Utilization of biogas released from palm oil mill effluent for power generation using self-preheated reactor

In palm oil mills, for one ton crude palm oil (CPO) production, 70 m3 biogas is released from palm oil mill effluent (POME) which can endanger the environment. Palm oil mills without appropriate strategies for biogas collection can participate in greenhouse gases (GHGs) generation actively. In this paper, a typical palm oil mill with annual capacity of 300,000 ton oil palm production and 3 MW electricity demand is considered as a pilot plant and feasibility of power generation by POME biogas is modeled by Aspen Plus considering flameless mode in combustion system. A new design of lab-scale flameless reactor called self-preheated flameless combustion (SPFC) system is presented and employed in power generation modeling. In SPFC system, the flameless chamber is employed as a heater to preheat an oxidizer over the self-ignition temperature of the fuel. A helical stainless steel pipe (called self-preheating pipe) is installed inside the chamber to conduct the oxidizer from exhaust zone to the combustion zone inside the chamber and preheat oxidizer. In the flameless mode, the diluted oxidizer is injected to the helical pipe from the exhaust zone and the preheated oxidizer at the burner is conducted to the flameless furnace through a distributor. In SPFC system external heater for preheating oxidizer is removed and the rate of power generation increases. The results show that 10.8 MW power could be generated in ultra-lean POME biogas SPFC. However, the rate of pollutant especially CO2 and NOx is high in this circumstances. In stoichiometric condition, 4 MW power could be available in stable conditions with lower pollutant formation. Since, hydrogen is one of the ingredients of POME biogas, calculations confirm that the rate of power generation increases around 0.7 MW when just 2% hydrogen is added to biogas

Thermal-Hydraulic performance in a microchannel heat sink equipped with longitudinal vortex generators (LVGs) and nanofluid

In this study, the numerical conjugate heat transfer and hydraulic performance of nanofluids flow in a rectangular microchannel heat sink (RMCHS) with longitudinal vortex generators (LVGs) was investigated at different Reynolds numbers (200-1200). Three-dimensional simulations are performed on a microchannel heated by a constant temperature with five different configurations with different angles of attack for the LVGs under laminar flow conditions. The study uses five different nanofluid combinations of Al2O3 or CuO, containing low volume fractions in the range of 0.5% to 3.0% with various nanoparticle sizes that are dispersed in pure water, PAO (Polyalphaolefin) or ethylene glycol. The results show that for Reynolds number ranging from 100 to 1100, Al2O3-water has the best performance compared with CuO nanofluid with Nusselt number values between 7.67 and 14.7, with an associated increase in Fanning friction factor by values of 0.0219-0.095. For the case of different base fluids, the results show that CuO-PAO has the best performance with Nusselt number values between 9.57 and 15.88, with an associated increase in Fanning friction factor by 0.022-0.096. The overall performance of all configurations of microchannels equipped with LVGs and nanofluid showed higher values than the ones without LVG and water as a working fluid. © 2020 by the authors

Flameless combustion of propane-air mixture in a laboratory scale burner

In this work, the operational and emission of the laboratory scale burner under the flameless combustion regime using propane is examined. The combustor is equipped with parallel jet burner systems with controlled gas fuel and oxidizer. The combustor consists of several ports that are used to measure temperature variation and analyze gas emission. The atmospheric air was heated by flowing it inside the chamber until the air temperature increased to approximately the auto ignition temperature of the fuel. The furnace under investigation has successfully produced temperature uniformity ratios that are one order of magnitude less than such of the visible flame mode. It is observed that, flameless combustion can be achieved by using propane as a fuel. The value of NOX emission during flameless combustion was reduced of about 70% in average compared to the conventional flame at certain range of equivalence ratio

Vortex combustion and heat transfer in meso-scale with thermal recuperation

Vortex flows were utilized as a means to stabilize gaseous flames in micro/meso scale non-premixed combustors for use in small scale power and propulsion systems. In the present study, computational and experimental investigation of a turbulent asymmetric vortex flame is studied. Three-dimensional modeling of reacting flows was conducted to explore flame distribution and flow evolution in the chamber. The wall temperature was measured by using an infrared thermometer under the specified flow conditions. The experimental results showed that in stoichiometric condition, by increasing the mass flow rate of air, the wall temperature increases. The emitter efficiency was evaluated based on the measured wall temperature for outside wall. The emitter efficiency was found to be significantly influenced by the position of flame distribution, for which the mixture preheating (by the combustor wall) is believed to be a main reason. The effect of increasing the swirl was to improve the mixing and flame stability for swirl numbers up to approximately one. Excessive swirl also had the advantage of forcing the flame to move upstream to a position closer to the burner wall, resulting in excessive wall heating and emitter efficiency as well

Phase change materials-assisted heat flux reduction: experiment and numerical analysis

Phase change materials (PCM) in the construction industry became attractive because of several interesting attributes, such as thermo-physical parameters, open air atmospheric condition usage, cost and the duty structure requirement. Thermal performance optimization of PCMs in terms of proficient storage of a large amount of heat or cold in a finite volume remains a challenging task. Implementation of PCMs in buildings to achieve thermal comfort for a specific climatic condition in Iraq is our main focus. From this standpoint, the present paper reports the experimental and numerical results on the lowering of heat flux inside a residential building using PCM, which is composed of oil (40%) and wax (60%). This PCM (paraffin), being plentiful and cost-effective, is extracted locally from waste petroleum products in Iraq. Experiments are performed with two rooms of identical internal dimensions in the presence and absence of PCM. A two-dimensional numerical transient heat transfer model is developed and solved using the finite difference method. A relatively simple geometry is chosen to initially verify the numerical solution procedure by incorporating in the computer program two-dimensional elliptic flows. It is demonstrated that the heat flux inside the room containing PCM is remarkably lower than the one devoid of PCM

Characterisation of aerosol combustible mixtures generated using condensation process

An accidental release of a liquid flammable substance might be formed as an aerosol (droplet and vapour mixture). This phenomenon might be due to high pressure sprays, pressurised liquid leaks and through condensation when hot vapour is rapidly cooled. Such phenomena require a fundamental investigation of mixture characterisation prior to any subsequent process such as evaporation and combustion. This paper describes characterisation study of droplet and vapour mixtures generated in a fan stirred vessel using condensation technique. Aerosol of isooctane mixtures were generated by expansion from initially a premixed gaseous fuel-air mixture. The distribution of droplets within the mixture was characterised using laser diagnostics. Nearly monosized droplet clouds were generated and the droplet diameter was defined as a function of expansion time. The effect of changes in pressure, temperature, fuel-air fraction and expansion ratio on droplet diameter was evaluated. It is shown that aerosol generation by expansion was influenced by the initial pressure and temperature, equivalence ratio and expansion rates. All these parameters affected the onset of condensation which in turn affected the variation in droplet diameter

The role of exhaust gas recirculation in flameless combustion

Recently, flameless combustion has been developed as an innovative combustion method to intensify combustion performance and to decrease the pollutant formation contemporaneously. The outstanding economic aspects and merits of flameless combustion have persuaded the combustion scientists to investigate about this unique technology in the various ways and conditions. In flameless chambers the roles of heat and mass transfer are more highlighted than traditional combustion due to Exhaust Gas Recirculation (EGR) method. Flameless systems are characterized by highly preheated combustion air and burned gases recirculation before reaction. This paper is concerned with the detailed theoretical analysis of thermodynamics relationships in flameless combustion method. © (2013) Trans Tech Publications, Switzerland

Thermal-hydraulic performance of fin-and-oval tube compact heat exchangers with innovative design of corrugated fin patterns

The flow field inside the heat exchangers is associated with maximum heat transfer, minimum pressure drop and smallest pumping power. During the recent decades, the developments in the application of longitudinal vortex generators as an effective technique and important research topic have increased the heat transfer enhancement in the design of compact heat exchangers. The main motivation of this research is to study thermal–hydraulic performance characteristics in a tube bank compact heat exchanger with introducing new design of fins and tube by using computational fluid dynamics approach. One-corrugated and three-corrugated fins with oval tubes are innovative design of the FTCHE (fin-and-tube compact heat exchanger) that promises a large leap in the development of minimized FTCHEs with increased thermal efficiency. The major advantage of such design is its ability to produce substantially increased thermal efficiency and performance criteria of FTCHE. The investigation of thermal–hydraulic performance criteria is conducted for Reynolds number in the range of 200–900. This study shows that the flow distinction between plain and corrugated fins has a profound influence on the thermal-hydrodynamic performance. The results reveal that the corrugated fins can considerably advance the thermal efficiency of the FTCHE with a moderate pressure loss penalty. The computational results indicate that the average Nusselt number for the FTCHE with corrugated fin can be increased up to 20.0% over the baseline case and the corresponding pressure difference decreased up to 19.0%. In addition, the results show that the average value of performance in one-corrugated and three-corrugated fins and oval tube compact heat exchangers up to 5% and 15% over the baseline case, respectively. The newly designed fin with oval tube shows potential improvement of heat transfer performance and moderate pressure loss in the FTCHE compared with the baseline case

Experimental and numerical investigations of biogas vortex combustion

Low calorific value of biogas is one of the most important barriers of biogas development in industrial scale. Since biogas upgrading is complicated and not economic, various characteristics of pure biogas combustion have been experimented in recent years. In this paper, the characteristics of biogas flame structure and emissions in nonpremixed vortex combustion are studied experimentally and numerically. A lab-scale asymmetric chamber is employed as an industrial vortex combustor model and characteristics of biogas vortex combustion such as temperature distribution inside the chamber, the flame stability and the combustion emissions are investigated with respect to the various mole fraction of CO2 in the biogas content. The flame structure and emissions were recorded by changing the percentage of CO2 mole fraction in the biogas from 0 to 40% by volume. The results indicate that the stability of nonpremixed biogas combustion decreases when the rate of CO2 mole fraction increases in the fuel. The rate of both CO2 and NOx formation of nonpremixed combustion reduce monotonically when the rate of CO2 fraction increases in the biogas ingredients

Effects of hydrogen addition on the entropy generation of biogas conventional combustion

Biogas has a great potential to be applied for heat and power generation throughout the world due to its availability from various resources. However, one of the most important barriers of biogas utilization development is its low calorific value. In order to increase the performance of biogas in industrial application, hydrogen enriched biogas could be substituted. In this paper a set of numerical simulations were conducted to estimate the variation of entropy generation in hydrogen enriched biogas flames due to hydrogen addition to the fuel. Reynolds Averaged Navier Stokes with a second order turbulence closure and laminar flamelet combustion model was applied to compute energy fields and flow in the flame. It was found that hydrogen enrichment resulted in an augmentation in the entropy generation rate of the biogas conventional flame. Such increase could be attributed to the increase in irreversibilities due to biogas flame temperature rise. © 2014 Penerbit UTM Press. All rights reserved