Current limiting reactors

These types of reactors can now be used as current limiting reactors and also as harmonic suppressors. They are also recommended for capacitor application due to their linear characteristic which will not disturb the tuning of the filter circuit. 

Figure 27.9 Use of current limiting reactor, (1) to limit the fault current, or (2) to limit inrush current during a capacitor switching...

Figure 27.11 Typical characteristics of a current limiting reactor (coreless, gapped iron core or magnetically shielded core type)...

These are meant to limit the ground fault current and are used between the neutral of the system and the ground. They are single-phase and may be short-time rated, otherwise they are the same as the current limiting reactors (Figure 27.12). Their ratings can be calculated by... 

Reduced-voltage starting. A reactor, resistor, or transformer is temporarily connected ahead of the motor during start to reduce the current inrush and limit voltage dip. This is accompanied by reduced starting torque. For reactor or resistor start, the torque decreases as the square of current for transformer start, the torque decreases directly with line current. The reactor, resistor, or transformer can be adjusted to give a proper balance between torque and current. 

There are many other examples in the literature where sealed-vessel microwave conditions have been employed to heat water as a reaction solvent well above its boiling point. Examples include transition metal catalyzed transformations such as Suzuki [43], Heck [44], Sonogashira [45], and Stille [46] cross-coupling reactions, in addition to cyanation reactions [47], phenylations [48], heterocycle formation [49], and even solid-phase organic syntheses [50] (see Chapters 6 and 7 for details). In many of these studies, reaction temperatures lower than those normally considered near-critical (Table 4.2) have been employed (100-150 °C). This is due in part to the fact that with single-mode microwave reactors (see Section 3.5) 200-220 °C is the current limit to which water can be safely heated under pressure since these instruments generally have a 20 bar pressure limit. For generating truly near-critical conditions around 280 °C, special microwave reactors able to withstand pressures of up to 80 bar have to be utilized (see Section 3.4.4). 

The scope for continuous reactors does have some limitations and it is unlikely that they will completely replace batch reactors in the foreseeable future. The most important current limitations are as follows ... 

Despite the obvious potential advantages of reactor systems, significant disadvantages exist which currently limit the implementation of this technology. The greatest of these is the material input requirement which mandates a... 

As was described in the review of previous work, over the last ten years MINLP optimization models have been reported for the synthesis of process flowsheets, heat-exchanger networks, separation sequences, reactor networks, utility plants, and design of batch processes. Rather than describing in detail each of these works, we will briefly highlight several examples from our research group at Carnegie Mellon to illustrate the capabilities and the current limitations of the MINLP approach. 

In the first case, the reactions of interest are those which are intrinsically fast and exothermic, but which are currently limited by the poor heat and mass transfer for rates achievable in a stirred pot. Existing technology routinely entails substantial hazardous process inventories, possible reactor runaway and indifferent product selectivity. Fast response reactors open up the possibility of switching to more severe process conditions which would be prohibited in conventional reactors in view of the tendency to degrade the product. It may therefore be possible to exploit a virtuous circle - short residence time -higher temperature - faster kinetics - smaller reactor - shorter residence time. 

The dielectric barrier in the corona reactor serves as a built-in current-limiting device, or ballast in the event of a short circuit or arc between the cell electrodes, so that the stored energy is dissipated in the barrier at breakdown. 

Reactors are indnctance coils and the name reactor is used to imply their use for limiting fault current. Current limiting is often achieved by adding reactance into part of the power system. Reactors perform this fnnction economically. 

Plasma reactors have been built utilizing a wide range of frequencies, from DC to microwave. DC plasmas are difficult to use because they require a current limiting resistor to prevent arc formation. This resistor wastes power and must be changed for each different gas and operating condition. Also, ion bombardment becomes a factor in DC plasmas. 

To overcome current limitations and restrictions in the monobromination of aromatic compounds, microstmctured reactors were tested by Loeb and coworkers [26-28] under intensified process conditions. Due to the improved safety features of microreactors, parameter screenings were extended to elevated temperatures and pressures. Moreover, undiluted elemental bromine was used as bromination agent, discarding the use of catalysts and radiation. In particular, the competitions between (a) single versus multiple substitutions and (b) core versus side-chain substitutions were investigated. 

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