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Coal Feasibility
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DESCRIPTION OF A TYPICAL PLANT
1. Coal
Storage
The coal is brought to site and stored in a safe yard. Since the coal itself is
a fire hazard therefore storage facilities should be equipped with normal fire
deduction and fighting capabilities.
The facility should be required to store at least 20,000 ton of coal all the
time
Proper handling gear is needed for handling and shifting the coal.
To transfer the coal to the crushing facilities conveyors are needed for smooth
flow of the fuel.
2. Coal
Grinding Facility
The coal from the storage unit is brought here for crushing and grinding to
convert it to powdered form. The basis logic for the conditioning of the coal is
to clean burn the
Coal as far as possible.
There are many other methods designed at this stage to condition the coal and
improve the combustion at later stage. These are additional processes and can be
added at little extra cost depending on the quality of fuel being used.
3. Combustion
This is the most important issue of this project and need careful study
Combustion is a chemical process where the fuels which constitute various
compounds and minerals heated to an elevated temperature and in the process it
eliminates the heat and various new compounds and gases formed due to oxidation.
Excess quantity of air is provided and normally the furnace pressures kept on
atmospheric.
To get the maximum thermal efficiency this is utmost important that more than
99% fuel is burned completely leaving only the exhaust gases. To achieve this
target burners are designed carefully and adjusted according to available fuel.
To get an optimum air fuel ratio various controls are incorporated which
continuously monitors the flame condition and combustion temperatures as well
exhaust gases chemistry and regulate the air fuel ratio continuously.
With the clean fuel like gas the combustion is not an issue. The gas having high
methane nr. ignite very easily and burn most efficiently. With light diesel the
combustion also is very efficient and with heavy viscous fuel oil also the oil
is heated to get the required viscosity of 12-15 CST and a perfect combustion is
achieved.
However with the coal the situation is problematic. The fuel obtained from each
source is different is chemistry and can constitute different compounds. When
this coal is burned at high temperatures then it can produce different kind of
harmful gases and solids.
Government regulatory Authorities are very much concerned of clean air
formation. The coal which consists of high percentage of Sulpher will produce
undesirable Sulpher- di-Oxide which when combines with rain water produce
Sulfuric- Acid and hence cause the famous Acid Rain. The 2nd
most undesirable gas is the Nitrous Oxide the percentage of which need to be
controlled within permissible limits.
The solutions for these issues are readily available. Because the most coal
using power plants are located in USA and the clean air act is much more
forceful in USA than in 3rd
world countries.
Two major combustion technologies are available in the market
Pulverized Coal Combustion (PCC)
The coal is ground (Pulverized) to a fine powder, so that less than 2% below 300
micro meter and 70-75% below 75 micro meter size for a bituminous coal is
achieved. The pulverized (powdered) coal is blown through the burners with the
air and the combustion takes place 1300-1700 degree Centigrade depending upon
the quality of the coal.
The particle residence time in the furnace is 2-5 seconds and this is most
important that the particle sizes are small enough to burn quickly and
completely with out any unburned fuel passing through the exhaust gases.
The technology is well developed and a large nr. Of power plant which is around
90% of world coal generating capacity is being used by this technology.
PCC is used for wide variety of coals and gives high thermal efficiency but
particularly not appropriate for the fuel with high ash contents.
Fluidized Bed Combustion (FBC)
FBC technology is particularly suitable for the coals of
high ash content or of variable characteristics. The relatively coarse
particles of around 3 mm are fed in to combustion chambers. Two formats are used
Bubbling beds (BBFC) and Circulating beds (CFBC)
Combustion takes place at around 800---900 degree centigrade, resulting reduced
production of NOX than PCC.
SO2 emission is controlled by injecting the sorbent in to the bed and subsequent
removal of ash with the reacted sorbent.
CFBC technology is designed for the particular coal to be used. The method is
only feasible for low grade fuel which is difficult to pulverize, or
co-generation systems where waster material is being used.
The direct injection of limestone gives an economic solution of removing sulpher
products.
Thermal efficiency is 2-3% lower than PCC
4. BOILERS
In boilers the thermal energy produced by the combustion process is transferred
to the water which is passing in the tubes. The water changes its state and
converts in to high pressure steam. This steam further heated to become
superheat which is more advantageous and efficient to run the turbines.
Boiler are of many design, they may be of tower shape or horizontal. The flue
gases can pass single passage or they may have two or three passes. In water
tube boilers the water which is called feed water is heated at high temperature
and pass through the tubes. In surrounding high temperature flue gases passing
through and hence raising the steam pressures.
Various mountings are accommodated in the boiler which is required for automatic
controls as well as for the approval of Government agencies.
5. TURBINES
Turbines convert thermal energy in to kinetic energy. When high pressure steam
passes through the rotor of turbine it starts driving the turbines with high
speed. The turbines at drive end are connected to a gear box and then to the
genset which start revolving at required speed. The electrical power is produced
which is transferred to end user through cables and switch gear.
The exhaust steam from the turbines is first pass through the condensers where
it changes its state in to water again. The same water is re-circulated to the
boilers and hence the high pressure steam is formed.
CAPITAL COST
The cost of the equipment varies considerable with the country of manufacturing
and quality of the equipment chosen. However as a budgetary guide line 1000
Euro/KWHR is a general rule of thumb.
For 36 MW power plant the capital cost is expected 36 Million Euro and in Pak
Rs. 2520 Million Rs.
Foe comparison purposes with a diesel engine power plant the capitol cost is
around 50% higher.
FUEL COST
As a standard practice the good quality 1 pound coal produce 1 KW energy and low
quality one kg fuel can produce 1 KWHR energy. Translating this amount in Pak
RS.
If imported fuel cost 5000 RS/ton at site
Energy Cost
2.20 RS/unit
For comparison purposes the Gas present day costing same amount
However with 50% increase in capital cost the pay back time is 50 % higher.
Steam turbine power plants have longer life than diesel engines and the
maintenance cost is lower.
EQUIPMENT MANUFACTURERS.
Boilers
There are many boiler manufacturers in the world which are producing high
pressure boilers with latest technologies to burn low quality fuel.
One of them is in India with the name Thermax Babcock Wilcox boilers, situated
in Pune India they claim to burn worst quality of coal. The supplier need to be
further explored.
Turbines
The following are some of the manufacturers of turbines
· Alstom
from France
· Peter
Brother Hood from England
· MAN
from Germany
Cooling Towers
Chinese cooling towers with low cost can be selected.
High Pressure Feed Pumps
The pumps are a vital auxiliary and
should be imported from any renowned pump manufacturer.
Piping and Valves
The high pressure steam pipes and valves should be imported with the valid
certificates from the manufacturers. Electrical Switch Gear
Complete switch gear is available in Pakistan by Siemens or Alstom
Coal Handling Facility and grinding unit
Local facility to be explored to fabricate the complete system.
Installation and Erection
Local facilities to be explored
CONCLUSION
1. With
the current prices coal plants are more or less compatible with the gas plants.
2. With
the projected fuel prices coal prices are being forecast as more stable than
crude and gas prices.
3. Looking
for the future the coal is one the best alternate solution for the power
generation.
4. Clean
burning of the low quality fuel is possible and technology is available today..
5. This
is suggested that the plant to be ordered for low quality fuel but the option
for high grade coal to be kept.
6. Initially
the plant to be fired with good quality fuel and then the low quality fuel is
mixed with gradual increase in proportions.
7. The
problems which come across by increasing low quality fuel can be solved one by
one.
8. High
cost of consultants and brokers as well as middle man should be curtailed.
9. All
equipment to be ordered to well known manufacturers with the performance
warranties coming directly from the manufacturer.
The equipment may be ordered in following order
· Turbines
· Boilers
for matching turbines
· Combustion
equipment for the available fuel
· Auxiliaries
like heat exchangers and cooling towers
· Coal
handling units
· Electrical
switch gear
· Pumps
and pumping system
· Piping
cables and valves etc.
PROJECT DURATION
18 months is expected when the project will start commercial productions.
PROJECT MANAGEMENT
1. Approval
from the top Management for the go-ahead of the project
2. Appointing
a project manager
3. Selecting
the site of the plant
4. Selecting
the suppliers
5. Commercial
Agreements with the suppliers
6. Ordering
the equipment
7. Civil
Work
8. Local
fabrication
9. Ordering
the mechanical and electrical equipments
10. Selecting
local erectors
11. Awarding
the contract
12. installation
of main and auxiliary equipments
13. Trials
and tests
14. Commercial
Production
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