Reforming methane slip

A promoted nickel type catalyst contained in the reactor tubes is used at temperature and pressure ranges of 700-800°C and 30-50 atmospheres, respectively. The reforming reaction is equilibrium limited. It is favored at high temperatures, low pressures, and a high steam to carbon ratio. These conditions minimize methane slip at the reformer outlet and yield an equilibrium mixture that is rich in hydrogen. ... 

The Methane Slip (or % Methane that is not converted) has a big influence on the selection of reformer operating conditions. As shown in Figure 5.8, the best operating conditions will be within the following ranges ... 

The reforming process is completed in the authothermic secondary reformer, which is a refractory lined vessel containing a fixed-bed catalyst. The remainder of the endothermic heat requirement is provided by the combustion of part of the primary reformer effluent directly with air. This allows much higher process temperatures, of the order of 1000°C, to be attained at the secondary reformer exit and consequently low methane slips in the range of 0.2-... 

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. 

Increased Process Air Supply to the Secondary Reformer. Decreased heat supply in the primary reformer means that increased internal firing is necessary to achieve approximately the same degree of total reforming. A somewhat higher methane slip (and thus a lower secondary reformer outlet temperature) is acceptable and preferable in this type of process. This is because methane is removed in the final purification.53... 

Key features are the high reforming pressure (up to 41 bar) to save compression energy, use of Uhde s proprietary reformer design [1084] with rigid connection of the reformer tubes to the outlet header, also well proven in many installations for hydrogen and methanol service. Steam to carbon ratio is around 3 and methane slip from the secondary reformer is about 0.6 mol % (dry basis). The temperature of the mixed feed was raised to 580 °C and that of the process air to 600 °C. Shift conversion and methanation have a standard configuration, and for C02 removal BASF s aMDEA process is preferred, with the possibility of other process options, too. Synthesis is performed at about 180 bar in Uhde s proprietary converter concept with two catalyst beds in the first pressure vessel and the third catalyst bed in the second vessel. 

As the H2/CO ratio is lowered below the stoiciometric ratio of 3 1 there is a progressive increase in the total and imported CO2 and, consequently, an increase in both the total feed rate to the reformer and the overall heat load. Even though the heat of reaction for conversion of carbon dioxide and hydrogen, and carbon dioxide and methane are lower than that of the reforming reaction, the total heat load is nevertheless increased. The methane slip falls only slightly and, as a result, the total syngas (CO + H2) product rate stays about the same. Even though low H2/CO ratios... 

The CALCOR process is similar to a conventional steam methane reformer with an amine acid gas removal system, except that the CO2 from the amine system is recycled to the reformer furnace. The reformer operates at a very low pressure to reduce reforming severity. The synthesis gas from the CO2 removal system is just above atmospheric pressure. It is saturated with water and residual CO2 and must be compressed before entering downstream separation equipment. The process features a very low methane slip below 500 ppm in the synthesis gas [11]. 

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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