FIELD OF THE INVENTION
The present invention relates to use the heat wasted and improve boiler overall
efficiency of Indian pulverized coal tangentially fired boiler by providing Heat
Exchanger - low pressure economizer. More particularly, the invention relates to
an improved tangentially fired boiler using low-sulphur-content pulverized coal.
BACKGROUND OF THE INVENTION
As known in the art, in a boiler system, the feed water from the Low Pressure
Heater enters a Low Pressure economizer and picks up heat from flue gases
after the Air Pre-Heater. Many types of economizer are known for picking up
heat from the flue gas. The economizers can be classified as an inline or
staggered arrangement based on the type of tube arrangement. A staggered
arrangement of economizer is compact and occupies a less volume for the same
amount of heat transfer when compared to an inline arrangement. Economizers
configured with plain tube and finned tubes are known. The fins can be
longitudinal or spiral. All these types of economizers are suitable for clean fuels
like gas, oil, and low ash coals. For high ash coals, only the plain tube inline
arrangement of economizer is used. This is mainly to reduce ash erosion and
thus reduce erosion failures.
The boiler designers always keep the economizer water outlet temperature to
about 20 to 25°C below the saturation temperature. This is done to mainly to
avoid steaming in the economizer. A steaming economizer is generally less
reliable. As a rule of thumb, for every 1°C pickup of economizer water
temperature, there will be a drop of about 3 to 3.5°C.
The coal used in Indian pulverized coal tangentially fired Boilers has very low
sulfur content compared to globally available coal. Accordingly a higher outlet
temperature at chimney does not exist.
US patent US 4829938 describes a Heat recovery steam Generator disposed at
the exhaust of a gas turbine. An Exhaust Boiler includes a low pressure steam
generator and a low-pressure economizer disposed sequentially from an
upstream side within an exhaust gas flow passageway, and a de-nitrification
apparatus disposed upstream of the high-pressure economizer. Such a Boiler
achieves maximum heat recovery regardless of whether or not sulfur oxides are
contained in the exhaust gas.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved tangentially
fired boilers using low-sulphur content pulverized coal.
Another object of the invention to propose an improved tangentially fired boilers
using low-sulphur content pulverized coal, which is enabled to recover waste
heat from the flue gas.
A still another object of the invention to propose an improved tangentially fired
boilers using low-sulphur content pulverized coal, which is capable of reusing the
recovered flue gas for increasing the efficiency of the boiler.
A further object of the invention to propose an improved tangentially fired boilers
using low-sulphur content pulverized coal, which is configured to recover the flue
gas from the flow-circuit after the air pre-heater.
SUMMARY OF THE INVENTION
According to the invention, there is provided an improved tangentially fired boiler
using low-sulphur-Content pulverized coal, the improvement is characterized in
that a low-pressure economizer is disposed between the air pre-heater and
the electrostatic precipitator in the flow circuit to allow the feed water from the
low pressure heater ingress the economizer and exchange heat of the flue gas
picked-up from the circuit at a location after the air preheater the feed water
after heat exchange supplied back to the deaerator.
According to the invention, a Heat Exchanger is used to improve Boiler overall
efficiency of low-sulphur content pulverized coal fired Boiler, by using the
recovered waste heat after Air Pre-Heater.
The present invention provides a heat exchanger at the outlet of the air pre-
heater to use the waste heat so as to supply heat to the feed water.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows a schematic of tangentially fired Boiler using low-sulphur-
content pulverized coal according to prior art.
Figure 2 - Shows schematic of an improved tangentially fired boiler using low-
sulphur-content pulverized coal according to the invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
Figure 1 shows a schematic diagram of a tangentially fired Boilers (1) using
pulverized coal with low sulfur content, which eliminates the necessity to
maintain a higher outlet temperature at the chimney with regard to Acid dew
point.
Figure 2 shows an improved tangentially fired boiler using low-sulphur content
pulverized coal. The improvement comprises in that a Heat Exchanger (Low
Pressure Economizer) (7) is to recover waste heat from flue gas (9). The Heat
Exchanger (7) is placed between the Air Pre-Heater (2) and the Electro Static
precipitator (ESP) (3). The feed water (8) from the Low Pressure heater (4)
enters the Low Pressure economizer (7) and picks up heat from the flue gases
(9) after the Air Pre-Heater (2) and the feed water (8) is sent to the deaerator
(5). This Heat Exchanger (7) is used to improve the overall efficiency of the
boilers of Figure 1.
Figure 1 shows that the operational circuit of boiler system comprises an air pre-
heater (2) connected to an electrostatic precipitator (3) and to a gas turbine (6).
A low pressure heater (4) supplying feed-water (8) to a deaerator (5) which is
fed to the boiler (1).
WE CLAIM :
1. An improved tangentially fired boiler using low-sulphur-Content pulverized
coal, the improvement is characterized in that:
- a low-pressure economizer (7) is disposed between the air pre-heater (2)
and the electrostatic precipitator (3) in the flow circuit to allow the feed
water (8) from the low pressure heater (4) ingress the economizer (7) and
exchange heat of the flue gas (9) picked-up from the circuit at a location
after the air preheater (2) the feed water after heat exchange supplied
back to the deaerator (5).
2. An improved tangentially fired boiler using low-sulphur-Content pulverized
coal as substantially described and illustrated herein with reference to the
accompanying drawings.

The invention relates to an improved tangentially fired boiler using low-Sulphur-
Content pulverized coal, the improvement is characterized in that a low-pressure
economizer (7) is disposed between the air pre-heater (2) and the electrostatic
precipitator (3) in the flow circuit to allow the feed water (8) from the low
pressure heater (4) ingress the economizer (7) and exchange heat of the flue
gas (9) picked-up from the circuit at a location after the air preheater (2) the
feed water after heat exchange supplied back to the deaerator (5).