FIELD OF THE INVENTION
The present invention relates to plurality of methods to utilizea low pressure heat exchanger to recover waste heat from flue gas after air heater and improve the overall efficiency of low Sulphurcontaining fossil fuel fired thermal power plant. More particularly this invention relates tothe introduction ofa low pressure Heat Exchanger between Air heater and Electro Static Precipitator in the flue gas path and taking bypass feed water line, passing it through the heat exchangerto recover heat from flue gas and connecting to deaerator inlet. Furthermore particularly this invention relates to improvingthe overall efficiency of thermal power plantfiring low Sulphur containing fuel by introducingLow Pressure (LP)heat exchangertoextract heatfromflue gas leavingthe Air Heater.
BACKGROUND OF THE INVENTION
If the steam power plant is of condensing type, the steam is converted to water by condenser. The boiler feed pump (BFP) feeds the water in to the boiler where it is heated to form the steam. The wet steam is again heated in super heater, before it is passed to the turbine. The super-heated steam is expanded in the turbine to run it.Depending upon the size of the power plant unit, there are different stages of prime mover i.e., High pressure (HP) turbine, Intermediate pressure (IP) turbine and Low pressure (LP) turbine. The steam after the expansion in HP turbine is sent back to boiler for reheating to increase the temperature and pressure and then expands in the IP and LP turbines. The steam leaving the final stage of turbine is condensed in a condenser positioned after the turbine. Condensate collected in the well of the condenser is pumped by one or more extraction pumps to condensate preheaters that preheat the condensate using steam extracted from the low and intermediatepressure steam turbines. The plant may further comprise one or more high pressure preheaters located downstream of a feed water pump system used to boost the temperatureof the condensate downstream of the low-pressure preheaters. Steam extracted from the IP and LP turbine stages may be used as a

heat source for these LP preheaters. Preheated condensate from the high pressure preheaters is then fed into the boiler thus completing a closed loop steam condensate cycle.
The flue gas emitted from power plants has lot of energy that could be recovered for useful boiler application. Thermal power plants let out flue gas at around 150˚C considering the acid dew point of high Sulphur coals with which the design guidelines were developed. Manyfossil fuel fired Boilersare firingfuels containing very low sulfur and the sulfur dew point temperature for the flue gas of these boilers is very low below 100 ˚C. So, the need to maintain higher outlet temperature at chimney does not exist and this is used as an advantage in this invention to recover heat by providing a heat exchanger at the outlet of the air heater and heat the feed water.Hence, the heat contained in this flue gas could be recovered up to above water dew point of 100˚C for useful boiler applications. For every 22˚C reduction in flue gas temperature by passing through an economiser or a pre-heater, there is 1% saving of fuel in the boiler. In other words, for every 6˚C rise in feed water temperature through an economiser, or 20˚C rise in combustion air temperature through an air pre-heater, there is 1% saving of fuel in the boiler.Finally, the overall efficiency of the thermal power plant will be increased.
US4829938 described about the Heat recovery steam Generator, at the exhaust of the gas turbine. An Exhaust Boiler includes a low pressure steam generator and a low-pressure economiser disposed sequentially from an upstream side within an exhaust gas flow passageway, and a de-nitrification apparatus is disposed upstream of the high-pressure economiser. Such Boiler is improved so as to achieve maximum heat recovery regardless of whether or not sulfur oxides are contained in the exhaust gas.
As perthis prior art, the Low Pressure economiser is available for only Gas Turbine heat recovery steam generators but the present invention is a Low Pressure heat exchanger that will be used for boilers firing low Sulphur containingfossil fuels.

EP2851616A1 described a power plant with a fossil fuel fired boiler, an air feed system, flue gas system and condensate system. A unitary flue gas heat exchanger spans a bypass line in the flue gas system and the condensate system so as to improve the thermal efficiency of the power plant while minimising complexity.
As per this prior art, the high pressureeconomiser is available for higher pressure and higher temperature zone in thermal power plant but the present invention is Low Pressure heat exchangerthat will be used for low Sulphurfossil fuel fired Boilers.
OBJECTS OF THE INVENTION
The object of the invention is to recover waste heat from the flue gas after Air Heater of a low Sulphurcontaining fossil fuel fired Boiler.
Another object of the invention is to improve the overall efficiency of a low Sulphur containingfossil fuel fired Boiler.
Still another object of the invention is to locate a Low Pressure (LP)heat exchanger between Air Heater and Electro Static precipitator (ESP) in theflue gas line and pre¬heat water.
Still another object of the invention is to establish plurality of options for the second condensate line of condensed system for Low Pressure Heat Exchanger.
Still further object of the invention to overcome or at least ameliorate the disadvantages and shortcomings of the prior art or provide useful alternatives.
SUMMARY OF THE INVENTION
Aimproved fossil fuel power plant arrangement are provided that address the dual problem of plant complexity and thermal efficiency.The Low Pressure (LP)heat exchanger is required to recover waste heat from flue gas for low Sulphur containingfossil fuel fired Boiler. Low Pressure heat exchangeris placed between Air Heater and Electro Static Precipitator (ESP). A first condensate line, connected to the

boiler for feeding condensate into the boiler, with a plurality of preheaters, and a second condensate line with first and second distal ends connected to the first condensate line.The feed water tapped from the condensate line enters the Low Pressure heat exchangerand picks up heat from the flue gases after the Air Heaterand is sentback to the condensate line. This Heat Exchanger is used to improve the overall efficiency of boilers firing low Sulphur containingfossil fuels.
In an aspect, the condensate line comprises condenser, hot well, one or more gland coolers preheaters, one or more low pressure preheaters, one or more high pressure preheaters, a condensate extraction pump that is fluidly located between the hot well and one or more gland coolersto maintain vacuum in the condenser system and a feed water pump system that is fluidly located between the one or more low pressure preheaters and the one or more high pressure preheaters. The feed water pump system is configured and arranged to boost condensate pressure in the first condensate line.A first end of the second condensate line is located upstream of the condensate extraction pump system orupstream of gland coolers or upstream of the low pressure heater and the second end of the second condensate line having an auxiliary feed water pump system ends back in main condensate line at a location after gland coolers or in-between LP coolers or after LP coolers.
In different aspects the auxiliary feed water pump system is located either upstream or downstream of the Low Pressure Heat Exchanger.
In an aspect, the second end of the second condensate line is located downstream of the one or more low pressure preheaters, while in another aspect the second end of the second condensate line is located in hot well.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
By way of example, an embodiment of the present disclosure is described more fully
hereinafter with reference to the accompanying drawings, in which:
Fig. 1 is a schematic of a prior art thermal power plant arrangement (Prior art);

Fig.2 is a schematic of an embodiment having a Low pressure (LP) heat exchanger combined with a secondary condensate line from the outlet of one or more gland cooler with an auxiliary feed water pump systemand connected to deaerator inlet.
Fig.3 is a schematic of a further embodiment having a Low pressure (LP) heat exchanger combined with a secondary condensate line from thedownstream of condensate extraction pump to deaerator inlet.
Fig.4 is a schematic of a further embodiment having a Low pressure (LP) heat exchanger combined with a cascade of condensate Low pressure preheaters and end of second condensate line connected to one or more Low pressure (LP) preheaters;
Fig.5 is a schematic of a further embodiment of a thermal powerplant having Low pressure (LP) heat exchanger and a secondary condensate line connected to intermediate hot condensate heat exchangerat low pressure region;
Fig.6 is a schematic of a further embodiment having a Low pressure (LP) heat exchanger combined with a secondary condensate line from thedownstream of one or more gland coolerto upstream of the auxiliary feed water pump.
Fig.7 is a schematic of a further embodiment having a Low pressure (LP) heat exchanger eliminate one or more low pressure preheaters and the auxiliary feed water pump system is located upstream of the Low Pressure (LP) Heat Exchanger.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION
Fig. 1 shows the partial schematic of a low Sulphurfossil fuel fired thermal power plant. Such a fossil fuel thermal power plant includes, a boiler (10), an airline (21) for feeding mainly combustion airinto the boiler, a flue gas line (12) for exhausting flue gasfrom the boiler, and a condensate line (3) that forms parts of a closed loop

water/steam circuit for feeding condensatethrough heaters (5, 6, and 9) into the boiler.
The condensate line (3) includes a condenser (1), a plurality of preheaters that may include one or more gland cooler (5), one or more low pressure preheaters (6) and one or more high pressure preheaters (9). In such an arrangement, a condensate extraction pump(4), located between the condensers hot well(2) and the gland coolers(5) boosts the pressure of condensate passing through the condensate line (3). In addition, a feed water pump (8), located between the Deaerator(7) and the high pressure preheaters (9) boosts the pressure of heated condensate passing in to the boiler. The flue gas line (12) includes an air preheater (11), Electrostatic precipitator (13), induced draft fan (15) and a chimney (16).
Fig. 2 shows one of the plurality of options of using Low Pressure (LP)heat exchanger (19)to recover heat from the exit flue gas (12) and preheat the condensate. The Low Pressure (LP)heat exchanger (19)shallbe placed in between air preheater (11) and Electro Static Precipitator (ESP) (13).
In addition, the condensate system includes a second condensate line (17) that extends from the condensate line (3) between the one or more gland coolers (5) and one or more low pressure preheaters (6), through an auxiliary feed water pump system (18) and then through a LP heat exchanger (19)located on the flue gas line (12), before returning back to a region of the condensate line (3) between the one or more low pressure preheaters (6) and deaerator (7).In an alternate not shown embodiment, the auxiliary feed water pump system is located downstream of the Low Pressure (LP)heat exchanger (19) instead of upstream of the Low Pressure (LP)heat exchanger (19).
The feed water leaving gland coolers (5) ofthe condensate system (3) enters the Low Pressure (LP)heat exchanger (19)and recover heat from the flue gases (12)

after the Air Heater(11) and the heated feed water is sentback to the deaerator (7) in the condensate system (3).
In a further embodiment shown in Fig. 3, the Low Pressure (LP) heat exchanger (19)may be placed in between air preheater (11) and Electro Static Precipitator (ESP) unit (13). In addition, the condensate system includes a second condensate line (17) that extends from the condensate line (3) between the condensate extraction pump (4) and one or more gland coolers (5), and then through a LP heat exchanger (19)located on the flue gas line (12), before returning back to a region of the condensate line (3) between the one or more low pressure preheaters (6) and deaerator (7).In an alternate not shown embodiment, the auxiliary feed water pump may beadditionally located upstream or downstream of the Low Pressure (LP)heat exchanger (19) as shown in Fig. 3.
The feed water from the condensate system (3) enters the Low Pressure (LP)heat exchanger (19)and recover heat from the flue gases (12) after the Air Heater(11) and the heated feed water is sentback to the deaerator in the condensate system (3).
In a further embodiment shown in Fig. 4, the Low Pressure (LP)heat exchanger (19)may be placed in between air preheater (11) and Electro Static Precipitator (ESP) (13). The Low Pressure (LP)heat exchanger (19)may extract the heat of exit flue gas from the air heater (12). The condensate system additionally includes a second condensate line (17) that extends from the condensate line (3) between the one or more gland coolers (5)and one or more low pressure preheaters (6), through and auxiliary feed water pump (18), a Low Pressure (LP)heat exchanger (19) located on the flue gas line (12) and then through the one or more low pressure preheaters (6) before returning back to the condensate line (3), either directly to the condensate line (3) or directly to thecondenser hot well (2) which is not shown in Fig. 4.

In an alternate not shown embodiment, the auxiliary feed water pump system is located end of downstream of the Low Pressure (LP)heat exchanger (19) instead of upstream of the Low Pressure (LP)heat exchanger (19).
The feed water from the condensate system (3) enters the Low Pressure (LP)heat exchanger (19)and recover heat from the flue gases (12) after the Air Heater(11) and the feed water is sentback to LP heaters (6) in the condensate system (3).
In a further embodiment shown in Fig. 5, the Low Pressure (LP)heat exchanger (19)may be placed in between air preheater (11) and Electro Static Precipitator (ESP) unit (13). In addition, the condensate system includes a second condensate line (17) that extends from the condensate line (3) between the condenser hot well (2) and condensate extraction pump (4),through an auxiliary feed water pump (18) and then through a LP heat exchanger (19)located on the flue gas line (12), and then through a condensate heat exchanger (22) before returning back to the same region of the condensate line (3), either directly to the line portion (3) which is not shown in Fig. 5 or else to a condenser hot well(2) that forms part of the condensate line (3).In an alternate not shown embodiment, the auxiliary feed water pump system may beadditionally located downstream of the Low Pressure (LP)heat exchanger (19).
The feed water from the condensate system (3) enters the Low Pressure (LP)heat exchanger (19)and recover heat from the flue gases (12) after the Air Heater(11), preheats condensate in condensate line (20)through the condensate heat exchanger (22) and the heated feed water is sentback to condensate system (3)/condenser well (2).
A third condensate line (20)from the condensate line (3) taken at a point between the condensate extraction pump system (4)and the one or more gland coolers (5)passes through the condensate heat exchanger (22) and ends at a point between

the one or more low pressure preheaters (6) and the deaerator (7). The second condensate line (17) and the third condensate line (20) to the condensate are thermally connected via a heat exchanger (22) as shown in Fig. 5.
In a further embodiment shown in Fig. 6, the Low Pressure (LP)heat exchanger (19)may be placed in between air preheater (11) and Electro Static Precipitator (ESP) unit (13). In addition, the condensate system includes a second condensate line (17) that extends from the condensate line (3) between the one or more gland coolers (5) and the one or more low pressure preheaters (6), through a Low Pressure (LP)heat exchanger (19) located on flue gas line (12), , before returning back to a region of the condensate line (3) between the auxiliary feed water pump system (18) anddownstream of the one or more low pressure preheaters (6).
The feed water from the condensate system (3) enters the Low Pressure (LP)heat exchanger (19)and recover heat from the flue gases (12) after the Air Heater(11) and the heated feed water send back to condensate system (3) after one or a plurality of LP heaters (6) and the auxiliary feed water pump (18).
In a further embodiment shown in Fig. 7, the Low Pressure (LP)heat exchanger (19)may be placed in between air preheater (11) and Electro Static Precipitator (ESP) unit (13). In addition, the condensate system extends from a point after a single LP heater (6) or in between a plurality of LP heaters in thecondensate line (3) passes through an auxiliary pump (18), theLP heat exchanger (19)located on the flue gas line (12) and returns back to condensate line at a point after one or more low pressure preheaters (6).In an alternate not shown embodiment, the auxiliary feed water pump system may be downstream of the Low Pressure (LP)heat exchanger (19).
The feed water from the condensate system (3) enters the Low Pressure (LP)heat exchanger (19)and recover heat from the flue gases (12) after the Air Heater(11) and the heated feed water is sentback to condensate system (3).

WE CLAIM
1. An improved low sulphur fossil fuel fired thermal power plant, comprising:
- a low sulphur containing fossil fuel fired Boilers having an air feed line for feeding air into the boiler;
- a flue gas line connected to the boiler for exhausting flue gas from the boiler;
- a main condensate line connected to a boiler economiser for feeding condensate into the boiler, the boiler further having a Condenser; a hot well; at least one gland cooler; at least one low pressure preheater ; a deaerator; at least one high pressure preheater;
- a condensate extraction pump system fluidically located between the condensate hot well and said at least one gland cooler, and configured to maintain vacuum in the condenser and a feed water pump system fluidically located between the deaerator and said at least one high pressure preheater, and configured to boost condensate pressure in a first condensate line, and
- at least one additional condensate line with first and second distal end connected to the main condensate line,
- characterized in that a Low Pressure (LP) Heat Exchanger is placed between an Air Heater and an Electro static precipitator (ESP); and in that the low Pressure (LP) heat exchanger configured such that the feed water from the condensate system enters the Low Pressure (LP) heat exchanger and recover heat from the flue gases after the Air Heater and the heated feed water is sent back to condensate system.
2. The thermal power plant as claimed in claim 1 wherein the condensate line
further comprising;
- a second condensate line, a first end of the second condensate line located
between downstream of the at least one gland cooler and upstream of the at

least one low pressure preheater, and wherein an auxiliary feed water pump system located in the second condensate line;
- a second end of the second condensate line located between the downstream of the at least one low pressure preheater and the deaerator; and
- said second end of the second condensate line passes through downstream of the at least one low pressure preheater and upstream of the auxiliary feed water pump before returning back to the condensate line or directly to the condenser hot well.
3. The thermal power plant as claimed in claim 1 wherein a first end of the second condensate line is further located between downstream of the condensate extraction pump and upstream of the at least one gland cooler; and wherein a second end of the second condensate line is further located between downstream of the at least one low pressure preheater and the deaerator.
4. The power plant as claimed in claim 1, wherein :
- the first end of the second condensate line is also located between said hot well and the condensate extraction water pump system and the second end of the second condensate line passing through the LP heat exchanger in flue gas path, and
- a condensate heat exchanger located in a third condensate line being fluidically connected to the condenser hot well,
- the third condensate line with a first end located between the Condensate extraction pump and the at least one gland cooler and the second end located between the at least one low pressure preheater and the deaerator after picking heat from the second condensate line in the condensate heat exchanger.

5. The thermal power plant as claimed in claim 1 wherein the condensate line passes through the LP heat exchanger located on the flue gas line eliminating at least one low pressure preheater and the auxiliary feed water pump system is located upstream of the Low Pressure (LP) Heat Exchanger.
6. The power plant as claimed in claim 1 to 5 wherein the auxiliary feed water pump system is located upstream of the Low Pressure (LP) Heat Exchanger.
7. The power plant as claimed in claim 1 to 5 wherein the auxiliary feed water pump system is located downstream of the Low Pressure (LP) Heat Exchanger.