High-temperature steam reforming furnace

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). 

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. 

An intrinsic, exothermic water-gas shift reaction occurs in the steam reformer reactor. The combined reaction, steam reforming and water gas shift, is endothermic. As such, an indirect high temperature heat source is needed to operate the reactor. This heat source usually takes the shape of an immediately adjacent high temperature furnace that combusts a small portion of the raw fuel or the fuel effluent from the fuel cell. Efficiency improves by using rejected heat from other parts of the system. Note that the intrinsic water-gas shift in the reactor may not lower the... 

A review of conventional hydrogen production via steam reforming is useful to appreciate the advantages of the POLYBED PSA system. The conventional system consists of a feed desulfurizer, reforming furnace, high-temperature and low-temperature shift converters, C02 removal system and a methanator (see Figure 2). 

The reformed gas leaves the furnace at a high temperature where high grade heat is recovered successively to a reformed gas boiler, steam superheater process feedstock heater and boiler, feedwater heater. The reformed gas then passes to the distillation area where low grade heat is efficiently recovered via column reboilers and a demineralized water heater. 

Description The gas feedstock is compressed (if required), desulfurized (1) and process steam is added. Process steam used is a combination of steam from the process condensate stripper and superheated medium pressure steam from the header. The mixture of natural gas and steam is preheated, prereformed (2) and sent to the tubular reformer (3). The prereformer uses waste heat from the flue-gas section of the tubular reformer for the reforming reaction, thus reducing the total load on the tubular reformer. Due to high outlet temperature, exit gas from the tubular reformer has a low concentration of methane, which is an inert in the synthesis. The synthesis gas obtainable with this technology typically contains surplus hydrogen, which will be used as fuel in the reformer furnace. If C02 is available, the synthesis gas composition can be adjusted, hereby minimizing the hydrogen surplus. Carbon dioxide can preferably be added downstream of the prereformer. 

Photograph and schematic diagram of sectional model furnace for a steam reformer using high temperature air combustion technology. 

Reactions 5.1 and 5.2 occur in parallel in the steam reformer the high temperature of the reactor, placed in a furnace, supports the steam reforming reaction to detriment of the WGS. 

First, sulfur is removed from the hydrocarbon stream (usually natural gas), in order to prevent catalyst poisoning and deactivation with the use of a guard bed. Steam is mixed in the main stream in a fixed steam to carbon molar basis. The steam reform reactor (SRR) is a multitubular catalyst filled furnace reactor where the hydrocarbon plus steam are converted into syngas at high temperatures (700°C - 850 C) according to the following reaction ... 

Although steam reforming is carried out at high temperature, a nickel catalyst is still required due to the high stability of methane. The catalyst is contained in tubes, which are placed inside a furnace that is heated by combustion of fuel (Figure 6.2.30). 

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