Feb’2012 Overhauling Report – E.S.P of 25 MW CPP, Gujarat Flurochemicals Ltd.

Overhauling Done by:

PRAMEELA TECHNICAL SOLUTIONS

Preface This report has been prepared in accordance with works awarded to Prameela Technical Solutions by Gujarat Flurochemicals Ltd, Dahej, Gujarat for overhauling of ESP of 90 TPH boiler of CPP. The Purchase Order details are as follows

P.O No. 21130100003 Dated 24.01.2012 – For ESP works

Some of the major milestones of the works were as follows:

S. no. 1 2. 3. 4. 5.

Event Unit Shut Down Air Leakage Test (During Boiler cool down) Works Commencement ESP Charging (Still Air) Boiler Light Up & Final Charging

Date 02/02/2012 02/02/2012 03/02/2012 10/02/2012

All the data and facts in the report have been done in accordance with the Maintenance Department from GFL. We also wish to acknowledge our gratitude towards the same to the entire CPP Team (Electrical & Mechanical) for quick response and helpful coordination to complete the works as per the schedule.

Submission By:

[VINEET MISHRA] For Prameela Technical Solutions

GFL ESP Overhauling Report

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Overview of ESP (Electrostatic Precipitators):

Electrostatic precipitators (ESP's) are used to reduce particulate emissions from blast furnaces, sintering operations in the steel industry, and for fly ash control from industrial and utility boilers. ESPs have been designed to collect particles with diameters of from 0.1µm to 10µm; collection efficiency is considered high, sometimes exceeding 99%. The ability of ESP's is to handle large exhaust gas volumes at temperatures between 175 and 700C. An electrostatic precipitator contains the following:  Discharge electrodes  Collection electrodes  Electrical system  Rappers  Hoppers  Shell The discharge electrode is usually a small-diameter metal wire or hollow pipe which is studded at the surface. This electrode is used to ionize the gas that charges the particles and to create a strong electric field. The collection electrode is either a tube or a flat plate with GFL ESP Overhauling Report

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an opposite charge relative to that of the discharge electrode. The collection electrode collects charged particles. The electrical system consists of high voltage components used to control the strength of the electric field between the discharge and collection electrodes. The rapper imparts a vibration or shock to the electrodes, removing the collected dust. Rappers remove dust that has accumulated on both collection electrodes and discharge electrodes. Occasionally, water sprays are used to remove dust from collection electrodes. These precipitators are called water –walled ESPs. Hoppers are located at the bottom of the precipitator. Hoppers are used to collect and temporarily store the dust removed during the rapping process. The shell structure encloses the electrodes and supports the entire ESP. A GD screen is erected in such a way that perforated plates are placed exactly between two collecting plates (air passage) to ensure maximum ionization of particles and result in good collection of Ash.

GFL ESP Overhauling Report

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Work Details For the works conducted under overhauling of ESP, the data below overviews each field with various attributes in them. Details of each field are considered as following:

 Numbering of fields is done from boiler towards chimney. This gives us four fields’ viz. Field 1, Field 2, Field 3 and Field 4.

 Initial Observation & Air leakage Test Status

 Ash Cleaning Status

 Rapping Mechanism – CRM (Collecting Rapping Mechanism) & ERM (Emitting Rapping Mechanism)

 Electrodes Status – Emitting & Collecting

 Support Insulator

 Hopper Status

 Miscellaneous

 Charging Status

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Field 1 Initial Observation & Air Leakage Test The field was shut down since 18th Jan’2012 due to sparks & short circuit. There were no leakages found in the structure, hopper and roof top. Side Manhole showed damage from inside as well as leakage from outside due to perishing of tightness rope. Field alignment was disrupted due to damaged electrodes (details mentioned in the electrodes section). Rapping was misaligned as the impact hammers had disoriented from actual position. Overall field had less ash deposition due to poor voltage built up owing to the reasons mentioned above. Ash cleaning status As per the instructions from the client, Ash was cleaned manually by using broom and compressed air to utmost limits. Rapping Mechanism 1 hammer of CRM was found misaligned which was corrected by mechanical means. Electrodes & Field Alignment In the rows no’s 11, 12, 13 & 14 Collecting electrodes were found bent in the first plate towards GD screen. This was affecting the overall field alignment and must have barred voltage from rising to desired levels. In the first two rows of emitting electrodes (from G.D Screen), 4 no.s Emitting electrodes each were found broken from its guide plate. An MS sheet of 6 mm was fabricated and repaired with the existing one. As the replacement was manually fabricated, the broken electrodes were welded instead of fastening to guide plate.

The picture shows the repaired guide plate as viewed from below.

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Support Insulator Both the support insulators were cleaned manually and with compressed air. No leakage or damage was detected on the surface. Hopper Status Hopper was drained of fly ash manually and by vibrating the surface due to hammering. No visible leakages were observed during air leakage test or manual inspection from inside. Miscellaneous Side Manhole door was repaired from inside and air tightness rope was changed to prevent leakages.

Side Manhole Door depicting repair

Field Charging Status

Field 1 Before Shutdown Still Air Test

DC – In mA -300

GFL ESP Overhauling Report

DC – In kV -71

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Field 2 Initial Observation & Air Leakage Test There were no leakages found in the structure and roof top. However a leakage in Hopper was identified. Side Manhole showed damage from inside as well as leakage from outside due to perishing of tightness rope. Field alignment was disrupted due to bent electrodes (details mentioned in the electrodes section). Rapping was misaligned as the impact hammers had disoriented from actual position. Overall field had substantial ash deposition from top to bottom. Ash cleaning status As per the instructions from the client, Ash was cleaned manually by using broom and compressed air to utmost limits. Rapping Mechanism 6 hammers of CRM were found misaligned which was corrected by mechanical means. Electrodes & Field Alignment Though the Collecting Electrodes were fine, the guide angle of collecting plates was bent at various places. Same was rectified by mechanical means. Emitting Electrode no. 16 was found bend and has been rectified manually.

Support Insulator Both the support insulators were cleaned manually and with compressed air. No leakage or damage was detected on the surface. Hopper Status Hopper was drained of fly ash manually and by vibrating the surface due to hammering. A leakage was spotted in the hopper and same was repaired by welding a fabricated strip.

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Hopper leakage repaired

Miscellaneous Side Manhole door was repaired from inside and air tightness rope was changed to prevent leakages.

Side Manhole Door depicting repair

Field Charging Status

Field 2 Before Shutdown Still Air Test

DC – In mA 20 300

GFL ESP Overhauling Report

DC – In kV 60 61

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Field 3 Initial Observation & Air Leakage Test There were no leakages found in the structure, hopper and roof top. Side Manhole showed damage from inside as well as leakage from outside due to perishing of tightness rope. Field alignment was disrupted due to bent electrodes (details mentioned in the electrodes section). Rapping was misaligned as the impact hammers had disoriented from actual position. Overall field had substantial ash deposition from top to bottom. Ash cleaning status As per the instructions from the client, Ash was cleaned manually by using broom and compressed air to utmost limits. Rapping Mechanism 4 hammers of CRM were found misaligned which was corrected by mechanical means. Electrodes & Field Alignment Collecting Electrode Alignment was fine. Emitting Electrode no. 11 was found bend and has been rectified manually.

Support Insulator Both the support insulators were cleaned manually and with compressed air. No leakage or damage was detected on the surface. Hopper Status Hopper was drained of fly ash manually and by vibrating the surface due to hammering. No visible leakages were observed during air leakage test or manual inspection from inside. Miscellaneous Side Manhole door was repaired from inside and air tightness rope was changed to prevent leakages.

GFL ESP Overhauling Report

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Side Manhole Door depicting repair

Field Charging Status

Field 3 Before Shutdown Still Air Test

DC – In mA 80 300

GFL ESP Overhauling Report

DC – In kV 62 71

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Field 4 Initial Observation & Air Leakage Test There were no leakages found in the structure, hopper and roof top. Side Manhole showed damage from inside as well as leakage from outside due to perishing of tightness rope. Field alignment was disrupted due to bent structure on collecting plates (details mentioned in the electrodes section). Rapping was misaligned as the impact hammers had disoriented from actual position. This field had maximum ash deposition. Ash cleaning status As per the instructions from the client, Ash was cleaned manually by using broom and compressed air to utmost limits. Rapping Mechanism 3 hammers of CRM were found misaligned which was corrected by mechanical means. Electrodes & Field Alignment Collecting Electrode Alignment was fine. There was a fabricated structure to keep spacing fixed between the plates. That structure was found bend. The same has been rectified manually.

Collecting frame structure was repaired

The emitting frame aligned with collecting frame by mechanical means since erection. Since the fields should be aligned independently, upon removal of the means, the fields collided as shown in the picture.

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View from Hopper showing collided Emitting & Collecting Frames after the rope was cut

We rectified the above error by aligning the entire field from top insulator till guide plate at the bottom. This resulted in maintaining a thorough gap of 100+ mm on all sides ensuring proper field charging.

Support Insulator Both the support insulators were cleaned manually and with compressed air. No leakage or damage was detected on the surface. Hopper Status Hopper was drained of fly ash manually and by vibrating the surface due to hammering. No visible leakages were observed during air leakage test or manual inspection from inside. Miscellaneous Side Manhole door was repaired from inside and air tightness rope was changed to prevent leakages. Field Charging Status

Field 4 Before Shutdown Still Air Test

DC – In mA 30 100

GFL ESP Overhauling Report

DC – In kV 54 45

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Recommendations Based on our observations and works conducted for ESP, we recommend the following for performance enhancement:  Water washing of ESP internals during next annual overhaul as well as intermediate shut down due to boiler tube leakages. The washing away of ash will strengthen the electrical field inside ESP for better ionization of particles.  Customer should be prepared for Dismantling and Erection of around 10-15 Emitting electrodes as many of them were found bent after around one year of operation. Though the same were rectified during this shutdown, they may not sustain after next year’s annual overhauling.  As hopper leakage was identified, conducting periodical air leakage test on hoppers, structure and manholes or identification of ruptured insulation is recommended. If the leakages are attended in time the overall efficiency of the ESP increases.  This ESP has no provisions for climbing up from inside. We recommend building of climbing structure inside ESP for all fields for better cleaning and repairs of the fields.

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