FIELD OF INVENTION
The present invention relates to an integrated Programmable Logic Controller
(PLC) based apparatus for online monitoring of the health of structures and also
the slag deposition on the surface of heat exchangers in coal fired boilers in
thermal power plants. More particularly the invention relates to an integrated
apparatus to continuously monitor the health of structures and the formation of
ash deposition on heat exchanger coils in a steam generator.
BACKGROUND OF THE INVENTION
Fossil fuel power plants generate about two-thirds of the world's total electricity
and are expected to continue to play an important role in the future. Increasing
global energy demands, coupled with the issues of aging, inefficient power plants
and increasing strict emission requirements require high levels of performance,
efficiency and environmental controls from thermal power plants. In this context,
use of advanced condition-monitoring apparatus will play an important role in
meeting these challenges by helping to enhance the overall performance and
reliability of coal fired boilers in thermal power plants.
The boilers in a thermal power plant, comprises a furnace enclosed by four
water cooled walls, flue gas channels arranged above the furnace and a second
pass. The various heat exchanger coils - superheaters, reheaters etc., are

mounted in upper part of furnace / second pass. When the boiler is in operation,
heat is transferred from hot flue gas to these heat exchangers. The furnace
walls, heat exchanger coils - superheaters, reheaters - steam cooled walls in
second pass etc., are supported (hangs) from suitable structures at the top.
The boiler supporting structure usually consist of vertical columns and horizontal
main beams supported on top of the columns, to which other supporting beams
of the structure and the suspending structure of the furnace are mounted. The
main supporting beams are usually 25 - 30 m length and weigh more than 100
tons. The main supporting beams are usually connected to other smaller
horizontal supporting beams. The total height of supporting structure of a 500
MW coal fired boiler is typically about 80 - 100 m. The furnace of the boiler is
suspended from a stationary bearing structure surrounding the furnace by means
of hanger rods.
Coal is one of the most significant natural resources in the world. The
abundance, wide distribution and versatility of coal make it an important source
of energy for the present and future. More electricity is produced from coal than
any other fuel. The design and performance of thermal power plants and the
costs of power generation are influenced by coal properties. Often power plants
are not sure of the quality of coal that they will be getting for the boiler and
hence there is a necessity to burn coals of varying quality on daily basis. Boiler
manufacturers are frequently asked to engineer / design the steam generator

capable of firing wide range of coals. However boilers are designed to burn a
specified range of coals only, since designing the boiler for a wide range of coals
will not allow the manufacturer to select optimum equipment for the particular
power station.
There are different ranks of coals including anthracite, bituminous, sub-
bituminous and lignite. Within each type, there are a variety of grades. From the
standpoint of boiler performance, the following coal properties are of the most
interest:
(a) Heating value;
(b) Volatile matter;
(c) Ash
Heating value: An important property, which indicates the useful energy content
of a coal and thereby its value as a fuel, is its calorific value (also known as
heating value), which is defined as the amount of heat evolved when a unit
weight of the fuel is burnt completely and the combustion products cooled to a
standard temperature of 298 K.
Volatile matter in coal refers to ' those products, exclusive of moisture, given off
by the fuel as gas or vapour'. The components of volatile matter are usually a
mixture of hydrocarbons, carbon monoxide, carbon dioxide, tar and water. The
composition of the volatile matter of coal is different for the different ranks of
coal.

Ash: All coals contain non-combustible mineral material called ash. Typical values
for the ash content in Indian coals ranges from 28% to 45% by weight.
In present day boilers, high furnace heat loading is employed to ensure optimum
design. Whenever the fuels burnt in the boiler changes from the design coal to
other coals, often severe slagging problem is encountered due to the lower ash
softening temperature. Also the firing of medium-to-high sulfur coal result in
high furnace exit gas temperature and low ash fusion temperature. This slagging
on the boiler surfaces results in formation of ash deposits on furnace walls, the
various heat exchanger coils - superheaters, reheaters etc,. Due to slagging and
deposit formation on furnace walls, the heat transfer in the furnace area gets
reduced resulting in increase in flue gas temperature beyond the design values
along the flue gas path. Formation of ash deposits on superheater / reheater
tubes has two undesirable effects. It reduces the tubes heat-transfer capacity
resulting in overheating and possibly tube failure. The deposits slowly grow in
size, becomes big enough and fall causing considerable damage to the tubes /
furnace bottom. In many occasions, it results in flame failures, or blockage in
the ash handling system at furnace bottom causing unscheduled boiler
shutdowns. The consequence of this is reduced boiler efficiency and plant
output. Accumulation of slag and ash deposit buildup on the tubes of
superheaters and reheaters represent a dynamic processes that sometimes
escape notice until removal of this material becomes a big problem.

According to prior art, cameras are provided in boilers to observe slag deposits
formation inside boiler furnaces and ash deposition on the heat exchanger coils
located above the furnace / at the entry point to the convection pass. In some
cases, an indirect method of measuring deposits such as monitoring differential
pressure across heat exchanger coils is used. For the purpose of monitoring the
condition of the boiler structures, no specific or integrated apparatus is used.
These measurement methods had limited success in detecting ash deposition on
heat exchanger coils early enough to remove them before they cause damage.
Nevertheless, in the prior art methods, slag deposits formation inside boiler
furnaces and ash deposition on the heat exchanger coils are not monitored
effectively. At times, this result in damage to furnace wall / heat exchanger coils.
Thus, the prior art methods for detecting accumulation of slag and ash deposit
buildup have had limited success in detecting early enough to remove them
before they cause damage.
The invention relates to an integrated apparatus employed for online monitoring
of the health of structures and ash deposition on heat exchangers in coal fired
boilers in thermal power plants using smart type sensors.

SUMMARY OF THE INVENTION
Accordingly, there is provided an integrated apparatus to continuously monitor
the formation of ash deposits on heat exchanger coils in a steam generator.
In the proposed invention an apparatus based on highly sensitive, wireless
based smart sensors are used to measure the weight of deposited ash. The
smart sensors are mounted / fixed on the hanger rods that support the heat
exchanger coils. The smart sensors detect the strain in the hanger rods caused
by the weight of the accumulated ash deposit. Since highly sensitive smart
sensors are used, even small tensions in the hanger rods can be detected. The
apparatus covered in this invention uses wireless, digital type smart sensors.
The smart sensors transmit signals to a PLC based system located in the control
room. Availability of this apparatus to detect ash deposition on heat exchanger
coils, in the early stages will be useful to thermal power plants.
The smart sensors measure changes in weight due to ash deposition forming on
the heat exchanging coils. The installation consists of smart sensors mounted on
the hanger or suspension rods for the superheaters / reheater coils, wireless
units and a PLC based system. The sensors provide an output corresponding to
the weight using the stress strain relationship. The weight measurement can be
started at any time during the measurement process and any subsequent
readings indicate the change in weight from starting conditions.

As mentioned in the earlier paragraphs, the boiler is suspended from a huge
structure. Continuous monitoring of the condition of main members of boiler
structures reduces the maintenance costs and enhances the reliability. Through
condition monitoring, an effective plan for maintenance can be determined, thus
enabling the possibility to prolong service life. To monitor the condition of main
members of the boiler structure, measurement of parameters like load, vibration,
displacement etc., using smart sensors is envisaged.
The installation consists of mounting of smart sensors on the hanger rods for the
heat exchanger coils and main members of boiler structure and providing signals
to a PLC based system through wireless units and measures change in weight
due to ash deposits formed on the heat exchanger coils. The method is sensitive
enough to measure the weight gain and assist plant operators in identifying
where deposits are formed. The sensors also monitor the condition of main
members of the boiler structure.
The advantages of this invention includes:
1. Formation of deposits on the heat exchanger coils (ie.,superheaters,
reheaters etc.,) is monitored continuously and detected in the early
stage itself. Based on the same, corrective measures for removal of
deposits can be initiated immediately and hence further damage can be
avoided.

2. Complete data on deposit formation can be collected and stored as part of
PLC based system.
3. Online data like temperature, strain etc., of main members of boiler
structure can be collected.
OBJECTS OF THE INVENTION:
It is therefore an object of the invention to propose an integrated apparatus to
continuously monitor the formation of ash deposits on heat exchanger coils in a
steam generator.
Another object of the invention is to propose an integrated apparatus to
continuously monitor the formation of ash deposits on heat exchanger coils in a
steam generator which is capable to also monitor the health of main members
of boiler structures online.
A further object of the invention is to propose an integrated apparatus to
continuously monitor the formation of ash deposits on heat exchanger coils in a
steam generator which employs smart sensors with wireless units to monitor the
load on the hanger rods supporting the heat exchanger coils and the health of
main members of boiler structures.

A still further object of the invention is to propose an integrated apparatus to
continuously monitor the formation of ash deposits on heat exchanger coils in a
steam generator, which is enabled to sound alarm whenever the weight of ash
deposit on the heat exchanger coils exceeds an allowable limit.
Yet another object of the invention is to propose an integrated apparatus to
continuously monitor the formation of ash deposits on heat exchanger coils in a
steam generator, which simultaneously generate a data base to guide the
operator for easy troubleshooting and maintenance.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows a schematic diagram of an apparatus with smart sensors for
monitoring the ash deposition on heat exchangers according to the present
invention.
Figure 2 - Shows a schematic diagram of the apparatus with smart sensors for
online condition monitoring of the main members of the boiler structure.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to an integrated apparatus for online monitoring of the
health of structures and slag deposition on heat exchangers in coal fired boilers
in thermal power plants. The total apparatus consists of smart sensors, wireless
units, a PLC based system and a Man-Machine interface.

The attached figures illustrate the details of components applicable to the
integrated apparatus.
Referring to figure-1, one or many smart sensors (1) is mounted / fixed on
suspension or hanger rods (2) supporting the heat exchangers (3) provided in a
boiler. The sensors are connected to one or many wireless units (4). The signals
from the wireless units are transmitted to a PLC based system (5) provided as
part of control room. The PLC based system takes care of signal processing and
computations. A Man-Machine interface (6) is provided for interfacing with PLC
based system (5).
Referring to figure-2, one or many smart sensors (1) is mounted / fixed on the
main members of boiler structure (7). The sensors are connected to one or many
wireless units (4). The signals from the wireless units are transmitted to the
same PLC based system (5) shown as part of figure-1 to take care of signal
processing, computations and other functions pertaining to the above smart
sensors also.

WE CLAIM:
1. An integrated apparatus to continuously monitor the load on the hanger rods
supporting heat exchangers in a steam generator and the condition of main
members of boiler structures comprising :
one or many smart sensors (1) mounted on the suspension or hanger
rods (2) supporting the heat exchangers (3) to monitor continuously the
ash deposition on the heat exchangers;
one or many smart sensors (1) mounted on the main members of boiler
structure (7);
a Man-Machine interface (6) provided for interfacing with PLC based
system; and
a PLC based system (5) to process the signals received, carry out
computations, provide alarms and maintain a data base.
2. The integrated apparatus as claimed in claim 1, wherein the smart sensors
are of digital type.

3. The integrated apparatus as claimed in claim 1, wherein data is provided in
wireless mode to the PLC based system.
4. The apparatus as claimed in claim 1, wherein said man-machine interface
further provides diagnostic features for quick troubleshooting.
5. The PLC apparatus as claimed in claim 1 wherein the PLC-based system has
provision for direct interface with Distributed Control System (DCS) of the
boiler.

ABSTRACT

The invention relates to an integrated apparatus, to continuously monitor the load on the hanger rods supporting heat exchangers in a steam generator and the condition of main members of boiler structures, comprising one or many smart sensors (1) mounted on the suspension or hanger rods (2) supporting the heat exchangers (3) to monitor continuously the ash deposition on the heat exchangers; one or many smart sensors (1) mounted on the main members of
boiler structure (7); sensors connected to one or many wireless units (4); a PLC based system (5) to process the signals received from wireless units, carry out computations, provide alarms and maintain a data base and a Man-Machine
interface (6) provided for interfacing with PLC based system.