Seyed Ehsan Hosseini

Biogas flameless combustion: a review

Biogas which is produced by the anaerobic digestion of biomass and organic wastes by micro-organisms is biodegradable. Biogas is a type of renewable energy sources that can be used for lighting, heating, and transportation and small-scale power generations. Although it seems that biogas is not economical due to its low calorific values, various investigations have been conducted by various researchers. Flameless combustion of fossil fuel was introduced during last decade and it has been proven that it could be the best technique for biogas combustion due to its low production of NOx pollution. In this paper, the review of biogas, its resources, and the utilization of biogas on flameless combustion is illustrated.

Pollutant in palm oil production process

Palm oil mill effluent (POME) is a by-product of the palm industry and it releases large amounts of greenhouse gases (GHGs). Water systems are also contaminated by POME if it is released into nonstandard ponds or rivers where it endangers the lives of fish and water fowl. In this paper, the environmental bottlenecks faced by palm oil production were investigated by analyzing the data collected from wet extraction palm oil mills (POMs) located in Malaysia. Strategies for reducing pollution and technologies for GHG reduction from the wet extraction POMs were also proposed. Average GHG emissions produced from processing 1 ton of crude palm oil (CPO) was 1100 kg CO2eq. This amount can be reduced to 200 kg CO2eq by capturing biogases. The amount of GHG emissions from open ponds could be decreased from 225 to 25 kg CO2eq/MT CPO by covering the ponds. Installation of biogas capturing system can decrease the average of chemical oxygen demand (COD) to about 17,100 mg/L and stabilizing ponds in the final step could decrease COD to 5220 mg/L. Using a biogas capturing system allows for the reduction of COD by 80% and simultaneously using a biogas capturing system and by stabilizing ponds can mitigate COD by 96%. Other ways to reduce the pollution caused by POME, including the installation of wet scrubber vessels and increasing the performance of biogas recovery and biogas upgrading systems, are studied in this paper. Implications: Around 0.87 m3 POME is produced per 1 ton palm fruit milled. POME consists of around 2% oil, 2–4% suspended solid, 94–96% water. In palm oil mills, more than 90% of GHGs were emitted from POME. From 1 ton crude palm oil, 1100 kg CO2eq GHGs are generated, which can be reduced to 200 kg CO2eq by installation of biogas capturing equipment.

Effect of diluted and preheated oxidizer on the emission of methane flameless combustion

In combustion process, reduction of emissions often accompanies with output efficiency reduction. It means, by using current combustion technique it is difficult to obtainlow pollution and high level of efficiency in the same time. In new combustion system, low NOxengines and burners are studied particularly. Recently flameless or Moderate and Intensive Low oxygen Dilution (MILD) combustion has received special attention in terms of low harmful emissions and low energy consumption. Behavior of combustion with highly preheated air was analyzed to study the change of combustion regime and the reason for the compatibility of high performance and low NOx production. Sustainability of combustion under low oxygen concentration was examined when; the combustion air temperature was above the self-ignition temperature of the fuel. This paper purposes to analyze the NOx emission quantity in conventional combustion and flameless combustion by Chemical Equilibrium with Applications (CEA) software.

Evaluation of palm oil combustion characteristics by using the Chemical Equilibrium with Application (CEA) software

Variety of edible and nonedible oils can be used as the feedstock for biodiesel production. Among the edible oil source includes both virgin vegetable oils and waste vegetable oils. Rapeseed, soybean, and palm oils are most commonly used to produce biodiesel. In addition to its sources, the combustion process, the amount of produced energy, and the rate of emissions from biofuel inflammation also are crucial in to the ability of biodiesel to meet global energy demands. The level of energy produced and the rate of emissions can be evaluated with Chemical Equilibrium with Applications (CEA) software. This paper attempts to scrutinize and determine the palm oil combustion properties under various thermodynamic conditions using the CEA software.

Effects of Burner Configuration on the Characteristics of Biogas Flameless Combustion

The purpose of this experimental and numerical investigation is to analyze the effects of burner configuration on the characteristics of biogas flameless combustion. In the four non-premixed studied burners, the inlet jet of the fuel is located at the center of the burner, surrounded by four oxidizer parallel jets in the coaxial burners and four perpendicular jets in the tangential configuration. In the three-dimensional (3D) computational fluid dynamic (CFD) study, a two-step reaction scheme, eddy dissipation concept (EDC), eddy dissipation method (EDM), and the realizable k- ϵ formulation were set for all simulations. The results illustrate that the volume of the flame is wider in a tangential burner and, hence, the temperature uniformity in the tangential flameless burner is more than coaxial configurations. The inside temperature of the furnace and the combustor’s wall temperature are higher in the tangential burner; consequently, higher heat loss from walls was recorded in tangential mode. Despite the higher energy loss from walls in the tangential burner, the efficiency of biogas flameless combustion in the tangential is more than the coaxial burners (66% and 64%, respectively). The concentration of CH4 in the exhaust gases was recorded at 48 ppm and 60 ppm in the tangential and coaxial burners, respectively, which confirms that the combustion of biogas is more complete in the tangential flameless burner. The lower concentration of oxygen in the tangential burner conducts the combustion system to generate higher carbon monoxide (CO) based on the two-step combustion concept.

Environmental Protection and Fuel Consumption Reduction by Flameless Combustion Technology: A Review

In recent years global fuel consumption has increased in the world due to modernization and progress in the standard of living. The conspicuous rate of carbon dioxide and nitrogen oxide released to the environment and fuel resources are depleted day by day due to inconsiderate fuel consumption. Requirement for efficient use of any kinds of fuel has become the other concern due to the oil crisis and limitation of fuel resources. In combustion process, the abatement of pollutants often associates with efficiency loss. In the other word, high efficiency and low pollutant which are the main requirements of combustion are not fulfilled by the existing combustion. Today, flameless combustion has received more attention because of its low NOx emission and significant energy saving. Generally, compatibility between high performance and low NOx emission has been observed by preheated air application and changing the combustion characteristics from traditional flame to flameless mode. This paper aims to review the concepts and the applications of flameless combustion and gathers useful information to understand the necessity of transient from traditional flame mode to flameless combustion.

Review of Numerical Studies on NOx Emission in the Flameless Combustion

Today one source of pollution emission in the combustion of fossil fuels is the formation of nitrogen oxides. To solve this problem many technologies have been introduced such as flameless combustion. Flameless combustion is of a great interest since it simultaneously provides higher thermal efficiency together with controlling the pollutant emission such as NOX. In this technology, the preheat temperature of the combustion air must be higher than the auto-ignition temperature of the reactant mixture. In this study, papers showing the numerical studies on the flameless combustion to reduce NOX emission are presented.

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.

Effects of Firing Mode on the Performance of Flameless Combustion: A Review Paper

Flameless combustion is of a great interest since it simultaneously provides higher thermal efficiency together with controlling the pollutant emission such as NOX. This technology has been used to provide large energy savings in power system and industrial heating applications. In this technology, the preheat temperature of the combustion air must be higher than the auto-ignition temperature of the reactant mixture. In this review, papers concern the effect of firing mode to reduce pollutant emissions such as NOX emission and combustion efficiency for flameless combustion were reviewed. Summaries on the influences of the firing mode in the flameless combustion were presented, discussed and analyzed. The review concludes that all the previous studies have asserted that a parallel firing mode gives much lower pollutant emissions and high efficiency compared with staggered and counter modes.

Impacts of inlet step on the performance of a micro-combustor

A Computational Fluid Dynamic (CFD) study on hydrogen-air premixed combustion in a micro-combustor is investigated by solving three-dimensional (3D) governing equations. The effects of inlet geometry on the flame temperature, flame stability and micro combustor efficiency under different inlet flow rates and various equivalence ratios were studied by a simulation of two micro-combustors with similar dimensions, in which one of them was designed with inlet step and the other without inlet step. The simulated results confirm that the temperature is higher in a micro-combustor with inlet step compared to that of the simple geometry. Thus the flame stability can be ensured by application of the step in the inlet of the micro-combustor. In a moderate equivalence ratio of lean mixture (Ø=0.5), the peak of maximum temperature takes place in the micro-combustor with inlet step in a lower velocity (V1a=4m/s) which was recorded around 1747°K. By enhancing the inlet flow rate of hydrogen-air mixture, the flame length raises and the flame is blown further downstream of both combustors. Also, in both micro-combustors fueled by lean hydrogen-air mixture, more heat can be released when the equivalence ratio is larger and a higher temperature level is recorded (1931°K). Indeed, in the fixed hydrogen-air mixture, inlet flow rate (=1.57×10-6 m3/s) when Ø=0.6, a maximum temperature was recorded in the micro-combustor with inlet step and consequently the temperature of exhaust gases was higher. In the same physical and chemical conditions, the micro-combustor with inlet step has higher performance efficiency.