WATER TREATMENT conditions of three once-through utility applications.
The water conditions are listed in Table 1. The final pH listed is the pH of the solution once the cation and anion solutions were combined and treated. Reporting of alkalinity is based upon customer provided detail and was replicated in the synthetic solutions.
Figure 3 shows the comparative QCM data for the untreated blank, 500 ppb phosphonate treatment and 500 ppb PEPMA / HPSP blend. In each synthetic utility water sample tested, the untreated blank exhibited the highest amount of deposition as would be expected.
Both PBTC and HEDP treatments at 500 ppb indicated an improvement in deposition amounts but did not necessarily effectively delay the onset of precipitation. In all cases, 500 ppb PEPMA / HPSP significantly limited the amount of total deposition observed and substantially increased the induction time where the onset of CaCO 3 precipitation was recorded. Table 2 compares the treated and untreated experiments with respect to induction time and ΔF change( amount of deposition).
Based on computer modelling and momentary excess calculations, Utility A would be expected to show the greatest amount of deposition and resulting decrease in frequency. This, in fact, was the case where a negative ΔF of > 250 Hz was observed over the 60-second duration of the test. C would have been expected to show the next greatest drop in frequency, followed by B. In fact, they showed utility drops of ~ 140 and ~ 190 Hz respectively.
As mentioned, calcite saturation can show potential for precipitation or driving force. C shows a calcite saturation of ~ 140x versus 94x for A and ~ 44x for B. As such, the induction time and subsequent measurement of deposition for the untreated blanks would be expected to follow this same order. In fact, C showed the longest observed induction time for the untreated blank, whereas A and B had similar times. There is not yet
Parameter Induction time( seconds) Frequency change( ΔHz) Blank < 5 > 250 500 ppb PBTC < 5 100 500 ppb PEPMA / HPSP > 60 0
Parameter Induction time( seconds) Frequency change( ΔHz) Blank < 5 190 500 ppb HEDP < 5 50 500 ppb PEPMA / HPSP 10 20 – 25
Parameter Induction time( seconds) Frequency change( ΔHz) Blank 30 140 500 ppb HEDP < 10 20 500 ppb PEPMA / HPSP 120 15
Table 2- Induction time & frequency change: Utilities A, B & C
enough experimental data to suggest why or propose a mechanism for cause and effect.
Conclusions
Given the current issues with supply of phosphonates, the use of certain polymer treatments in once-through applications seems to be a viable option for utilities. In particular, the PEMPA / HPSP combination shows efficacy when compared to untreated blank and phosphonate-treated samples in three synthetic oncethrough cooling waters. Further, the use of a QCM proves to be a valuable tool for the evaluation of additives in short holding time applications due to the QCM’ s sensitivity.
The work presented in this paper provides a good start to proving both the use of the PEPMA / HPSP alternative treatment as well as the use QCM as a laboratory evaluation tool. However, this methodology does not consider many important factors such as surface discontinuities, pre-existing deposition resulting in increased nucleation sites or fluid dynamics.
Additional work is also needed to understand causes of deviation from saturation models, correlation to field use of scale inhibitors, examination of different polymeric additives, evaluation of the combination of phosphonate and polymerics, and investigation of additional water chemistries.
This would help bolster the methodology and develop data sets to support dosage model development. Despite the limitations of the data and work conducted thus far, the approach demonstrates promise and has led to a commercially successful product in the field. ●
References: 1: US Patent 11,358,891 B2. 2: M. Standish, AWT Annual Convention, 12 – 15. 3: C. Garcia, G. Courbin, C. Noik & F. Ropital, Corrosion, 1999, 99, 2 – 4.
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Mike Standish
FOUNDER
RADICAL POLYMERS mstandish @ mfgchemical. com www. mfgchemical. com www. campanyname. com a
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