Online pressure measurements

FIG. 8-86 Online partial stroke diagnostic used to validate the operability of a pneumatically operated safety shutdown valve, (a) Input command generated by the diagnostic and resulting travel, (b) Actuator pressure measured over the tested range of travel. 

To measure the gas phase speciation, the choice of optical spectrometries was made. These online techniques allow concentration measurements (Hartmann, 2009) and then partial pressures measurements without altering the gas phase composition. 

Ismail I, Shafquet A, Karsiti MN. (2011) Application of electrical capacitance tomography and differential pressure measurement in an air-water bubble column for online analysis of... 

There is extensive work on measuring, controlling, and engineering more robust polymerization reactors, elaborated in Chapter 16. Richards and Congalidis have also provided a concise summary [50]. Much attention has been devoted to maintaining pressure, temperature, level, and flow (PTLF) in the reactor [51, 52]. Different online composition measurement techniques, such as IR analysis, Fourier transform infrared (FTIR), near IR (NIR), Raman spectroscopy [53], calorimetry [54], and gas chromatography (GS) are available, as discussed in Chapters 6,9,10,18, and 20. 

One way of avoiding droplet shear and gas flotation effects is to conduct an online sample measurement. This technique, however, requires specialized equipment, such as the Melvem Mastersizer, and is constrained in terms of the maximum pressure it can tolerate. Alternatively, a sample pressure cylinder (homh) can he used to avoid droplet shear and the gas flotation effect. Here, the sample is taken in a stainless steel cylinder with a needle valve and a ball valve and thus minimizes the shearing of droplets during sampling. 

Where-high purity MU is provided for higher pressure WT boiler plant FW, some form of continuous analyzers for measuring treated water pH and conductivity are almost always installed, as are sodium (Na) ion-selective electrodes for detection of sodium leakage. Automatic online silica analyzers also may be installed, but they measure only reactive (ionizable) silica (Si02), not colloidal or total silica, so caution is required where unforeseen silica leakage may present a problem. 

In the highest pressure boilers, where online measurement equipment is installed, steam and condensate sampling is taken from the following points, as a minimum ... 

The core - flood apparatus is illustrated in Figure 1. The system consists of two positive displacement pumps with their respective metering controls which are connected through 1/8 inch stainless steel tubing to a cross joint and subsequently to the inlet end of a coreholder 35 cm. long and 4 cm. in diameter. Online filters of 7 im size were used to filter the polymer and brine solutions. A bypass line was used to inject a slug of surfactant solution. Two Validyne pressure transducers with appropriate capacity diaphragms are connected to the system. One of these measured differential pressure between the two pressure taps located about one centimeter from either end of the coreholder, and the other recorded the total pressure drop across the core and was directly connected to the inlet line. A two - channel linear strip chart recorder provided a continuous trace of the pressures. An automatic fraction collector was used to collect the effluent fluids. 

After the activation period, the reactor temperature was decreased to 453 K, synthesis gas (H2 CO = 2 1) was introduced to the reactor, and the pressure was increased to 2.03 MPa (20.7 atm). The reactor temperature was increased to 493 K at a rate of 1 K/min, and the space velocity was maintained at 5 SL/h/gcat. The reaction products were continuously removed from the vapor space of the reactor and passed through two traps, a warm trap maintained at 373 K and a cold trap held at 273 K. The uncondensed vapor stream was reduced to atmospheric pressure through a letdown valve. The gas flow was measured using a wet test meter and analyzed by an online GC. The accumulated reactor liquid products were removed every 24 h by passing through a 2 pm sintered metal filter located below the liquid level in the CSTR. The conversions of CO and H2 were obtained by gas chromatography (GC) analysis (micro-GC equipped with thermal conductivity detectors) of the reactor exit gas mixture. The reaction products were collected in three traps maintained at different temperatures a hot trap (200°C), a warm trap (100°C), and a cold trap (0°C). The products were separated into different fractions (rewax, wax, oil, and aqueous) for quantification. However, the oil and wax fractions were mixed prior to GC analysis. 

For some reactions, has been determined by direct measurement over a broad range of temperature, pressure, and salinities. Enough data exist to formulate empirical equations that enable extrapolation to the exact temperature, salinity, and pressure of interest. This has been done for the chemical reactions in the carbonate system, for the dissociation of water and for the dissolution of gases. These equations have been used to formulate look-up tables, such as those presented in the online appendix on the companion website. 

In tile next section we cover the major types of measurement devices used in the process industries, principally the big five measurements temperature, flow rate, pressure, level, and composition, along with online physical property measurement techniques. Table 8-8 summarizes the different options under each of the principal measurements. 

In order to ensure an adequate quality of products and a safe operation, the monitoring of a batch reactor should include, at least, online measurements of temperature, pressure, and of some composition-related variables. In this context, online measurements may be defined as measurements obtained via instruments strictly connected to the reactor and characterize by response times markedly smaller than the characteristic times of the chemical reaction. In general, this is the case of temperature and pressure, which can be easily measured online by means of reliable, relatively cheap, and poorly intrusive sensors. This allows the introduction of sensor redundancy, a common practice to increase reliability. On the other hand, online... 

It is also interesting to briefly consider online measurements of variables different from temperature [5], Since pressure is defined as the normal force per unit area exerted by a fluid on a surface, the relevant measurements are usually based on the effects deriving from deformation of a proper device. The most common pressure sensors are piezoresistive sensors or strain gages, which exploit the change in electric resistance of a stressed material, and the capacitive sensors, which exploit the deformation of an element of a capacitor. Both these sensors can guarantee an accuracy better than 0.1 percent of the full scale, even if strain gages are temperature sensitive. 

Flow rates through the system were controlled by quartz capillaries connected in parallel and were measured with a gas buret connected to the capillary tips. Using this method, a wide range of flow rates at various system pressures were attained. To obtain a particular flow rate, all valves except Vj and V3 in the reactant addition system (see Figure 2) were closed and the appropriate combination of capillary tips (in the exit manifold) were valved online. 

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