Lakvijaya Power Station(Norochcholai)
Us...
In this article, I mainly focus what I had experiences during the 2 weeks (08/08/2016 to 19/08/2016). On the first day we were assign to 3 main sections of the plant that are I&C(Instrumentation and controlling) Unit,EM(Electrical Maintenance) Unit, and Operation Unit. Our group was 10 members from G5 & G6 groups.But HRM was 3 groups. Suditha Shamika (Me), Kavinda Geeth, Janith Chamikara and Kanchana Lakmal are together.Background
Lakvijaya Power station is the one and only coal power plant in Sri Lanka. It feed 900MW power to the national grid by 3 of 300MW generators. It is about more than 40% of electricity demand in the country.There are many various negative misconceptions in the society. In my opinion most of the politicians spread them for their personal cartels. We had a talk with Eng.Shami Mudunkotuwa about how should be electricity generation in future. In there I realized as a 3rd world country power is the most significant sector for developments. But the major problem is the against of the internationals and internal politicians and ignorant eco-friendly people. You can make your own view by analyzing whats really happen in Sri Lanka.
Technology
You can get an idea about how is this plant working --->
Basically I try to give some technical tips what I could get during the internship period in there.Main transformer tap changer issue
In the main transformer HV side(220kv) is connected to the 220kv GIS. Because of that when grid is loaded 220kv voltage is vary with time frequent. So the main transformer should be maintain 220kv on Hv side constant. to do this there can be used 2 methods.
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The idea for the Lakvijaya coal power project was
successfully completed with the help from China National Machinery and
Equipment Import & Export Corporation (CMEC) as main contractor and project
funded by EXIM Bank of China. This is the largest proposed power plant in Sri
Lanka (3 x 300 MW) located in Norochchole in Puttalam district.
Option 1- When 20kv is changed in UAT LV side voltage(6kv) will be changed because UAT has off-load tap changer.If 20kv is changed it will be harmful to motors and auxiliary components.So the option 1 can't be implemented.Change the LV side voltage (20kv) by using AVR |
Option 2- So this is the best fit way to overcome this issue. Standard tap changing is 1000 times per year.But in here there was happen around 11000 times in past 3 years. Due to that reason tap changer should keep up properly. (Note- Transformer issues will be in here)
Coal Handling
The process of coal handling is very much important to power
generation by the plant. The coal is transported from the respective country by
ships (65 tons per ship) and they are kept anchored about 4-5 km away from the
shore. Then, the coal is transferred in to barges (long flat-bottomed boats) by
which the coal is transported to the jetty.
After coal is transported to the jetty by the barges, there
is a conveyor belt system to transfer coal to the bunker bay where it is stored
before feeding the furnace. The coal is first unloaded to conveyor belt No. 0
directly from the barge with the help of coal unloaders. The plant is provided
with two coal unloaders each having unloading capacity of 500 tons per hour.
Conveyor belt No. 0 runs directly to the junction tower at which the coal
travelling path divides into two. These two paths are called the emergency path
and the normal path. The normal path is numbered as conveyor belt No.6. The
emergency path is used under an emergency situation where the normal path
cannot be used due to malfunctioning. This arrangement is needed because delays
in unloading process would cause heavy demurrage by the shipping companies to
CEB.
Quality of coal is checked on samples taken at every hour at
the junction tower itself. Then the normal path runs into a stockpile where a
bucket wheel stacker reclaimer is installed to reclaim coal in to the conveyor
or stack coal in to a stock pile. The Normal path or the conveyor belt 6 ends
at transfer tower 3 where an iron separator is installed to separate iron from
coal. After this, the coal is fed using conveyor belt No.3 in to the crusher
house where the coal is crushed so as to reduce the particle size.
Thereafter, the coal is taken to the transfer tower 1 with
the help of conveyor belt No. 2. The coal brought in should be maintained
around 10% moisture content immediately before use. There exist five mills which
are used to pulverize (grind) coal into further small particles. Actually coal
is fed only in to four ball mills for pulverizing process and the 5th
mill acts as a standby. In here, the coal is pulverized. Then the pulverized
coal particles are conveyed to the furnace in the boiler by means of primary
air.
Boiler
The Lakvijaya Power Plant has the largest boiler in the
country. It was manufactured in China by Harbin Boiler Company. Its efficiency
is 88.58% and a capacity of 1025 t/hr. The sub critical pressure of the boiler
is 173 bar and the temperature of steam at super heater outlet is 541 0C.
The boiler arrangement consists of burners, super heaters, re-heaters, an economizer
and an air pre heater. Two numbers of induced draft fans are installed in the
boiler in order to create negative pressure inside the boiler. This is
necessary to expel flue gas in the boiler easily. There is a booster fan as
well, to support the process of the expulsion of flue gas. Circular firing
system is employed in the furnace and the temperature in the furnace is
maintained below 1200 0C.
Turbine
There are three turbines in deferent levels for each
units. They are High pressure (HP) turbine, Intermediate Pressure (IP) turbine
& Low pressure (LP) turbine.
There are three phase main transformer which is rated as 20 kV/220
kV, 360 MVA & an auxiliary transformer which is rated as 20 kV/6 kV for
each unit. And the primary winding is delta connected & the secondary
winding is star connected & solidly earthed.
I. Change LV side voltage (20 kV) by using AVR
II. Change tap position of main transformer
According to first option, when 20kV is changed in Unit
Axillary Transformer (UAT) LV side voltage (6 kV) will be changed because UAT
has off load tap changer. So 6 kV can’t be kept constant. If 20 kV is changed.
It will be harmful to motors and other auxiliary components. Then option 1
can’t be implemented. So option 2 is the best fit way to overcome this problem.
To keep tap changer in better state, they have to do maintenance frequent and
well.
Bottom Ash Handling
The residual after coal combustion is called bottom ash and
is about 20% of the total ash produced during combustion. A submerged scraper
conveyor belt system conveys the bottom ash from the furnace. This bottom ash
is used as land fill material.
Fly Ash Handling
This is the fine particles generated during coal combustion
and they escalates with flue gas. If the fly ash is mixed with the atmosphere,
it will cause a huge environmental impact. Therefore a special mechanism has
been installed to grab fly ash from the flue gas which is called the
electrostatic precipitator.
