Hydrothermal Liquefied Petroleum Gas Vaporization System

Abstract

A hydrothermal, indirect fired liquid petroleum gas vaporization system employed as a stand-by liquefied petroleum gas unit utilizes a forced draft power burner firing into a multiple pass gas fire tube immersed in a heat exchange liquid and isolated from a vaporization assembly through which liquefied petroleum gas is passed. A vaporization assembly for vaporizing the liquefied petroleum gas insures low gas velocities and delivery of dry gas vapor and eliminates liquid gas carryover. The liquefied gas from storage enters a manifold and is distributed into multiple heat exchange tubes immersed in the heat exchange liquid. The liquefied gas vaporizes during passage through the heat exchange tubes and passes into a vapor header and vapor outlet riser, all designed to prevent any liquid gas carryover.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is directed to an indirect fired liquid petroleum gas vaporization system and method of operating the same.

2. Prior Art Relating to the Disclosure

Liquified petroleum gas units normally maintained on a stand-by basis are employed by industrial users of natural gas having "interruptible gas" rates. Liquefied petroleum gas is not compatible with natural gas and requires vaporization and mixture with air before utilization. Vaporization of liquefied petroleum gas can be accomplished by the use of atmospheric heat for natural vaporization within a storage tank, by a direct fired vaporizer or an indirect fired vaporizer. The indirect fired vaporizer has many advantages over direct or natural vaporization systems as far as maintenance, cost, economy of operation, and safety. Indirect fired vaporizers generally consist of a heat exchanger that utilizes steam or heated liquid to vaporize the liquefied petroleum gas from a remote storage facility to produce gas vapor. When liquefied petroleum gas is vaporized, however, the volume conversion ratio of liquid gas to gas vapor is approximately 1 to 273. Thus the exit velocity of gas vapor passing through a heat exchange tube is approximately 273 times the entering liquid velocity. The rapid boiling or vaporizing of liquefied petroleum gas as it progresses through heat exchange tubes together with the extremely high velocity results in considerable liquid gas carryover which must be removed before utilization of the vaporized gas. Generally this has been accomplished by a separate trap downstream from the vaporization unit. Such a separate trap presents problems of both economy and safety.

SUMMARY OF THE INVENTION

This invention is directed to an immersion type, liquefied petroleum gas vaporization system utilizing a vaporization assembly which insures low gas vapor velocities with no liquid gas carryover. A dual-header, multiple tube vaporizer together with a specially designed gas vapor outlet riser prevents liquid gas carryover. The heat exchange liquid surrounding the vaporizer is heated by a forced draft power burner, the hot flue gases of which pass through a multiple-pass fire tube immersed in the heat exchange liquid. Use of the multiple-pass fire tube minimizes the stack temperature and insures even temperature distribution of the heat exchange liquid. The forced draft burner is powered by gas vapor taken from the outlet of the vaporizer.

The objects of this invention are to provide: (1) an immersion type vaporization system for liquefied petroleum gas employing a forced draft power burner which eliminates the need of a high flue gas stack and eliminates burner "blow-out"; (2) an immersion type vaporization system for liquefied petroleum gas employing a vaporization assembly including a dual-header, multiple tube vaporizer immersed in the liquid heat exchange medium, the vaporizer insuring low gas vapor velocities with no liquid gas carry-over; (3) an immersion type vaporization system for liquefied petroleum gas employing a multiple pass fire tube assembly which minimizes stack temperature and insures even temperature distribution of the heat exchange medium; (4) an immersion type vaporization system for liquefied petroleum gas which is trouble free, simple to install, operate and maintain; and (5) an immersion type vaporization system for liquefied petroleum gas which is substantially automatic in operation and which utilizes gas vapor from the vaporization end of the system for powering the burner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an overall side view of the vaporization unit;

FIG. 2 is an end view of the burner end of the vaporization unit of FIG. 1;

FIG. 3 is an end view of the vapor outlet end of the unit of FIG. 1;

FIG. 4 is a perspective view of the fire tube assembly;

FIG. 5 is a top view of the vaporization assembly;

FIG. 6 is a side view of the vaporization assembly of FIG. 5;

FIG. 7 is an end view of the vaporization assembly of FIG. 5;

FIG. 8 is a cross-sectional view along section line 8--8 of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The hydrothermal vaporization system of this invention comprises a forced draft power burner firing into a multiple pass fire tube assembly isolated from a dual-header, multiple tube liquid petroleum gas vaporizer by a heat exchange medium. Both the fire tube assembly and the vaporizer are immersed in the heat exchange medium.

FIG. 1 shows an insulated cylindrical shell 10 having end walls 11 and 12 secured thereto to provide a watertight vessel for the heat exchange medium, generally water to which antifreeze, such as ethylene glycol, may be added. The burner shell is preferably of double wall construction with an insulating material between the inner and outer walls 10a and 10b. The shell 10 has two openings in the upper end, one opening 13 fitted with a filler cap 14 through which the inner vessel is filled with heat exchange liquid and the other opening 15 provided for extension of the stack 16 of the fire tube assembly therethrough.

In the end wall 11 a capped drain 17 is provided for the heat exchange medium and a generally rectangular opening 18 for insertion of the vaporization assembly. The vessel is supported on legs 19. The rear or burner end 12 of the shell is provided with a cylindrical opening 20 near the lower end thereof to which the fire tube assembly is connected. Connections 21a and 21b may be provided near the upper end of the shell communicating with the interior thereof for circulation of water in the vessel, for external heating purposes.

FIG. 4 is a perspective view of the fire tube assembly 30 through which hot combustion gases from a forced draft burner pass for transfer of heat to the heat exchange medium. The inlet tube 31 of the fire tube assembly 30 is secured around the opening 20 in the burner end 12 of the shell and extends horizontally to a manifold 32 near the end 11 of the shell. From the manifold 32 multiple heat exchange tubes 33, 34 and 35 extend back towards the rear end of the shell. These heat exchange tubes connect with a second manifold 36. A flue 16 is secured to the manifold 36 and extends upwardly through the shell 10 of the vessel. The flue is insulated from the shell wall by suitable means such as vermiculite or glass fiber insulation. Although three heat exchange tubes are shown interconnecting the manifolds 32 and 36 more, or less, may be provided if necessary. The multiple heat exchange tubes insure even distribution of heat within the heat exchange medium and also reduce the temperature of the flue gases considerably during passage through the heat exchange medium.

The burner 37 is a forced air draft burner of conventional type connected to the inlet end of the fire tube assembly. By using a forced draft burner the high stack requirement is eliminated the high stack being necessary to pull a draft for non-forced air draft burners. The burners may be one of several available commercially such as one manufactured and sold by Gordon and Piatt, Inc. A housing 38 provided around the burner prevents blowout by draft or wind. The end doors of the housing are provided with suitable locks so that tampering with the burner is prevented by unauthorized personnel.

The vaporization assembly 40 is designed to provide low tube gas velocities with no liquid gas carry-over, thereby insuring delivery of dry liquefied petroleum gas vapor. Further, the vaporization assembly is designed to be easily removed from the shell of the unit for maintenance. All the components of the vaporization assembly are mounted within a frame 41 which fits into the opening 18 in the forward end 11 of the vessel shell. Details of the vaporization assembly are shown in FIGS. 5 to 8. Referring to FIG. 7 frame 41 of generally rectangular shape is designed to fit through opening 18 and is bolted to the end wall 11. A liquefied petroleum gas inlet manifold 42 is welded to the lower horizontal member of the frame 41 and a vapor outlet manifold 43 welded to the upper horizontal frame member. The two manifolds are innerconnected by an insert 44 welded to insure a water-tight vessel. The frame 41 is bolted in place around the opening 18 of the end wall 11 of the vessel. The manifold 42 is provided with a liquefied petroleum gas inlet 42a. Multiple heat exchange tubes 45 spaced along the length of the lower manifold 42 extend back and forth in multiple pass configuration substantially the full length of the vessel and innerconnect with the upper manifold 43 as shown in FIG. 6. Although eight heat exchange tubes are shown more or less may be provided as necessary. The heat exchange tubes are braced with braces 46 as necessary. Referring to FIG. 6 the exchange tubes 45 connect with manifold 43 at an angle of about 45.degree. (see FIG. 8) with respect to a horizontal plane. This reduces liquid gas carry-over into the upper manifold. By changing the flow direction of the vaporized gas into the manifold liquid gas carry-over is minimized. The upper manifold may be provided with a vapor tap 47. A vapor outlet riser 48 communicates with the upper manifold 43, the vapor riser having a J-shaped configuration as shown in cross-section in FIG. 8. In the upper portion of the vapor outlet riser is disposed a dip tube 49 with the inlet opening 50 thereof facing upwardly. The dip tube extends through the wall of the vapor outlet riser and connects with a gas vapor shut-off valve 51. Gas vapor outlets 52 and 53 are provided in the dip tube, these exits extending through the wall of the vapor outlet riser as shown in FIG. 5. Outlet 52 provides gas vapor to the forced draft burner while outlet 53 connects to float chamber 63a which is also connected to outlet 47. The vapor outlet riser is provided with a threaded opening 56 mounting a relief valve 57. A thermometer opening 58 may be provided in the lower end of the vapor outlet riser.

The multiple heat exchange tubes reduce the gas velocity at the outlet end considerably and substantially reduce liquid gas carryover. Should any liquefied gas be carried through the multiple heat exchange tubes the change of direction as the tubes connect with the outlet manifold discourages liquid carry-over as do the changes of direction of the gas vapor as it passes into the vapor outlet riser and out through the dip tube. The multiple changes of direction due to the angular connection of the heat exchange tubes to the manifold, the configuration of the vapor outlet riser and the dip tube inserted in the riser with its opening facing upwardly prevent liquid carry-over under normal operating conditions. There is thus no necessity for a trap downstream from the unit described. Dry liquefied petroleum gas vapor is delivered for use as needed from startup to full load condition.

OPERATION

Referring to FIG. 3 liquefied petroleum gas enters through pipe 60 from a remote location such as a storage tank or liquid pressure stabilization pump and flows through valve 61. A solenoid valve 62 interlocked with a float switch 63 through conduit 55 prevents liquid gas carry-over into the vapor outlet riser 48. Solenoid valve 62 and float switch 63 are also interlocked with the forced draft burner control as will be described to prevent entry of liquid gas into the vaporization assembly if the burner becomes inoperative. A back check valve 64 in line 65 is provided as shown to allow free flow of liquid gas back to the storage tank when the unit is deactivated or when the load decreases. By-pass valve 66 in line 67 allows liquefied gas to be introduced into manifold 42. Leading from the vapor outlet riser 48 and connected to opening 52 is a liquefied petroleum gas vapor shut-off valve 68 and a primary regulator 69 connected in line with line 70 which extends through the insulation between the inner and outer skin of the shell. Line 70 supplies fuel for the forced air draft burner. A pressure gauge 71 may be provided as shown in FIG. 3 indicating the vapor pressure in the upper manifold 43. Likewise a temperature indicator 72 showing the vapor outlet temperature may be provided in the vapor outlet riser 48 as shown in FIG. 3.

Referring to FIG. 2 illustrating the burner end of the unit, liquefied petroleum gas vapor coming through line 70, passes through a burner fuel supply regulator 73, safety valve 74 and main gas control valve 75 into the gas burner 37. A pilot line 76 leading from the main fuel supply line 70 supplies fuel to the pilot of the burner. An exhaust valve 77 may be provided to exhaust gas vapor. Low liquid level cut-off switches 78 sense the liquid level within the vessel which render the burner inoperative should the level of the heat exchange medium be too low. Reference numerals 79 and 80 refer, respectively, to operating controls which sense the temperature of the heat exchange medium and control operation of the burner accordingly.

The vaporization unit shown in FIG. 1 is generally installed outside of the plant building on a flat concrete pad and the liquefied gas petroleum supply line 60 connected to a source of liquefied petroleum gas from a remote storage tank or other location. Suitable electrical connections are made. The vessel is filled with water containing an appropriate amount of an antifreeze, such as ethylene glycol, through opening 13 until the level is above the vaporization tubes. The unit is then ready for operation. Liquid propane from the storage tank is introduced into inlet line 60. By-pass valve 66 is opened slowly to introduce liquid gas into manifold 42. As soon as normal operation is attained by-pass valve 66 is closed. Normal flow of liquefied gas is through valve 61, solenoid valve 62 and valve 61a. However, since the solenoid valve 62 is interlocked with the burner no fuel can enter the unit until the burner is operative. The pressure gauge 71 will gradually rise as by-pass valve 66 is slowly opened until the pressure is equal to that being delivered from the storage tank. Fuel to the burner is taken off the vapor outlet riser through shutoff valve 68 and regulator 69. Natural vaporization in the multiple vaporization tubes is sufficient to provide sufficient fuel for start-up of the burner. Valve 61 controlling flow of liquefied gas to manifold 43 must be left closed until the entire unit is up to temperature. The valves on the fuel supply line 70 and the pilot valve on the pilot supply line 76 are opened to allow vaporized gas to flow to the burner. The burner is ignited and begins heating the heat exchange medium in the vessel. Controllers 79 and 80 cycle the burner off when the control temperature is reached, generally at about 150.degree. F. The high limit controller is generally set at about 15.degree. above the operating controller. After the unit is up to temperature the shut-off valve 51 on the vapor outlet is slowly opened introducing vapor into a pressure regulator. The pressure regulator is set to the desired output pressure. The unit is then ready for automatic operation and will operate essentially maintenance free. In the event of malfunction of the burner solenoid valve 62 closes preventing further flow of liquefied gas to the vaporization assembly.

Claims

The embodiments of the invention in which a particular property or privilege is claimed are defined as follows:

1. A hydrothermal, immersion type, indirect fired liquefied petroleum gas vaporization system, comprising:

a vessel containing a heat exchange liquid therein at atmospheric pressure,

heating means for heating the heat exchange liquid to a temperature sufficient to vaporize the liquefied petroleum gas;

an integral vaporizer assembly immersed in the heat exchange liquid for vaporizing the liquefied petroleum gas, the vaporizer assembly including (1) an inlet manifold having a liquefied petroleum gas inlet therein, (2) an outlet manifold having a liquefied petroleum gas vapor outlet therein, ( (3) multiple heat exchange tubes interconnecting the inlet and outlet manifolds, the tubes immersed in the heat exchange liquid, the multiple heat exchange tubes resulting in lowering of the velocity of the exit gas vapor into the outlet manifold and substantially preventing liquid gas carry-over.

2. The system of claim 1 wherein the multiple heat exchange tubes are connected to the lower side of the outlet manifold at an angle of about 45.degree. with respect to the horizontal plane and wherein the gas vapor outlet of the manifold is connected to a vapor outlet riser which curves upwardly from its connection to the vapor outlet manifold, the vapor outlet riser having a dip pipe disposed in the upper portion thereof having an open gas vapor inlet facing upwardly opposite the direction of flow of the gas vapor, the dip pipe having a gas vapor outlet extending through the body of the riser; the configuration of the vapor outlet riser, the multiple heat exchange tubes, angular connection of the multiple tubes to the vapor outlet manifold, and the disposition of the dip pipe in the riser preventing liquid gas carry-over.

3. The system of claim 1 wherein the heating means includes (1) a fire tube immersed in the heat exchange liquid having an inlet end extending through the vessel wall and an outlet end extending through the upper shell, (2) a forced draft power burner connected to to the inlet end of the fire tube, the burner providing hot combustion gases passing through the fire tube for transfer of heat to the heat exchange liquid, the hot combustion gases passing through the tube outlet into the atmosphere at lower temperature.

4. The system of claim 2 wherein the inlet and outlet manifolds are secured to a frame member serving as a portion of the sidewall of the vessel, the vaporizer assembly being removable for maintenance and replacement.

5. The system of claim 2 including means connecting the gas vapor outlet of the dip tube with the forced air draft burner for supplying fuel to the burner.

6. A hydrothermal immersion-type indirect fired liquefied petroleum gas vaporization system, comprising:

an insulated cylindrical vessel having a burner end wall and vapor outlet end wall and containing a heat exchange liquid therein atmospheric pressure,

a fire tube immersed in the heat exchange liquid having an inlet and extending through the burner end wall and an outlet end extending through an opening in the upper cylindrical shell,

a forced draft power burner connected to the inlet end of the fire tube, the burner providing hot combustion gases passing through the fire tube for transfer of heat to the heat exchange liquid and thereafter passing through the outlet end of the fire tube into the atmosphere at lower temperature,

an integral vaporizer assembly immersed in the heat exchange liquid for vaporizing liquefied petroleum gas including (1) a frame member adapted to be secured in an opening in the vapor outlet end wall of the vessel, (2) an inlet manifold having a liquefied petroleum gas inlet therein secured to the lower portion of the frame member, (3) an outlet manifold having a liquefied petroleum gas vapor outlet therein secured to the upper portion of the manifold, (4) multiple heat exchange tubes interconnecting the inlet and outlet manifolds, the tubes extending substantially the length of the cylindrical vessel in a multiple pass configuration and immersed entirely in the heat exchange liquid, the heat exchange tubes connected to the lower side of the outlet manifold at an angle of about45.degree. with respect to a horizontal plane, (5) a vapor outlet riser having a J-configuration secured to the gas vapor outlet of the outlet manifold, (6) a dip pipe disposed in the upper portion of the vapor outlet riser having a gas vapor inlet facing upwardly opposite the direction of flow of the gas vapor, the dip pipe having a gas vapor outlet extending through the body of the vapor outlet riser, and

control means controlling the temperature of the heat exchange liquid.