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

CAUSE & EFFECT

MATERIALMACHINE

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

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

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

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

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

HYBRID ESP - PERFORMANCE

127111

99 9281

71 6655

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 SPMAverage SPM

Before

After

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

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

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

THANK YOU