Feedwater analysis

Membrane module performance can to some degree be predicted as a function of operating parameters and feedwater characteristics. Calculation methods [40,41] exist for various membrane operating conditions, but computer modeling programs available from the membrane manufacturers have largely superseded these. These programs predict the performance of a membrane plant based on feedwater analysis and performance requirements. 

A key feature of the RO process is cross-flow filtration. While some water is passing through the membranes there is a constant flow of water flushing the rejected salts away from the membrane surface. The ratio of these two flows is determined by the design recovery rate, the product flow divided by the feed flow. This is an important design factor that should be determined by the membrane manufacturer. Most manufacturers have special computer programs to calculate the maximum recovery rate based on a feedwater analysis. 

Caution should be observed in copying another analysis. No previous analysis would have anticipated the TMI-2 accident. Other near misses were the Davis-Besse loss of feedwater incident of 1985, the Salem breaker problem of 1983, the Brown s Ferry Fire of 1975 and the scram problem at Brown s Ferry. 

A long evolving use of PSA was for Anticipated Transients without Scram (ATWS) which extended over 15 years to culminate in NUREG-0460 which was upset by the Salem failure-to-scram incident and the subsequent SECY Letter 83-28. Other special studies have been (a) value-impact analysis (VIA.) studies of alternative containment concepts (e.g., vented containment, NUREG/CR-0165), (b) auxiliary feedwater studies, (c) analysis of DC power requirements, (d) station blackout (NUREG/CR-3220), and (e) precursors to potential core-damage accident.s (NUREG/CR-2497), to name a few of the NRC sponsored studies. 

Since our purpose is limited to introducing essergetic functional analysis, only simplified models will be considered. Let us first restrict our attention to closed feedwater heaters for which... 

Evans, R. B., and Hendrix, W. A., "Second Law Analysis for Optimum Design of Feedwater Heaters," AIChE Annual Meeting, San Francisco, CA, Nov. (1979). 

Chemical analysis of scale deposits present on the surface of the failed clamp by X-ray diffraction revealed the presence of predominantly sodium iron oxide, sodium carbonate sodium chloride ( 10%), iron oxide and iron sulfide. The scale composition was consistent with the evaporated residue from the 80% quality steam, which had been leaking from the joint prior to the failure. The high sodium concentration in the scale was attributed to the zeolite ion exchange system used to soften the boiler feedwater, while the chlorides and sulfides were naturally present in the feedwater. 

Second-law techniques are applied to the problem of determining when to replace feedwater heaters. This analysis was performed by Fehring and Gaggioli (6) as a test of a decision which had recently been made by a utility. The details of the analysis, omitted here, are contained in reference (6). 

The cycle studied in the ensuing analysis is a fairly typical one, with seven stages of extraction to the feedwater heaters. This unit is shown schematically in Figure 5. The properties of H20 at various points in the feedwater system as well as the mass flow rates are given in reference (6). Three cases are analyzed, Case A at design conditions, while Cases B and C represent deteriorated conditions to be described presently. 

The economic analysis to follow depends upon the evaluation of the various available-energy supplies for feedwater heating and, in turn, the costs associated with those supplies. In particular, the costs of interest, for each case, are those required to take the feedwater from the conditions at the inlet to heater number 4 to the normal temperature of feedwater entering the boiler. These costs include the cost of bleeder steam, which is used to increase the temperature of feedwater in the heater and, under the conditions of Case C, the cost of the additional boiler fuel required when the heater is out of service and the temperature of the feedwater is below normal. The hourly cost of feedwater heating for Cases A and B is given by... 

Consider Figure 5 again. Bleeder steam line B5 extracts 55351 lbm/hr (6.974 kg/s) at 93.8 psia (0.65 MPa) and 603 F (317 C) from the intermediate-pressure turbine delivering it to a feedwater heater. Steam line B5 was chosen to illustrate the design procedure for two reasons. First, the design has sufficient flexibility there are no extraordinary constraints on the pipe material and size, or on insulation thickness. Secondly, the available energy analysis and unit-cost computations for this power plant, and for steam line B5, have been presented in previous papers (5, 6 ) ... 

Analysis of limit cycling on a boiler feedwater control system. Boiler Dynamics and Control in Nuclear Power Stations 3, Proceedings of the third international conference held in Harrogate,... 

Once the pretreatment study had been completed, it will be possible to decide on the type of elements to be used in the reverse osmosis unit. If the SDI of the pretreated feed is 3.0 or less, then either the spiral wound or hollow fine fiber elements can be used. The choice will depend on economics (element price) and desalination characteristics (flux and rejection). If the pretreated feed SDI is more than 3.0, then the spiral wound element should be used. When the decision as to element type is made, then it is appropriate to forward a copy of the pretreated feed water analysis to reverse osmosis element manufacturers to obtain a prediction of product water quality, recommended type of element, total number of elements required, possible problems with sparingly soluble compounds in the feedwater, allowable recovery, and price and delivery. 

Figure 7.47 LC-OCD analysis of permeate samples of ferric chloride pretreated NF and with feedwater containing OPS colloids compared to feed HA characteristicsfor TFC-SR membrane.

Note, ppt = part per trillion, or ng/L. The Model PFP-7C is designed specifically for clinical chemistry and displays the Na and K concentrations in mmol/L. The Model 300 is designed for high sensitivity analysis of power plant feedwater. 

Compensation of shrinkage was investigated in the analysis No. 8. (see Appendix 4) to determine the time of possible feedwater de-isolation by the operator, when the RCS cooldown rate falls below the 60°C/h limit value. This occurs at 19 minutes when the RCPs are running and at 26 minutes when the MCPs are stopped. These time periods are sufficiently long to permit the operator to intervene and de-isolate feedwater flow according to this procedure. However, it should be noted that the normal feedwater reserves will be exhausted by about 25 minutes. 

The rate of feedwater flow reduction is different in all these cases. For analysis it is practical (even if unrealistic) to consider the flow to decrease to zero so as to produce an enveloping scenario for the transient. 

Interrupted on April 23 for a few days by a fast shutdown that occurred as a result of faulty water flow control following the activation of a turbine-driven feedwater pump, this period of steady state operation ended, running solely on the B train turbo-generator. The A train transformer was shut down as the analysis made periodically of the cooling oil of the transformer had revealed that a preventive internal inspection was required. 

The Model 300 is designed tor high sensitivity analysis of power plant feedwater. 

Examination of the results for the conventimial parameters tested in the feed and permeate (Table 3) provides some insight into the separation mechanism. High concentrations of oil and grease found in the feedwater suggests that cmisiderable oil remained in a dispersed or colloidal form. This oil would be removed by a membrane with ultrafiltration or hyperfiltration characteristics. Since the PAHs are more soluble in oil than in water, concurrent removal of the PAHs entrained within the oil may have occurred. The phenols with relatively high solubility in water are, also as expected, removed more poorly. This also is reflected in the poor rejections calculated for TOC and COD. Other contaminants, not quantified by the semivolatile analysis, also may contribute to the high TOC and COD in the permeate. 

To achieve the desired volumes and concentrations, the feedwater was introduced during the first two hours (approximately) of each day s run. For the remainder of each day s run, the reject (concentrate) was recycled, becoming the feed, while the permeate was continuously removed and discharged after samples were composited for analysis. Each day s run was terminated when the flowmeters indicated Aat the... 

The criteria applied in the design of the Reactor Coolant System supports are that the specific function of the supported equipment be achieved during all normal, earthquake, safety valve actuation and Branch Line Pipe Break (BLPB) conditions. (BLPB includes feedwater line breaks and all loss-of-coolant-accident conditions resulting from breaks not eliminated by leak-before-break analysis in piping to branch nozzles of the reactor coolant system.) Specifically, the supports are designed to support and restrain the Reactor Coolant System components under the combined Safe Shutdown Earthquake and Branch Line Pipe Break loadings in accordance with the stress and deflection limits of Section III, ASME Code. 

D. No credit is taken for letdown, charging, pressurizer spray, turbine bypass, or feedwater addition after the turbine trip in the loss-of-load analysis. Letdown and pressurizer spray both act to reduce primary pressure. By not taking credit for these systems the rate of pressurization is increased. By not taking credit for the addition of feedwater the steam generator secondary inventory will be depleted at a faster rate. This in turn reduces the capacity of the steam generator to remove heat from the primary loop and maximizes the rate of primary pressurization. 

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