High alloy tubes

The mixed steam/feedstock mixture is then passed to the tubular reformer where it is reformed to synthesis gas over a nickel catalyst contained in high alloy tubes. 

A high reformer exit temperature of 1616°F is made possible by high alloy tube materials such as Manaurite 36X and Paralloy. This leads to a reduction in methane slip, and an increase in the CO/CO ratio. Both effects enhance the plant s efficiency and result in a reduction of feedstock natural gas consumption of 3.5% over previously used reforming conditions. 

A conventional typical convection section often has tube bundles for fuel gas or air preheat, feed preheat, boiler feed water preheat, steam generation, and steam superheating. In the convection section, the heat transfer is mainly gas-to-gas heat transfer and the overall heat-transfer coefficients are relatively low. Finned tubes are generally used to improve heat-transfer rates. Material for the convection section tubes varies from carbon steel to a high temperature alloy. Sometimes, high-alloy tubes are positioned in the lower section... 

In order to supply the heat for the overall endothermic reaction, the catalyst is loaded into a number of high alloy tubes placed inside a furnace, the tubular reformer. 

The SMR-based technologies typically have a somewhat higher capital cost because the SMR furnace with its high alloy tubes and large flue gas heat recovery section is inherently more expensive than the ATR or POX technologies which are refractory lined carbon steel vessels without external flue gas heat recovery. 

Smooth high alloy tubes Low-finned tubes Sintered metal tubes Spiral heat exchanger Tube inserts Twisted tubes Helical tube support baffles... 

Use of smooth high alloy tubes in otherwise corrosive service has been common practice since the 1950s. Tube metallurgy is selected to minimize corrosion while in service. The tubes therefore maintain their smooth, shiny finish. Without sites for fouling deposits to attach or accumulate, the clean heat-transfer coefficient is maintained. This idea has been used with success in refinery catalytic cracker feed preheat service, placing slurry oil on the tube side and vacuum gas oil on the shell side. 

We also note that while there is an obvious advantage to maintaining smooth, shiny tubes for applications in sensible heat transfer, this may not be true if it is necessary to vaporize liquid in the exchanger. Some of our clients have experienced difficulties due to film heat-transfer resistance and lack of nucleate boiling sites when attempting to use smooth tubes to vaporize relatively pure component liquids. This would be true for high alloy tubes or simply new replacement bundles for bundles of lesser metallurgy. 

Fresh reducing gas is generated by reforming natural gas with steam. The natural gas is heated in a recuperator, desulfurized to less than 1 ppm sulfur, mixed with superheated steam, further preheated to 620°C in another recuperator, then reformed in alloy tubes filled with nickel-based catalyst at a temperature of 830°C. The reformed gas is quenched to remove water vapor, mixed with clean recycled top gas from the shaft furnace, reheated to 925°C in an indirect fired heater, and injected into the shaft furnace. For high (above 92%) metallization a CO2 removal unit is added in the top gas recycle line in order to upgrade the quaUty of the recycled top gas and reducing gas. 

Some of the earlier BWR units had feedwater heaters having copper alloy tubes. The environment of high oxygen and neutral pH water led to high copper concentrations in the feedwater and to undesirable deposits on the fuel and inlet fuel nozzles (20). In some instances, the copper deposits resulted in an increase in core pressure drop and necessitated plant power reduction. The copper alloys were eliniinated from the feedwater system in subsequent plants and most existing plants. 

The hydrocarbon gas feedstock and Hquid sulfur are separately preheated in an externally fired tubular heater. When the gas reaches 480—650°C, it joins the vaporized sulfur. A special venturi nozzle can be used for mixing the two streams (81). The mixed stream flows through a radiantly-heated pipe cod, where some reaction takes place, before entering an adiabatic catalytic reactor. In the adiabatic reactor, the reaction goes to over 90% completion at a temperature of 580—635°C and a pressure of approximately 250—500 kPa (2.5—5.0 atm). Heater tubes are constmcted from high alloy stainless steel and reportedly must be replaced every 2—3 years (79,82—84). Furnaces are generally fired with natural gas or refinery gas, and heat transfer to the tube coil occurs primarily by radiation with no direct contact of the flames on the tubes. Design of the furnace is critical to achieve uniform heat around the tubes to avoid rapid corrosion at "hot spots."... 

Tube material includes any that can be formed into a coil, but usually copper, copper alloys, and stainless steel are most common. The casing or shell material can be cast iron, cast steel, cast bronze, fabri-catea steel, stainless, and other high-alloy materials. Units are available with pressure vessel code conformance. 

Above temperatures of 900°F, the austenitic stainless steel and other high alloy materials demonstrate inereas-ingly superior creep and stress-rupture properties over the chromium-molybdenum steels. For furnace hangers, tube supports, and other hardware exposed to firebox temperatures, cast alloys of 25 Cr-20 Ni and 25 Cr-12 Ni are frequently used. These materials are also generally needed because of their resistanee to oxidation and other high temperature corrodents. 

Tube O.D. Carbon Steel High Alloy Steel (750) Low Alloy Steel (850) Nickel-Cooper (600) Nickel (850) Nickel-Chromium-Iron (1000) Alum mum Almninmn Alloys, Copper Copper Alloys, Titanimn Alloys at Code Maximmn Allowable Temperature... 

Aluminum has many of the characteristics and qualities required for fluid power lines. Is has high resistance to corrosion and is easily drawn or bent. In addition, it has the outstanding characteristic of lightweight. Since weight elimination is a vital factor in the design of aircraft, aluminum alloy tubing is used in the majority of aircraft fluid power systems. 

Copper-base alloys will corrode in aerated conditions. It is, therefore, sometimes appropriate to consider cathodic protection. It becomes particularly relevant when the flow rates are high or when the design of an item causes the copper to be an anode in a galvanic cell (e.g. a copper alloy tube plate in a titanium-tubed heat exchanger). Corrosion can be controlled by polarisation to approximately — 0-6V (vs. CU/CUSO4) and may be achieved using soft iron sacrificial anodes. 

Certain pre-boiler cupronickels, such as 70 30 alloy tubes, subjected to high temperature, stress, and stop-start operation may suffer oxygen corrosion-induced dealloying followed by exfoliation corrosion, in which oxidized sheets peel away from the solid metal. 

This may even lead to blockage owing to accumulation of corroded material in the tube. In [38] it is also claimed that steels are not suited for nitration however, since the grade of the steel employed is not given, it cannot be excluded that high-alloy steels may behave better. Silicon, glass and titanium are recommended materials [38]. 

The subsequent steam reforming section is operated at very high temperatures 850-900 °C. The SMR catalysts themselves are already active below 400 °C, but high temperatures are necessary to drive the strongly endothermic reaction forward [8]. In industry, nickel catalysts are used in high-alloy reaction tubes, which are heated by external burners. This design is expensive and leads to heat losses, although much of the heat is recuperated. Noble metal catalysts such as sup-... 

Uranium dioxide for use in nuclear fuel must be produced to a stringent specification so that it can be pressed into pellets and sintered at high temperature in hydrogen to produce dimensionally stable, crack-free UO2 pellets with a density typically 97% of theoretical. The fuel pellets are loaded into zirconium alloy tubes, welded closed and assembled into fuel bundles. 

Fig. 1. High-heat-transfer bayonet-style exchangers employing tantalum alloy tubes. Each exchanger uses 104 tubes. (Fansteel)...

A striking property of many interstitial metal hydrides is the high rate of hydrogen diffusion through the solid at slightly elevated temperatures. This mobility is utilized in the ultra-purification of H2 by diffusion through a palladium-silver alloy tube. 

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