Carbon steam-methane/stoichiometric

Figures 10 - 12 present calculated equilibrium compositions at 1100°K neglecting CHz, for the carbon-steam system with various ways of providing the needed heat. The reactants are indirectly heated for Fig. 10, heated by addition of a stoichiometric mixture of air and methane for Fig. 11, and by consumption by oxygen of some of the carbon for Fig. 12. The results for heating by an air-carbon reaction are given in Fig. 7.

Steam Utilization. Less steam is used in the RMProcess than is required for conventional shift conversion even though in other methanation processes as little as one-half of the total syngas is processed through shift conversion in order to achieve a near-stoichiometric balance of hydrogen and carbon monoxide for methanation. 

To assess the tolerance of the Sn/Ni surface alloy catalyst to carbon-induced deactivation, the alloy catalysts were tested in steam reforming of methane, propane, and isooctane. The reaction tests were performed in a packed-bed isothermal reactor at close to stoichiometric S/C ratios. The catalyst sample was packed between layers of... 

CO2 reforming of methane can be used to adjust the H/CO ratio and provide the correct H2/CO ratio for Fischer-Tropsch synthesis and could potentially be used to reduce CO2 emissions from other processes however, it is even more endothermic than steam reforming. Partial oxidation is exothermic and has the correct H2/CO ratio for methanol synthesis, but requires a pure oxygen source, adding to the cost. In addition to the individual drawbacks, all of these processes must be run with 0/C ratios of greater than 1 to prevent coking of the catalyst. This makes the processes more expensive in practice than would be expected under optimized conditions for the stoichiometric reactions. The propensity of these processes to form carbon at low 0/C ratios is even more pronounced at... 

Steam and methane can react to form hydrogen, carbon monoxide, and carbon dioxide, (a) Obtain the stoichiometric coefficients and a set of independent reactions for this system, (b) If a reactor initially contains 4 moles of steam and 2 moles of methane, find the composition of the mixture when 1 mole of steam and 0.1 mole of methane remain. 

Beyond the operating temperature and pressure, another important process variable is the steam to carbon ratio (S/C), defined as the ratio between the steam flow rate to the methane flow rate in the reactor feedstock (Fig. 5.5). On the basis of SR reaction stoichiometry S/C should be 2, but ratios greater than the stoichiometric value promotes the reactions and reduces the possibility of coke formation on the catalyst. In industry, the ratio is usually within the range 2.5-6 [1]. 

In a partial oxidation process, methane and other hydrocarbons in natural gas react exothermically with less than stoichiometric oxygen to produce carbon monoxide and hydrogen. Typically, the partial oxidation of natural gas is much faster than steam reforming and, therefore, requires smaller reactors. Partial oxidation reactions are given as follows [1] ... 

Desulfurized natural gas or naphtha is then mixed with process steam and preheated before passing to the primary reformer. The steam ratio, which is the molar ratio of steam to carbon, is typically between 3.0 and 4.0 moles of steam per atom of carbon in the hydrocarbon feedstock. An excess of steam over the stoichiometric quantity is required to suppress carbon-forming reactions and to provide a favorable equilibrium composition for the reaction of methane. The primary reformer consists of a large number of tubes packed with supported nickel oxide catalyst and contained in a furnace. The purpose of>the furnace is to heat the reactants to... 

Reforming with the stoichiometric amount of process air (i.e. the amount of air required to give a hydrogen to nitrogen ratio of 3.0 at the ammonia synthesis converter inlet without dedicated installations for adjustment of the gas composition). Steam to carbon ratio about 3.3 low methane leakage (approximately 0.3% dry). 

Reforming with stoichiometric air and low methane leakage. Steam to carbon ratio about 3.3. 

It is possible to adjust the ratio of hydrogen to caibon oxides by the addition of caibon dioxide to the synthesis gas, either just before the methanol synthesis loop, or directly into the feed for the steam reformer. It is also possible to use a secondary reformer using oxygen rather than air, after the primary reformer. The amount of oxygen used is adjusted to provide the stoichiometric ratio of hydrogen and carbon oxides and, at the same time, reduce the amount of inert methane in synthesis gas. (Table 9.9)... 

---