## 1 Introduction  
Methanol is rated among the most important feedstocks for the chemical, petrochemical and energy industries, with a worldwide production of 83 million metric tons in 2015. The global production is forecasted to grow annually by an average rate of 7.2% to reach 117 million metric tons in 2020 [1]. The industrial applications range from the further processing to bulk chemicals, e.g., formaldehyde and acetic acid, to the production of synthetic fuels, including methyl-tert-butylether (MTBE) and dimethylether (DME). The increasing demand will particularly be driven by energy applications, which today already account for 40% of the methanol consumption [2]. Applications in the energy sector mainly include refined product displacement, in the form of methanol to olefins (MTO) and gasoline blends [1,2]. Methanol can be synthesized from any hydrocarbon source, including renewable and fossil resources, via direct and indirect conversion processes. Direct synthesis processes (e.g., the direct selective oxidative transformation of methane) have the major advantage of avoiding the energy intensive step of syngas production, but are technically difficult to accomplish. The main disadvantagesrefer to a low conversion of the feedstock and the production of undesired byproducts, due to the higher reactivity of the oxidation products compared to methane [3]. Although direct processes are getting more into the focus of research, industrial methanol is exclusively produced by indirect conversion routes via syngas production. Since synthesis gas routes are capital intensive, there is a great interest in optimizing the process concepts. Due to abundant resources, a low-price level which is subject to moderate volatilities, and low content of impurities, natural gas is the predominating feedstock for methanol production. In general, a synthesis route comprises a pretreatment of natural gas, a reforming unit for syngas generation, a gas conditioning section, a low-pressure methanol synthesis unit and several distillation columns for product purification. The reforming of natural gas has been investigated thoroughly in the literature and has been commercially applied to the most important branches of chemical industry [4; 5]. From an economic point of view, the highest sensitivity of the overall cost of a methanol plant is related to the reforming section, accounting for more than 60% of the capital investment. Catalytic steam reforming of methane (SMR) is the most widely used technology for syngas generation in methanol plants, while the implementation of alternative technologies such as autothermal reforming (ATR), dry methane reforming (DMR) and gas heated reforming (GHR) has started in the last decade. The variety of available reforming technologies differs in construction, in supply of reforming agents and in operation conditions. Accordingly, the reaction turnover and the syngas composition vary significantly. Therefore, the choice of a reformer option decisively determines the plant design. The consideration of alternative reforming technologies resulted from the ever-rising single train capacities and the economies of scale. The capacity of new plant constructions increased from 2.500 MTPD a decade ago to about 5.000 MTPD today [6; 7]. The SMR technology is typically applied to plants with a maximum capacity of 2.500 MTPD, while oxygen-based technologies (and combinations of ATR and SMR) cover the range above. The capacity demarcation is caused by the economies of scale being different for the tubular reformer and the oxygen plant that is required for the supply of gaseous oxygen (GOX) to the ATR [8]. Operation parameters and syngas production concepts incorporating SMR technology have been investigated intensively in [9; 10]. Data on parameters and consumption for two-step reforming concepts (SMR + oxygen blown secondary reformer) and ATR are reported in [7; 8].