FIELD OF THE INVENTION
The present invention generally relates to a compact and leak-proof regenerative
air pre-heater with reduced auxiliary power consumption. More particularly, the
present invention relates to an improved nano fluid based liquid coupled air
heater for preheating combustion air in pulverized coal fired boilers. The
invention further relates to a method of operating such an improved air pre-
heater.
BACKGROUND OF THE INVENTION
The liquid coupled air pre-heater using nano- fluid as a working fluid is known in
the art, which reduces the size and weight of conventional regenerative air pre-
heater used in coal fired boilers. This air pre-heater also known to reduce the
auxiliary power consumption and configured to be leak-proof compared to the
typical regenerative type air pre-heater.
The weight of the conventional Air heaters used in power plants are quite high
and they are huge in size. Nano-materials are used to prepare Nano-fluid as a
working fluid for the known liquid coupled Air heater. The drawbacks of the
existing system is the leakages of air, huge size of the heater, and high power
consumption. The nano materials exhibit thermal conductivity in the fluid which
increases heat transfer from the gas to the liquid and the liquid to the air.
Hence, the size and the operational efficiency of the air pre-heater are enhanced.
OBJECTS OF THE INVENTION
It is therefore an object of the invention is to propose an improved Nano-fluid
based liquid coupled air pre-heater for coal fired Boiler, which eliminates the
disadvantages of prior art.
Another object of the invention is to propose an improved Nano-fluid based liquid
coupled air pre-heater for coal fired Boiler, which is capable to recover heat from
flue gas after economizer and heat the combustion air.
A still another object of the invention is to propose an improved Nano-fluid based
liquid coupled air pre-heater for coal fired Boiler, which allows reduction of the
heat transfer surface area and weight of the Nano-fluid based liquid coupled air
pre-heater.
A further object of the invention is to propose an improved Nano-fluid based
liquid coupled air pre-heater for coal fired Boiler, which reduces the auxiliary
power consumption and leakage of heated air from the pre-heater.
A still further object of the invention is to propose a method for operating an
improved Nano-fluid based liquid coupled air pre-heater for coal fired Boiler.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved nano fluid based liquid coupled air
heater for preheating the combustion air in pulverized coal fired boilers.
The invention makes use of the nano-fluid in a closed loop which allows transfer
of heat from the gas to the air. Initially, the nano fluid takes the heat from the
flue gas, which is at a temperature of around 350°C and the nano fluid conveys
the acquired heat to the section where air passes over the tube to take away the
heat form the nano fluid. The air is typically heated to a temperature about
300°C. The system as whole reduces the air leakage due to a closed loop formed
by the air pre-heater.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1- Shows a schematic view of a pulverized coal fired Boiler.
Figure 2- Shows schematic of pulverized coal fired Boiler with a nano fluid based
Liquid coupled air pre-heater of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides an improved air pre-heater in a boiler system, which is
configured and disposed so as to allow circulation of nano-fluid in a closed loop
to transfer heat from the gas to the air. Initially the nano fluid takes the heat
from the flue gas, which is at a temperature of around 350°C and the nano fluid
takes up the heat and is conveyed to the section where air passes over the tube
to take away the heat form the nano fluid. The air is typically heated to the
range of 300°G
Fig. 2 shows a nano-fluid based air pre heater circuit of the improved pre-heater,
comprising an inlet header (7) followed by a first heat exchanger (8) located in
the flue gas duct, a second heat exchanger located in the combustion air duct
(9), an outlet header (10), and a circulation pump (6).
The working fluid (nano-fluid) (13) enters the first heat exchanger located in the
flue gas duct (8) through the inlet header (7) and picks up heat after the
economizer (5) from the flue gases (3) having temperature around 350°C, and
passes to the second heat exchanger located in the combustion air duct (9)
where cold air enters (11) over the heat exchanger tubes. The air picks up the
heat from the nano fluid and leaves as the higher temperature combustion air
(12). The condensed working fluid (nano-fluid) (13) passes to the outlet header
(10) and is re-circulated through the circulation pump (6). Accordingly, the air
heater of the invention is enabled to pre-heat the combustion air upto 300°C to
increase efficiency of the boiler. Due to operation of the pre-heater in the boiler
as a closed-loop circuit, the leakage of heated air is eliminated which interalia
reduces the auxiliary power consumption of the boiler system.
WE CLAIM :
1. A method for operating an improved an improved Nano-fluid based liquid
coupled air pre-heater for coal fired Boiler, the improved nano-fluid based
liquid coupled air heater comprising an inlet header (7), a first heat
exchanger (8) disposed adjacent to the inlet header (7) and
accommodated in the flue gas duct (8) of the boiler, a second heat
exchanger interposed in the combustion air duct (9), an outlet header
(10) being connected to a circulation pump (6), the method comprising
the steps of :
- inputting a nano-fluid (13) through the first heat-exchanger (8) via the
inlet header (7);
- allowing the flue gases (3) through the boiler system;
- picking-up heat from the flue gases (3) when passing at temperature
around 350°C after the economizer (5) of the boiler system by the flowing
nano-fluid (13);
- arranging the de-tempered flue gases (3) to pass through the second
heat-exchanger located in the combustion air duct (9);
- passing cold air (11) over the heat exchanger's tubes which take away the
heat from the nano-fluid (13) and exit at a temperature around 300°C for
use as the combustion air (12); and
- passing the condeused nano-fluid through the outlet header (10) for
recirculation by the circulation pump (6).

ABSTRACT

"A method for operating an improved an improved Nano-fluid based liquid coupled air pre-heater for coal fired Boiler"
The invention relates to an improved nano fluid based liquid coupled air heater for preheating the combustion air in pulverized coal fired boilers. The invention makes use of the nano-fluid in a closed loop which allows transfer of heat from the gas to the air. Initially, the nano fluid takes the heat from the flue gas, which is at a temperature of around 350°C and the nano fluid conveys the acquired heat to the section where air passes over the tube to take away the heat form the nano fluid. The air is typically heated to a temperature about 300°C. The system as whole reduces the air leakage due to a closed loop formed by the air pre-heater.