Lower heating value conversion requirements

The efficiency of the fuel processor is defined as the ratio of the lower heating value (LHV) of the hydrogen produced to the LHV of the fuel consumed by the fuel processor. The major factors affecting the efficiency are 1) the conversion in the reformer and shift reactors, 2) the recovery of hydrogen in the PSA, 3) the recovery of the process heat, and 4) the minimization of heat losses and parasitic requirements in compressors. 

Effect of Heat Of Reaction Figure 2.5 shows what happens if the heat of reaction is 10 or 20% higher than the base case value. The conversion is 80% for all these cases. As expected, the heat of reaction has no effect on the reactor volume, diameter, or area. These parameters are set by throughput, temperature, and conversion. Higher heats of reaction require higher heat transfer rates Q, which lower the jacket temperature and increase the cooling water flowrate. As shown in Figure 2.6, the result is an increase in the reactor stability index, which indicates more difficult control problems. 

The Methyl Fuel produced has a higher heating value (HHV) of 20,000,000 Btu/ton and it requires an input of from to 2 times as much heat based on the coal s HHV. Thus the overall energy conversion is in the range of 50 to 65% and the lower efficiencies in this range are for poorer coals. About 2 tons of a subbituminous coal as mined with 8600 Btu per pound HHV will produce 1 ton of Methyl Fuel at an overall conversion efficiency of 58%. 

A similar problem is involved in determining the initial set of numbers of moles in adiabatic chemical conversions, when it is required that a predetermined temperature should be maintained. This can be achieved by either adding an inert constituent, which by increasing its own temperature lowers the reaction temperature to the required value or, by adding another reactive constituent. The constituent added must cause at least one endothermic reaction to take place, thus consuming the excess heat of reaction. The result is a process, in which the overall enthalpy change is zero for the temperature given, i.e. reaction is enthalpically autonomous. 

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