FIELD OF INVENTION
The present invention relates to an optical measurement system to determine
operating temperature of heat exchanger tube metal including surface
temperature of the heat exchanger.
BACKGROUND OF THE INVENTION
Power Plants, Refineries, and other large industries, deploy steam generating
units having water tubes for producing steam. The furnace in these steam
generators is designed for firing fuel oil, fuel gas or coal. After attaining the
conductive conditions for firing the fuel, the fuel is admitted into the furnace of
the boiler. The fuel gets lighted-up by ignitors and the flame gets established in
the boiler furnace. The high temperature flue gas from the furnace passes
through several heat absorbing elements deployed at different locations in the
steam generator. Overheating of components like superheater, headers etc., in a
steam generator considerably shorten life of the boiler. The speed at which a
steam power plants can be brought to full-load is largely dependent on the rate
of change of metal temperatures of the various plant components. So
temperature measurements of various plant items are necessary for quick start-
up of the plant.
Monitoring the condition of heat exchanger tube surface is critical in a steam
generator plant particularly operating at a relatively high temperature and
pressure.

The prior art temperature measuring systems utilise one or more temperature
monitoring devices operating by electric or mechanical means for measurement
of heat exchanger tube metal or skin temperature in a steam generator.
Accordingly, the prior art monitoring devices normally constitutes thermocouples
- a device based on thermoelectric effect - which may be deployed staggeredly
throughout the furnace including the heat transfer surfaces. The thermocouples
are placed in the steam generator in such a way that a plurality of protective
sheaths arranged to separate each thermocouple. This is done to protect the
relatively fragile thermocouple junctions from the hostile environment inside the
steam generator. Consequently, the thermocouples are not enabled to sense the
reaction temperature directly, but instead respond to the transmitted heat. As a
result, the lag time inherent in the conductive heat transfer, causes a substantial
delay in thermocouple response to the changes in temperature within the
combustion chamber. This phenomenon is especially exhibited during system
startup when the initiation of combustion reaction results in a rapid temperature
rise which needs to be detected in order to confirm combustion initiation. In
addition, heat transfer lag times affect thermocouple response to the changes in
operating condition during normal system operation. Moreover the
thermocouples constitute spot measurement devices.
Another prior art system of temperature measurement in a furnace adapts the
acoustic pyrometers. Physically, the acoustic pyrometer is mounted external to
the furnace wall. It is connected to the furnace wall via a purgeable lance tube
which normally extends from the pyrometer into the furnace internals. The
medium temperature is deduced from the time of flight it takes for a calibrated
sound signal to travel across from a transmitter to a receiver of the device which

are separated across the width of the furnace. A major limitation of this
pyrometer temperature monitor, is the difficulty encountered in keeping the
lance tube free of obstructions. Further, the signals arising out of auxiliary
equipment like soot blowers coupled with steam leakage in the furnace also
influence the measurand to a considerable extent. Acoustic pyrometer can only
provide an averaged value of the measurand in a path between its receiver and
transmitter.
OBJECT OF THE INVENTION
*
It is therefore, an object of the invention to propose an optical measuring system
to determine the temperature in a heat exchanging apparatus of a steam
generator which eliminates the disadvantages of prior art.
Another object of the invention is to propose an optical measuring system to
determine the temperature in a heat exchanging apparatus of a steam
generator, based on data representing associated change in physical property of
optical sensing means of the system.
A still another object of the invention is to propose an optical measuring system
to determine the temperature in a heat exchanging apparatus of a steam
generator in which an array of multi point sensors are arranged in a single
optical means.

A further object of the invention is to propose an optical measuring system to
determine the temperature in a heat exchanging apparatus of a steam generator
by utilizing the interference signal produced by the measurand induced change in
the optical sensing means.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a Schematic of a Fiber optic based Temperature sensor according
to the invention.
DETAILED DESCRIPTION OF THE INVENTION
As shown in figure. 1, an optical measuring system (1), comprises an optical
sensing array deployed within a steam generator structure (2). The embedded
optical sensing array receives the light originating from a light source when
launched into it via a fiber optic cable (3). The received light undergoes
reflection within the sensing array at a reflector located at a distal end of the
sensing means. The reflected light interacts with the incident light from the light
source to produce an interference pattern at the junction (a gap) between light
guide and the reflector within the optical sensing array. As the sensing array
undergoes geometric deformation due to change in process conditions in the
steam generator, the extent of change in the interference signal varies relatively.
As the light travels, through the optical sensing array, the interference signal
undergoes a relative modulation. A signal interrogating means (4) deployed at
the end of the optical array determines the measurand value at the sensor points
as a function of the modulation in the interference signal. The measurand of
interest being the temperature in a heat exchanging apparatus of a

steam generator, a signal processor (5) is provided to process the interference
signal data and output measurand profile of the heat exchanging apparatus in
the steam generator from the acquired temperature values by the sensor array.

WE CLAIM
1. An optical measuring system to determine the temperature in a heat-
exchanging apparatus of a steam generator, comprising:
- an optical sensing array (1) consisting of a plurality of temperature
sensors deployed within the steam generator structure (2), a reflector
placed at a distal end of the sensing array (1);
- a light source launching light rays via an optical cable (3) which
undergoes reflection within the sensing array (2) by the reflector;
- a light guide deployed at a spaced apart location from the reflector, by
maintaining a gap;
- an interference pattern generated at said gap by the reflected light
when interacting with the incident light which causes a geometric
deformation of the sensors in the array (1) due to change in the
process parameters inside the steam generator corresponding to
modulation in the pattern of changed interference signals;
- a signal interrogation means (4) deployed in the sensing array (1)
determining the temperature data in the heat exchanging apparatus as
a function of the modulation in the interference signal; and
- a signal processor (5) to process the input data and output of the
temperature profile of the heat exchanging apparatus.

2. The system as claimed in claim 1, wherein the components that comprise
the heat exchanging apparatus comprises a fuel burner, evaporator tubes,
superheater tubes, reheater tubes, a separator, a steam header, and a
water header.

This invention relates to an optical measuring system to determine the
temperature in a heat-exchanging apparatus of a steam generator, comprising
an optical sensing array (1) consisting of a plurality of temperature sensors
deployed within the steam generator structure (2), a reflector placed at a distal
end of the sensing array (1); a light source launching light rays via an optical
cable (3) which undergoes reflection within the sensing array (2) by the
reflector; a light guide deployed at a spaced apart location from the reflector, by
maintaining a gap; a'n interference pattern generated at said gap by the reflected
light when interacting with the incident light which causes a geometric
deformation of the sensors in the array (1) due to change in the process
parameters inside the steam generator corresponding to modulation in the
pattern of changed interference signals; a signal interrogation means (4)
deployed in the sensing array (1) determining the temperature data in the heat
exchanging apparatus as a function of the modulation in the interference signal;
and a signal processor (5) to process the input data and output of the
temperature profile of the heat exchanging apparatus.