ASME PTC 19.11-2008 pdf download

ASME PTC 19.11-2008 pdf download.STEAM AND WATER SAMPLING, CONDITIONING, AND ANALYSIS IN THE POWER CYCLE.
2-1 INTRODUCTION Sample point and analysis selection depend upon the purpose of testing. Each cycle component has a particu- lar function. An agreement between the buyer and seller defines the specification. The sampling and analysis are designed todetermine thatthe componentis functioning as specified and that it is functioning properly in opera- tion. Proper function is determined completely in a per- formance test by analyzing the sample to ascertain that all specifications are met. In operation, the proper func- tion is assessed by less complete testing that concen- trates on the most important impurities and most likely failures. Section 2 focuses on the selection of sample point locations and the analyses that are commonly conducted for those locations. Most of the sample points are con- cerned withwater quality assurance and equipmentper- formance evaluation. For these points, continuous analysis is preferred. A few points are present largely to provide special data for analysis of problems. Grab samples will usually suffice at these points. Section 6 focuses onthe analyses, theirmeaning, and the methods.2-2 THERMAL POWER GENERATION CYCLES The following discussion reviews components of a thermal power cycle that can affect the chemistry of the water and steam. Figure 2-2-1 shows these components and sampling points schematically for a generalized fos- sil cycle. The steam cycle of nuclear power plants is similar to the fossil plants except that many nuclear plants do not have a deaerating feedwater heater, and most nuclear plants have a moisture separator reheater that extracts moisture from the steam and superheats the vapor. Not all these components will necessarily be present in a particular application. Their presence in Fig. 2-2-1 does not imply that they are always needed. Figure 2-2-2 shows a typical heat recovery steam gen- erator (HRSG) system. There are many variations on the system, but the one shown has most of the features of an HRSG system. Three important variations are one or two pressure stages instead of three, the deaerating LP drum, and the once-through stages. In some systems, only two pressure stages exist. These systems are often nonreheat. In many systems, suction for a boiler feed- pump is taken from the LP drum. This configuration makes the liquid withdrawal from the LP stage approxi- mately 90% of the feedwater.drum is present, although some steam separation equip- ment is usually present and used at startup. There are systems where IP steam is used to cool combustion turbine parts. The steam purity require- ments for the combustion turbine cooling may be signifi- cantly different from those for steam turbine. In those cases, the monitoring must support both sets of steam purity requirements. Table 2-2 summarizes the sample points and analyses for both Figs. 2-2-1 and 2-2-2. The text and Table 2-2 suggestmore analyses than mostplants would use. They should be used as a guide for consideration of analyses at each location. IMPORTANT NOTE: For proper testing, a sample must be pro- vided at each cycle point for which there is a specification. Figures for other fossil cycles can be found in Chapter 17 of the ASME Handbook on Water Technology for Thermal Power Systems. [1] Since nuclear power generation cycles can be vendor specific, more detailed information on them should be provided by vendors and/or other industry sources. However, the following general comments are appropriate: (a) Special problems associated with radioactivity and gas concentrations in water are not addressed here. (b) In BWR systems, no pH control additives are pres- ent; therefore, specific conductivity is the only conduc- tivity measurement used. Oxygen, chloride, and sulfate are the only other common analyses. When zinc is added to the reactor to control radiation, a zinc analysis will be performed. In systems with copper alloys in the condenser or feedwater heaters, the analysis ofcopper will commonly be appropriate. In all-ferrous systems, the analysis of copper will usually not be appropriate, but occasional analysis may be desired to be sure that no copper is entering the system from unsuspected sources.