Temperature In Combustion Zone Research Articles

Reduced Pollutant Emissions and Slagging Rate of Biomass Pellet Combustion by Optimizing the Multilayer Distribution of Secondary Air.

The utilization of coal and other fossil fuels is becoming increasingly restricted. Biomass, as a clean and renewable energy, plays a significant role in achieving zero carbon emissions. However, biomass is prone to slagging in the combustion process due to its high alkali metal content. The ash slagging rate and pollutant emission level of flue gas can be reduced by optimizing the air distribution, in order to decrease the fuel layer temperature in the combustion chamber. The results reveal opposite change trends of CO and NOx concentrations in the flue gas. The NOx emissions of corn stalk combustion under the multilayer secondary air distribution are obvious compared with those of rice husk combustion. The slagging rate of corn stalks is highly correlated with temperature T1 of the fuel bed. The silica ratio (G), alkali/acid ratio (B/A), Na content index (Na (index)), and alkaline index (Alc) cannot accurately predict the slagging tendency when temperature T1 changes. Therefore, the modified predictive index (Gt) was proposed to predict the slagging tendency of corn stalks with the combustion zone temperature T1 effectively. The experimental results can contribute to the efficient combustion and low pollutant emissions of biomass.

Thermal operation of superlayer space in Romelt furnace

From the point of metallurgical heat engineering, the Romelt process is promising for processing industrial waste, poor ores and secondary metals without their preliminary preparation and the use of coke. But one of the main disadvantages of this process is high specific consumption of oxygen and fuel for the production of 1 ton of primary metal. The peculiarity of the Romelt process is that the main amount of heat required for implementation of the technological process is supplied to the bubbling layer from the superlayer space due to afterburning of the exhaust gases with technical oxygen. Heat transfer is carried out by a radiation-convective mechanism. Any changes in the afterburning process are possible, if they do not entail an unacceptable change in temperature in combustion zone. In the work, a study was conducted to reduce the specific oxygen consumption per 1 ton of primary metal, based on the data of melting a mixture of blast furnace and converter slurries for pig iron. The authors studied the possibility of reducing the specific oxygen consumption supplied to the superlayer space of the furnace for afterburning gases leaving the bubbling layer during the Romelt process. When using blast heating supplied to the lower tuyeres and oxygen heating supplied to the afterburning zone, it is possible to reduce the specific oxygen consumption per 1 ton of cast iron by 11 % without reducing the furnace performance. In the afterburning zone, it is recommended to use oxygen heated up to 400 °C in the recuperator with simultaneous supply of a blast heated up to 600 °C to the lower tuyeres.

Performance improvement of biomass combustion-basedstove byimplementing internally air-distribution

This research aimed to enhance the performance of biomass combustion-based stove. Thermal performances were assessed in terms of power output (Pout), specific fuel consumption (SFC), thermal efficiency (ηth), and burning rate (BR). These performances were expected to meet the minimum standards established by the Indonesian biomass stove alliance regarding the use of a healthy and energy-saving of biomass stove in Indonesia. The stove tested was an improved stove with an advantage on the air distributor by adding a component to administrate air combustion needed placed on the centre of the combustion zones. This is a very effective way to distribute air for combustion required where the air could reach all the fuel and the combustion product that occupy entire the combustion zones to ensure high combustion zone temperature. Coconut shell was used as feedstock. This biomass was found abundant in Indonesia and was widely used as heat source by burning it directly. The coconut shell was sized uniformly about 5 cm x 5 cm, dried by utilizing sun energy. To estimate the stove performances, several combustion tests was carried out where the air flow rate into the stove (Qa) and the amount of biomass fuel (mb) referred as the air–fuel ratio (A/F) were considered. The Water Boiling Test (WBT) was performed to assess this improved stove. Parameter required such as initial mass of coconut shell, the mass of residual ash, the initial mass of water, mass of water after boiling, and the time required to boil as well as combustion flame temperature were recorded and used to determine the performance of the improved stove studied.

Investigation of aging induced processes on thermo-kinetic and combustion characteristics of tungsten pyrotechnic delay composition

A degradation in performance parameters related to thermal decomposition and combustion behaviour of tungsten based pyrotechnic delay composition can occur when subjected to accelerated aging conditions in a controlled environment. The present study utilizes various methods to quantify the extent of degradation in thermo-kinetic and burning characteristics as well as to postulate a fundamental aging mechanism for traditional tungsten (W) pyrotechnic delay material, which has not been attempted in the past. The delay composition based on metallic fuel (W) and perchlorate oxidizer is subjected to aging at constant temperature of 71 °C and 95% relative humidity, for 2 and 12 weeks, respectively. Experiments including thermal analysis, combustion temperature profile and burning rate measurements are conducted together with numerical simulation of an actual pyrotechnic delay device. Moreover, the reaction mechanism, chemical kinetics, and combustion behaviour between pristine and aged cases are examined. Results illustrate that there exist two aging induced processes, which increases the presence of large agglomerated particles, high metal oxide content by thickening the outer oxide layer of metallic fuel, and more unreacted oxygen to instigate incomplete combustion in aged samples. This alters the reaction pathway of combustion process, lowers average thermal conductivity, and reduces diffusion of reactants in aged samples, thus causing significant decrement in the heat of reaction (31%), combustion zone temperature (10%), reactivity (12%), and burning rates (10%), such that the overall pyrotechnic delay device experiences misfiring during operation or a failure in accomplishing its actual intended task.

Effect of H2 enrichment ratio and N2/CO2 dilution on swirl-stabilized partially premixed H2/CH4/C3H8 SNG combustion

This paper discusses the N2 and CO2 dilution effects and H2 enrichment ratio of H2/CH4/C3H8 synthetic natural gas (SNG). As H2 enrichment ratio increases, the dump plane temperature and the combustion zone temperature increase because of shortened length of H2 flame. Even with a shorter flame length and a narrower chemical reaction regime, NOx emissions increase at same heat load because energy density is inversely proportional to flame length. As the CO2 diluent has a higher specific heat than the N2 diluent, the flame temperature is more greatly reduced by the effect of diluent heat capacity. Even a small amount of CO2 dilution can effectively reduce NOx emissions. The H2 enrichment ratio increases the OH radicals in the flame due to the increase in flame temperature. In addition, the burning velocity increases because the reaction rate in the flame increases, resulting in a decrease in flame length. NOx emissions increase exponentially with respect to global OH∗ chemiluminescence intensity per heat load, and these fit well into a single line. The results show that N2 and CO2 diluents can be used in SNG turbine combustors to control NOx emissions and that the H2 enrichment ratio in SNG.

Determination of the propagation state of the combustion zone during in-situ combustion by dimensionless numbers

Ensuring the sustainable propagation of the combustion zone is a prerequisite for in-situ combustion (ISC). The combustion zone propagation processes with different gas injection parameters and reservoir properties were simulated with CMG STARS and a method of determining the propagation state was proposed based on the theoretical analysis of the simulation results. The simulation results of 67 cases with different gas injection parameters and reservoir properties show that there are three states of combustion zone propagation: the sustainable state, the declined state and the extinguished state. The temperature of the combustion zone shows a good correlation with the state of the combustion zone propagation. With increases in the gas injection rate, oxygen concentration, and oil saturation and decrease in the rock permeability, the combustion zone temperature increases and the propagation state changes from the extinguished or declined state to the sustainable state. Analysis of the nondimensionalized energy conservation equation shows that the combustion zone temperature is determined by the two dimensionless numbers HD and CW with the determined core property and domain. A diagram for determining the time-averaged temperature of the combustion zone using the HD and CW numbers was established, with relative deviations within 7%. The combustion zone propagation state under the combination conditions of the gas injection rate, oxygen concentration, oil saturation and reservoir permeability can be judged according to the predicted combustion zone temperature. The proposed method helps optimize the design of gas injection parameters in combustion tube tests and ISC oilfield applications.

Effect of reservoir pay thickness on the performance of the THAI heavy oil and bitumen upgrading and production process

The increasing energy demand has to be met while we transitioned to a decarbonized energy future. Heavy oil and bitumen reserves are urgently needed to be developed to ensure that a smooth transition is provided. In this work, field-scale kinetics parameters are used to study the effect of reservoir pay thickness on the performance of toe-to-heel air injection (THAI) process. Air was injected at constant rate into three different models with the thicknesses of 24 m, 16 m, and 8 m, respectively. The oil produced is slightly affected by the reservoir thickness. It is found that the lower the reservoir thickness, the larger the cumulative air-to-oil ratio (cAOR), indicating that heat loss increases with the decrease in the reservoir thickness. This trend is similar to steam-based processes. At constant air injection flux, it is found that both the cumulative oil produced and the cAOR decrease with the decrease in the reservoir thicknesses. This decrease is attributed to the decrease in the rate of heat generation in the thinner reservoirs, which in turn results in lower combustion zone temperature and thus lower temperature gradients between the reservoir and the overburden and the reservoir and the underburden. Consequently, a more general conclusion is that decreasing the air injection rate by the same factor the reservoir thickness is decreased (i.e. keeping the air injection flux constant) results in a more economical THAI process operation compared to when the air injection rate is kept constant (i.e. allowing increase in air injection flux).

Development of information modeling system of coal-dust fuel injection into tuyeres of blast furnace

The article considers a mathematical model of combustion zone of blast furnace working with the use of injection of coal-dust fuel. In this model, two subsystems were identified: 1) subsystem of heating the particles of coal dust and volatiles release in the combustion zone; 2) subsystem of heat exchange and combustion processes in the tuyere. A two-dimensional velocity field of gas in the combustion zone was investigated. The combustion processes are considered as a set of simultaneously developing phenomena of coke burning in a layer, single pieces of coke and particles of coal dust. The model includes following equations: total gas mass balance, gas component mass balance, gas heat balance, movement of coal dust particles and heat balance of coal dust particles. The model calculates maximum burning temperature in combustion zone; the distance from the cut of the tuyere to the focus of combustion; the length of the oxygen combustion zone; gas temperature; the content of gas phase components and the degree of carbon burnout of pulverized coal at the outlet of the tuyere combustion zone. Information-modeling system has been developed. It allows investigation of influence of combined blast characteristics, the properties of coke and coal-dust fuel, the geometric dimensions of tuyeres and other factors on temperature fields and concentrations of components of gas phase in combustion zone. The model also helps to select a rational mode of pulverized coal that will ensure completeness of its combustion in the tuyere combustion zone. Main functions of the program are as follows: representation of results of calculation in form of tables and diagrams, storage of options of basic data in a database and export of results of calculation to Microsoft Excel. Conclusions were made on reduction of combustion temperature in combustion zone and the approach of focus of combustion to the tuyere when pulverized coal was injected. The authors also have established the need to use coals with certain quality characteristics and place where coal dust was introduced into the blast stream.

Influence of injection mode on the combustion characteristics of slight temperature rise combustion in gas turbine combustor with cavity

Interstage turbine combustors can be used to improve the thrust-to-weight ratio of gas turbines, but their operating conditions and technical requirements are obviously different from those of traditional gas turbine combustors. A typical feature of these combustors is the slight temperature rise combustion under the high velocity conditions of combustor inlets. In this study, a new type of interstage turbine combustor with high performance was proposed, and the influence of the injection mode on the combustion characteristics was investigated. Seven combustion modes with a trapped-vortex combustion zone and preheated fuel nozzles were designed. The effects of the average temperature of the combustion zone (changed by the air injection mode) and the combustion-zone temperature distribution (changed by the combustion-zone configuration) on the combustion characteristics, including the stable combustion boundary, the combustion efficiency, and the temperature distribution, were studied experimentally and numerically. The results showed that high-efficiency combustion in a wide, stable working range was achieved. The new combustor had a shorter length than the conventional combustor and had a wider lean blowout boundary compared to the same type of combustor. Based on the results, the optimal combustor configuration that could be used for practical applications in high-efficiency gas turbines was determined.

Influence of coke content on sintering process of chromium-containing vanadium-titanium magnetite

The sintering of chromium-containing vanadium-titanium magnetite using different coke contents was studied through the sintering pot tests, X-ray diffraction analysis and mineralogical phase analysis. Results showed that, as the coke content increased from 3.2% to 4.4%, the liquid phase and combustion zone thickness increased while the vertical sintering rate and ratio of sintered product decreased. In addition, the combustion ratio of exhaust gas also increased with increasing the coke content, indicating that combustion zone temperature also increased, and the excessive the coke content in the sintering process of vanadiumtitanium magnetite is harmful. As the coke content increased, the magnetite, silicates, and perovskite contents of the sintered ore increased while the contents of hematite and calcium ferrite of sintered ore decreased; drum strength decreased, and reduction degradation properties increased while reduction ability decreased. We found that the appropriate coke content for the sintering process is 3.6 wt%.

2D CFD numerička simulacija fluidizacione komore sagorevanja bazirane na Euler-Euler granularnom modelu

U radu je predložen dvodimenzijski model numeričke simulacije sagorevanja tečnih goriva u flu-idizovanom sloju, koji se zasniva na dvo fluidnom Euler – Euler pristupom modeliranja fluidizovanog sloja uz određivanje polja brzina gasa i čestica u dvofaznim, granularnim tokovima zasnovane na ana-logiji sa kinetičkom teorijom gasova (KTGF). Sveobuhvatan model kompleksnih procesa u fluidizacio-noj komori sagorevanja podrazumeva, pored određivanja polja brzina gasne i čestične faze, inkorpori-ranje energetskih jednačina gasne i čestične faze, kao i transportnih jednačina hemijskih komponenti sa izvornim članovima usled konverzije komponenata. Brojni numerički eksperimenti pokazuju da je izbor koeficijenata u izrazima za sile trenja prilikom interakcije faza ima izuzetan značaj i mora se sprovesti za svaki, značajno različit režim fluidizacije, posebno. Urađene su serije numeričkih eksperi-menata sa simulacijom procesa sagorevanja u FS sa i bez značajnog sadržaja vode u gorivu. Proračuni su nestacionarni, a modelirani vremenski period odgovara vremenu za koje gas prođe kroz celu visinu reaktora. Numerički eksperimenti, na osnovu predloženog matematičkog modela, su takođe korišćeni za potrebe analize uticaja različitih snaga pri kojima radi reaktor, kao i različitih stepena fluidizacije, na efikasnost sagorevanja kao i na profile temperatura u zoni sagorevanja.

Effects of nitrogen dilution on the NOx and CO emission of H2/CO/CH4 syngases in a partially-premixed gas turbine model combustor

In this study, the nitrogen dilution effect in H2/CO/CH4 syngas flames on the characteristics of NOx and CO emissions were investigated in a partially premixed gas turbine model combustor. Nitrogen was diluted into the fuel side and combustor liner temperature, and the flame structures were observed in order to find information that was critical for analyzing the results of the NOx and CO emissions. The addition of nonflammable N2 was effective in decreasing the combustion temperature, which was attributed to the reduction in the reaction rate of syngas oxidation as well as the increase in the overall heat capacity of the air-fuel mixture at a constant heat input. NOx suppression was successfully achieved up to the one digit ppmv level for all heat input and all fuel composition by the 60%-fuel side dilution of nitrogen. However, increases in nitrogen dilution increased the possibility of CO emission; therefore, extremely high CO was emitted in a 100%-CO flame at a low load with 60%-nitrogen dilution reaching 10,000 ppmv. The dilution of nitrogen in syngas considerably changed the flame structure, such as flame length, thickness, angle, location, and intensity. These flame structures provided valuable clues for the analysis of the NOx and CO emission results in relation to the flame temperature results. Based on the integration of the test results, a cause-and-effect diagram of NOx and CO emissions was plotted, and the root causes of NOx suppression were determined to be the decreases in both temperature and residence time in the hot combustion zone, and the critical path of these root causes was clarified. Although the nitrogen dilution technique has been investigated in detail, and the effects are fully understood, the careful monitoring of CO and flame detachment from the fuel nozzle is recommended when applying the nitrogen dilution technique to reduce NOx emission, especially in cases of low load operation. A practical dataset was collected from the combustion test at gas turbine relevant conditions for a wide range of fuel compositions. These results and the knowledge gained from this study could be usefully applied for the environmentally friendly and safe operation of integrated gasification combined cycle and synthetic natural gas firing gas turbine power plants.

Combustion of lean methane–air mixtures in monolith beds: Kinetic studies in low and high temperatures

The paper summarizes results of Gosiewski et al. (2009), Pawlaczyk and Gosiewski (2013) and Pawlaczyk (2013) kinetic studies of non-catalytic (thermal) combustion of lean methane–air mixtures, carried out in a low and high temperature, in monolith bed and compared with similar results for a free space. The study reveals an influence of size, type of monolith’s surface and temperature in combustion zone on the reaction mechanism and its kinetics. It was formulated a hypothesis that the share of combustion type: heterogeneous with surface effect (on the monolith’s wall) and homogeneous (in the free space) depends on the temperature in the combustion zone. The appropriate kinetic equations were estimated. Moreover the paper presents corrected values of kinetic parameters which in contrast to Gosiewski et al. (2009) and Pawlaczyk and Gosiewski (2013) were estimated using concentrations of components related to actual gas volume in the combustion zone.

A Novel Approach for Utilization of Ultra-Fines Iron Ore in Sintering Process

The current study presents a novel approach for the utilization of ultra-fines iron ore (−0.2 mm) in sintering process through its conversion into mini-pellets (4–9 mm). The mini-pellets were composed of ultra-fine iron ore and calcium hydrate while coke fines were used as a coating layer. One part of mini-pellets was cured with CO2 to improve the strength of green pellets while another part was kept uncured. The trails were carried out in sinter pot after adjusting the operating parameters. The utilization of 30% cured mini-pellets was accompanied by the constant highest temperature (≈1400 °C) in combustion zone. On the contrary, the sinter prepared using 30% uncured mini-pellets showed the highest temperature (≈1471 °C) at the beginning of sintering process followed by a gradual decreasing in the temperature. The permeability of sinter bed was improved by using cured mini-pellets in the sinter mixture. The sinter indices including the product yield, tumbler index and fuel consumption are measured. Reflected light microscopy, scanning electron microscopy, and X-ray diffraction analysis were used to characterize the microstructure and the developed phases.

Study on one-dimensional steady combustion of highly densified biomass briquette (bio-coke) in air flow

Combustion experiments on cylindrical bio-coke (BIC), a highly densified biomass briquette, have been conducted to observe whether quasi-one-dimensional steady combustion can be attained in room temperature air flow. In the experiments, the air flow velocity was the main test condition and the fuel consumption rate when the bottom surface of the BIC sample burned was evaluated as the regression rate of the combustion zone at the bottom surface. In addition, one-dimensional calculations based on an energy equation at the combustion zone were conducted to understand the mechanism that results in steady combustion and predict the effect of water and volatile matter content in BIC on the extinction limit. The results showed that steady combustion of the BIC sample could be attained in 4.67m/s or more, and, in contrast, extinction was observed in 3.82m/s or less. The critical regression rate explained by the combustion zone temperature was shown, and the reason combustion becomes unsteady could be explained by the energy balance at the combustion zone. Though the main reason for extinction was radiation heat loss, the heat loss by water and volatile matter was not negligible. Therefore, the effect of water and volatile matter content on steady combustion must be considered.

Fuel prereforming and combustion characteristics study of chemically recuperated gas turbine

The chemically recuperated gas turbine cycle testing platform was designed and built based on theoretical research and experimental study, which included the dual-stage flash evaporation, the diesel steam reformer, and the dual-fuel combustion system. In this paper, an experimental study on the oil (C7H16) prereforming performance is analyzed and the relative increment of the equivalent calorific value is 46.2%. Combustion characteristics are calculated with oil and reformed gas and the results show that main combustion zone temperature drops from 2280 to 1910 K, which leads the ultra-low NO emissions of 1.8 ppm. The flame is stable using reformed gas and the wall temperature is low, but the nonuniformity of outlet is relatively high. Thermal efficiency of combustion is more than 99% even at low load condition.

Experimental evaluation of a 35 kVA downdraft gasifier

Energy conversion systems based on biomass are particularly interesting because biomass utilization effectively closes the carbon cycle besides achieving self-sustainability. Biomass is particularly useful for highly populated and agriculture dependent economic nations like China and India. A compact and cost effective downdraft gasification system was developed. The present paper describes an experimental investigation on a biomass based gasifier engine system with a capacity of 35 kVA for power generation application. The problem of cooling and cleaning the hot and dirty gas from the gasifier has been satisfactorily solved by the effective cooling and filtration system. The gasifier developed is observed to be operation friendly. The quality of gas was evaluated in terms of its composition, conversion efficiency and total particulate matter. The maximum output of the power plant was obtained at the combustion zone temperature of 850°C. The experimental investigations showed that the percentage reduction in total particulate matter is 89.32%. The conversion efficiency of the biomass gasifier is found to be dependent on the operation conditions and fuel properties of the gasifier. The optimum value of equivalence ratio was observed to be 0.3134 for achieving the maximum gas conversion efficiency of the present gasifier configuration.

Fire-flooding technologies in post-steam-injected heavy oil reservoirs

Abstract The mechanism and problems associated with development engineering of fire-flooding in post-steam-injected heavy oil reservoirs was studied using 1D & 3D physical simulation experiments and reservoir numerical simulation. The temperature of combustion zone decreased and high-temperature zone enlarged because there existed secondary water formed during steam injection, which could absorb and carry heat towards producers out of the combustion front during fire flooding, but high saturation of water in layers caused by secondary water had less influence on the quantity of fuel deposit and air consumption. In the process of 3D fire flooding experiment, air override was observed during the combustion front moving forward and resulted in a coke zone in the bottom of the layer, and the ultimate recovery factor reached 65% on fact that the remaining oil saturation within the coke zone was no more than 20%. The flooding model, well pattern, well spacing, and air injection rate were optimized according to the specific property and the existed well pattern in the post-steam-injected heavy oil reservoir, and the key techniques of ignition, lifting, and anticorrosion was also selected at the same time. The pilot of fire flooding in the H1 block in the Xinjiang Oilfield was carried out from 2009 based on these research works, and now begins to show better performance.

Gasification characteristics of woody biomass in the packed bed reactor

Gasification technology is recognized as one of the possibilities for utilizing biomass effectively. This study focused on woody biomass gasification fundamentals, using a bench-scale packed-bed reactor. In this experiment, pellets of black pine were gasified, using air as the oxidizing agent. Gasification tests were carried out under both updraft and downdraft conditions. Temperature distributions and compositions of syngas inside the gasifier were continuously monitored during gasification experiments at several ports on the wall of the reactor. The syngas at the exit of the gasifier was also sampled to estimate the amount of tar. Lower heating values of the syngas under updraft and downdraft conditions were 4.8 and 3.8 MJ/m 3N, respectively. It was easier to control the height of the packed bed under the downdraft condition than under the updraft condition. Under the updraft condition, a bridging phenomenon occurred. Tar generation under the downdraft condition was lower than that under the updraft condition. This is because tar passes through a partial combustion zone or higher temperature zone in the downdraft gasifier.

A Theoretical and Experimental Study of Combustion Tubes

When the air injection technique is used in a reservoir, the usual way to determine the fuel that would be burned and the temperature profiles, among other parameters, is by experimentation in a combustion tube. In this work, using medium oil (27 API) from the Gulf of Mexico, combustion tube experiments were carried out. A mathematical model, which takes into account the heat transfer ahead and behind from the combustion front, the combustion zone thickness, and the heat generated and loss in the combustion front, was solved numerically and used to predict the experimental temperature profiles. After validation of the mathematical model, further investigations of the effect of heat losses (along, at the top, and at the bottom of the combustion tube) on temperature profiles were done. The calculated combustion zone temperature and temperature profiles are in good agreement with our experimental data. It was found that not considering an isolated boundary in the mathematical model allows obtaining better predictions for the temperature profiles behind and ahead from the combustion front. On the other hand, the combustion front temperature increases as the heat losses decrease and the combustion front temperature attains its maximum value when there is no heat loss.