Lower Steam to Carbon Ratio on Reformer

A reduction of the steam/carbon ratio will result in energy savings in the form of reduced heat input to the primary reformer and in savings in process steam. In addition, it will lower the pressure drop, resulting in energy savings in the synthesis gas compressor. The optimum steam to carbon ratio is typically around 3.0, although the feedstock quality, purge gas recovery, primary reformer capacity, shift operation, and the plant steam balance are factors that may influence the actual optimum steam/carbon ratio in a specific facility (Christensen, 2001; IPTS/EC, 2007 p.40; Nand and Goswami, 2009).

Typically, the minimum allowable steam to carbon ratio is determined by requirements set by the shift section. With the use of Cu-promoted High Temperature Shift (HTS) catalysts the permissible steam to carbon ratio can be reduced to 2.8. The heat requirements in the CO2 removal section can hinder the reduction of the steam to carbon ratio. Several revamp measures (i.e. change the packing materials in the tower, use enhanced CO2 removal solvents) can be applied to decrease the energy use in the CO2 removal section.

Design value for steam/carbon ratio is decided based on various factors, including:

  • Reformer tubes skin temperature;
  • Sudden fluctuations of feed gas composition;
  • Presence of higher hydrocarbons in reformer feed gas;
  • Distribution of duty between primary and secondary reformer;
  • Material of construction of reformer tubes, and;
  • Requirement of steam in CO2 removal section (FAI, 2013). 

In new plants, the steam/carbon ratio may be lower than 3.0. Lowering the steam/carbon ratio from 4 to 3 will result in approximately 0.8 GJ/ t NH3 energy savings (Christensen, 2001). Steam/Carbon ratio can be reduced in existing plants as a revamp measure. However, this should only be performed following detailed assessments on the plant as lower Steam/Carbon ratios may cause damage to catalyst in case of sudden increase of higher hydrocarbons in feed gas. It may also lead to side reactions like cracking resulting in carbon deposition on catalyst (FAI, 2013). 

Development Status Products
Commercial
Ammonia

Lower Steam to Carbon Ratio on ReformerCosts & Benefits

Parent Process: Steam Reforming
Energy Savings Potential
CO2 Emission Reduction Potential
Costs

Lower Steam to Carbon Ratio on Reformer Reference Documents

Reference Document on Best Available Techniques for the Manufacture of Large Volume Inorganic Chemicals - Ammonia, Acids and Fertilisers

Prepared by the Institute for Prospective Technical Studies of European Commision, this document provides detalied information on Best Available Technologies applicable to Ammonia production – as well as on the production of Acids and Fertilizers.  

Page Number: 

40

Lower Steam to Carbon Ratio on Reformer Conference Papers

Energy Efficiency Gains in Indian Ammonia Plants – Retrospect and Prospects

The paper documents the major efforts behind energy efficiency improvements in Indian ammonia plants which include use of better feedstock, revamp and retrofit and adoption of better operation and maintenance practices. The paper also outlines the potential for further energy savings and measures required for the same including feedstock change, revamp/retrofit and optimization of critical operating parameters.