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

Picture2

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