Separate stacks

Preferably, the HjS flare system should consist of a segregated header and separate line routed up the side of a conventional elevated flare stack, sharing the same structure, pilots and igniters. However, the HjS header may be tied into the regular flare seal drum if there are special mechanical design problems associated with the separate stack e.g., in the case of a flare which is to be dismantled for overhaul. Flare elevation must be sufficient to meet atmospheric pollution and ground level concentration requirements for the sulfur dioxide produced. 

Where a multi-boiler installation is being considered a multi-flue chimney is preferred. This is where the required number and size of flues are enclosed in a single windshield. It is preferred by planning offices and has the advantage of a greater plume rise than from separate stacks. 

The narrow tolerances to be maintained for the total separator thickness are tightened even further by the trend towards high-performance batteries with many thin electrodes, and therefore many separators also. One can easily calculate that for, say, ten or more electrodes and an equal number of separators per cell, the permitted tolerances become very small for fitting the electrodes/separators stack into the cell container. With electrodes and separators... 

A generic Jablonski diagram for a molecular system is shown in Figure 15.2. Singlet states and triplet states are shown as separate stacks. Associated with each electronic state is a vibrational/rotational manifold. The vibrational/rotational manifolds of dif-... 

As examples of an (ET) conductor with clearly separated stacks, we mention /]-(ET)2PF6 (60) and (ET)2AsF6 (103). They have structures which clearly resemble those typical of the earlier mentioned M(TCNQ)2 conductors and while / -(ET)2PF6 undergoes a metal-insulator transition at 297 K (60), the same type of transition occurs above 125 K in (ET)2AsF6 (103). 

The synthesis of the first organic metal TTF-TCNQ was reported in 1973 by Coleman etal. and Ferraris et alP In this compound, TTF and TCNQ molecules are in 1 1 ratio and form separate stacked donor (TTF) columns and stacked acceptor (TCNQ) columns. A partial charge transfer between TTF and TCNQ transforms the molecular stacks into one-dimensional conductive paths via the formation of partially filled bands. Although TTF-TCNQ shows metallic conductivity down to around 60 K, it abruptly transfers to an insulator below 54 K, which was explained by a charge-density wave (CDW) phase-locking (Peierls transition ) due to its one dimensionality. 

The crystal structure of TTF-TCW2, shown in Figure 2, consists of parallel conducting chains of TTF (Figure la) and TCNQ (Figure Id) molecular ions, separately stacked along the crystallographic b-axis. In the limit of... 

Another feature of AGM separators is their compressibility. With compression of the plate and separator stack, this AGM property guarantees good plate-separator contact, even if the plates are not perfectly smooth. Also, battery assembly is facilitated since the stack can be easily inserted into the cell after compression to a thickness lower than the cell dimension. An undesirable result of the compressibility is that the AGM separator does not exert sufficient resistance against expansion of the positive plate during battery cycle-life. This expansion is particularly prevalent in deep-cycle applications and can cause the battery to suffer premature capacity loss (PCL) via reduced inter-particle conductivity — a phenomenon known as PCL-2 [7]. In the literature, two additional characteristics, which are related to the PCL-2 failure mode, are discussed, namely, AGM separators shrink when first wetted with electrolyte and their fibres can be crushed at high pressure levels [8-10]. These features result in a loss of separator resilience, i.e., a lessening of the ability to display a reversible spring effect. 

Fig. 2.8 Costal structure of the radical-ion salt tetracyano-quinodimethane (TCNQ) Tetra-thiofulvalen (TTF). The crystal is monoclinic. The donors (TTF) and the acceptors (TCNQ) are arranged in separate stacks which are parallel and alternate along the a direction. These form a herringbone pattern. The molecular planes are inclined relative to the stack axes at an angle of 24.5° (TTF) or -34°...

Stacks in which the neighbouring molecules are equidistant are termed regular, while those with dimerisation are termed alternating. The different stackings are of vital importance for determining the character of these materials as insulators, semiconductors, or metallic conductors. Fig. 2.17 indicates schematically that the TTF-TCNQ crystal is built up from separate stacks. An example of mixed stacks is the insulator anthracene-PMDA (Fig. 6.14). 

Fig. 9.1 The arrangement of the molecular ions in single crystals of organic CT complexes, a mixed stacking of donor (D) and acceptor (A) molecules such crystals are insulators or semiconductors, b separate stacking with partial electron transfer S < 1) such crystals exhibit high metallic conductivities along the stacks or they are semiconductors with a strong anisotropy.

Typical and important for the strong CT and the radical-ion crystals is in many cases an arrangement of donors and acceptors in separate stacks, as in the compound TTF-TCNQ, Fig. 2.17. This is shown schematically in Fig. 9.1b. 

In many radical-ion salts with separate stacks, one finds conversely a high electrical dark conductivity, sometimes also with metallic character. One then refers to organic metals. We shall concern ourselves with these salts in more detail in the following sections of this chapter. There are, however, also numerous strong CT complexes with separate stacks in which the conductivity is lower. Table 9.1 lists the conductivities of some CT complexes and radical-ion salts of TCNQ. 

One can divide the conducting CT complexes and radical-ion salts with separate stacks phenomenologically into three classes which differ especially in the temperature dependence of their conductivities ([5] and [Ml], Chap. V see Fig. 9.2) ... 

The crystal lattices consist of separate stacks, either of planar organic donors and planar organic acceptors, or of planar organic radical ions and suitable inorganic counterions. 

Another long-known example of 2D inclined interpenetration is the structure of trimesic acid (1,3,5-benzene-tricarboxylic acid). It contains hydrogen-bonded (6.3) sheets that interpenetrate such that each window of each sheet is penetrated by three other inclined sheets. It is also possible for more than two stacks of parallel sheets to show inclined interpenetration—the remarkable structure of Co2(azpy)3(N03)4-Me2CO-3H20 [a /73 =4,4 -azo/ zT-(pyridine)] contains four separate stacks of parallel (6,3) sheets that all interpenetrate at mutually inclined angles.Combinations of network and interpenetration topologies are also possible. Inclined interpenetration between (4,4) and (6.3) sheets has been reported,and... 

The (CH3)4N+ 4 salt has been crystallized [9]. X-ray diffraction shows a 1-D structure of stacked semiquinone units. Each anion is flat and symmetrical, and the spacing between anions in the stack is constant (3.31 A). Each (CH3)4N+ is held between the four oxygens of two anions in separate stacks. TTiese stacks are at al ut 90 to each other. It seems likely that the conductivity is along the stacks, so that the molecular length plays a minor role. It is important, however, for conductance, that there are two quinone units in one molecule. The presence of two quinones and one electron may impart some mixed-valence character to the species in the solid. 

Some of the more sophisticated unloaders provide sorting mechanisms whereby individual piece parts are moved from the machine table to separate stacks or bins. In this scenario, the scrap or skeleton which remains after the... 

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