Normalized Product Flow

Equation 11.1 is shows how temperature, in terms of the temperature correction factor, TCF pressure, P and concentration, as osmotic pressure,, are used to normalize product flow rate.3 

AP = pressure drop from feed inlet to concentrate effluent Pperm = permeate pressure 

All n = difference between the osmotic pressure on the membrane feed and permeate sides TFC = temperature correction factor (membrane and manufacturer dependent) 

In practice, data normalization is calculated using a spreadsheet or other of computer program. The best programs are integrated into a package that includes the hardware to actually capture the raw data. This eliminates the need to manually enter data. In general, systems that require manual data entry do not stand up to the test of time operators will usually cease manually entering data within the first couple of months after start-up, and they are left with only observed data with which to analyze performance. As discussed previously, observed data are unreliable due to the effects of pressure, temperature, and concentration on product flow and salt rejection. 

Given that the operators were able to maintain a constant product flow rate, albeit by increasing the operating pressure, one might ask why we should even care about the NPF When systems are allowed to operate in fouling or scaling mode for extended periods of time, the foulant or scale can become resistant to removal via cleaning. Thus, NPF is used to determine when it is time to clean the membranes before the surface contamination becomes permanent. 

Normalized [(AAP -ATI )1TCF, Actual flow ((AAP-AnJlTCP flow 

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A note in clause 4.12 points out that location of product in the normal production flow does not constitute suitable indication of inspection and test status unless inherently obvious. 

In some situations the location of a product can constitute adequate identification of inspection status. However, these locations need to be designated as Awaiting Inspection , Accepted Product , or Reject Product or other such labels as appropriate to avoid the inadvertent placement of items in the wrong location. The location of product in the normal production flow is not a suitable designation unless an automated transfer route is provided. 

Once the normalized product flow (NPF) is calculated, it is best graphed to observe trends. Figure 11.1 shows various trends in the NPF. Curves with a positive slope are indicative of membrane... 

Figure 11.3 Normalize product flow rate data from a facility operating on cold lime softened Delaware River water.

Normalized salt passage is generally not used as the primary indicator of when to clean membranes. This is because normalized product flow and/or differential pressure drop (see below) will usually indicate problems with the membranes before product quality becomes an issue. However, normalized salt passage should be used in conjunction... 

Performance of an RO system, specifically the permeate flow rate, salt rejection and pressure drop, is a function of membrane fouling, scaling, and degradation, as previously discussed (See Chapter 11.3). This chapter covers the detailed effects of membrane fouling, scaling, and degradation have on normalized product flow, normalized salt rejection, and pressure drop. 

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