Co-firing of sugar cane bagasse with rice husk in a conical fluidized-bed combustor

This paper presents experimental results on co-firing of ‘as-received’ sugar cane bagasse and rice husk in a conical fluidized-bed combustor (FBC) using silica sand as the bed material. Axial temperature, O₂, CO₂, CO and NO concentration profiles in the conical FBC operated at 82.5-82.8 kg/h fuel feed rate and various values of excess air (of about 40, 60, 80 and 100%) for different rice husk energy fractions (of 0.60, 0.85 and 1.0) are discussed. The bed temperature, CO and NO emissions from the combustor, as well as the heat losses and combustion efficiency, are also provided for the above operating conditions. The axial temperature profiles in the conical FBC were almost independent of excess air but noticeably affected by the rice husk energy fraction. The CO emissions were found to reduce for higher values of excess air and rice husk energy fractions. Meanwhile, the NO concentrations at all the points over the combustor volume and, accordingly, NO emissions from the reactor increased with higher excess air and energy contributions by rice husk. The co-firing of these fuels in the conical FBC at the rice husk energy fractions greater than 0.6 resulted in the sustainable combustion, with 95-96% combustion efficiency, and lower NO emissions compared with those for firing pure rice husk. Through co-firing with rice husk, an effective use of ‘as-received’ sugar cane bagasse becomes feasible for energy conversion in the fluidized-bed combustion systems.     

Experimental investigation on the combustion behaviour of pre-dried Greek lignite

The present paper includes the results of the combustion tests with Greek dried lignite performed at a 1 MWth semi industrial scale pulverized coal combustion facility. Scope of the campaign is the investigation of the combustion behaviour of Greek lignite, i.e. temperature fields, ignition, burnout, emissions, as well as slagging and fouling tendency, while firing with varying levels of recirculated flue gas. Dry coal co-firing conditions in a large scale boiler are simulated by adjusting the volume flow of recirculated flue gas.Two test series representing different boiler operation modes are performed. During the first series the maximum flue gas temperature increase, when co-firing dry coal, is determined, while in the second test series the needed load decrease, in order to keep constant furnace outlet temperature in dry coal co-firing conditions is recorded. A detailed measurement set is carried out including temperature profiles, emissions, fuel, fly ash sampling and slagging and fouling investigations through the installation of dedicated deposition probes.The anticipated increase of the furnace temperature profiles by decreasing the inserted recirculated flue gas is confirmed by the experimental results. No clear trend of dry coal co-combustion on the emissions' behaviour is noticed, while dry coal firing appears to have a moderate effect on the deposition behaviour of Greek lignite. These preliminary investigations indicate that no significant operational problems are expected during a potential future demonstration of dry lignite co-firing in a Greek large scale boiler.     

A PM 2.5 Inlet Impactor Designed for a High Flow Application

Two potential strategies for reducing diesel emissions are exhaust aftertreatment and the use of reformulated or alternative fuels. Little is yet known about the impact on ultrafine particle emissions of combining exhaust aftertreatment with such increasingly common fuels. This paper reports ultrafine particle size distribution measurements for a study in which the impact of such fuels on emissions from a heavy duty diesel engine employing different aftertreatment configurations was evaluated. Eight different fuels were tested: Canadian No. 1 and No. 2 diesel; low sulfur diesel fuel; two different ultra low sulfur diesel fuels (< 30 ppm S); Fischer-Tropsch diesel fuel; 20% biodiesel blended with ultra low sulfur diesel fuel; and PuriNO_x?. The fuels were tested in combination with four exhaust configurations: engine out, diesel oxidation catalyst (DOC), continuously regenerating diesel particle filter (CRDPF), and engine gas recirculation with CRDPF (EGR-DPF). In general, aftertreatment configuration was found to have a greater impact on ultrafine particle size distributions than fuel composition, and the effects of aftertreatment tended to be uniform across the entire particle size distribution. Steady state tests revealed complex behavior based on fuel type, particularly for PuriNOx. This behavior included bimodal particle size distributions with modes as low as 8–10 nm for some fuels. Unlike previous results for gravimetric PM from this study, no significant correlation for ultrafine emissions was found for fuel properties such as sulfur level.     

Measurements of dioxin emissions during co-firing in a fluidised bed

The emissions of dioxins could be considerable when fuels with high chlorine content are used, particularly in fluidised beds due to constraints to use temperatures in the range 800-900 °C for other considerations. However, mixing of fuels with different characteristics may lead to a reduction in dioxin emissions. Studies are currently being undertaken at the above-mentioned department in mixing fuels of varying chlorine and sulphur contents to monitor the emissions of dioxins both in the gas and solid phases. Furthermore, the influence of certain elements like Cu in the ash in the emissions of dioxins is also studied to verify the catalytic effect.The INETI pilot-scale test facility is used for the combustion work. Two different coals, namely Colombian and Polish, are used as the base fuel. The supplementary fuels for co-firing include MBM and straw pellets. The combustion temperature is maintained at about 800-830 °C range without any limestone addition. The residence time of over 2 s is respected.Results obtained by far suggest that the presence of sulphur in both fuels have a very strong effect on the eventual emissions of dioxins and the synergy regarding to reduce the dioxins below the levels permitted is possible by mixing fuels based on their characteristics. The paper reports the results obtained and evaluates the effect of fuel nature and operating conditions on the emissions of dioxins.     

Influence of the co-firing on the leaching of trace pollutants from coal fly ash

The (co)-firing of low-cost alternative fuels is expected to increase in the forthcoming years in the EU because of the economic and environmental benefits provided by this technology. This study deals with the impact of the different coal/waste fuel ratio of the feed blend on the mineralogy, the chemical composition and especially on the leaching properties of fly ash. Different blends of coal, petroleum coke, sewage sludge, wood pellets, coal tailings and other minor biomass fuels were tested in PCC (pulverised coal combustion) and FBC (fluidized bed combustion) power plants. The co-firing of the studied blends did not drastically modify the mineralogy, bulk composition or the overall leaching of the fly ash obtained. This suggests that the co-firing process using the alternative fuels studied does not entail significant limitations in the re-use or management strategies of fly ash.     

Use of grey relational analysis to assess and optimize small biomass boilers

This paper presents a new methodology for the evaluation of the environmental and economic feasibility of combustion of different biomass fuels in small boilers. The study focuses on pellets as the basic co-firing product and forest residues as the complementary product. Although the co-firing of forest residues can be economically profin, it is difficult to evaluate the general economic advantages due to the worsening of combustion in terms of performance and emissions caused by the presence of the forest residues in the fuel mixture. The grey relational analysis of different energetic and emission variables and also residue prices allows for the definition of a new single variable called the grey relational grade. Thus, evaluation and optimization of complicated multiple responses can be converted into the optimization of a standardised single variable. Experimental analyses by means of the Grey theory of different forest residues have revealed the possibility of co-firing crust of pine combined with wood pellets as a way of reducing fuel costs, keeping performance and emissions within average standards in small pellet boilers.     

Combustion properties of some power station biomass fuels

In this study, the combustion properties of three of the UK’s commonly imported biomass fuels for co-firing, which are palm kernel expellers, shea residue, and waste from olive oil production are examined. The fuels were characterised and their thermal decomposition properties were studied by thermogravimetric analysis (TGA). Additionally the products from their devolatilisation were identified by gas chromatography-mass spectrometry (py-GC-MS) analysis of the evolved vapours and tars from high heating rate pyrolysis tests. Finally, chars from the fuels were prepared, analysed, and combustion studies were conducted by TGA-MS to determine the conversion of char-nitrogen to different nitrogen-containing species. In general, the main constituents of their ash fractions were K, Si, Ca and Mg, resulting in high alkali indices, which predict a large tendency to fouling. The pyrolysis and combustion kinetic parameters, estimated from TGA studies of these fuels and their chars, are much lower than those reported in the literature for lignocellulosic biomass. It is suspected that there is oil/fat evaporation processes overlapping with the decomposition of their lignocellulosic fractions, which significantly affects the apparent kinetics. The pyrolysis conditions used promoted depletion of nitrogen in the char, resulting in approximately 79-91% of the fuel-N being released with the volatiles. In combustion of the char, NO_x and N₂ are the major nitrogen compounds detected. Another primary product, HCN, was detected from the combustion of some of the fuel chars, as well as C₂N₂.     

Emission Reduction of Regenerative Fuel Powered Co-Generation Plants with SCR- and Oxidation-Catalysts

Since the beginning of combustion engine development in this recent century various different fuels have been successfully tested. Diesel engines have been adapted to fuels made from mineral oils because of the rising importance and the cheapness in comparison to other fuels. On the other hand, it is possible to burn regenerative fuels in engines and achieve some significant advantages in comparison to fossil diesel fuel. This is, for example, a closed carbon dioxide (CO₂) cycle which causes no green house effect. It is possible to extract oil from various seeds like rapeseed. It is also possible to burn used oil from the food processing industry or waste grease and oil from food recycling companies. The great advantages: (1) food recycling oils can produce energy instead of use as animal food, and (2) as nobody knows exactly the consistency of the collected oils, poisonous pollution is possible. These regenerative fuels can be burned without any further processing in special adapted diesel engines, for example an Elsbett engine, or in precombustion engines with large swept volumes. Most researchers focused on operating diesel engines with regenerative fuels and reducing the emissions caring only about regulated exhaust components. In comparison to these studies it is necessary to learn more about the emissions beyond the exhaust regulations. Additionally emission reduction is possible by using an SCR-catalyst (selective catalytic reduction) to reduce the NO₂ combined with an oxidation-catalyst which reduces any kind of oxidisable emissions. The TU München, Lehrstuhl für Energie- und Umwelttechnik der Lebensmittelindustrie, operates a small co-generation plant with the ability of analysing the standard emission components (CO, NO₂, HC, particles, CO₂, O₂) and unregulated components (SO₂, NH₃, polycyclic aromatic hydrocarbons (PAH), aldehyde, ketone). The emissions show some significant differences in comparison to fossil diesel fuel which is caused by the diversity of each fuel. Results of an investigation on four different fuels (wastefat methyl ester (WME), rapeseed methyl ester (RME), rapeseed oil and diesel fuel) burned in a small co-generation plant with a SCR- and oxidation-catalyst will be presented. A comparison to the emissions before and after the catalysts will be shown additionally to the results of the different reduction potential of diesel fuel, methyl ester or untreated oils. The combination of regenerative fuel and catalyst shows good potential for reducing the emissions. Furthermore the use of regenerative fuels is a sustainable production of energy with an overall efficiency of almost 90%. Regenerative fuels based on vegetable oils and waste fat are a valuable form of energy and have some significant advantages in comparison to diesel fuel, like an almost closed carbon dioxide cycle, rapid biological decomposition and lower CO, HC and particle emissions. Regenerative fuels should also meet minimum standards discussed in the paper to avoid the risk of engine damage and to reduce emissions.     

The influence of biomass co-combustion on boiler fouling and efficiency

The paper presents an attempt to evaluate the influence of biomass co-combustion on the fouling of boiler convection surfaces. In order to show the influence of co-firing biomass with bituminous coal on boiler efficiency, the calculations of pulverized fuel (PF) OP 140 steam generator have been carried out. Typical Upper Silesian coal with medium fouling inclination has been chosen as a basic fuel. Three kinds of biomass have been taken into consideration: straw, wood and dried sewage sludge. The results confirm that the properties of additional fuels cause deterioration of the boiler efficiency as well as the changes in boilers operational parameters (amount of water injected in attemperators, ash stream, hot air temperature). The biomass during cofiring in fact replaces the coal, but always the additional fuel consumption is higher than that of the substituted coal. Therefore, the actual decrease of coal consumption is smaller than the thermal fraction of the biomass.     

Minimizing fuel and environmental costs for a variable-load power plant (co-)firing fuel oil and natural gas: Part 1. Modeling of gaseous emissions from boiler units

This work was aimed at modeling of major gaseous emissions (NO_x, SO₃, SO₂, CO₂) from boiler units of a power plant firing (or co-firing) fuel oil and natural gas for variable operating conditions (load and load-related variables: excess air, flue gas recirculation, etc.). The emission rate of the pollutants for the co-firing was estimated for a particular boiler using these characteristics for the burning of each fuel in the boiler on its own and taking into account energy fractions (contributions) of fuel oil and natural gas to the boiler heat input. The gaseous emissions (in terms of emission concentrations, emission rates and specific emissions) from a 200-MW boiler unit firing low-S fuel oil and from a 310-MW boiler unit firing (or co-firing) medium-S fuel oil and natural gas were estimated and compared for 50–100% unit loads based on actual fuel properties and load-related operating variables of these units. Upper limit for the energy fraction of medium-S fuel oil was determined for the 310-MW boiler unit co-firing the two fuels with the aim to meet the national emission standard for SO₂.     

Application of chemical fractionation methods for characterisation of biofuels,waste derived fuels and CFB co-combustion fly ashes

In the important efforts to decrease the net CO₂ emissions to the atmosphere, new, alternative fuels are being included in the fuel mixes used in utility boilers. However, these fuels have ash properties that are different from those of the traditionally used fuels and in some cases technical problems, such as ash fouling and corrosion occur due to this. Therefore, diagnostic and predictive methods are developed and used to avoid such problems. Determination of the chemical association forms of important elements, such as potassium and sodium, in the fuel by chemical fractionation is a method well defined for coal and biofuels, such as wood pellets, bark and forest residues. Chemical fractionation is a step by step leaching method extracting water soluble salts in the first step, ion exchangeable elements, such as organically associated sodium, calcium and magnesium in the second step and acid soluble compounds such as carbonates and sulfates in the third step. The solid residue fraction consists of silicates, oxides, sulfides and other minerals. The compound extracted in the two first steps is considered reactive in the combustion with a few exceptions. In this work, it has been applied to some waste fuels, i.e. sewage sludge, straw and refuse derived fuel (RDF), as well as to coal and wood. The present work also includes results from combustion tests in a fluidised bed boiler where three blends of the investigated fuels were used. The fractionation results for the fuel blends are weighted results of the fractionations of the pure fuels discussed above which are compared with fractionations of their corresponding fly ashes. The co-combustion strategy gave very good results in reducing ash problems. Possible chemical mechanisms involved are discussed in the article.     

Numerical investigation of Solid Recovered Fuels’ co-firing with brown coal in large scale boilers – Evaluation of different co-combustion modes

In the current work the co-combustion of Solid Recovered Fuels’ (SRFs’) with brown coal in large scale pulverised coal boilers under different operational conditions is numerically investigated. In order to overcome the difficulty of the complex, inhomogeneous nature of waste recovered fuels, SRF is modelled as a mixture of two different fractions, the biogenic and the plastic one. For each fraction different combustion mechanisms are presented, whilst for the first time the proposed combustion mechanism of the plastic fraction is incorporated in a commercial CFD code and validated against available experimental data. A 600 MW_e brown coal boiler is simulated as a reference and its operational characteristics are compared with parameterised scenarios of SRF co-firing conditions. Based on the numerical results, the optimum co-firing concepts regarding the more efficient operation of the boiler (hot spots and fuel’s burnout) are identified, decreasing the environmental impact of the boiler’s emissions.     

Experimental investigation of fluidised bed co-combustion of meat and bone meal with coals and olive bagasse

Meat and bone meal (MBM) was co-fired in a laboratory scale fluidised bed combustion (FBC) apparatus together with three different primary fuels: two coal types and olive bagasse residues. Several two component fuel blends were tested under different combustion conditions to study how primary fuel substitution by MBM affects flue gas emissions as well as fluidised bed (FB) agglomeration tendency. MBM, being a highly volatile fuel, caused significant increase of CO emissions and secondary air should be used in industrial scale applications to conform to regulations. The high N-content of MBM is moderately reflected on the increase of nitrogen oxides emissions, which are reduced by MBM derived volatiles. The MBM ash, although containing bone material rich in Ca, did not create any noteworthy desulphurisation effect. The observed slight decrease in SO₂ emissions is predominantly attributed to the lower sulphur content in the coal/MBM fuel mixtures. The experimental work is evaluated with bed agglomeration indices from literature. The SEM/EDS analysis of bed material samples from the coal/MBM tests revealed the formation of conglomerates of bed material debris and ash with sizes that do not greatly exceed the original bed inventory and thus are not problematic. On the contrary, the co-combustion tests of olive bagasse residues with MBM led to a prompt loss of fluidisation, as a consequence of the high potassium and silicon content of the olive bagasse, the chlorine contents in both MBM and olive bagasse, and the high phosphorus content in the MBM also forming eutectics with potassium.     

Combustion of poultry-derived fuel in a coal-fired pilot-scale circulating fluidized bed combustor

Poultry farming generates large quantities of waste. The current practice is to spread this waste onto farmland as fertilizer. However, as the factory farms for poultry grow both in numbers and size, the amount of waste generated has increased significantly in recent years. In consequence, excessive application of poultry wastes on farmland is resulting in more and more nutrients entering the surface water. One of the options being considered is the use of poultry waste as power plant fuel. Since poultry-derived fuel (PDF) is biomass, its co-firing will have the added advantage of reducing greenhouse gas emissions from power generation. To evaluate the combustion characteristics of co-firing PDF with coal, combustion tests were conducted in CanmetENERGY's pilot-scale circulating fluidized bed combustor (CFBC). The goal of this program was to verify that PDF can be co-fired with coal and, more importantly, that emissions from the combustion process are not adversely affected by the presence of PDF in the feed. The test results were very promising and support the idea that co-firing in an existing CFBC boiler firing coal is a good way to utilize PDF, resolving a potential waste disposal problem while reducing the amount of CO₂ released from the boiler.     

Biomass co-firing in a pressurized fluidized bed combustion (PFBC) combined cycle power plant: A techno-environmental assessment based on computational simulations

The co-utilization of coal with biomass and biomass waste in a pressurized fluidized bed combustion (PFBC) system is a promising power generation option for addressing various areas of concern relating to the anthropogenic sources of harmful emissions, the global reliance on fossil fuel and the overall energy supply issues. In this study, coal with a wide range of biomass and biomass waste types such as straw, willow chips and switch grass as well as miscanthus and olive pits are fired in an advanced PFBC system. The produced gases and the evolved heat energy are employed to run a combined cycle. To understand the behavior of the proposed system, detailed computational simulations are carried out utilizing various feedstock mixtures ranging from 100% coal to 40% biomass. The results of the simulations are used to show the effect of co-firing on the technical and environmental performance of the power plant.The results show that the main parameters affecting the overall power plant efficiency are the co-firing ratios and the specific properties of the chosen biomass/waste types. Furthermore, the investigation indicates that the steam cycle output reacts more sensitive to the fuel configurations than the gas turbine cycle. As expected, the increased fraction of biomass or waste significantly reduces net CO₂ emissions, and has a beneficial influence on SO_x emissions. NO_x emissions tend to rise for all biomass types, except the high moisture content willow chips, with increasing co-firing fraction.     

Firing of coal and biomass and their mixtures in 50 kW and 12 MW circulating fluidized beds - Phenomenon study and comparison of scales

The combustion dynamics of coal, wood chips and their mixture is investigated. Load change capability and the effect of the individual control variables, for example the mixture ratio of different fuels, on pilot-scale CFB boiler dynamics were also studied.Disturbances in fuel feeding cause fluctuations in the flue gas concentrations. Changes in the heating value are possible due to varying moisture content of the fuel. Both these disturbances affect the instantaneous firing rate in a boiler. Also the characteristics of the fuels have to be taken into consideration when designing boiler control systems. When co-firing two fuels with clearly distinct combustion characteristics, direct assumptions based on each fuel’s characteristics cannot be made about combustion behaviour of their mixture.Combustion experiments with coal and wood chips and their co-firing were carried out in a pilot-scale CFB reactor (VTT) and a large-scale CFB boiler (Chalmers). A comparison of the combustion in the two different size reactors, provides information about scaling. The combustion responses due to changes in the fuel feeding of the two circulating fluidized beds are analyzed by a dynamic model.     

A technical and environmental analysis of co-combustion of coal and biomass in fluidised bed technologies

The use of biomass, which is considered to produce no net CO₂ emissions in its life cycle, can reduce the effective CO₂ emissions of a coal-fired power generation system, when co-fired with the coal, but may also reduce system efficiency.The technical and environmental analysis of fluidised bed technologies, using the ECLIPSE suite of process simulation software, is the subject of this study. System efficiencies for generating electricity are evaluated and compared for the different technologies and system scales.Several technologies could be applied to the co-combustion of biomass or waste and coal. The assessment studies here examine the potential for co-combustion of (a) a 600 MWe pulverised fuel (PF) power plant (as a reference system), (i) co-firing coal with straw and sewage sludge and (ii) using straw derived fuel gas as return fuel; (b) a 350 MWe pressurised fluidised bed combustion (PFBC) system co-firing coal with sewage sludge; (c) 250 MWe and 125 MWe circulating fluidised bed combustion (CFBC) plants co-firing coal with straw and sewage sludge; (d) 25 MWe CFBC systems co-firing low and high sulphur content coal with straw, wood and woody matter pressed from olive stones (WPOS); (e) 12 MWe CFBC co-firing low and high sulphur content coal with straw or wood; and (f) 12 MWe bubbling fluidised bed combustion (BFBC), also co-firing low and high sulphur content coal with straw or wood.In the large systems the use of both straw and sewage sludge resulted in a small reduction in efficiency (compared with systems using only coal as fuel).In the small-scale systems the high moisture content of the wood chips chosen caused a significant efficiency reduction.Net CO₂ emissions are reduced when biomass is used, and these are compared for the different types and scales of fluidised bed technologies. NO_x emissions were affected by a number of factors, such as bed temperature, amount of sorbent used for SO₂ capture and HCl emitted.     

固硫灰渣的基本特性及其作水泥混合材的关键问题研究进展

固硫灰渣是循环流化床燃煤技术的主要副产物,如何高效、清洁地利用这一类固体废弃物是一个亟待解决的问题。本文根据近年来国内外对固硫灰渣的研究成果,从化学组成、矿物组成、微观结构、典型特性等方面综述了固硫灰渣的主要特征。相较于粉煤灰等其他燃煤副产物,固硫灰渣中存在游离氧化钙、硫酸钙和无定形铝硅酸盐物质,且颗粒疏松多孔,这导致其具有明显的火山灰活性、自硬性和水化膨胀性等特性。同时本文分析了固硫灰渣作为水泥混合材使用时需要注意的几个关键问题。结果表明,固硫灰渣特殊的组成、微结构和性质导致其作为水泥混合材使用时,必须考虑使用合适的激发剂提高灰渣活性,调整养护工艺、用水量等条件提高制品的安定性,并以添加减水剂等方式控制水泥制浆中的需水量,提高水泥石强度。这为有效实现固硫灰渣的建材资源化利用提供一定指导。     

Impact of biodiesel bulk modulus on injection pressure and injection timing. The effect of residual pressure

As the demand for energy rises fossil fuel reserves are depleted daily, increasing the interest in alternative fuels. Biodiesel is one of the best candidates in this class and its use is expected to expand rapidly throughout the world. Numerous researchers have been investigating how biodiesel affects combustion, pollutant formation and exhaust aftertreatment. There is general agreement that its combustion characteristics are similar to those of standard diesel fuel, except for a shorter ignition delay, a higher ignition temperature, and greater ignition pressure and peak heat release. Engine power output is similar with both fuels. As regards emissions, reductions in particulate matter (PM) and carbon monoxide (CO) and increases in nitrogen oxides (NOx) are described with most biodiesel blends. The latter is referred to as the ‘biodiesel NOx effect’. The vast majority of researchers who explored the effect of biodiesel did so in mechanical injection engines. They found that the primary mechanism by which biodiesel increases NOx emissions is by an inadvertent advance in the start of injection timing, caused by a higher modulus and viscosity. However, more recent studies show that NOx emissions also increase in biodiesel-fuelled common rail engines, and that in some cases they actually decrease in engines with mechanically controlled fuel injection systems. This cannot be explained solely by differences in compressibility and remains an open question. The present study provides a contribution to the discussion in this field by describing a new method to evaluate the injection advance in engines with mechanically controlled pumps. The experimental data show that the advances in the start of injection timing, using biodiesel rather than mineral diesel, are smaller than those calculated with standard methods and may even not occur at all, depending on injection system design. In addition, they demonstrate that, contrary to common belief, injection pressure does not always increase when using biodiesel. These data may help explain why some researchers have found similar or even reduced NOx emission also with mechanical injection systems.     

Various strategies for reducing Nox emissions of biodiesel fuel used in conventional diesel engines: A review

Energy demand, decreasing fossil fuel reserves, and health-related issues about pollutants have led researchers to search for renewable alternative fuels to either partially or fully replace fossil fuels. Among many alternative fuels, biodiesel became one of the most popular choices due to similar properties to that of conventional diesel. Biodiesel produces slightly lower brake thermal efficiency compared to that of conventional biodiesel, but has an advantage of reduced emissions of CO₂, CO, HC, and smoke. However, biodiesel shows higher NOx emission which, when used in increased biodiesel market, may become a serious problem. Various strategies were attempted by different researcher to reduce NOx emissions. In this paper, various strategies, adapted for reducing NOx emissions of biodiesel fuel used in diesel engines for automobile applications, are reviewed and discussed. The strategies are grouped into three major groups, namely combustion treatments, exhaust after-treatments, and fuel treatments. Among various strategies discussed, fuel treatments, such as low temperature combustion, mixing fuel additives and reformulating fuel composition, reduce NOx emission without compromising other emission and performance characteristics and they seem to be promising for future biodiesel fuel.