Reformer furnace tubes

UNS S30409) stainless steel (SS) for metal temperatures above 1,200°F (650° C). Caustic stress corrosion cracking (SCC) from solids can occur in the steam preheat coils if solid carry-over is excessive (see Chapter One, Steam and Condensate section). The inlet connections to the steam methane reformer furnace tubes are either IViCr-V Mo (1,100°F [595°C] maximum) or 21/4Cr-1Mo (1,200°F [650°C] maximum). 

Hinchley (1975) discusses the design and operation of waste heat boilers for chemical plant. Both fire tube and water tube boilers are used. A typical arrangement of a water tube boiler on a reformer furnace is shown in Figure 3.12 and a fire tube boiler in Figure 3.13. The application of a waste-heat boiler to recover energy from the reactor exit streams in a nitric acid plant is shown in Figure 3.14. 

Figure 8.1 is based on field-erected cost for furnaces designed to elevate hydrocarbon streams to 700°F at 500 psi (maximum) with absorbed heat duties in excess of 10 mmBtu/h. All tube banks are carbon steel, except pyrolysis or reformer furnaces, which have stainless tubes. Process furnaces generally have overall fuel efficiency of 75% (lower fuel heating value conversion to actual absorbed heat). Although most furnace vendors claim much higher efficiencies, this 75% efficiency value is... 

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. 

Fig. 1.4. S implified scheme ofan industrial steam reformer furnace, (a) Furnace with radiation burners adapted from [6], (b) Lateral temperature profile inside a single reformer tube.

Because hydrogen is used in the reforming reaction, materials must be selected according to API 941, except that C-V Mo should not be used (i.e., the minimum alloy for hydrogen service should be lCr-M Mo). As mentioned previously, this is because of C- Mo failures in catalytic reformers that some refiners have related to the catalytic reformer process regeneration. When selecting furnace tubes, for example, it is important to select the steel with the hydrogen resistance based on the metal temperature,... 

The layout of a primary reformer furnace is a complex task in which a number of parameters have to be well balanced. Two aspects have to be considered the heatconsuming reaction of the hydrocarbon with the steam inside the tubes and the heat supply by radiation from the outside. The objective is to match both properly with respect to the desired conversion of the hydrocarbon at an economic steam/carbon... 

Their thermal efficiency is not very different and in a top-fired furnace can be as high as 95 %. The enthalpy difference between inlet and exit, often referred to as reformer duty, is made up of the heat required to raise the temperature to the level at the tube exit and the enthalpy of the reforming reaction. In a typical tubular steam reforming furnace, about 50% of the heat generated by combustion of fuel in the burners is transferred through the reformer tube walls and absorbed by the process gas (in a conventional ammonia plant primary reformer 60 % for reaction, 40% for temperature increase). 

Although Maui gas is very low in sulphur, the incoming gas is desulphurised as a precaution against poisoning catalysts used in the process. Following desulphurisation, water, in the form of medium pressure steam, is added and the mixture passed through reformer reactor tubes which contain a nickel catalyst. The tubes are located inside the reformer furnace where the process temperature is raised to 900°C and the reaction to form synthesis gas occurs. The synthesis gas is cooled to 35°C, compressed to 100 bar, reheated and reacted at 250-300°C over a copper/zinc catalyst to form a water-methanol mixture with about 17 percent water. The methanol product is reduced in pressure and passed to the methanol-to-gasoline (MTG) plant. 

New tube materials allow the design for much higher exit temperatures and heat fluxes, in particular when applying a side wall fired reformer furnace to ensure better control of the maximum tube wall temperature and optimum use of the high alloy material. Thinner tube walls made possible by the use of the new materials reduce the risk for creep due to faster relaxation of stresses at start and stop of the reformer (14). 

Rectangular reformer furnace, 44 Reductive carbonylation, 248-251 Reformer furnace, 44, 47-50, 67 Reformer tubes, 46, 56 Reforming reaction, 48, 55, 62 Refrigeration cycles ... 

From a design point of view, a conventional steam reformer typically consists of a large reformer furnace that contains long vertical tubes that are filled with catalyst [8]. The reformer tubes are supported with counterweights and are heated from burner flames that radiate within the furnace cavity or radiant box. The radiant box is sufficiently large to provide a relatively uniform radiant heat flux. 

Amuay HYAY-2 9.5 mmscf/d Hydrogen Plant (Reformer) Furnace F-SSl Explosion- Plugged tubes, not dried out, exploded and ruptured adjacent tubes. 

Figure 16 shows a conventional reactor tube configuration as present in a steam reformer furnace. The preheated hydrocarbon feedstock passes through the catalyst tube in which it reacts producing an equilibrium mixture of hydrogen and carbon oxides the reformer effluent, at a temperature, which is in the range of 800-950°C, is then sent to the process gas boiler where steam is generated. 

As such, the reactor tube is a cylindrical vessel exposed to significant internal pressure and stress and temperature G)oth inside and outside the reactor tube). The high temperature reactor tubes present in the steam-reforming furnace are the most critical in terms of design and overall plant economics and require, therefore, a separate discussion. The materials used in the other lower temperature reactors in the synthesis gas production process are much less critical. 

Materials for catalyst tubes are selected in combination with the process conditions employed. Alloys with high chromium and nickel content are used for the reactor tubes in a steam-reforming furnace. The first centrifugally cast tubes such as HK 40 contained 25% Chromium and 25% Nickel. Today, tube material containing 25% Chromium and 35% nickel, niobium, and traces of zirconium and titanium are used (so called HP alloys) (50). The HP alloys are more expensive but allow a higher tube design temperature and have a better creep strength and oxidation as well as carburization resistance. 

As an example, the flue gas heat duty profile (in W per m of catalyst tube surface) is shown in a top-fired steam reformer furnace, which was designed with the use of CFD, in combination with a kinetic model (Fig. 29). The top part of this picture shows the burners, the bottom part shows the position of the flue gas discharge ducts, where the flue gas exits the reformer box. 

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