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Feb-2009

Medium-sized hydrogen plants based on convection reforming

Topsoe offers clients flexible and tailor-made solutions for hydrogen production by integrating catalyst and technology. The integrated approach ensures a fundamental understanding of the hydrogen process, backed up by decades of industrial experience.

Erik Broman and Jack Heseler Carstensen
Haldor Topsøe

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Article Summary

Topsøe has designed more than 250 hydrogen plants with maximum capacity exceeding 200 000 Nm3/h. For medium-scale hydrogen production (5–30 000 Nm3/h, 5–27 MM SCFD), Haldor Topsøe recommends a technology based on the Haldor Topsøe convection reformer (HTCR), which is a high-efficiency, compact heat exchange reformer. The HTCR technology was developed in the 1980s and has been in large-scale industrial operation since 1997. This paper describes this technology and the industrial experience with designs up to 30 000 Nm3/h (27 MMSCFD)

HTCR
The convection reformer as shown in Figure 1 is the key equipment in a HTCR plant. The HTCR reactor consists of a vertical, refractory lined vessel containing the tube bundle with several bayonet tubes. Below the vertical section is a horizontal combustion chamber containing a single burner. In a HTCR, the heat is transferred mainly by convection, and the improved utilisation of the heat input provides a design with low consumption figures and no steam export. Feedstock can range from natural gas to naphtha. A typical feed and fuel consumption figure is 3.4 Gcal/1000 Nm3 hydrogen (362 BTU/SCF), which will lead to very substantial savings in operating costs and furthermore reduces CO2 emissions. Depending on the process layout, the energy consumption can be further decreased towards 3.3 Gcal/1000 Nm3 H2 (351 BTU/SCF) for a HTCR plant.

HTCR reformer tube
Each tube assembly consists of three tubes.Outermost is the flue gas tube, where the heat flux is adjusted by a proprietary flue gas control device. As the flue gas flows upwards through the flue gas annulus, heat is transferred to the catalyst by convection. The catalyst is placed in the annuli between the reformer tube and the centre tube. The centre tube through which reformed gas leaves the reformer is inside the catalyst tube. Hereby, the reformed gas is cooled on its way out, and the heat is passed on to the catalyst.

HTCR process layout
A simplified process flow diagram for a 30 000 Nm3/h (27 MMSCFD) HTCR hydrogen plant is shown in Figure 2. The process comprises the same main steps as a traditional hydrogen plant:
• Desulphurisation of feedstock
• Pre-reforming in an adiabatic reactor
• Convective reforming in two parallel HTCR reformers
• High-temperature shift conversion
• Purification by pressure swing adsorption (PSA).
For smaller capacities, a single HTCR reformer is used.

Energy consumption
The convection principle of a HTCR hydrogen plant leads to a low energy consumption. Table 1 shows the consumption of feed and fuel in a HTCR plant compared with a traditional hydrogen plant. It is seen that the performance of the HTCR is quite attractive compared to the traditional process, with a yearly cost saving
of $3.1 million (natural gas price of €25/Gcal ($8/MMBTU)).

Plot plan area
The convection principle allows for the design of compact reformers, and a HTCR hydrogen plant can be supplied as a very compact unit, with part of the equipment supplied skid-mounted. Typical plot plan area for a 30 000 Nm3/h (27 MMSCFD) plant is 50 x 40m (164 x 131ft) and can be adjusted according to conditions at client’s site. The required plot plan area for a HTCR unit is approximately 30% less than a conventional hydrogen unit with a box-type reformer (SMR). Figure 4 shows the plant layout for a 30 000 Nm3/h (27 MMSCFD) plant currently under construction.

Scope of supply
In connection with HTCR hydrogen plant projects, Haldor Topsøe’s typical scope of supply is:
• Licence
• Basic and detailed engineering
• Full plant documentation
• Supply of all materials and equipment within battery limits
• On-site supervision (for assembly, pre-commissioning, startup, test run)
• Training of operators.

Workshop skid assembly
Due to the compact layout, a large part of a HTCR plant can be pre-assembled in skids in a workshop outside the client’s plant site. Depending on plant capacity, the skids are assembled in the workshop with vessels, heat exchangers, reactors, valves instrumentation, piping, etc (see Figure 5). For transport reasons, the skids are subsequently separated by cutting the interconnecting piping (see Figure 6).

Site Installation
The use of pre-assembled skids minimises installation time and erection costs compared to a traditional plant. Typically, the site installation can be completed in three months and, where the site installation work for a traditional steam reformer plant often amounts to 30–35% of the investment cost, an estimate of only 15–20% can be applied for a skid-mounted HTCR unit.

Operating experience
HTCR designs include plants with capacities up to 30 000 Nm3/h (27 MMSCFD), and with 32 reformers and more than 10 years’ operating experience a HTCR plant provides a well-proven, efficient and reliable concept for hydrogen production. Operating data from HTCR plants meet or outperform the flow sheet figures and confirm the high energy efficiency of the HTCR technology.


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