Skids and Package Units Discover the Building Blocks for Modular Plant Projects

Author / Editor: Dominik Stephan* / Dominik Stephan

Package unit integration: how do you assemble a modular system? — Package units, modular system design and process skids are hot topics at the moment. Thinking in systems is becoming a familiar soundbite in the component manufacturing and chemical industries, but the building block approach is not making as much headway as had been expected. Interfaces to existing automation and control systems are lacking. An overview.

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Enter the building block plant: Modules, package units and process skids make it possible.
Enter the building block plant: Modules, package units and process skids make it possible.
( © montego6 - Fotolia)

Wouldn’t it be nice if everything were as easy as Lego? Anyone who has to deal with a multiplicity of technologies, pipe networks, connections and special tools would certainly agree. The idea of assembling an entire production facility out of pre-fabricated modules is not new. Yet, an increasing number of component manufacturers are now jumping on the bandwagon.

They are delivering subsystems featuring varying degrees of complexity as package units (often known simply as skids because they are mounted on a common base frame) which can then be integrated into the customer’s production process.

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Skids Already Commonplace in Oil and Gas

Pump and compressor manufacturers in particular sense new opportunities for selling system solutions instead of individual components. The magic word is plug-and-play. In addition, tight schedules and parallel activity make the option of outsourcing portions of the overall design an attractive proposition.

This approach has become common practice in the oil & gas industry. Production sites are often located in the wilderness far from civilization, making the advantages of autonomous, complete turnkey solutions particularly obvious. Space is at a premium on oil rigs, and this is another situation where pre-assembled modular units help minimize the effort needed for installation and test. Companies such as the pump manufacturer Sulzer are proud to have delivered hundreds of skids and frame-mounted systems around the world.

Mega–Trend Modular Systems

Now the sights are set on the chemical industry. The list of solutions on offer ranges from micro-liter range dosing equipment all the way up to large container modules for complete production lines. The vision of the chemical park as a huge container complex remains something for the future, but projects like the modular F3 Factory or Evonik’s Evotrainer already provide a glimpse of things to come.

Modular systems will also play a key role in Industry 4.0. In a study published in 2014, VDI (Association of German Engineers) came to the conclusion that modularization will be one of the defining trends in the chemical industry over the next five years. The Association is convinced that in future, production and finishing of end products will be fully distributed, with production modules being installed at the customer site.

Chemicals are Next for Skids and Modules

There is, however, still a long way to go. The chemical injection packages which companies like Lewa, Check Point and Stewart & Stevenson deliver to oil & gas fields are huge container modules capable of handling hundreds of cubic meters per hour, whereas smaller skids are the norm in the pharmaceutical, food and chemical industries. Products which combine mixers, dosing pumps and material handling equipment or multiple compressors with air dryers, filters, tanks and motors in a single module are commonly used in these industries.

Package units come in all sizes: From smaller modules...
Package units come in all sizes: From smaller modules...
(Source: PROCESS)

The industry can deliver complete solutions for entire process steps either off the shelf or tailored to customer specifications. Four types of package units are very common:

  • Simple remote boxes which have a remote I/O module but no controller/visualization
  • Stand-alone boxes with interfaces to the control system
  • Integrated solutions which contain a complex process module, for example a separation stage
  • Modular boxes containing a complete process unit which has a series of configurable process modules

However, it is a big step up from a single unit to an entire facility. Good modular plant design depends on integration of modules from different suppliers to create a working production process. This goes beyond the actual material flows. If the skid as delivered is not a pure standalone solution, then it needs interfaces.

Data Exchange and Integration are Necessary

Data exchange is not the only consideration. Seamless integration into existing safety, automation and operating environments is equally important. Package units must communicate with each other, with the control system and with the operator.

...to huge process skids
...to huge process skids
(Source: PROCESS)

Experts say that the solutions currently on offer have shortcomings in this respect. Many component manufacturers also quietly admit that on-board intelligence is often not regarded as important and is not really used. So a lot of work remains to be done. Even the ever-optimistic VDI believes that the future of modularization depends on interface standardization.

The solution may come from an unexpected source. Automation suppliers are devoting more attention to integration of package units. In recommendation NE 148, Namur expresses its support for autonomous, decentralized controllers which have the capability to independently monitor internal flows. DIMA (Distributed Intelligence in Modular Systems) unveiled by Wago in 2014 is one of the first implementations of this recommendation. The module is based on a standardized, open, non-proprietary systems communication and interface architecture which supports integration of process flows in decentralized automation and package unit environments. Intelligent modules with on-board automation capability have the versatility needed for integration into, or disconnection from, a higher-level system.

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Integration is Crucial

Once the integration issue is resolved, it will be possible to exploit the full potential of package units: short lead times, integrated designs and lower overall investment costs. Pre-assembly minimizes the time to install and connect the equipment on-site and also reduces downtime particularly when enhancements and extensions are made to the production line. The modules are produced at the supplier’s manufacturing plant, so conditions on site are generally not a major consideration. Regardless of whether the destination is a chemical plant or a windy off-shore drilling platform, the modules are assembled in a safe, clean, reliable production environment. Functional testing and a completeness check are performed prior to shipment. One-stop shopping also reduces the number of organizational interfaces, if not the number of process control system interfaces.

Stand-alone solutions are not the answer if the future objective is large-scale rollout of package units at chemical parks. The systems will have to operate as part of the network in a complex production environment. It may well be that automation solutions such as DIMA are the piece that is missing in the modular system toolkit. At any rate, there is still a big need for plug-and-play products.

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