Low NOx Combustion Research Articles

One approach to temperature distribution control in thermal power plant boilers

ABSTRACTOptimization of the combustion control process in a tangentially fired pulverized coal boiler, to achieve uniform temperature distribution, is discussed in the paper. This issue is even more critical in those thermal power plants which are not equipped with modern systems for combustion enhancement, such as low NOx burners. Research has shown that the temperature distribution inside the boiler of such power plant can be controlled by adjusting firing, through coal redistribution among the mills. Furthermore, disturbed flame symmetry (i.e. non-uniform temperature distribution in the boiler) is reflected in a large difference between the output temperatures measured on the left and right sides of the boiler. Given the non-stationary conditions typical of thermal power plant boilers, an adaptive control approach is proposed, based on PI controllers which are very popular in industry and widely accepted. Self-tuning of the PI controllers is based on dynamic model parameters derived applying the weighted recursive least squares (WRLS) method to real data recorded at Nikola Tesla B thermal power plant in Serbia, whose nominal power is 650 MW. The same model was later used to test the proposed control approach.

Commissioning of a Combined Hot-Streak and Swirl Profile Generator in a Transonic Turbine Test Facility

AbstractBy enhancing the premixing of fuel and air prior to combustion, recently developed lean-burn combustor systems have led to reduced NOx and particulate emissions in gas turbines. Lean-burn combustor exit flows are typically characterized by nonuniformities in total temperature, or so-called hot-streaks, swirling velocity profiles, and high turbulence intensity. While these systems improve combustor performance, the exiting flow-field presents significant challenges to the aerothermal performance of the downstream turbine. This paper presents the commissioning of a new fully annular lean-burn combustor simulator for use in the Oxford Turbine Research Facility (OTRF), a transonic rotating facility capable of matching nondimensional engine conditions. The combustor simulator can deliver engine-representative turbine inlet conditions featuring swirl and hot-streaks either separately or simultaneously. To the best of our knowledge, this simulator is the first of its kind to be implemented in a rotating turbine test facility.The combustor simulator was experimentally commissioned in two stages. The first stage of commissioning experiments was conducted using a bespoke facility exhausting to atmospheric conditions (Hall and Povey, 2015, “Experimental Study of Non-Reacting Low NOx Combustor Simulator for Scaled Turbine Experiments,” ASME Paper No. GT2015-43530.) and included area surveys of the generated temperature and swirl profiles. The survey data confirmed that the simulator performed as designed, reproducing the key features of a lean-burn combustor. However, due to the hot and cold air mixing process occurring at lower Reynolds number in the facility, there was uncertainty concerning the degree to which the measured temperature profile represented that in OTRF. The second stage of commissioning experiments was conducted with the simulator installed in the OTRF. Measurements of the total temperature field at turbine inlet and of the high-pressure (HP) nozzle guide vane (NGV) loading distributions were obtained and compared to measurements with uniform inlet conditions. The experimental survey results were compared to unsteady numerical predictions of the simulator at both atmospheric and OTRF conditions. A high level of agreement was demonstrated, indicating that the Reynolds number effects associated with the change to OTRF conditions were small. Finally, data from the atmospheric test facility and the OTRF were combined with the numerical predictions to provide an inlet boundary condition for numerical simulation of the test turbine stage. The NGV loading measurements show good agreement with the numerical predictions, providing validation of the stage inlet boundary condition imposed. The successful commissioning of the simulator in the OTRF will enable future experimental studies of lean-burn combustor–turbine interaction.

Low NOX combustion mechanism of coke oven gas with excess air coefficient and flue gas recirculation

With the more stringent NOX emission limit from the coking chemical industry, the coking production with only one type of low NOX combustion technologies cannot meet the emission requirement. Thus a new low NOX experimental system was developed with the help of the external flue gas recirculation (FGR) and reasonable excess air coefficient, where the goal is to reduce NOX emission effectively. And an experiment was carried out on the 18 KW coke oven gas (COG) combustion device, and the effects of excess air coefficient, the ratio of flue gas recirculation and air preheating temperature on the combustion characteristics and NOX formation were extensively studied. The results show that there is an important effect of excess air coefficient, ratio of FGR and air preheating temperature on the temperature distribution inside the furnace and the formation of NOX. When the air excess coefficient of 1.2 and an external flue gas recirculation rate of 20% to 25%, the emission of thermal nitrogen oxides can be significantly reduced.

Numerical Study on NOx Emissions of Methane Re-Combustion in a 600 MWe Coal-Fired Boiler

The fuel staging combustion technology is a promising low NOx combustion technology for coal-fired boiler. In order to reduce NOx emissions, the burners of a 600 MWe coal-fired boiler are retrofitted in which methane gas is selected as a secondary fuel for re-combustion. The CFD models of combustion process are built to investigate effects of the methane gasratio on combustion process and NOx emissions. A total of 4 cases are numerically studied, including the pure coal combustion case, the coal combustion with 7.5%, 10%, 12.5% of methane gas re-combustion cases respectively. The results show that the re-combustion of methane can reduce the temperature at primary combustion zone, but increase the temperatures at the re-combustion area and the furnace outlet. The NOx concentration at the furnace outlet reduces with the increasing methane gas ratio. Methane re-combustion can greatly benefit to the NOx emissions reduction.

Performance Analysis of Novel Flue Gas Self-Circulated Burner Based on Low-NOx Combustion

AbstractA new type self-circulating structure for flue gas was designed, with a corresponding low-nitrogen oxides (NOx) burner developed. A three-dimensional finite element model was established, a...

NOx Emission Reduction in Flue Gas of Coal Fired Thermal Power Station and its Control Measures by Secondary Measures

The ever increasing demand for power is mostly met out by electricity produced with the available resources. One such source where generation of power is by making use of the fossil fuel such as coal. Thermal generation using coal accounts for 69% of the total power produced in India. Flue Gases emitted from coal fired thermal stations consists of CO2,(Carbon-di-oxide),SOx (Oxides of Sulphur), NOx (Oxides of Nitrogen), PM (Particulate matter) along with carbonaceous material, soot and Fly ash. These gaseous pollutants are considered as environmental burden which ultimately results in smog formation, formation of acid rain, eutrophication and global warming which has to be controlled and regulated within the permissible limits as stipulated by MOEF &CC (Ministry of Environmental Forest and Climate Change). This project describes about the analysis of reduction of NOx Emission in Flue Gas of Coal fired thermal stations and the measures to control the NOx emission within the permissible limits for the new thermal power plants by treating the flue gas emitted from the stack. The secondary measure to reduce the NOx emission is achieved by treating the flue gas with urea or ammonia which bring about 90% NOx emission reduction. The application of Low Nox Burner with Over Fire Air Technology along with Selective Catalytic Reduction in the new thermal power plant reduce the emission of NOx to a considerable extent and to meet the norms

수소 가스터빈 연소기술 개발 동향 고찰

There is a strong need for carbon-free and low NOx gas turbine power plants. In order to keep up with this global need, major gas turbine manufacturers are making great efforts to develop low NOx combustion technologies that can afford a high fraction of hydrogen. The purpose of this paper is to review the trends of research and development for low NOx hydrogen gas turbines carried out by major gas turbine manufacturers and research institute. Technical issues that should be considered for hydrogen combustion under wide gas turbine operating conditions will be briefly summarized, and then state-of-the-art development status for premixed-type hydrogen gas turbine combustor will be followed.

NOx Emission Analysis in Flue Gas of Coal Fired Thermal Power Station and it’s Control Measure

The growth and development of any country is measured by the electricity generation which paves way for industrialization and mechanization. To meet the ever increasing demand, the best way to generate consistent power is setting up of large thermal power plants. India is rich with coal reserves and is very cheap when compared with other fuels, hence coal is used as the primary fuel for power generation in India. Thermal generation using coal accounts for 65% of the total power produced. Power plants in India uses different qualities of coal, different combustion technologies and operating conditions. Flue Gases emitted from coal fired thermal stations consists of CO2,(Carbon-di-oxide),SOx (Oxides of Sulphur), NOx (Oxides of Nitrogen), PM (Particulate matter) along with carbonaceous material, soot and Fly ash. These gaseous pollutants are considered as environmental burden which ultimately results in smog formation, formation of acid rain, eutrophication and global warming and has to be controlled and regulated to be within the permissible limits as stipulated by MOEF &CC (Ministry of Environmental Forest and Climate Change). This project describes about the analysis of NOx Emission in Flue Gas of Coal fired thermal stations and the measures to control the NOx emission within the permissible limits for the existing thermal power plants by modifying the combustion technology without affecting the power generation. The primary measure to control NOx emission is achieved by in - combustion control by modifying the conventional burner with the Low Nox Burner combined with Over Fire Air which bring about 45-80% NOx emission reduction, which is cost effective and could be implemented with minimum down time for installation. The application of Low Nox Burner with Over Fire Air Technology in the existing thermal power plant has reduced the emission of NOx to a considerable extent and to meet the norms within minimum period without affecting the power generation.

Experimental study on influencing factors of NOx reduction by combining air staging and reagent injection

ABSTRACT This work indicates the functionality of injection reagent combined with air staging, which achieves a better NOx reduction than bare air staging in coal combustion. The key influencing factors of NOx reduction were investigated by experiments on a bench-scale combustion test system. The results showed that the NOx reduction efficiency could be increased by 22.2% compared to bare air staging. The primary stoichiometric ratio SR1 was the key parameter, and the optimum SR1 for NOx reduction by injection was 0.85. There was no benefit for NOx reduction by injection urea in the very fuel-rich zone, but when SR≥1, the injected urea solution at the higher temperature leads to more NOx formation. A higher temperature greatly improved NOx reduction by injection when SR1 was less than 1. It is because that high temperatures were the necessary condition for a greater generation of OH free-radicals, which promoted NOx reduction with NH3 in the absence of oxygen. Therefore, this technology broken through the limitation of narrow temperature window in the traditional technologies with NO reduction by NH3 reagent. Moreover, deeper NOx reduction can be achieved by this technology combined with the existing low NOx combustion technologies.

Large eddy simulation of pulverized coal combustion in multi-burner system–effect of in-furnace blending method on NO emission

Large-eddy simulation (LES) is applied to a multi-burner pulverized coal combustion furnace in which three advanced low-NOx burners, each with a coal combustion capacity of approximately 100 kg/h, are vertically installed. The effects of an in-furnace blending method, in which different types of coal (high-fuel-ratio coal and low-fuel-ratio coal) are injected at each burner stage, on NO emission and unburned carbon fraction in fly ash are investigated. Pulverized Newlands coal and Tanito Harum coal that are classified as high-fuel-ratio coal and low-fuel-ratio coal, respectively, are used as fuels. The results indicate that oxygen is consumed rapidly and NO decreases near the burner from which the high-fuel-ratio coal is injected because the reducing atmosphere becomes dominant owing to the lack of oxygen. Further, the unburned carbon fraction decreases when low-fuel-ratio coal is injected from the upper burner because the residence time is longer for the combustion of high-fuel-ratio coal than when low-fuel-ratio coal is injected from the lower burner.

Effect of Natural Gas Composition on Low Nox Burners Operation in Heavy Duty Gas Turbine

Abstract Development of lean-premixed combustion technology with low emissions and stable operation in an increasingly wide range of operating conditions requires a deep understanding of the mechanisms that affect the combustion performance or even the operability of the entire gas turbine. Due to the relative wide range of natural gas composition supplies and the increased demand from Oil&Gas customers to burn unprocessed gas as well as liquified natural gas (LNG) with notable higher hydrocarbons (C2+) content, the impact on gas turbine operability and combustion related aspects has been matter of several studies. In this paper, results of experimental test campaign of an annular combustor for heavy-duty gas turbine are presented with focus on the effect of fuel composition on both emissions and flame stability. Test campaign involved two different facilities, a full annular combustor rig and a full-scale prototype engine fed with different fuel mixtures of natural gas with small to moderate C2H6 content. Emission trends and blowout for several operating conditions and burner configurations have been analyzed. Modifications to the burner geometry and fuel injection optimization have shown to be able to reach a good tradeoff while keeping low NOx emissions in stable operating conditions for varying fuel composition.

Theoretical Study on the Reactions Originating from Solid Char(N): Radical Preference and Possible Surface N2 Formation Reactions

In this work, density functional theory calculations were performed to study the reactions originating from char(N). This study first provides a clear indication of the radical preference order for char(N). The approaching oxygen inhibits the formation of the N–N bond by attracting electron density from the surface nitrogen. On the contrary, CO is beneficial considering its large partial of the electronic distribution. The structure sensitive energies resulting from the electron difference and steric hindrance give us the indication that NCH3, HNC, NH, and NCO are very important in the reduction of char(N) to N2. Furthermore, our calculations suggest that the exothermic surface desorption by about −233.9 kJ/mol is the dominant reaction for N2 formation. It is expected to be competitive with surface migration. The results will provide reliable data required to predict NOx destruction, which will help in design of the low NOx burner to enable the expanded use of coal in China.

Low-NOx and High-Burnout Combustion Characteristics of a Cascade-Arch-Firing, W-Shaped Flame Furnace: Numerical Simulation on the Effect of Furnace Arch Configuration

A cascade-arch-firing low-NOx and high-burnout configuration (CLHC) was proposed as a solution for the W-shaped flame furnace's incompatibility problem of strengthened low-NOx combustion and high burnout. Numerical simulations verified by industrial-size measurements of a 600 MWe W-shaped flame furnace were used to confirm the CLHC's low-NOx and high-burnout characteristics and evaluate its cascade-arch configuration effect on the gas/particle flow, coal combustion, and NOx formation. The furnace with the existing low-NOx combustion art showed NOx emissions of about 900 mg/m3 at 6% O2 and carbon in fly ash of about 5%. In applying CLHC as a replacement for the prior art, numerical simulations at typical cascade-arch configurations of CL = 1/5, 1/4, and 1/3 (CL signifying the ratio of the lower arch depth to the total arch depth) showed that as CL increased, both the flow field and combustion symmetry initially improved but then deteriorated. In conjunction with the improvement in both NOx emissions and burnout, the CL = 1/4 setting achieved the best furnace performance with NOx emissions 707 mg/m3 at 6% O2 and carbon in fly ash of 5.5%. In comparison with the prior low-NOx art, CLHC reduced further NOx emissions by 22% and almost maintains the burnout rate.

Influence of near-wall air position on the high-temperature corrosion and combustion in a 1000 MWth opposed wall-fired boiler

Low NOx burner together with air-staging system are commonly used in coal-fired power plants in China to reduce NOx emission. However, severe high-temperature corrosion on the water-cooled wall have occurred frequently, because this combustion system result in fuel-rich atmosphere in the main combustion zone and generates a large amount of CO and H2S, which is the main reason for the high-temperature corrosion in the furnace. Near-wall air (NWA) is an economical and effective way to reduce the concentration of CO and H2S. There are two common NWA arrangement, one position is on the side walls, the other is on the front and rear walls. This study numerically investigated the effects of NWA positions on the high-temperature corrosion and combustion of a 1000 MWth opposed wall-fired boiler for better solution of the high-temperature corrosion. The numerical models were validated by the measured data of CO concentration on the side walls. Then the effect of NWA position and NWA ratios (0–1%) on the reducing atmosphere, combustion, and NO generation were numerically studied. The results show that both NWA positions have no effect on the reducing atmosphere and combustion condition when the NWA ratio is lower than 0.5%, but it works when the ratio increase to more than 0.5%. Moreover, it is recommended to arrange NWA on the side walls with the NWA ratio at 1% for better controlling the high-temperature corrosion problems and maintaining good combustion conditions simultaneously, since the concentrations of CO and H2S near side walls were significantly decreased.

110th Anniversary: MILD Combustion of Liquid Hydrocarbon–Alcohol Blends

Among the various low NOx combustion technologies, MILD combustion combines low pollutant emissions, combustion stability and efficiency, fuel flexibility, and noise reduction through a high preheating of the combustion chamber coupled with a massive exhaust gas recirculation at high turbulence level. In this work, the sustainability of MILD combustion for liquid hydrocarbon–alcohol blends (as possible constituents of surrogate fuels representing the behavior of blends of fossil fuels and biofuels) has been investigated experimentally using a dual-nozzle laboratory-scale burner. Several hydrocarbon–alcohol blends have been investigated to identify the regions (in the furnace temperature vs dilution ratio space) where MILD combustion can be sustained with low NOx and CO emissions. It has been found that the MILD combustion conditions of the various liquid fuel blends investigated differ slightly one to each other and are quite similar to that of the hydrocarbons without any oxygenated species. This means t...

Evaluation and comparison of saltation velocity correlations in the context of pulverised fuel transportation

The reduction of harmful emissions is an important issue to be dealt with in coal-fired power stations. There are several technologies that have been successfully applied to modern power stations to reduce the emissions of oxides of sulphur and nitrogen. One such technology is low NOx burners, which employ directed fuel and air staging to create a NOx reduction zone. A requirement for effective operation is to supply these burners with a uniform stream of pulverised fuel (PF). A corequisite is to maintain a homogeneous flow through the pneumatic conveying system without particle settling. PF systems can be analysed and designed using semi-empirical correlations. Some correlations used in predicting settling were developed by Rizk [1], Matsumoto [2][3], Mewing [4], Rose and Duckworth [5], and Thomas [6]. These, however, were based on lab experimentations with pipe diameters and conveying mass flow rates much less than PF transport conditions and predictions show significant variability when the correlations are compared. This work compared the settling velocities predicted by various correlations in literature to an experimental study by Herbreteau and Bouard [7]. Correlations for saltation velocities by Rizk, Thomas and Matsumoto were noted as the more reliable of the correlations evaluated.

Review on Reaction Mechanisms of Sulfur Species During Coal Combustion

Various low-NOx combustion technologies have been widely applied as primary measures to limit NOx emission in coal-fired boilers. However, this leads to the formation of high concentrations of H2S in the fuel-rich zone and thus causes high-temperature corrosion of the water-wall. In order to suppress the formation of H2S near the water-wall, it is necessary to have adequate knowledge of the reaction mechanisms of sulfur species during coal combustion. Therefore, this work systematically reviews the current state-of-the-art concerning reaction mechanisms for sulfur species, including global mechanisms, detailed mechanisms, and reduced mechanisms. Additionally, two operation techniques, namely, near-wall air and multi-hole-wall air, are introduced to avoid high-temperature corrosion caused by H2S. Finally, some new research directions are recommended to further reveal the reaction mechanisms of sulfur species and to test the feasibility of multi-hole-wall air on preventing high-temperature corrosion.

Promising designs of water-heating boilers is great power for centralized heat supply systems.

The article is devoted to the actual theme - an increase of energy efficiency of powerful heating boilers and heat supply stations of centralized heat supply systems of Ukrainian cities, in particular replacing their operational term and physically worn water heat boilers of high capacity.In fact, in high-power boiler-houses of district heating systems of the cities of Ukraine, water-heating boilers of two series - PTVM and KVGM are used. Both types of boilers today do not meet the needs of the market - the requirements of normative documents on the environment and on energy efficiency. In the post-Soviet countries of the Baltic and Eastern Europe, there has been a great deal of experience in modernizing these boilers in order to increase their environmental and thermal performance. In particular, due to the replacement of burners by more than one hour, reduction of their number for boilers of the PTV series, the arrangement of gas-density screen surfaces in boiler furnaces, on-the-spot molding on light fibrous materials, deep automation of boilers operation and equipment with frequency regulators of load-bearing machines. However, if it is necessary to increase the capacity of large boiler-houses, it is inappropriate to use boilers of the types of PTVM and KVGM.In the article reviewed in the technical literature, a large amount of information was analyzed with the results of studies on optimization of the design of powerful steam boilers, in particular, to optimize the design of burners in furnaces. The analysis of this information has shown that it can be used for the design of high-power water heat boilers (from 30 MW to 200 MW).On the basis of information analysis, selected directions of optimization of structures of water-heating boilers of high capacity of the location of burners in the vault or in the subsoil, the use of gas-density screen surfaces, part of which is carried out by two-colored, the use of as few modulated low-NOx burners of high power, deep automation of boilers and boiler-houses in general.The article gives an example of a conceptual design of a 120 MW water boiler using the above principles in comparison with a boiler of the same capacity, which is an upgraded variant of the boiler PTVM-100 capacity of 116 MW. The equation shows that the proposed conceptual design of a water-heating boiler has almost 2.5 times less metal capacity, almost 2 times less than height, which has much more flexibility and wide regulation, which leads to lower cost of the boiler itself and, accordingly, the cost of installation work.

Wall roughness modification of a standard Lagrangian model for the prediction of saltation velocities in gas-solid flows

The reduction of harmful emissions is an important issue in coal fired power stations and a technique used to reduce the emissions of oxides of Sulphur and Nitrogen is low NOx burners. A requirement for effective operation is to supply the burners with a uniform stream of pulverised fuel (PF) without incurring particle settling.A valuable tool in analysing multiphase flows in PF systems are numerical models in the form of Computational Fluid Dynamics (CFD) simulations. Various models can be used to simulate the transportation of particles, the closer the model is to the physics of reality, the more computationally expensive it is. Commercial CFD codes have proven to be valuable in the analysis of multiphase flows. This study evaluates a numerical technique that can offer results that reasonably predict the onset of settling at the most economic computational cost.Numerical models were compared to literature to evaluate ability of the Lagrangian model to predict the onset of settling. The standard Lagrangian model predicted excessive settling of the particle phase because the effects of wall roughness and inter-particle collisions were not accounted for. A wall roughness modification enhanced the particle distribution in the pipe and predicted better pressure drops.

Investigation on high temperature corrosion of water-cooled wall tubes at a 300 MW boiler

Because of the updated requirement on ultra-low NOx emission (<50 mg/Nm3), most of Chinese coal-fired boilers have to be operated at a low NOx combustion mode. However, for high-sulfur coal, water-cooled wall tubes probably suffer severe corrosion in such a strong reduction atmosphere. This work aims to investigate the high temperature corrosion behavior of water-cooled wall tubes inside a 300 MW boiler unit. A short length of corroded water-cooled wall tube was cut down and was analyzed by various characterization methods to further figure out the detailed corrosion mechanism. The typical corrosion products can be distinguished by blue, black and pale-green. Results showed that blue and black color products were mainly consisted of iron sulfides and iron oxides while the pale-green ones were identified as zinc sulfide. Along the radial direction, a layered structure of corrosion products can be observed. The formation of inner layer resulted from the reaction between iron oxide and hydrogen sulfide. The sulfur element displays a gradual increase trend while the Fe element gives out an opposite trend along the radially outward direction. The intermediate layer comes from the fly ash deposition and the outer layer is formed via condensation and deposition of ferrous sulfide gas on the water-cooled wall. The corrosion in this power plant is typical sulfide type for large amounts of Fe and S element were found in the corrosion products.