A low CO2 emission process for methanol production using syngas generated by combined H2O and CO2 reforming with CH4 (bi-reforming) is proposed in this work. A detailed process model was developed using Aspen Plus. The operating conditions of the bi-reforming and methanol synthesis were derived from a detailed sensitivity analysis using plug flow reactor models with Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetics. A molar feed ratio of CH4:CO2:H2O of 1:1:2, instead of conventional 3:1:2 in the bi-reforming was found to be optimum and resulted in ∼99% conversion of CH4, 44% conversion of CO2, and a H2/CO ratio of 1.78 at 910 °C and 7 bar. A higher methane conversion eliminated the need for cryogenic separation of CH4. The optimum feed ratio of 1:1:2 resulted in an ∼33% higher consumption of CO2 per mole of CH4 required than the conventional process. An acid gas removal process using MDEA was used for CO2 separation, and a network of heat exchangers was configured for heat recovery. The proposed process resulted in ∼0.37 tonne of CO2 per tonne of methanol, which is ∼2–4 times lower than several published data and commercial methanol processes.

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The present study investigated the effect of impeller speed and vortex ingestion on vortex shape, gas holdup, and bubble size distribution in an unbaffled stirred tank using optical probe measurements. Further, the ability of the volume of the fluid model to predict vortex shape was examined. Without vortex ingestion, an increase in impeller speed resulted in a significant variation in vortex shape, whereas it had a negligible effect on vortex shape with ingestion. This suggests that when vortex ingestion occurred, most of the energy was consumed for the dispersion of gas rather than the deformation of the gas‐liquid interface. It was observed that a large number of gas bubbles were entrained into the vortex core around the impeller region, which led to a lower gas holdup at the top axial locations. An increase in the impeller speed also resulted in the formation of larger bubbles. The absence of baffles limits shear for bubble break up, resulting in larger bubbles above the impeller plane.

For a detailed characterisation of multiphase flows, a local measurement technique that is capable of quantifying both continuous and dispersed phases has to be employed. In the present study, a new optical probe was tested for its ability to provide simultaneous local measurements of gas and liquid/solid in a three-phase system. The new probe can measure the intensity of light reflection due to the presence of gas or liquid medium surrounding the probe tip in conjunction with the Doppler frequency caused by the approach of a solid particle. The experiments were carried out in a pseudo-2D rectangular column by passing gas bubbles through a stationary liquid with suspended seeding particles. In these experiments, measurements were carried out by using three techniques namely optical probe, particle image velocimetry (PIV), and high-speed imaging (HSI). PIV measurements were used to validate seeding particle velocity obtained using the optical probe, whereas HSI technique was used to validate bubble chord length data from optical probe. The difference between the particle velocity from the probe and PIV was in a range of 13%-20%, while the difference between chord length measured by the probe and HSI was within ±8%.