Journal of Selected Topics in Energy

An introduction to various technologies for pre-extraction of hemicellulose from lignocellulosic biomass to produce synthetic gas and biofuels

Iman Akbarpour

On a global scale, the pulp and paper industry lead to produce significant amounts of effluents, solid wastes and gaseous wastes, and these wastes originate mainly from the pulping process, deinking and wastewater treatment. Solid biomass in wood waste as well as black liquor of pulping process can be converted to synthetic gas, mainly CO and H₂ by thermal processes, with small amounts of methane, Co₂ and H₂o, and this can be a good opportunity to revive the pulp and paper industry. The main raw materials of biomass in the biorefinery process include hemicellulose, cellulose, lignin and skin, and with mechanical-thermal methods including biomass gasification, black liquor gasification, pyrolysis or liquefaction and carbonization of biomass, synthetic gas can be converted into electricity as well as liquid fuels and chemicals. The results obtained by comparing different hemicellulose pre-extraction technologies of lignocellulosic materials indicate that the steam explosion method is much more environmentally friendly than other alternative methods requiring less investment cost. At present, the use of steam explosion method has increased at the commercial level due to its cost-effectiveness and this method is very efficient for hardwood residues as well as crops leftovers. Also, the organosolve fractionation technology for the separation of hardwoods is well operational and leads to the production of high purity cellulose and the selective dissolution of lignin and hemicellulose. Nanofiltration is a desirable separation method for the recovery of hemicellulose from hydrolysates, and in this regard, the combination of a twin-screw extruder system can be the best way to extract hemicelluloses from hardwood chips. Nanofiltration is much better than ultrafiltration to separate hemicelluloses from hydrolysates by alkaline methods.

A Review on inhibitory compounds and it reducing methods in bio-ethanol production from lignocellulose materials

Aliasghar Tatari

The gradual reduction of fossil resources has caused increasing concern about their supply and the emission of greenhouse gases and global warming, and in this context, biofuels can play an important role in solving these problems. Meanwhile, ethanol produced from corn starch, sugarcane molasses, lignocellulosic materials and biodiesel produced from rapeseed oil are the most important commercial uses in recent years. Ethanol production is a complex biochemical process in which yeasts, fungi, and certain bacteria are able to convert fermentable sugars into ethanol, carbon dioxide, and other metabolic byproducts. These byproducts contribute to the chemical composition and sensory properties of fermented foods. Ethanol production is important in a wide range of secondary products (such as health, medical and industrial). Controlling the fermentation process is usually a prerequisite for determining the quality of the final product. In this regard, monitoring the fermentation process is a basic need to ensure effective control of variable factors at all stages of the ethanol production process. Reducing the rate of fermentation in the process of ethanol production due to inhibitory compounds is considered a fundamental and significant problem in the economics of the process. In this review paper, the main aspects of ethanol fermentation and inhibitory compounds and their reduction methods in the ethanol production process from lignocellulosic materials have been discussed.

Investigation of energy recovery from solid oxide fuel cell

afsaneh rahimi

According to the sources and methods of energy extraction and conversion and consumption in the world, in this article the types of fuel cells as an efficient system with the ability to convert different fuels into electricity with high efficiency compared to other energy conversion systems is studied. The advantages and disadvantages of each fuel cell is reviewed. Also, the research done in this field by the researcher during the last 20 years all over the world is collected and the presented results are compared. According to the results of this study the solid oxide fuel cells which have many advantages compared to other similar systems, are carefully studied and different methods of energy recovery from this system in combination with different systems and in different applications and different scales for production of heating, cooling and added power and as a result, efficiency and energy performance of the system is considered. In addition to these advantages, the investigated system faces several problems such as the lack of necessary infrastructures for its production and use and its high price compared to other methods of energy supply. In the future, these problems will be solved with the increase in the investments and supports of new technologies and it is expected that by using this system, every building will reach self-sufficiency in production and supply of energy consumption needs.

Numerical study of forced convection heat transfer in a tube

Pedram Pournaderi

Heat transfer has an effective role in industrial and engineering applications. In this study, the effect of Al₂O₃ nanoparticles on laminar forced convection heat transfer flow in a tube is studied. Governing Equations are discretized using the finite difference method on a staggered grid. Nanofluid flow is simulated using single-phase and mixture models. Simulation results show that the average Nusselt Number increases with an increase in the Reynolds Number. Also, by increasing the volume fraction, the average Nusselt number and consequently the heat transfer rate increases. The results of the mixture model are in better agreement with experimental results than the single-phase model.

Numerical study of heat transfer rate of an isothermal circular cylinder in the presence and absence of a splitter plate under pulsating flow

Amir Omidvar

In this study, the effects of non-dimensional amplitude and frequency of pulsating flow are investigated on the heat transfer rate of a circular cylinder in the presence and absence of a splitter plate, for this purpose, at first the heat transfer rate of unpulsating flow is investigated and then compared with the results obtained from the pulsating flow. The pulsating flow over a circular cylinder is studied in the range of pulsating Strouhal number (0.1-2) and amplitude of pulsating flow A=0.75 in the Reynolds number of Re=100. Pulsating flow is one of the factors that can be effective on the heat transfer rate. But in general, the change in the heat transfer rate under pulsating flow depends on non-dimensional amplitude and frequency of pulsating flow. The best case for increasing the heat transfer rate is when the splitter plate is attached to the body. In all range of the pulsating Strouhal number, increase in the Nusselt number in the presence of a splitter plate is reported relative to the absence of splitter plate in pulsating flow.

Laboratory study of drag reduction and heat transfer improvement in vertical pipe using crude oil/nanosilica/Polyisobutylene polynanofluids

Abdolrasoul Pouranfard

In this study, the effect of adding polyisobutylene (PIB) as drag reducing agent (DRA) and nanoSiO₂ particles as heat transfer enhancer to crude oil, separately and also the simultaneous addition of these materials to crude oil as poly-nanofluids (PNFs) in a vertical pipe and under constant heat flux conditions is investigated. The use of drag reducers is one of the most important and simplest methods to overcome some of the energy losses during fluid transpotation. The aim of this study is to investigate the effects of PIB solution and crude oil/silica nanofluid, separately and also the simultaneous effect of adding these two materials, called polyanofluid, on heat transfer and drag reduction in a vertical pipe. In order to make PNFs, polymer-based solutions with concentrations of 10-30 ppm are prepared. Then, nanoSiO₂with concentrations of 0.1-0.5wt% are added to the base fluid. The experiments were performed in the range of Reynolds 5800-8700 and temperature was 25°C. Experimental conclusions predicted that with increasing Reynolds number, temperature and concentration, Nusslet number and heat transfer rate in supplied nanofluids and PNFs enhanced with nanoparticle concentrations, while PIB concentration cause to reduce thermal propertied and improve the tribological properties of prepared PNFs. This occurrence can be attributed to the formation of the polymeric layer around the nanosilica particles.