US3196925A

US3196925A - Two-temperature fuel oil burner supply systems

Info

Publication number: US3196925A
Application number: US341935A
Authority: US
Inventors: William J Trabilcy
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-02-03
Filing date: 1964-02-03
Publication date: 1965-07-27
Anticipated expiration: 1982-07-27

Description

TWO-TEMPERATURE FUEL OIL BURNER SUPPLY SYSTEMS Filed Feb. 3, 1964 July 27, 1965 w. J. TRABILCY 2 Sheets-Sheet 1 WILL/AM J. TRAB/LCY BY MMQ M ATTORNEYS July 27, 1965 w. J. TRABILCY 3,196,925

TWO-TEMPERATURE FUEL OIL BURNER SUPPLY SYSTEMS Filed Feb. 3, 1964 2 Sheets-Sheet 2 o 8 -IO T m a g) E INVENTOR FIG. 4

W/LL/AM J. TRAB/LCY WQMQM ATTORNEYS United States Patent 3,196,925 TWll-TEh HPERATURE FUEL OIL BURNER SUFPLY SYSTEMS William J. Trabiley, 280 Prospect Ave, Hackensack, NJ. Filed Feb. 3, 1964, Ser. No. 341,935 14 tClaims. (Cl. 158-36) The present invention relates to fuel oil burner supply systems and is particularly concerned with systems for handling the temperature-controlled delivery of preheated viscous fuel oils, such as No. 6 grade, to oil burning equipment.

The change over the past ten years to refinement of crude petroleum by catalytic cracking processes has had a significant effect on the operation of fuel oil burner supply systems which handle high viscosity oils such as No. 6' grade fuel oil sometimes called Bunker C. In these burner supply systems the fuel oil is stored in a tank which is usually underground, and the stored oil is drawn from the tank by pumps which supply the fuel under pressure through preheating units for delivery to the burner equipment. The preheating units heat the fuel to the desired burning temperature for obtaining efficient and complete combustion. The amount of fuel oil delivered by the pumps and heated by the preheating units normally is about double the maximum burning rate of the burner equipment in the system so that there is always a predetermined amount of excess hot oil heated to the burning temperature.

Conventionally, this heated excess oil is returned to the storage tank in close proximity to the inlet end of the pump suction line in the tank to mix with the cold viscous tank oil and bring it to a flowable and pumpable temperature which is approximately 120 F. 'A typical system of this type is described in United States Letters Patent No. 2,802,520, issued August 13, 1957, to William I. Trabilcy and entitled Transportation System for Viscous Liquids.

As a result of the presently used catalytic refining processes, it is necessary to heat the fuel oil to considerably higher temperatures than ever before in order to assure satisfactory and substantially complete combustion. Thus, the temperature of excess unburned hot oil being returned to the storage tank to render the cold tank oil fiowable and pumpable is higher and thus heats the cold stored oil to a higher temperature. A conventional system is adjusted to operate satisfactorily under these conditions when the burning equipment is being fired at its maximum rates. However, serious operational difiiculties are encountered with multiple burners particularly when there is a reduction in the burning rate or when one or more of the burners being supplied is shut down. When this happens, more hot oil is returned to the storage tank to further increase the temperature of the mixed suction oil. This condition of over-heated suction oil temperatures at the relatively low pump suction pressure objectionably promotes vaporization of the suction line oil with the result that oil flow is interrupted, and burner failure ensuingly occurs. Such burner failures are especially dangerous since they frequently result in explosion or burner puff-back.

Owing to the present refinement practices, objectionable overheating of the fuel oil pump suction due to variations in load conditions has become so prevalent in the conventional supply systems that it has prompted the relocation of the hot oil return outlet to a region in the storage tank considerably remote from the suction line inlet. While this change permits the objectionable heat of the hot return oil to be dissipated, it is, at the same time, a waste of energy and usually requires that additional heating means, such as, for example, a steam heating coil, be placed in the tank to bring the cold stored oil up to a pumpable temperature.

The present invention contemplates and has as its major object a novel fuel oil temperature control system which prevents overheating of the suction line oil regardless of load conditions and without deliberate dissipation or loss of heat.

More specifically, it is an object of the present invention to provide a novel oil temperature control system wherein the flow of the preheated unburned oil returned to the storage tank is thermostatically controlled in response to the oil temperature at the pump suction or discharge to prevent the oil drawn from the tank from being objectionably overheated. Thisis essentially accomplished, in accordance with the present invention, by placing a thermostatically controlled valve in a hot fuel oil return line and passing at least substantially all of the unburned preheated pump discharge oil through the valve so that the rate of return oil flow is regulated thereby.

A further object of the present invention is to provide a novel two-temperature viscous fuel oil burner preheating system which is especially adapted to handle No. 6 grade fuel oil without objectionably overheating the suction line oil.

Still a further object of the present invention is to provide a novel two-temperature viscous fuel oil burner supply system wherein the cold stored fuel is heated to burning temperature in two stages and'wherein only a sufiicient amount of oil is heated to burning temperature in the second stage to equal the burning rate and to heat cold stored oil to a controlled pumpable temperature.

Further objects will appear as the description proceeds in connection with the appended claims and annexed drawings wherein:

FIGURE 1 is a partially diagrammatic view illustrating one embodiment of the two-temperature preheating system of the invention;

FIGURE 2 is a diagrammatic view of piping details at the fuel oil burners being supplied with the system shown in FIGURE 1;

FIGURE 3 is a fragmentary diagrammatic view of another embodiment of the present invention;

FIGURE 4 is a partially diagrammatic view of still another embodiment of this invention; and

FIGURE 5 is an enlarged fragmentary longitudinal section of the three-way thermostatically controlled valve illustrated in FIGURE 4.

In the embodiment of the invention shown in FIGURE 1, fuel oil is withdrawn from a storage tank 11 and supplied to one or more oil burner assemblies of which there are two indicated at 12 and 13 respectively. 1 So far as the invention is concerned, there may be any number of oil burner assemblies including only one.

Storage tank 11 is of conventional construction and usually is buried below the surface of the ground outside of a building in which

burners

12 and 13 are disposed. The oil used in buildings larger than domestic dwellings such as, for example, public schools and most industrial plants, is the relatively viscous type known as Bunker C or No. 6 grade which flows slowly especially when the tank temperature is about 50 F. m

Supplying burners 1.2 and 13 with fuel oil under pressure is a remote pump set 16 which draws fuel oil from storage tank 11 through a suction line generally indicated at 13. Suction line 18 comprises a suction stub pipe 20 connected by a T-fitting 21 to a supply conduit 22 made up of suitable pipe sections and leading to pump set 16 located in the boiler room. Conduit 22 preferably contains a check valve 24 to prevent reverse flow back to tank 11. Suction pipe 20 extends downwardly through a detachable manhole cover 23 on tank 111 and has an open lower end projecting into a conventionally constructed bell 25 on the bottom of tank 11. A heater 36 in stub 20 may be energized in any suitable manner.

Pump set 16 comprises two conventionally constructed oil pumps 39 and 40 having inlets respectively connected to supply conduit 22 in parallel relationship by branch lines 42 and 4-4 which contain manual shut-off valves 46 and 47 respectively. The discharge sides of pumps 38 and 40 are respectively connected in parallel to an oil discharge pipe section 48 by

branch lines

50 and 52. Each

branch line

50 and 52 contains a manual shut-off valve 54 and a check valve 56, the latter valve being efiective to permit flow into line 48 and to block return flow of oil to the discharge side of each of the pumps. With this piping arrangement, either pump 39 or pump 40 may be operated while the other is inactive, or both pumps may be operated at the same time.

Pipe section 48 has an upwardly extending open end 62 received in an air-separation chamber 63 defined by a cylindrical housing 64 having a top air and oil outlet port 65 and a side oil supply port 66. Oil delivered by pump set 16 flows into chamber 63. There, any entrained air separates from the cascading oil and exits through outlet port 65 for return to tank 11 in a manner to be presently described. Thus, air bubbles or pockets entrained in the pumped oil will separate from the oil which otherwise substantially fills chamber 63 causing the separated air to rise upwardly to port 65.

Oil pumped into chamber 63 flows through outlet port 66 which is connected by a pipe section 68 to an inlet 70 of a low density electric immersion heater assembly 72. Heater assembly 72 is of conventional construction and essentially comprises a hollow metal tubular casing 7 4 of larger diameter than the piping connected thereto and through which oil flows in contact with end mounted electrical heater elements disposed in casing 74 and indicated generally at 76. Casing 74 is provided with a hot coil outlet 78. Additional low density conversion heaters (not shown) may be provided in series with heater assembly 72 if needed;

Each set of heater elements 76 is separately energized by current from a main electric source passing through a normally closed manual disconnect switch 79 and an adjustable thermostatic unit 80 having a control dial 81 for selecting the temperature to be imparted to the oil. The heater element sets 76 and associated units 80 are preferably mounted on

outer flanges

82 and 83 so that the circuits may be electrically separate at this region.

In practice, the thermostatic units 80 are set to open the electrical circuits de-energizing their respective heater element sets 76 when the oil temperature reaches approximately 180 F. and to close the electrical circuits when the oil temperature drops below approximately 175 F. As a result, the temperature of oil flowing through the heater assembly outlet 78 for delivery to

burners

12 and 13 is usually maintained within the range of approximately 160 F. to 200 F. which is satisfactory for assuring substantially complete combustion.

With continued reference to FIGURE 1, outlet '78 of heater assembly 72 is connected to a burner feed line 86. Feed line 86 is connected to

burners

12 and 13 by

fluid branch conduits

88 and 90 respectively to thus furnish

burners

12 and 13 with a continuous supply of heated oil. Contained in

lines

88 and 90 respectively are manual valves 91 and 92 for selectively permitting and blocking oil flow to

burners

12 and 13.

Burners

12 and 13 are each of conventional construction for burning No. 6 grade fuel oil and may be either of the gravity (non-pump) or pump type. In the present embodiment (as shown in FIGURE 2), the burners are of the pump type each having a continuously running pump 93 in a feed line 94, a control valve 95 downstream of pump 93 for controlling the flow rate of oil to the burner nozzle (not shown), a solenoid operated burner shut-off valve 96 downstream of valve 95, and a tailpiece heater 97 upstream of shut-ofl valve 96 for heating oil at the burner on start-up. Valves 95 and 96, pump 93 and tailpiece heater 97 are all standard parts of burners equipped 4 to handle No. 6 grade fuel oil and therefore need not be described further.

With continued reference to FIGURES l and 2,

burners

12 and 13 are respectively provided with recirculating lines 93 and 99 each containing a check valve 100. Recirculating lines 98 and 99 are normally connected to their respective burner feed lines 94 between burner pump 93 and control valve 95 for returning oil to line 86. Thus excess unconsumed oil delivered by the burner pumps 93 is returned through lines 98 and 99 to line 86 for mixture with oil delivered by pump set 16 and recirculation through

branch lines

88 and 90. It will be noted that, in accordance with the present invention, excess unconsumed hot oil at

burners

12 and 13 resulting from throttling of control valve 95 or closing valve 96 is not returned to the storage tank 11 but rather is recirculated back to the inlets of the burners.

Feed line 86, as shown in FIGURE 1, contains a T- fitting 101 immediately downstream of heater assembly outlet 78 and upstream from the connection of

branch conduits

88 and 90 to line 86. Connected to fitting 101 is a burner by-pass return line 102 which is joined at its opposite end to a T-fitting 104 in an oil storage tank return line 106. Excess hot oil delivered by pump set 16 through heater assembly 72 and not burned by

burners

12 and 13 flows through line 102 and into line 106 for return to tank 11.

In accordance with the present invention, line 102 contains a thermostatically controlled flow regulating valve 108 disposed between

fittings

101 and 104. Valve 108 preferably is a conventional normally open self-powered modulating type needle port valve through which flow of oil is controlled by a suitable thermostatic element comprising a temperature responsive fluid filled bulb 110 inserted into a T-fitting 112 contained in suction line 18. Bulb 110 is connected to valve 103 by a capillary tubing 114 and may be located anywhere in the oil supply lines upstream from the inlet 70 of heater assembly 72. Advantageously, bulb 110 is located in suction line 18 to accurately sense the temperature of oil drawn from tank 11.

According to the present invention, valve 108 is responsive to the fuel oil temperature sensed by bulb 110 to vary the flow rate of oil being returned through line 102 inversely with respect to the oil temperature. Thus, as the oil temperature increases toward F., valve 108 responds to reduce the flow rate of oil through line 102. Conversely, as the oil temperature sensed by bulb 110 decreases, control valve 108 will open wider to permit a greater flow of hot oil to return line 106.

With continued reference to FIGURE 1, return line 106 is provided with a vertical pipe section 116 extending downwardly through manhole cover 23 and having an open lower end projecting into suction bell 25 in close proximity to the inlet end of suction pipe 20.

Suction bell 25 is of standard construction and serves two important functions. One is to limit the heat loss by confining the return hot oil within the bell. The other is to serve as a mixing or blending chamber where the return hot oil is mixed with cold viscous tank oil flowing into the bottom of the bell to replace the oil consumed by the burner operation. In this way, the contents of tank 11 outside of hell 25 remain at substantially the temperature prevailing outside the tank while the liquid fuel oil in the bell is at an elevated temperature suitable for pumping. With the system thus far described, as long as pump set 16 continues to operate, heater assembly 72 normally supplies substantially all the heat required to bring the oil flowing to

burners

12 and 13 up to the desired temperatures. After start-up, the heat required to bring cold tank oil flowing into bell 25 up to the desired pumping temperature of about 120 F. is supplied by the hot return oil flowing through

line

102 and 106. During stand-by periods when the pump set 16 is not operating, the fuel oil supply and return lines are advantageously electrically heated by the electrical system described in the previously mentioned Patent No. 2,802,520 or by any other suitable means such as conventional steam heating means. This keeps the oil in the supply system warm and flowable for quick, easy and dependable starting.

Particularly where high pressures are used, line 152 preferably contains a pressure reducing valve 126 between valve 198 and T-iitting 101 to provide a low pressure drop across valve 108. This renders the response of valve 108 more sensitive to small oil temperature changes and assures a smoother operation in the control of the amount of hot oil returned to tank 11. Pressure reducing valve 126 may be of any suitable type.

With continued reference to FEGURE 1, the air separator outlet port 55 is connected by a conduit 123 to fitting 104% in return line 1%. Air separated in chamber 63 passes through port 65, conduit 128, and line 106 into storage tank 11. Under conditions especially where valve 108 is operated to reduce the flow rate of hot return oil through line 102, the excess oil flows through conduit 128 for return to tank 11. A pressure regulating valve 150 contained in conduit 128 is set to maintain the oil being supplied to

burners

12 and 13 at a desired pressure. It is clear that the oil returned through conduit 128 is not heated to an elevated temperature by preheater 72. In-

ead, the temperature of return oil flowing through conduit 128 is no higher than the temperature of oil drawn through suction pipe 20, and the temperature of this oil is controlled, during normal running periods, by the operation of valve 105.

With continued reference to FIGURE 1, emergency pressure safety relief valves 135 and 138 are connected to the discharge sides of pumps 38 and 49 respectively. The outlet ports of

release valves

136 and 138 are connected by a common pipe section 141 to conduit 123 downstream of valve 130. Valves 136 and 133 are normally closed pressure responsive valves that open only when the oil pressure increases beyond a predetermined limit, as caused by, for example, a line blockage to thus relieve the system of excessive oil pressure by by-passing the oil from either or both pump outlets to conduit 128 for discharge to tank 11 through return line 166.

in starting up the oil burner supply system shown in FIGURE 1, heater assemblies 35 and 72 are energized and either or both pumps 39 and 40 are started. Cold tank oil in suction pipe 25 is heated to a flowable and pumpable temperature of about 120 F. by heater rod 36. Normally, the temperature of oil stored in tank 11 corresponds to temperature of the ground (about 50 F.) in which tank 11 is buried. The cold oil standing in suction pipe 20 is heated by heater 55 to a pumpable 120 temperature and then is withdrawn by pumps 39 and/or 40 and discharged into separation chamber 63 where entrained air is separated and returned to tank 11 through port 65.

With excess oil, the air-free oil discharged from the separation chamber outlet port 56 is passed under pump pressure through heater 72 which raises the temperature of the oil to about 180 F. Although the oil in supply line 85 is very hot, it will not vaporize owing to the pump discharge pressures. This hot preheated oil is then supplied to

burners

12 and 13 through lines 88 and 5d. The capacity of each of the pumps 39 and 40 is such that the amount of oil supplied thereby is substantially fixed and about double the maximum burning rate of

burners

12 and 13. Thus, when

burners

12 and 13 are being fired at their maximum rate, there will always be an excess quantity of oil which is passed through and heated by heater assembly 72. This excess unburned hot oil, instead of being delivered to

burners

12 and 13, is by-passed through line 102 and control valve 103 for return to storage tank 11 through line 106.

The excess oil returning through line 1% mixes with cold tank oil entering suction bell 25 to elevate the temperature of the oil being withdrawn through suction pipe 20 to a pumpable temperature of about 120 F. After preheated oil has begun to return to suction bell 25 through line 102 to heat cold stored oil to pumpable temperature, heater 36 will automatically deenergize, especially to prevent overheating of oil in the suction line to avoid vapor lock in the oil pumps 39 and 40.

Responding to the oil temperature sensed by thermostatic bulb 110, valve 108 is automatically actuated to control the flow rate of hot excess oil returning to tank 11 through line 102. Thus, if the oil temperature sensed by bulb rises above F., valve 103 will close. The excess oil delivered by pumps 3% and 40, instead of flowing through heater assembly 72, will pass through separation chamber 63, through conduit 123 and through return line 106 to suction bell 25 in storage tank 11. This return oil will lose some heat in returning to tank 11 and, as a result, the temperature of oil at the discharge sides of pumps 39 and 40 will begin to decrease.

Upon sensing a temperature decrease, thermostatic bulb 110 will cause valve 108 to open, thus increasing the flow rate through line 102 and decreasing the flow rate through conduit 128. The further valve 108 is opened, the lower the flow rate through conduit 1128 becomes. As a result, oil at a higher temperature is returned to suction bell 2.5 to increase the temperature drawn through suction pipe 20.

When one of the

burners

12 or 13 is shut down, or when the firing rate of

burners

12 and 13 is reduced, pumps 39 and 40 continue to deliver the same amount of fuel oil. With the reduction of burning rate, the flow of oil through valve 10% remaining the same, hot preheated oil will increase. If this condition were allowed to persist, the temperature of the oil in suction line 18 would become so hot that it would eventually vaporize under the low pump suction pressure. Such vaporization and consequent pump vapor lock would interrupt the steady flow of oil to

burners

12 and 13, causing burner failure and possible explosion or puff-back.

With the present invention, however, the increasing oil temperature is sensed by bulb 110 before entering heater 72. As a result, valve 108 will respond by closing to reduce the flow rate through line 102 and thus reduce the amount of heated oil being returned to bell 25.

In this manner, valve 108, in responding inversely to the oil temperature sensed by bulb 110, regulates the flow of heated return oil to maintain a suitable oil pump suction temperature of approximately 120 F. As a result the objectionable condition of suction line oil vapor lock is overcome without wastefully dissipating any heat and thus rendering the system very economical to operate. Thus, the invention provides a dependable, easily started, two-temperature fluid system.

The embodiment illustrated in FIGURE 3 is the same, with one exception, as embodiment of FIGURE '1, and to the extent that both embodiments are alike, like reference numerals have been used to identify like parts.

In the embodiment of FIGURE 3, burner lines 98 and 99 are connected to an oil purge line and respectively contain

orifices

151 and 152. Purge line 150 is connected by a T-fitting 154 to return line 106 downstream from T-fitting 104.

Orifices

151 and 152 permit very small amounts of hot oil to circulate through

lines

88 and 90, through the burner piping, and through lines 98 and 99. This prevents the fuel oil from objectionably cooling off in cold un heated parts of the piping around the burners especially during stand-by periods. The amount of oil which orifices 151 and 152 permit to flow through line 150 is very small and not enough to cause any objectionable effect on the temperature of the oil in hell 25 or suction pipe 20. Line 150 is advantageously employed during cold start-ups when there may be the likelihood that collected oil has objectionably been cooled in unheated piping at the burners.

The upstream pressure maintained by valve 130 in line 128 and also in line 102 upstream from valve 126 depends upon the type of burners employed in the system such as, for example, the pump-type burners illustrated in FIGURE 2 or the gravity-type burners illustrated in FIGURE 1. Normally, an upstream pressure of about 80 p.s.i. is required for gravity-type burners. Valve 130 is adjusted to regulate pressure to maintain a sufiicient downstream pressure for overcoming pipe line friction resulting from oil flow to tank 11. Usually, valve 139 is adjusted to reduce line fluid pressure to about to psi. Valve 126 is advantageously adjusted to provide a line fluid pressure at the inlet to valve 108 which is approximately equal to the line fluid pressure on the downstream side of valve 130 to provide a low pressure drop across valve 108 as previously described.

FIGURE 4 illustrates a preferred embodiment of this invention wherein a three-way thermostatically controlled valve 160 of conventional construction is employed in place of

valves

108 and 126. To the extent that the construction shown in FIGURE 4 is like the previous embodiments illustrated in FIGURES 13, like reference numerals have been used to identify like parts.

As shown in FIGURE 4, the air separator comprising chamber 63 in the construction of FIGURE 1, has been omitted, and discharge pipe section 48 is connected directly to a T-fitting 162 contained in a fluid conduit 164. One end of conduit 164 is connected to inlet 70 of heater assembly 72.

With reference now to FIGURES 4 and 5, valve 160 is shown to comprise a housing 166 having axially opposed

inlet ports

168 and 170 and an outlet port 172. The end of conduit 164 opposite from the connection to the heater inlet 70 is connected to inlet port 168. The other inlet port 170 is connected by a by-pass return line 176 to feed line 86 upstream from

burners

12 and 13. A check valve 178 contained in line 176 permits fluid flow only from feed line 86 to inlet port 170.

With continued reference to FIGURE 4, outlet port 172 is connected to the inlet port of a conventional pressure regulating valve 180 by a fluid conduit 182. The function of valve 180 is the same as valve 130 in FIGURE 1. The outlet port of valve 180 is connected to return line 106 by a fluid conduit 184. In this embodiment, pipe section 140 is connected to conduit 184 downstream from valve 180.

Preferably, valve 160 is a Sarco No. 58 valve as shown in the Sarco Bulletin No. 620, dated January 1962, and is shown in FIGURE 5 to have a valve operating member 186 which is slidably mounted in housing 166 along an axis extending at right angles to the common axis of

ports

168 and 170. As shown, member 186 comprises a plurality of axially spaced apart flow control pistons mounted on a common rod and is spring biased into engagement with a plunger 188. Axial displacement of valve member 186 in one direction will proportionately open and block

ports

168 and 170 respectively. Similarly, displacement of member 186 in the opposite direction will proportionately open port 170 and close port 168.

As shown in FIGURE 4, thermostatic bulb 110 is connected to control the position of valve member 186 to thus proportion the flow of hot oil entering at port 170 and cooler oil entering at port 168. The

oil entering ports

168 and 170 is mixed and discharged through port 172 for return to suction bell 25 through

lines

184 and 186. This returned heated oil mixes with and heats cold viscous tank oil in suction bell 25, and the mixture is drawn through suction line 18 by pump set 16 and is supplied under pump pressure through heater 72 to

burners

12 and 13 in a manner previously described in the embodiments of FIGURES 13.

At full capacity with all of the burners operating at their maximum firing rates under normal conditions, port 168 will be substantially closed and port 170 will be proportionately open. If the heating load is reduced as by shutting down one or more of the burners or by reducing the firing rates of any of the burners, the amount of excess hot oil returning to suction bell 25 through line 176 will start to increase. This will result in a temperature increase in the mixture of hot and cold oil in hell 25 to cause a corresponding temperature increase in the suction line oil. This temperature increase is sensed by bulb 110 which displaces valve member 186 to respectively close and

open ports

170 and 168 by proportionate amounts with the result that the amount of cooler oil supplied through port 168 will increase and the amount of hot oil flowing through port 170 will proportionately decrease. As a consequence, the temperature of oil returning to suction bell 25 through port 172 and return line 186 will be maintained at the control setting established by bulb 110.

If all of the burners are shut down so that there is no load at all, no oil will be burned so that substantially all of the oil passing through heater 72 and line 86 will return through line 176. This increases the temperature of the oil discharged through port 172 to cause a corresponding temperature increase in suction bell 25 and suction line 13. In response to this temperature increase bulb 110 shifts valve member 186 to substantially close port 170 and open port 168 by a corresponding amount with he result that most of the oil discharged by pump set 16 through line 48 will not pass through heater 72 but rather will pass directly through line 164, port 168 for return to suction bell 25 through line 184.

Assume now that burner 12 is operating and burner 13 is shut down and valve 160 has automatically responded to maintain the 120 temperature in suction line 18. If burner 13 is now started up, the amount of hot oil consumed will increase and the amount of excess hot oil returning to suction bell 25 through line 176 will correspondingly decrease. As a result, the temperature of the blended oil passing through port 172 will start to decrease to cause a corresponding decrease in the temperature of oil in suction bell 25 and in suction line 18. This temperature decrease is sensed by bulb 110 which displaces valve member 186 to increase the amount of hot oil flowing through port 170 and to proportionately decrease the amount of cooler oil flowing through port 168. As a result, the temperature of the oil returning to suction bell 25 will be increased. Thus, it is clear that valve 160 is automatically responsive to suction line oil temperature to maintain the supply oil in suction line 18 at a predetermined temperature regardless of load conditions and the temperature setting for the oil burners.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In a preheating system for heating and transporting viscous liquid fuel from a storage tank to a burner, a supply pipeline extending between said tank and said burner, a pump in said line for withdrawing fuel from said tank and supplying it to said burner in predetermined excess of the maximum firing rate of said burner, heating means in said line between said pump and said burner for materially raising the temperature of pumped fuel flowing through said line to effect efircient combustion thereof at said burner, a return pipeline connected to said supply line downstream from said heating means for returning heated fuel to said tank, means including temperature responsive valve means connected to control fuel flow through said return pipeline inversely with respect to the temperature of supply line fuel upstream supply pipeline extending between said tank and said 1 burner, a pump in said supply line for Withdrawing fuel from said tank and supplying it to said burner in predetermined excess of the maximum firing rate of said burner, heating means in said line between said pump and said burner for materially raising the temperature of fuel flowing through said line to efiect efficient combustion thereof at said burner, a return pipeline connected to said supply line downstream of said heating means for returning at least substantially all of the heated unburned fuel to said tank in close proximity to the inlet of said supply line, flow control valve means connected to control the rate of fuel flow through said return line, a bypass line connected to said supply line between the discharge of said pump and said heating means for returning to said tank fuel which is diverted from said return pipeline by operation of said control valve means, and thermostatic means for controlling said valve means to vary the fuel flow rate through said return line inversely with respect to the temperature of supply line oil upstream from said heating means for maintaining fuel withdrawn by said pump at a predetermined temperature which is lower than the temperature imparted to said fuel by said heating means.

3. The preheating system defined in claim 2 comprising pressure regulating valve means in said bypass pipeline to maintain a predetermined fuel oil supply pressure at said burner.

4. The preheating system defined in claim 3 wherein said return line is connected to said supply line upstream from the connection of said burner.

5. The preheating system defined in claim 4 comprising a recirculating pipeline connected to circulate unburned fuel from said burner to said supply line upstream from the connection of said return line to said supply line.

6. The preheating system defined in claim 3 comprising a suction bell in said tank, the inlet and outlet respectively of said supply line and said return line being in said bell.

7. The preheating system defined in claim 3 comprising a purging line for returning heated fuel from said burner to said tank and means in said purging line for restricting fuel flow rates so as not to adversely heat the fuel withdrawn by said pump above said predetermined temperature.

8. In a preheating system for heating and transport ing viscous fuel oil from a storage tank to an oil burner, a supply line extending between said tank and said burner, a pump in said line for withdrawing fuel from said tank in excess of the burner firing rate and supplying it to said burner, heating means in said line between said pump and said burner for heating pumped oil flowing through said line to a predetermined temperature for effecting proper combustion, a return line having separate branches respectively connected to said supply line upstream and downstream from said heating means for returning excess unburned oil to said tank, and valve means disposed in said return line and being responsive to the Cit temperature of the oil in said supply line upstream from aid heating means tor automatically proportioning the nount of excess oil returned to said tank through said ranches to maintain the supply fuel at the suction side of said pump at a predetermined temperature.

9. The preheating system defined in claim comprising means connecting one of said branches to said supply linebetween said heating means and said burner and the other of said branches to said supply line between said pump and said heating means.

re. The preheating system defined in claim wherein said valve means comprises a three-way valve having a pair of inlet ports respectively connected to said branches and an outlet port connected to said return line leading to said tank.

11. The preheating system defined in claim It wherein said three-way valve comprises a temperature responsive valve operating member that is displaceable to inversely proportion the amount of oil flowing through said inlets.

The preheating system defined in claim 8 comprising a suction bell disposed in said tank, the outlet end of said return line and the inlet end of said supply line being disposed in said bell in close proximity to each other.

13. The preheating system defined in claim it comprising a pressure regulating valve disposed in said return line downstream from said three-way valve.

In a preheating system for heating and transporting viscous fuel oil from a storage tank and to an oil burner, a supply line extending between said tank and said burner, a pump in said line for Withdrawing fuel oil from said tank inexcess of the burner firing rate and supplying it to said burner, heating means in said line between said pump and said burner for heating pumped oil iiowing through said line to a predetermined temperature for effecting proper combustion, a return line for returning excess, unburned oil to said tank in close proximity to the inlet of said supply line and including first,

eeond and third branches, said first branch being connested to said supply line downstream from said heating means, said second return line branch being connected to said supply line downstream from the discharge of said pump and upstream from said heating means, said third branch extending into said tank, valve means hav ing first and second inlet ports respectively connected to said first and second branches and an outlet port connected to said third branch, means responsive to the temperature of the oil in the supply line upstream from said heating means for controlling said valve means to proportion the amount of excess oil returned to said tank through said first and second branches to maintain the supply fuel oil at the suction side of said pump at a predetermined temperature, and pressure regulating valve means disposed in said third branch for maintaining a predetermined fuel oil supply pressure at said burner.

References Qited by the Examiner UNETED STATES PATENTS 2,892,520 8/57 Trabilcy 158-36.0 2,876,830 3/59 Duy 158-360 3,067,809 12/ 62 Dresing.

FREDERICK L. MATTESON, IR. Primary Examiner.

ROBERT A. DUA, JAMES W. WESTHAVER,

Examiners.

Claims

1. IN A PREHEATING SYSTEM FOR HEATING AND TRANSPORTING VISCOUS LIQUID FUEL FROM A STORAGE TANK TO A BURNER, A SUPPLY PIPELINE EXTENDING BETWEEN SAID TANK AND SAID BURNER, A PUMP IN SAID LINE FOR WITHDRAWING FUEL FROM SAID TANK AND SUPPLYING IT TO SAID BURNER IN PREDETERMINED EXCESS OF THE MAXIMM FIRING RATE OF SAID BURNER, HEATING MEANS IN SAID LINE BETWEEN SAID PUMP AND SAID BURNER FOR MATERIALLY RAISING THE TEMPERAWTURE OF PUMPED FUEL FLOWING THROUGH SAID LINE TO EFFECT EFFICIENT COMBUSTION THEREOF AT SAID BURNER, A RETURN PIPELINE CONNECTED TO SAID SUPPLY LINE DOWNSTREAM FROM SAID HEATING MEANS FOR RETURNING HEATED FUEL TO SAID TANK, MEANS INCLUDING TEMPERATURE RESPONSIVE VALVE MEANS CONNECTED TO CONTROL FUEL FLOW THROUGH SAID RETURN PIPELINE INVERSELY WITH RESPECT TO THE TEMPERATURE OF SUPPLY LINE FUEL UPSTREAM FROM SAID HEATING MEANS TO PREVENT THE TEMPERATURE OF