Feed Flexibility of CH4 Combined Reforming for Methanol Production

NELIDA BEATRIZ BRIGNOLE; BENJAMIN CAÑETE; CARLOS GIGOLA

Computer-Aided Chemical Engineering

Elsevier

Lugar: Amsterdam; Año: 2015 vol. 37 p. 1343 - 1348

AbstractNatural gas with high CO2 content is a readily available resource, whose application forsynthesis gas (syngas) production through dry reforming is strictly limited to processesthat require low H2/CO ratios. In a recent work we have demonstrated that methanolproduction through a process scheme based on combined reforming of methane (withCO2 + H2O) becomes a viable alternative from both technical and economic viewpoints.The use of a H2 separation membrane, as well as a partial H2 reinjection into the loopreactor, has been considered for the syngas composition adjustment to stoichiometricconditions (M 􀂧 2). The reformer and the methanol synthesis reactor were assumed tobe working at thermodynamic equilibrium conditions, i.e. at 950 °C and 20 bar for theformer, and at 250 °C and 71 bar for the latter. By using a natural gas feed containing30 % CO2 and H2O/CH4 = 2, it is feasible to operate the synthesis reactor with a lowerrecycle ratio, as well as a CO2 concentration close to the one employed in industrialpractice. Under the operating conditions mentioned above, the use of combinedreforming for methanol synthesis turns out to be economically advantageous over theclassical steam reforming process.In this work a study of the feed flexibility for combined reforming is carried out takinginto account the existence of gas fields with CO2 contents higher than 30 %. Feedmixtures containing 35 % and 40 % CO2 were analyzed, while maintaining the operatingconditions for the reformer (P, T, H2O/CH4) and the synthesis reactor (P, T, M). Forcomparative purposes, a methanol plant producing 400,000 mtpy was considered. Ahigher CO2 content in the feed does not significantly alter the CH4 conversion, butincreases the CO2 conversion and lowers the H2/CO ratio. Consequently, it is necessary toincrease the separation and reinjection of H2 to keep stoichiometric conditions in thesynthesis reactor. However, a moderate increase in CO2 concentration in the synthesisreactor cannot be avoided. It is also shown that the recycle ratio should be markedlyreduced in order to achieve stable operation. This situation reduces the operating cost ofthe recycle compressor. On the other hand, the flow of CH4 + CO2 to the reformer shouldbe increased for a constant methanol production, which in turn affects the reformer?senergy balance. The main operating costs of the methanol plant, with respect to thereference case (CO2/CH4 = 0.43), grow for CO2/CH4 = 0.55 and CO2/CH4 = 0.67 by 9.5 %and 25 %, respectively. This preliminary technical and economic analysis shows thatcombined reforming of natural gas with CO2 content up to 40 % is a feasible process toproduce methanol without CO2 removal.Keywords: CO2/CH4, methanol, CO2 removal, energy, natural gas.