Using Improved Materials for Reformer Tubes

Stress to Rupture Diagram

The reformer contains about 200-400 tubes made off chromium nickel steel, 10-13 meters long, with an inner diameter of 75-140mm and a wall thickness of 11-18mm (Ullmann’s, 2011 p.175). Under the severe conditions taking place in the reformer the tubes start to creep and rupture. Determining factors for such deformation are the internal pressure and the tube-wall temperature. Figure shows the stress to rupture of different materials. To avoid tube rupture, lower pressures are employed, leading to higher power use for compression in ammonia synthesis. The reaction in the reformer is endothermic and proceeds with an increase in volume. To compensate for the lower conversion rate due to the increased pressure the reaction temperature needs to increase. However, tube materials limit the allowable increase in temperature (Ullmann’s, 2011 p.175). 

The standard material for many years was the HK 40. The HP modified (1.5% Nb) material, due to its improved temperature properties (40 bar reforming pressure at a tube wall temperature of 900oC), has been used in many tube replacements and tubes in new plants (Ullmann’s, 2011 p.175). The use of microalloys containing Ti and Zr are another improvement (see Figure 11). Their use permits the reduction of tube-wall thickness while maintaining the same tube lifetime (100,000 hours). By installing tubes with smaller wall thickness and/or wider diameter the capacity of the front end of an ammonia plant can be increased (Beyer et al., 2005 p.7).

The use of microalloyed tubes with minimum wall thickness can increase the catalyst volume, increase firing and lower the pressures drop (A2A Toolkit). According to Fertilizer Association of India, with the new improvements in materials it is possible to increase the life time of the reformer tubes (by up to 20 000 hours) and have higher tube-wall temperatures (up to 906 oC) (FAI, 2013).

Development Status Products
Commercial
Ammonia

Using Improved Materials for Reformer TubesCosts & Benefits

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

Replacement of the reformer tubes in the Indian plant required an investment of Rs. 50 million. The payback time was 40 months (PCRA,, 2009 p.335).

Indian Flag  Investments for a 1 300 tpd plant are around US $ 2 million [2011 values] (FAI, 2013).

Using Improved Materials for Reformer Tubes Publications

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335

Using Improved Materials for Reformer Tubes Tools

Assessment to Action (A2A) Toolkit

Developed by IIP, in collaboration with energy expertsat ICF Marbek, members of the IFA and experts in China, the A2A (Assessment to Action) Toolkit is a free suite of resources on energy management and technology best practices created for ammonia companies. The A2A Toolkit provides a first-order, high-level assessment to identify and prioritize energy efficiency opportunities. It does so by drawing on various assessment modules on technical best practices, management best practices (based on ISO 50001 standard) and productivity improvements. 

Using Improved Materials for Reformer Tubes Conference Papers

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