Feed water source design

Measurable Process Parameters. The RO process is relatively simple ia design. It consists of a feed water source, feed pretreatment, high pressure pump, RO membrane modules, and ia some cases, post-treatment steps. A schematic of the RO process is shown ia Figure 2a. 

In some cases, the actual design permeate flow rate of the RO system may differ from the "name plate" flow rating. In most of these situations, the RO system is de-rated by design due to a poor feed water source or as a natural result of low feed water temperature. 

Feed water source also influences the design array of the RO unit. This is because the feed water flow and concentrate flow rates are also determined based on feed water quality. Higher feed water quality allows for higher feed flows and lower concentrate flows to be employed. Higher feed water flows and lower concentrate flows reduce the number of membrane modules required in the RO system. 

The starting point in any RO design is the water flux. The desired water flux should be selected by the designer based on the feed water source and quality (see Chapter 3.4 and Table 3.3). 

Other data that should be entered into the screen shown in Figure 10.8 includes the "Water Type." Clicking on this button will open up a box that allows the designer to select the feed water source (see Chapter 9.1 for details about the importance of the source of the feed water to the RO system). This box also lists the recommended percent salt passage increase per year and fouling factor that corresponds to the type of feed water selected. (These guidelines should be entered... 

The first input screen is the water analysis screen, shown in Figure 10.12. This screen is where the designer inputs the water analysis, either as ppm ion or ppm calcium carbonate. The screen also has inputs for iron, SDI, hydrogen sulfide, and turbidity. There is a drop-down menu where the feed water source is input. The bottom of the page lists the scaling indices. 

Once the feed water source has been determined, analysis of the feed water composition is necessary before a treatment system can be designed. Feed water constituents that must be analysed prior to designing a RO/NF membrane system as per ASTM Designation D4195-88 Standard Guide for Water Analysis for Reverse-Osmosis Applications are discussed in Chapter 6. Typical water treatment methods are summarised in Table 2.2. 

After items one through seven above plus the water source are entered into the screen shown in Figure 10.8, the feed water analysis is entered. The input screen can be accessed from the menu under "Options," or by clicking on the "+/-" button on the input screen (located just left of the "Water Type" button). The designer can enter water quality data as either ppm as ion, ppm as calcium carbonate, milli-equivalents per liter or milli-moles per cubic meter. 

To reduce operating costs, the design should consider alternative utility sources high-pressure steam (HPS) and intermediate-pressure steam (IPS), boiler feed water (BFW), and cooling water. 

One design solution to this requirement that was considered was to include a dedicated containment spray system with its own pumps, valves, water source and containment penetrations. An alternative, simpler solution was to feed the contaimnent spray headers and nozzles from an existing system within the containment. The selected system was that portion of the fire protection system that is within the contaimnent. This provides the containment spray function, without the need for the additional equipment of a dedicated spray system. 

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