Indirect thermal generation

Many steam-generating plants have more than one type of direct or indirect FW heater to increase the FW temperature, which reduces the potential for boiler thermal shock and increases boiler operational efficiency. 

Cation radicals may be generated by direct or indirect electrochemical oxidation of the molecule of interest, and many such oxidations are synthetically useful. However, several other methods are also available, which fall into two broad categories thermally-induced electron transfer (TIET) and photo-induced electron transfer (PIET). 

The procedure involved in indirect cremation is much more fuel-intensive than that of direct cremation, since the former requires that the entire fireproof mass of the recuperator be heated to 1000°C (about 1830°F). The frequency of cremations has a very significant effect on fuel consumption, since the oven s firebrick absorbs most of the heat generated during the first cremations. For this reason fuel consumption is lowest when the oven is operating at thermal equilibrium. 

Indirect (Multi-step) Solar Thermal Water Splitting to Generate Hydrogen Fuel... 

Early studies performed on H2O splitting thermochemical cycles were mostly cha racterized by the use of process heat at temperatures below about 1200 K, available from nuclear and other thermal sources. These cycles required multiple steps (more than two) and had inherent inefficiencies associated with heat transfer and product separation at each step. An overview of indirect thermochemical processes for hy drogen generation using more than two steps has been presented by Funk,4 and sev eral of these cycles are summarized in Table 3. An example includes cycle No. 2 in Table 3, which utilizes the following reaction steps ... 

Cationic polymerizations induced by thermally and photochemically latent N-benzyl and IV-alkoxy pyridinium salts, respectively, are reviewed. IV-Benzyl pyridinium salts with a wide range of substituents of phenyl, benzylic carbon and pyridine moiety act as thermally latent catalysts to initiate the cationic polymerization of various monomers. Their initiation activities were evaluated with the emphasis on the structure-activity relationship. The mechanisms of photoinitiation by direct and indirect sensitization of IV-alkoxy pyridinium salts are presented. The indirect action can be based on electron transfer reactions between pyridinium salt and (a) photochemically generated free radicals, (b) photoexcited sensitizer, and (c) electron rich compounds in the photoexcited charge transfer complexes. IV-Alkoxy pyridinium salts also participate in ascorbate assisted redox reactions to generate reactive species capable of initiating cationic polymerization. The application of pyridinium salts to the synthesis of block copolymers of monomers polymerizable with different mechanisms are described. 

PET-sensitization means that the desired radical pair D + A is produced indirectly by first generating another radical pair D + X using an auxiliary sensitizer X and then exchanging X for A by a thermal electron transfer. X is chosen such that the photophysical parameters and redox potentials bar all other pathways except the PET-sensitized one. Of particular significance for the above mechanistic question is that neither D nor A are excited hence, an exciplex (D A) cannot be formed. Chart 9.2 juxtaposes the direct and the PET-sensitized formation of D- + A-. ... 

The transition split divides direct-type sphts from indirect-type splits as discussed by Doherty and Malone (Conceptual Desisn of Distillation Systems, 2001, chaps. 4 andS) also see Fidkowski, Doherty, and Malone [AlChE J., 39,1301(1993)]. The upper line in Fig. 13-70 is the minimum vapor flow leaving the reboiler of the main column, which also corresponds to the minimum vapor flow for the entire system since all the vapor for the total wstem is generated by this reboiler. For P = 0 the minimum vapor flow for the entire thermally coupled system (i.e., main column) becomes equal to the minimum vapor flow for the side rectifier system (i.e., main column of the side-rectifier system see Fig. 13-65b or c) (Vsr) for P = 1 it is equal to the minimum vapor flow of the entire side stripper system (Vss) (which is the sum of the vapor flows from both the reboilers in this system see Fig. 13-66h or c). Coincidentally, the values of these two minimum vapor flows are always the same (Vsr), = (Vss)mm- For P = Pr the main column is pinched at both feed locations i.e., the minimum vapor flows for separations A/B and B/C are equal. 

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