Showing posts with label ESP. Show all posts
Showing posts with label ESP. Show all posts

Slop fired Boiler bag filter commissioning & shutdown procedure




Pre-Coating & Pre-heating

  • Box – up the bag house and close all access doors properly.
  • Keep the module outlet damper full open.
  • Close the Bypass dampers 100%.
  • Close the inlet damper 100%.
  • Make sure that the lime injection system is ready
  • Run the ID Fan and adjust the fan controls for effective suction for pre coating. (the air will flow from the boiler section .If required doors in the economizer section can be opened to draw fresh air into the bag filter)
  • Run the ID Fan and adjust the fan controls for effective suction for pre coating. (the air will flow from the boiler section .If required doors in the economizer section can be opened to draw fresh air into the bag filter)
  • Switch ON the lime injection system and start lime spray into the inlet duct. (Note : Dolomite powder can be used for pre coating)
  • Do not start pulsing during this period.
  • Observe the change in Differential pressure across the tube sheet.
  • After sufficient pre coating, as observed from the Diff Pressure gauge, around 10-  15 mmWG increases, stop the pre coating. Record the readings.
  • Stop the ID fan.
  • Switch on the hopper heaters
  • Switch on the Close Circuit heating system as follows
  • Close the bag filter inlet & outlet dampers.
  • Open the heating system inlet and outlet valves.
  • Start the blower.
  • Switch on the heaters.
  • Allow the hot air circulation to push up the internal temp > 140 Deg C (Approx).

Bag filter start up

  • Open the Bypass dampers both multi lower and puppet dampers by 100%
  • Keep Bag filter inlet and outlet dampers closed.
  • Ensure that the operation of dust conveying system below the hoppers is checked thoroughly and should be kept in operation
  • Light up the boiler and take the exhaust gases through the bypass path.
  • Continue with only coal firing.
  • Once the gas temperature reaches 140 Deg C +, then take the bag filter in line
  • Keep the BF pulsing OFF from the beginning
  • Open the bag filter inlet and outlet dampers 100%
  • Start closing the multi lower damper in the bypass line gradually, by maintaining the furnace pressure. This will divert the gas gradually through the bag filter. The ID fan speed will go up gradually. This process will take some time
  • When the entire gas is diverted through the bag filter and the multi lower damper in the bypass line is fully closed, and then close the puppet damper in the bypass line fully. (Caution: If the bypass dampers is not fully closed then the dust gases can escape to the stack through this route and push up the emission level).
  • Continue Coal firing and allow Bag filter inlet temperature to cross 180 Deg C.
  • Put the Bag pulsing in demand cleaning mode – Cleaning to start at 175 mmWG and stop at 150 mmWG. This can be readjusted if required.
  • Adjust the pulse air pressure to 3.5 Kg/Cm2.
  • Adjust Sol. Valve ON time 100 msec , OFF time 25 Sec (to start with)
  • Start spent wash firing and increase it gradually in small steps. (Caution: Sudden increase in spent wash firing rate can lead to clinker formation in boiler and chocking of bags in the filter.)
  • Start the lime injection system ( Quantity : Lime powder with 50 to 150 microns mesh size @ 150 kg/Hr)
  • Restrict the bag filter inlet temp between 180 – 220 Deg C (Max 240 DegC for ½ Hr).
  • Record all readings every one hour as given in the log sheet.

Bag filter shut down

Slop fired boiler start up procedure

  • After shutdown or tripping the boiler follow following procedures to shutdown bag filter
  • Start opening the puppet


    damper fully, after full opening of puppet damper, slowly start opening regulating damper adjusting the furnace pressure & ensure full opening of the damper.
  • Close inlet and outlet dampers of the bag filter.
  • Keep the pulsing on through timer mode for around ½ hr to dislodge the dust from the bags when the inside temp is high (Caution: Do not pulse the bags when the inside temp is low this may clog the bags.
  • Keep the hoper heaters ON.
  • Open the inlet and outlet valves of the heating system.
  • Start the heating system fan & heater to keep the internal temp to above 140Deg C for ½ hr, till the bag pulsing is over. Keep the dust conveying system ON for at least 1 hr to remove all the dust from the hopper.
  • After ½ hour a) Stop the bag pulsing b) Stop the close Circuit heating system. c) Stop the hopper heating system
  • Allow the bag filter to cool down in boxed up condition before opening the access doors. Then open the access doors and allow the natural purging before entering inside the filter. 

Question & Answers on ESP troubleshooting

                                 ESP TROUBLESHOOTING GUIDE

1-What are the potential reasons for large dust collection on collecting plates & discharge electrodes?
  • Higher dust load on ESP
  • Improper rapping
  • Low velocity of flue gas
  • Higher resistivity of ash
  • ESP running under capacity
2-Why there is sparking in the fields?
  • Excessive dust formation on plates
  • Very less gap between collecting plate & emitting electrodes
  • Improper alignment of electrodes
  • Obstacle of foreign material in the field & touching the discharge electrode
  • Improper charge ratio
3-What are the reasons for higher emission at stack outlet?
  • Under size ESP or wrong design
  • Improper rapping
  • Higher spark rate
  • Improper distribution of flue gas
  • Transformer not working or under capacity
4-What are the reasons for damage/corrosion of ESP electrodes & casing plates?
  • Operation of ESP at lower flue gas temperature <120 deg C continuously
  • More ash deposition on plates
  • Leakages in ESP, due to which air ingress & cause condensation of flue gas on electrodes & other internals
  • No insulation or using lesser thickness insulation material
  • Wrong operation of rapping system
  • Not cleaning of ash in shutdowns

5-Why there is a difference in hopper temperatures of ESP fields?

It is due to the different load on different fields. Field which discharge more ash has more temperature & field discharging low ash is having low hopper temperature
6-What do you mean by Back Corona effect?
A phenomenon that occurs when the gas within a high resistivity dust layer becomes ionized, which causes heavy positive ion back flow, which neutralizes negative ion current and reduces voltage levels.
7-Why there is fluctuation in ESP current & Voltage
  • Movement or swaying of discharge electrodes & creating close contact with collecting plates
  • Close contact of foreign material with discharge electrodes
  • Loose connection of cables which are connected to control panel
  • Leakage current & Induction
  • High ash level in hopper & touching discharge electrodes
8-What are the reasons for failure of support insulators?
  • Higher operating temperature
  • Higher dust collection & electrical arcing
  • Shock loads
9-Why there is more ash collection at ESP 1st Field as compared to other fields?

In ESP 1st field there is huge drop of flue gas velocity that is from 12 m/sec to around 1 m/sec, which causes more ash collection in 1st field. So current for ESP 1st field is kept lesser as compared to other fields.
10-Why ESP field voltage reduces when the current increased?
It is due to the back corona effect due to higher resistivity of ash. To get rid of this increase rapping frequency.
11-Why explosion occurs always in ESP? How do you avoid it?
Generally ESP has low velocity zone, where there is possibility of collection of explosive gases & unburnt fuel. The explosive gas namely carbon monoxide associated with unburnt fuel settles at ESP corners or at collecting plate rapping system, when the cold air or hot unburnt particle comes in contact with this gas it suddenly explodes.
So in order to avoid this need to take care on following points
  • Maintain balanced draught in furnace to achieve good combustion as well as to avoid carryover of unburnt particles
  • Arrest all lair leakages in ESP
  • Avoid charging ESP at flue gas temperature < 125 deg C
  • DO not bypass any of the ESP interlocks
  • Ensure proper operation of rapping system
  • Ensure healthiness of explosion vent provided at ESP inlet & outlet cones

12-How the air ingress affects on ESP performance?
  • Air ingress lowers the flue gas temperature, there by corrosion of ESP internals
  • Pressure drop across ESP increases
  • Load on ID fans increases
  • Leads secondary combustion of unburnt particles in ESP
13-What operation parameters affect on ESP performance?
  • Flue gas temperature
  • Flue gas volume
  • Flue gas composition
  • Inlet dust load
  • Density of ash
14-How do you calculate the ESP efficiency?

ESP efficiency = ( Dust in –Dust out) X 100 / Dust in

It is around 99% for best performing ESPs

15-What do you mean by the term Emission?
Emission is the release of pollutants into the air from a source.
16-What do mean by Aspect ratio? How doe it affect on dust collection?
It is the ratio of collecting plates length to the height. It should be around 0.5 to 2
If collecting plates height is more than their length, then there is a possibility of carryover of dislodged dust particles with flue gas

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