FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2006
COMPLETE
Specification
(See Section 10 and Rule 13) A STEAM BOILER SYSTEM FOR AIR HEATING APPLICATIONS
THERMAX LIMITED
an Indian Company
of D-13, MIDC Industrial Area, R.D. Aga Road,
Chinchwad, Pune -19,
Maharashtra, India
The following specification particularly describes the invention and the manner in which
it is to be performed.

FIELD OF THE INVENTION
The present invention relates to the field of heating systems.
BACKGROUND OF THE INVENTION & PRIOR ART
Hot air is used for industrial applications including heating, drying, dehumidifying, desiccating and disinfecting in process industries, manufacturing units, food processing units and the like. The heating systems used for obtaining the hot air typically consist of a steam boiler and a steam radiator.
Steam is generated in a steam boiler at the required pressure and passed through a steam radiator, where steam is condensed and the latent heat of the steam is transferred to the cold air. The condensate comes out of steam radiator through steam traps and is collected in a flash tank. A significant quantity of steam is flashed as the condensate water can not remain at a temperature higher than the saturation temperature corresponding to flash tank pressure. There is no appropriate system for the recovery of this flash steam and this is mainly lost to the atmosphere.
FIGURE 1 illustrates the schematic diagram of a conventional steam boiler system for air heating application, referred in FIGURE 1 by numeral 100. The system 100 primarily consists of a steam boiler 102 with a smoke chamber 104 having a flue gas outlet 108, and a steam radiator 110 to transfer the heat of steam from the boiler 102 to cold air received therein. The boiler 102 and the steam radiator 110 are connected by a steam pipe 114 provided with a steam stop valve 112. The steam generated in the boiler 102 is transferred to the steam radiator 110 through the steam pipe 114. Cold air

enters the steam radiator 110 through a cold air inlet 116 and exits from a hot air outlet 118. The steam condenses in the steam radiator 110 and transfer heat to the cold air. Condensed water leaves the steam radiator 110 through a steam trap 120 at saturation temperature corresponding to steam pressure in steam radiator 110. The condensed water is collected in a flash tank 122. As the pressure in the flash tank 122 is maintained below the steam pressure in the steam radiator 110, a significant quantity of water is flashed into steam. The condensate collected in the flash tank 122 is pumped to a feed water tank 124 by using a condensate pump 128, which is finally fed to the boiler 102 by a feed water pump 126. The feed water enters the boiler 102 through a feed water inlet pipe 106. The system 100 is less efficient due to flash steam loss and higher flue gas temperature.
Several attempts have been made to design heating systems; some of the related systems are discussed in the following section dealing with the prior art.
US Patent No. 3572588 discloses a trapless condensate and heat recovery system provided with a common condensate recovery tank to collect the condensate from a plurality of heat exchangers which are arranged in parallel. The system as disclosed in US3572588 does not require a steam trap and the. condensate from the plurality of heat exchangers directly flow to the condensate recovery tank due to difference in pressure. The condensate flashes in to steam due to reduction in pressure. This flash steam is transferred to the make up water tank and regulated based on pressure in condensate recovery tank. The condensate recovery tank is connected with make up water tank and de-aerator tank regulates the steam quantity based

on water level in condensate recovery tank. This system cannot work if there is not a significant quantity of make up water to provide as heat sink.
US Patent No. 4304197 discloses a condensate recovery system for a steam apparatus wherein a condensate receiver is provided between a boiler and a feed water pump of a feed water means. The condensate stored in the condensate receiver is fed to the boiler for vaporizing, when the boiler is not in operation make-up water is fed to the condensate receiver, which is fed to the boiler during the next cycle.
US patent 4878457 claims a zero flash condensate system with a pressurized flash condenser where flash steam is condensed by using cold feed water and the hot condensate enters into water to water heat exchanger and rejects remaining heat to the feed water.
The aforementioned heating systems are suitable for a system with a sufficient amount of cold feed water serving as heat sink. But cannot work for zero or less make water system.
US patent 4428328 claims a blowdown heat recovery flash tank and a heat exchanger at the outlet of flash tank to recover the heat from waste water before throwing it. This system can work if the condensate water is not suitable for boiler use.
The heating systems as discussed in the prior art aim to reduced flash steam loss by transferring the heat from flash steam to make-up water. These systems can work only in the presence of sufficient make-up water

availability: Therefore, there is felt a need for a heating system, which will overcome the drawbacks of the existing systems discussed in the prior art.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a steam boiler system for air heating applications.
Another object of the present invention is to provide a steam boiler system for air heating applications which provides hot air for industrial applications.
Still another object of the present invention is to provide a steam boiler system for air heating applications which minimizes flash steam losses.
Yet another object of the present invention is to develop a waste heat recovery system to maximize flue gas and condensate heat recovery.
One more object of the present invention is to develop a flue gas heat recovery system to utilize for process heating application.
SUMMARY OF THE INVENTION
In accordance with the present invention, is provided a steam boiler system for air heating applications, said boiler system comprising:
• a boiler adapted to receive water and further adapted to vaporize the water by using a heat input to provide steam and hot combustion gases;
• a radiator consisting of:

(i) a second heat exchanger adapted to receive hot circulating water and air and to provide pre-heated air and heat-extracted circulating water; and
(ii) a first heat exchanger adapted to receive the steam from the boiler and the pre-heated air from the second heat exchanger, to provide heated air and steam condensate;
• a flash tank adapted to receive the steam condensate from the first heat exchanger and further adapted to flash the steam condensate to provide flashed steam;
• a flash steam condenser embedded in the flash tank adapted to receive the heat-extracted circulating water and further adapted to exchange heat with the flashed steam to provide re-heated circulating water and condensed feed water to be fed to the boiler; and
• a smoke chamber having an inlet for hot combustion gases received therein from the boiler and an outlet for heat-extracted combustion gases provided therein a flue gas heat exchanger with at least one tube passing through the smoke chamber having an inlet for the re-heated circulating water and an outlet for hot circulating water to be fed to the second heat exchanger.
Typically, in accordance with the present invention, the boiler system comprises an integrated heat recovery loop for heat recovery from combustion gas and condensate.

Preferably, in accordance with the present invention, a steam trap is operatively connected between the first heat exchanger and the flash tank, the trap being adapted to provide a low pressure drop.
Typically, in accordance with the present invention, a feed water pump is directly provided at the outlet of the flash tank.
Additionally, in accordance with the present invention, a circulating pump is provided to circulate water through the integrated heat recovery loop.
Typically, in accordance with the present invention, the flash tank is maintained at a pressure above the atmospheric pressure.
Preferably, in accordance with the present invention, the radiator is a single chamber divided into two sections comprising the first heat exchanger and the second heat exchanger for utilizing steam and circulating water as heating medium.
In accordance with the present invention, is provided a method of recovering heat in a steam boiler system for air heating applications, said method comprising the following steps:
(i) vaporizing water in a boiler using a heat input to generate
steam and hot combustion gases; (ii) extracting heat from the hot combustion gases in a smoke chamber by means of a flue gas heat exchanger haying at least one tube provided therein to carry pre-heated circulating

water, to generate heat-extracted combustion gases which are discharged through an outlet and hot circulating water;
(iii) pre-heating air in a second heat exchanger of a radiator by using the hot circulating water to provide pre-heated air and heat-extracted circulating water;
(iv) heating the pre-heated air in a first heat exchanger of the radiator by utilizing the steam from the boiler to provide heated air and discharge steam condensate;
(v) flashing the discharged steam condensate in a flash tank to generate flashed steam; and
(vi) absorbing heat from the flashed steam in the heat-extracted circulating water by means of a flash steam condenser embedded in the flash tank, to generate water to be fed to the boiler and pre-heated circulating water which is fed;to the smoke chamber.
Typically, in accordance with the present invention, the method of recovering heat in a steam boiler system for air heating applications includes the step of providing an integrated heat recovery loop for heat recovery from combustion gas and condensate.
Preferably, in accordance with the present invention, the method of recovering heat in a steam boiler system for air heating applications includes the step of extracting heat from the hot combustion gases and the flashed steam into circulating water to be used for pre-heating air.

Additionally, in accordance with the present invention, the method of recovering heat in a steam boiler system for air heating applications includes the step of providing two circulation loops: a first circulation loop comprising the boiler, the first heat exchanger, a steam trap, the flash tank, and a feed water pump; and a second circulation loop comprising the flue gas heat exchanger, the second heat exchanger, and the flash steam condenser.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described with reference to the accompanying drawings, in which;
FIGURE 1 illustrates a conventional air heating system; and
FIGURE 2 illustrates the steam boiler system for air heating applications, in accordance with the present invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described with reference to the accompanying drawing which does 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 steam boiler system for air heating applications for providing hot air for heating, drying, dehumidifying, desiccating and disinfecting applications in industries, and a method thereof. The system in accordance with the present invention is particularly

concerned about wastage of heat and energy in the conventional heating systems used for providing hot air for industrial applications and low system efficiency.
FIGURE 2 illustrates the preferred embodiment of the steam boiler system for air heating applications in accordance with the present invention, the steam boiler system referred in FIGURE 2 by numeral 200. The steam boiler system 200 is provided with an integrated heat recovery loop for heat recovery from combustion gas and condensate: The boiler system 200 comprises a boiler 202, a radiator 208, a flash tank 228, a flash steam condenser 230, and a smoke chamber 204. The radiator 208 further comprises a first heat exchanger 212 and a second heat exchanger 210; wherein the first heat exchanger 212 is a primary heat exchanger adapted to extract the major portion of heat in the system 200 and the second heat exchanger 210 is a secondary heat exchanger adapted to extract heat from hot combustion gases and flashed steam. Alternatively, the radiator 208 is a single chamber divided into two sections, the sections comprising the first heat exchanger 212 and the second heat exchanger 210 for utilizing steam and heated circulating water as the heating medium.
Thus, the first heat exchanger 212 is the prime heat exchanger of the system 200 which uses steam from the boiler 202 as the heating medium. Further, the second heat exchanger 210 is an auxiliary heat exchanger which uses circulating water heated by hot combustion gases in the smoke chamber 204 and flashed steam in the flash steam condenser 230, as the heating medium. The boiler system 200 is provided with two circulation loops: a first circulation loop comprising the boiler 202, the first heat exchanger 212, a

steam trap 226, the flash tank 228, and a feed water pump 234; and a second circulation loop comprising a flue gas heat exchanger 236, the second heat exchanger 210, a circulating pump 232, and the flash steam condenser 230. The boiler 202 is adapted to receive water and vaporize the water by using a heat input to provide steam and hot combustion gases. The first heat exchanger 212 receives the steam from the boiler 202 through a steam stop valve 221 provided along a steam pipe 222. The steam condenses in the first heat exchanger 212 while exchanging heat with pre-heated air received therein at an inlet 220 from the second heat exchanger 210, to provide heated air which is discharged through an outlet 224 and a steam condensate. The steam condensate is discharged from the first heat exchanger 212 through the steam trap 226 and collected in the flash tank 228. The steam trap 226 is operatively connected between the first heat exchanger 212 and the flash tank 228 and is adapted to provide a low pressure drop. The flash tank 228 is maintained at a pressure above the atmospheric pressure and is adapted to flash the steam condensate received therein to provide flashed steam.
The second heat exchanger 210 receives hot circulating water from the flue gas heat exchanger 236 and cold air through an inlet 214, to provide preheated air which is discharged through an outlet 218 and fed to the first heat exchanger 212 through the inlet 220, and heat-extracted circulating water which is discharged through the circulating pump 232 which is adapted to circulate water through the integrated heat recovery loop. The heat-extracted circulating water is received in the flash steam condenser 230 which is provided embedded in the flash tank 228 and is adapted to exchange heat with the flashed steam, to provide re-heated circulating water and condensed feed water obtained as the flashed steam rejects the latent heat to the

circulating water and condenses. At equilibrium condition, the rate of flash steam generation will match the rate of flash steam condensation. The condensed feed water is discharged from the flash tank 228 and received in the boiler 202 through the feed water pump 234 directly provided at the outlet of the flash tank 228 at an inlet 206 for vaporizing.
The feed water pump 234 is designed to handle higher pressure water at saturation temperature. The re-heated circulating water from the flash steam condenser 230 is received in the flue gas heat exchanger 236 which is provided embedded in the smoke chamber 204. The smoke chamber 204 can be an integral part of the boiler 202 or could be provided as a separate chamber. Further, the smoke chamber 204 is provided with an inlet for receiving hot combustion/flue gases generated in the boiler 202 when vaporizing water and an outlet 238 for discharging the heat-extracted combustion gases from the system 200 after rejecting substantial amount of heat to the circulating water. The smoke chamber 204 comprises provided therein the flue gas heat exchanger 236 with at least one tube passing through the smoke chamber 204 and adapted to extract heat from the hot combustion gases, the flue gas heat exchanger 236 having an inlet for the re-heated circulating water from the flash steam condenser 230 and an outlet for heated circulating water which is to be fed to the second heat exchanger 210. Thus, the heat from the hot combustion gases and the flashed steam is used to heat circulating water which is used for pre-heating air. The heated circulating water enters the second heat exchanger 210, where it rejects heat to the cold air. The cold air first enters to the second heat exchanger 210 through the inlet 214 and finally exits from the outlet 218 after receiving heat from the heated circulating water. Then the pre-heated air enters the

first heat exchanger 212 through the inlet 220, where it is further heated by steam and finally heated air exits from the outlet 224.
EXAMPLES
The invention will now be described with respect to the following example which does not limit the invention in any way and only exemplifies the invention.
The boiler system of the present invention is intended to meet a heat load of 6,00,000 Kcal/Hr with 170 °C air temperature. The boiler system used in the present example is a husk fired boiler for steam generation. The steam is generated at 9 kg/cm2 . As only latent heat of steam is used to heat the process air, the system requires approximately 1,245 kg/hr steam. Approximately 188 kg condensate is flashed as steam, which is approximately 14.5 % of the total steam generation. The steam boiler has an efficiency of 80 % with 283 kg/Hr fuel consumption.
The present system consists of a high pressure flash tank. The operating pressure of the flash tank is kept 4 kg/cm2. This pressure can vary with design and application. As the pressure drop is only 5 kg/cm2 in comparison with the 9 kg/cm2 in the conventional systems, the flash steam quantity is only 5.7 % in the present system. This flash steam is condensed by using flash steam condenser by using circulating water. The temperature of circulating water at the inlet of flash steam condenser is 80 °C, This receives the latent heat of the flash steam and exit at 83 °C. Then it enters in the flue gas heat exchanger receiving the waste heat of the flue gas and exit at 90.1 °C. This finally enters the second heat exchanger of the radiator, where it

rejects the heat to the process air and again enters to the flash steam condenser at 80 °C.
Cold air first enters the second heat exchanger at atmospheric temperature 30 °C, where it receives heat from circulating water and exits at 54.6 °C. Finally it enters the first heat exchanger to heat it to 170 °C. As the certain amount of heat load is met by circulating air, this system requires comparatively less amount of steam. Feed water is directly fed to the boiler from flash tank at 4 kg/cm2 and approx. 151 °C temperature.
Performance data of the present system is as follows:

Air temperature profile- Unit
Inlet to secondary heat exchanger 30 Deg C
Outlet to secondary heat exchanger 54.6 Deg C
Inlet to primary heat exchanger 54.6 Deg C
Outlet to primary heat exchanger 170.0 Deg C
Circulating water temperature profile
Inlet to the flash condenser 80.0 Deg C
Outlet to the flash condenser 83.0 Deg C
Inlet to the flue gas heat exchanger 83.0 Deg C
Outlet to the flue gas heat exchanger 90. 1 Deg C
Inlet to the secondary heat exchanger 90.1 Deg C
Outlet to the heat exchanger 80.0 Deg C

Other parameters
Boiler steam pressure 9.0 Kg/cm2
Flash tank pressure 4.0 Kg/cm 2
Feed water temp. 151.1 Deg C
% Flash steam 5.7% %
Heat recovery in flash condenser 30178.5 Kcal/Hr
Heat recovery, in flue gas heat exchanger 70953.9 Kcal/Hr
% Steam saving 16.9% %
% Fuel saving 24.6% %
The system as disclosed in the present invention has less flash steam loss and more flue gas heat recovery and the recovered heat is directly used to heat cold air. This system requires less steam quantity and less fuel consumption.

The comparative benefit of the present system with respect to the conventional system is presented in the following table.

Conventional Present Invention Units
Heat Load 600000 600000 Kcal/Hr
Air qty 17142.9 17142.9 Kq/Hr
Air inlet temp. 30.0 30.0 Deg C
Air outlet temp. 170.0 170.0 Deg C
Steam pressure 9.0 9.0 Kg/cm2
Steam qty 1245.4 1035.5 Kg/Hr
Flash steam qty 187.4 59.9 Kg/Hr
Flash steam loss 14.5 0.0 %
Fuel Husk Husk
Fuel GCV 3100.0 3100.0 Kcal/kg
Boiler efficiency 80.0 80.0 %
Fuel qty 282.7 213.3 Kg/Hr
As a substantial portion of heat is transferred in the second heat exchanger using heated circulating water, net steam requirement decreases by 16.9 %. As the flash tank is pressurized, there is significant reduction in flash steam. This flash steam is not a loss as it is condensed by using flash steam condenser. The feed water fed in boiler is at very high temperature, which further leads in fuel saving. The total fuel saving achieved is 24.6 %.: These parameters can change under different pressure and temperature conditions.
TECHNICAL ADVANCEMENTS
A steam boiler system for air heating applications and a method thereof for providing hot air for heating/drying applications in industries, in accordance with the present invention has several technical advantages including but not limited to the realization of:
• the boiler system is adapted to recover optimum quantity of heat from the hot combustion gases and the flashed steam by using

embedded heat exchangers provided in the smoke chamber and the flash tank;
• the boiler system is adapted to reduce the quantity of flash steam by using the flash tank and to reduce the flash steam loss by using the flash steam condenser;
• the radiator comprising the first heat exchanger for recovering heat from steam and the second heat exchanger for recovering heat from heated circulating water which receives heat from the flue gases and the flash steam, optimizes heat recovery in the boiler system; and
• the boiler system is adapted to integrate flue gas heat recovery and flash steam heat recovery to maximize system efficiency.
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 steam boiler system for air heating applications, said boiler system comprising:
• a boiler adapted to receive water and further adapted to vaporize the water by using a heat input to provide steam and hot combustion gases;
• a radiator consisting of:
(i) a second heat exchanger adapted to receive hot circulating water and air and to provide pre-heated air and heat-extracted circulating water; and
(ii) a first heat exchanger adapted to receive the steam from the boiler and the pre-heated air from the second heat exchanger, to provide heated air and steam condensate;
• a flash tank adapted to receive the steam condensate from the first heat exchanger and further adapted to flash the steam condensate to provide flashed steam;
• a flash steam condenser embedded in the flash tank adapted to receive the heat-extracted circulating water and further adapted to exchange heat with the flashed steam to provide re-heated circulating water and condensed feed water to be fed to the boiler; and
• a smoke chamber having an inlet for hot combustion gases received therein from the boiler and an outlet for heat-extracted combustion gases provided therein a flue gas heat exchanger with at least one tube passing through the smoke chamber

having an inlet for the re-heated circulating water and an outlet for hot circulating water to be fed to the second heat exchanger.
2. The boiler system as claimed in claim 1, wherein the boiler system comprises an integrated heat recovery loop for heat recovery from combustion gas and condensate.
3. The boiler system as claimed in claim 1, wherein a steam trap is operatively connected between the first heat exchanger and the flash tank, the trap being adapted to provide a low pressure drop.
4. The boiler system as claimed in claim 1, wherein a feed water pump is directly provided at the outlet of the flash tank.
5. The boiler system as claimed in claim 1 & 2, wherein a circulating pump is provided to circulate water through the integrated heat recovery loop.
6. The boiler system as claimed in claim 1, wherein the flash tank is maintained at a pressure above the atmospheric pressure.
7. The boiler system as claimed in claim 1, wherein the radiator is a single chamber divided into two sections comprising the first heat exchanger and the second heat exchanger for utilizing steam and circulating water as heating medium.

8. A method of recovering heat in a steam boiler system for air heating
applications, said method comprising the following steps:
(i) vaporizing water in a boiler using a heat input to generate steam and hot combustion gases;
(ii) extracting heat from the hot combustion gases in a smoke chamber by means of a flue gas heat exchanger having at least one tube provided therein to carry pre-heated circulating water, to generate heat-extracted combustion gases which are discharged through an outlet and hot circulating water; . (iii) pre-heating air in a second heat exchanger of a radiator by using the hot circulating water to provide pre-heated air and heat-extracted circulating water;
(iv) heating the pre-heated air in a first heat exchanger of the radiator by utilizing the steam from the boiler to provide heated air and discharge steam condensate;
(v) flashing the discharged steam condensate in a flash tank to generate flashed steam; and
(vi) absorbing heat from the flashed steam in the heat-extracted circulating water by means of a flash steam condenser embedded in the flash tank, to generate water to be fed to the boiler and pre-heated circulating water which is fed to the smoke chamber.
9. The method as claimed in claim 8, which includes the step of
providing an integrated heat recovery loop for heat recovery from
combustion gas and condensate.

10. The method as claimed in claim 8, which includes the step of extracting heat from the hot combustion gases and the flashed steam into circulating water to be used for pre-heating air.
11. The method as claimed in claim 8, which includes the step of providing two circulation loops: a first circulation loop comprising the boiler, the first heat exchanger, a steam trap, the flash tank, and a feed water pump; and a second circulation loop comprising the flue gas heat exchanger, the second heat exchanger, and the flash steam condenser.