Effect of Low Steam Ratio on the Steam Reformer Effect of Low Steam Ratio on H T Shift & PSA Effect of Low Steam Ratio on Gross Efficiency Effect of Low Steam Ratio on Net Efficiency Alternative schemes for improving heat recovery

1. Effects of Steam Ratio
Gerard B. Hawkins
Managing Director

2.  The basic process is very simple:
◦ Steam Reformer
◦ H T Shift
◦ P S A
 The fuel balance is a key constraint:
◦ Waste gas fuel value must be less than the
total reformer fuel requirement.
◦ Typically waste gas = 90% of total fuel.

3.  Adverse effects on methane/steam and shift
equilibria (more CH4 & more CO).
 This increases the CV of the waste gas - reformer
exit temp must be increased to maintain the fuel
balance.
 Small increase in reformer duty.
 Increased Flue Gas Temperature.
 Increased risk of C formation in top section.
 Lower pressure drop (provided there is no carbon
formation).

4.  Adverse effect on shift equilibrium (more CO).
 Increased risk of over-reduction.
 Reduced pressure drop (assuming no loss of
catalyst strength as a result of low SR).
 More CO to be removed in PSA.

5.  No significant change :
 Total Feed + Fuel increases slightly at Low
Steam Ratio.

6.  The major effect of Low Steam Ratio is improved
heat recovery downstream of the H T Shift; this
has a significant effect on plant economics.
 In a conventional plant the latent heat of
condensation cannot be recovered effectively; a
lower steam ratio reduces the steam content at
the exit of the shift and reduces the heat lost to
cooling water.

7.  1. Low Steam Ratio + Catalyst Development.
 2. Direct recovery of low grade waste heat.
◦ For example, LP boiler or Saturator circuit
◦ Capital cost - probably too high ?
◦ High gas prices will favor energy recovery
schemes and we should understand the
relative merits of these two different
approaches.