Process Description
Compression
As will be seen from the following, one mole of methane produces four moles
of hydorgen, and since the ammonia synthesis reaction requires high pressure, it is
obviously far more economical to compress the methane than to compress the hydrogen at
a later step in the process.
However, the information of hydrogen out of methane is favoured by lower pressure, but
at low pressure the volume of the gases is much longer, which results in a much bigger size
of all equipment. A very high pressure increases the investment because the equipment must be
stronger. The choice of operating pressure is made on an economic basis.
Desulfurization
Sulfer is a poison to almost all catalyst used in the process and should be removed from the gas.
The feed is desulfurized with zinc oxide at high temperature before it enters the reforming section.
Reforming
The reforming process is carried out in two steps. Feedgas from the desulfurizer is mixed with steam.
The combined steam is preheated and sent to the primary reformer furnace.
The reforming reaction takes place in catalyst filled tubes in the radiant section of the furnace.
Roughly 40% of the methane is converted to carbon oxides and hydrogen.
The effluent of the primary reformer is sent to the top of the secondary reformer where the formation
of hydrogen and carbon oxides out of methane is completed. Process air which is compressed and preheated
in the convertion section of the primary reformer, is also fed to the secondary reformer.
In the upper section of the reactor, oxygen in the air reacts with primary reformer effluent to form
carbon oxides and water. The mixture then passes over a bed of catalyst where the heat of the
above oxidation reaction converts methane to hydrogen and carbon oxides.
|