## 2 Materials and Methods
### Process Model Description
#### 2.2.3 GTM Process Model Description  
This section describes the comprehensive development of the GTM process (mostly methanol synthesis), excluding gas treatment for the natural gas fuel (feed gas). Natural gas is utilised as the input gas to make synthesis gas, which is needed in the methanol production process. This study utilises a Lurgi low-pressure methanol technology with a two-step reforming synthesis gas production system (a combination of steam methane reforming and autothermal reforming). The process is ideally suited for the manufacture of methanol on small to large scales and is a mature technology. Figure 6 illustrates the ASPEN HYSYS methanol production process. Mass and energy balances have been constructed in every instance. The description of the simulation is divided into the following sections: feed conditioning, pre-reform, autothermal reformation (ATR), methanol synthesis, and methanol purification. Feed conditioning--Natural gas at 50 \({}^{\circ}\)C and 7000 kPa is brought in and expanded to 3000 kPa pressure via a valve (VLV-100) until preheated to 497 \({}^{\circ}\)C. By heating fresh water, reformer steam with a temperature of 500 \({}^{\circ}\)C and a pressure of 3000 kPa is produced. Then, the natural gas and reformer steam are transferred to the pre-reforming section (steam methane reforming with water shift gas reaction). Figure 5: CTV ASPEN HVSYS process flow diagram. Pre-reforming--Pre-reforming is a concept utilised in a standard adiabatic reactor for low-temperature steam-reforming of hydrocarbons. The heat content of the natural gas supply stream is used to execute the steam reforming process at low temperatures in the pre-reformer. It consists of two reactors. The first is a conversion reactor where higher hydrocarbons such as ethane, propane, and n-butane are converted into hydrogen and carbon monoxide. This reactor is adiabatic and completely converts all reactants. Preheated natural gas (feed gas) and steam are crucial components for reactions to continue. The unconverted natural gas (mostly methane) and its components are then sent to the next pre-reformer, the equilibrium reactor, which is modelled as an adiabatic reactor because of the three reactions of the reformer's combustor feed at 291 \({}^{\circ}\)C. The equilibrium reactor's processes consist of the methane steam reforming process and the water gas change or shift reaction. Both processes generate heat. The principal products (shift-1 feed) of the second pre-reformer are methane, water, hydrogen, carbon monoxide, and carbon dioxide. Due to a water gas change or shift reaction, carbon monoxide content in the shift-1 feed is reduced. Table 2 shows pre-reforming reactions. Autothermal reforming (ATR)--The autothermal reformer is an adiabatic reactor and is presented in ASPEN HYSYS as an equilibrium reactor; all reactions are also specified as equilibrium reactions. The outputs of a pre-reformer are then preheated to 753 \({}^{\circ}\)C and 3000 kPa. Another stream entering the ATR reactor is pure oxygen at 5 \({}^{\circ}\)C and 3000 kPa pressure, which is heated by a heater to 200 \({}^{\circ}\)C at constant pressure. The output is then cooled or refrigerated before being separated into a syngas component (synthesis gas) and water (stream 11) in a separator (V-101). The combined reforming approach used in this procedure resulted in a steam-to-carbon ratio of 0.6, as lower ratios support the formation of particulate matter and coke, which are unnecessary for the autothermal reform process. Table 3 shows Autothermal reforming reactions. Methanol synthesis--The synthesis gas that exits the separator is mixed with recycled methanol reactor products, and the blend is pre-heated to 154 \({}^{\circ}\)C and roughly 3000 kPa before being compressed by a compressor (K-100) to 8000 kPa and blended with the flash drum recycling stream (stream 26).