Re: Clogging Issues In Ship Unloader
Dear deepakkhandal,
The Soft starter is selected for a reason.
To reduce the starting current, in order not to overload the electric power supply and preventing the e-motor from overheating. (certainly, when the starting time is long)
When you want to by-pass the soft starter, starting can be done in star-delta and direct on line (DOL).
In case of a stalled screw, you need the maximum torque available and that can only be delivered when starting in DOL.
(Star/delta starting is with 1/3 of the DOL torque)
The electric system must be sized for DOL and the heating up of the e-motor during DOL starting must keep the maximum temperature below the allowable temperature.
The PT100 sensors will check that, if installed in the windings.
Before you can execute your solution (bypass the soft starter) you have to investigate if that is possible without damaging the installation or causing frequent tripping. (hopefully not fuses).
Obviously, the unloader is not designed for foreign material nor for wet material.
You are experiencing still problems with normal material. (50mm coal and dry)
Why this occurs is difficult to assess, as a lot of information is now missing.
-What cause did you find for the current clogging?
-Is the unloader new or old?
-Was there a time that those clogging problems did not occur?
-What is the manufacturer’s comment?
-Has the material changed?
-Are the screw flights worn?
The advise is to contact the manufacturer of the unloader. ■
Teus
Re: Clogging Issues In Ship Unloader
Hi Sir Teus,
Thankyou for your response.
The electrical system is sized for DOL and we did contact the OEM. In case of clogs it is very essential to have high torque to try and declogg the screw but with soft starter in place the torque is limited.
For your queries the response is as under
- What cause did you find for the current clogging: We could not reach to an exact cause as the material was properly sized and no foreign material was found stuck in the crew. One possibility was the raining during unloading where the ship hatch are open. Corrective actions are in place to close the hatch and stop unloading in case of heavy rains.
- Is the unloader new or old? Unloader is new and in operation for last 3 years
- Was there a time that those clogging problems did not occur? After we implemented the corrective actions for foreign materials we had no clogging for 4 shipments.
- What is the manufacturer’s comment? Awaiting for an official reply to check all the parameters and settings
- Has the material changed? No
- Are the screw flights worn? No, the support screws are the ones to wear out but are with in allowable limits. ■
Re: Clogging Issues In Ship Unloader
Dear deepakkhandal,
After we implemented the corrective actions for foreign materials, we had no clogging for 4 shipments.
Currently we have issues of clogging in vertical screw and tripping of the screw on overcurrent.
Foreign materials do not clog the screw.
Foreign materials get stuck between the flights and the tube, thereby causing the high torque on the drive and tripping.
Having no problems during 4 shipments and suddenly the stalling problem comes back, indicates there is a difference in circumstances between the undisturbed shipments and the failed shipments.
You must have solved the current clogging issues and thereby found the cause.
It could be that the measures to prevent material coming into the screw are not efficient enough to catch the minimum size that can stuck between the flights and the tube.
It is well known that screw conveyors are very sensitive for foreign matter in the cargo.
- Has the material changed? No
Coal can be crushed between the flights and the tube wall.
Suppose the coal is contaminated with hard rocks (which can not be seen in the cargo)
Then it is possible that such a rock gets stuck and your problem manifests again.
I once had a screw conveyor, where the feeding flights were not worn, but the flights further in the pipe were significantly worn out.
The result was that the feeding capacity was higher than the (worn) conveying capacity.
Causing overfeeding and high friction forces.
That screw stalled frequently.
After replacing a new screw the problem was solved. ■
Teus
Re: Clogging Issues In Ship Unloader
Originally Posted by deepakkhandal
Thankyou for your response.
The electrical system is sized for DOL and we did contact the OEM. In case of clogs it is very essential to have high torque to try and declogg the screw but with soft starter in place the torque is limited.
For your queries the response is as under
- What cause did you find for the current clogging: We could not reach to an exact cause as the material was properly sized and no foreign material was found stuck in the crew. One possibility was the raining during unloading where the ship hatch are open. Corrective actions are in place to close the hatch and stop unloading in case of heavy rains.
- Is the unloader new or old? Unloader is new and in operation for last 3 years
- Was there a time that those clogging problems did not occur? After we implemented the corrective actions for foreign materials we had no clogging for 4 shipments.
- What is the manufacturer’s comment? Awaiting for an official reply to check all the parameters and settings
- Has the material changed? No
- Are the screw flights worn? No, the support screws are the ones to wear out but are with in allowable limits.
Dear Mr.Deepak,
Could you please post the cross section elevation drawing of this screw assembly ? If not available , even a hand made sketch may be posted ( - only if not available ).
Thanks and regards, ■
Re: Clogging Issues In Ship Unloader
Originally Posted by Teus TuinenburgForeign materials do not clog the screw.
Foreign materials get stuck between the flights and the tube, thereby causing the high torque on the drive and tripping.
Having no problems during 4 shipments and suddenly the stalling problem comes back, indicates there is a difference in circumstances between the undisturbed shipments and the failed shipments.
You must have solved the current clogging issues and thereby found the cause.
It could be that the measures to prevent material coming into the screw are not efficient enough to catch the minimum size that can stuck between the flights and the tube.
It is well known that screw conveyors are very sensitive for foreign matter in the cargo.
Coal can be crushed between the flights and the tube wall.
Suppose the coal is contaminated with hard rocks (which can not be seen in the cargo)
Then it is possible that such a rock gets stuck and your problem manifests again.
I once had a screw conveyor, where the feeding flights were not worn, but the flights further in the pipe were significantly worn out.
The result was that the feeding capacity was higher than the (worn) conveying capacity.
Causing overfeeding and high friction forces.
That screw stalled frequently.
After replacing a new screw the problem was solved.
In the previous clogging issues metal was found to be stuck in the support screw during manual cleaning. For the shard rocks stuck between the tube and screw, we are still investigating it.
Foreign materials is directly not the reason for clog but once the screw trips on overload and does not respond to the reverse rotation, all the coal stuck in the flights needs to be manually cleaned and pressure washed to normalize the equipment.
Metal contact between the screw and tube due to sagging of screw is minimized by the adjustable support screw and cover with provision of shim to adjust the gap. However the wear of screw flight due to coal cannot be ruled out and we have scheduled an inspection by borescope.
For the feed rate we have started capturing the data of coal feed, position of screw, pendulum angle etc. to look for any correlation with the clogging. Will update the findings if any. ■
Clogging Issues in ship unloader
Hi Everyone,
I have been working on a Ship unloader and have been facing issues with vertical screw clogging. We looked for different possible causes for the clogs and implemented corrective actions as under. The ship unloader is designed for unloading -50mm size coal at a feed rate of 1500 TPH.
1. Foreign material: On many occasion foreign material was found stuck in the vertical Screw. As a corrective action strict usage of magnetic separator at loading point was implemented.
2. Wet material: Feed rate was reduced by controlling the inlet feeder VFD .
With the above corrective actions there was a immediate drop in the instances of clogging but are not eliminated completely.
Currently we have issues of clogging in vertical screw and tripping of the screw on overcurrent. Once clogged the screw would not rotate in anti clockwise direction and the clogging has to be cleared manually which is a time taking process.
There is a soft starter for the VFD with a bypass logic in the SCADA normally this is not for the underlying risk of damaged to the motor and the starting equipment. But does any one have experience on what is the risk factor if we are meant to bypass the soft starter and try operate the screw in reverse direction.
Requesting your valuable feedback for the above concerns. ■