Volume 37, Issue 5

Compressed air energy storage in aquifers (CAESA) can be considered a novel and potential large-scale energy storage technology in the future. However, currently, the research on CAESA is relatively scarce and no actual engineering practices have yet been performed due to a lack of detailed theoretical and technical support. This article provides a summary and analysis of the current research about the key problems in CAESA. The theoretical foundation and evaluation methods are first addressed, and then the aquifer selection criteria are proposed by analyzing the impact of the main geological factors on the performance. Subsequently, the optimal design of wellbore and the operation parameters are discussed, and different possible enhanced methods are proposed for extending the application of CAESA. Finally, conclusions are made and application outlook is addressed.

Since surfactants have been recognized as the most frequently faced contaminants of bubble column-related processes over time, their impact on the mass transfer operation of these columns has become a demanding research interest for two recent decades. Despite the similarities expressing the overall negative and positive influence of these chemicals on mass transfer coefficients and specific interfacial area, respectively, the discrepancies and, sometimes, paradoxical results are still under debate in the literature. To make a more comprehensive recognition of the mentioned subject, the current paper has tried to pave the path by reviewing all the major methods utilized in related research works. Thereafter, an interpretative argumentative comparison of the main findings of relevant studies has also been proposed, enlightening some of the research gaps which can be the potential candidates for future studies.

Various strategies are proposed to date in order to convert CO 2 to large diversity of useful chemicals. The following review discusses two important approaches that produce methanol from CO 2 . These two includes CO 2 hydrogenation and electrocatalytic routes. These processes could recycle CO 2 , permitting a carbon neutral, closed loop of fuel combustion and CO 2 reduction to prevent a rising concentration of this greenhouse gas in the atmosphere. Besides, intermittent electricity generation can be stored in an energy-dense, portable form in chemical bonds. The present review reports more recent findings and drawbacks of these two processes. The present review study revealed that the hydrogenation process could become readily operational in comparison to electrocatalytic process. The electrocatalytic approach still has serious technical issues in terms of kinetically sluggish multi-electron transfer process during CO 2 reduction reaction that requires excessive over-potential, relatively poor selectivity, poor durability in the long term, and the absence of the optimized standard experimental and commercial systems.

Pyrolysis has been considered as a promising thermochemical process that can convert biomass in nonoxidizing atmospheres to value-added liquid bio-oil, solid biochar, and noncondensable gas products. Fast pyrolysis has a better economic return because of the valuable biofuel production (e.g. bio-oil, syngas). Because of the complexity and heterogeneity of the feedstocks, the one-step pyrolysis often leads to the mixed, acidic, and highly oxygenated liquid products. Moreover, the downstream processes (e.g. deoxygenation) for the desired fuels require high costs on energy and catalysts consumption. Stepwise pyrolysis is defined as a temperature-programmed pyrolysis that can separately obtain the products from each temperature step. It is a feasible approach to accomplish the fractionation by optimizing the pyrolysis process based on the decomposition temperature ranges and products among the biomass constituents. In recent years, the stepwise pyrolysis technology has gained attentions in thermochemical conversion of complex organic solid wastes. Through the stepwise pyrolysis of a real waste, oxygenated and acidic products were concentrated in the first-step liquid product, whereas the second-step product normally contained a high portion of hydrocarbon with low acidity. The stepwise pyrolysis of biomass, plastics, and their mixtures is comprehensively reviewed with the objective of fully understanding the related mechanisms, influence factors, and challenges.