3 research outputs found
Fungi solubilisation of low rank coal: Performances of stirred tank, fluidised bed and packed bed reactors
Coal biosolubilisation was investigated in stirred tank reactor, fluidised bed and fixed bed bioreactors with a view to highlight the advantages and shortcomings of each of these reactor configurations. The stirred aerated bioreactor and fluidised bioreactor represent slurry reactor systems enabling a comparative study. Direct comparison between these and the fixed bed bioreactor could not be carried as the corresponding particle sizes will result to a pressure drop in the fixed bed reactor.
Coal solubilisation showed a higher coal weight loss in the stirred tank slurry bioreactor in comparison to the fluidised bed slurry bioreactor at 5% (w/v) coal loading and 600–850 µm coal fractions. Higher aeration is required in the fluidised bed bioreactor than in the stirred tank slurry bioreactor at constant coal loading and particle size because in fluidised bed bioreactor aeration was also used for mixing.
Coal biosolubilisation in the packed bed bioreactor was minimal. The low performance was attributed to the large coal particle size fraction (1.5–2 mm) used. Minimal damage to the fungal culture was observed. However, clogging of bed by fungi resulted in channelling or misdistribution that ultimately leads to poor and unpredictable internal mass transport
Thermal energy processes in direct steam generation solar systems: Boiling, condensation and energy storage
Direct steam generation coupled with solar energy is a promising technology which can reduce the dependency on fossil fuels. It has the potential to impact the power-generation sector as well as industrial sectors where significant quantities of process steam are required. Compared to conventional concentrated solar power systems, which use synthetic oils or molten salts as the heat transfer fluid, direct steam generation offers an opportunity to achieve higher steam temperatures in the Rankine power cycle and to reduce parasitic losses, thereby enabling improved thermal efficiencies. However, this is associated with non-trivial challenges, which need to be addressed before such systems can become more economically competitive. Specifically, important thermal-energy processes take place during flow boiling, flow condensation and thermal-energy storage, which are highly complex, multi-scale and are multi-physics in nature that involve phase-change, unsteady and turbulent multiphase flows in the presence of conjugate heat transfer. This paper reviews our current understanding and ability to predict these processes, and knowledge that has been gained from experimental and computational efforts in the literature. In addition to Rankine cycles, organic Rankine cycle applications, which are relevant to lower operating temperature conditions, are also considered. This expands the focus to beyond water as the working fluid and includes refrigerants also. In general, significant progress has been achieved, yet there remain challenges in our capability to design and to operate effectively high-performance and low-cost systems with confidence. Of interest are the flow regimes, heat transfer coefficients and pressure drops during the thermal processes present in direct steam generation systems including those occurring in the solar collectors, condensers and relevant energy storage schemes during thermal charging and thermal discharging. A brief overview of some energy storage options are also presented to motivate the inclusion of thermal energy storage into direct steam generation systems