Heat intensification

Automatic design techniques of the heat exchanger network can increase dramatically the designer s productivity, making free more time to conceptual tasks. New techniques are available for retrofitting existing networks, as well as for guiding the implementation of heat intensification devices. 

Methyl- and dimethylnaphthalenes are contained in coke-oven tar and in certain petroleum fractions in significant amounts. A typical high temperature coke-oven coal tar, for example, contains ca 3 wt % of combined methyl- and dimethylnaphthalenes (6). In the United States, separation of individual isomers is seldom attempted instead a methylnaphtha1 ene-rich fraction is produced for commercial purposes. Such mixtures are used for solvents for pesticides, sulfur, and various aromatic compounds. They also can be used as low freezing, stable heat-transfer fluids. Mixtures that are rich in monomethyinaphthalene content have been used as dye carriers (qv) for color intensification in the dyeing of synthetic fibers, eg, polyester. They also are used as the feedstock to make naphthalene in dealkylation processes. PhthaUc anhydride also can be made from m ethyl n aph th al en e mixtures by an oxidation process that is similar to that used for naphthalene. 

Substitution If intensification is not possible, then an alternative is to consider using a safer material in place of a hazardous one. Thus it may be possible to replace flammaole solvents, refrigerants, and heat-transfer media by nonflammable or less flammable (high-boiling) ones, hazardous products by safer ones, and processes which use hazardous raw materials or intermediates by processes which do not. As an example of the latter, the product manufactured at Bhopal (carbatyl) was made from three raw materials. Methyl isocyanate is formed as an intermediate. It is possible to react the same raw materials in a different order so that a different and less hazardous intermediate is formed. 

D) 1-p-Chlorobenzoyl-2-Methyl-S-Methoxy-3-lndolylacetic Acid A mixture of 1 g ester and 0.1 g powdered porous plate is heated in an oil bath at 210°C with magnetic stirring under a blanket of nitrogen for about 2 hours. No intensification of color (pale yellow) occurs during this period. After cooling under nitrogen, the product is dissolved in benzene and ether, filtered, and extracted with bicarbonate. The aqueous solution is filtered with suction to remove ether, neutralized with acetic acid, and then acidified weakly with dilute hydrochloric acid. The crude product (0.4 g, 47%) is recrystallized from aqueous ethanol and dried in vacuo at 65°C MP 151°C. 

Diffenbaugh NS, Pal JS, Giorgi E, Gao X (2007) Heat stress intensification in the Mediterranean climate change hotspot. Geophys Res Lett 34 L11706. doi 10.1029/2007GL030000... 

The chromatograms are freed from mobile phase in a stream of warm air, then immersed in the dipping solution for 2 s or homogeneously sprayed with the appropriate spray solution. Then, in the case of N-ethyl derivatives, the plate is heated to 105-110 °C for 2 min to accelerate the reaction [7]. Heating (e. g. to 80-105 °C for 15 min) can also lead to color intensification and color change in the case of other alkaloids [5, 6]. 

Intensification of Heat Transfer in Chemical Reactors Heat Exchanger Reactors... 

I 72 Intensification of Heat Transfer in Chemical Reactors Heat Exchanger Reactors Table 12.5 Effusivity values according to the reactor material. 

C.H. (1997) Compact heat exchangers as chemical reactors for process intensification (PI). Process Intensification in Practice, BHR Group Conference Series, Publication No. 28, pp. 175-189. 

S. H., and Stitt, E.H. (2007) intensification of the solvent-free catalytic hydroformylation of cydododecatriene comparison of a stirred batch reactor and a heat-exchange reactor. Catal. Today, 128, 18-25. 

Anxionnaz, Z., Cabassud, M., Gourdon, C., and Tochon, P. (2009) Hydrodynamic study and optimisation of the geometry of a heat exchanger/reactor. 2nd European Process Intensification Conference 2009, Venice. 

For the sake of developing commercial reactors with high performance for direct synthesis of DME process, a novel circulating slurry bed reactor was developed. The reactor consists of a riser, down-comer, gas-liquid separator, gas distributor and specially designed internals for mass transfer and heat removal intensification [3], Due to density difference between the riser and down-comer, the slurry phase is eirculated in the reactor. A fairly good flow structure can be obtained and the heat and mass transfer can be intensified even at a relatively low superficial gas velocity. 

In practice, the process regime will often be less transparent than suggested by Table 1.4. As an example, a process may neither be diffusion nor reaction-rate limited, rather some intermediate regime may prevail. In addition, solid heat transfer, entrance flow or axial dispersion effects, which were neglected in the present study, may be superposed. In the analysis presented here only the leading-order effects were taken into account. As a result, the dependence of the characteristic quantities listed in Table 1.5 on the channel diameter will be more complex. For a detailed study of such more complex scenarios, computational fluid dynamics, to be discussed in Section 2.3, offers powerful tools and methods. However, the present analysis serves the purpose to differentiate the potential inherent in decreasing the characteristic dimensions of process equipment and to identify some cornerstones to be considered when attempting process intensification via size reduction. 

Substantial heat-transfer intensification was also described for a special micro heat exchanger reactor [104]. By appropriate distribution of the gas-coolant stream, the axial temperature gradient can be decreased considerably, even under conditions corresponding to very large adiabatic temperature rises, e.g. of about 1400 °C. 

A detailed characterization of micro mixing and reaction performance (combined mixing and heat transfer) for various small-scale compact heat exchanger chemical reactors has been reported [27]. The superior performance, i.e. the process intensification, of these devices is evidenced and the devices themselves are benchmarked to each other. 

Phillips, C. H., Development of a novel compact chemical reactor-heat exchanger, in Green, A. (Ed.), Proc. of 3rd Int. Conf on Process Intensification for the Chemical Industry, BHR Group Conference Series, Vol. 38, pp. 71-87, Professional Engineering Publishing (1999). 

Groschel, L, Agar, D. W., Worz, O., Morgenschweis, K., The capillary-microreactor A new reactor concept for the intensification of heat and mass transfer in liquid-liquid reactions. Catalysis Today,... 

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