Steam Reforming
Introduction
Synthesis gas (or syngas) - mixtures of hydrogen and carbon monoxide in various ratios
Steam reforming of natural gas or light hydrocarbons
Partial oxidation of (heavy) hydrocarbons with steam and oxygen
Partial oxidation of coal (gasification) with steam and oxygen
Reaction of HCs + steam + catalyst
non-catalytic reaction of hydrocarbons with oxygen and steam
an important process for syngas production in countries with abundant coal resources
feed has to be desulfurized
Sulfur is a poison for metal catalysts because it can block active sites
transition-metal-based catalysts are used
adsorption on activated carbon, reaction with an oxide (eg. zinc oxide), or scrubbing with a solvent
Syngas conditioning includes such processing steps as the water–gas shift reaction, carbon dioxide removal, methanation
Steam Reforming Process
catalyst is still required to accelerate the reaction - steam reforming is carried out at high temperature (>1000 K) due to the very high stability of methane
In the convection section, heat recovered from hot flue gases is used for preheating of the gas feed and process steam and superheated steam generation
In the radiant section the reforming reactions take place
Carbon Formation
higher hydrocarbons exhibit a greater tendency to form carbonaceous deposits
At high temperature (>920 K) steam cracking occur to form alkenes that easily form carbon through reaction:
CnH2n → carbon + H2 ∆ rH298 < 0 kJ/mol
Methane slip
steam reformers operate at pressures far above atmospheric, although thermodynamically unfavorable
syngas at elevated pressure
Advantages of operating at elevated pressure - lower syngas compression costs and a smaller reformer size
counterbalance the negative effect on the equilibrium, higher temperatures are applied and excess steam is used
Advances in Steam Reforming
better materials for reformer tubes, better control of carbon limits, better catalysts regarding sulfur tolerance and carbon deposition, and better process concepts with high feedstock flexibility
worst carbon precursors are removed
Heat exchange between the high temperature of the reformer effluent with additional feed, allowing reforming part of the feed in a multi-tubular reactor without using a furnace