This document discusses the retrofitting of existing electrostatic precipitators (ESPs) with fabric filter plants to reduce emissions. It notes that ESPs were not achieving the required emission standard of 50 mg/Nm3 due to inconsistencies in coal quality and ash characteristics. After evaluating various alternatives, installing fabric filter bags on the last two fields of the ESPs was selected as the most economically feasible option. The hybrid ESP-fabric filter system has successfully reduced emissions to below 40 mg/Nm3 while improving ESP performance and reducing operating costs. Regular maintenance and monitoring of the system is required to ensure continued compliance with emission standards.

2. CHALLENGE
 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.
HIGH EMISSIONS

3. CAUSE & EFFECT
MATERIAL
MACHINE
METHODSMEN
High Ash
High resistivity
Distribution screen
Electrode alignment
PF Coal/Ash grain size
Ash Evacuation
Control of O2
Uniform coal
feeding
Conveying air flow/pressure
Rapping cyclesTemp monitoring
ESP Controllers
Slurry disposal/SILO level control
Maintenance
practices
Ash evacuation
cycle timing
Size of Fields
SPM around 100
mg/Nm3
High flue gas
volume
Transformer sizing
High SCC

4. ALTERNATIVES CONSIDERED
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
bags:
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

5. 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
fabric medium
 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

6. 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

7. 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.

8. 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

9. 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
bags.
 Maintenance friendly.
 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

10. HYBRID ESP - PERFORMANCE
127
111
99 92
81
71 66
55
47 41 45
24 22 20 23 25 26 28 24 26
0
40
80
120
160
200
Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Aug-12 Sep-12 Oct-12 Nov-12 Dec-12 Jan-13 Feb-13 Mar-13 Apr-13 May-13 Jun-13
Average SPM Average SPM
Before
After

11. HYBRID ESP – ASH REMOVAL SYSTEM
 Fiber filter always adopts differential pressure control mode for cleaning
the ash
 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
expands

12. 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
point
Main monitoring Screen

13. 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

14. THANK YOU