Low Emission Combustion Research Articles

Разработка и создание отечественного высокоэффективного энергетического оборудования малой мощности

One possible way of achieving more efficient and environmentally friendly use of fuels is to develop domestic high-efficient low-emission power equipment, in particular, compact hot-water boilers in self-contained heat supply systems. Increasing the boiler efficiency entails the need to decrease the flue gas temperature, which, in turn, can be achieved by installing additional heating surfaces. The reliability and environmental safety of boiler operation depends in many respects on burner devices. The aim of this work is to determine the basic design solutions for a 3 MW high-efficient hot water boiler firing crude oil and to develop a modern low-emission burner for it. High-efficient performance of the boiler is achieved by using an external topping economizer, a solution that makes it possible to reduce the boiler sizes, to facilitate the equipment layout within the limited space of a modular boiler house, and almost completely eliminate low-temperature corrosion of the heat transfer surfaces. The study results were used as a basis for designing the structural components of an external economizer arranged above the boiler in a modular boiler house, and for designing a new combined low-emission burner. Both the newly designed economizer and burner have a number of advantages over their foreign analogs and have successfully passed factory tests.

Numerical modelling of retrofitting an industrial boiler type OP-230 for predicting NOx reduction

This study focuses on the indirect co-firing CFD simulations of reductions in NOx emissions relative to the coal combustion. For the given biomass-derived syngas composition and 15% syngas heat input, two arrangements of nozzles dedicated to the syngas injection into the furnace of an older PC-fired boiler of type OP-230 with low-emission burners on the front wall were chosen to investigate the impact of their location on the reduction in NOx emissions. It was shown that the highest reduction achieved by means of the improvement of the air staging via the dual-fuel technique can reach up to 40% (Case 1: nozzles at the elevation of the bottom row of burners) and up to 32% (Case 2: nozzles above the upper level of the burners). The modelling results also showed that one can meet the requirements for co-firing of coal with waste derived syngas. The boiler can be retrofitted for the fulfilment of the prospective environmental protection regulations relating to levels of NOx emissions by combining the described technology with SNCR methods. It is also very important that the indirect co-firing enables reduction of carbon dioxide emissions proportionally to the syngas heat input.

Концепция управления малоэмиссионной камерой сгорания авиационного ГТД и ее эксперт-модель для обучения нейронной сети смарт-регулятора

Концепция управления малоэмиссионной камерой сгорания авиационного ГТД и ее эксперт-модель для обучения нейронной сети смарт-регулятора

Ignition improvement by injector arrangement in a multi-fuel combustor for micro gas turbine

The novel combustor design also has an impact on the ignitor arrangement. The conventional ignitor system cannot guarantee optimal ignition performance in the usual radial position. The difficult ignitability of gaseous fuels was the main challenge for the ignitor system improvement. One way to improve the ignition performance significantly is a torch ignitor system in which the gaseous fuel is directly mixed with a large amount of the combustor air. To reach this goal, the ignition process was investigated in detail. The micro gas turbine (MGT) ignition was optimised considering three main procedures: torch ignitor operation, burner ignition and flame propagation between the neighbour injectors. A successful final result of the chain of ignition procedures depends on multiple aspects of the combustor design. Performed development work shows an important step towards designing modern high-efficiency low-emission combustors.

Low-Emission combustion of fuel in aeroderivative gas turbines

The paper is the first of a planned set of papers devoted to the world experience in development of Low Emission combustors (LEC) for industrial Gas Turbines (GT). The purpose of the article is to summarize and analyze the most successful experience of introducing the principles of low-emission combustion of the so-called “poor” (low fuel concentration in air when the excess air ratio is about 1.9–2.1) well mixed fuelair mixtures in the LEC for GTs and ways to reduce the instability of combustion. The consideration examples are the most successful and widely used aero-derivative GT. The GT development meets problems related to the difference in requirements and operation conditions between the aero, industrial, and power production GT. One of the main problems to be solved is the LEC development to mitigate emissions of the harmful products first of all the Nitrogen oxides NOx. The ways to modify or convert the initial combustors to the LEC are shown. This development may follow location of multiburner mixers within the initial axial envelope dimensions or conversion of circular combustor to the can type one. The most interesting are Natural Gas firing GT without water injection into the operating process or Dry Low emission (DLE) combustors. The current GT efficiency requirement may be satisfied at compressor exit pressure above 3 MPa and Turbine Entry temperature (TET) above 1500°C. The paper describes LEC examples based on the concept of preliminary prepared air–fuel mixtures' combustion. Each combustor employs its own fuel supply control concept based on the fuel flow–power output relation. In the case of multiburner combustors, the burners are started subsequently under a specific scheme. The can type combustors have combustion zones gradually ignited following the GT power change. The combustion noise problem experienced in lean mixtures' combustion is also considered, and the problem solutions are described. The GT test results show wide ranges of stable operation at needed levels of NOx and CO emissions. The world experience analysis and generalization and investigation of the further development directions for the high performance GT will assist development of domestic LEC for prospective GTs.

Increasing the Ecological Efficiency of Combustion Chambers in Gas-Turbine Engines Using Low-Current Plasmochemical Stabilizers

Consideration is given to the numerical experiment carried out using the state-of-the-art tools of computational hydrodynamics to predict the emission level of toxic components at the engine design stage that would allow for a considerable reduction of expenditures required for the engine design and its development and also increase the operation efficiency of power systems. The purpose of this research was to increase the ecological efficiency of the combustion of gaseous fuel in the low-emission combustion chambers of gas turbine engines (GTE) due to the use of low-current plasmochemical stabilizers. The theoretical research done showed that the use of low current plasmochemical stabilizers for low-emission combustion chambers of GTE enables to expand the range of stable operation of the fuel firing device and decrease the emission level of toxic components. Theoretical investigation of pulsation performances of the low-emission combustion chamber with a preliminary mixing of the fuel-&-air mixture of GTE 25 MW allowed us to establish that the plasmochemical stabilization of processes in the combustion chamber would enable an increase in the service life of flue tubes and gas-turbine engines on the whole, getting an economic effect due to the reduction of the emissions of toxic components.

Numerical study of a low emission gas turbine like combustor for turbulent ammonia/air premixed swirl flames with a secondary air injection at high pressure

The present study is dedicated to understand the emission characteristics of turbulent premixed ammonia/air swirl flames in a gas turbine like combustor at high pressure with and without secondary air injection. Ammonia has recently created an attention as a sustainable energy source not only because of its carbon free nature but also owing to its high hydrogen capacity of 17.8% in weight. Thus, in the present study, the effect of pressure on NO, unburnt NH3, and H2 emissions in ammonia/air premixed combustion was discussed by having space and time average emissions (STAE) at the exit of cylindrical combustor for various equivalence ratios and high pressures up to 0.5 MPa. The study found that NO emission decreases with an increase in pressure whereas unburnt NH3 emission in rich flame conditions also decreases with increase in pressure, and the study realizes that, at the equivalence ratio of 1.2, NO and unburnt NH3 emissions are minimal and in the same order of 200 ppm of mole fraction, even though still there is an unburnt H2 emission of 6% volumetric exhaust flow at the operating pressure of 0.5 MPa. Subsequently, secondary air injection system was introduced to the combustor, and eventually, the study realizes a low emission combustor with the STAE of NO in the order of 100 ppm of mole fraction at 16% of O2 concentration and zero NH3 and H2 emissions, at the primary zone equivalence ratio of 1.2.

Experimental Investigation of Spray and Combustion Performances of a Fuel-Staged Low Emission Combustor: Effects of Main Swirl Angle

In order to reduce NOx emissions, modern gas turbines are often equipped with lean-burn combustion systems, where the high-velocity fuel-lean conditions that limit NOx formation in combustors also inhibit the ability of ignition, high altitude relight, and lean combustion stability. To face these issues, internally staged scheme of fuel injection is proposed. Primary and main fuel staging enable fuel distribution control, and multi-injections of main fuel lead to a fast and efficient mixing. A fuel-staged low emission combustor in the framework of lean-burn combustion is developed in the present study, i.e., the central pilot stage for low power conditions is swirl-cup prefilming atomization, the main stage is jet-in-crossflow multi-injection, and a combination of primary and main stage injection is provided for higher power output conditions. In lean-burn combustors, the swirling main air naturally tends to entrain the pilot flame and quench it at low power conditions, which is adverse to the operability specifications, such as ignition, lean blow-out (LBO), and high-altitude relight. In order to investigate the effects of the main swirl angle on combustion performances, the ignition and LBO performances were evaluated in a single dome rectangular combustor. Furthermore, the spray patterns and flow field are characterized by kerosene-planar laser induced fluorescence and particle image velocimetry (PIV) to provide insight into spray and combustion performances. Flow–flow interactions between pilot and main air streams, spray–flow interactions between pilot spray and main air streams, and flame–flow interactions between pilot flame and main air streams are comprehensively analyzed. The entrainment of recirculating main air streams on pilot air streams enhances with the increase of main swirl angle, because of the upward motion and increasing width of main recirculation zone. A small part of droplets are entrained by the recirculating main air streams at periphery of combustor and a majority of droplets concentrate near the centerline of combustor, making that entrainment of recirculating main air streams on pilot spray and quenching effects of recirculating main air streams on pilot flame are slight, and the extinguishing effects can be ignored. The contributions of main swirl strength to improvement of ignition and LBO performances are due to enhancement of air/fuel mixing by strengthening turbulence level in pilot zone.

Identification and thermodynamic analysis of reaction pathways of methylal and OME-n formation

Renewable energy from wind and solar sources is affected by fluctuations which do not correspond to the demand for electrical energy. Storage options are therefore required and also other possibilities of utilizing this power in a future energy system. Fuel synthesis using CO2 from industrial waste gases and hydrogen from electrolysis is an attractive approach. Methylal and higher oxymethylene ethers represent one fuel option due to the low-emission combustion of ethers with their characteristic CO bonds. However, conventional synthesis is an elaborate process because of the large number of intermediate steps. The direct synthesis of methylal and higher oxymethylene ethers would considerably simplify the technical implementation. Here we present a method that considers Gibbs energy in order to analyze the possibilities of direct synthesis from CO2-H2. High operating pressures and influence of the critical states of educt and products on the thermodynamic state parameters of enthalpy and entropy mean that the real gas properties can be modeled by an equation of state. Methylal can be formed with high conversion rates at pressures of 100 bar and temperatures below 373 K. Formation of dimethyl ether as a potential by-product must be suppressed by a suitable catalyst since it is thermodynamically favored.

Development of combined low-emissions burner devices for low-power boilers

Low-power water boilers are widely used for autonomous heat supply in various industries. Firetube and water-tube boilers of domestic and foreign manufacturers are widely represented on the Russian market. However, even Russian boilers are supplied with licensed foreign burner devices, which reduce their competitiveness and complicate operating conditions. A task of developing efficient domestic low-emissions burner devices for low-power boilers is quite acute. A characteristic property of ignition and fuel combustion in such boilers is their flowing in constrained conditions due to small dimensions of combustion chambers and flame tubes. These processes differ significantly from those in open combustion chambers of high-duty power boilers, and they have not been sufficiently studied yet. The goals of this paper are studying the processes of ignition and combustion of gaseous and liquid fuels, heat and mass transfer and NO x emissions in constrained conditions, and the development of a modern combined low-emissions 2.2 MW burner device that provides efficient fuel combustion. A burner device computer model is developed and numerical studies of its operation on different types of fuel in a working load range from 40 to 100% of the nominal are carried out. The main features of ignition and combustion of gaseous and liquid fuels in constrained conditions of the flame tube at nominal and decreased loads are determined, which differ fundamentally from the similar processes in steam boiler furnaces. The influence of the burner devices design and operating conditions on the fuel underburning and NO x formation is determined. Based on the results of the design studies, a design of the new combined low-emissions burner device is proposed, which has several advantages over the prototype.

Modeling and simulation of combustion and detonation by subcritical streamer discharge

We consider the possibilities of combustion and detonation initiation for propane mixtured with air by microwave discharges created by a quasi-optical electromagnetic beam. Comparison of initiation is performed by different types of discharge: spark, streamer, and attached one. The formation theory of streamer discharges is given, the velocity of their propagation and the volume of energy supplies are analyzed. Experiments have been carried out together with calculation of the propane-air mixture ignition by various types of discharges. It is shown that when burning is initiated by a streamer discharge, a multiple increase in the propagation velocity of the flame front and the completeness of the fuel combustion is obtained as compared to a spark discharge with an equal energy contribution. In the prechamber initiation of combustion by igniting a streamer discharge on the inner walls of the quartz tube, a significant acceleration of combustion was obtained up to the rates characteristic for the transition of deflagration to detonation. The results can be applied in the development of multi-volumetric volumetric ignition systems in internal combustion engines, gas turbine engines, low-emission combustion chambers, for combustion in supersonic flow, and in combustion chambers for detonation engines.

Preliminary aerodynamic design methodology for aero engine lean direct injection combustors

ABSTRACTThe Lean Direct Injection (LDI) combustor is one of the low-emissions combustors with great potential in aero-engine applications, especially those with high overall pressure ratio. A preliminary design tool providing basic combustor sizing information and qualitative assessment of performance and emission characteristics of the LDI combustor within a short period of time will be of great value to designers. In this research, the methodology of preliminary aerodynamic design for a second-generation LDI (LDI-2) combustor was explored. A computer code was developed based on this method covering the design of air distribution, combustor sizing, diffuser, dilution holes and swirlers. The NASA correlations for NOxemissions are also embedded in the program in order to estimate the NOx production of the designed LDI combustor. A case study was carried out through the design of an LDI-2 combustor named as CULDI2015 and the comparison with an existing rich-burn, quick-quench, lean-burn combustor operating at identical conditions. It is discovered that the LDI combustor could potentially achieve a reduction in liner length and NOxemissions by 18% and 67%, respectively. A sensitivity study on parameters such as equivalence ratio, dome and passage velocity and fuel staging is performed to investigate the effect of design uncertainties on both preliminary design results and NOxproduction. A summary on the variation of design parameters and their impact is presented. The developed tool is proved to be valuable to preliminarily evaluate the LDI combustor performance and NOxemission at the early design stage.

Experimental and computational investigations of flow dynamics in LPP combustor

ABSTRACTA Lean Premixed Prevaporised (LPP) low-emission combustor with a staged lean combustion technology was developed. In order to study cold-flow dynamics in the LPP combustor, both experimental tests using the particle image velocimetry (PIV) to quantify the flow dynamics and numerical simulation using the commercial software (FLUENT) were conducted, respectively. Numerical results were in good agreement with the experimental data. It is shown from the observation of the results that: there is a Primary Recirculation Zone (PRZ), a Corner Recirculation Zone (CRZ) and a Lip Recirculation Zone (LRZ) in the LPP combustor, and the exchanges of mass, momentum and energy between pilot swirling flow and primary swirling flow are contributed by the velocity gradients, and the shear flow is transformed into a mixing layer exhibiting the higher Reynolds stresses, which suggests the mixing process is strictly affected by the Reynolds stresses.

Development of high-temperature corrosion risk monitoring system in pulverized coal boilers based on reducing conditions identification and CFD simulations

Low-emission combustion (for example the use of low-NOx burners and air staging) contributes to formation of a reducing atmosphere in the furnace, that is accompanied by oxygen depletion and excess of CO in the vicinity (boundary layer) of waterwalls. Corrosion of boiler tubes is often caused by reducing atmosphere. O2 and CO measurement in the boundary layer of evaporators can be a good indicator of corrosion risk assessment. System based on the on-line measurement of the O2 and CO concentration in the boundary layer of the industrial scale boiler walls was described. To improve the functionality of the monitoring system Computational Fluid Dynamics may appear helpful. A validated CFD model capable of properly predicting the CO and O2 concentration in the vicinity of the combustion chamber walls may help to adjust the monitoring system during variable boiler operating conditions or different fuel properties without the necessity to repeat the measurements for new conditions. The scientific part of the current research is concentrated on volatiles combustion simulation with the emphasis on CO burnout. Four popular global mechanisms have been implemented into CFD code and their CO and O2 predictive capabilities are demonstrated. Additionally global mechanisms have been compared to detailed one in Perfectly Stirred Reactor model. It appears that the choice of global mechanism has significant influence on CO and O2 prediction. The measurements of the CO and O2 in the waterwalls boundary layer have been extracted from the monitoring system and compared to simulation results. One of the tested mechanisms demonstrated acceptable qualitative agreement with the measurement in terms of O2 predictions. The quantitative accuracy of CFD-based oxygen prediction in the boundary layer was described as moderate. CFD-based CO prediction was less satisfactory.

Development of Prognostic Tool for High-temperature Corrosion Risk Assessment in Pulverised Coal Boilers Based on the Waterwalls Boundary Layer Monitoring System and CFD Simulations

The implementation of the low-emission combustion techniques for NOx emission reduction often results in the intensification of high-temperature corrosion of the boiler heating surfaces. The corrosion of boiler tubes increases the operational costs and have strong negative effect on the reliability and availability of the whole power unit. Low-emission combustion (for example the use of low-NOx burners and air staging) contributes to formation of a reducing atmosphere in the furnace chamber, that is accompanied by oxygen depletion and excess of CO in the vicinity (boundary layer) of waterwalls. A research has been conducted on the implementation of a monitoring system in the boundary layer of the combustion chamber walls. This system is based on the on-line measurement of the oxygen concentration in the boundary layer of the boiler chamber walls and allows to identify reduction zones and may be useful for preventing intensified corrosion. To improve the functionality of the monitoring system Computational Fluid Dynamics may appear helpful. A validated CFD model capable of properly predicting the CO and O2 concentration in the vicinity of the combustion chamber walls may help to adjust the monitoring system during variable boiler operating conditions or different fuel properties without the necessity to repeat the measurements for new conditions.

Possible mechanism of self-oscillations in a combustor working on a premixed methane/air mixture

The process of combustion of a premixed lean methane/air mixture in the model low-emission combustor is studied. Several known mechanisms of the self-oscillation generation and the flame flashback are analyzed. Numerical LES and SAS calculations of several combustors of typical configurations and regime parameters are presented. Some means of suppressing the flame flashback are proposed and analyzed.

Influence of wood chip quality on emission behaviour in small-scale wood chip boilers

The introduction of wood chips into the market for small-scale heating appliances of below 100 kW has become more challenging due to stricter regulations on emission levels for carbon monoxide and particle emission, e.g. in Germany. Therefore, it is important to identify high wood chip qualities that are suitable for failure-free and low-emission combustion. In this investigation, several wood chip assortments produced from stem wood and forest residues were analysed and combusted in up to two different wood chip boilers with a nominal heat capacity of 50 and 99 kW at full load. Some combustion tests were performed at part load (i.e. 30% heat output). Throughout experiments, the emission behaviour was measured (CO, NOX and total particulate matter (TPM)). In total, seven different wood chip assortments were tested in the large boiler, whereas ten wood chip assortments were combusted in the smaller furnace. Wood chips from stem wood are characterized by lower ash contents (0.27–1.05 w%, d.b.), lower nitrogen contents (0.04–0.14 w%, d.b.) and lower aerosol forming elements (379–1075 mg/kg, d.b.) compared to forest residues (A = 0.58–2.05 w%¸ N = 0.13–0.32 w%, aerosols = 728–2199 mg/kg, d.b.). Combustion of stem wood caused lower emissions compared to forest residues at full-load operation. Overall, part-load operation caused higher CO and particle emissions. In addition, increases of fine woody particles lead to increases in CO emissions. The influence of moisture content was more pronounced especially for CO emissions.

Predictive, adaptive model of PG 9171E gas turbine unit including control algorithms

Contemporary thermal diagnostic systems require computational tools, including mathematical models. Because of required short computation time, these models should have a simple structure. Therefore very often, for these purposes, analytical-empirical models are used. Such models encompass both mass and energy balances and additional empirical functions whose coefficients are estimated by using the measurement results. As a result, changing technical conditions are taken into account. This paper presents a simulation model of PG 9171E gas turbine unit by General Electric which contains partial models of an axial compressor, low-emission combustion chambers, and an axial expander. The unknown values of empirical coefficients were estimated based on the operating data using the least squares method. The simulation model allows the calculation of non-measured operating parameters and energy assessment indicators, e.g. efficiency of electricity production. An important advantage of the developed model is that it has the capability of adapting to the changing technical conditions of the machine. The results of calculations were compared to the results of measurements. Model predictive quality was verified with the use of the determination factor and root mean square error.

Effect of Pressure on NO x Emissions and Combustion Stability in the GT-110 Low-Emission Combustion Chamber1

Results are presented from comprehensive tests of a sample low-emission combustion chamber for a GTU-110M gas turbine at partial (350 kPa) and full (1500 kPa) pressures. Data on the emission characteristics are shown that confirm low emissions of nitrogen oxides and high fuel burnup during operation of the combustion chamber with 50 to 100% load on the gas turbine. The effect of the pressure in the low-emission combustion chamber on the emission characteristics and combustion stability is analyzed. Away of controlling the combustion chamber to obtain the required performance is demonstrated. A comparison and analysis of data obtained with partial and full air parameters confirms that they are identical with respect to the temperatures of the walls of the fire tube and gas collector, and with respect to the temperature distribution and temperature nonuniformities of the flue gases and to the completeness of fuel burnup. Models of the acoustic boundary conditions on a test stand with partial and full parameters are also confirmed.

KESAN SUDUT PUSARAN TERHADAP PEMBENTUKAN EMISI MENGGUNAKAN DWI PEMUSAR UDARA ALIRAN JEJARIAN

Combustion of liquid fuel sprays produces NOX, CO and other emissions that have an adverse impact on the environment and humans. This study is conducted to produce low-emission combustion with the use of double radial swirler. Swirling flow burning will enhance the mixing of fuel and air to produce a flame that is more stable and efficient. In this study, weak swirler with an angle of 30º is set as a primary swirler and strong swirlers each with an angle of 40º, 50º and 60º are set as the secondary swirler. Combinations of these swirlers helped the mixing of fuel and air during combustion. The results show, the combination of swirlers 30º/60º produced the highest temperature profile, the best flames, more stable and shorter than other combinations. NOX emissions for the combination of swirlers 30º/60º at stoichiometric are 15.6% lower than the combinations of swirlers 30º/40º. Other emissions such as CO, also shows 8.4% of reduction in the combination of swirlers 30º/60º. These results indicated that double swirlers helped in reducing emissions during combustion and also producing an environmentally friendly combustion system.