Effects of Steam Ratio

Gerard B. Hawkins Managing Director

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.

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).

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.

No significant change : Total Feed + Fuel increases slightly at Low

Steam Ratio.

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.

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.