Convective reformers

Selection of the high pressure steam conditions is an economic optimisation based on energy savings and equipment costs. Heat recovery iato the high pressure system is usually available from the process ia the secondary reformer and ammonia converter effluents, and the flue gas ia the reformer convection section. Recovery is ia the form of latent, superheat, or high pressure boiler feedwater sensible heat. Low level heat recovery is limited by the operating conditions of the deaerator. 

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. 

Pre-Keformer A pre-reformer is based on the concept of shifting reforming duty away from the direct-fired reformer, thereby reducing the duty of the latter. The pre-reformer usually occurs at about 500°C inlet over an adiabatic fixed bed of special reforming catalyst, such as sulfated nickel, and uses heat recovered from the convection section of the reformer. The process may be attractive in case of plant retrofits to increase reforming capacity or in cases where the feedsock contains heavier components. 

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. 

Hycar (1) A reforming process for making syngas from light hydrocarbons, differing from the standard process in using two reactors. The second reactor (a convective reformer), operated in parallel with the primary reformer, preheats the feedstock. Developed by Uhde. 

The tube supports in the convection section must be considered when up-rating a reformer furnace. They are exposed to the hot flue gas without the cooling effect of process fluids. Tube supports in the hotter regions of the convection section are made ofhigh alloy material and may operate in the creep range - like catalyst tubes86. 

One of the most effective reformer modifications is to use heat from the convection section to preheat radiant section feed. This will reduce radiant section duty and firing rate. The effectiveness of this option is limited only by the risk of coking in the preheat coil, the metallurgy of the preheat coil and the metallurgy of the radiant inlet system. This option has been used to increase capacity by 10% without increasing the arch temperature in the radiant section86. 

Convective Heat Transfer Reformers provide additional reforming capacity by using the heat contained in the primary reformer exit gases. Several designs are available, but not all have been commercialized. These units typically replace a portion or the entire duty of the waste heat boiler. So they significantly reduce the steam capability of the reformer. Potential increases in capacity of between 10% and 30% are possible. The modifications are capital intensive but relatively easy to implement170. 

Increase Reformer Firing 7 to 10% Proportional, Assuming Adequate Convection Surface... 

The Haldor Topsoe Convection Reformer (HTCR) has been developed for the production of hydrogen from hydrocarbons without steam generation. The elementary unit of the reformer consists of two concentric tubes (Fig. 1.21). The annular space... 

Since the mid 1970 s, changes in the design of reformers have produced improvements in overall thermal efficiency, accomplished primarily by improved heat recovery in the convection section, ultimately reducing the temperature of the flue gas to the limit imposed by the condensation point of water, or in the case of some fuels, sulfur trioxide. Extensive use of air preheat in newer designs lowers fired fuel requirements. 

The Haldor Topsoe Convection Reformer (HTCR) is a relatively small piece of equipment that combines the radiant and waste heat sections of the conventional reformer. It uses PSA (pressure swing absorption) to make 99.9 percent hydrogen purity. It is best for small and medium-sized hydrogen plants (500 to 10,000 Nm3/hr).75... 

Convection Section. The effects on the reformer of increased gas flow and temperature are multiplied in the convection section because additional load is placed on convection... 

Also important is the effect of the size and shape of the catalysts [428] on heat transfer and consequently performance. Unlike the most processes carried out under substantially adiabatic conditions, the endothermic steam reforming reaction in the tubes of the primary reformer has to be supplied continuously with heat as the gas passes through the catalyst. The strong dependency of the reaction rate on the surface temperature of the catalyst clearly underlines the need for efficient heat transfer over the whole length and crosssection of the catalyst. However, the catalyst material itself is a very poor conductor and does not transfer heat to any significant extent. Therefore, the main mechanism of heat transfer from the inner tube wall to the gas is convection, and its efficiency will depend on how well the gas flow is distributed in the catalyst bed. It is thus evident that the geometry of the catalyst particles is important. 

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 ...

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