Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Reaction heat-transfer

It is generally desirable to minimize the diameter of a tubular reactor, because the leak rate in case of a tube failure is proportional to its cross-sectional area. For exothermic reactions, heat transfer will also be more efficient with a smaller tubular reactor. However, these advantages must be balanced against the higher pressure drop due to flow through smaller reactor tubes. [Pg.30]

There are two basic types of packed-bed reactors those in which the solid is a reactant and those in which the solid is a catalyst. Many e.xaniples of the first type can be found in the extractive metallurgical industries. In the chemical process industries, the designer normally meets the second type, catalytic reactors. Industrial packed-bed catalylic reactors range in size from units with small tubes (a few centimeters in diameter) to large-diameter packed beds. Packed-bed reactors are used for gas and gas-liquid reactions. Heat transfer rates in large-diameter packed beds are poor and where high heat transfer rates are required, Jluidized beds should be considered. ... [Pg.136]

Enthalpy of input streams — enthalpy of output streams -I- heat generated by reaction — heat transferred out = accumulation of energy... [Pg.158]

Whether the mixing is associated with other operations reaction, heat transfer. [Pg.468]

There may be radial temperature gradients in the reactor that arise from the interaction between the energy released by reaction, heat transfer through the walls of the tube, and convective transport of energy. This factor is the greatest potential source of disparities between the predictions of the model and what is observed for real systems. The deviations are most significant in nonisothermal packed bed reactors. [Pg.262]

Heat of reaction + Heat transfer = Gain of sensible and latent heats. This establishes the temperature as a function of the composition,... [Pg.264]

Mass-Transtcr-Controllcd Flcctrodic Reaction Heat-Transfer systems, i.e.. Heat Transler Involved in Cooling Molten Metals... [Pg.499]

What problems face the theory of combustion The theory of combustion must be transformed into a chapter of physical chemistry. Basic questions must be answered will a compound of a given composition be combustible, what will be the rate of combustion of an explosive mixture, what peculiarities and shapes of flames should we expect We shall not be satisfied with an answer based on analogy with other known cases of combustion. The phenomena must be reduced to their original causes. Such original causes for combustion are chemical reaction, heat transfer, transport of matter by diffusion, and gas motion. A direct calculation of flame velocity using data on elementary chemical reaction events and thermal constants was first carried out for the reaction of hydrogen with bromine in 1942. The problem of the possibility of combustion (the concentration limit) was reduced for the first time to thermal calculations for mixtures of carbon monoxide with air. Peculiar forms of propagation near boundaries which arise when normal combustion is precluded or unstable were explained in terms of the physical characteristics of mixtures. [Pg.163]

Based on the investigation of reaction, heat transfer and mass transfer of the KD306-type sulfur-resisting methanation catalyst [9-11], the non-isothermal one-dimensional and two-dimensional reaction-diffusion models for the key components have been established, and solved using an orthogonal collocation method in this paper. The scope is to study the catalyst intraparticle reaction-diffusion processes that involve parallel, non-first order, equilibrium-restrained reactions. [Pg.33]

Process intensification can be considered to be the use of measures to increase the volume-specific rates of reaction, heat transfer, and mass transfer and thus to enable the chemical system or catalyst to realize its full potential (2). Catalysis itself is an example of process intensification in its broadest sense. The use of special reaction media, such as ionic liquids or supercritical fluids, high-density energy sources, such as microwaves or ultrasonics, the exploitation of centrifugal fields, the use of microstructured reactors with very high specific surface areas, and the periodic reactor operation all fall under this definition of process intensification, and the list given is by no means exhaustive. [Pg.388]

A major difference to mass transfer is that now the real reaction rate can be higher than the apparent one. The concentration in the particle is always lower or equal to the concentration in the bulk fluid phase and therefore, from this perspective, the real rate is always lower or, at best, equal to the apparent rate. However, in strong exothermic reactions heat transfer cannot cope with the high rates of generation of reaction heat and the temperature in the catalyst particle can be much higher than in the fluid phase, resulting in a much higher reaction rate than the apparent one. [Pg.35]

The simplifying assumption that the properties of the reaction mixture are those of air is justified by the maximum benzene concentration of 1.5 mol percent. It has also been assumed that the gas volume is unchanged by the reactions. Heat transfer to the walls from the distributer was evaluated by Froment s expression for fixed beds ( ) ... [Pg.62]

Vaporization and Condensation of Ash Species Deposit Chemistry - Specie Migration and Reaction Heat Transfer To and From the Deposit... [Pg.291]

Fast reactions are usually highly exothermic. Therefore, heat removal is also an important factor in controlling extremely fast reactions. Heat transfer takes place through the surface of the reactor. By taking advantage of the fact that microspaces have a large surface area per unit volume compared with macrospaces, heat transfer occurs very rapidly in microsystems, making precise temperature control possible. [Pg.102]

In this paper we will discuss the application of a general batch reactor model that considers the reaction kinetics, heats of reaction, heat transfer properties of the reactor, physical properties of the reactants and the products, to predict 1) The concentration profile of the products, thus enabling process optimization 2) Temperature profile during the reaction, which provides a way to avoid conditions that lead to a thermal runaway 3) Temperature profile of the jacket fluid while maintaining a preset reactor temperature 4) Total pressure in the reactor, gas flow rates and partial pressure of different components. The model would also allow continuous addition of materials of different composition at different rates of addition. [Pg.95]

Liquid-solid (catalytic) reactions. Heat transfer is likely to be more important within the pellet than in the surrounding film, and mass transport more important in the film than within the pellet. In other words, intraphase heat transfer and interphase mass transfer would normally be the dominant transport processes. [Pg.764]

Preparation of dry beans involves preliminary hydration followed by various heat treatments to obtain a tender, palatable product. Water and heat play an important role in chemical reactions, heat transfer and chemical transformations, such as protein denaturation and starch gelatinization. Inadequate water uptake may result in insufficient heat transfer to inactivate antinutritional factors and result in reduced cookability. In general, beans with an initial moisture content between 12 and 18%, are soaked to hydrate the seed to a moisture content of 53 to 57% and subsequently blanched, cooked or canned. This cooking step, if done for an optimal time, renders the seed nontoxic, improves digestibility, develops acceptable flavor and softens the seed coat and cotyledon. [Pg.112]

Low feed rates are suitable for trickle bed reactors where for gas-liquid-solid mixing, the gas and the liquid are fed into the top of the reactor. This gives long gas residence times but short liquid residence times. Such a configuration is often used in hydrogenation reactions. When the gas-liquid is fed into the bottom of the reactor, it is known as a bubble reactor. Here the gas residence times are short but the liquid residence times are relatively long. This is commonly used in oxidation reactions. Heat transfer can be a major problem with both trickle and bubble reactors and in such cases a slurry bubble column reactor can be employed. [Pg.8]

For exothermic reactions, heat transfer is usually also an important factor, for reasons of temperature control and energy costs. In this respect, slurry reactors are superior to fixed-bed reactors. In particular, the jet-loop reactor with its external heat exchanger provides excellent temperature control. [Pg.52]

Figure 2.15. The temperature change along the cross section of the sample in the case of a dynamic heating program. T, temperature space coordinate t, time A T. temperature drop. 1, Furnace 2, sample holder 3, sample 4. thermoelement 5, a single grain of the sample. Time and temperature of the beginning (/, Ts), maximum rate (tj, T6), and end (f4, 7"0) of an endo-thermal reaction. Heat transfer between furnace and sample surface (U), surface and center of the sample (F), surface and center of a single grain (Z) (114). Figure 2.15. The temperature change along the cross section of the sample in the case of a dynamic heating program. T, temperature space coordinate t, time A T. temperature drop. 1, Furnace 2, sample holder 3, sample 4. thermoelement 5, a single grain of the sample. Time and temperature of the beginning (/, Ts), maximum rate (tj, T6), and end (f4, 7"0) of an endo-thermal reaction. Heat transfer between furnace and sample surface (U), surface and center of the sample (F), surface and center of a single grain (Z) (114).
Plug flow reactors are applied mainly for gas-phase reactions. Heat transfer coefficient inside the reactor tube usually controls the overall heat transfer. High turbulent flow regime is recommended. However, the fluid velocity is constrained by the allowable pressure drop, by the feasible reactor length, catalyst attrition, etc. Figure 8.20... [Pg.330]

Rapid absorption and desorption is clearly desirable from an application s point of view. Intrinsic isothermal rates of hydriding and dehydriding are not easy to determine experimentally. In the case of rapid reactions, heat transfer becomes a difficult variable to control and the surface structure is always a problem. It is a fortunate circumstance that the reaction kinetics of most... [Pg.543]

The heterogeneities of most concern to us are those that involve the presence of more than one phase. The analysis of multiphase systems can be important to the design and operation of many industrial processes, especially those in which multiple phases influence chemical reactions, heat transfer, or mixing. For example, phase-equilibrium calculations form the bases for many separation processes, including stagewise operations, such as distillation, solvent extraction, crystallization, and supercritical extraction, and rate-limited operations, such as membrane separations. [Pg.256]

The real thermodynamic inefficiencies in a thermal system are related to exergy destmction and exergy loss. All real processes are irreversible due to effects such as chemical reaction, heat transfer through a finite temperature difference, mixing of matter at different compositions or states, unrestrained expansion, and friction. An exeigy analysis identifies the system components with the highest thermodynamic inefficiencies and the processes that cause them. [Pg.251]

Water is present in the continuous phase and plays a role of reaction heat transfer material. The reactants are present in the discontinuous phase. As the reaction proceeds, particles of ABS resins are produced in water, and thus the high reaction heat peculiar to ABS polymerization can be readily removed by water. [Pg.105]


See other pages where Reaction heat-transfer is mentioned: [Pg.525]    [Pg.184]    [Pg.188]    [Pg.265]    [Pg.424]    [Pg.76]    [Pg.715]    [Pg.309]    [Pg.1613]    [Pg.1301]    [Pg.2922]    [Pg.6]    [Pg.316]    [Pg.1449]    [Pg.1449]   
See also in sourсe #XX -- [ Pg.36 ]




SEARCH



Fast Chemical Reaction Accompanied by Heat and Mass Transfer

Heat Transfer with Reaction

Heat and mass transfer with chemical reaction

Heat transfer in gas-solid reactions

Heat transfer to reaction vessels

Heat transfer with chemical reaction

Mass and Heat Transfer Effects on Heterogenous Catalytic Reactions

Reaction calorimetry heat transfer

Reaction external heat transfer

Reaction heat

Reaction spinning heat transfer

Reaction vessels, heat transfer

Reaction vessels, heat transfer with jacket

Reactions with an interface Mass and heat transfer effects

© 2024 chempedia.info