Adiabatic minimisation

Because process heating is expensive, lagging is invariably applied to heated process vessels to minimise heat loss, particularly during long-term hot storage. Such adiabatic or near-adiabatic systems are potentially hazardous if materials of limited thermal stability, or which possess self-heating capability, are used in them. Insufficiently stabilised bulk-stored monomers come into the latter category. 

The success of INADEQUATE may be compromised by deleterious off-resonance effects that are particularly troublesome for nuclei such as carbon-13, which have a relatively large chemical shift range. Variations employing composite pulses to counteract offset effects have therefore been developed to minimise losses [89, 90]. An alternative approach is to replace the 180° pulses with composite adiabatic refocusing pulses (see Chapter 10). 

In an adiabatic flame calorimeter, the fuel, for example natural gas, or oil, is burnt completely in an atmosphere of oxygen at 1 atmosphere pressure, and the heat is transferred into a known mass of liquid, usually water and the temperature rise AT is measured. Provided heat losses are minimised, the enthalpy change (AH) per mole of fuel is given by the equation ... 

The reason for this is twofold, for not only is the number of initial states minimised, but the choice of rotational state for the product N2 molecule drops out also. It has been pointed out, rightly, [80.L1] that this is a considerable assumption reaction is considered to take place as a non-adiabatic transition between two electronic states of the N2O molecule, and although the ground state is linear, the other one is not consequently, the bending motions should play a part in the reaction process. Thus, whilst one may regard the numerical results of the simpler treatment with some circumspection, it remains an ideal vehicle for illustrating the state-to-state synthesis of specific rate functions. 

Pan and Wang switched four adiabatic preferential oxidation reactors in series downstream of the reformer/evaporator described in Section 7.1.3 [546]. Heat-exchangers were installed after each reactor. The four reactors were operated at the same inlet temperature of 150 °C, and the O/CO ratio in the feed increased from 1.6 to 3, to minimise the heat formation in the first reactors. Despite these measures, the temperatures rise in the first reactor was as high as 121 K, in the second reactor it was still at 82 K and decreased to 28 K in the third and 8 K in the last reactor. While only 50% carbon monoxide conversion could be achieved in the first reactor, conversion was complete after the last stage. The combined steam reformer/clean-up system was operated for 24 h. The carbon monoxide content ofthe reformate could be maintained below 40 ppm. 

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