Modular, skid-mounted process equipment—such as CIP systems, bio processors, blowers and dryers, and compressors and pumps—is increasingly common. The following design recommendations will help ensure that your skid-based systems are flexible and easy to integrate, and simplify maintenance:
1. Create interface layer. To apply S88 in an environment with many different OEM equipment units, which all have their own way of handling recipes, create an integration layer for central control, monitoring, and recipe and batch management. Don’t force the OEM vendor to customize his product to your wishes. This creates issues with vendor support, qualification and additional costs, etc. Use the vendor standard, but implement an integration layer to do the specific translation of the unit procedure into the OEM equipment language using the specific required interface (OPC, XML, etc.). The integration layer acts as the only interface between ISA 95 level 2 and level 3.
2. Skid design tips. All pipe outlets and inlet should be self-sealing and quick connect on one side of the skid, with horizontal bend of 90 degree (or 45 degree if more convenient). Inlet and outlet should be marked with an arrow that is etched or otherwise made permanent. Valves should be accessible for removal from one side of the skid. The skid should be fully protected and guarded with a controlled interlock if doors are provided, allowing for natural ventilation or directed ventilation if needed. Guards need to be strong enough for incidental forces. Provide tempered safety glass windows where gauges or mechanical action needs to be observed for either casual process verification or debugging.
3. Skid construction. Ensure that the materials used in construction are acceptable for the intended plant environment. Some facilities will not allow wooden skids, for example, and the substitute for this must be approved well in advance.
4. Similar to rafting. Skid mounting is similar to “rafting” of roll forming equipment. There are many elements of the roll forming line, but the pre-process equipment incorporates the coil handler and straightener and the post-process equipment, including welder, cutter, deburrer and stacker, which are all easy to change over. The roll form can take hours; that piece is duplicated and indexed left or right. When left is forming, right is in changeover. Duplicating and indexing an element of a line that requires extra attention could be interesting. Indexing allows equipment to be swapped in a controlled manner, without the need for a forklift.
5. Modular design. The best way to design a skid is to lay out the design in the beginning and determine the area required. In the design phase, a layout can be made to determine the best location fit. Although skid designs vary according to the engineer involved with the design of the equipment, the best approach is to provide a modular layout so that in the future changes can be made with the least amount of effort. Modular is the best layout because it makes it possible to change the requirements.
6. Base skid design on components. Create standard skids based on the most important and standard components, such as number of membranes for RO units or other membrane systems, or based on typical capacity of blowers and tanks. Make sure to simulate the system to determine whether it will permit selection of a range of operation. Work in modules located in parallel or series to increase capacity.
7. Size for container frames. If you want mobile equipment, design and choose the machines that can fit inside a container frame. Some plumbing systems can be preengineered in the frame; install and test these in a dedicated workshop to make sure the quality standards are met. Mount starters and controls on the wall. Install vacuum pump/blower setup plugs in with supplied power only, allowing for plug-and-play replacement of spare units.
8. Test before buying. Thoroughly inspect a demo unit prior to specifying and ordering. Specify parts that you already have access to in network. Drive standardization.
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