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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
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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.