Exit Gas Temperature Research Articles

Numerical study of co-firing lignite and agricultural biomass in utility boiler under variable operation conditions

The co-combustion of biomass and coal in a utility boiler could provide cleaner power production and ensure sustainable utilization of the solid fuels. This paper aims to numerically investigate complex processes in the tangentially-fired 900 MWth boiler furnace during direct co-firing of lignite and biomass with 10% thermal share of agricultural residues (wheat straw, corn straw and soybean straw) under variable boiler loads (100%, 85% and 70%). Simulations are conducted by means of in-house developed computer code, supported by the specially designed user-friendly graphical interface. Co-firing of agricultural residues provides lower pollutant emissions, somewhat higher furnace exit gas temperature and increase in unburnt carbon in bottom/fly ash, compared to the lignite combustion without biomass. Soybean is found to be the most suitable for co-firing regarding its ash melting point, however due to its abundance and availability the wheat straw is selected for this study. Co-combustion at partial boiler loads results in reduction of NOx and SOx up to 34% and 9.5%, respectively. Burners arrangement and furnace aerodynamics affect the abatement of pollutants. This study may help the global efforts in fighting the climate change, efficiently and cost-effectively, thus offering considerable economic and social benefits.

Optimization of operating conditions to achieve combustion stability and reduce NOx emission at half-load for a 550-MW tangentially fired pulverized coal boiler

The off-peak period of the grid load (i.e., deep peak load) prevents a power generation boiler from operating at full load. To achieve stable combustion of 550-MW tangentially fired pulverized coal boiler and ultra-low pollutant emissions (nitrogen oxides and unburned carbon) under half-load conditions, different operating parameters have been analyzed and optimized. In this study, under half-load conditions, the numerical method was used to simulate the flow field characteristics, combustion stability, and pollutant emissions of the boiler under various operating conditions. The operating conditions included various burner group arrangements, close-coupled overfire air (CCOFA)/separated overfire air (SOFA) distributions, and excess air ratios. The simulation prediction results showed that the middle burner group (BCDE) arrangement has a good flow field distribution. Compared with the upper burner group (CDEF) arrangement, this reduces NOX by approximately 62 ppm and also maintains a higher pulverized coal burnout rate than the lower burner group (ABCD) arrangement. Considering the stability of the combustion and lowest emissions, the ratio of CCOFA of 5% and SOFA of 15% were preferred as the operating conditions for the air-staging distribution. The high excess air caused an increase in NOX while the combustion temperature significantly reduced in the furnace, made the furnace exit gas temperature (FEGT) too low, and affected the steam temperature. In addition, the simulation results of the optimized scheme were in good agreement with the field test results.

Prediction of lean blowout performance on variation of combustor inlet area ratio for micro gas turbine combustor

PurposeThis paper aims to predict the effect of combustor inlet area ratio (CIAR) on the lean blowout limit (LBO) of a swirl stabilized can-type micro gas turbine combustor having a thermal capacity of 3 kW.Design/methodology/approachThe blowout limits of the combustor were predicted predominantly from numerical simulations by using the average exit gas temperature (AEGT) method. In this method, the blowout limit is determined from characteristics of the average exit gas temperature of the combustion products for varying equivalence. The CIAR value considered in this study ranges from 0.2 to 0.4 and combustor inlet velocities range from 1.70 to 6.80 m/s.FindingsThe LBO equivalence ratio decreases gradually with an increase in inlet velocity. On the other hand, the LBO equivalence ratio decreases significantly especially at low inlet velocities with a decrease in CIAR. These results were backed by experimental results for a case of CIAR equal to 0.2.Practical implicationsGas turbine combustors are vulnerable to operate on lean equivalence ratios at cruise flight to avoid high thermal stresses. A flame blowout is the main issue faced in lean operations. Based on literature and studies, the combustor lean blowout performance significantly depends on the primary zone mass flow rate. By incorporating variable area snout in the combustor will alter the primary zone mass flow rates by which the combustor will experience extended lean blowout limit characteristics.Originality/valueThis is a first effort to predict the lean blowout performance on the variation of combustor inlet area ratio on gas turbine combustor. This would help to extend the flame stability region for the gas turbine combustor.

Computational and Experimental Analysis of a Compact Combustor Integrated Into a JetCat P90 RXi

Abstract Ultra compact combustors (UCCs) look to reduce the overall combustor length and weight in modern gas turbine engines. Previously, a UCC achieved self-sustained operation at subidle speeds in a JetCat P90 RXi turbine engine with a length savings of 33% relative to the stock combustor. However, that combustor experienced flameout as reactions were pushed out of the primary zone before achieving mass flow rates at the engine's idle condition. A new combustor that utilized a bluff body flame stabilization with a larger combustor volume looked to keep reactions in the primary zone within the same axial dimensions. This design was investigated computationally for generalized flow patterns, pressure losses, exit temperature profiles, and reaction distributions at three engine power conditions. The computational results showed the validity of this new UCC, with a turbine inlet temperature of 1080 K and a pattern factor (PF) of 0.67 at the cruise condition. The combustor was then built and tested in the JetCat P90 RXi with rotating turbomachinery and gaseous propane fuel. The combustor maintained a stable flame from ignition through the 36,000 revolutions per minute idle condition. The engine ran self-sustained from 25,000 to 36,000 revolutions per minute with an average exit gas temperature of 980 K, which is comparable to the stock engine.

An experimental study of an ejector-boosted transcritical R744 refrigeration system including an exergy analysis

The field of refrigeration witness a massive transition in the supermarket with a strong focus reflected on energy consumption. The use of ejector allows for overcoming the significant exergy destruction lays on the expansion processes of the cooling systems and led to spark improvement in the system performance by recovering some of the expansion work. In this study, a detailed experimental work and exergy analysis on the R744 transcritical ejector cooling system was investigated. The experiment was implemented on the commercial ejector cartridge type (032F7045 CTM ELP60 by Danfoss). The impact of different operating conditions determined by exit gas cooler pressure and temperature, evaporation temperature and receiver pressure was examined. The ejector performance of the pressure lift, mass entrainment ratio, work rate recovery and efficiency were evaluated. In addition, exergy efficiency and the variation of exergy produced, consumed, and destruction were assessed based on the transiting exergy. The result revealed better overall performance when the ejector operated at transcritical conditions. The ejector was able to recover up to 36.9% of the available work rate and provide a maximum pressure lift of 9.51 bar. Moreover, it was found out that the overall available work recovery potential increased by rising the gas cooler pressure. Out of the findings, the ejector could deliver maximum exergy efficiency of 23% when working at higher motive nozzle flow temperatures along with providing lower exergy destruction. The experiment results show that the amount of the exergy consumed and destruction were gradually increased with higher gas cooler pressure and, in contrast, decreasing with higher motive nozzle flow temperature.

Integrated mathematical modelling of a 105 t/h biomass fired industrial watertube boiler system with varying fuel moisture content

In this paper, a steady-state 1D computer model of a complete sugarcane bagasse-fired boiler system is presented, which pays special attention to the different heat transfer phenomena encountered in the boiler heat exchangers. The model solves the mass, momentum and energy balance equations for water, flue gas and air streams in an integrated manner which utilizes fundamental equations and empirical correlations for pressure drop, radiative heat transfer and convection. The integrated model is successfully applied to model a 105 t/h industrial watertube boiler at three different load cases namely 100 t/h, 65 t/h and 35 t/h. The model results are validated using typical plant measurements. The mean relative predicted gas temperature errors are 1.47%, 0.58% and 4.84% respectively for the different load cases simulated, and for the water circuit temperature predictions the mean errors are 1.48%, 0.85% and 5.31% respectively. Additionally, a sensitivity analysis is performed on the integrated model, which investigates the influence of selected modelling parameters such as flame height on key boiler output variables such as the furnace exit gas temperature.

Experimental and numerical prediction of lean blowout limits for micro gas turbine combustor

PurposeThe lean blowout (LBO) limit of the combustor is one of the important performance parameters for any gas turbine combustor design. This study aims to predict the LBO limits of an in-house designed swirl stabilized 3kW can-type micro gas turbine combustor.Design/methodology/approachThe experimental prediction of LBO limits was performed on 3kW swirl stabilized combustor fueled with methane for the combustor inlet velocity ranging from 1.70 m/s to 6.80 m/s. The numerical prediction of LBO limits of combustor was performed on two-dimensional axisymmetric model. The blowout limits of combustor were predicted through calculated average exit gas temperature (AEGT) method and compared with experimental predictions.FindingsThe results show that the predicted LBO equivalence ratio decreases gradually with an increase in combustor inlet velocity.Practical implicationsThis LBO limits predictions will use to fix the operating boundary conditions of 3kW can-type micro gas turbine combustor. This methodology will be used in design stage as well as in the testing stage of the combustor.Originality/valueThis is a first effort to predict the LBO limits on micro gas turbine combustor through AEGT method. The maximum uncertainty in LBO limit prediction with AEGT is 6 % in comparison with experimental results.

Modelling the effect of sinter machine speed on bed temperature and coke combustion characteristics in iron ore sintering process

ABSTRACT In the present study, the influence of industrial sinter machine speed on the temperature distribution of the bed is evaluated using a one-dimensional transient mathematical model. The model is developed considering the law of conservation of mass, momentum, and energy of solid and gas phases. The prediction of bed temperature from the model is compared with the measured lab scale pot test and the exit gas temperature of an industrial sinter machine wind boxes shows a reliable agreement. The effect of machine speed on the temperature of the bed is quantified using Maximum Temperature, and the coke combustion characteristics are expressed in terms of Duration Time of Coke Combustion and Combustion Zone Thickness. Eventually, the Melting Zone Thickness and melt fraction of the bed is evaluated. This model result demonstrates that the increasing industrial sinter machine speed significantly affects the temperature distribution of the top layer of the sinter bed.

Turbojet Engine Parameters Calculation Based on Fuel Flow and Exhaust Gas Temperature

<div class="section abstract"><div class="htmlview paragraph">The aircraft jet engine is one of the most complex multivariable systems with multiple inputs and multiple outputs. To attempt to optimize control functions or to address diagnostic problems, a detailed knowledge of all jet engine design parameters and performances is required. Although jet engines have been around for almost a century, there are only a few companies in the world presently designing and manufacturing them; as such these companies possess detailed knowledge of all relevant design characteristics and performance parameters. In the event where jet engine technical details are unknown, or only a few of them are known from manufacturer’s catalogues, the challenge becomes how to calculate and extrapolate critical performance parameters based on only fuel flow, jet exhaust temperature and total thrust. The brief engineering concept of calculation steps presented herein has the goal of identifying unknown turbojet engine parameters and design characteristics based on limited measurements and test data obtained at static conditions and single operating point. Test data included steady state fuel flow, turbine gas exit temperature and total jet engine thrust. For the purpose of jet engine parameters estimate and identification, the Rolls-Royce VIPER 11 Mk 22-6 jet engine was used. Calculated and estimated jet engine design parameters were evaluated and compared with measured parameters under the same initial conditions. The results show that calculation and identification processes are accurate with an overall error of less than 1 percent. The presented numeric algorithm combined with off design parameters calculation, can be used in jet engine health monitoring and fault detection processes.</div></div>

CFD Modeling to Analyze Palm Shell Co-firing Percentage on Ketapang CFB Power Plant

Biomass is one of the world’s greatest sustainable energy potentials. Utilization of biomass in the form of Co-firing coal fuel with biomass is one alternative to reduce the dependence of fossil fuels towards green power plant. This paper addresses Co-Firing modelling test results up to 50% biomass using palm kernel shell (palm kernel shell) in Ketapang Coal Fired Power Plant (CFPP) 2x10 MW. Ketapang CFPP has circulating fluidized bed (CFB) boiler. There are several advantages by using direct co-firing in CFB boiler: direct co-firing has the lowest investment cost, CFB has a wider range of biomass selection characteristics and characteristics than PC Boilers, CFB can process biomass materials with higher moisture content, etc. Result shown that the optimum percentage of palm kernel shell biomass use in the Ketapang Power Plant is 30% palm kernel shell. This is caused by the temperature value at 18 cm above the furnace bed and furnace exit gas temperature of 30% palm kernel shell which is not too much different from the temperature value at 18 cm above the bed furnace and furnace exit gas temperature of 0% palm kernel shell. This is also strengthened by the high value of the CO2 mass fraction in the 30% palm kernel shell mixture, which indicates that an ideal combustion.

Co-firing characteristics of wood pellets on pulverized coal power plant

Co-firing testing of the wood pellets was carried out in Pulverized Coal Boiler type tangential firing with a capacity of 315 MWe to determine the effects on the performance, emission, and characteristics of the operational boiler parameters such as mill outlet temperature (MOT) and furnace exit gas temperature (FEGT). Fuel was mixed on stockpile with a fuel composition of 5 % wood pellets and 95 % coal. Fuel was initially filled in four bunkers for each mill operated. The co-firing testing was carried in six hours and the data was collected for four hours after the stabilization period. To observe the further impact on the performance, emission and characteristics of operational boiler parameters, two different fuel (100 % coal fuel and 5 % wood pellet – 95 % coal fuel) were set up through the boiler. The result shows that co-firing by 5 % of wood pellets contributed to the decreasing FEGT by 15 °C from 1,192 °C to 1,177 °C equal to 1.27 % lower than the existing condition. The mill outlet temperature is relatively the same for two types of fuel with mill current slightly increasing by 0.70 Ampere. Emissions of SOx increased by range from 8.22 % to 20.51 %. NOx content in flue gas on the air heater inlet side is almost the same of 310 mg/Nm3 and only an increase of 3.62 % on the air heater outlet side. This test also affected specific fuel consumption which has increased by 4.40 % from 0.556 kg/kWh to 0.580 kg/kWh.

Performance prediction of the tangentially fired pulverised-Coal boiler furnace using a mathematical model and its validation

ABSTRACT A simple thermodynamic model is developed for performance prediction for a tangentially fired pulverized-coal boiler furnace. For this purpose, the furnace is sliced into number of zones of rectangular parallelepiped. These zones are further divided into heat release zones and non-heat release zones. The major sub-routines of the program include framing equations for the definition of the heat release zones, a reasonably approximate flow model to simulate tangential firing, radiation formulation and equations for the calculation of emissivity of CO2 and H2O. A few of the inputs required for this model have been obtained from offline-CFD simulations. The solution for the model’s equations is obtained using the Newton Raphson method. The outputs of the program include the variation of the heat flux along with the height of the boiler furnace and furnace exit gas temperature (FEGT). The influence of operating conditions on the furnace in terms of its performance is also studied. The FEGT predicted using the mathematical model is in fairly good agreement with the site measured data. The model can be used as an effective tool by powerplant operators to optimize the performance of the boiler furnace.

Effect of different turbulence model on prediction of lean blowout limit for micro gas turbine combustor

ABSTRACT This paper aims to present turbulence modelling results of methane/air combustion in a micro gas turbine combustor. Modelling studies were carried out with different turbulence models to evaluate Lean Blowout (LBO) performance on the micro gas turbine combustion chamber by using a commercially available computational fluid dynamics code. Turbulence models implemented in this study are k-epsilon standard, k-epsilon RNG, K-epsilon realisable, k-omega standard, and k-omega SST. A two-dimensional axisymmetric 3 kW swirl stabilised micro gas turbine combustor model was built to investigate the impact of various turbulence models on the prediction of LBO behaviour of the combustor fuelled with methane. Performance evaluation of these models was executed by calculating the average exit gas temperature (AEGT) that have been used for predicting the blowout conditions. Results obtained from this study were validated with experimental results. Numerical results showed that two-equation turbulence models give consistent simulation results with experimental results employing trend and value. Standard k-epsilon was found to give consistent simulation results with experimental data.

Catalytic Decomposition of Nitrous Oxide for Use in Hybrid Rocket Motors

In recent years, there has been significantly increased interest in using nitrous oxide as an oxidizer in hybrid rocket motor systems. The attraction of nitrous oxide is its low relative toxicity and high vapor pressure, potentially enabling self-pressurizing systems. Its decomposition is highly exothermic with a large energy barrier, typically requiring high temperature (700°C) to achieve appreciable decomposition rates. One solution is to use a catalyst to enable decomposition at significantly lower temperatures. This Paper uses a commercially available rhodium-based catalyst in a custom test cell to decompose nitrous oxide at temperatures well below the uncatalyzed self-sustaining decomposition temperature. This Paper also demonstrates that decomposition using the tested catalyst is direct to and at all temperature ranges observed and is incomplete with residual present at lower temperatures. Further, this Paper couples our test cell with a counterflow burner to ignite and burn hydroxyl-terminated polybutadiene fuel with the decomposed nitrous oxide and evaluate performance via fuel regression rate at a variety of conditions. The fuel autoignites when the gas exit temperature reaches 750°C, and regression rate is shown to increase with both mass flux and temperature.

Optimization of separated overfire air to reduce NOX emissions under combustion stability for the retrofit of a 500 MW tangentially pulverized coal boiler

Retrofitting of an aging 500 MW tangential coal-fired boiler with high pollutant emissions in South Korea was investigated to achieve low nitrogen oxide (NOX) emissions and high combustion efficiency. This study evaluated and analyzed the combustion and emission characteristics of five arrangements to optimize the position and direction of a separated overfire air (SOFA) installation using a computational fluid dynamics (CFD) simulation. The results show that the air injection of SOFA at the center of the boiler wall causes substantial obstruction of the rising airflow below, causing unstable combustion behavior in the boiler, and increasing the amount of unburned carbon (UBC). However, combining the wall injection with corner SOFA helps reduce the formation of NOX and has the effect of promoting the burnout of UBC. For the direction of the wall injection under combined conditions, a clockwise airflow helps to reduce the formation of NOX with increasing UBC. Otherwise, the counter-clockwise airflow weakens the flow rate of the ascending airflow, increasing the residence time of unburned particles, increasing the coal burnout rate, and increasing the furnace exit gas temperature (FEGT). Among the five SOFA arrangements studies, this study recommends Case 4, which has a clockwise wall SOFA (30%) with corner SOFA (70%). This case has the best performance in terms of combustibility, NOX emission, UBC, and FEGT. The proposed condition was verified through a field test, and the results indicate that NOX emissions decreased from 169 ppm to 57 ppm, the UBC content decreased from 3.64% to 0.7%, and the boiler efficiency increased by 2%.

Assessment of Combustion and Gasification Behavior in a Bubbling Fluidized Bed Reactor: A Comparison between Biomass with and without Chemical Additives

During the storage of biogenic materials for energy utilization, destructions by microbial attacks are inevitable. Besides material degradation, self-ignition of wood chip piles also occurs consistently. Treating the feedstock with, for example, mineral additives such as Dolomite can inhibit the microbial destructions, though such treatment may affect the thermochemical conversion of the fuel particles. This study therefore demonstrates the effect of mixing 4 wt % calcium hydroxide with wood chips used as feedstock in a 20 kW (fuel input) bubbling fluidized bed reactor. The reactor consists of a 100 mm (inner diameter) cylindrical column with 1.0 m height, where both gasification and combustion modes can be applied. Six different tests within equivalence ratios of 0.1–1.1 are conducted, and in each run, both fluidization behavior and quality of the product gas at different reaction temperatures (750–900 °C) are analyzed and compared with the results from wood chips of the same particle size but without the additive. The results show that there is no significant difference in the product gas composition, but evidence shows that the chemical additive impacts on the bed pressure drop over the equivalence ratio tested. The gasification window is increased and the energy value of the product gas is higher with a lower hydrogen content. During the combustion, both the exit gas temperature and oxygen concentration are lower, suggesting that additional light molecules such as water vapor are released during the conversion of biomass mixed with additive.

Numerical simulation of the heat transfer and NOX emissions in a 660 MW tangentially fired pulverised-coal supercritical boiler

Numerical simulation of the influence of operating conditions of the furnace on its performance characteristics like heat flux distribution, Furnace Exit Gas Temperature (FEGT) and NOx emission levels was performed for a tangentially fired pulverised coal boiler. The results revealed that the FEGT and NOx emission are slightly higher when the top seven coal nozzles are in operation compared to the bottom seven coal nozzles. While the increase in burner tilt led to an increased FEGT, the least NOx emission was obtained for the burner tilt with 0°. The NOx emission started to increase with both increase and decrease in tilt from 0°. In addition, the FEGT and NOx emission were directly and inversely proportional to the percentage of SOFA (Separated OverFire Air) opening respectively. NOx emission was lower by around 7.5% when the air staging was done with the top-most SOFA nozzle instead of the bottom-most SOFA nozzle. However, the FEGT was higher in the former case.

Investigating the effect of high pressure heater elimination on power generation of Shazand power plant

Due to some problem in high pressure (HP) heaters in Shazand steam cycle power plant, sometimes these heaters should be eliminated from the cycle. At his condition, the main concern is keeping the constant value of power generation. The elimination of each heater changes the thermodynamic states in the numerous points of the cycle especially boiler and may put it in a destructive condition. The main goal of this paper is to find the maximum net power in elimination of HP heaters. For this purpose, total cycle is modeled and verified by the experimental data in which a lot of trial and error process has been done for each modeling of the whole cycle and the boiler outlets are required for many times in each cycle simulation. Then, ANN is used as an alternative and fast method for simulation of boiler and consequently the whole cycle. Different set of HP heaters have been eliminated from the cycle and new cycle condition is obtained. Afterwards, two boiler important parameters including metal and furnace exit gas temperatures have been checked at these new conditions. Finally, the cycle could provide 300 MW net power in elimination of HP heaters in each unit.

Online adjustment of Furnace Exit Gas Temperature field using advanced infrared pyrometry: Case study of a 1500 MWth utility boiler

The Furnace Exit Gas Temperature (FEGT) is a key parameter of the combustion process in utility boilers that needs to be accurately monitored, especially in order to increase their load- and fuel-flexibility. However, neither the average FEGT nor its spatial distribution over the boiler cross section can be measured using standard equipment. Advanced pyrometry provides an accurate and efficient way to monitor the FEGT: by combining the signals from several pyrometers installed around the boiler, the FEGT 2D field can be reconstructed. In this paper, we show the results of a measurement campaign carried out on a 1500 MWth boiler using a system comprising 9 infrared pyrometers. Thanks to online adjustments of the combustion air distribution, the FEGT peak initially observed has been reduced by approximately 100oC, and the flame has been recentered.

Influence of burner nozzle configuration, and inlet gas composition on combustion, gas dynamics, temperature and concentration profile in a rotary hearth furnace

ABSTRACT A CDF model for simulating gas dynamics, heat and mass transfer in the freeboard of a pilot-scale Rotary Hearth Furnace (RHF) is developed in conjunction with an independent solid reduction model at the bottom of the hearth. The effect of air-inlet configuration and inlet fuel composition on the fuel requirement, exit gas composition, fluid flow, temperature, and gaseous composition distribution have been investigated using this model. The lower air-inlet tubes orientated at 5° upwards keeping remaining air and fuel tubes horizontal emerged as the most recommended burner configuration. Various alternative fuels categorized in terms of calorific values, demonstrated that the fuel with high calorific value required less fuel and produced less CO2 emission. Interestingly, it was found that for the same calorific value a combination of blast furnace gas and coke oven gas (BF+COG) produced less CO2 emission compared to a combination of COG+BF+NG (Natural gas).