FIELD OF THE INVENTION
The present invention relates to solar thermal system for vaporizing liquefied petroleum gas and more particularly, a system for converting liquid form of liquefied petroleum gas stored in liquefied petroleum gas tanks into gaseous form for use in industrial heat treatment furnaces through recuperative heat exchange between water heated by solar water heater and liquefied petroleum gas.
BACKGROUND OF THE INVENTION
The engineering industries use various alloys of steel as raw materials for their products. Any productive operation like cutting, welding, cold and hot forming etc. results in the deformation of material structures. This results in the loss of mechanical strength. In order to regain the lost mechanical strength of steels, various heat treatment processes are carried out. Stress relieving, normalizing, solution annealing etc. are the different types of heat treatment activities according to the materials and applications. Heat treatment of steels are carried out in furnaces designed for the application temperatures. These furnaces burn fuel in order to raise the temperatures to the required levels. Fuels used for heat treatment application can be like electricity, liquefied petroleum gas (LPG), coal-gas, fuel oil etc. LPG is stored in high pressure metallic containers to ensure safer transport and storage. However, the furnaces are designed to burn only gaseous form of LPG.

Gasification of LPG (conversion from liquid to gas) is traditionally carried out using LPG vaporizer. The vaporizers heat fluids to temperatures in excess of 60 °C. LPG is fed into this hot fluid bath inside curling tubes and gets converted to gaseous LPG by way of recuperative heat transfer. Gasified LPG is then fed to furnaces as fuel for the heat treatment processes.
In the prior art, the water bath for LPG gasification is heated by electrical methods. Electric vaporizers employ resistance heaters which are directly immersed in water bath to heat the water bath which in turn, heats the liquid LPG to vaporize the same. In the US Patent Nos. US2775683 and US4255646A, and in Chinese Patent No.CN203500839 U, the inventors have disclosed methods of LPG gasification by heating the water bath using electrical coils immersed in within. Electric heating of liquefied petroleum gas described by the above reference creates a safety hazard. Any mishandling or malfunction of the heating element or a puncture/ crack in the metal tubes carrying the LPG will lead to major fire explosions.
On the other hand, solar thermal systems are capable of heating water to temperatures more than 65 degree Celsius under normal sunshine. In tropical countries, these temperatures will be much higher and the sunshine will be available throughout the year. The hot water shall be directly fed into the LPG vaporizer chamber for LPG gasification.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to develop a solar water heating system using thermosiphon process for gasification of LPG.
Yet another objective of the invention is to develop a solar water heating system using thermo siphon process for gasification of LPG which ensures total safety in the said process by eliminating electric elements which can cause risk of fire or fire explosion when contacted with the highly flammable LPG.
SUMMARY OF THE INVENTION
In this apparatus, hot water in excess of 60°C temperatures is fed into the water bath inside the vaporizer for gasification of LPG. Cold water in a steel tank is circulated through solar collector panels inside copper tubes curled into circuitous coils. Heat energy from the sun is transferred to the water by the greenhouse effect and black-body absorption. Convection allows for the movement of the heated liquid out of the solar collector to be replaced by colder liquid which is in turn heated. Due to this principle, it is necessary for the water to be stored in a tank above the collector. Hot water obtained at the outlet of these panels is then fed into the water bath inside the vaporizers.
Inside the vaporizer, coils of hollow tubes are immersed in water. LPG is circulated inside these coils. Hot water from the apparatus is fed into the vaporizer from the top.

Cold water from the bottom of the bath is pumped out to storage tank using an electrically operated pump. Thermal energy from the hot water is transferred to coils and in turn the LPG inside them via recuperative heat transfer. LPG absorbs the heat from the water and is converted into its gaseous form. This gas is then supplied via dedicated pipelines to the heat treatment furnaces in the industry.
Thus the apparatus provides safe and efficient gasification of LPG for use as fuel in heat treatment furnaces of industries.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows the thermosiphon principle of solar water heating system.
Figure 2 shows the schematic of the apparatus with solar collectors and vaporizer
assembly.
Figure 3 shows the operation of the proposed system in conjunction with the LPG storage
facility and heat treatment furnace.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Figure 1 shows the thermosiphon principle of solar water heating system used in the embodiment. The entire solar water heating assembly is mounted on an inclined stand [1]. The angle of inclination generally corresponds to the latitude of the location which ensures that the sun’s ray are almost always perpendicular to the collector surface. The storage tank or separator [2] in the form of a cylinder is mounted on the higher end of inclined stand [1]. This arrangement ensures that proper convection occurs.

A semi-circular fillet or mount [3] keeps the separator [2] horizontally balanced. The separator [2] consists of two concentric vessels made of stainless steel. Polyurethane Foam (PUF) [4] is provided as thermal insulation between the inner [5] and outer [6] vessels. The separator [2] is initially filled with cold water from an external source. Cold water is then taken out from the bottom via pipelines [7] and fed into the lower section of the solar collector [8]. The cold water traverses through the solar collector [8] and gradually gets heated from solar thermal energy. During this heat transfer process, cold water [9] is present at the entry levels of the collector [8]. As the water gradually absorbs heat from the sun, it becomes medium hot water [10] and moves higher up the collector tubes. With further influx of heat from the sun’s rays, the medium hot water [10] further gets heated up to become hot water [11]. This hot water [11] is present at the top portion of the collector [8] inclination. The hot water [11] is then poured again into the separator [2] where it stays above the cold water due to convection. It is taken out via another set of pipelines [12] to the next stage. The hot water pipelines [12] are insulated for safety.
Figure 2 shows the schematic of the apparatus with solar collectors and vaporizer assembly. Cold water is stored in overhead storage tanks [13]. The tank is replenished with water from an external source via pipelines [14]. The overhead tank [13] fills the separator [2] with cold water through a different set of pipeline [15]. The solar water heating system consists of 4 interconnected flat-plate collectors [8].

The interior of the collectors [8] have two horizontal pipes at the top and bottom, called headers [16], and many smaller vertical pipes connecting them, called risers [17]. The exterior of these tubes are coated with black color to ensure that more heat is absorbed. The top and bottom headers [16] of each collector [8] are connected to the next. The header [16] and riser [17] assembly of the collector [8] are topped with a glass frame [18]. The type of glass used in flat plate collectors is almost always low-iron, tempered glass. The glass top [18] ensures that the heat from the sun is retained inside the box due to greenhouse effect. The cold water from the separator [2] is fed to the bottom entry point [19] of the first collector [8] through [7]. Hot water accumulating at the top header [16] is then drained from the top exit point [20] of the fourth collector [8] into the top portion of the separator [2]. Upon sufficient exposure to sunlight, the top part of the separator [2] is now filled with hot water in excess of 60 °C. This hot water is then fed to the vaporizer [22] via another set of insulated pipelines [21]. A water pump [23] is provided to pump out cold water from inside the vaporizer and pour into the reservoir.
Figure 3 shows the operation of the proposed embodiment in the fuel delivery system for furnaces. LPG is stored in two pressurized storage tanks [24]. Separate pipelines [25] are provided at the bottom of the tanks [24] to pump out the LPG. These individual lines [25] are then fed to common header [26] which neutralizes pressure difference between both the lines, if any. From the header [26], LPG moves to the vaporizing area via [27] where

another infeed header [28] feeds into a set of 4 vaporizers [22]. Vaporizer [22] consists of a water bath which holds the hot water. Hollow tubes inside the bath carry the LPG for gasification. The proposed embodiment comprising of separator [2] and flat-plate solar collectors [8] fill the four vaporizers with hot water at temperatures over 60°C. The hot water is poured into the vaporizers [22] through an insulated common header [28]. From the header [28], individual sets of pipelines [29] connect the header [28] to the vaporizer [22]. The LPG is fed into the hot water bath inside the vaporizer [22] from the bottom. Due to the process of recuperative heat transfer between the hot water and LPG, the LPG gets gasified. Gaseous form of LPG is then taken out from the vaporizers [22] through a common header [30]. The outlet pipeline [31] of the vaporizer [22] which connects to the header [30] is pressure regulated by a solenoid valve. The opening and closing of the solenoid valve ensures that the required pressure is maintained in the delivery header [30]. From the delivery header [30], the gaseous LPG is sent to the factory premises through a dedicated pipeline [32]. This LPG is then utilized as fuel for heat treatment furnaces [33] which carry out various processes like stress relieving, normalizing, tempering, solution annealing etc. on cold-formed alloy steel materials [34].
WE CLAIM
1. A solar water heating system using thermosiphon process for gasification of LPG
comprising:
a separator [2] receiving cold water from storage tank [13] through pipe [15], the said separator [2] connected with plurality of interconnected flat plate solar collectors [8] where cold water is heated by solar energy, the interior of the said plurality of collectors [8] having two horizontal pipes at the top and bottom called headers [16] and many smaller vertical pipes connecting them called risers [17]; top header [16] at top exit point [20] of fourth collector [8] connected to the separator [2] for supplying hot water to the separator [2] through pipe [12] from which it is sent to the plurality of vaporizers [22] via a set of insulated pipelines [21];
a pair of pressurized storage tanks [24] for storing LPG, the said storage tanks [24] connected to header [26] via separate pipelines [25] for neutralizing the pressure difference of LPG wherein the outlet of the header [26] connected
to the vaporizer [22] for supplying LPG where the hot water from the separator [2] and through the header [28] and individual sets of pipeline [29] entering the vaporizers [22] from the top transferring heat to the LPG which is entering the vaporizers [22] from bottom via [27], thus converting the LPG into gaseous state for further use in the furnace.

2. The solar water heating system as claimed in claim 1, wherein the interior of the solar collectors have two horizontal pipes at top and bottom called headers [16] and plurality of smaller diameter vertical pipes connecting them called risers [17] wherein the top and bottom headers [16] connected to the next.
3. The solar water heating system as claimed in claim 2, wherein the header [16] and riser [17] assembly of solar collector [8] are topped with a glass frame [18] to ensure retaining of the solar energy inside the enclosure due to green house affect.
4. The solar water heating system as claimed in claim 3, wherein the exterior of the headers [16] and risers [17] tubes are coated with black paint for absorption of heat from solar energy.

5. The solar water heating system as claimed in claim 1, wherein a pump [23] is provided for supplying cold water from inside the vaporizer [22] to the reservoir/overhead storage tank [13].
6. The solar heating system as claimed in claim 1, wherein the outlet pipeline [31] of the vaporizer [22] is pressure regulated by a solenoid value.