FORM - 2
THE PATENTS ACT, 1970
(39 OF 1970)
AND
THE PATENT RULE, 2003
COMPLETE SPECIFICATlON
(SEE SECTION 10 AND RULE 13)
"AN IMPROVED AND COMPACT SUPER EFFICIENT, PACKAGED, GAS FIRED, FIRETUBE (SMOKE TUBE) CONENSING BOILER"
TRANSPARENT ENERGY SYSTEMS PRIVATE LIMITED
AN INDIAN COMPANY,
"PUSHPA HEIGHTS", 1ST FLOOR,
BIBWEWADI CORNER,
PUNE SATARA ROAD,
PUNE-411 037, MAHARASHTRA,
INDIA.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THE INVENTION AND THE MANNER IN WHICH IT IS TOM BE PERFORMED

FIELD OF THE INVENTION:-
The Present invention relates to improved and compact, super efficient, packaged, gas fired, firetube (smoke tube) condensing boiler. More particularly present invention relates to improved and compact super efficient packaged gas (e.g. Natural Gas) fired firetube (smoke tube) boiler having integral but separate economizer and water pre-heater on the flue gas side, as heat recovery units and a radiator type (Water to Air Heat Exchanger) as a combustion air pre-heater.
PRIOR ART:-
Conventionally the gas fired firetube (smoke tube) boilers have a three pass construction on flue gas side. First pass is in the furnace and the next two passes are consisting of multiple firetubes. Some designs of these boilers are without any Heat Recovery Unit i.e. Combustion Air pre-heater or Water pre-heater or Economizer and the efficiency of these boilers without any heat recovery unit typically ranges between 85 - 90% when calculated on Net Calorific Value (NCV) of the fuel. Some designs of conventional gas fired firetube (smoke tube) boilers also have Heat Recovery Unit i.e. Combustion Air pre-heater (Flue gas to air) or Water pre-heater or Economizer or combination thereof and the efficiency of such boilers with heat recovery unit ranges from 92 - 95% when calculated on NCV of fuel. These heat recovery units of the conventional boilers recover the heat from flue gases for heating the boiler feed water or combustion air. The flue gases generated after combustion of fuel contains combustion products such as Carbon Dioxide, Oxygen, Nitrogen and also water vapors, due to hydrogen in the fuel and oxygen in combustion air. The conventional heat recovery units recovers only "Sensible Heat" portion of these water vapors.
Taking into consideration the conventional gas fired firetube (smoke tube) boilers following are the disadvantages-

1. The conventional heat recovery units such as Economizers, Water Pre-heaters, Air Pre-heaters or their combinations recovers only sensible heat from water vapors in flue gases. The latent heat portion of water vapors in flue gases is not recovered. Hence, latent heat contained in water vapors is wasted to atmosphere and overall efficiency of boiler is limited up to 95% on NCV of the fuel.
2. Due to sub-optimal thermal configuration as explained above, the fuel consumption of the conventional boiler is higher for a given heat output.
3. The overall dimensions of firetube boilers of this design are large and these boilers are bulky in size. Also the weight of these boilers is high.
4. The cold start time required for these boilers is higher due to higher water hold up and higher thermal inertia of the boiler body. This results in higher energy losses during cold start up and stopping of boiler.
NEED OF THE PRESENT INVENTION:-
It is object of the present invention to provide improved and compact, super efficient, packaged, gas fired firetube (smoke tube) condensing boiler by recovering the heat of condensation from water vapors in the flue gases. It is also the object of the present invention to provide the gas fired smoke tube boiler which overcomes all the disadvantages and shortfalls of the prior art.
Due to rapid increase in fuel cost, land and civil costs, transportation and erection costs, manufacturing costs etc. there is a need to innovate a compact boiler which will also be more efficient than the designs of conventional boilers available.

SUMMARY OF THE 1NVENTION:-
According to the boiler of present invention i.e. an improved and compact super efficient packaged gas fired firetube (smoke tube) condensing boiler, there are five flue gas passes, first in the furnace of the main boiler, second and third consisting of firetubes of the main boiler, the fourth pass consisting of an integral but separate economizer and the fifth pass in a water pre-heater. The fuel i.e. natural gas is fired in the furnace. The flue gases which are generated after combustion of fuel .are passed through the furnace and smoke tubes and steam generation takes place in the boiler shell. The flue gases coming out of boiler section are then passed through the economizer where water is heated before entering the boiler section. After recovery of heat in the economizer, these flue gases are passed through the water pre-heater for additional heat recovery. The heat recovered in water pre-heater is used to pre-heat boiler feed water and also it is used in a radiator type heat exchanger to preheat the combustion air supplied to the boiler.
The flue gases generated after combustion of fuel are mixture of various gases such as Caron Dioxide, Oxygen, Nitrogen and Water Vapors. When mixture of these gases enters the condensing type water pre-heater, heat is recovered from gases as well as the "Sensible Heat and Latent Heat" is recovered from the water vapors. These water vapors in flue gases gets condensed in the water pre-heater, after recovery of sensible and latent heat. The heat recovered in the water preheater is used for preheating of boiler feed water and also it is used for pre-heating of the combustion air. This additionally recovered heat increases the overall efficiency of boiler up to 104% on NCV of natural gas, i.e. up to 94% on Gross Calorific value (GCV) of natural gas.
STATEMENT OF INVENTION:-
Accordingly invention provides an improved and compact super efficient, packaged, gas fired, fire tube (smoke tube) condensing boiler comprises a main boiler shell of cylindrical shape with two pass fire tube assembly; a furnace, with a fuel burner

concentrically provided at front end and other end opening connected to fire tubes of the boiler, placed adjacent to the said boiler shell; an economizer unit formed integrally in the boiler unit separated from the boiler shell in the flue gas path having economizer water tube s therein; the out let path of flue gas of economizer is connected to inlet on the top of the water pre-heater of cylindrical shape having water tubes; the outlet path of the said pre-heater flue gas connected to the chimney; a forced draft fan provided to the air inlet of said furnace through a combustion air pre-heater; the said water pre-heater inlet of tube connected to feed water tank and outlet connected through the three way control valve to the deareator tank and to the feed water tank passing the tube s in the air pre-heater; the outlet of deareator tank connected to the inlet of economizer water tube ; the feed water inlet of boiler connected to the outlet of water tube of economizer; and water pre-heater is having conical shape bottom with a valve controlled outlet below tYie said flue gas out let path to chinney .
BRIEF DESCRIPTION OF THE SCHEMATIC DRAWING:-
The present invention is described with the accompanying Figures 1, 2, 3 and 4.
Figure 1 describes the flow diagram for feed water and steam circuit for improved and compact super efficient packaged gas fired smoke tube gas fired boiler.
Figure 2 shows the flow diagram for air and flue gas circuit for improved and compact super efficient packaged gas fired smoke tube boiler.
Figure 3 describes gas train circuit for the gas burner.
Figure 4 describes sketch of typical fin shape and finned tube.

DETAIL DESCRIPTION OF THE SCHEMATIC DRAWING:-
The invention will now be described with reference to the drawings of the accompanying specification and the parts of the figure shown by suitable numeral and referred to appropriately in the following description.
Referring to Figures 1, 2, 3 and 4, the following components can be identified in improved and compact super efficient packaged, gas fired, smoke tube condensing boiler -
1. Gas Burner.
2. Fabricated assembly of boiler.
3. Integral separate economizer.
4. Water pre-heater.
5. Combustion Air Preheater
6. Feed Water Tank
7. Chemical Dosing System.
8. Deaerator Tank.
9. Three Way Divertor Valve
10. Chimney
11. Forced Draft fan
12. Gas Train
The main boiler is a shell and tube assembly and is cylindrical in shape. The outer shell of boiler holds the water in boiler up to certain level and all smoke tubes in the shell are submerged in the water. Two separate gas flow sections can be identified in the boiler assembly viz. furnace and smoke tubes. The water level in outer shell is maintained such that all these smokes tubes are always below the water level in boiler shell. The gas burner 1 is placed at front end of the furnace and it is concentric to the furnace. Its axis is coincident with the axis of furnace. The fuel, i.e. natural gas is supplied to the gas burner with the help of Gas Train 12 as shown in Figure 3. The air required for

combustion of gas is supplied by Forced Draft fan 11 through a combustion air pre-heater 5 in figure 1 and combustion is initiated in the furnace i.e. start of first pass. The radiation heat transfer takes place in the furnace and heat is transferred to the water in the boiler. The flue gases at the outlet of furnace, which are at about 850 Deg C to 1150 Deg C, enter in to the smoke tubes in second pass of the boiler. The boiler is of smoke tube type i.e. flue gases are passed through tubes in second and third pass of the boiler. As flue gases are passing through the boiler tubes, heat from flue gases is transferred to the water surrounding these tubes in outer shell and steam is generated in the outer shell.
The flue gases leave the third pass of boiler i.e. tubular pass at about 220 Deg C and then passed through the integral but separate economizer 3 in figure 1 where feed water is pre-heated before entering in to the boiler. The economizer having 'L' type carbon steel fins (press fit to the twin tubes of economizer) makes economizer compact. A sketch of typical fin shape and finned tube is attached as figure 4. On water side, the feed water supplied to the economizer is first deareated in a pressurized deaerator tank 8 in figure 1 at typical temperature of 105 Deg C. The deaeration process in the pressurized deaerator tank removes the dissolved oxygen in feed water before it enters in the economizer tubes. In this economizer, heat is recovered from flue gases and it is used to pre-heat the feed water before entering the boiler. The pre-heated water is fed to the smoke tube boiler shell. In this heat recovery unit, temperature of flue gases is reduced up to 120 Deg C at outlet of economizer.
After recovery of heat in the economizer, flue gases enter next heat recovery unit i.e. fifth pass, Water Pre-heater 4 in figure 1. The water pre-heater has finned tube type construction. Water from feed water tank 6 in figure 1 is supplied to the water pre-heater tubes.
The flue gases which are entering the "Water Pre-heater" are mixture of various gases such as Caron Dioxide, Oxygen, Nitrogen and Water Vapors. When mixture of these gases enters the water pre-heater, heat is recovered from gases and "Sensible as well

as Latent Heat" is recovered from the water vapors. The latent heat of water vapors is recovered till it reaches the saturation point at the humidity ratio of the flue gases. This humidity ratio depends on amount of water vapors in the flue gas. As the latent heat of water vapors in flue gases is recovered in the condensing water pre-heater, condensation of water vapors takes place on the surface of finned tubes in the water pre-heater. The condensed water is collected at the bottom of water pre-heater and it is periodically removed through condensate removing system. The flue gases can be further cooled down by recovering "Sensible and Latent Heat" of water vapors till the maximum efficiency is achieved.
The heat recovered from flue gases in water preheater is used to preheat the boiler feed water and it is also used in a radiator type heat exchanger 5 in figure 1 to preheat the combustion air.
The humidity ratio of flue gases goes on reducing as we further go on recovering heat and condensing the water vapors. The amount of water vapors in flue gases depends on hydrogen in fuel and oxygen supplied through combustion air. The Oxygen analyzer based control system is provided at the flue gas outlet of the water pre-heater to control the amount of excess air supplied through the combustion air, in order to ensure complete and efficient combustion.
By recovery of heat from water vapors, the efficiency of overall system can be further increased, which is 6-8% higher as compared to conventional gas fired boiler systems. The condensate produced is slightly acidic, hence appropriate material such as stainless steel is used for the wetted part of the Condensing Water Pre-heater.
After maximum recovery of heat, the flue gases are released to atmosphere through Chimney (marked as item no (10) in figure 1) at about 45 Deg C.
A three way diverter valve 9 in figure 1 is provided at the inlet of condensing water pre-heater. The flue gases can be diverted to the chimney or Condensing Water pre-heater

as and when required online during operation of the boiler. The provision of three way diverter valve allows the same boiler to be operated as Oil-cum-gas fired boiler. When oils containing higher sulphur are to be used as fuel in the same boiler, the flue gases are diverted directly to the chimney, due to limitations in heat recovery pertaining to dew point of acid vapors in flue gases.
The steam generation and steam pressure is controlled through the stepless modulating control system. The flow of feed water into the boiler through integral but separate economizer is controlled by the single element boiler water in drum level controller or two element drum controller or three element drum level controller. The use of single / two / three element drum level controller makes sure that the feed water pump of the boiler runs continuously and a steady flow of feed water through integral economizer thereby maintaining the steady flue gas temperature profile and also this avoids the possible scale up of economizer on water side.
A Chemical Dosing System 7 is provided for treating feed water in deaerator tank 8. a steam blower is provided in the dearetor tank receiving steam from the boiler output.
The water pre-heater 4 cylindrical shape having an opening on top for flue gas inlet of conical shape bottom with an outlet provided with condensate removing system controlled valve below the said flue gas out let path to chimney .
ADVANTAGES OF THE PRESENT INVENTION:-
1. By recovery of latent heat from water vapors in Condensing Water Preheater, the thermal efficiency of overall boiler can be increased by 7-9 % than the conventional boilers. The thermal efficiency of such system with water preheater is up to 104% on NCV of fuel, which correspond to 94% efficiency on GCV of the
fuel.

2. The provision of Three Way Divertor Valve at flue gas inlet to Water Pre-heater allows online diversion of flue gases to the water pre-heater or Chimney.
3. Large number of safeties and interlocks are provided to ensure safe, reliable and automatic operation of the boiler.
4. The boiler of the present invention is much compact in size and overall dimensions are substantially lower.
5. The manufacturing cost of these boilers is substantially reduced due to optimized thermal configuration and heating surfaces.
6. Location of the lumace is at the bottom most point in the shell. The water content
above the top up to normal working level is huge. This feature provides very high sinking time.
7. Centrally located furnace ensures symmetrical water circulation hence uniform temperature profile.
8. Due to compact size the water holdup as well as thermal inertia of the boiler is reduced. This reduces the cold start-up time of the boiler. This results in lower starting and stopping losses as well as lower starting and stopping time. This means better availability of boiler.
MAIN FEATURES OF INVENTION:-
1. The tubes used in Condensing water pre-heater can be bare tubes or finned tube type.

2. The heat recovered in water preheater may or may not be used in a radiator type heat exchanger for preheating of combustion air.
3. The type of fins used in Condensing water pre-heater can be "L-shaped", Circular or any other type of fins.
4. Materials of construction of tubes and fins of water pre-heater could be alloy steels, stainless steels, aluminum etc. which can be selected based on flue gas quantity and composition. The partial section of water pre-heater can be made of different materials as per requirements.
5. Superheater can be provided in to the system to superheat the steam generated in the boiler.
6. Oil-cum-gas burner can be used in the same boiler, allowing multi fuel (fuels other than natural gas) operation of the same boiler. The flue gases can be diverted directly to the chimney instead of Condensing Water pre-heater, depending on dew point of acid vapors in flue gases, when fuels with higher sulphur contents are used.
7. The same boiler can be operated without additional heat recovery in condensing water pre-heater by diverting flue gases directly to the chimney.
8. An improved and compact super efficient packaged gas fired firetube (smoke tube) condensing boiler comprising of main boiler assembly of furnace, smoke tube, burner; integral but separate economizer, water pre-heater, a radiator type combustion air preheater (Water to air heat exchanger), deaerator tank, three way Divertor valve, ducting for air and flue gas and control system.
9. An improved and compact super efficient packaged gas fired firetube (smoke tube) condensing boiler wherein the water pre-heater is condensing type water

pre-heater. The condensing water pre-heater recovers the sensible and latent heat of water vapors produced from the burning of fuel. By this additional heat recovery in the condensing water pre-heater, the overall efficiency of system can be increased by 7-9% on NCV of fuel over conventional boiler design. The thermal efficiency of gas fired boiler can be reached up to 104% on NCV of fuel, which is up to 94% on GCV of fuel.
10. An improved and compact super efficient packaged gas fired firetube (smoke tube) condensing boiler wherein the flue gases are passed through five flue gas passes, first in the furnace of the main boiler, second and third consisting of firetubes of the main boiler, the fourth pass consisting of an integral but separate economizer and the fifth pass in a condensing type water pre-heater.
11. An improved and compact super efficient packaged gas fired firetube (smoke tube) condensing boiler wherein Condensing type water pre-heater is provided for heating the feed water coming from feed water tank before it enters the said deaerator tank. The heat recovered in condensing type water preheater is used for preheating of the feed water and it is also used to preheat the combustion air in a radiator type heat exchanger.
12. An improved and compact super efficient packaged gas fired firetube (smoke tube) boiler wherein a three way diveror valve is provided for online bypass of the condensing water pre-heater system as and when required.

WE CLAIM:-
1. An improved and compact super efficient, packaged, gas fired, fire tube (smoke tube) condensing boiler comprises a main boiler shell of cylindrical shape with two pass fire tube assembly; a furnace, with a fuel burner concentrically provided at front end and other end opening connected to fire tubes of the boiler, placed adjacent to the said boiler shell; an economizer unit formed integrally in the boiler unit separated from the boiler shell in the flue gas path having economizer water tube s therein; the out let path of flue gas of economizer is connected to inlet on the top of the water pre-heater of cylindrical shape having water tubes ; the outlet path of the said pre-heater flue gas connected to the chimney; a forced draft fan provided to the air inlet of said furnace through a combustion air pre-heater; the said water pre-heater inlet of tube connected to feed water tank and outlet connected through the three way control valve to the deareator tank and to the feed water tank passing the tubes in the air pre-heater; the outlet of deareator tank connected to the inlet of economizer water tube ; the feed water inlet of boiler connected to the outlet of water tube of economizer; and water pre-heater is having conical shape bottom with an outlet having condensate removing system controlled valve below the said flue gas out let path to chimney .
2. A gas fired, firetube (smoke tube) condensing boiler as claimed in claim 1 wherein the said water pre -heater having water tube with bare tube or finned tube.
3. A gas fired, firetube (smoke tube) condensing boiler as claimed in claim 2 wherein the said fins on the pre heater water L-shaped /circular/any geometrical shape.

4. A gas fired, fire tube (smoke tube) condensing boiler as claimed in claims 1 to 4 wherein the tubes and fins of water pre-heater made of alloy steels, stainless steels, aluminum/any suitable metal selected based on flue gas quantity and composition.
5. A gas fired, fire tube (smoke tube) condensing boiler as claimed in claims 1 to 4 wherein the partial section of water pre-heater made of different materials as per requirements
6. A gas fired, fire tube (smoke tube) condensing boiler as claimed in claims 1 and 5 wherein the said thee way valve controllable for allowing the the water of the said pre-heater for heating in a radiator type heat exchanger for preheating of combustion ah.
7. A gas fired, fire tube (smoke tube) condensing boiler as claimed in claims 1 and
5 wherein the said gas gas burner replaced by an oil-cum-gas burner for allowing
multi fuel (fuels other than natural gas) operation made possible by providing
three way diverter valve in the gas flue path between economizer and pre-heater
section so as to connect directly to the chimney bypassing the said
Condensing Water pre-heater.
8. A gas fired, fire tube (smoke tube) condensing boiler as claimed in claims 1 and
6 wherein the said air pre-heater is radiator type heat exchanger.
9. A gas fired, fire tube (smoke tube) condensing boiler as claimed in claims 1 to 8
wherein the flow of feed water into the boiler through integral but separate
economizer is controlled by the single element boiler water in drum level
controller or two element drum controller or three element drum level controller.

10. A gas fired, fire tube (smoke tube) condensing boiler as claimed in claims 1 to 8 wherein the steam generation and steam pressure is controlled through the stepless modulating control system.