Series, reactors

FIOR Process. In the FIOR process, shown in Figure 5, sized iron ore fines (0.04—12 mm) are dried in a gas-fired rotary dryer. A skip hoist dehvers the dry fines to lock hoppers for pressurizing. The fines pass through four fluidized-bed reactors in series. Reactor 1 preheats the ore to 760°C in a nonreducing atmosphere. Reactors 2, 3, and 4 reduce the ore at 690—780°C. At higher (ca 810°C) temperatures there is a tendency for the beds to defluidize as a result of sticking or hogging of the reduced material. 

With the availability of more advanced interrupters in future, it will be possible to upgrade the present guidelines and permit connections of more feeding lines on an existing grid without having to resort to a series reactor. 

Resonance may also occur between the line inductance, series reactors and shunt capacitors. 

In an HT system, either the star is not grounded or it is a delta-connected system and hence the third harmonic is mostly absent, while the content of the. second harmonic nuiy be too small to be of any significance. For this purpose, where harmonic analysis is not possible, or for a new installation where the content of harmonies is not known, it is common practice to use a series reactor of 6% of the reactive value of the capacitors installed. This will suppress most of the harmonics by making the circuit inductive, up to almost the fourth harmonic, as derived subsequently. Where, however, second harmonics are significant, the circuit may be tuned for just below the second harmonic. To arrive at a more accurate choice of filters, it is better to conduct a harmonic analysis of the system through a harmonic analyser and ascertain the actual harmonic quantities and their magnitudes present in the system, and provide a correct series or parallel filter-circuits for each harmonic. 

Refer to Table 23.1, which shows the average cumulative effect of all the harmonics that may be present in a power system. If we can provide a series reactor of 6% of the total kVAr of the capacitor banks connected on the system, most of the harmonics present in the. system can be suppressed. With this reactance, the system would be tuned to below the fifth harmonic (at 204 Hz) for a 50 Hz system as derived below. 

But w hen the third and/or second harmonics are also present in the system, at a certain fault level it is possible that there may occur a parallel resonanee between the capacitor circuit and the inductance of the system (source), resulting in very heavy third or second harmonic resonant currents, which may cause failure of the series reactor as well as the capacitors. In such cases, a 6% reactor will not be relevant and a harmonic analysis will be mandatory to provide more exacting filter circuits. 

Figure 23.16 Voltage across the capacitor units rises with the use of series reactors...

V( = voltage across the capacitor banks = Ic Ul = voltage across the series reactor = /[ X ... 

When a capacitor circuit is compensated through a series reaetor. either to suppress the system harmonics or to limit the switching inrush currents (Section 23.11) or both, it will require suitable adjustment in its voltage and capacitive ratings, fhe series reactor will dampen the switching currents but consume an inductively reactive power and offset an equivalent amount of capacitive kVAr. and require compensation. The following example w ill elucidate this. 

To determine the basic parameters of a 6% series reactor and its capacitive compensation, consider Example 23.6 with 3000 kVAr banks (1000 kVAr per phase) rated for 33.4 kV ... 

In HT systems, where a series reactor is already being used, to suppress the system harmonics this would also serve to limit the switching inrush currents and no separate reactor would be necessary,... 

Since a series reactor is of a relatively small value, it may not be able to withstand the system fault conditions. In that case, it is advisable to connect it on the neutral side of the star-connected bank rather than on the line side. 

See also Example 23.1 to account for the voltage rise due to series reactor in case series reactors are used. 

Use of high series reactor, with or without resistance across the capacitor terminals. Open-delta VT (Section 15,4,3) is one such device, which is a combination of an inductance and a resistance and is to di.scharge an HT capacitor unit quickly. 

The series reactor may not be suitable to withstand the system fault level, nor add significantly, to the circuit impedance to diminish its fault level. 

For ihe proleeiion of series reactors, w hen used t)ii large installations, and are oil cooled, a Buchholz relay may be provided for oil temperature indication once any other proieciion deemed necessary... 

The harmonic content may be measured through harmonic analysers and expressed as a percentage of the fundamental component. The cuiTent and voltage ratings of the reactors will depend upon their application. A series reactor connected permanently in the circuit, for instance, will be rated continuously and for full system voltage, whereas a reactor used in the ground circuit may be short-time rated and rated for the likely maximum ground fault current. 

These are meant to limit the inrush currents occurring during a switching operation of a capacitor. They are connected in series with the capacitors and may be short-time rated for the values of the inrush currents and continuously rated for normal line currents. They are almost the same as the series reactors with fixed reactance. 

If the fault level is required to be limited to 50 MVA, a series reactor of reactance, X% may be introduced into the transformer circuit, as illustrated in Figure 27.13(b),... 

A series reactor of reactance 5.35% may be used to limit the fault to the required level. 

For ratings of 25(300 A and above it is possible that the fault level of the system may exceed the rupturing capacity of the available interrupting devices. To reduce the fault level in such cases, ctirrent limiting series reactors can be provided with the btis system, as noted above and ilhistrated in Fiszttre 3 1.8. 

Tanks-in-series reactor configurations provide a means of approaching the conversion of a tubular reactor. In modelling, they are employed for describing axial mixing in non-ideal tubular reactors. Residence time distributions, as measured by tracers, can be used to characterise reactors, to establish models and to calculate conversions for first-order reactions. 

EXAMPLE 6.10 Air-Stripping tower with first-order degradation, modeled as plugfiow, plug flow with dispersion, and mixed tanks-in-series reactors... 

Reaction conditions were as follows reaction temperature = 863 K contact time 3 sec CH4 02 molar ratio = 11. A, B and I refer to acid, basic and intermediate AHM impregation pH media, respectively. Notice that 0.8 Mo nm-2 is common for the two catalysts series. Reactor 2. 

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