the care and operation of several of the better kinds. Groups of fifty to seventy heaters of each kind were operated, for a combined total of 350 to 400 hours for the types tested. This operating time is equivalent to about fifteen years of aver- age field heating experience. Description of Heaters Operated in Field Tests. — In selecting the kinds of heaters to be tested, the object was to include representatives of the various general types used in orchards. The following heaters were included in these tests : 1. Lazy-flame (Hy-Lo 230 A) 2. Jumbo Cone 3. Exchange model, 7-inch stack 4. Kittle 5. Fugit 6. Experimental return-stack-gas heater 7. Experimental coke heater Lazy-flame heaters are designed to have most of the combustion take place at the top of the stack or above. The Hy-Lo 230A (fig. 1) is one of the more modern heaters of the lazy-flame type. During the winter of 1938-39 these heaters were equipped with the usual type of draft regu- lators, which must be closed and regulated by hand after lighting (fig. 1). This type of regulator will be referred to here as "standard." During 1939-40, the lazy-flame heaters were equipped with a late-model, automatic, starting-draft control. This, commonly known as an "auto- matic" regulator, will be so called, though the only automatic feature is 1 Eeceived for publication August 28, 1940. 2 This publication is not a report on the phase of the work at Eiverside dealing with the relative heating effectiveness of different types of heaters, but presents observa- tions and experiences in the operation of heaters without regard to their effect in the orchard, obtained concurrently with the heating studies. Further heater studies are in progress. 3 Associate in Agricultural Engineering in the Experiment Station. [3] University of California — Experiment Station the closing of the excess draft by means of a thermostat, to terminate the starting period. The design of the burning-rate control differs, however, from that of the standard regulator and, as will be shown later, is an im- provement. Figure 2 gives two views of these automatic regulators. At the left in the figure the regulator is open, ready for lighting. This view shows, on the bottom side of the upturned regulator plate, the small box containing the thermostat element that controls the starting draft. Im- mediately after lighting, the regulator is closed by hand to the position shown at the right. After the heater has burned for 2 or 3 minutes, the thermo- stat element warms up and causes the regulator plate to drop automatically, which reduces the draft opening to a predetermined operating value. The Jumbo Cone (fig. 12, A) is an example of a combustion-chamber type of heater in which a coni- cally shaped combustion chamber is used. For this type, combustion takes place mainly within the combustion chamber and stack, in contrast to the lazy-flame heaters, in which most of the combus- tion occurs above the stack. The 7-inch Exchange stack (fig. 12, B) is a com- bustion-chamber type, but it differs from the Jumbo Cone in having a higher stack and a cylin- drical combustion chamber of the same diameter as the stack. The Kittle (fig. 12, C), the only drip-type heater now in general use, differs from the distilling type in that the combustion takes place di- rectly over a shallow, circular fuel trough in the base of the stack, to which fresh oil is fed continuously at the desired rate, either from a pipe line or from a container adjacent to the heater. In the field tests a pipe- line system was used with these heaters, each heater being equipped with a small fuel chamber (fig. 12, C, at the right of the stack) in which the oil level was controlled by a float valve, with gravity feed from the cham- ber to the fuel trough. The Fugit (fig. 13), a generator-type heater, is operated from a pipe- line system. In this type, the fuel is volatilized while passing through a small evaporation chamber kept hot by the heater flame. The fuel vapor then issues, as a vapor jet, from an orifice, where it burns in a self -in- duced draft. Burning rate is regulated by a needle valve at each heater. The return-stack-gas heater, not yet commercially available, is a com- bustion-chamber type with a return pipe for recirculating part of the Fig. 1. — Lazy-flame heater with standard regulator. (From Ext. Cir. 111.) Bul. 643] Operation of Orchard Heaters stack gases. It was developed in the Experiment Station laboratories at Davis primarily to answer the demand for a distilling-type heater that will operate for reasonably long periods and over a moderate range of burning rates without objectionable smoke. The portion of stack gases returned to the bowl dilutes the fuel vapors and reduces smokiness. Sev- enty of these heaters were built at the Experiment Station laboratories at Davis for testing in the field. The return-stack-gas heater is illus- Fig. 2. — Two views of automatic regulator: A, open, ready for lighting B, closed after lighting. trated in figure 3, B. The round bowl, cover, regulator, and downdraft tube are of the usual type except that an adapter for the return tube is added to the cover. On the inside of the stack is an elbow connected with the one outside and with its open end extending downward at the stack center. The experimental coke heater (fig. 3, A) used in these field tests was developed by one of the commercial oil companies as a practical, low- cost unit for burning petroleum coke. It has no grate, but merely a solid removable bottom of galvanized iron. Its height is 30 inches, and its top and bottom diameters are 12 inches and 15 inches, respectively. It was constructed this size to produce heat outputs comparable with those of oil-burning orchard heaters. In these studies lazy-flame heaters with standard regulators, lazy- flame with automatic regulators, return-stack-gas heaters, and coke heat- ers were burned 60 to 80 hours each, while the heaters of the other types 6 University of California — Experiment Station were operated 20 to 30 hours each. All bowl- or distilling-type heaters used in these tests were equipped with round bowls. Reasons for Improving Heater Management. — In determining the best operating practices for orchard heaters, one should keep in mind Fig. 3. — Experimental heaters: A, coke heater; B, return- stack-gas heater. several objectives or purposes for improving heater management : 1. To minimize smoke output 2. To minimize fuel contamination 3. To reduce labor requirements where possible 4. To prolong the life of the heaters 5. To get adequate frost protection with minimum fuel consumption4 Assuming that adequate frost protection can be obtained with the heating equipment that a grower has available, the most important prob- lem from a public viewpoint is to eliminate the smoke nuisance. 4 For any given type of heater, this involves frequent checking of orchard tempera- tures and regulation of heaters to keep them at the lowest burning rates that will maintain safe temperatures. Bul. 643] Operation of Orchard Heaters 7 SMOKINESS OF HEATERS Previous Tests on Smoke Output of Heaters. — In 1932 the results of smoke tests on most of the oil-burning orchard heaters then in use were reported in Bulletin 536.5 The thirty-one heaters tested were classified into four groups according to their smokiness when clean : 1. Five heaters reasonably free from smoke at all usual burning rates under good operating conditions (Jumbo Cone; Kittle; Fugit; Ex- change model, 7-inch stack; Hy-Lo, 1929 model). 2. Six heaters that can be operated with little smoke up to burning rates used in moderately cold weather, but which may produce excessive smoke under certain conditions (Baby Cone ; Exchange model, 5%-inch stack ; National Double Stack ; Citrus, high stack ; National Junior Lou- ver, 15-inch; Exchange model, 6-inch stack). 3. Seven heaters that are smoky, but which were commercially impor- tant in 1932 (Hy-Lo double stack, square bowl; Hy-Lo single short stack, round bowl; Citrus regular; Citrus, 15-inch stack; Hy-Lo double stack, round bowl; Hy-Lo single short stack, square bowl; Citrus Gas Flame). 4. Thirteen heaters that are very smoky but which are mostly of obso- lete types. Additional heaters now on the market would fall in groups 1 and 2. A discussion of the better heaters now available, with the range of their smoke outputs when clean, is included in Extension Circular 111.6 Factors Affecting Smokiness. — The smoke tests referred to above and the heater classification are for heaters operating under optimum condi- tions— that is, with clean stacks and covers, tight-fitting covers, prop- erly set drafts, clean fuels, and quiet atmospheric conditions. These results, representing the minimum smoke outputs to be expected from these heaters, are lower than those normally found in the field, especially after 1 or 2 nights of heating. The smokiness of heaters is influenced by the following factors : 1. Burning rate. Curves of smokiness vs. burning rate included in the previously mentioned publications, and in figure 4 show definitely that most heaters when clean have a more or less fixed range of burning rates within which the smoke output is a minimum for that particular type of heater. Within this range the smokiness is not greatly affected by the 5 Schoonover, Warren R., and F. A. Brooks. The smokiness of oil-burning orchard heaters. California Agr. Exp. Sta. Bul. 536:1-67. 1932. 6 Schoonover, Warren R., F. A. Brooks, and H. B. Walker. Protection of orchards against frost. California Agr. Ext. Cir. 111:1-70. 1939. 8 University of California— Experiment Station burning rate, whereas at rates above this range, smokiness increases rap- idly with increase in burning rate. For some heaters this range is narrow, but for the better heaters it is relatively wide. The grower should deter- mine the range of burning rates over which his heaters will burn with the least smoke and should regulate his heaters accordingly. If the smoke 4 J 6 7 3V#MA/G ZATEj poy/?ds per foi/r Fig. 4. — Eelation of smokiness to burning rate for clean heaters (laboratory tests). output is to be kept within acceptable limits, the heaters must not be operated at excessive burning rates. Judging from curves of smokiness vs. burning rate for the stack-type heaters studied in the field tests (fig. 4), these heaters all have relatively low smoke outputs over fairly wide ranges of burning rates when they are clean. Curves are not shown for the Fugit and petroleum-coke heaters, since their smoke outputs are relatively low for all practical operating rates. 2. Soot accumulation. All oil-burning orchard heaters accumulate considerable soot while burning, some rather rapidly and others at a lower rate. Soot accumulations, particularly in the stacks, contribute directly to heater smokiness. For this reason, stacks and covers should Bul. 643] Operation of Orchard Heaters 9 be cleaned regularly. The frequency of these cleanings will depend upon the type of heater and the rate of burning. In general, high burning rates contribute to rapid soot accumulations, whereas lower rates of burning result in slower soot accumulations. The simple cylindrical stacks are readily cleaned by running a wire brush through them, but the stack should first be removed in order to avoid pushing the soot deposits into the bowl. Combustion chambers should be taken apart if this is necessary to secure thorough cleaning. While the stacks are off, one should clean the covers by reaching through the stack opening with a scoop or ladle (fig. 5) with which the soot may be scraped off, caught, and removed from the bowl. Downdraft tubes may need cleaning occasionally, particularly if filling of the heaters is done through some opening in the cover other than the one above the draft tube. Smokiness is increased if the slots in the downdraft tube become clogged with soot. 3. Air leakage around covers and regulators. In the handling of heat- ers between heating seasons, covers, regulators, and stacks are apt to become bent and otherwise damaged so that they do not fit tightly. It is much easier to keep the covers tight-fitting on round bowls than on square bowls; this feature is the chief disadvantage of the latter. Air leakage into the bowl increases soot accumulations and smokiness, be- sides making it difficult to control the burning rates accurately. Air leakage at the base of the stack, especially with lazy-flame heaters, causes a marked increased in smokiness. Careful handling of heaters, and the discarding or repairing of damaged bowls, covers, and stacks, help to overcome these problems. Heaters left in the field from season to season should give less trouble from this cause than those emptied and hauled out of the orchard every year. The more times a cover is removed, even though not damaged, the greater the tendency for air leakage. 4. Type of oil. Smokiness is not much affected by the usual variations in characteristics of clean oils that are within the range of fuels satisfac- tory for distilling-type heaters. To be satisfactory for use in orchard heaters,7 however, a fuel must have certain qualities. The amount of 7 Bowl- or distilling-type heaters use gas oil generally known as bunker-grade ma- rine Diesel fuel of 27+° A.P.I. (American Petroleum Institute) gravity. The refin- eries list this grade of oil as Pacific Standard 200, selected for low pour point. (For specification values of this grade of fuel see : Schoonover, Warren K., F. A. Brooks, and H. B. Walker. Protection of orchards against frost. California Agr. Ext. Cir. 111:47. 1939.) The fuel used in the bowl-type heaters during the field tests reported herein had a gravity of 31.3° A.P.I. , a 50 per cent distillation temperature of 508° Fahrenheit, and an open crucible self -burning residue of 1.8 per cent (higher than the recommended maximum). The fuel used in the Kittle and Fugit heaters was a kero-distillate of approximately 38° A.P.I, gravity. 10 University of California — Experiment Station residue formed in the bowls is affected somewhat by variations in fuel characteristics. For drip-type heaters the amount of coking in the fuel troughs is increased by the use of poor grades of heater oil. The operation of generator-type heaters is sensitive to oil characteristics. 5. Wind. Stack- type heaters are more smoky in a breeze than during Fig. 5. — Scraper and brush for cleaning covers and stacks. calm weather. Since this condition cannot be controlled by the grower, it need not be discussed further. Soot Accumulation in Lazy-Flame and Beturn-Stack-Gas Heaters. — Extensive observations and measurements of soot accumulation and smokiness, in relation to burning rate and total time interval since clean- ing of heaters, were made for the lazy-flame with standard regulator, lazy-flame with automatic regulator, and return-stack-gas heaters. In these tests the heaters were extinguished after every 3 to 4 hours of burn- ing. After each burning period of 3 to 4 hours a group of ten heaters was cleaned, the accumulations of soot being removed separately from Bul. 643] Operation of Orchard Heaters 11 the stacks and covers and measured. A different group was cleaned each time, so that each successive group had burned from 3 to 4 hours longer since cleaning than the previous group. In figure 6 the relation of the soot accumulations to the burning time is shown separately for stacks and for covers of the lazy-flame heaters. The lazy-flame heaters with automatic regulators were tested at two STACKS & 020 0.15 !"• c i/erage rate - S4 /£>s./nr. .- — " -x — x — *»* o _ — ■ 1 i - o /' •' X • ^ •— +re:*ZW/t/? ai/to/na//c rega/aters. .jf< '^-— ■— r — V mu o c//o/nat ic rejv/a/ors ai/erage rate -36 /6s./Ar ~ s l^ iserag e ra/e '-4-4 '6s./Ar Vj ozs k O.20 I ^ 0./5 6 0/0/2 /4 /6 /S 20 22 HOl/fiS BI//WED SWCE CLEAN/MO HEATEGS COVERS lri//te standard rayo/aters, aireraje rate - 6-4 /6s.//>r l/i//te ac//a/7?a//c rega/a/ors, average rate -44 /6s. /Ac n^ 6 /O /2 /4 /6 /S 20 22 //OVfiS BdfiNED SWCE CLEAN/N6 //EATEP5 Fig. 6. — Soot accumulation in lazy-flame heaters (ten heaters averaged for each point plotted). burning rates, and the heaters with the standard regulators were tested at one rate, this being higher than with the automatic regulators. In the stacks of the lazy-flame heaters with standard regulators, soot accumulated much more rapidly than when the same heaters were with automatic regulators (top of fig. 6) . For the two burning rates with the automatic regulators there was little difference in rate of soot accumula- tion during the first 10 hours, after which the higher burning rate re- sulted in more rapid accumulation of soot. If the stacks are not cleaned, soot accumulations build up to the maximum amount that will adhere to the stacks, after which the soot is carried away by the stack gases or falls into the bowls as fast as it is formed. After the heaters with standard regulators had burned for 15 to 18 hours, the stacks had accumulated the maximum amount of soot that would adhere to them. After 27 hours 12 University of California — Experiment Station of burning, the soot load in the stacks of the heaters with automatic regulators was still less than the maximum reached when the standard regulators were used. The covers of the lazy-flame heaters with standard regulators accumu- lated soot more rapidly than did covers with automatic regulators (bot- tom of fig. 6) . For the two burning rates at which heaters with automatic regulators were tested, there was little difference in the amounts or rates of soot accumulation on the covers. As with the stacks, there is a maxi- mum amount of soot that will cling to the covers. As additional soot is deposited, the flakes or streamers tend to break loose from the support- ing cover surface and fall into the oil, which keeps the total amount of soot on the covers about constant. After the heaters with standard regu- lators had burned for 12 to 15 hours, their covers could hold no addi- tional soot. Covers with automatic regulators accumulated about the same maximum amount of soot as those with standard regulators, but only after a much longer burning period (22 to 25 hours) . The heaters with standard regulators, operated at a higher burning rate than those with automatic regulators, might be expected to accumu- late soot somewhat more rapidly. Since, however, there was no great difference in this respect for the two burning rates used for heaters with automatic regulators, very little of the increased rate of soot accumula- tion for heaters equipped with standard regulators should be attributed to the higher burning rate. The fact that soot accumulations in the stacks and on the covers attain a maximum does not indicate that no more soot is being formed : the rate of formation is undoubtedly higher than dur- ing the early stages after cleaning. The additional soot formed either is carried away by the stack gases or falls into the oil and contributes to sludge residue in the bowls. For this reason stacks and covers should be cleaned frequently in order to avoid fuel contamination. Curves for soot accumulation in the return-stack-gas heaters are not shown ; but for the covers, the curve is practically the same as for the lazy-flame heaters with automatic regulators when burning at a rate of 3.6 pounds per hour. The average burning rate for the return-stack-gas heaters was 4.4 pounds per hour. In the stacks, the soot accumulation was much less than with the lazy-flame heaters. The amount of soot in the stacks increased rather uniformly to about 0.05 pound per heater after 16 hours of burning and then, with added burning, remained nearly constant. In the return-stack-gas heaters, only a thin, smooth layer of soot is deposited in the stack above the combustion chamber. Some fluffy carbon is formed in the throat and just below the bottom row of louvers. The return-stack-gas-heater construction may be modified so as to elimi- Bul. 643] Operation of Orchard Heaters 13 nate most of the soot accumulations on the cover ; but the resulting heater costs more, is more difficult to light, and has a narrower range of possible burning rates than the present heater. Effect of Soot Accumulation on Smokiness of Heaters. — During each series of soot measurements for lazy-flame heaters, smoke tests were made at regular intervals on ten heaters, which were cleaned only at the beginning of each series of tests. Figure 7 shows the apparatus used Fig. 7. — Smoke-measuring apparatus, showing heater in position to be tested. All products of combustion from the heater, as Avell as some outside air, are drawn through the apparatus by a centrifugal blower. The carbon, or soot, from a portion of the gases is collected on a white felt filter pad. The blackness of the felt, a measure of the smokiness of the heater, is determined by a photoelectric cell. for measuring smokiness. A comparison of the smokiness vs. time of operation since cleaned is included in figure 8 for these heaters with automatic regulators and with standard regulators. As figure 4 indi- cates, the smoke output of clean lazy-flame heaters at any given burning- rate is the same with either type of regulator. The difference indicated in figure 8, for the two types of regulators when the heaters were clean, would be expected, since the average rates were 5.4 and 4.4 pounds per hour for the standard regulators and the automatic regulators, respec- tively. A series of tests for the heaters with automatic regulators at an average rate of 3.6 pounds per hour (curve not included) showed about the same smoke output as at 4.4 pounds per hour, for the first 3 to 4 hours after cleaning. After 25 hours of burning, the smoke output was about 25 per cent less at the lower burning rate. 14 University of California — Experiment Station After the heaters with standard regulators had burned for a few hours, the average smoke output increased rapidly for a time ; but even- tually, after there was no further increase of soot adhering to the stacks, it became about constant. Apparently the amount of soot clinging to the cover has little effect on the smokiness of heaters. Each point on the curves of figure 8 represents the smokiness of one heater. As the heaters with standard regulators became dirty, the smoke outputs of individ- ual heaters became very erratic, with wide variations within the group tested. Some of the heaters flash back and puff or "blow up" when extin- »A r? IA////1 standard reya/ators. average rate -5-4 /6 s. //?r • « \ • • l • > • ^JU- /if ram S/ 7?oAe //, 17/i-} •, >y/^ •• • 9\ / • • t • I///M oi/comat/c • • 3 A rejfa/a/ors, average rale - 4- 4 /6s. /6r > ty»& •J • / — > A ~* *=* r * +■ V t b- 100 \ \i a 75 I 25 0 50 025 0 2 4 6 S /O /2 /4 /6 IS 20 22 24 26 MOMS Bl/M£D S//VC£ CL£AMW //£AT£/?S Fig. 8. — Smokiness of lazy-flame heaters as affected by time since cleaning. guished. In so doing, they partially clean the stacks, which reduces their smoke output. Also, when standard regulators are used there is much variation in burning rates, which causes differences in smokiness, par- ticularly for individual heaters burning at high rates. In direct contrast, the smokiness of heaters with automatic regulators increased slowly and at a nearly uniform rate ; it was still low after 25 to 30 hours of burning. The smoke outputs of individual heaters equipped with automatic regulators were relatively consistent and remained well within the smoke limit of 1 gram per minute. Whereas lazy-name heaters equipped with standard regulators had an average smoke output of 1 gram per minute after only 7 hours of burn- ing and 1.5 grams at 15 hours, the heaters with automatic regulators had less than 0.5 gram per minute after 28 hours of burning. The higher burning rate of the heaters with standard regulators accounts for some of the increase in smokiness as compared with the heaters having auto- Bul. 643] Operation of Orchard Heaters 15 matic regulators; but the difference in smokiness after 8 hours' burn- ing was much more than would be explained by the difference in burning rates. The superiority of automatic regulators over standard regulators on lazy-flame heaters, in regard to soot accumulation and smoke output, may result in part from the automatic control of the starting draft. More probably, however, it is due to improved design of the regulating device. The introduction of air through the smaller regulating holes, the reduc- tion of air leakage around the edges of the regulator, and the more uni- form burning rates obtainable with this regulating device are all factors which tend to reduce the soot accumulations and the corresponding smokiness. Since the return-stack-gas heaters burn relatively free of smoke under most conditions, smoke tests as a function of burning time since cleaning were considered less important for them. Three series of smoke measure- ments were made, however, on nine heaters, at 1, 16, and 25 hours after cleaning. The heaters were operated at different draft openings in order to get a range of burning rates as a basis for curves of smokiness vs. burn- ing rate (fig. 9) . Even heaters that had burned for 25 hours at nearly a gallon an hour (1 gallon = 7.25 pounds) were still well within the smoke limit of 1 gram per minute. At moderate burning rates ( y2 to % 0 gallon per hour) the smoke output of the return-stack-gas heaters does not in- crease very rapidly with time. The effect of soot accumulation on the smokiness of Jumbo Cone and Exchange stack heaters was not measured in these tests. Curves of smoki- ness vs. burning rate for these heaters when clean, and also after a burn- ing period of 20 hours, are included in Bulletin 536.8 These indicate that the smoke outputs are several times greater after 20 hours of burning than when the heaters are clean. Soot accumulations in the stack of the Kittle heater are small, and the smoke output does not change appreciably with time. Unless a high- grade fuel is used, however, coking (the formation of hard carbon de- posits) takes place in the circular fuel trough of the heater. Unless these deposits are scraped out regularly, the oil will overflow into the base pan and upon ignition will produce large quantities of smoke. Fugit heaters burn without appreciable smoke as long as the jets are clean and will continue to burn clean until the evaporating chamber fills with coke. Complete vaporization of the oil is then impossible. The petroleum-coke heaters involve no soot-accumulation problems 8 Schoonover, Warren E., and F. A. Brooks. The smokiness of oil-burning orchard heaters. California Agr. Exp. Sta. Bul. 536:30, 50. 1932. 16 University of California — Experiment Station and consequently no cleaning. Except for the starting period they burn without appreciable smoke regardless of how long they have been oper- ated. Economic Considerations of Smoke Reduction. — The reduction of smoke has little effect on the heating efficiency of heaters or none, and, /2 /.o ^ as i 0.6 04 J-$rr0/7? s/noAe //'/n/£ ~? I fso/newfot tv/rtcty tvfe/? tested) " / g 0.2 £3 4 5 6 7 S 3£//?MA/G 8/irE; />o£//?rfs per fot/r Fig. 9. — Eelation of smokiness to burning rate for return-stack-gas heaters at various times after cleaning (field tests). therefore, cannot be justified on the basis of savings in fuel costs. Since, however, the elimination of the smoke nuisance is essential, each grower must determine the most economical way to accomplish this result. Heaters of obsolete types that cannot be operated without excessive smoke should be replaced, but if a grower's heaters can, by careful man- agement, be kept reasonably free from smoke, he can hardly afford to discard them all immediately and buy new ones. Against the cost of new heaters, however, he must balance the added cost of the careful manage- ment required in keeping his old heaters within the smoke-tolerance limits. Bul. 643] Operation of Orchard Heaters 17 RESIDUE IN DISTILLING-TYPE HEATERS With the usual fuel oils burned in distilling-type heaters, a sludge resi- due will form in the bowls in amounts about proportional to the total oil burned; but the quantity depends somewhat upon the characteristics of the fuel. The sludge is made up of the heavier fractions of the oil, along with soot that forms in the bowls and stacks and then falls into the oil. The amount of residue is greatly increased if one allows the soot to fall into the bowls when cleaning stacks and covers. Since the residue de- creases the effective fuel capacity of the bowls, it should be disposed of from time to time. Residue in Lazy-Flame Heaters. — Twelve lazy-flame heaters with automatic regulators, which had burned for about 70 hours at an aver- age rate of 4 pounds per hour, were lighted and allowed to burn until they went out of their own accord. Near the end of the burning-out period, the drafts had to be wide open to keep the heaters burning. Eleven out of the group of twelve heaters burned dry ; but during the last 5 or 6 hours, the operation of the heaters was unsatisfactory, with much smoke, and large amounts of soot forming in the bowls and stacks. The residue remaining was only 1.5 per cent of the total oil burned ; but it was mostly fluffy soot, which nearly half filled the bowls and would have to be removed before the heaters were refilled with oil. Return- stack-gas stacks and covers, placed on twelve other lazy-flame bowls, burned the residue satisfactorily. No attempt was made to burn out the remaining lazy-flame heaters. Instead, the reclaimable oil was pumped out of the bowls, a filter screen being placed over the intake end of the pump hose. The residue left after pumping out amounted to about 7 per cent of the total oil burned in the lazy-flame heaters with automatic regulators as well as those with stand- ard regulators. This figure is higher than general field observations pre- viously reported,9 namely, 1 inch or more of sludge in the bowls for every 25 gallons of oil burned, probably because of the relatively high carbon content of the fuel used in these tests. Residue in Return-Stack-Gas Heaters. — After the return-stack-gas heaters had been burned from 45 to 70 hours, they were lighted and allowed to burn until they went out. The draft openings were set at one-third hole (about % gallon per hour burning rate) when lighted and were opened up to one hole during the last part of the burning period to counteract the normal falling off of the burning rate caused by 9 Schoonover, Warren E., F. A. Brooks, and H. B. Walker. Protection of orchards against frost. California Agr. Ext. Cir. 111:67. 1939. 18 University of California — Experiment Station lower fuel levels. During this burning-out period the heaters did not smoke visibly, and there was no excessive formation of soot. When the heaters had burned out, the residue remaining was observed and measured. Twenty-eight heaters that had previously burned from 45 to 60 hours at rates of 5% to 6 pounds per hour burned completely dry, with only hard flaky carbon left in the bottoms of the bowls. Of thirty other heaters that had burned 70 hours at rates of 4% to 6 pounds per hour, about one third failed to burn dry. The cause may have been due partly to water in the bowls. In all the heaters that did burn dry, the carbon residue amounted to only about 0.5 per cent of the total oil burned. The bottoms of the bowls showed no appreciable damage from being burned dry, probably because exces- sive burning rates were not required. Disposal of Residue.— The disposal of the sludge residue formed in bowl-type heaters is a problem. With the return-stack-gas heat- ers it is practical to get rid of the residue by burning the heaters dry, because burning rates that might damage the bowls are not required. Some of the other distilling types can be burned dry; but this procedure usually requires opening the drafts to obtain high burning rates, and the result is exces- sive smoke and soot formation and damage to bowls. The residue may be hauled from the orchard and dumped in a dry wash or other suitable place, or burned at some central location. Another method of disposal would be to accumulate the residue in barrels distributed throughout the orchard and later to burn it in spe- cially constructed heaters during regular heating periods. Heaters which will burn most residues satisfactorily may be built from ordinary heater parts. The principles involved in such a heater are : (1) introduction of air into the bowl at several places so that the flame is not all concentrated at one spot; (2) introduction of this air in the form of jets directed against the surface of the contaminated oil; (3) creation of additional Fig. 10. — Heater for burning sludge residue. Bul. 643] Operation of Orchard Heaters 19 draft by using a relatively tall stack above a louvered combustion- cham- ber section. Such a heater was constructed and tested in the laboratory, using a 6-inch Exchange stack with about 6 feet of straight stack above the louvered section (fig. 10) . A round bowl and an ordinary cover equipped with standard regulator and downdraft tube were used. Holes were drilled in the cover and 7 jets were installed. Six of these were spaced at equal intervals around the bowl cover (that is, 60 degrees apart) and 2 inches from the outside edge. The seventh jet was placed between the draft regulator and the stack collar, 1 inch out from the latter (fig. 11) . In the original design, tapered jets were used, but subsequent tests hidi- ng. 11. — The inside of the bowl cover of the residue burner, with the pipe jets and down- draft tube in place. cated that short lengths of %-inch iron pipe could be substituted for the tapered jets, which simplifies the construction. A 3-inch length of pipe was used for the center jet, and 2-inch lengths were used for the outside jets. By threading one end of each length of pipe and drilling clean %-inch holes in the cover, the pipe jets could be screwed into the holes in the cover (from the underside), the sharp edge of the sheet metal serving as a single thread for the pipe. If clean holes are not obtained, or if the pipe jets should become loose-fitting, lock nuts may be used to fasten the jets to the cover. If properly regulated, this heater will burn residue without excessive smoke, although the burning rate is higher than normal (1 to 1% gallons per hour). If the burning rate is much below 1 gallon per hour, the heater does not "louver" properly, and may not burn dry. Rates in excess of IV2 gallons per hour cause objectionable smoke and result in high stack temperatures with rapid deterioration, particularly of the lou- 20 University of California — Experiment Station vered portion. These heaters should be located where they may be readily observed, since occasional regulation is necessary to keep them burning properly. Normal operation is with the draft regulator completely closed and all jets open, although the regulation depends upon the quality of the residue and the fuel level in the bowl. The draft may be decreased from the normal amount by plugging one or more of the outside jets with metal plugs such as %-inch machine bolts, and it may be increased by opening the draft regulator. Since the primary purpose of these heaters is the disposal of residue, they should be burned dry each time they are lighted. The residue burn- ers would consume approximately twice as much fuel as the ordinary heaters since they burn at a higher rate and should burn dry each time. Hence, although the amount of residue produced by ordinary bowl-type heaters is from 5 to 10 per cent of the total quantity of fuel oil burned, the number of residue burners need not be greater than 3 to 5 per cent of the total number of heaters operated. OPERATION OF OIL-BURNING HEATERS Lazy-Flame. — Lazy-flame heaters are harder to light than many of the other types because the flame tends to lift from the top of the stack and not keep the stack vapors ignited. Heaters with automatic regulators are a little better in this respect than those with standard regulators, be- cause the starting draft is less strong. In lighting heaters equipped with automatic regulators, the follow-up man is eliminated, so that one third to one half of the usual lighting labor is saved. These regulators are so constructed as to close 2 to 3 minutes after lighting. Ordinarily, very little trouble was experienced with regulators' failing to close auto- matically, except on one occasion, when the heaters were only about half full of oil when lighted. Under the latter conditions about 10 per cent failed to close automatically, and the thermostats never did get hot enough to allow closing by hand. Since, however, heaters are normally kept filled, this condition should not occur under good management. As previously mentioned, the regulating device of the automatic regu- lator surpasses the ordinary type ; there is less air leakage around the edges of the regulator plate, and the draft holes are smaller, which per- mits more accurate adjustment and more uniform burning rates. With the automatic regulators the rates of individual heaters for any one night varied only about 15 per cent from the average, as compared with variations up to 50 per cent when the standard regulators were used. The automatic regulators give a maximum rate of % to % gallon per hour when open the full three holes, though provision is made for raising the Bul. 643] Operation of Orchard Heaters 21 regulator plate slightly to give higher rates for emergencies. This value of % gallon per hour is the recommended maximum burning rate for these heaters regardless of the type of regulator used. When equipped with standard regulators, the lazy-flame heaters tend to flash back and blow off the stack caps and occasionally the bowl covers after they have supposedly been extinguished. With the automatic regu- lator, the cap over the regulator parts fits tightly, so that lazy-flame heaters with tight bowl covers may be extinguished without closing the stack caps and without the usual tendency to flash back. Closing the stack caps, even for the heaters with automatic regulators, results in occa- sional flashing back. Lazy-flame heaters of the type included in these tests are relatively low-priced, and will burn without excessive smoke if operated properly. They are easy to clean, but need cleaning frequently, particularly when equipped with standard regulators. To keep such heaters within the smoke-tolerance limits one must clean them after every 8 to 10 hours of burning. With automatic regulators, the heaters may be operated 20 to 25 hours without cleaning. Since the automatic regulators were new at the beginning of the one season during which they were used, field observation did not include information on their life or on the functioning of the automatic starting- draft control after they had been used for several years. The superiority of the draft-regulating device over the standard regulator will not di- minish because of depreciation, irrespective of whether or not the auto- matic starting-draft control continues to function satisfactorily. Return-Stack Gas. — These heaters (fig. 3, B) are easy to light; but when they are equipped with standard regulators, the stack caps must fit snugly. Otherwise, they are likely to be blown off by flashing back after the heaters have supposedly been extinguished. The return-stack- gas heaters should be regulated as soon as possible after lighting (1 to 3 minutes is preferable) ; otherwise the stacks get extremely hot, and there is excessive smoke. Unlike other bowl types, the return-stack-gas heaters have a minimum rate at which they burn when the draft is entirely closed. With standard regulators, which have some air leakage when closed, the minimum rate is slightly above % gallon per hour. Because of the larger number of parts, the handling and assembly of these heaters in the field is more difficult than for many bowl-type heat- ers. In the field tests of the experimental heaters some trouble was had with the inside elbows' falling off into the bowl during operation. In com- mercial design it is proposed to fasten the inside elbow to the stack, which would eliminate this trouble and also facilitate assembly and handling. 22 University of California — Experiment Station Two of the return-stack-gas heaters were equipped with automatic regulators of the type used on the lazy-flame heaters but set to close more quickly — that is, about 1 minute after lighting. The automatic control of the starting draft, by reducing the initial draft rate, reduced the smoke output during the starting period and kept the stacks at lower temperatures. Soot tended to collect on the thermostat box and, unless scraped off before lighting, acted as an insulator and thus delayed the action of the thermostat in terminating the starting period. The tight cap used over the parts of the automatic regulator eliminates flashing back after the heaters are extinguished and reduces the minimum burn- ing rate to about 4/10 gallon per hour. As with the lazy-flame heaters, the improved regulating device allows more accurate control of burning rates. The effects of using automatic regulators on other combustion- chamber-type heaters with tight bowl covers would probably be similar to those described above. The return-stack-gas heater, if produced commercially, would be in a price range with the Jumbo Cone heater. The rate of depreciation would be less than for the Jumbo Cone but greater than for lazy-flame types. The experimental heaters were built with stacks and combustion cham- bers of 24-gauge galvanized iron, and two 28-gauge galvanized-iron el- bows were used on the recirculating system of each heater. The stacks and combustion chambers of heaters that had burned for 60 to 70 hours at rates from % to % gallon per hour showed very little depreciation. The combustion chambers and lower 6 inches of the stacks of heaters operated at higher burning rates were oxidized to some extent, but were still in good condition. The use of galvanized-iron elbows inside the stacks is unsatisfactory because of their relatively short life, especially at high burning rates. The galvanized-iron outside elbows were in good condition after 60 to 70 hours of operation, but the inside elbows should be made of some heat-resistant material such as cast iron or chromium steel. One of the most important features of the return-stack-gas heater, as compared with other bowl-type heaters, is its ability to burn the ordi- nary 27+ heater oil with little smoke over a relatively wide range of burning rates (fig. 4). In general practice the return-stack-gas heaters should be burned at rates below %0 gallon per hour. Rates of 1 gallon per hour may be obtained without excessive smoke ; but at these higher rates soot accumulates on the covers more rapidly, and the depreciation of the stacks is higher. Although these heaters will burn for long periods without becoming smoky, the covers and throats of the stacks should be cleaned regularly — that is, after 25 to 30 hours of burning — to keep soot Bul. 643] Operation op Orchard Heaters 23 from contaminating the oil. It would seem good practice to burn such heaters dry after every 50 to 75 hours of use, to avoid accumulations of undesirable residue in the bowls. Jumbo Cone. — Jumbo Cone heaters (fig. 12, A) are easy to light, but difficult to keep regulated. The draft setting is sensitive, and the burn- ing rates keep changing after the draft controls have been set, so that frequent regulation is required. As with the return-stack-gas heaters, Fig. 12. — A, Jumbo Cone heater; B, 7-inch Exchange model ; C, Kittle with float regulator, for use with pipe-line system. the Jumbo Cones should be regulated as soon as possible after lighting. This is generally true for all combustion-chamber or hot-stack-type heaters. The Jumbo Cone does not burn satisfactorily at rates much below y% gallon per hour. From the smoke-output standpoint it is, if cleaned frequently, reasonably satisfactory over a fairly wide range of burning rates. The burning rate must not be allowed to exceed the ca- pacity of the combustion chamber, or excessive smoke will result. This limit is about 1 gallon per hour. Cleaning is more difficult than for heaters with straight stacks, because the combustion chamber must be taken apart for thorough cleaning. Exchange Model, 7-inch Stack. — The performance of the 7-inch Ex- 24 University of California — Experiment Station change stacks (fig. 12, B) is more erratic than for stacks with conical combustion chambers such as the Jumbo Cone. Otherwise, most of the discussion for the Jumbo Cone heater applies to this heater. Like the Jumbo Cone, the Exchange stack, if cleaned frequently, has a fairly wide range of satisfactory burning rates; but it is easier to clean. The Ex- change stacks deteriorate rapidly, especially at the higher burning rates. Kittle. — As long as the fuel trough of the Kittle heater (fig. 12, C) is kept level and free from coke, the heater operates satisfactorily at burning rates below % gallon per hour. If the rate is above this limit, the oil is likely to over- flow the trough and spill into the base pan, where it eventually ignites and pro- duces much smoke. Unless a good grade of fuel is used, the trough soon fills with carbon, and overflowing is likely to occur at rates lower than % gallon per hour. This carbon residue must be scraped from the trough at intervals depending on the rate of burning and quality of fuel. With these heaters there is no problem of accu- mulation of sludge residue or contamina- tion of the fuel supply with heavy ends (pour-back oil). Kittle heaters are among the easiest to light ; and since they are ex- tinguished simply by shutting off of the fuel supply, no flashing back oc- curs. When they are used in a pipe-line system, it is hard to find a satisfactory method of regulating the oil flow to the heaters. Ordinary needle valves are unsatisfactory : they are rather sensitive and tend to clog. The float-valve regulating devices used in these field studies gave trouble because of sticking of floats, dirt in the float valves, and other difficulties that would cause the float chambers to overflow on the ground. This fuel upon ignition would often generate enough heat to melt the solder in the joints of the chamber, and thus ruin the device. The Kittle heater, when used with an individual oil container comparable in size with the bowl of a distilling-type heater is equipped with a satisfactory regulating device. Fugit. — The outstanding advantages of the Fugit heater (fig. 13) are low smoke output, elimination of the task of hauling oil and filling indi- vidual heaters, and the absence of pour-back problems. These heaters do not, however, operate satisfactorily with burning rates much below 1 Fig. 13.— Fugit heater (1937 model) with generator parts shown below. (From Ext. Cir. 111.) Bul. 643] Operation of Orchard Heaters 25 gallon per hour, which is higher than should be used for the best utiliza- tion of heat in the orchard. They tend to waste fuel, especially on nights that are only moderately cold. The cost of installation per heater being higher, there is a tendency to install too few per acre and to burn them at relatively high rates, which results in an uneven distribution of heat in the orchard. Generating heaters require a comparatively high grade of orchard- heating fuel (kero-distillate) . Even then there is trouble because the jets may plug with carbon and because the evaporating chambers eventually coke so badly on the inside that they must be discarded. The needle valves for regulating burning rates tend to plug with dirt and scale from the pipe lines and with other foreign matter unless a good filter — for exam- ple, one of lamb's wool — is installed ahead of each valve. Even with these precautions one must check the heaters often, during the night, to maintain a uniform burning rate. To keep pipe lines full and to have oil immediately available at each heater when lighting, one should extinguish the Fugits by closing the valve at each heater. If the heaters are extinguished by closing only the main valve for the system or for a lateral, the oil in the pipe lines will slowly drain to the low heaters and overflow on the ground. COKE HEATERS In the past, less than 10 per cent of the orchard heating has been done with heaters burning petroleum coke, coke briquettes, or other solid fuels, largely because of the unavailability and the high cost of these fuels as compared with oil. In 1939, however, petroleum coke (a by- product of oil refining) was made available in quantities ample for orchard-heating needs, at a price ($4.50 a ton, in bulk, at the refinery) comparable with that paid for ordinary heater oil. Since this makes the use of coke for heating orchards more practical from the cost standpoint, the operation of coke heaters was extensively studied at Riverside dur- ing the winter of 1939-40. A total of about 20 tons of petroleum coke (size 1 to 4 inches) was burned during field tests of the experimental heaters. Most of the solid-fuel heaters on the market have burning rates rang- ing from 2 to 5 pounds per hour, which is equivalent in heat output to only %0 to % gallon of fuel oil per hour. The experimental heaters tested (fig. 3, A) were built of a larger size to provide a heat output comparable with that of an oil heater burning at a normal rate ( % to % gallon per hour) . In the field these heaters were filled to the lower row of holes with earth to protect the sheet-metal bottom from heat. 26 University of California — Experiment Station Lighting and Burning-Bate Characteristics. — One objection to solid- fuel heaters, often advanced by growers, is that they are hard to light and slow in getting started. The usual method of starting is to add oil- soaked wood kindling at the top of the heater, though other kindling materials are sometimes used. Then the heaters are lighted by pouring burning torch fuel on top of this kindling. A mixture containing 50 per cent heater oil or crankcase drainings and 50 per cent gasoline is a better torch fuel for coke heaters than is the customary mixture of kerosene and gasoline. According to tests conducted by one of the commercial oil companies the optimum amount of oil-soaked wood kindling is from 1% to 2 pounds per heater. If the kindling has been in the heaters for a con- siderable length of time, a small amount of oil should be poured over it before lighting. The dotted curve of burning rate vs. time, shown in figure 14, is char- acteristic for the experimental coke heaters when started with oil-soaked wood ; and it bears out the growers' criticism that coke heaters are slow in coming up to their normal burning rate. The rate is fairly high during the first 15 minutes, while the kindling is burning; but then it drops, and upwards of an hour is required for the heater to come up to its nor- mal burning rate. To remedy this fault, various lighting methods were studied. By pour- ing ordinary 27+ heater oil over the coke before lighting (using no other kindling material), one can control the initial burning rates by the amount of oil added. Also, if desirable, one can add this oil several days before lighting, with good results. The solid curve in figure 14 shows a typical burning-rate curve when 1.5 quarts of oil was added to about 40 pounds of coke 20 hours before the heaters were actually lighted. The burning rate starts at a fairly high value, drops only to about 7 pounds per hour, slowly rises to a peak of about 8 pounds per hour, and then gradually drops off as the supply of coke becomes exhausted. For 40 pounds of coke the burning rate remains between 7 and 8 pounds per hour for about 4 hours — a rate equivalent to burning about % gallon of orchard-heater oil per hour. Except for the starting period of an hour or less, all the burning-rate curves for coke heaters started with oil have about the same shape with respect to the 8-pound peak, regardless of the amount of oil used or the initial amount of coke. For smaller amounts of coke, the peak and subse- quent falling off of the rate occur sooner after lighting; but the peak value is about the same for different amounts of coke, provided the heat- ers are not filled above the top row of holes. The amount of coke in the heater has little effect on the amount of starting oil required. The use Bul. 643] Operation of Orchard Heaters 27 of 1.5 quarts per heater gives the most nearly uniform burning rate. One may increase the initial burning rate to as much as 12 to 14 pounds per hour by using 1.8 quarts of oil, whereas if only 1.3 quarts are used the initial rates will be a little less than that shown by the solid curve in figure 14. The heaters can be lighted as much as a week after adding the starting oil, but the lighting is then more difficult and less certain. If the starting oil has for some reason been added one or two weeks before lighting of the heaters, 0.5 quart more oil per heater should be added just before ! fcT 38 /6s. coke j ml/? /£