Re: Conveying Pipeline Leakage Problems
Dear Ashishsteag,
a thermal power plant,600x4 MW
Or is it 4x 600 MW?
I understand:
-The ash is conveyed pneumatically.
-The fly ash is conveyed through pipes with a ceramic tiles on the inside.
-Conveying pressure is abt. 4 to 5 barg
-The experienced problem is the leakages of the conveying pipe throughout the whole length.
-Detached ceramic tiles are ending up in the slurry pumps
-The conveying air is supplied by 12 screw compressors.
-You are searching for a possibility to reduce the required amount of conveying air.
The given information is not sufficient to come up with the solution.
The approach should be:
-Check the pneumatic conveying design, for which a better description of the installation is required (conveying length horizontal and vertical, number of bends and size). For a recalculation of the design, the fly ash data (particle size, particle density and temperature) are required
In addition, the ambient conditions (temperature, RH, pressure, altitude) are necessary and the type of air compressors. 4 to 5 bar conveying pressure suggests that you are using oil filled compressors.
-Find out why the ceramic tiles are getting loose (expansion movements of the pipes, because of temperature changes?)
-Are the leakages occurring where the tiles are missing? (at such a location, a swirl will wear out the pipe fast) or at the bends.
A recalculation of the pneumatic system will indicate whether the velocities are (too) high and whether it is possible to reduce the air volume and the influence on the capacity and/or pressure if the air volume is reduced.
Have a nice day
Teus ■
Teus
Re: Conveying Pipeline Leakage Problems
Originally Posted by Teus Tuinenburg
Or is it 4x 600 MW?
I understand:
-The ash is conveyed pneumatically.
-The fly ash is conveyed through pipes with a ceramic tiles on the inside.
-Conveying pressure is abt. 4 to 5 barg
-The experienced problem is the leakages of the conveying pipe throughout the whole length.
-Detached ceramic tiles are ending up in the slurry pumps
-The conveying air is supplied by 12 screw compressors.
-You are searching for a possibility to reduce the required amount of conveying air.
The given information is not sufficient to come up with the solution.
The approach should be:
-Check the pneumatic conveying design, for which a better description of the installation is required (conveying length horizontal and vertical, number of bends and size). For a recalculation of the design, the fly ash data (particle size, particle density and temperature) are required
In addition, the ambient conditions (temperature, RH, pressure, altitude) are necessary and the type of air compressors. 4 to 5 bar conveying pressure suggests that you are using oil filled compressors.
-Find out why the ceramic tiles are getting loose (expansion movements of the pipes, because of temperature changes?)
-Are the leakages occurring where the tiles are missing? (at such a location, a swirl will wear out the pipe fast) or at the bends.
A recalculation of the pneumatic system will indicate whether the velocities are (too) high and whether it is possible to reduce the air volume and the influence on the capacity and/or pressure if the air volume is reduced.
Have a nice day
Teus
Dear sir,
Kindly elaborate the point you mentioned regarding expansion movement of pipes,because of temperature changes?
I frequently notice pipe lateral vibrations which are severe due to the misalignments and lack of proper supports on the channel beams,its causing gasket failures,i have been suggested earlier to use metallic gaskets for high temperature fly ash conveying applications,can you suggest me the type of gasket to be used for conveying of fly ash,temperature of fly ash is slightly above 120 degrees celcious,secondly how does conveying pressure affects the gasket thickness required?
As mentioned above regarding pipe vibration problems,can it possibly detach ceramic tiles?? ■
Re: Conveying Pipeline Leakage Problems
Dear Ashishsteag,
regarding expansion movement of pipes, because of temperature changes?
The pipeline changes in temperature when 120 degrC fly ash is conveyed and when no fly ash is conveyed.
This temperature fluctuation causes expansion of the steel pipes and depending on the supports, the deformation can cause tiles to break loose.
Also flanges can fail because of excessive movements.
The piping layout should be designed to cope with this by special locations where the deformation can be absorbed.
Also the fluctuating temperature difference between ceramic tiles and pipe can cause thermal forces.
pipe lateral vibrations which are severe due to the misalignments and lack of proper supports on the channel beams, it is causing gasket failures,
If the conveying occurs in batches (small sender tanks compared to a long pipeline volume), considerable slamming can take places.
The supports should be designed to absorb these mass forces without damaging deformations.
(I once experienced complete pipes falling from their poorly designed supports, caused by this phenomena)
As mentioned above regarding pipe vibration problems, can it possibly detach ceramic tiles?
Depends on the way the ceramic tiles are attached to the steel pipe.
Ceramics are known to be brittle and sensitive to deformation.
Is it necessary to clad the straight pipes internally with ceramic tiles?
Have you checked with ceramic tile suppliers about the application?
use metallic gaskets for high temperature fly ash conveying applications
For 120 degrC., hard gaskets can easily be used.
All for now ■
Teus
Re: Conveying Pipeline Leakage Problems
Dear sir,
Thanx for the reply,your experience and suggestion matters a lot.
Well yes we convey fly ash in small batches from the intermediate silo(transfer silo) to terminal silo,beneath the intermediate silo we have Delivery pumps(D-pumps) termed as master and slave vessels.We are currently operating it under timer mode for filling and conveying alternately
Sir,there is considerable amount of pipe erosion in the conveying pipelines,we are searching for an economical solution to it.
The bends have ceramics tiles in it,but we also have been using cast basalt coatings in the straight pipelines but inspite of the hard wear resistant coating,there are frequent leakages.
We have been demetering the pipes every month,I expect cast basalt to give a life of about 1 year but its not even serving the purpose for 3 months ■
Re: Conveying Pipeline Leakage Problems
Dear Ashishsteag,
Wear problems are induced by:
-impact angle
-velocity
-mass flow
Regarding the impact angle, 2 extremes can be considered:
-0 degrees (sliding)
-90 degrees (100% impact)
Cast basalt is perfect for sliding wear, but probably not for impact wear.
Regarding velocity and mass flow:
Impact energy is proportional to 1/2mv2
The mass flow equals the fly ash production and cannot be changed. However the velocity, being an important wear factor could be reduced if there is conveying time available for the same amount of batches at a lower velocity.
Impact force is proportional to m*dv/dt.
Impact forces, causing vibrations in the piping will also reduce with lower velocities.
Many cement conveying installations operate with normal, standard pipes and 1.5D bends.
Straight pipes last for very long periods. Bend life can be extended by welding an outer box to the bend, where the material collected and material wears on material.
Fly ash wear behavior is more or less comparable to cement.
Without having the installation geometry and data, it is difficult to formulate relevant answers.
A recalculation of the installation is the first step in order to recognize problem areas.
Further, step by step, research can follow.
Best regards ■
Teus
Re: Conveying Pipeline Leakage Problems
Originally Posted by AshishsteagPresently I m working in a thermal power plant,600x4 MW here in india,we have pneumatic conveying system along with a high concentration disposal system including slurry pumps and patented GEHO system.There's a typical situation of never ending leakages throughout the conveying ash pipelines,i think its due to the high silica content(coal is basically of inferior quality with more than 45% ash) and arguably people debate about conveying more than the designed capacity of the pipeline.The pipe is coated with ceramic tiles and the conveying pressure is about 4-5 kg/cm2.Furthermore i seen many times the ceramic tiles get conveyed along the pipes into the slurry pumps followed by geho pump suction.Is this something normal?How can we rectify this problem??Is using cast basalt instead of ceramic lined pipes a better option.?
We are trying to minimize the air consumption,for two units we have a total of 12 screw air compressors.Any suggestions regarding that?
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++
Dear Ashish,
In large capacity dense phase conveying, pipeline vibrations are caused by wide and uncontrolled fluctuations in the conveying pressure. In well-designed systems, these fluctuations are controlled within plus/minus 0.1%. In these systems, the incoming air flow automatically changes with conveying pressure. You have not given any information on your air supply and control system design, so it is not possible to suggest any changes. But I think you should look into it.
Regards,
Amrit Agarwal
Pneumatic Conveying Consulting
Email:Polypcc@aol.com ■
Re: Conveying Pipeline Leakage Problems
Dear Ashishsteag, Amrit,
Pipeline vibrations are caused by fluctuating forces.
These fluctuating forces are caused by irregular material feeding according:
F = m/dt * dv
m/dt is the mass flow in kg/sec
dv is the velocity change at the point of impact.
In addition, the irregular material feeding causes a fluctuating mass flow, which in return causes the fluctuating pressures.
In this event, the fluctuating pressures as well as the pipe vibrations are a result of fluctuating mass flows.
As stated, the fly ash is conveyed in small batches.
Between each batch there will be a period of no conveying and the pattern of conveying and no conveying causes the fluctuating mass flow at each impact zone (bends).
Automatically changing the incoming air flow with the pressure seems not easy to me.
How is the air flow adapted to the pressure?
- Increasing pressure followed by a decreasing air flow
- Decreasing pressure followed by a decreasing air flow
-Increasing pressure followed by an increasing air flow
- Decreasing pressure followed by an increasing air flow
Controlling pressure fluctuations in a pneumatic conveying system is possible by:
- Mechanical feeder devices (rotary lock, screw feeder)
- Kettle by-pass regulation.
By reducing the opening pressure, the first (unavoidable) mass flow fluctuation, the magnitude of the impact force is also reduced.
(Although this method has also by-effects)
If the installation description is given, then I can run a calculation.
All for now ■
Teus
Conveying Pipeline Leakage Problems
hello everyone,
Presently I m working in a thermal power plant,600x4 MW here in india,we have pneumatic conveying system along with a high concentration disposal system including slurry pumps and patented GEHO system.There's a typical situation of never ending leakages throughout the conveying ash pipelines,i think its due to the high silica content(coal is basically of inferior quality with more than 45% ash) and arguably people debate about conveying more than the designed capacity of the pipeline.The pipe is coated with ceramic tiles and the conveying pressure is about 4-5 kg/cm2.Furthermore i seen many times the ceramic tiles get conveyed along the pipes into the slurry pumps followed by geho pump suction.Is this something normal?How can we rectify this problem??Is using cast basalt instead of ceramic lined pipes a better option.?
We are trying to minimize the air consumption,for two units we have a total of 12 screw air compressors.Any suggestions regarding that? ■