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| Open Coal Storage |
Coal is the
primary fuel being used for power generation in thermal power plants. Most of the power generation in India is generated
by coal based power plants where
coal is received from coal blocks/Mines by means
of transportation (by belt conveyors, by rail or by ship depending upon the
distance and availability of transport). Then the Coal is dropped in a coal
yard and stored in stockpiles.
As far as optimum power generation is concerned,
a healthy emphasis needs to be given for its bulk storage and proper
handling. Preparation of coal before feeding it into the boiler plays crucial role for
achieving better combustion. Irregular and big-sized lumps of coal may cause the following
problems:
• Improper combustion & inadequacy in
furnace temperature.
• Increment in unburnts of the ash.
• Reduction in thermal efficiency.
Once Coal is reduced in size by crushing and pulverizing, crushed coal not
only ensure efficient combustion but also become an economical asset for power generation in thermal power plant.
Coal Storage
Types
1.
Open coal storage
2.
Covered coal storage
Most of the coal stockpiles in the power plant are open
type. But with the passage of time, various problems are experienced with open
stockpile system and potential need for covered coal storage system is felt. The
salient features and benefits of the covered coal storage as compared to open coal
storage are as follows:
·
Reduction in spontaneous combustion
of coal, by virtue of no exposure to sun.
·
Minimum dust emission in the
stockpile.
·
No air pollution.
·
Elimination of rainfall and
moisture problem :
·
Prevention of Loss of Gross
Calorific Value (GCV) of coal
Stocking of coal in covered coal storage system not only minimizes the above various problems that had
occurred in stocking of coal in open coal storage system, but also improves combustion,
boiler efficiency and overall power generation in thermal power plant.
Factors to maximize output Power Generation
In coal/lignite storage systems, the
implementation of a various factors needs to be performed to maximize power
generation in a way, which is consistent and flexible enough to suit the
requirements without extensive modifications. These major factors are as
follows:
1.
‘Fuel
quality’: Fuel quality of coal which is generally quoted
in terms of its gross calorific value (GCV) along with its moisture and ash
content impacts on whole plant
operational efficiency. Assessing fuel quality and choosing fuel of
maximum gross calorific value and less moisture & ash content improves
combustion and power generation as well.
2.
‘Reheat stages’: Earlier heat cycles were not used in power plants, but
with time, the potential benefits of reheat cycles are considered and come as
one of the correction factor in improving overall plant efficiency.
3.
‘Maintenance
of Ambient temperature’: Ambient temperature is the temperature in the
surrounding of boiler during plant operation. Change in the ambient temperature
tends to affect performance
and load capability of gas turbines, cooling system
performance . Hence it is better to keep the ambient temperature maintained
during plant operation for maximum power output.
4.
‘Fuel sulphur content’: Sulphur
content in fuel have adverse effect on plant efficiency. ‘Formation of
corrosive acids’ and ‘boiler sensible heat loss’ can be avoided by properly
supervising and eliminating the sulphur content in coal.
5.
‘Excess air and unburned carbon in ash’: One of the major
operation issues in power plant is presence of excess air and unburned carbon
content is ash which may directly affect boiler thermal losses and can be suppressed
by site level operations.
Safety
Measures to avoids hazards in coal storage
These safety measures are steps taken to increase or ensure safety or protection from perils
of coal storage and handling. In the publications of National
Fire Protection Association (NFPA), they identifiy the threats associated with coal
storage, and its handling & gives recommendations for protection against
these threats. In addition to those safety preventions, some addition safety
measures are as follows:
·
The coal stockpiles should be kept away from
moisture.
·
Coal
storage or lignite Storage
piles should be emphasized to prevent those pockets of coal, which are potential
source of spontaneous combustion. Coal storage should be done for as short a
duration as possible. In order to reduce air within the stockpile, Coal should
be piled in layers.
·
Coal stockpiles should be monitored constantly
for hot spots using temperature detection systems. These sensors are designed to avoid harsh
conditions in coal handling and processing.
·
A management strategy should be followed to
replace the ignited coal on its occurrence. In addition
to this, the access should be provided for firefighting.
·
There should be no scope for dust to accumulate
inside the coal storage shed.
Otherwise, dust removal systems should be provided for all surfaces where dust
may accumulate.
·
An absolute minimum distance should be
maintained between Ignition sources and coal stockpile. Every electrical
equipment should be properly grounded, to minimize the effect of static
electricity hazards. All machinery and electrical equipment inside coal storage
shed should be checked properly for use in hazardous locations.
·
There should be automation in turning all electrical
circuits on/off without the need for personnel to enter dust-emitting
locations.
·
In order to reduce the chance of methane (and,
in case of fire, smoke) to occur around coal storage, a sufficient ventilation
system should be provided. At the apex, adequate ventilation should be provided
to take advantage of the chimney effect.
-
Hindustan Alcox Limited, New Delhi.
