Title of Invention

IMPROVED METHOD FOR THE RECOVERY OF HEAT FROM HOT FLUE GASES OF EXHAUST GAS BOILER AND A SYSTEM THEREFOR

Abstract IMPROVEMENTS IN OR RELATING TO EXHAUST GAS BOILER (SF-EGB) There is disclosed an improved method for the recovery of heat from hot flue gases of exhaust gas boiler, which comprises passing the hot flue gases through a combustion zone, introducing a fuel steam into the combustion zone, allowing the so injected fuel to be burnt by the oxygen present in the flue gases, to create additional heat energy, passing the hot flue gases exiting the combustion zone to a heat exchanger in order to recover heat in terms of steam by indirect heat exchange in the heat exchanger and subjecting the flue gases exiting the heat exchanger, if required, to a treatment to remove solid carryovers and suspended solid and a heat recovery system therefor.
Full Text THE PATENT ACT, 1970 COMPLETE
SPECIFICATION
(SECTION-10)
TITLE
"Improved method for the recovery of heat from hot flue gases of exhaust gas boiler and a system therefor "
APPLICANTS
M/S. THERMAX LTD., D-13, MIDC Industrial Area,
Chinchwad, Pune-411 019 Maharashtra, India, an Indian Company.
The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed.

ORIGINAL
4-3-2005
28-9-2000

INTRODUCTION TO THE INVENTION
This invention related to improvements in or relating to exhaust gas boiler (EGB).
PRIOR ART AND DRAWBACKS
In the conventional EGB, it is known to recover the heat from the hot exhaust gases, in the form of steam/hot water, by passing them through a heat exchanger.
The main drawbacks of conventional EGB is that the gas flow rate and the exhaust temperature limits the steam generation rate at the required pressure through exhaust gas boiler.
The rate of recovery is slow because of lower gas entry temperature and the operating steam pressure limits the flexibility of the known process and the equipment.
Moreover, still useful heat energy is left in the exhaust gases.
OBJECT OF THE INVENTION
It is therefore a principle object of this invention to propose improvement in exhaust gas boiler.
It is another object to propose such an improved exhaust gas boiler, which will have flexibility of operation and ensure quicker and higher rate of recovery to an extent greater than possible so far.
It is a further object to propose such an improved exhaust gas boiler, which will greatly reduce the pollution problem.
It is a still further object of this invention to propose a method for the recovery of useful heat from exhaust gas boiler, which will be economical and commercially viable.


"Further discussion on the prior art"
The applicant is aware of the following prior art.
(1) EP 0368599 (2) GB 603874 and (3) US 5357746.
The discussion on each prior art is given distinguishing from the applicant's invention.
EP 0368599 - This Patent relates to an apparatus for recovering latent heat of condensation of moisture from the exhaust gas resulting from the burning of fuel in a heating installation. There is a heat exchanger for recovering sensible heat followed by a two stage condensing heat exchangers for recovering latent heat of condensation and the moisture of combustion is condensed to form droplets. This is totally different from the applicant's invention, which is for a system for recovering heat from exhaust gas burner and has nothing to do in the recovery heat from condensation of moisture.
GB 603874 - This Patent relates to a plant for the recovery of waste heat from industrial furnace that also includes compressor in association with a turbine. The compressor supplies working fluid to the turbine through a heat exchanger. There are control means for turbine, which are responsive to variation in turbine speed. The constructional features and operation of this British Patent is entirely different from our invention, which relates to a system for recovery of heat from hot fluid gas of exhaust boiler and there is no use of any turbine in our system.
US 5357746 - This US Patent relates to a system for recovery waste heat from a combustion turbine which also includes at least one steam turbine and several heat recovery system. This has nothing in common with the applicant's invention.
None of the above three prior art either alone or in combination can destroy the novelty and inventive character of the applicant's invention.


STATEMENT OF THE INVENTION
Thus according to this invention, there is provided an improved method for the recovery of heat from flue gases of DG exhaust which comprises passing the hot flue gases through a combustion zone, introducing a fuel into the combustion zone, passing the hot flue gases exiting the combustion zone to a heat exchanger in order to recover heat in terms of steam by indirect heat exchange in the heat exchanger and subjecting the flue gases exiting the heat exchanger, if required, to a treatment to remove solid carryovers and suspended solid characterized by allowing the fuel injected into the combustion zone to be burnt by the oxygen present in the flue gases, to create additional heat energy.
It will thus be noticed that, we have found that the extra oxygen available in the flue gases can be usefully employed for generating additional amount of steam.
This also helps us in avoiding use of separate boiler to meet the total process steam demand. What is done by us is to inject additional supplementary fuel to the system which can be burnt using the extra oxygen available in the flue gases, thereby generating additional steam which makes the process economical and viable.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be more fully described with reference to the accompanying drawings wherein;

Figure 1, schematically represents an improved exhaust gas boiler according to the invention and
Figure 2, schematically represents another modification of the improved exhaust gas boiler according to the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
A typical and preferred configuration of the system illustrated in Figure 1 is a supplementary fired exhaust gas boiler. The hot flue gases from the DG set are passed through a gas bypass valve (2) into a refractory lined combustion chamber (3). Initially, the temperature of the combustion chamber (3) is increased by firing a small amount of fuel with the help of fresh air supplied by forced draft fan (5). Once the required temperature is achieved, the fresh air supply is cut off gradually and simultaneously the flue gases are introduced in the combustion chamber (3). The fuel firing with the help of fuel pump (6) is continued with the help of oxygen present in the flue gases. The hot flue gases at the combustion chamber (3) outlet are then passed through a heat exchanger (4) in order to recover the heat in terms of steam. The exhaust temperature remains same as in the case of any standard exhaust gas boiler. The additional steam generation would be on account of consumption of excess oxygen in DG exhaust by firing additional fuel without supplying fresh air. This particular arrangement of combustion chamber (3) helps in minimizing the flue gas exhaust losses and gives rise to the conversion efficiency for additionally fired fuel of the order of around 93% as against a standard efficiency of 84% for a conventional oil fired boiler on GCV basis.
Special advantages of the invented process are as follows:
1. Upto 140% boost in steam generation compared to conventional EGB.
2. Higher efficiency of supplementary fuel firing @ 93% on GCV basis as against 84%.


3. Recovery of energy from CO/Soot from the DG set exhaust with reduced emission upto 30 ppm and cleaner, soot free stack.
4. Lower power cost for additional steam since the FD fan power is low and the FD fan is used only for startup.
5. Option of using FO/LSHS/LDO/HSD as supplementary fuel.
6. Smaller footprint.
7. Single installation in supplementary fired EGB compared to a combination two installations of EGB and oil fired boiler.
8. Lower manpower cost.
Further according to this invention, there is provided a improved gas boiler wherein for recovering heat from the exhaust gases, there is provided
a) a system having a combustion chamber for burning additional fuel with the help of the additional oxygen present in the flue gases,
b) the system also including an indirect heat exchanger, down steam of the combustion chamber both connected in series,
c) the combustion chamber being provided with necessary inlet for the admission of additional fuel and

d) wherein the heat exchanger is provided with usual inlet for water and outlet for exhaust gases and
e) means for recovery of steam produced therein.
The following table indicates the improvements/advantages in the invention over the conventional exhaust gas boiler.

PARAMETERS IMPROVED SF EGB- LIQUID/GASEOUS FUELS
Increased steam generation Upto 140% compared to conventional EGB
Efficiency of supplementary firing 93% on GCV compared to 84% for conventional boiler.
Reduction in 02% From 10 - 12% to 7%
Reduction in CO emissions From 650 ppm to 30 ppm
Reduction in smoke index From more than 8 to less than 4
Power economy Approx. 2.25 KW of power saved per 1 ton of extra steam generated.
Overall size/footprint Reduced to 0.75 times compared to conventional EGB and additional boiler

In an embodiment, the combustion chamber can be an ordinary refractory like combustion chamber.
In this instance, the additional fuel fed to the combustion chamber is burnt substantially and there is no perceptible carry over of solids in the exiting flue gases, which can be directly sent to the stack.
However, in another embodiment, the combustion chamber can be a fluidized column where the additional fuel is subjected to fluidization in a hot fluidized bed and thereby burnt.
However, in this instance, the hot flue gases which pass through the heat exchanger are not directly vented to the stack, because some perceptible amount of solids are carried from the combustion zone by the flue gases.
In order to remove these solids, the flue gases exiting the heat exchanger are subjected to conventional fine solid separation technique preferably using a cyclone separator.
The clean flue gas is then vented to the stack.
Such a system is explained with reference to the drawings shown in Figure 2.
A typical configuration of the system illustrated in Figure 2 is a supplementary coal fired fluidized bed exhaust gas boiler. The hot flue gases from the DG set (1) are passed through a gas bypass valve (2) into a refractory lined fluidized bed combustor (4) through plenum chamber (3) and distributor (4). The flue gases are made to pass through the sand bed (6) which in turn gets fluidized. Initially the temperature of sand bed (6) is increased to a level of 350° C - 400° C with

the help of hot flue gases from DG set. Once the required temperature is achieved, then a small amount of charcoal is introduced through screw feeder (5) into the hot sand bed (6). The charcoal burning inside the fluidized bed (6) further increases the temperature to a level of 700° C - 750° C. Then, coal feeding is started through screw feeder (5). The combustion of charcoal during startup as well as coal combustion is continued with the help of oxygen present in the flue gases. The hot flue gases at the combustion chamber (4) outlet are then passed through a heat exchanger (10) in order to recover the heat in the form of steam /hot water. The cooled flue gases are then passed through a cyclone separator (7) to separate out the particulate matter in the flue gas. This clean flue gas is sucked by an ID fan (8) and passed into the stack.
The exhaust temperature remains same as in case of any standard exhaust gas boiler. The additional steam generation would be on account of consumption of excess oxygen in DG exhaust by firing additional solid fuel like coal without supplying fresh air. This particular arrangement of combustion chamber (4) helps in minimizing the flue gas exhaust losses and give rise to conversion of efficiency for additional fired fuel of the order of around 80% similar to conventional fluidized bed coal fired boiler on GCV basis.
It is however possible to use bag filter or other fine solids separation units in place of the cyclone separator.
The following table indicates the improvements/advantages in the invention over the conventional exhaust gas boiler according to this modification.

PARAMETERS IMPROVED SF EGB- COAL
Increased steam generation Upto 140% compared to conventional EGB
Efficiency of supplementary firing 80% on GCV comparable to conventional fluidized bed boiler
Reduction in 02% From 10-12% to 4%
Reduction in CO emissions From 650 ppm to 150 ppm
Reduction in smoke index From more than 8 to less than 4
Power Approx. 3.5 KW of power saved per 1 ton of extra steam generated.
Overall size/foo{print Reduced to 0.75 times compared to conventional EGB and additional boiler





We Claim:
1. An improved method for the recovery of heat from flue gases of DG/exhaust which comprises passing the hot flue gases through a combustion zone, introducing fuel into the combustion zone, passing the hot flue gases exiting the combustion zone to a heat exchanger in order to recover heat in terms of steam by indirect heat exchange in the heat exchanger and subjecting the flue gases exiting the heat exchanger , if required, to a treatment to remove solid carryovers and suspended solid characterized by allowing the fuel injected into the combustion zone to be burnt by the oxygen present in the flue gases to create additional heat energy.
2. A method as claimed in claim 1, wherein, initially the combustion chamber temperature is increased by firing a small amount of fuel with the help of fresh air supplied by forced draft fan.
3. A method as claimed in claim 2, wherein, once the required temperature is achieved , the fresh air supply is cut off gradually and simultaneously the flue gases are introduced in the combustion chamber.
4. A method as claimed in claim 1, wherein, the combustion is carried out directly in a combustion zone.
5. A method as claimed in claim 1, wherein The combustion is carried out in a fluidized combustion zone, where the additional fuel is introduced into a fluidized bed of inert material like sand, which is fluidized by means of the hot flue gases.
6. A method as claimed in claim 5, wherein, the flue gases are made to pass through the sand bed, which in turn gets fluidized.
7. A method as-claimed in claims 5 and 6, wherein, initially the temperature of the sand bed is increased to a level of 350-400°C with the help of hot flue gases from a DG set.
8. A method as claimed in claims 5 to 7, wherein, once the required temperature is achieved, then the small amount of charcoal is introduced into the hot sand bed.


9. A method as claimed in claim 8, wherein, the charcoal burning in the fluidized bed further increases the temperature to a level of 700-750°C and the combustion of charcoal during start up as well as coal combustion is continued with the help of oxygen present in the flue gases.
10. A method as claimed in claims 5 to 9, wherein, the cooled flue gases are then passed through a cyclone separator to separate out the particulate matter in the flue gas before being admitted to the stack.
11. An improved heat recovery system for an exhaust gas boiler for recovering heat from the "DG exhaust gases", by the method claimed in Claims 1 to 10, comprising a combustion chamber for burning additional fuel with the help of additional oxygen present in the flue gases, the system also including an indirect heat exchanger, downstream of the combustion chamber both connected in series, the combustion chamber being provided with necessary inlet for the admission of additional fuel and wherein heat exchanger is provided with usual inlet for water and outlet for exhaust gases and means for recovery steam produced therein.
12. An improved heat recovery system as claimed in Claim 11, wherein in a preferred embodiment, there is provided a fluidized bed combustor, having a plenum chamber for admitting the hot flue gases followed by a fluidized bed zone having inert material like sand and having perforated distributor means upstream, which is followed upstream with a combustor chamber, there being also provided a feeder for additional fuel into the fluidized bed, a heat exchanger being provided following the combustor for recovering heat from the exhaust gases.
13. An improved method for the recovery of heat from DG exhaust flue gas in a exhaust gas boiler substantially as herein described.
14. An improved heat recovery system for an exhaust gas boiler substantially as herein described with reference to the accompanying drawings.
Dated this 23rd day of September 2000
DILIP WAMAN BAPAT for THERMAX LIMITED

Documents:

888-mum-2000-canceleld pages(04-03-2005).pdf

888-mum-2000-claims(granted)-(4-3-2005).doc

888-mum-2000-claims(granted)-(4-3-2005).pdf

888-mum-2000-correspondence(9-5-2005).pdf

888-mum-2000-correspondence(ipo)-(9-1-2006).pdf

888-mum-2000-drawing(28-9-2000).pdf

888-mum-2000-form 1(28-9-2000).pdf

888-mum-2000-form 19(12-3-2004).pdf

888-mum-2000-form 2(granted)-(4-3-2005).doc

888-mum-2000-form 2(granted)-(4-3-2005).pdf

888-mum-2000-form 26(4-3-2005).pdf

888-mum-2000-form 3(2-1-2002).pdf

888-mum-2000-form 3(4-3-2005).pdf

888-mum-2000-form 5(4-3-2005).pdf

888-mum-2000-petition under rule 137(18-2-2005).pdf

888-mum-2000-petition under rule 138(18-2-2005).pdf

888-mum-2000-power of attorney(2-1-2002).pdf

888-mum-2000-power of attorney(28-9-2000).pdf

abstract1.jpg


Patent Number 198182
Indian Patent Application Number 888/MUM/2000
PG Journal Number 41/2007
Publication Date 12-Oct-2007
Grant Date 09-Jan-2006
Date of Filing 28-Sep-2000
Name of Patentee THERMAX LIMITED
Applicant Address D-13, MIDC INDUSTRIAL AREA, CHINCHWAD, PUNE MAHARASHTRA,INDIA
Inventors:
# Inventor's Name Inventor's Address
1 BAPAT DILIP WAMAN C/O THERMAX LIMITED D-13, MIDC INDUSTRIAL AREA, CHINCHWAD, PUNE-411019. MAHARASHTRA,INDIA
2 AUTADE PRASAD KISAN C/O THERMAX LIMITED D-13, MIDC INDUSTRIAL AREA, CHINCHWAD, PUNE-411019.
3 LOBO ALTEN CARMO C/O THERMAX LIMITED D-13, MIDC INDUSTRIAL AREA, CHINCHWAD, PUNE-411019.
PCT International Classification Number F22B33/00 F22B33/18
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA