FIELD OF INVENTION:
The invention generally relates to boilers or steam generators employed in steam
power plants and in industries. In particular, the invention relates to control
system to regulate the fuel including air inputs to satisfy the changing load
demand. More particularly, the present invention relates to an improved control
system for combustion control of a boiler or a steam generator in which online
capture and processing of data is made in advance during boiler operations to
address the effects of fuel composition changes (fuel switching over).
BACKGROUND OF THE INYENDION:
The abundance and comparatively low price of coal compared to other fossil
fuels make it an important source of energy for the present and future. More
electricity is produced from coal than any other fuel source. Although coal is less
expensive than other fossil fuels but it is considerably more difficult to burn. For
coal fired power plants, the cost of fuel represents about 60-75% of the total
operating costs. The design and performance of thermal power plants and the
costs of power generation are highly influenced by coal properties vis-a-vis fuel
cost. Specifically, coal quality impacts not only on coal cost but also on capital,
operating and maintenance costs of the plants.

The boiler manufacturers are frequently required to engineer the steam
generator so as to enable the generator to burn a wide range of coals.
Accordingly the acceptability requirement of a wide range of coals does not allow
the manufacturers to select an optimum equipment for a particular power
station.
The major equipments in a thermal power plant includes a steam generator (or
boiler), a turbine, and a generator. In the steam generator, chemical energy is
converted into thermal energy. The main inputs to a steam generator are the
fuel, air, feed water and spray water while the main output from the steam
generator is steam. The electrical power output depends on the steam flow and
steam enthalpy which, is a function of the temperature and pressure of the main
steam. Therefore, an objective of the control of a thermal power plant is to
produce an optimum quantity of steam from the boiler which is needed for
generating electric power.
As it is known, coal is a fuel with inconsistent properties. Coal is less
homogeneous than natural gas. There are different types of coal for example,
anthracite, bituminous, sub-bituminous and lignite. Within each type of coal,
there are again a variety of grades. Generally, none of the mines produces

identical quality of coal. The coal quality can vary considerably, from mine to
mine and even from seam to seam in the same geographic region. Since coal has
been commonly used as a fuel for centuries, it is one of the most widely studied
substances on earth. Understanding of coal properties is an important criteria for
the engineers who design steam generators for burning coal. From the
standpoint of boiler performance, the following coal properties are important:-
- Heating Value
- Moisture
- Grindability or Hardness
- Volatility
- Ash Content
The efficiency of a boiler is affected by changes in the fuel composition. During
the steady state operation (constant load demand) a change in the fuel
composition results in increased or decreased heat input rate to the boiler
furnace, causing a corresponding increase or decrease in steam production. This
leads to change in pressure and temperature profile at different nodes of the
boiler. In most of the boiler control mechanism, a change in the conditions of
outlet steam requires a corresponding corrections in the fuel inflow rate which in

turn causes the outlet steam conditions ultimately return to desired values. The
present invention is related to an improved arrangement in which corrections
based on prediction are made in advance to address the effects of fuel
composition changes on boiler performance/operation.
In steam power plants, it has been common to control fuel input to hold outlet
steam pressure from boilers at a regulated value and independently to compare
inlet air flow to outlet steam flow and operate the fans to make corrective inlet
air flow changes. During load changes, this "steam flow/air flow" system results
in overfiring on load increase and underfiring on load drops. After occurrence of
disturbance in outlet steam conditions because of a fuel composition change, the
control mechanism makes the boiler to correspondingly operate in order to
ultimately correct the steam conditions in the steady state. However, an
improper fuel/air balance can ultimately result in inefficiency. For example, the
air flow to the boiler although can be increased to a maximum beyond which
further load increase is not permitted; however the maximum load still cannot be
achieved because the heat input from the fuel can not be increased in
registration with the increase in inlet air, because of the detonated quality of
fuel.

Patent no. US 4064698 relates to boiler control mechanism having a heating
value computer and providing improved operation with fuels having variable
heating values. Here a boiler control means regulates the input fuel and air to
satisfy load demand. Simultaneously, fuel flow is adjusted by a fuel flow control
means in order to match the changes in fuel heating value. A computer circuit
generates a heat balance ratio of outlet steam flow and input mass fuel flow as a
function of the imbalance between a presumed heat input and an actual heat
output and by taking an inference from the imbalance or change in fuel heating
value. The heat balance ratio is then multiplied against an actual fuel feedback
signal and the ratio corrected signal is applied to the fuel flow control.
OBJECTS OF THE INVENTION
It is therefore, an object of the invention is to propose an improved control
system for combustion control of a boiler of a steam generator in which online
capture and processing of data is made in advance dUring boiler operations to
address the effects of fuel composition changes.

Another object of the invention is to propose an improved control system for
combustion control of a boiler or a steam generator in which online capture and
processing of data is made in advance during boiler operations to address the
effects of fuel composition changes for a boiler or a steam generator which
provide a continuous control adjustment with the changes in fuel heating value.
A still another object of the invention is to propose an improved control system
for combustion control of a boiler or a steam generator in which online capture
and processing of data is made in advance dUring boiler operations to address
the effects of fuel composition changes, which is enabled to directly and
continuously sense fuel heating value and generate a signal representaiive of the
sensed value.
A further object of the invention is to propose an improved control system for
combustion control of a boiler or a steam generator in which online capture and
processing of data is made in advance during boiler operations to address the
effects of fuel composition changes , which is capable of providing boiler
operating corrections in response to the changes in the fuel heating values.

A still further object of the invention is to propose an improved control system
for combustion control of a boiler or a steam generator in which online capture
and processing of data is made in advance during boiler operations to address
the effects of fuel composition change, which utilizes a signal representative of
the fuel composition commensurating with the fuel heating value.
Yet further object of the invention is to propose an improved control system for
combustion control of a boiler or a steam generator in which online capture and
processing of data is made in advance during boiler operations to address the
effects of fuel composition changes , which is enabled to store the changing
composition of the fuel in an embedded controller.
Another object of the invention is to propose an improved control system for
combustion control of a boiler or a steam generator in which online capture and
processing of data is made in advance during boiler operations to address the
effects of fuel composition changes, which ensures automatic fuel switching
over.

A further object of the invention is to propose an improved control system for
combustion control of a boiler or a steam generator in which online capture and
processing of data is made in advance during boiler operations to address the
effects of fuel composition changes, which is capable to restrict the variation in
the outlet steam pressure and temperatures to a minimum under fuel switching
over to maintain a reduced cyclic stress and thereby increase the life of boiler
components.
SUMMARY OF THE INVENTION
In the proposed arrangement wherein as the composition of the fuel is changing
during the boiler operation the inventive system allows in-situ measurement of
the changing composition by online means and this data is stored in an
embedded controller. The embedded controller is enabled to calculate the total
air flow reqUirement (including excess air) based on the composition of the fuel
currently used in the boiler. From the total air flow demand, the primary air flow
(if applicable) is subtracted and the remaining demand is shown as an input

signal for adjustment of the combustion air fans. The new system provides the
following benefits:
• Air flow is adjusted according to the composition of fuel fired.
• Fuel switching over is taken care automatically.
Efficiency of the boiler is optimized under all conditions.
Thus, the control system for a boiler or steam generator or other fluid heaters is
adaptable for heating an inlet fluid to an elevated temperature and pressure. The
said system comprises means for generating data representing the load on the
boiler, generating a data relating to the demand for input fuel, and data
respecting to the demand for input air as a function of the boiler load.
The system further comprises means for generating respective data on boiler
outlet fluid flow, input fuel flow and input air flow. In the proposed system, the
changing composition of the fuel is measured by suitable online means and the
captured data is used for calculating and controliing the input flow of air by
employing an embedded controller.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS.
Fig. 1 shows a schematic representation of a boiler control system in a steam
generator.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to an apparatus and method used to control boiler
combustion with an embedded controller enabling improved operation facilitating
switching over of fuels with varying composition. The attached figure illustrates
the details of components applicable to the apparatus/method.
The apparatus according to the invention comprises an embedded controller (4).
The embedded controller (4) is interfaced and/or configured as a part of the
combustion control (6) of a boiler. In a boiler, coal is stored in bunkers (1)
located at an elevation. To provide an isolation between the boiler and the
bunkers, a shut off gate (2) is provided at the outlet of each bunker. At least one
on line coal analyzer (3) is provided at outlet of the shut off gate (2). The
analyzer (3) analyses the composition of the coal conveyed or transported from
the bunker (1) to the pulverizers. The analyzer (3) continuously analyze the
various parameters of the coal and generate signals representing the contents of
Carbon, Sulphur, Hydrogen, Nitrogen, and ash as available in the coal. These

signals from the analyzer (3) are provided as the inputs to the embedded
controller (4). Additional signals representing the boiler operational parameters
for example, boiler load demand, steam flow and oxygen level at economizer
outlet of the flue gas, are acquired from a distributed control device (5) as inputs
to the embedded controller (4). This embedded controller (4) is configured with
software support structure with built-in intelligence. After analysis of the data,
the controller (4) estimates the primary air demand and secondary air demand
for the coal being fed into the boiler. The controller also has the provision to set
the amount of excess air to be used or determine the same by the software
based on the coal analysis. The signal representing the air flow demand is given
as input to the combustion control(6) and other associated controls to enable
adjustment in secondary air flow and primary air flow to the boiler.
Salient features/advantages of the apparatus/method are:
Ensures qUick correction/adjustment of air flow reqUirement to maintain boiler
safety and efficiency under all operating conditions including transients.
Reduces overshoot and undershoot of boiler outlet steam pressure and
temperature under fuel switchover conditions enabling reduction in cyclic stress
and associated creep and fatigue of various boiler components.

We claim:
1. An improved control system for combustion control of a boiler of a steam
generator, comprising an embedded controller (4) interfaced to an on line
coal analyzer (3) and operably connected to a distributed control device
(5) of a boiler, the system is configured to:
-receive input signals representing contents of fixed Carbon, Sulfur,
Hydrogen, Nitrogen, and ash content in the coal from the on line coal
analyzer (3);
- additional inputs relating to boiler load demand, steam flow and oxygen
level of the flue gas at economizer outlet from the control device (5);
- process the input data and provide the output representing primary air
demand, and secondary air demand; and
- implement an adjustment in the primary and the secondary airflow via a
setting means capable of determining the amount of excess air to be used
depending on the data from the coal analyzer (3).

2. The system as claimed in claim 1, comprising means for restricting in the
fluctuation in main steam pressure and temperature during switching over
from one fuel to another fuel.
3. The system as claimed in claim 1, wherein, the control means is enabled
to reduce the cyclic stress and associated creep and fatigue of the critical
boiler components.