Thermal energy endothermic reactions

Thermal decomposition of spent acids, eg, sulfuric acid, is required as an intermediate step at temperatures sufficientiy high to completely consume the organic contaminants by combustion temperatures above 1000°C are required. Concentrated acid can be made from the sulfur oxides. Spent acid is sprayed into a vertical combustion chamber, where the energy required to heat and vaporize the feed and support these endothermic reactions is suppHed by complete combustion of fuel oil plus added sulfur, if further acid production is desired. High feed rates of up to 30 t/d of uniform spent acid droplets are attained with a single rotary atomizer and decomposition rates of ca 400 t/d are possible (98). 

When a gas reacts with a solid, heat will be transfened from the solid to the gas when the reaction is exothermic, and from gas to solid during an endothermic reaction. The energy which is generated will be distributed between the gas and solid phases according to the temperature difference between the two phases, and their respective thermal conductivities. If the surface temperature of the solid is T2 at any given instant, and that of the bulk of the gas phase is Ti, the rate of convective heat transfer from the solid to the gas may be represented by the equation... 

Generally, under either isothermal or noniso-thermal conditions, intrapartiole diffusional limitations are undesirable because they reduce the selectivity below that which can be achieved in their absence. The exception to this generalization is a set of endothermic reactions that take place in nonisothermal pellets where the second reaction has an activation energy that is greater than that of the first. 

This problem indicates the considerations that enter into the design of a tubular reactor for an endothermic reaction. The necessity of supplying thermal energy to the reactor contents at an elevated temperature implies that the heat transfer considerations will be particularly important in determining the longitudinal temperature profile of the reacting fluid. This problem is based on an article by Fair and Rase (1). 

Typically, ATR reactions are considered to be thermally self-sustaining and therefore do not produce or consume external thermal energy. In fact, since ATR consists of the combination of an exothermic reaction (CPO) which produces heat, with an endothermic reaction (CSR) where heat must be externally generated to the reformer, the balance of the specific heat for each reaction becomes a very distinctive characteristic of this process. This makes the whole process relatively more energy efficient since the heat produced from CPO can transfer directly to be used by CSR. However, other exothermic reactions may simultaneously occur, such as WGS and methanation reactions. 

The suitability of a cycle for hydrogen production depends upon the overall thermal efficiency and operational feasibility. A highly endothermic reaction step is required in a cycle to achieve effective heat-to-chemical energy conversion. For efficient mass and momentum transfer a fluid based system is preferred [96] and, ultimately, for large-scale hydrogen production other factors such as environmental effects and cost effectiveness must also be considered. 

Endothermic reactions require the input of energy, which can include the input of thermal energy. This gives the molecules greater kinetic energy, which can help their collisions to be more effective. 

We shall find the temperature distribution in the gas in those layers adjacent to x — 0 in which the chemical reaction has not yet started. The evaporation heat or the heat of endothermic reaction of gas-formation, L, is equal to the jump in the thermal energy of the original substance. Thus, at x = 0 at the phase-boundary the magnitude of the thermal flux experiences a jump. Using one prime for the c-phase and two primes for the gas, we construct the equation... 

This reaction is generally carried out in the forward, endothermic direction at temperatures up to 1100K and pressures of around 40 bars. The reverse, exothermic reaction (generally referred to as the methanation reaction) is capable of yielding thermal energy at peak temperatures in excess of 800K. The water-gas shift reaction... 

Temperature gradients in endothermal reactions amplify the effects of concentration gradients. In exothermal reactions the thermal effects can compensate the concentration effects or dominate completely. In the latter cases the apparent activation energy can become higher than the true one due to a kind of ignition [5], Also in this case at the highest temperatures the apparent Ea approaches zero. 

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