DESC:FORM – 2

THE PATENTS ACT, 1970
(39 of 1970)

COMPLETE SPECIFICATION
(SECTION 10, RULE 13)

“AN IMPROVED FLUIDIZED BED COMBUSTION THERMIC
FLUID HEATER WITH INTERNAL GAS
RE-CIRCULATION SYSTEM”

ISOTEX CORPORATION PVT LTD.
A Company Incorporated under
The Indian Companies Act
having address at
181/2&3, 178/1/C GIDC,
Naroda Industrial Estate, Naroda,
Ahmedabad- 382330, Gujarat, India

The following specification particularly describes the nature of this invention and manner in which it is to be performed: -
FIELD OF INVENTION:
The present invention relates to an improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system. In particular present invention relates to an improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system which facilitates the cooling by using re-circulated flue gas which replaces greater amount of excess air which is normally required to maintain bed temperature as the said flue gas has high heat capacity than air to carry more heat away from the fuel bed maintaining the bed temperature within safe operation limit also significantly increasing the thermal efficiency making the entire system highly efficient.

BACKGROUND AND PRIOR ART:
Various types of fuels are used for combustion in the heaters. For solid fuel like coal, lignite, pet coke and Bio mass fuels of various types, in case of FBC (fluidized bed combustion) system, bed temperature is required to be controlled between 700°C to 850°C depending upon fuel type to avoid clinker formation and to ensure proper fluidization for trouble free operation.
Currently available thermal fluid heaters provide 150 % more excess fresh air for bed cooling. But higher the excess air level increases O2 % in fuel gas and results in lower thermal efficiency due to higher stack losses. Further, higher combustion air volume requires high kw fan increasing electric power consumption.
Further, in case of steam boilers, water cooled in-bed tubes are provided to cool down bed, to obtain required bed temperature. The same technology is also used to provide thermic fluid in bed tube for bed cooling. But since thermic fluid is very sensitive to over heating and increasing film temperature at tube wall surface may result into deterioration of thermic fluid which requires thermic fluid to be replaced at faster interval. The said replacement cost is very high as thermic fluid is expensive. Also in case of power failures and over heating of tubes the tube may be punctured or damaged or eroded which may result into leakage of thermic fluid in the bed and may cause fire or explosion leaving the operation unsafe.
Thus, there was a unmet need to provide a fluidized bed combustion thermic fluid heater with internal gas re-circulation system which would solve the problems associated with the prior art.

DISADVANTAGES OF PRIOR ART:
Currently available thermal fluid heaters face at least on the below mentioned disadvantages:
- None of them utilize the flue gas for cooling which has high heat capacity than air so to carry more heat away from the fuel bed maintaining the bed temperature within safe operation limit also maintaining the thermal efficiency making the entire system efficient.
- Most of them faces problem of clinker formation due to the over heating of the bed.
- Most of them require excess fresh air for bed cooling and higher the excess air level increases O2 % in fuel gas and results in lower thermal efficiency due to higher stack losses.
- Most of them require high kw fan for higher combustion air volume which increases electric power consumption.
- Most of them use thermic fluid in bed tube for bed cooling but such thermic fluid is very sensitive to over heating and increasing film temperature at tube wall surface may result in to deterioration of thermic fluid which require thermic fluid to be replaced at faster interval which becomes very expensive.
- Most of them use bed tube for bed cooling where in case of power failures and over heating of tubes, the tube may be punctured or damaged or eroded which may result in to leakage of thermic fluid in the bed and cause fire or explosion leaving the operation unsafe.
- Most of them consume high electric power and high maintenance, thus making the system uneconomic.
- Most of them have short shelf life.

OBJECTS OF INVENTION:
The main object of the invention is to provide an improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system which facilitates the cooling by using re-circulated flue gas which replaces greater amount of excess air which is normally required to maintain bed temperature as the said flue gas has high heat capacity than air to carry more heat away from the fuel bed maintaining the bed temperature within safe operation limit also significantly increasing the thermal efficiency making the entire system highly efficient.
Another object of the invention is to provide an improved fluedized bed combustion thermic fluid heater with internal gas re-circulation system which avoids clinker formation by maintaining the bed temperature.
Yet another object of the invention is to provide an improved fluedized bed combustion thermic fluid heater with internal gas re-circulation system which maintains the bed temperature by significant cooling with maintaining the thermal efficiency.
Yet another object of the invention is to provide an improved fluedized bed combustion thermic fluid heater with internal gas re-circulation system which has low maintenance making it economic.
Yet another object of the invention is to provide an improved fluedized bed combustion thermic fluid heater with internal gas re-circulation system which has a long shelf life.
Yet another object of the invention is to provide an improved fluedized bed combustion thermic fluid heater with internal gas re-circulation system which is safe to operate.

BRIEF DESCRIPTION OF DRAWINGS:
Fig.1: Shows the schematic diagram of the traditionally used solid fuel fired thermal oil heater.
Fig.2: Shows the schematic diagram of the proposed system.
Fig.3: Shows the schematic diagram of re-circulation of the hot flue gasses through primary source in the proposed system.
Fig.4: Shows the perspective view of the mixing chamber of proposed system.
Fig.5: Shows the schematic diagram of re-circulation of the hot flue gasses through secondary source in the proposed system.

Meaning of reference numerals used in the figure:

100 : System
1 : Plenum chamber
2 : Fuel combustion bed
3 : Feeder
4 : Primary air nozzles
5 : Refractory lined combustion chamber
6 : Thermal oil heater
7 : Heat recovery device
8 : Pollution control equipment
9 : Pollution control equipment outlet duct I
10 : O2 and flue temperature gas analyzer
11 : Pollution control equipment outlet duct II
12a : Secondary air fan inlet duct
12 : FGR fan inlet duct
13 : FGR fan inlet damper
14 : FGR fan
15 : Flow control damper
16 : Primary air fan
17 : Primary air fan outlet damper
18 : Mixing chamber
19 : Duct
20 : Ambient air inlet damper
21 : Secondary air inlet damper
22 : Secondary air fan
23 : Secondary air nozzles
24 : ID fan inlet damper
25 : ID fan
26
27 :
: PLC control panel
Chimney

DETAIL DESCRIPTION OF INVENTION:
The features, nature and advantages of the disclosed subject matter will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference numerals identify correspondingly throughout.

Referring to fig.1 and fig.2, an improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) is provided with refractory lined combustion chamber (5) for combustion of fuel. The fuel is fed to the fuel combustion bed (2) through feeder (3). The said feeder (3) can be over bed or under bed depending upon the type of fuel. The said feeder (3) uniformly spreads fuel on entire fuel combustion bed (2) at required rate. The atmospheric air for combustion is supplied by forced draft fan (16) to the plenum chamber (1) and primary air nozzles (4). The combustion takes place resulting in the production of hot flue gases which passes through the thermal oil heater (6) and heat recovery device (7) where the radiation and convection heat transfer takes place and the hot flue gases are cooled down. The hot flue gases further passes through pollution control equipment (8) where the particulate emissions are controlled. The said flue gases then passes to pollution control equipment outlet duct I (9) to ID fan (25) which exhausts hot flue gases to atmosphere via chimney (27). The ID fan inlet damper (24) is provided to control the flow of the flue gases to the ID fan (25).

Referring to fig.2 and fig.3, when the firing mode is established and the hot flue gas temperature in outlet duct I (9) increases beyond the set limit by 1500 C or above depending upon the fuel type, the part of flue gas is supplied through primary supply. The pollution control equipment outlet duct II (11) is provided to re-circulate the part of the hot flue gasses cleaned in pollution control equipment (8) to FGR fan inlet duct (12) which is connected to the suction of FGR fan (14). PLC (Programmable Logic Controller) control panel (26) starts FGR fan (14) and also opens the flow control damper (15) which otherwise remains closed. The part of the hot flue gasses cleaned in pollution control equipment (8) passes via connected pollution control equipment outlet duct II (11) to FGR fan inlet duct (12) which is connected to the suction of FGR fan (14). The FGR fan inlet damper (13) is provided to control the flow of the flue gases to FGR fan (14) as per the requirement. The flue gas pressure is increased by FGR fan (14) and the required hot flue gas is supplied to mixing chamber (18) at required pressure. The flow control damper (15) is opened by PLC control panel (26) which control the air flow of the flue gases to the mixing chamber (18) from FGR fan (14) to facilitate required hot flue gas at required pressure to the said mixing chamber (18). The said flue gas thus passes to the mixing chamber (18).

Referring to fig.4, the mixing chamber (18) has three connections. The bottom end of the mixing chamber (18) is connected to primary air fan (16) to supply atmospheric combustion air to mixing chamber (18). The primary air fan outlet damper (17) is provided to control the air flow from primary air fan (16) to the mixing chamber (18) as per requirement. The side of the mixing chamber (18) is connected to FGR fan inlet duct (12) to supply the flue gas via FGR fan (14), whereby the said FGR fan (14) increases the pressure of the hot flue gases to match with the pressure of the atmospheric air supplied via primary air fan (16). The flow control damper (15) allows the required air flow of the flue gases to the mixing chamber (18). Thus, the mixing chamber (18) uniformly mixes hot flue gases from FGR fan inlet duct (12) and atmospheric air from primary air fan (16). The said hot flue gases contain 6 to 10% O2 depending upon the fuel type whereas the atmospheric combustion air contains 20.9% O2 at atmospheric temperature. The resultant mixture of hot flue gases and atmospheric combustion air which contains lesser O2% compare to fresh air. The said mixture of hot flue gases and atmospheric combustion air then passes to plenum chamber (1) via duct (19) which is connected to the top of the mixing chamber (18).

The higher volume of mixture of hot flue gases and atmospheric combustion air passed to plenum chamber (1) is further supplied to the fuel combustion bed (2) from the primary air nozzles (4) for combustion of fuel.

Referring to fig.5, when the firing mode is established and the hot flue gas temperature in outlet duct I (9) increases beyond the set limit by 1500 C or above depending upon the fuel type, the part of flue gas is also supplied through secondary air supply in addition to the primary air supply. The secondary air fan (22) is provided to facilitate sufficient quantity of air over the fuel combustion bed (2) to complete combustion. PLC control panel (26) starts secondary air fan (22) and also opens the secondary air inlet damper (21) which otherwise remains closed. In order to provide the sufficient quantity of air for proper mixing with combustion products for complete combustion, the secondary air fan inlet duct (12A) is provided which is connected to pollution control equipment outlet duct II (11) at one end and connected to secondary air fan (22) at another end. The secondary air inlet damper (21) is provided for flue gases quantity regulation to the secondary air fan (22). Further, the ambient air inlet damper (20) is provided for facilitating the required flow of fresh air to secondary air fan (22). Thus, the mixture of flue gases via secondary air inlet damper (21) and fresh air via ambient air inlet damper (20) is supplied to the secondary air fan (22) which further supplies the said mixture to secondary air nozzles (23). The said secondary air fan (22) supplies the mixture of flue gases and fresh air to the secondary air nozzles (23) at required pressure and volume to ensure complete combustion and reduce soot formation with the objective to reduce excess air.

The O2 and flue temperature gas analyzer (10) is provided to measure the parameters such as O2% in flue gas and flue gas temperature and transfers the data of the said parameters to PLC control panel (26) to control the present system (100) to maintain the bed temperature accordingly. The PLC control panel (26) in turn control the variable frequency drive (VFD). The said PLC control panel (26) controls the flow of air from primary air fan outlet damper (17) to supply required quantity of atmospheric air to mixing chamber (18). The said PLC control panel (26) also controls the flow of flue gases from flow control damper (15) to supply required quantity of flue gases to mixing chamber (18) for supplying to plenum chamber (1) to maintain the bed temperature. Moreover, the PLC control panel (26) controls the flow of air from ambient air inlet damper (20) to supply required quantity of atmospheric air to the secondary air fan (22). Further, the PLC control panel (26) also controls the flow of flue gases from secondary air inlet damper (21) to supply required quantity of flue gases to the secondary air fan (22). The O2 and flue temperature gas analyzer (10) measures the excess air (O2%) and accordingly adjust the speed of FGR fan (14) and secondary air fan (22) to control excess air level. Further, the said PLC control panel (26) also controls the rate of fuel feeding from feeder (3) on fuel combustion bed (2) to keep the temperature below ash fusion temperature of particular fuel in use. Thus the clinker formation problem is eliminated for any type of fuel used in the combustion chamber.
The proposed heater with internal gas re-circulation system uses 35 % to 60% of excess fresh air to facilitate cooling of combustion bed to combustion requirements which is significantly lesser than the existing heaters which uses excess fresh air around 130% to 150%. Further, lower excess air translates directly into fuel saving and reduced NOX.
Thus, the proposed heater with internal gas re-circulation system allows the cooling of combustion bed to combustion requirements whereby the proposed system facilitates the cooling effect through the mixture of flue gas and fresh. The flue gas has high heat capacity than air so it carries more heat away from the fuel bed and reduces the peck temperature by approx 150°C to 200°C.
The fuel used in the proposed system for combustion can be all type of fuels such as fuels including coal, wood, biomass or agro waste. The proposed heater with internal gas re-circulation system has capacity to burn the said raw material in range of 10 lac K cal/Hr to 150 lac K cal /Hr.
Having described what is considered the best form presently contemplated for embodying the present invention, various modifications and variations in its form of manufacture will be promptly apparent to those skilled in the art. Therefore, it is to be understood that the present invention is not limited to the practical aspects of the actual preferred embodiments hereby described and that any such modifications and variations must be considered as being within the spirit and the scope of the invention, as described in the attached claims.
,CLAIMS:WE CLAIM:

1. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) provided with refractory lined combustion chamber (5) for combustion of fuel whereby the fuel is fed to the fuel combustion bed (2) through feeder (3) and the atmospheric air for combustion is supplied by forced draft fan (16) through primary air nozzles (4) and by secondary air fan (22) through secondary air nozzles (23) for combustion of the fuel resulting in the production of hot flue gases which passes through the thermal oil heater (6) and heat recovery device (7) where the radiation and convection heat transfer takes place and the hot flue gases are cooled down and further passes through pollution control equipment (8) where the particulate emissions are controlled followed by passing to pollution control equipment outlet duct I (9) to ID fan (25) which exhausts hot flue gases to atmosphere via chimney (27)

where improvement comprises in re-circulating the part of flue gas

(a) through primary supply
when the firing mode is established and the hot flue gas temperature in outlet duct I (9) increases beyond the set limit by 1500 C or above depending upon the fuel type, PLC control panel (26) starts, FGR fan (14) and also opens the flow control damper (15) which otherwise remains closed whereby the part of the flue gasses cleaned in pollution control equipment (8) passes via connected pollution control equipment outlet duct II (11) to FGR fan inlet duct (12) which is connected to the suction of FGR fan (14) where the flue gas pressure is increased and the required hot flue gas is supplied to mixing chamber (18) at required pressure, whereby the mixing chamber (18) has three connections
(i) the bottom end of the mixing chamber (18) is connected to primary air fan (16) to supply atmospheric combustion air to mixing chamber (18) and the primary air fan outlet damper (17) is provided to control the air flow from primary air fan (16) to the mixing chamber (18) as per requirement;
(ii) the side of the mixing chamber (18) is connected to FGR fan inlet duct (12) to supply the flue gas via FGR fan (14), whereby the said FGR fan (14) increases the pressure of the hot flue gases to match with the pressure of the atmospheric air supplied via primary air fan (16) and the flow control damper (15) allows the required air flow of the flue gases to the mixing chamber (18), thus, the mixing chamber (18) uniformly mixes hot flue gases from FGR fan inlet duct (12) and atmospheric air from primary air fan (16) and
(iii) top of the mixing chamber (18) is connected to duct (19) for passing the said mixture of hot flue gases and atmospheric combustion air to plenum chamber (1),
whereby from the plenum chamber (1) the said mixture of hot flue gases and atmospheric combustion air is further supplied to the fuel combustion bed (2) from the primary air nozzles (4) for combustion of fuel
(b) through secondary supply
when the firing mode is established and the hot flue gas temperature in outlet duct I (9) increases beyond the set limit by 1500 C or above depending upon the fuel type, PLC control panel (26) starts, secondary air fan (22) which is provided to facilitate sufficient quantity of air over the fuel combustion bed (2) for proper mixing with combustion products for complete combustion, whereby the said secondary air fan (22) is connected to the
(i) secondary air fan inlet duct (12A) which is connected to pollution control equipment outlet duct II (11) for supplying the part of the hot flue gasses cleaned in pollution control equipment (8) whereby the secondary air inlet damper (21) is provided for flue gases quantity regulation to the secondary air fan (22) and
(ii) the ambient air inlet damper (20) which is provided for facilitating the required flow of fresh air to secondary air fan (22),
thus, the mixture of flue gases via secondary air inlet damper (21) and fresh air via ambient air inlet damper (20) is supplied to the secondary air fan (22) which further supplies the said mixture to secondary air nozzles (23).
2. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, whereby the O2 and flue temperature gas analyzer (10) is provided to measure the parameters such as O2% in flue gas and flue gas temperature and transfers the data of the said parameters to Programmable Logic Controller (26) to control the present system (100) to maintain the bed temperature accordingly and the Programmable Logic Controller (26) in turn control the variable frequency drive (VFD).
3. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, whereby the PLC control panel (26) controls the flow of air from primary air fan outlet damper (17) to supply required quantity of atmospheric air to mixing chamber (18).
4. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, whereby the PLC control panel (26) controls the flow of flue gases from flow control damper (15) to supply required quantity of flue gases to mixing chamber (18).
5. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, whereby the PLC control panel (26) controls the flow of air from ambient air inlet damper (20) to supply required quantity of atmospheric air to the secondary air fan (22).
6. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, whereby the PLC control panel (26) controls the flow of flue gases from secondary air inlet damper (21) to supply required quantity of flue gases to the secondary air fan (22).
7. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, whereby the PLC control panel (26) controls the rate of fuel feeding from feeder (3) on fuel combustion bed (2) to keep the temperature below ash fusion temperature of particular fuel in use.
8. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, O2 and flue temperature gas analyzer (10) measures the excess air (O2%) and accordingly adjust the speed of FGR fan (14) and secondary air fan (22) to control excess air level.
9. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, whereby flue gas has capacity to carry away heat away from the fuel bed and reduces the peak temperature by approx 150°C to 200°C.
10. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, whereby FGR fan inlet damper (13) is provided to control the flow of the flue gases to FGR fan (14) as per the requirement.
11. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, whereby the hot flue gases contain 6 to 10% O2 depending upon the fuel type whereas the atmospheric combustion air contains 20.9% O2 at atmospheric temperature and the resultant mixture of hot flue gases and atmospheric combustion air contains lesser O2% compare to fresh air.
12. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, requires 35 % to 60% of excess fresh air to facilitate cooling of combustion bed to combustion requirements which is significantly lesser than the existing heaters which uses excess fresh air around 130% to 150%.
13. An improved fluidized bed combustion thermic fluid heater with internal gas re-circulation system (100) as claimed in claim 1, has the capacity of the present system to burn the said raw material in range of 10 lac K cal/Hr to 150 lac K cal /Hr.

Dated this 1st day of May, 2014

______________________
GOPI J. TRIVEDI (Ms.)
Patent Attorney
At Y. J. Trivedi & Co.
Authorized Patent Agent of the Applicant

To,
The Controller of Patents,
The Patent Office,
Mumbai.