There are two primary methods to produce water-for-injection (WFI) for cleanroom applications: multiple-effect distillation and vapor compression. Each method offers different advantages. Here are some key features to consider when determining the right WFI for you:
- The breaking point for ROI is 600 gallons/hour. The capital cost of vapor compression is higher than multiple-effect. However, this additional cost breaks even at 600 gph or more. Vapor compression costs $10-12 per 1000 gallons at this rate compared to $18-$25 using multiple-effect. Any lower than 600 gph, however, and vapor compression does not provide a desirable return.
- Your facility’s required volumes of clean utilities make a difference. When there’s only a small need for USP, you can couple a vapor compression unit with minimal pretreatment and use the WFI for both applications. If you have a small pure steam requirement, multi-effect can be more advantageous. It’s capable of being tapped for pure steam.
- Consider the utilities that are readily available. If you have a USP system onsite, it can feed a multiple-effect still, offsetting the smaller volumes of steam capabilities with the multiple-effect design. If you want to minimize the use of cooling water, a vapor compression still is more advantageous.
- Consider your maintenance resources. With minimal moving parts, the multiple-effect still requires little maintenance. However, it may need annual descaling. The vapor compression still demands more maintenance, but a newer compressor requires less time to accomplish this.
- Consider your space constraints. Multiple effect systems take up less floor space, but gravity feed to a WFI holding tank may require more headroom than is available. Falling film tape systems are more compact, but tall. A natural circulation method is shorter but takes up more floor space.
As you can see, the criteria for choosing your WFI system go beyond cost. You need to know what space you have and what complementary equipment you have available. If you have questions about cleanrooms, contact Gerbig Engineering Company. We’ve expertly handled cleanroom equipment and services since 1985. Reach us at 888-628-0056 or email info@gerbig.com.