Low-temperature shift converter

Use of a low temperature shift converter in a PSA hydrogen plant is not needed it does, however, reduce the feed and fuel requirements for the same amount of hydrogen production. For large plants, the inclusion of a low temperature shift converter should be considered, as it increases the thermal efficiency by approximately 1% and reduces the unit cost of hydrogen production by approximately 0.70/1000 (20/1000 ft ) (140,141). 

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). 

Although the reformer catalyst tends to be rugged and reliable, the catalyst in the low-temperature shift converter and the methanator tends to be less so. In addition, the potential exists for temperature excursions in the methanator in the event of C02 breakthrough from the wash system. The C02 removal system requires a significant heat input and a corrosive solvent, which can present difficulties. 

The POLYBED PSA system replaces several of the units associated with hydrogen purification in a conventional plant — specifically, the low temperature shift converter, the C02 removal system and the methanator (see Figure 2). The tail gas from the PSA system is used as fuel to the reformer and it is supplemented by an external supply. However, the amount of fuel consumed is greatly reduced. Because some hydrogen... 

In 2001 Hyprotech and Synetix announced an ammonia plant simulation that can be used for modeling, on-line monitoring and optimization of the plant. The simulation includes Synetix reactor models, customized thermodynamic data and information to simulate the performance of a range of catalysts. The reactor models in the simulation include Primary and Secondary Reformers, High Temperature Shift converter, Low Temperature Shift Converter, Methanator and Ammonia Synthesis Converter80. 

A consequence of the steam reformation process and the subsequent clean up steps of high and low temperature shift converters and a selective oxidizer (called the prox unit) the typical levels of CO at the inlet stream of a PEMFC s are expected to be in the range of 50 and 100 ppm, higher levels in the range of 500 to... 

The conventional ammonia production line consists of seven gas-solid catalytic reactors, namely desulfurization unit, primary reformer, secondary reformer, high temperature shift, low temperature shift, methanator and finally the ammonia converter. In addition the production line includes an absorption-stripping unit for the removal of CO2 from the gas stream leaving the low temperature shift converter. The ammonia converter is certainly the heart of the process with all the other units serving to prepare the gases for the ammonia synthesis reaction which takes place over an iron promoted catalyst under conditions of high temperature and pressure. 

The nuKlclling, siimilution and optimization of the low temperature shift converter is very similar lo the high temperature shift converter (Alhabdan, 1990) c.u cpl for the conslants of the rate equations. 

The flow diagram for a steam methane reformer is illustrated in Figure 3, This is a conventional reformer designed to maximize the production of hydrogen, A plant designed for production of syngas or carbon monoxide would not include the high and low temperature shift converters and the... 

This reaction equilibrium is favored at low temperatures, and most of the carbon monoxide is converted to carbon dioxide in a high-temperature shift furnace (HTS) operating at 350 to 450°C. This step is followed by low-temperature conversion of the remaining carbon monoxide to carbon dioxide in a low-temperature shift converter (LTS) after cooling. The usual catalyst for the low-temperature shift converter is copper oxide supported on zinc oxide and alumina. 

The typical concentrations of methanol in an HTSC application are approximately 100 to 300 ppmw. In a Low Temperature Shift Converter (LTSC) application, the methanol production is greater than that of an HTSC application. The formation of methanol is not just related to equilibrium for an LTSC but also by the catalyst characteristics and kinetics. Therefore, the catalyst vendor should be contacted in reference to calculating the expected amount of methanol from an LTSC application. 

The gas is now sufficiently cool for the first shift converter, where the majority of the CO is converted to CO2. At D the gas is further cooled, giving up heat to the incoming steam, before passing to the low-temperature shift converter, where the final CO is converted. The final cooling is accomplished at B, where the incoming steam is heated. 

Use of heat downstream of the low temperature shift converter for absorption refrigeration which is used in the ammonia recovery section. In conventional plants this low level heat is used for reboiling in the carbon dioxide removal process. 

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