Reformer convection section

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. 

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. 

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. 

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... 

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. 

Shell Oil Company has recently patented a process and apparatus for the production of pure hydrogen by steam reforming. This process integrates the steam reforming and shift reaction to produce pure hydrogen with minimal production of CO and virtually no CO in the hydrogen stream, provides for CO2 capture by sequestration, uses a steam reforming MR and is powered by heat from a heater convection section. 

F304 is the common convection bank for two fired heaters in the reforming unit. Currently 1300-1900 t/day of flue gas from F304 leaves the stack at temperatures around 390 °C. This is considerably higher than the typical value of 220 C seen in peer units within the industry. One of the options proposed is to add surface area in the convection section for extra MP steam generation of 85 t/day with a cost savings of 703,800 per year at the expence of 1.9 MM capital cost. 

Natural gas is derived from the town gas line and is available at battery limits at a pressure of 12 barg. It is introduced through the pressure regulator and flow controller to the feed desulfurization (DS) reactor, where sulfur compounds are removed up to 0.1 ppm. The DS feed is then mixed with steam in a ratio ranging from 3 to 5, preheated in the convection section and fed to the first reformer tube. 

The reactor tubes are fired by burners, which may be located at the bottom, at the side, or at the top of the furnace. Combustion of the fiiel takes place in the radiant section of the furnace. After the flue gas has been supplied all the reactor duty, it passes into the convection section where it is further cooled by heating other streams such as process feed, combustion air and boiler feed water, as well as producing steam. The product gas, leaving the reformer at a temperature of 850-950°C, is cooled in a process gas waste heat boiler (PGWHB), which produces process steam for the reformer. 

The HTCR reactor consists of a number of bayonet reformer tubes and combines basically the radiant section and the convection section of a conventional HSR in a single piece of equipment. The reaction heat is provided by the flue gas fiowing on the outside of the reformer tubes and by reformed gas fiowing in an upward direction in the bayonet tubes. This results that is about 80% of the fired duty is utilized in the process, and steam export is minimized. 

The right-hand side of this figure shows the radiant reformer box, and the left-hand side show the convection section and the flue gas stack. 

Reformer In a reformer furnace, shown in Exhibit 7-5, preheated process fluid flows through catalyst-filled tubes, which are usually located in the center of the radiant section. This type of furnace may have single or multiple compartments burners may be mounted in the roof, wall, or floor. Heat recovery systems may also be employed through the use of waste heat boilers or the convection section s steam generation coils. 

The radiant box of the reformer is typically about 50% efficient. Thus, to ensure a thermodynamically efficient operation, the heat liberated but not absorbed in the reforming reaction must be recovered in the convection section of the reforming furnace. Typically the reformer flue gases are redueed to about 150°C, resulting in an overall furnace efficiency of 9293%. 

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... 

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. 

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