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Why does vacuum in steam condenser reduce or drop??

  1-High exhaust temperature: Vacuum drops or maintains at lower side due to high exhaust steam temperature flow into steam condenser. This high exhaust temperature is mainly due to 1-Operation of Turbine at lower loads 2-More clearance in labyrinth seals 3-Not operating exhaust hood sprays 4-More load on condenser 5-Breaking of ejector U loop 2-Low circulating cooling water flow Vacuum in condenser reduces due to inadequate cooling water flow through steam condenser. This is mainly due to; 1-Problems associated with pumps 2-Air pockets in pipe line 3-Leakages in cooling water line 4-Stuck of discharge valve of pump 3-High cooling water temperature at condenser inlet Higher cooling water temperature at condenser inlet results into reduction of vacuum due to poor heat transfer from steam to water 4-Poor heat transfer in condenser Very less or poor heat transfer in steam condenser reduces vacuum to very low level resulting into high exhaust temperature &am

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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