Oct-2010

Additional hydrogen production by heat exchange steam reforming

Applying the heat exchanger principle in hydrogen manufacture can significantly reduce the consumption of hydrocarbon feedstock

Jack Heseler Carstensen
Haldor Topsøe

Article Summary

Many refiners are in need of additional hydrogen in order to process more feed or lower-quality crude. Over the past 20 years, Haldor Topsøe has developed a number of steam reforming technologies that can be implemented for additional new hydrogen plant capacity and also as an add-on to an existing hydrogen plant to provide extra hydrogen capacity.

These technologies are based on heat exchange steam reforming and are characterised by efficient heat transfer, resulting in feed and fuel savings of up to 20% compared to a traditional box-type hydrogen plant.

Heat exchange steam reforming in hydrogen production is not a new development. Back in the 1980s, Haldor Topsøe developed the first small-scale steam reformers based on the heat exchange principle, encouraged by increasing energy prices. The capacity of the first hydrogen units ranged from 100 000 scfd to 1 million scfd and were typically used for fuel cell applications. As the technology matured, it became possible to increase the capacity and, in 1997, the first industrial-scale (5 million scfd) hydrogen units were successfully put into operation. The development of the heat exchange reformer technology has continued, and Topsøe has licensed hydrogen plants, including a heat exchange reformer, with capacities of up to 185 million scfd. At the same time, a number of different variants of heat exchange reforming technologies have been developed, enabling the construction of new, tailor-made hydrogen plants or the revamp of existing units to create maximum value. Industrial feedback has confirmed that the use of heat exchange reforming can save up to 20% on feed and fuel consumption (and corresponding savings in CO2 emissions) compared to conventional steam reforming.

Heat exchange reforming: principles
Being an endothermic reaction, the steam reforming of hydrocarbons requires a significant heat input to obtain the desired conversion to hydrogen. In a conventional steam reformer, heat transfer takes place by radiation, which leads to a limited thermal efficiency, as evidenced by a high flue gas temperature — typically more than 1800°F (980°C). The thermal efficiency of a conventional steam reformer is around 50%, and the surplus heat is used for steam production. Many refiners have little or no use for the steam export generated in a hydrogen plant, which is therefore considered of low value.

Heat exchange reformers are very compact and have a high thermal efficiency. The majority of the heat transfer takes place by convection with hot flue gas or hot process gas, whereby the thermal efficiency can be increased by as much as 60–70% compared to the radiant solution. You could say that, in a heat exchange reformer, the waste heat energy is used for producing extra hydrogen instead of surplus steam.
Heat exchange reforming is well suited to both standalone units and as a revamp option for increasing the capacity of existing plants.

Heat exchange reforming technologies
HTCR
The Haldor Topsøe Convection Reformer (HTCR) is a heat exchange reformer in which the process gas is heated mainly by hot flue gas. The HTCR is very compact and suited to new hydrogen units and to add-on revamps for increasing the capacity of existing plants.

The reformer is shown in Figure 1 and the principle is shown in Figure 2. The reformer consists of a vertical refractory-lined vessel containing the tube bundle with bayonet tubes. The heat from the flue gas is transferred to the process gas inside the bayonet reformer tubes, resulting in low feedstock consumption and zero steam export. In an HTCR reformer, the heat input is provided by only one burner, which ensures a very easy operation and a fast load response. The easy operation implies that only a minimum of operator attendance is required, and there are examples of unattended operation of HTCR plants.

The unit is to a high degree skid-mounted and the reformer is shop-lined, minimising erection time and cost on site. Industrial experience with HTCR includes more than 30 plants and design capacity of up to 27 million scfd.

Case study 1
Grassroots 27 million scfd HTCR
hydrogen plant
In connection with an extensive revamp of an existing refinery in the Russian Federation, an analysis of the future hydrogen balance showed that an additional 160 million scfd of hydrogen would be required. The majority of the hydrogen was needed for a new hydrocracking unit, whereas the remaining part would be needed for hydrotreating purposes. The new hydrotreating unit was scheduled to come on stream one year before the hydrocracking unit, and the refinery decided to build two separate grassroots plants to cover the hydrogen requirement: a 27 million scfd unit and a 130 million scfd unit. HTCR technology was chosen for the smaller unit due to its low feed and fuel consumption and fast implementation time, and requirements to export steam would be covered by the larger hydrogen unit.

Table 1 shows the consumption figures for a 27 million scfd HTCR hydrogen plant compared to a conventional SMR process typically used for this capacity range.

The example clearly illustrates the advantage of the HTCR process in the case of low or no value of steam export. Based on a feed and fuel cost of $5.36/million BTU,1 the annual savings for a HTCR plant amount to $2 million compared to a conventional steam reformer process. Furthermore, the 11% lower consumption of feed and fuel results in a correspondingly lower emission of CO2.

HTER
In the Haldor Topsøe Exchange Reformer (HTER), the reaction heat is provided by hot process gas. The HTER can be used in grassroots hydrogen plants in combination with a radiant wall steam reformer and also as an add-on unit for additional capacity in an existing plant.