Routine maintenance and periodic adjustments could help optimize optical sorters operating in material recovery facilities.

With increasing age and hours of operation, the performance of optical sorters can start declining. General lack of cleaning and maintenance as well as the ever-changing composition of input material can exacerbate performance challenges.

During the early days of startup, commissioning and break-in, new optical sorters often operate at peak performance. The challenge for operators is to keep them sorting at that level consistently day in and day out, without any long-term deterioration or fluctuations over the course of the day, or even during different seasons.

To keep optical sorters in peak performance, it is important to perform standard maintenance. Also, changing material streams might require making adjustments. These tasks are important for older (5 to 15 years old) and newer (less than 5 years old) optical sorters. Good maintenance is necessary for optical sorters in all material recovery facility (MRF) applications, whether they are sorting plastics by resin and color, positively or negatively sorting newspaper and mixed paper or working on the residue line.

Mandatory maintenance

Keeping all relevant areas of the optical sorter clean and mechanically maintained will have the biggest impact on uptime and performance. This includes monitoring and, if required, adjusting the tracking of the high-speed acceleration belt, its bearings and areas around and below the return idlers, tail and head pulleys. The splitter roller inside the catcher hood as well as the air valve/nozzle assembly are spots where materials can build up over time as well. Keeping those areas clean and easily accessible to maintenance personnel will reduce the risk of jams.

The halogen lamps that illuminate the sensing zone have a limited lifetime and must be replaced eventually. On older machines, manual monitoring of the light intensity might be required. Newer units have the capability to alert the operator when lamps should be replaced. While some optical sorters available in the marketplace will keep sorting when halogen bulbs have burned out, they will do so at reduced efficiency.

Especially during rain and snow events, the air ejectors will generate mist and liquid splatter that will settle over time on the glass surfaces that cover the halogen light assemblies as well as the sensor itself. Keeping those surfaces as clean and transparent as possible will ensure the maximum amount of light reaches the near-infrared (NIR) color spectrometers.

In the summer, air conditioning units help to keep the sensor housings as well as the operator touch-screen control panel from overheating. The dust filters for those units need to be checked, cleaned and possibly replaced on a regular basis. Extended exposure to high temperatures is a sure way to shorten the lifetime of the internal electronics.

An important aspect to increase the longevity of optical sorters is providing ultraclean compressed air that is free of moisture, oil and dust. Monitor the air quality coming from the compressor on a regular basis, otherwise the internal valve mechanisms could fail, causing the valves to remain in the open or closed position.

Testing the functionality of each air valve on a regular basis is crucial to ensuring optimum sorting performance. An 80-inch-wide, single-eject optical sorter normally uses 80 valves. If just four valves are not functional, that means 5 percent of the machine width is not performing at all, causing recovery of the targeted commodities to decline.

Check in on software

Basic monitoring of sensor performance and the status of internal optical and electronic components is becoming more automated and self-reported through optional push notifications, making it easier for the operator to monitor what is happening on each optical sorter in the facility in real time and what, if any, actions should be taken.

For example, while older units needed to be manually calibrated on a regular, sometimes weekly, basis, the latest generation of optical sorting technology can virtually eliminate this task using internal calibration routines and algorithms that can compensate for changes in the immediate environment of the machine, mostly temperature, over the course of a day.

The amount of operational and material composition data generated by the latest generation of optical sorters sometimes can be overwhelming. Advanced statistics and data analysis tools are readily available to monitor performance parameters. Integrating data generated by optical sorters throughout the MRF into the main programmable logic controller (PLC) or supervisory control and data acquisition (SCADA) system facilitates monitoring groups of machines and adjusting mechanical separation equipment as well as optical sorters. Data from other sensors installed throughout the plant that monitor conveyor speeds, disc screen angles and vacuum system air speeds also can be monitored in this way.

Like any computer system, optical sorter libraries, databases and parameter settings should be backed up on a regular basis and in accordance with a company’s information technology (IT) policies after changes have been made by the operator.

If required, all these described tasks can be outsourced to the optical sorter vendor to ensure nothing falls through the cracks. Nowadays, remote access and support via wireless or Ethernet connection make this easy and affordable.

For customers who require additional assistance, trained service technicians can conduct preventive maintenance visits and machine audits and provide additional operator training on-site.

Adjusting for the ever-evolving ton

It seems that the only constant for MRF operators is the ever-changing composition of incoming material. With a declining volume of newspaper and a higher percentage of cardboard, the optical sorters that perform quality control of the fiber streams might have to be constantly monitored and adjusted. They can be made more or less sensitive to certain prohibitives or outthrows with the touch of a few buttons in the latest machines.

On the container side, the increase in full-sleeve bottles, featuring a wide variety of label resins, have made it necessary to adjust optical sorters accordingly. The reference library containing the different material and color categories should be updated to maximize recovery of plastic containers in general and polyethylene terephthalate containers in particular.

On older units, sometimes the only way to perform this work is by using a trained technician on-site; however, the newer generation of optical sorters can be accessed remotely by factory-trained staff, and reference library and parameter settings can be updated more easily and quickly, requiring minimum support by on-site operations and maintenance staff.

These guidelines should assist MRF operators in getting their optical sorters back up to speed and ensure they perform at their peak for a long time to come.