FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2006
COMPLETE
Specification
(See Section 10 and Rule 13)
A WATER HEATER AND SYSTEM THEREOF
THERMAX LIMITED
an Indian Company
of D-13, MIDC Industrial Area, R.D. Aga Road,
Chinchwad, Pune -19,
Maharashtra, India
Inventors: a) Jha R.S., b) Kharat Rahul, c) Mane Abhay, d) Prajeendran C.P.
The following specification particularly describes the invention and the mariner in which it is to be performed.

FIELD OF INVENTION
The present invention relates to the field of water heater systems.
DEFINITIONS OF TERMS USED IN THE SPECIFICATION
The term "natural convection circulation" used in the specification means the circulation caused by density gradient in conjunction with gravitational field, which causes a less dense fluid (hot fluid) to rise above a more dense fluid (cold fluid).
BACKGROUND
Many industrial processes require hot water at 140 - 180 °C for various heating applications. The hot water is to be maintained under pressure to avoid boiling or steam formation, as the boiling point of water is 100 °C at atmospheric pressure. An external expansion tank is generally provided for this purpose, where, by using inert gases like nitrogen, the hot water is pressurized. The expansion tank also provides space for the volumetric expansion of water after being heated to such high temperature. Such a system is costly, complex, bulky, and involves a high operating cost. Some of these problems can be alleviated by providing a steam pressurization system; typically, the system comprises a fire tube boiler with a drum including convective tubes, furnace and an expansion space for hot water and steam.
However, one of the major problems associated with such configurations, is that, the hot water generated in the boiler is present at the saturation

pressure, once discharged, there is a high possibility of the hot water becoming steam, especially during transportation, which will hamper a smooth and continuous flow of hot water to the process operation. Further, a stream comprising a mixture of water and steam causes a higher pressure drop across the supply line, resulting in increased pumping costs. Where, in a conventional system, a circulation pump is positioned before the boiler to pump cold water thereto; in this situation, to overcome the flow resistance, the circulation pump can be positioned at the outlet of the boiler, to raise the water pressure. When the pressure at the outlet of the circulation pump, is maintained, equal to or higher than the saturation pressure, phase change in the hot water can be prevented. However, for such application, the circulation pump must be adapted to handle hot water at saturation level, which will substantially increase the capital and operating costs of the system.
Several attempts have been made to provide water heater systems which overcome one or more of the drawbacks listed above. Some of the disclosures are listed in the prior art below:
US3226300A discloses a pressurized water reactor with integral steam generator and a self-pressurized primary system. The reactor assembly comprises a core of fissionable fuel, a cylindrical shell, and a top head, wherein, the core, comprising a large number of tubes for passing a primary coolant there through for heating by the fission, is operated under self-pressurization due to a steam space formed above water level, as the mean temperature of the water above an core outlet, at steady state, remains equal

to the saturation temperature. The water heating system as disclosed in US3226300A is complex and primarily developed for nuclear application.
US 2903187 discloses a system to generate hot water using an external drum and steam generator. The cold water received from the process is mixed with steam received from steam generator in external drum to produce hot water at saturation pressure. The circulation pump is kept at the outlet of external drum to eliminate the possibility of vapor formation before reaching to the process heat exchanger. The water heating system disclosed in US2903187 is a complex system and requires an additional drum. Further, the system also requires a circulation pump at the outlet of the drum, which is adapted to handle high temperature water.
The heaters disclosed in the prior art above have a complex construction and do not singly overcome all the listed drawbacks like phase change, higher cost and higher circulation power. The present invention, therefore, aims at providing a water heater and system thereof, which has a simple construction, is compact, and can be used for heating water for large, medium or small scale, industrial process applications.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a water heater and system thereof for large and small scale industrial water heating applications.
Another object of the present invention is to provide a water heater which has a simple construction.

Still another object of the present invention is to provide a water heater working on self pressurization due to the steam generated in the shell and occupied in the expansion space, therefore, does not need any external pressurization device using inert gases.
Yet another object of the present invention is to provide a water heater system which prevents phase change in high pressure hot water leaving the water heater.
One more object of the present invention is to provide a water heater system which prevents considerable pressure drop in hot water leaving the water heater.
Still one more object of the present invention is to provide a water heater system which is compact.
Yet one more object of the present invention is to provide a water heater system which is efficient.
SUMMARY OF THE INVENTION
In accordance with the present invention, is provided a water heater
comprising:
■ a fired water heater having: a combustor adapted to burn a fuel, a furnace adapted to form an enclosure around the flames emanating from said combustor, a set of convective tubes

comprising a first subset of convective tubes and a second subset of convective tubes for conveying hot flue gases, wherein, an internal reversal chamber is provided to operatively connect said furnace and said first subset of convective tubes and an external reversal chamber is provided to operatively connect said first subset of convective tubes and said second subset of convective tubes, and a shell adapted to enclose said combustor, said furnace, said set of convective tubes and said internal reversal chamber, wherein, an expansion space is provided at the operative top of said shell to provide steam space thereby allowing self pressurization and providing space for thermal expansion;
■ an interchanger provided in operative communication with said fired water heater to receive hot water at saturation temperature and adapted to prevent any phase change in the hot water, said interchanger being adapted to receive cold water there through to reduce the temperature of the hot water below saturation level, to provide partly heated water to be conveyed to said fired water heater and hot water below saturation temperature;
■ a circulation circuit comprising said fired water heater, said interchanger, a process heat exchanger, and a circulation pump;
■ said circulation pump adapted to overcome any pressure loss in said circulation circuit.
Typically, in accordance with the present invention, said furnace is provided for the combustion of fuel and for enclosing flames emanating from combustion of the fuel.

Preferably, in accordance with the present invention, an internal reversal chamber is provided between said combustor and said set of convective tubes.
Typically, in accordance with the present invention, operative bottom of said shell is filled with water, wherein, the water level is maintained above said furnace, said internal reversal chamber, and said set of convective tubes.
Preferably, in accordance with the present invention, the water temperature is controlled by controlling the water pressure of the water heater.
Typically, in accordance with the present invention, the water pressure is controlled by a pressure transmitter and a PID controller.
Preferably, in accordance with the present invention, the fuel firing is switched off and switched on by providing a pressure switch and the pressure is relieved after attainment of the maximum limiting pressure by providing a safety valve.
Typically, in accordance with the present invention, said interchanger is adapted to reduce the hot water temperature below the saturation level by transferring heat to the cold water which is subsequently conveyed to said water heater.
Preferably, in accordance with the present invention, said interchanger comprises a two-pipe configuration having an inner pipe which traverses the

hot water at saturation temperature to provide hot water below saturation temperature.
In accordance with the present invention, is disclosed a water heater system comprising a circulation circuit, said circulation circuit comprising:
■ a first conduit for conveying cold water;
■ pumping means operatively connected to said first conduit for pressurizing the cold water;
■ a fired water heater operatively connected to be in communication with said pumping means for receiving pressurized cold water, said water heater being adapted to heat the pressurized cold water for providing hot water at saturation pressure;
■ a second conduit for conveying the hot water at saturation pressure;
■ wherein, a heat exchanger is operatively connected to said second conduit to be in communication with said water heater for receiving the hot water at saturation pressure, said heat exchanger being adapted to cool the hot water below saturation temperature; and
■ a process heat exchanger adapted to receive the hot water below saturation temperature to transfer heat there from to a process fluid.
In accordance with the present invention, is disclosed a method for providing hot water, said method comprising the following steps:
■ combusting a fuel in a combustor to generate hot flue gases;

■ supplying water to a shell, wherein, the water pressure is adjusted depending on the water temperature requirement;
■ circulating the hot flue gases through a set of convective tubes enclosed in said shell parallel to the operative longitudinal axis;
■ heating the water by hot flue gases to provide hot water at saturation pressure;
■ allowing an expansion space for steam and the hot water at saturation pressure at the operative top of the said shell;
■ discharging the hot water at saturation temperature from said shell;
■ cooling the hot water at saturation temperature in an interchanger by transferring heat to cold water received therein from a process heat exchanger, to obtain hot water below saturation temperature;
■ circulating the hot water below saturation temperature to the process heat exchanger to transfer heat there from to a process fluid and become cold water; and
• pumping the cold water to said interchanger to receive heat from the hot water at saturation temperature before being conveyed to said water heater.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described with the help of the accompanying drawings, in which,

Figure 1 illustrates a cross-section of the preferred embodiment of the water heater, in accordance with the present invention;
Figure 2 illustrates a schematic of the preferred embodiment of the water heater system, in accordance with the present invention; and
Figure 3 illustrates a schematic of the preferred embodiment of the heat exchanger in the water heater system, in accordance with the present invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described with reference to the accompanying drawings which do not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.
The present invention envisages a modified layout of a water heater and system thereof, which has a simple construction and fewer components, thus, making the system easy to work and maintain. The system of the present invention is adapted to use steam pressurization to maintain the water pressure at the saturation level so as to eliminate steam vapors in the hot water outlet line. Due to the self pressurization of the water heater by using steam and expansion within boiler steam space, the system eliminates the requirement for any external expansion tank or pressurization system. But in this system, even a small pressure drop can decrease the water pressure below the saturation level, which will cause vapor formation

resulting in a higher pressure drop and flow inconsistency. To overcome this drawback, an interchanger is introduced which reduces the water temperature below the saturation level to eliminate the probability of any vapor formation. These and other benefits of the water heater and the water heater system of the present invention will be apparent from the description provided here below.
The water heater of the present invention primarily comprises: a combustor or a furnace located at an operatively lowest level for providing hot flue gases; at least one set of convective tubes arranged at a level operatively above the combustor for receiving the hot flue gases; and a closed tubular shell or drum having: a operative bottom section for receiving pressurized water, the first section enclosing the set of tubes, wherein, the set of tubes is arranged parallel to the operative longitudinal axis to be in contact with the pressurized water, being adapted for heating and boiling the pressurized water, by the hot flue gases, at saturation pressure; and a top section located operatively above the first section in the shell, being adapted to be in communication with the first shell for providing an expansion space for steam and boiled water at saturation pressure.
Figure 1 illustrates a cross-section of the water heater in accordance with the present invention, generally represented by numeral 100. Referring to Figure 1, a furnace 102 is located at the lower most level for combusting a fuel selected from coal, wood, husk, biomass, and the like. The hot flue gases generated in the furnace 102 are communicated to at least one set of convective tubes 104, via an internal reversal chamber 124 integrated in the shell 106 between the combustor 102 and the set of convective tubes 104, to

provide heated water at saturation pressure by absorbing heat from the hot flue gases. The shell 106 typically having a closed tubular structure with a cross-section selected from circular, ovular, elliptical, rectangular, polygonal, and the like, is located around the furnace 102. The set of convective tubes 104 is placed sufficiently below the water level to eliminate any over heating of tube or tube plate. The shell 106 is divided in two parts with operative bottom section 108 filled with water and operative top section 114 for steam storage and water expansion.
In the preferred embodiment 100, the set of tubes 104 comprise a first subset of tubes 110 and a second subset of tubes 112. The first subset of tubes 110, positioned proximal to the furnace 102, receives the hot flue gases from the furnace 102 via an internal reversal chamber 124 provided there between. The pressurized water received in the shell 106, gains heat from the hot flue gases passing through the furnace 102 and first subset of tubes 110. The partly cooled flue gases are then communicated through the second subset of tubes 112, positioned above the first subset of tubes 110 via an external reversal chamber 128 provided between the first subset of tubes 110 and the second subset of tubes 112 along the operative exterior wall of the shell 106. The heated pressurized water, contained in the shell 106, gets further heated by absorbing heat from the partly cooled flue gases passed through the second subset of tubes 112. The set of tubes 104 is connected to a flue gas outlet at the other operative end for discharging the cooled flue gases. In the preferred embodiment 100, the cooled flue gases after passing through the second subset of tubes 112 are discharged via the flue gas outlet (not shown in Figure) provided in communication with the operative end of the second subset of tubes 112.

As the water is heated, it expands and second section 114 located towards the operative top of the shell 106 provides the space for expansion. Initially the water in the boiler is at atmospheric pressure, when the hot water reaches to the saturation temperature after heating, the steam generation takes place and occupies the empty space provided for expansion. This causes an increase in the boiler pressure and the water in the boiler always remains at the saturation temperature corresponding to boiler pressure. The water outlet temperature is controlled by the controlling boiler pressure. The boiler pressure is controlled by controlling fuel firing rate using pressure transmitter and PID controller. The minimum and maximum pressure is controlled by using pressure switches. If the pressure reaches beyond a set pressure limit, the fuel firing in the water heater is switched off. As the heat is taken out by the process, the water heater pressure starts decreasing and falls below the set lower limit. The fuel firing is again switched on. If the pressure reached beyond the specified limiting pressure, the safety valve 118 opens up to relieve water heater pressure.
Figure 2 illustrates a schematic of the water heater system in accordance with the present invention, generally represented by numeral 200. A first conduit 202 is provided in communication with a process heat exchanger 210 to receive the hot water having temperature in the range of 120 - 170 °C there from. The hot water is converted to the relatively cold water by transferring heat to the process fluid in process heat exchanger. The cold water, conveyed via the first conduit 202, is pressurized by passing through pumping means 204 which is a circulation pump, to a pressure to overcome the pressure loss in the circulation circuit. The pressurized water is then fed

to the water heater 100 as disclosed in Figure 1, at the inlet means 120, for being heated. An interchanger, referred to as heat exchanger and represented generally by numeral 208, is positioned between the outlet of the pumping means 204 and the inlet means 120 of the water heater 100. The pressurized water, from the pumping means 204 is circulated through the heat exchanger 208, where the pressurized cold water absorbs heat from the hot water discharged at the saturation temperature from the water heater 100, to become partly heated. The water heater 100 is adapted to provide hot water at saturation pressure having temperature in the range of 130 - 180 °C, which is discharged from the outlet means 122 provided at the operative bottom of the shell 106 via a second conduit 206. The temperature of the hot water at saturation pressure is just slightly reduced, by passing through the heat exchanger 208, so as to bring the hot water below saturation pressure, before feeding the hot water to the process heat exchanger 210. Thus, the heat exchanger 208 is primarily provided to cool the hot water at saturation pressure, by exchanging heat with the ingoing pressurized cold water to the water heater 100, such that, the hot water so obtained has a temperature in the range of 120 - 170 °C and pressure above the saturation level, to be used for various process applications in the process heat exchanger-210.
A preferred embodiment of the heat exchanger 208 is illustrated in Figure 3, wherein heat exchanger 208 is a double pipe heat exchanger comprising an inner pipe 214 and an outer pipe 212. The inner pipe 214 is operatively connected to the outlet means 122 of the water heater 100 via the second conduit 206 at a first inlet 216 to receive the hot water at saturation pressure and the process heat exchanger 210 at a first outlet 218 to provide the hot water below saturation temperature thereto. The outer pipe 212 is

operatively connected to the outlet of the pumping means 204 at a second inlet 220 to receive the pressurized cold water and the inlet means 120 of the water heater 100 at a second outlet 222 to provide partly heated pressurized water to the water heater. The hot water at saturation pressure, conveyed through the second conduit 206, after passing through the heat exchanger 208, can be conveniently fed to the process heat exchanger 210. The process, as discussed above, prevents any phase change in the hot water leaving the water heater 100, as the water exiting from the interchanger 208 is well below the saturation temperature required for the boiling. Further, the heat exchanger 208 uses a two-pipe construction to prevent a drastic pressure drop in the hot water conveyed to process heat exchanger 210. Therefore, the temperature of the hot water exiting the water heater 100 is higher so as to consider the heat transfer to the cold water in the heat exchanger 208. The hot water exiting the heat exchanger 208 sufficiently provides the requirement in the process heat exchanger 210, wherein after rejecting heat in the process heat exchanger 210, the cold water is sent to the pumping means 204 via the first conduit 202. The water heater 100 is provided with the safety valve 118 (shown in Figure 2) for reliving the high pressure conditions within the water heater 100 and pressure transmitter (not shown in Figure) and pressure switches (not shown in Figure) for controlling water pressure in the water heater. The flue gas outlet, illustrated by numeral 116 in Figure 2, provides for venting the air during the starting of water heater.
TECHNICAL ADVANTAGES
A water heater and system thereof for large and small scale industrial water heating applications, the water heater comprising: a combustor or furnace for

providing hot flue gases, a closed tubular shell or drum containing pressurized water, and at least one set of convective tubes enclosed in the shell adapted to transfer heat from the hot flue gases to the water, to provide hot water at saturation pressure, wherein, expansion space is provided within the shell for steam and the hot water at saturation pressure, further, the system comprises a heat exchanger or interchanger installed between pumping means and the water heater to only sufficiently reduce the temperature of the hot water such that the temperature is below saturation level; as described in the present invention has several technical advantages including but not limited to the realization of:
• the water heater system has a simple construction with fewer components, thus, the system is easy to work and maintain;
• the water heater system works on self pressurization and does not need any external pressurization device using inert gases;
• the water heater system is adapted to prevent any phase change in the hot water at saturation pressure, after exiting the water heater, by providing a heat exchanger which sufficiently reduces the temperature below the saturation level; and
• the water heater system is compact and efficient.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.

In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only. While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principle of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We Claim:
1. A water heater apparatus comprising:
■ a fired water heater having: a combustor adapted to burn a fuel, a furnace adapted to form an enclosure around the flames emanating from said combustor, a set of convective tubes comprising a first subset of convective tubes and a second subset of convective tubes for conveying hot flue gases, wherein, an internal reversal chamber is provided to operatively connect said furnace and said first subset of convective tubes and an external reversal chamber is provided to operatively connect said first subset of convective tubes and said second subset of convective tubes, and a shell adapted to enclose said combustor, said furnace, said set of convective tubes and said internal reversal chamber, wherein, an expansion space is provided at the operative top of said shell to provide steam space thereby allowing self pressurization and providing space for thermal expansion;
■ an interchanger provided in operative communication with said fired water heater to receive hot water at saturation temperature and adapted to prevent any phase change in the hot water, said interchanger being adapted to receive cold water there through to reduce the temperature of the hot water below saturation level, to provide partly heated water to be conveyed to said fired water heater and hot water below saturation temperature;
■ a circulation circuit comprising said fired water heater, said interchanger, a process heat exchanger, and a circulation pump;

■ said circulation pump adapted to overcome any pressure loss in said circulation circuit.
2. The water heater apparatus as claimed in claim 1, wherein said furnace is provided for the combustion of fuel and for enclosing flames emanating from combustion of the fuel.
3. The water heater apparatus as claimed in claim 1, wherein an internal reversal chamber is provided between said combustor and said set of convective tubes.
4. The water heater apparatus as claimed in claim 1, wherein operative bottom of said shell is filled with water, wherein, the water level is maintained above said furnace, said internal reversal chamber, and said set of convective tubes.
5. The water heater apparatus as claimed in claim 1, wherein the water temperature is controlled by controlling the water pressure of the water heater.
6. The water heater apparatus as claimed in claim 5, wherein the water pressure is controlled by a pressure transmitter and a PID controller.
7. The water heater apparatus as claimed in claim 5, wherein the fuel firing is switched off and switched on by providing a pressure switch and the pressure is relieved after attainment of the maximum limiting pressure by providing a safety valve.

8. The water heater apparatus as claimed in claim 1, wherein said interchanger is adapted to reduce the hot water temperature below the saturation level by transferring heat to the cold water which is subsequently conveyed to said water heater.
9. The water heater apparatus as claimed in claim 8, wherein said interchanger comprises a two-pipe configuration having an inner pipe which traverses the hot water at saturation temperature to provide hot water below saturation temperature.
10.A water heater system comprising a circulation circuit, said circulation circuit comprising:
■ a first conduit for conveying cold water;
■ pumping means operatively connected to said first conduit for pressurizing the cold water;
■ a fired water heater operatively connected to be in communication with said pumping means for receiving pressurized cold water, said water heater being adapted to heat the pressurized cold water for providing hot water at saturation pressure;
■ a second conduit for conveying the hot water at saturation pressure;
■ wherein, a heat exchanger is operatively connected to said second conduit to be in communication with said water heater for receiving the hot water at saturation pressure, said heat

exchanger being adapted to cool the hot water below saturation temperature; and
■ a process heat exchanger adapted to receive the hot water below
saturation temperature to transfer heat there from to a process
fluid.
11.A method for providing hot water, said method comprising the following steps:
■ combusting a fuel in a combustor to generate hot flue gases;
■ supplying water to a shell, wherein, the water pressure is adjusted depending on the water temperature requirement;
■ circulating the hot flue gases through a set of convective tubes enclosed in said shell parallel to the operative longitudinal axis;
■ heating the water by hot flue gases to provide hot water at saturation pressure;
■ allowing an expansion space for steam and the hot water at saturation pressure at the operative top of the said shell;
■ discharging the hot water at saturation temperature from said shell;
■ cooling the hot water at saturation temperature in an interchanger by transferring heat to cold water received therein from a process heat exchanger, to obtain hot water below saturation temperature;
■ circulating the hot water below saturation temperature to the process heat exchanger to transfer heat there from to a process fluid and become cold water; and

■ pumping the cold water to said interchanger to receive heat from the hot water at saturation temperature before being conveyed to said water heater.