Turning Trash into Cash
by Michael Gurney
January 1, 2010
Recycling systems for customer bulk handling systems.
Control system automation success stories abound among production lines that manufacture new goods. So why not apply some of the same techniques to deliver cost and productivity benefits to the other end of the supply chain: recycling? Bulk Handling Systems (BHS), Eugene, Ore., which recently celebrated its 30th anniversary, is doing just that as they develop and install automated solid waste handling plants around the world.
Automating the process of identifying and separating different types of recyclable waste is critical to speeding up the handling of recyclable material. In an effort to increase the amount of recycling among their constituents, many municipalities are making recycling easier to do by allowing consumers to mix different types of recyclable materials in the same containers, and allowing trash haulers to do the same in their trucks. This puts the burden on the material recovery facilities, or MRFs, to separate the recyclables by type for further processing. This is where automation comes in.
The process involves both high- and low-tech elements. At lower-tech stations, screens separate small items from larger ones, and glass is separated and broken before being deposited in bins. At the high end, optical inspection techniques incorporating spectral analysis are used to differentiate between types of recyclable plastics by identifying the polymers they contain. Optical sensors also differentiate between two-dimensional waste (likely to be paper) and three-dimensional items. As much material processing as possible takes place untouched by human hands, but before the automated screening. Human inspectors must still grab and discard the obvious contaminants.
While there are many similarities between various waste handling systems in different locales, no two are completely alike. Some systems may incorporate as few as 20 motors to transport materials, others as many as 100. Some systems do not use optical sorting. The installations vary because the separated recyclable waste is processed differently. Some facilities are owned by municipalities, while others are private. Therefore, each new system requires a new engineering design and customized manufacturing.
Developing a control system
Providing control systems of this nature for an original equipment manufacturer offers unique challenges to a system integrator. Even though customer's systems are configured differently, BHS's desire was for its system to be as standardized as possible; standardization ensures their support team does not need to gain complete familiarity with each individual configuration. Standardization minimizes the learning curve for new members to the support team, and gives the company flexibility from a resource standpoint. This provides a pool of resources to support all of their installations, as opposed to certain individuals being tied to certain installations.
Making the whole system function smoothly requires attention to control design. Operators use touch screens to set up and control the system, and receive operational feedback from the equipment. Menu options (recipes) control how the various elements work together (e.g. set up different speeds for the drives). More sophisticated systems also employ on-the-fly mode switching to allow the system to adapt to varying conditions, such as decreased crew or seasonal changes, without stopping. This adaptation also allows sections of the line to be shut down for maintenance without stopping the system. The control system will automatically divert materials and will change line speeds to adapt to the change. With a large number of motors, setting up the different options is typically very involved.
BHS brought in Concept Systems Inc., Albany, Ore., to provide the control system development for the recycling lines.
Modular software is key to keeping project costs down
The challenge was to standardize the controls and reporting systems, while supporting the requirements of custom system installations. Systems engineer Jason Connor was experienced in software development in object-oriented environments, and developed modular software programs for controlling the company's equipment. The software was designed with user-defined tag-names, or UDTs, and standard equipment routines. The software also was designed in a hierarchal manner, starting at the smallest elements such as motors and push-button stations, and those elements grouped into larger elements such as zones. Zones were then grouped into regions. This let the system be customized into the configuration required for each new system that was developed. All groups were then integrated together with a single routine responsible for the overall sequencing of the system.
Using these modular software elements, Connor was able to design all the HMIs and ladder logic code for the PLCs in each BHS installation to look similar.
When a new job comes up, he pulls software code from a library and integrates the various pieces together, while also updating the libraries with any new equipment that is introduced or any equipment that has been altered in the new project.
Customizable automation
Automation drives growth for the 30-year old bulk handling company, which has grown seven times in size over the last three years (in 2005, the company had 38 employees; today, it has 140). Technology investments have allowed the company to pursue markets far from home; the company has installations in New Zealand, London and Saudi Arabia.
By designing a standardized control system, all of the company's installations have the same look and feel, and new customer needs are quickly met. PE
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