US 3570828 A
Description (OCR text may contain errors)
J. A. CQWAN 3,570,828
PROPANE VAPORI ZER Filed April 2l, 1969 March 16, I1971 United States Patent O 3,570,828 PROPANE VAPORIZER James A. Cowan, Marengo, Ill., assignor to Chicago Eastern Corporation, Marengo, Ill. Filed Apr. 21, 1969, Ser. No. 817,656 Int. Cl. F231 9/ 04 U.S. Cl. 263-19 4 Claims ABSTRACT OF THE DISCLOSURE A hot air drying system wherein a vaporizing heatexchanger in a hot air duct or plenum chamber of the system heats and vaporizes liquid fuel from a liquid fuel supply in a storage tank and returns heated, Vapor enriched liquid to the tank. A burner in the system draws vaporous fuel from the tank for combustion upon demand during starting and normal operation; whether the system operates continuously or cyclically.
BACKGROUND OF THE INVENTION This invention relates in general to the drying of diverse products by artificial means. It deals more particularly with a hot air drying system.
Hot air drying systems are, in general, relatively wellknown. Among their many uses, they are frequently employed to dry agricultural crops or the like, either by batch or continuous flow drying, for example. In any case, the system ordinarily employs a burner which operates on a vaporous fuel such as propane or butane or the like. Air is heated by the burner as it is driven by the blo-wer into the proximity of the product and drying is effected by the heated air.
Drying systems presently using a petroleum fuel such as propane or butane have one common short-coming, however, and that is obtaining sumcient vaporous fuel from conventional storage vessels during all stages of operation. One method of overcoming this short-coming in commercial systems includes using multiple or large volume fuel tanks which are capable of naturally vaporizing the required amount of fuel. Another method is to use a separate, in-line fuel vaporizing device independent of the drying system. Yet another method is to use a so-called liquid fueled, self-vaporizing burner in the drying system.
The rst two of the aforementioned types of drying systems are relatively expensive. The necessity of using multiple, or large volume fuel tanks, or separate, in-line fuel vaporizing devices, obviously raises the cost of the system.
The third type of system, that is, one using a liquid fueled, self-vaporizing burner is extremely dangerous from a fire or explosion stand-point. Since many, if not all of the drying systems using such burners must modulate at a wide range of B.t.u. input or be controlled in a cycling attitude by a thermostat or humidistat turning the dryer on or off as controlled, it is not uncommon for the burner to be actually burning liquid fuel rather than vaporized fuel. More precisely, liquid fueled vaporizing burners depend in theory upon the burner being able to vaporize one-hundred percent of the liquid fuel supplied to it prior to the fuel entering the combustion chamber of the burner. However, in on-otf burner cycling operations where a cold burner has had no opportunity to start the Vaporizing cycle, or Where modulated high firing rates exceed the vaporizing capabilities of the burner, unvaporized or liquid fuel can and is introduced to the burner combustion chamber with devastating results.
SUMMARY OF THE INVENTION The drying system of the present invention is simple, efficient, and inexpensive, yet affords a high vapor withdrawal capacity from a relatively small storage tank without the use of costly fuel line vaporizers. It is an object of the present invention to provide a system wherein liquid fuel is heated and vaporized by hot air from the system itself. Hot, vapor enriched liquid fuel is returned to the storage tank where vaporous fuel, uncontaminated by liquid, is constantly available for use by the burner. A primary feature of the invention is that the greater the firing rate of the burner, the greater the vaporizing rate in the system, whereby the system automatically balances itself to the demand of the burner. It is still another object to provide a system of the aforedescribed character wherein fuel is circulated through a vaporizer only during burner operation so that the tank is not cooled by unheated liquid being circulated.
The foregoing and other objects are realized in accord with the present invention by providing a hot air drying system utilizing a burner wherein pro-pane, for example, is vaporized in a heat-exchange loop separate from the supply line or lines to the burner. A heat-exchange unit is built into a hot air duct or plenum chamber of the system and liquid propane is pumped to it from a storage tank during operation of the burner. Liquid propane is vaporized in the heat-exchanger and vapor enriched liquid, i.e., hot propane liquid and entrapped gas is returned to the storage tank.
As the hot, vapor enriched liquid propane is returned to the storage tank, the gas is trapped in the dome above the liquid in the tank. The hot liquid serves to heat the liquid stored in the tank, thus increasing its propensity to vaporizie. Vaporous propane is instantaneously available to the burner when it is started; at the beginning of a drying operation, for example, or when it is cycled during normal operation. No liquid is circulated through the vaporizer when the burner is not operating so that the liquid in the storage tank retains a substantial amount of the heat and is not cooled by circulating, unheated liquid.
VBRIEF DESCRIPTION OF THE DRAWING The invention, together with its construction and method of operation, taken with other objects and advantages thereof, is illustrated more or less diagrammatically in the drawing, in which:
FIG. 1 is a diagrammatic illustration of a drying system embodying features of the present invention; and
FIG. 2 is a perspective view of a continuous flow grain dryer employing a modified drying system embodying features of the invention.
Referring now to the drawing, and particularly to FIG. 1, a drying system embodying features of the invention is illustrated diagrammatically at y10. The drying system 10 is constructed and arranged to drive heated air into a drying enclosure 11. The drying enclosure 11 might contain one or more of various products which it is desired to dry. In the present illustration of the invention, the drying system 10 is employed as a crop dryer and the drying enclosure 11 would normally contain a crop such as shelled corn, for example, for drying.
The drying system 10 includes a burner and blower assembly 15. The assembly 15, in turn, includes a gas burner 16 which is adapted to burn a vaporous fuel, such as propane or the like, to generate heat. The blower 17 of the assembly forces air through the burner whereby the driven air is heated. In practice, a blower assembly as illustrated by Cowan U.S. Pat. No. 3,193,265, issued July 6, 1965, entitled Blower, and assigned to the same assignee as the present invention, might be employed.
The burner and blower assembly is mounted on one end of a hot air duct 18 and adapted to drive heated air through the duct in the direction of the arrows illustrated. The heated, driven air passes through the duct 18 into the drying enclosure 11 to dry the crop stored therein.
In the drying system 10 embodying features of the invention, the burner is supplied with vaporous propane from a propane storage tank 25. The storage tank contains a supply 26 of liquid propane and, above the level of the liquid in the tank, an atmosphere or dome 27 of vaporous propane. It is from this dome of vaporous propane in the storage tank 25 that fuel for the burner 16 is drawn through a burner fuel line 3).
As the heated air is driven through the duct 18, it also passes transversely across a vaporizing heat-exchanger 4t). The vaporizing heat-exchanger 40 inludes a carrier pipe 41 mounting heat-exchange ns 42 in generally conventional relationship. The inlet end 45 of the pipe 41 is connected by a liquid fuel supply line 46 to the fuel tank 25, where it depends into the supply 26 of liquid propane, adjacent the bottom of the tank 25. Disposed in the line 46 is a conventional fuel pump 47.
During normal operation of the drying system 10, the pump 47 pumps liquid fuel from the supply 26 thereof, through the pipe 41 in the vaporizing heat-exchanger 40. The heated air flowing over the heat-exchanger pipe 40 is effective to heat liquid propane in the pipe 41 and vaporize a portion of it. Accordingly, heated liquid propane with entrained vaporous propane, i.e., vapor enriched liquid propane, departs the outlet end 48 of the pipe 41.
According to the invention, this hot, vapor enriched liquid propane is returned to the tank 25 through a fuel return line 49. The heated liquid serves to heat the reservoir 26 of liquid in the tank 25 while the vaporous propane 27 is stored in the space or domein the tank 25 above the liquid. The returning heated liquid propane is effective to raise the overall temperature of the stored liquid 26 in the tank 25 and the volatility of the stored liquid 26 increases as its temperature increases.
The system also has the capability of balancing itself; i.e., vaporization rate against burner 16 consumption rate. As the burner 16 is adjusted to a higher B.t.u. output, the vaporizer 40 receives more heat. Accordingly, the rate of vaporization increased. The burner 16 actually creates a larger supply of vaporous fuel as it, in turn, demands more fuel.
When the burner and blower assembly 1S is not operating, the pump 47 is ineffective to circulate liquid propane through the heat-exchanger 40. Accordingly, the liquid 26 in the tank 25 remains relatively warm and volatile, absent circulating unheated liquid which would tend to cool it.
The drying system 10 has been described in the context of a batch dryer wherein the product is dried while in a drying enclosure 11. As such, the heated, driven air passes through the duct 18 to reach the drying enclosure 11. It should be understood, however, that in the crop drying ield alone, the system 10 might be employed in other ways; for example, in the context of a continuous flow crop dryer.
Turning to FIG. 2 of the drawing, a continuous ow grain dryer is illustrated generally at A, The continuous ilow grain dryer A is designed to receive undried grain through its inlet manifold B and discharge dry grain into a dry grain auger C for conveyance to disposal. Intermediate the inlet manifold B and grain auger C, three drying units D are disposed in vertical series alignment.
The dryer A illustrated is designed to handle approximately 700 bushels of grain per hour. The two uppermost drying units D employ hot air drying systems 110 simliar to the system 10 hereinbcfore described, while the lower unit D forces cool air over the grain to accomplish cooling of the grain without cooling shocks. The grain ows downwardly through the units D between the side walls of the units and inner screens (not shown). The inner screens define an axial plenum chamber within each unit D through which air is driven in drying relationship with the grain.
In this embodiment of the invention, a burner and blower assembly 115 in each of the systems 110` of the two upper drying units D drives heated air through the axial plenum chamber (not shown) in a manner hereinbefore discussed in relation to the drying system 10; the plenum chamber being the counterpart of the duct 18 in the system 10. The hot air drying systems incorporated in the upper drying units D are, in all other respects, substantially identical to the system 10 hereinbefore discussed with the exception that, in practice in the system 11), the vaporizing heat-exchanger (not shown) in the plenum chamber is normally arranged axially of the chamber, rather than transverse to it.
Although the system 10 (and the system 110) has been described in the capacity of a crop drying system, it should be understood that various and diverse drying operations could advantageously be accomplished with the system. As such, while the embodiments described herein are at present considered to be preferred, it is understood that various modifications and improvements may be made therein.
What is desired to be claimed and secured by Letters Patent of the United States:
1. A hot air drying system, comprising:
(a) `burner means adapted to burn a vaporous fuel to heat driven air,
(b) fuel storage tank means containing a supply of liquid fuel,
(c) heatexchanger means within the environment of said heated, driven air, and
(d) fuel line means from said supply of liquid fuel in said tank to said heat-exchanger means, from said heat-exchanger means to said tank means, and from said tank means to said burner means, for carrying liquid fuel from said tank means to said heat-exchanger means, returning heated vapor enriched liquid fuel to said tank means, and providing a constant supply of vaporous fuel to said burner means.
2. A hot air drying system, comprising:
(a) burner means adapted to burn a vaporous fuel to heat driven air,
(b) fuel storage tank means containing a supply of liquid fuel,
(c) heat-exchanger means within the environment of said heated driven air,
(d) rst fuel line means from said supply of liquid fucl in said tank to said heat-exchanger means,
(e) second fuel line means from said heat-exchanger means to said tank means for returning heated vapor enriched liquid fuel to said tank, and
(f) third fuel line means from said tank to said burner means for providing a constant supply of vaporous fuel to said burner means.
3. A hot air drying system, comprising:
(a) burner means adapted to burn a vaporous fuel to heat driven air,
(b) duct or plenum means for receiving the heated driven air,
(c) fuel storage tank means containing a supply of liquid fuel,
(d) heat-exchanger means in said duct or plenum means in the environment of said heated driven air,
(e) first fuel line means from said supply of liquid fuel in said tank means to said heat-exchanger means and means for forcing liquid fuel to said heat-exchanger means through said rst fuel line means,
(f) second fuel line means from said heat-exchanger means to said tank means for returning heated vapor enriched liquid fuel to said tank means, and
(g) third fuel line means from said tank means to said burner means for providing a constant supply of vaporous fuel to said burner means.
4. A method of fueling the burner in a hot gas blower comprising the steps of:
(a) providing a tank containing a body of liquid fuel having a body of vaporous fuel above it,
(b) removing vaporized fuel from said tank and delivering it directly to the burner to fuel said burner during burner operation,
(c) removing liquid fuel from said tank and passing Iit through the hot gas heated by said burner in said hot gas blower only during burner operation to vaporize a portion of said liquid fuel and create vapor enriched liquid fuel, and
(d) returning said hot vapor enriched liquid fuel directly to said tank to increase the amount of the body of References Cited UNITED STATES PATENTS Mohn 26S- 19A Martin 26S-19A JOHN I. CAMBY, Primary Examiner U.S. C1. X.R.