Conveyor System Troubleshooting

Jul 26, 2019

The following is a detailed technical example of how MATL have approached an investigation into machinery malfunction and offered solutions to be able to overcome the traced problems.

The Immingham Renewable Fuels Terminal (IRFT) is an assembly of material handling machines controlled through a central Terminal Control System. A number of systems within the assembly encountered issues where performance and operability were not functioning as per the original intent. MATL were tasked to investigate the issues and deliver a report along with potential solutions.

As part of our investigation on the live plant, we needed to gain an understanding from the operations personnel how the plant was behaving along with a knowledge of how it was intended to perform

Industry Focus: Renewable Energy

Issue 1: Reported

A telescopic chute intended to form a seal with the receiving chute above a selected silo had failed to locate correctly which resulted in excess biomass dust released into the operational area which presented a range of hazards due to the material properties.

Issue 1: Investigation

It was quickly apparent that the possible ranges of movement from the traversing conveyor above had not been considered when locating and maintaining the telescopic chute position sensors. This resulted in misalignment of the sensors and supports, caused excessive release of dust and also damage to the controls devices and support structures.

Issue 1: Solution

We identified that modification of the chute seal was necessary to increase the seal depth and enable surface to surface contact rather than overlap which provided a degree of tolerance to the positioning of the chute.

MATL also advised that a modification to the position sensor application, from position switch and target plate to a snap action plunger switch which would also provide increased control and reliability of the positioning and indication without the risk of damage caused by lateral movement. The image below demonstrates a concept image of the potential solution provided.

Existing chute
Silo Chute Section
Modified Silo Chute

Issue 2: Reported

The traversing/reversing conveyor was travelling past its intended resting point on traversing in one direction. This prevented alignment of the telescopic chute and receiving silo chute sections during the silo fill selection routine. Operators were having to manually position the conveyor using local control stations.

The anecdotal reports suggested that the safety system designed to ensure the conveyor travel stops had also failed to act correctly and the shuttle had travelled fur- ther and damaged some of the steel access ladders and platforming. This also indicated that the physical buffers had not acted in the way intended.

Issue 2: Investigation

Our investigation looked into how the field devices communicated with the control system, the control system logic, safety functionality and the application of the physical buffers as a final barrier preventing the overrun hazard occurring.

The resulting assessment indicated several possibilities which included: Inaccurate encoder count, sensor positions and encoder count positions not correctly commissioned, control system logic not implemented as specified and traversing conveyor braking system failing to operate.

The Operators reported that the encoder that controlled the speed break points of the traversing conveyor drives had been reported to “skip”; this may have been due to incorrect assembly or reduced traction on the wheel due to build-up of dust deposits on the encoder track.

Issue 2: Solutions

MATL recommended several actions be taken independently to address the possible causes.

The encoder was the first thing to be addressed, MATL advised installing scrapers to ensure the track was free of large dust deposits and a spring on the wheel arm to increase traction between the encoder wheel and the track.

Secondly we recommended that  the brake conditions on all four drive motors was verified, including an inspection of the internal housing for dust and glazed surfaces that would reduce the efficiency. Excessive wear may also have been caused if the brake had not been releasing correctly therefore an inspection was required to ensure that the brake was released on application of power and re-engaged on power loss.

Once the above elements had been checked or implemented we recommended the following follow-up actions:

For abnormal operation

  • Verify the installation of the Emergency Shutdown (ESD) lever switch through aligning the traversing carriage frame with the ESD switch whilst the lever arm was in the contact/energised position.
  • Validate the ESD switch operation through manual switching whilst the traversing conveyor was at the opposite end of the building
  • Verify the stopping distance of the traversing carriage under the ESD stop command.
  • Verify the distance of the rubber blocks from the ESD switch, ensuring the distance was greater than the traversing carriage stopping distance but still preventing the carriage from impacting with the building infrastructure.
  • If the distance between the rubber bump stop to the ESD switch was less than the physical stopping distance to investigate if the rubber block could be moved further away whilst still preventing the traversing carriage from impacting with the building infrastructure.

For normal operation

  • Verify the suitability of the traversing carriage drive motors braking systems.
  • Verify the speed step-up/down operation of the traversing carriage drive motors.
  • Verify that the TCS input from the encoder could receive a pulse stream at the rate of 5.3 pulses per second.
  • Calculate and implement into the TCS the encoder pulse count requirements for the speed step up/down operation of the traversing carriage drive motors.
  • Verify the stopping distance of the traversing carriage whilst validating the low speed operation of the traversing carriage drive motors.

In the event where the use of the encoder and counter signal for position monitoring continued to be problematic, we proposed an alternative but direct robust system could be implemented:

The use of strategically placed digital position switches, and/or target plates with alterations to the FDS would enable the traversing conveyor to be moved between fixed positions. Position 1 – Silo 1 and 3, Position 2 – Silo 2 and 4, Position 3 – connection to IRFT 2. Step up/down of the drive speed could be performed either on a timer based on calculated distance travelled or intermediate position sensors or flags.

The disadvantage to this would be that there would be no real-time monitoring of the conveyor position. This disadvantage could be offset in that, in the event that no position feedback was given, the programme could

Consideration would need to be given to the real travel distance when braking and at both drive speeds to enable the locations to have precision, and there was also an awareness that the number of available spare cores in the chain cable was minimal.

The above is an illustration of how MATL take an open approach to fault-finding and optimisation, with a view to not only rectifying current issues, but to improve future productivity.

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