SPM levels of all the Units were much higher than the standard norms.
Degradation in the performance of ESP’s.
Chances of enforcement of norms of emissions less than 50 mg/Nm3.
Characteristics of coal and ash not consistent with the design.
Requirement of frequent maintenance of ESP’s.
Reduction in the collection efficiency of ESP’s.
CAUSE & EFFECT
PF Coal/Ash grain size
Control of O2
Conveying air flow/pressure
Rapping cyclesTemp monitoring
Slurry disposal/SILO level control
Size of Fields
SPM around 100
High flue gas
a. Continue to run with present ESPs with ammonia dosing:
This option was investigated but was not viable due to PCB standards, which
may be even reduced in near future.
b. Going for dual conditioning system Ammonia & SO3 to reduce
emission below 50 mg/Nm3.
This option was investigated and evaluated, and trials were taken with the test
kit for ammonia dosing. This option was financially not viable.
c. Retrofit the ESP and install a fabric filter plant with high temperature
After comparing this option with the other options and evaluating the
economic benefits of each, it was found that this was both economically and
strategically, the most feasible option
CONCEPT OF HYBRID ESP’s
ESP-FF hybrid precipitator is a combination of ESP & Fabric filter
It has an advantage of both ESP & Fabric filter
Gases are separated from dispersed particles by passing it through
Particles that are not able to penetrate will remain on the surface of
medium so called “Filter cake”
90% dust collection is done by ESP
fields rest by bag filters
HYBRID ESP- THE PROJECT
VAL-CPP has undergone Bag filter modification in a phased manner
Last two fields of ESP were removed and bag filter was installed
Modification completed for all the 9 units.
EPC contractor – SEPCO
HYBRID ESP- THE PROJECT
Project Zero date – Nov-2011
Manpower involved in each unit is around 300
123 m3 of concrete is installed
454 tones of steel erection
Timely completion of the project as per schedule.
HYBRID ESP- AFTER COMMISSIONING
Fabric filter system is fitted with high temperature bags -
Polyphenylenesulphide (PPS) were considered taking the worst scenario
Low temperature bags - Polyacrylonitrile (PAN) may also be used
The performance of the plant is good with emission values consistently
below the 50mg/Nm3
Filter Plant Type : Pulse Jet
Filtration Velocity : 1.04 m/min
Bag Material : PPS (PTFE Impregnation Treatment)
Bag Quantity : 5002
Bag Specification : Dia 130 X 8065
Injection Pressure : 0.25 -0.35 MPa
HYBRID ESP- PERFORMANCE
Reductions in SPM < 40 mg/Nm3
Improvement in collection efficiency and stable operation of ESP’s.
Reduction in energy consumption of ESP’s.
Increase in life of bag filters due to small pressure difference across filter
OPTIPOW pulse valve adopted to guarantee high efficiency and for.
stable and reliable ash removal
The operation of the equipment is controlled by PLC through the
temperature, pressure differential pressure, current, voltage and the
travel feedback signal
HYBRID ESP – ASH REMOVAL SYSTEM
Fiber filter always adopts differential pressure control mode for cleaning
Differential pressure of dust collector is the enhancer of ash removal
from bag filters
Ash removal will not stop until differential pressure of bag filter drops
below the set value
when the differential pressure of the dust
collector surpasses a setting value, PLC will
transmit a signal to the pulse controller, then
the pulse valve will open, the compressed air
in the air tank will instantly release and enter
into the filter bag. The dust cake accumulated
on the outside will break and get loose and
then drop into dust hopper when the filter bag
HYBRID ESP – OPERATION
Amount of moist, acid and sticky dust collected on the filter bags during
the start-up phase to be minimized
The FF shall not be connected to the flue gas stream until coal starts to
be fired in the boiler and the thermal power achieves 80% above the
total thermal power
The flue gas temperature ought to be at least 20℃ above the acid dew
Main monitoring Screen
HYBRID ESP – MAINTENANCE
Regular checking of differential pressure of dust collector.
Monitoring of gas flow.
Checking the compressed air of pulse cleaning dust collector
Checking nozzle compartments and dust hopper for dust accumulations
When about 10% of the bags in a compartment have been blocked, all
damaged bags shall be replaced