On-line monitoring instrumentation

Electrochemical On-Line Corrosion Monitoring On-line corrosion monitoring is used to evaluate the status of equipment and piping in chemical process industries (CPI) plants. These monitoring methods are based on electrochemical techniques. To use on-line monitoring effectively, the engineer needs to understand the underlying electrochemical test methods to be employed. This section covers many of these test methods and their applications as well as a review of potential problems encountered with such test instruments and how to overcome or avoid these difficulties. 

Topnir Not a chemical process but an instrumental process for on-line monitoring of hydrocarbon process streams by infrared spectroscopy. Developed by BP and offered for license in 1997. 

The critical part of such an optimization scheme is the analysis and reconciliation of the measurements, to ensure accurate and consistent data and the detection of instrument errors and faults. The overall scheme for the on-line monitoring and optimization of the column is also shown in Fig. 10. Data from the plant are first... 

Over the past decade, instrumentation has undergone substantial developments in the areas of optics, electronics and data processing software. These have led to improvements in the reliability, accuracy and ease of use of associated instruments. Particularly, the introduction of fiber optics has allowed a greater degree of flexibility in application areas. These include, for example, measurement of oil droplet dispersion in the ocean, on-line monitoring of... 

Similar work was performed by Shaw et al.3 in 1999 when they used FT-Raman, equipped with a charge coupled device (CCD) detector (for rapid measurements) as an on-line monitor for the yeast biotransformation of glucose to ethanol. An ATR (attenuated total reflectance) cell was used to interface the instrument to the fermentation tank. An Nd YAG laser (1064 nm) was used to lower fluorescence interference and a holographic notch filter was employed to reduce Rayleigh scatter interference. Various chemometric approaches were explored and are explained in detail in their paper. The solution was pumped continuously through a bypass, used as a window in which measurements were taken. 

J. Rantanen, S. Lehtola, P. Ramet, J. Mannermaa, J. Yliruusi, On-line monitoring of moisture content in an instrumented flnidized bed grannlator with a multi-channel NIR moistnre sensor. Powder TechnoL, 99(2), 163-170... 

Figure 3.10 shows the specific instrument design for trace mercury measurements. It provides a reliable on-line monitoring cycle, as well as the ability to analyse samples collected remotely from other sites. The system is described in more detail by Stockwell and Corns [16]. 

Rantanen J, Lehtola S, Ramet P, Mannermaa JP, Ylirussi J. On-line monitoring of moisture content in a instrumented fluidized bed granulator with multichannel NIR moisture sensor. Powder Technol 1998 99 163-170. 

ATR-IR spectroscopy can be used as a spy inside a reactor for on-line monitoring and control of a reaction. The emphasis in this kind of application of ATR spectroscopy is on the detection of reactants and products in the bulk fluid phase. Such applications benefit from the excellent time resolution of FTIR instruments compared to other analytical tools, such as chromatographs. The method can be used in investigations of kinetics of reactions in batch reactors instrumentation has been developed and even commercialized that allows measurements at elevated temperatures and pressures. 

The portable instrumentation and low power demands of stripping analysis satisfy many of the requirements for on-site and in situ measurements of trace metals. Stripping-based automated flow analyzers were developed for continuous on-line monitoring of trace metals since the mid-1970s [16,17]. These flow systems involve an electrochemical flow detector based on a wall-jet or thin-layer configuration along with a mercury-coated working electrode, and downstream reference and counter electrodes. 

Nicomp Model 380/L is designed for on-line monitoring either by itself or in combination with the Particle Sizing System AccuSizer. These instruments are available from Particle Sizing Systems. 

In many cases, process control comprises only the on-line monitoring of temperature and pH value as well as an accompanying enzymatic analysis of glucose and lactic acid. Since this represents an indirect process control, product yields may only be marginally improved according to these analytical results. In contrast, a number of instrumental methods are now available which allow the analysis of essential components of the fermentation process within a short time, so that a timely intervention in the process is possible and the product yield may be optimized. 

Munson and Field reported in 1966 on a technique of ionizing molecules by gas phase ion-molecule reactions, which they called chemical ionization (Cl). In this way, break-up of the molecules can be greatly reduced or even avoided. Thus, measured ion currents can be correlated with the densities of the respective parent neutral compounds, allowing for on-line monitoring of rather complex gas mixtures. The fundamental principles of gas phase ion chemistry on which Cl is based, as well as the instrumentation for Cl, have been reviewed in great detail by Harrison." The wide variety of Cl methods that has been developed includes Medium Pressure Mass Spectrometry, Fourier Transform Mass Spectrometry, Quadrupole Ion Trap Mass Spectrometry, Pulsed Positive Ion-Negative Ion Chemical Ionization, and Atmospheric Pressure Ionization Mass Spectrometry (API-MS). Of these, API-MS has developed into a very reliable and widely used technique for analysis of VOCs in flavor release studies and human breath. A variety of API-MS applications in these fields of research has been described in a recent volume by Roberts and Taylor. ... 

The first of the separation techniques to be used in process measurement was gas chromatography (GC) in 1954. The GC has always been a robust instrument and this aided its transfer to the process environment. The differences between laboratory GC and process GC instruments are important. With process GC, the sample is transferred directly from the process stream to the instrument. Instead of an inlet septum, process GC has a valve, which is critical for repetitively and reproducibly transferring a precise volume of sample into the volatiliser and thence into the carrier gas. This valve is also used to intermittently introduce a reference sample for calibration purposes. Instead of one column and a temperature ramp, the set up involves many columns under isothermal conditions. The more usual column types are open tubular, as these are efficient and analysis is more rapid than with packed columns. A pre-column is often used to trap unwanted contaminants, e.g. water, and it is backflushed while the rest of the sample is sent on to the analysis column. The universal detector - thermal conductivity detector (TCD)-is most often used in process GC but also popular are the FID, PID, ECD, FPD and of course MS. Process GC is used extensively in the petroleum industry, in environmental analysis of air and water samples" and in the chemical industry with the incorporation of sample extraction or preparation on-line. It is also applied for on-line monitoring of volatile products during fermentation processes" ... 

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