HARRISON AND GERBER: PROPANE FUELED HEATERS 41 PROPANE FUELED HEATERS FOR COLD PROTECTION. -tt 6 Q <> 0 <

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1 HARRISON AND GERBER: PROPANE FUELED HEATERS 41 PROPANE FUELED HEATERS FOR COLD PROTECTION D. S. Harrison and J. F. Gerber1 Introduction During the past five years a number of pro pane fueled cold protection systems, involving open-flame heaters, have been installed in citrus groves in Florida. Adantages claimed for such systems are that they can be installed permantly and the same distribution lines can be used for a permanent irrigation system (Fig. 1 and 2), thus reducing labor costs for both heating and irrigation. Due to the fact that very little published in formation has been obtained on protection from open-flame propane systems, a field study of an existing system appeared useful. Materials and Methods The groves and heating system used in the study are owned by Mr. Frank Mirth of SaralAssociate Agricultural Engineer, Florida Agricultural Extension Service, and Associate Climatologist, Fruit Crops Department, Agricultural Experiment Station, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, respectively. sota, Florida. Through his cooperation these tests were made possible. A 9-acre portion of the heated grove (Fig. 2) located on the east side of the road was instrumented and compared to a 9-acre non-heated grove on the west side of the road. Both groves were of the same age and cultural practices, rootstock and scion were similar. The location of the grove is southeast of Dade City. The owner reported that cost per-acre for the completed system was $1, of which $ was for heating system and $ for the irrigation phase (Table 1). 'Valencia' orange trees in the grove were planted on a 25 ft. x 25 ft. spacing. The trees were severely damaged by the 192 freeze; how ever, they recovered well and were feet tall at the time of the experiment. The trees yielded about 10 boxes per tree prior to the freeze. Tests of the heating system were conducted during 195 and 19 using the check and test groves (Fig. 2). Temperatures, ambient and leaf, were measured with a thermistor temper ature indicator, long lead wires and a junction STORAGE VAPORIZER DISTRIBUTION A -tt Q <> LINES A GAS PLANT HEATER^ 0 < o O- BURNERS Fig. I Block Diagram of Propane Gas Heater System Dade City, Florida

2 42 FLORIDA STATE HORTICULTURAL SOCIETY, 19 I3OO1- NON-HEA- GROV POLE -.ACRES 900*.^ftSS^f^^w^^w^w+f*, res 900* LR-- GAS Sfij I 0 PROBE LOCATION LEAF + «AIR TEMPERATURE LOCATION 1st DIGIT' 51 ABOVE GROUNO, S. SIDE» SINGLE HEATER [SCALE 2nd DIGIT-TOP 1/3 CANOPY OF TREE "\«TRIPLE HEATER Fig. 2 Diagram of Mirth Grove Heater and Installation f box. All the temperature measurements could be obtained rapidly with a minimum of dis turbance in the grove. Rapid sampling was im portant to avoid time produced errors due to changing meteorological conditions. Leaf tem peratures were measured with thermistors at tached to masking tape to the top surface of semi-exposed leaves located at heights of 5 and 15 feet on the side of the tree opposite to the heater. This measurement indicated average response rather than that directly in the heated plume of the flame of the heater. Air temperatures were measured at heights of 5, 20, 35, and 50 feet on inversion towers (Fig. 2). Wind velocity was measured atop a thirty foot pole (Fig. 2). At room temperature propone gas stored un der pressure will be a mixture of liquid and gaseous vapor. The ratio of liquid to vapor de pends mostly upon the amount of propane in the tank. When gas is withdrawn more liquid vaporizes which requires heat. Most of the heat comes from the liquid propane; consequently, its temperature falls. If large amounts of gas are withdrawn the temperature drops rapidly, the pressure falls and the liquid propane freezes. When this happens there will be essentially no more gas available to the distribution system. To avoid this a vaporized can be used. Vapor izers either heat the storage tank directly or liquid propane may be withdrawn and then vaporized. This is an essential feature of all propane cold protection systems and without it they will not work. The heating system used contained all the components shown in the block diagram (Fig. 1), which were required for the heating system to function adequately, especially at low ambi-

3 HARRISON AND GERBER: PROPANE FUELED HEATERS 43 Table 1. Owners stated per-acre cost of a 1+0-acre propane gas grove heating and irrigation system.* Per Acre 1. Storage tank & regulators, vaporizer, globe valves and security fence 2. Main line " transmission, 188 steel wall wrapped and stringing and welding 3. PVC lateral lines, schedule 10 pipe, plus concrete riser supports and concrete regulator boxes & burners k. Trenching and laying of distribution lines 5. Line regulators and globe valves and gauges Propane gas heating system, per-acre cost $ * W* Irrigation phase: 55* 10" well 70 H.P. propane gas industrial engine and 10" turbine pump and pump house, together with sprinkler heads. Average per-acre cost Total system cost 385.OO $1, *based on 193 installation costs. ent temperatures. An 18,000 gallon propane storage tank, and a vaporizer which heated the tank directly was used. Approximately one gal lon of propane was burned by the vaporizer for every 3 gallons burned by the heaters during the coldest night. The distribution system was PVC (polyvinyl chloride) class 10, type I, plas tic pipe with a pressure regulating valve serv ing each three laterals. Pipe sizing was such that an irrigatin rate of 0.15 inch per hour was obtained with the same system. All pipes are buried 18 inches deep. The burners were no. 57 open-flame burners mounted on a concrete post located one each under the canopy on the north side of each tree. On the north and northwest borders of the grove there were three burners under each tree. When the burners were in oper ation they had a yellow to blue flame. The yellow flames were due to dirt and carbon entrainment. A clean propane flame is almost colorless or faint blue. The operating pressure of the system was varible, but psi was the normal operating pressure. At this pressure the burner output was 50,000 Btu per hour per burner or 3,500,000 Btu per acre-hour, at 12 psi the output was about 72,000 Btu per hour burner or 5,000,000 Btu per acre-hour. The total fuel required per acre-hour for vaporization and heating at psi was between 55 and 0 gallons per acre-hour. Lighting was done 3 laterals at a time. Some gas accumulated around the burners prior to ignition, but not enough to constitute a hazard. Approximately 0.2 man hours per-acre were re quired for lighting. Results and Discussion Field tests were made during the and 195- seasons. Because of the nature of the season and instrumentation difficulties little reliable data were obtained in the first season. One difficulty was the improper placement of temperature sensors which gave biased results. However, data from 3 nights have been obtained which were reliable data (Table 2). One night occurred in February 195 and the other 2 in January 19. The test in February 195 was conducted on a night with fairly high tempera tures, but with a strong wind. Since wind is a critical factor in determining the effectiveness of any system the results obtained this night were very important. Other cold windy nights occurred during the tests, but the direction was from the heated area into the check area which ruined the results. Periods during individual nights were selected rather than whole nights

4 44 FLORIDA STATE HORTICULTURAL SOCIETY, 19 Table 2. Protection obtained with a propane system Protection ' UF Date Temp. (leaf) Protection 5' 15' Wind mph psi Jan 28, 19 it Feb 25, 195 n it Jan 30, * * Very gusty because meteorological conditions changed. The data shown are not nearly all those collected, but are typical. While these data are too few to be conclusive they are believed to be indica tive of what can be expected. The results obtained suggest a relation be tween wind speed and protection such as shown in Fig. 3. On calm or nearly calm nights 3 to 5 F of protection were obtained. As the wind speed increased the protection decreased, es pecially at 15 feet. This was expected to occur, and is common to almost all heating systems. About 2 of protection was observed at 5 feet even under windy conditions. It was not obvi ous why more protection was observed at 5 feet with winds of around mph than with 5 mph. Perhaps at higher wind speeds the heated plume from the burner was sheared by the wind at lower levels and throughly mixed. Thus, the heat may have been diluted less at u. 7 o Z O No. 57 Burner PROPANE 3,300,000 BTU/ACRE HOUR 5.0 u 10.0 IS.0 WIND (m.p.h) Fig.3 Protection as Related to Wind Speed for Propane System

5 GERBER: SOLID FUELED HEATERS 45 5 feet than under more calm conditions. In any event, very little protection was obtained at 15 feet with mph of wind. The heaters used were basically a convective type. They were not designed to produce radi ant heat. Experience with oil fired stack heaters has shown that more protection will be obtained on windy night from heaters which produce radi ant heat than from heaters which produce most ly convective heat. The protection obtained under calm condi tions compares very favorable with protection from other devices with about the same heat output per-acre-per hour. Increasing the heat output, by increasing the pressure increased the protection, but only slightly. The system pro vided more protection at 15 feet on calm nights than at 5 feet. Labor requirements were cer tainly less than with most any other system; however, skilled labor was required for opera tion of the vaporizer. Vaporizer operation must be carefully supervised. Even with the careful supervision during these trials, there was at least one occasion when the gas pressure in the tank dropped and heat output and protection also dropped. Adequate vaporizer performance can hardly be overemphasized. Summary A propane heating system was field tested for 2 seasons. Aside from vaporizer supervision it appeared to oprate adequately and few prob lems were encountered. Protection varied from 3 to 5 on calm nights to 0.5 to 2 on windy nights. This compared favorably with other convective heaters. Acknowledgements The authors wish to express their gratitude to Mr. Frank Mirth, and Mr. Fred Hutchinson, whose cooperation and contributions made these trials possible. SOLID FUELED GROVE HEATERS1 J. F. GERBER2 Wood, coke, used rubber tires and charcoal have been used as solid fuels for grove heating and cold protection, and they were probably the oldest fuels used (8, 5). Coke and charcoal usually were used as fuels in heaters or open trays, but wood and rubber tires were burned in open fires (2). Wood as a fuel for cold pro tection had many desirable qualities. It was easily stored, easily lit, had a reasonably high heating value, was locally available and modest ly priced (8). Coke and charcoal had higher heating values than wood and burned longer with less attention, but a heater was required, and it was difficult to light and refuel the heat ers. Rubber tires created still new problems; they trapped rain water in the summer which served as a breeding ground for mosquitoes; they produced a heavy, noxious pall of smoke when burned and they left a residue of wire from the tire bead in the grove which was a nuisance. lflorida Agricultural Experiment Stations Journal Ser ies No Associate Climatologist, University of Florida, Depart ment of Fruit Crops, Gainesville, Florida Most growers who were faced with an an nual cold protection problem switched to oil fueled grove heaters for cold protection (1). These devices have given very good results in most instances, but they require a capital ex penditure of from $350 to $450 per acre for adequate protection. Moreover, labor require ments to light and refuel the heaters are greater than can be supplied from the normal grove crews so that an additional heating crew is re quired. Following the disastrous freeze in the Lower Rio Grande Valley in Texas in 192 (3), several of the major oil companies reached the decision to attempt to design grove heaters which would burn solid fuels in a burnable container or in a very low cost container. The objectives of the design were to reduce or eliminate the capital cost, eliminate special fuel storage facilities and in most cases provide cold protection by placing the heater under the canopy. Most of these de vices were manufactured and tested first in the Rio Grande Valley in Texas (9, ). The idea was fairly prevalent in the Texas citrus region that cold protection could only be