Patent Application
20070175412
Not Applicable
Not Applicable
Not Applicable
1. FIELD OF INVENTION
This invention relates to Liquefied Petroleum Gas (LPG) vaporizers, specifically a vaporizer utilizing infrared (IR) heat sources and heat exchangers.
2. PRIOR ART
Vaporized LPG is primarily used in standby, backup, and peak-shaving systems; in some instances, LPG is used as a primary fuel source instead of natural gas. In low flow volume applications, LPG can be vaporized by relying on the natural expansion that occurs when it is exposed to atmospheric pressure; however, this produces a refrigeration effect that can have deleterious consequences by freezing valves and burners in high flow volume applications. Vaporizers can be used to heat the LPG into vapor, which avoids the refrigeration effect.
Known designs of LPG vaporizers consist of three main elements: a source of heat, a vaporization tube, and a heat transfer medium to convey the heat from the source to the vaporization tube. Common sources of heat include burners, boilers (for steam and hot water vaporizers), and electricity. Heat transfer media used in known designs of LPG vaporizers include water, water/glycol mixtures, steam, flue gasses (from burners), and metal (in electric vaporizers).
U.S. Pat. Nos. 4,203,300 and 4,131,084 to Hanson (1980 and 1978) disclose LPG vaporizers that utilize burners that heat an aqueous solution, which in turn transmits heat to helical vapor tubes submersed in a water bath. Similar designs utilize tubes of hot water enclosing a central heat exchanger or pressure vessel. The water bath separates potential leaks of the flammable LPG from the heat source; therefore, these vaporizers are perceived by some users as safer than vaporizers that use gaseous heat exchange media which do not offer this buffer. The major disadvantage of using liquid heat transfer media like water or water/glycol mixtures is the inherent increase of density and therefore mass when compared to an equivalent volume of gaseous heat transfer media like steam or flue gasses. This has the potential to limit the range of applications, since these installations tend to be large and heavy, therefore not easily moved or installed.
Another heat transfer medium option is the use of metal blocks, such as the design for an electrical LPG vaporizer disclosed by U.S. Pat. No. 4,645,904 to Moraski (1987). A number of electric resistance heating elements heat aluminum blocks, which in turn transmit the heat to the LPG inside the vaporization tube. Though electric LPG vaporizers avoid the need for fluid heat transfer media, the electric resistance heating elements need powerful sources of electricity and are therefore not suitable for installation and use in locations without easy access to power sources.
LPG vaporizer designs that rely on gaseous heat transfer media like steam or flue gases tend to have smaller footprints and lower weight than liquid media vaporizers. Burners used in LPG vaporizers of known designs are often fueled by diverting a small portion of the vaporized LPG, which makes the vaporizers independent from external fuel supplies. This greatly increases flexibility in placement and installation over electrical designs. The major cause for consumer concern in the case of vaporizers that utilize flue gasses or products of combustion as heat exchange media is the proximity of open flames to the vaporization tubes. The possibility of an LPG leak directly into an environment with open flames causes some users to perceive these designs as less safe; however, all known designs in current use are required to comply with the regulations and guidelines of national agencies that have jurisdiction over the manufacturing, installation, and operation of such devices. In the U.S., these agencies include the American Society of Mechanical Engineers (ASME) and the National Fire Protection Agency (NFPA). A more realistic drawback is that gaseous media vaporizers tend to have lower flow capacities than liquid bath vaporizers, though significant overlap in capacities exists.
No new design for LPG vaporizers that uses a gaseous heat transfer media has been granted a patent in 30 years, though liquid bath vaporizers have been continually refined and redesigned for a number of applications. Nevertheless, all currently extant LPG vaporizer designs suffer from one or more of a variety of disadvantages and drawbacks:
a) Designs that utilize the direct application of an open flame to a pressure vessel containing flammable LPG are perceived as less safe and draw closer scrutiny by relevant authorities than designs utilizing non-flame heat sources.
b) Liquid bath vaporizers have a longer startup time, since the bath needs to be warmed before it can be used in vaporization.
c) Liquid bath vaporizers have a larger footprint and mass significantly more than vaporizers that do not use a transfer medium.
d) Vaporizers that utilize multiple heat-exchange fluids or multi-chambered and intricately connected pressure vessels increase complexity and cost of both manufacture and maintenance.
e) Significant energy of the flame is wasted as visible light that does not appreciably increase the energy input to the vaporization of LPG.
f) Electric designs require large-capacity power sources and are not suitable for emplacement in locations where the existing infrastructure does not support such large electricity users.
Accordingly, several objects and advantages of the present invention are:
a) to provide an LPG vaporizer that does not utilize the direct application of flame to the pressure vessel or uses gaseous heat transfer media to vaporize the LPG;
b) to provide an LPG vaporizer that has a short startup time;
c) to provide an LPG vaporizer that is compact and light weight;
d) to provide an LPG vaporizer that provides for non-complex manufacture and maintenance; and
e) to provide an LPG vaporizer that makes efficient use of heat energy.
Further objects and advantages will become apparent from a consideration of the ensuing description and drawings.
In accordance with the present invention an infrared vaporizer comprises infrared heat sources, heat exchangers, connecting piping and valves, controls, and an enclosure that holds individual components in place and provides protection from external elements.
Multiple instances of the same part are differentiated by letter suffixes.
The preferred embodiment of the present invention is illustrated in
Burner panels 30A and 30B hold IR burners 32A and 32B in place, respectively, and act as thermal bulkheads. Hanging clamps 36A and 36B hold the primary heat exchanger in place. Top clamps 38A-D secure the secondary heat exchanger.
The operation of the vaporizer is performed as follows. After applying control voltage, a solenoid valve at the liquid inlet 10 opens and admits LPG into the primary heat exchanger 14 from an LPG storage tank. The level of liquid begins to rise inside the liquid carryover prevention switch 16, causing the liquid carryover prevention switch to interrupt control voltage to the solenoid valve at the liquid inlet, causing the solenoid valve to close. A temperature switch at the vapor outlet 20 senses that the outlet temperature is below the specified operating range required for vaporized LPG and opens the burner control valves 34A and 34B on the IR burners 32A and 32B. The IR burners emit infrared radiation, which directly heats the primary heat exchanger and thereby the LPG. The LPG begins to expand and the overflow drains back into the storage tank through a check valve at the liquid inlet. As the temperature of the LPG inside the primary heat exchanger increases, the LPG vaporizes and flows through the liquid carryover prevention switch into the secondary heat exchanger 18. The secondary heat exchanger utilizes the rising flue gases produced by the IR burners to recover thermal energy and increases the thermal efficiency of the IR vaporizer. The exhaust stack 42 vents the flue gasses. The vaporized LPG continues to flow through the vapor outlet 20, where the temperature switch continually monitors output temperature. Once the vaporized LPG is within the specified temperature limits, the switch closes the burner control valves on the IR burners to maintenance levels. Residual heat inside the heat exchangers continues to vaporize the remaining LPG, until the temperature at the outlet drops below the specified level again, at which point the burner control valves are opened again. The supply of LPG is replenished through the solenoid valve at the liquid inlet, which stays open while control voltage is applied, and the liquid carryover prevention switch does not detect liquid. Should operating pressure rise above the design pressure, the LPG vapor is automatically vented through the pressure relief valve stack 40.
The IR burners possess standing pilot lights and are fueled by a small portion of the vaporized LPG. Fuel line valve 22 is located at the vapor outlet and allows fuel flow to fuel line 24A. The fuel line feeds into pressure regulator 26, which reduces the pressure of the LPG vapor from the vaporizer operating pressure to the pressures required by the IR burners. Fuel lines 24B and 24C lead to the IR burners. Drip leg 28 allows the collection and removal of condensate from the fuel lines.
From the description above, a number of advantages of the IR LPG vaporizer become evident:
a) The employment of IR radiation to heat the heat exchanger directly rather than using a heat transfer medium greatly increases the efficiency of the heat exchange, since the number of transactions required to transmit the heat energy into the LPG, and thereby the number of times their inherent inefficiencies are incorporated into the transfer, has been reduced.
b) No liquid heat transfer media are used, reducing both weight and required footprint of the IR LPG vaporizer.
c) The design of the IR LPG vaporizer is simpler and less complex than known designs of gas fueled vaporizers, since no primary heat transfer medium needs to be controlled or contained.
d) The IR burners used in the vaporizer are fueled with a portion of the vaporized LPG, making the IR LPG vaporizer independent from external fuel sources.
e) The secondary heat exchanger increases the overall efficiency of the IR LPG vaporizer by utilizing heat from the flue gasses that would otherwise be lost.
f) The IR LPG vaporizer does not rely on external sources of electricity to run or control vaporization.
This has been a description of examples of how the invention can be carried out. Those of ordinary skill in the art will recognize that various details may be modified in arriving at other embodiments, and these embodiments will come within the scope of the invention. These modifications include but are by no means limited to the following:
Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.
