Primary reformer Convection section

In some cases a plant may have a pre-reformer. A pre-former is an adiabatic, fixed-bed reactor upstream of the primary reformer. It provides an operation with increased flexibility in the choice of feed stock it increases the life of the steam reforming catalyst and tubes it provides the option to increase the overall plant capacity and it allows the reformer to operate at lower steam-to-carbon ratios166. The hot flue gas from the reformer convection section provides the heat required for this endothermic reaction. 

Incorporation of a feed gas saturator cod in the convection section of the primary reformer allows for 100% vaporization of the process condensate. The steam is used as process steam in the reformer. 

Figure 105. Modern integrated single-train ammonia plant based on steam reforming of natural gas (Clide process) a) Sulfur removal b) Primary reformer c) Steam superheater d) Secondary reformer e) Waste heat boiler f) Convection section g) Forced draft fan h) Induced draft fan i) Stack k) TIT and LT shift converters ...

It can also be used to expand an existing steam methane reformer. This technology will allow the capacity of an existing unit to be increased by about lO /o. However, it is expensive because of the need to revamp the convection section of the primary reformer in order to add an additional prereforming coil. 

In the CAR process, the natural gas feed is mixed with steam and introduced into the CAR reactor via a tube sheet to the catalyst-filled tubes in which reforming to synthesis gas takes place. The natural gas is partially converted, and the slip methane is allowed in the lower chamber where partial oxidation takes place. In this lower section, temperatures are about 1300-1400°C. The resulting hot synthesis gas then passes upward and supplies heat to the primary reforming reaction inside the catalyst tubes. An important element in the CAR reactor is the tube sheet, which acts as a feed stream distributor to the reformer tubes. In addition, there are enveloping tubes around the catalyst tubes, which constrict the flow of the autothermal product gas, thereby increasing the convective heat transfer coefficient. The CAR reactor, due to the high temperatures, is also jacketed with water. 

As discussed for ammonia (Section 2.5), the fired steam reformer in the two-step process might be replaced by a convective reformer heated by the hot S5mgas fi om the autothermal (secondary) reformer. In contrast to what is the case for ammonia plants, Ihe heat of the ATR exit gas matches the heat required for the primary reforming [395] [479],... 

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