Preheater Research Articles

Experimental investigation on combustion characteristics of novel preheated air swirl burner operating on the heavy oil fired furnace for reducing NOx emission

ABSTRACT This paper presents an experimental study carried out to evaluate the influence of air swirl vane angles on pollutants in a heavy oil fuel fired furnace with a recuperator. A novel burner system with a range of concentric air swirl generators (vane angles of 15°, 20°, 30°, 45°, 60°, and 90°) was ultimately incorporated to the combustion chamber of a 250 kg crucible furnace. This study examined the thermal efficiency and the polluting emission parameters of CO2, HC, CO, and NOx. According to the results, preheated air-fuel and air swirl generators with vane angles of 45° and 30° emit the least HC and CO, whereas air swirl vane angles of 90° emit the most. A preheated primary air swirl vane angle of 45° results in the lowest NOx emission (25 ppm) value. Furthermore, with larger air swirl vane angles of 45° results in increased temperature and premixed combustion, as well as a raise in NOx emission. To ensure accurate airflow for complete combustion, secondary air entry area kept twice the primary air entry area in the novel burner. The results showed that when the temperature of the preheated primary and secondary air and heavy oil fuel combination increased, so did the mean effective temperature of the combustion gases. Conversely, when the vane angle is reduced and no preheated air-fuel combination is present, the mean temperature of the combustion gas drops dramatically.

Gasoline compression ignition (GCI) combustion in a light-duty engine using double injection strategy

Controlling the oxides of nitrogen (NOx) and particulate matter (PM) emissions is one of the vital goals of compression ignition (CI) engines. Implementing stringent emissions regulations has motivated researchers to adopt various strategies for controlling emissions. Gasoline compression ignition (GCI) has emerged as a prime technology to control emissions and increase engine efficiency, while using low-octane gasoline as fuel in CI engines. Preheated air, hot exhaust gas recirculation (EGR), and negative valve overlap, are required to manage the combustion instabilities in the GCI engines. However these techniques have not been used in this study in order to reduce system complexity. Low octane test fuel was prepared (G80) by blending 80 % v/v gasoline and 20 % v/v diesel. This study involved experiments to evaluate the effects of main injection timing, split injection quantities (10–30 %), and engine load (brake mean effective pressure (BMEP): 3–5 bar) on a two-cylinder GCI engine’s performance, combustion, cyclic variability, emissions, and particulates. Conventional diesel combustion (CDC) mode experiments were performed using diesel. The results indicated a 5 % higher brake thermal efficiency (BTE) and comparable exhaust gas temperature (EGT) for the GCI mode compared to the baseline CDC mode. GCI combustion with low split ratio showed higher in-cylinder pressure than CDC mode. Baseline CDC mode showed < 3 % coefficient of variation of indicated mean effective pressure and peak pressure, whereas these parameters varied from 1 % to 9 % in the GCI mode. GCI mode engine exhibited ∼ 60 and 50 % lower NOx and PM emissions than baseline diesel mode engine. The double injection strategy improved GCI engine's performance and emission characteristics.

SO3 Migration and Emission Characteristics of CFB Boilers

In order to study the migration and transformation of SO3 from circulating fluidized bed boiler (CFB) in the air preheater and flue gas treatment facilities, 10 circulating fluidized bed boilers with installed capacities between 150 MW and 330 MW were measured by controlled condensation method. Ten circulating fluidized bed boilers with installed capacities ranging from 150 MW to 330 MW were measured using the controlled condensation method. It is showed that the SO3 removal rate of the air preheater was affected by the air preheater flue gas exit temperature, which ranged from 6.7 % to 36.5 %, and the SO3 removal rate of the rotary air preheater was higher than that of the tubular air preheater. The SO3 removal rate of cloth bag filter and electric bag filter is above 40 %; the SO3 removal rate of electrostatic precipitator is between 6.1 % and 10.8 %. The SO3 removal rate of wet desulfurization method ranges from 41.7 % to 73.4 %, with the highest SO3 removal rate of double tower double cycle. The SO3 removal rate of off-furnace CFB semi-dry desulfurization reached 89.7 %~97.9 %, and the dry process inside the furnace + off-furnace CFB semi-dry process could reduce the SO3 at the desulfurization outlet to below 0.3 mg/m3 under the tested conditions. The conclusions of the test analysis in this paper can provide reference for SO3 control in circulating fluidized bed boilers and related policy formulation.

Experimental and CFD simulation of performance analysis of steam generators of boilers

Abstract In contemporary power plants, poor air temperature is one of the primary causes of rising unit temperatures and deteriorating boiler performance. The primary issue with an air preheater is air leakage on the gas flue side, which results in poor thermal performance. The high ash content of Indian coal exacerbates the issues with air tube heating. Air preheaters re developed to fulfill operational needs while taking into account the most important factors. Heat transmission, leakage, and pressure reduction are all factors to consider. The performance of the air-conditioning heater is being evaluated in this study using the Fluent 14.0 analytical tool from Computational Fluid Dynamics (CFD).

COMPUTATIONAL MODELING FOR THE PERFORMANCE PREDICTION OF QUAD-SECTOR ROTARY AIR PREHEATER AND COMPARATIVE STUDY WITH TRI-SECTOR AND BI-SECTOR ROTARY AIR PREHEATERS

Rotary air preheaters are mainly used to improve the economy of a steam power plant by preheating the air with the help of hot flue gases from the boiler. Modern steam power plants are preferring tri-sector and quad-sector rotary air preheaters over bi-sector due to their better performance and lower leakage. In the present work, thermal behavior of a quad-sector rotary air preheater is the focus using computational fluid dynamics. The porous media approach is used for numerical simulation assuming local thermal equilibrium condition between fluid and solid. The performance of the air preheater is accessed by effectiveness and pressure drop. Porosity is estimated for four different cell shapes, which are used in the rotary preheater core for numerical investigation. The study reveals that the core consisting of a triangular cell has the highest effectiveness. The effect of porosity on performance is also investigated for various cell shapes. The effect of important operating parameters, such as rotor speed, aspect ratio, and mass flow rate of fluids on the effectiveness, as well as pressure drop is investigated for a quad-sector rotary air preheater. The study ends with a comparative performance analysis between bi-, tri-, and quad-sector rotary air preheaters. The performance of quad-sector air preheater is found to be better than other two preheaters in terms of effectiveness, whereas its pressure drop is maximum.

Distribution of PCDD/F and PCB at Different Positions of Circulating Fluidized Bed Municipal Solid Waste Incinerators

Because of a high moisture content and a low heating value of Chinese municipal solid waste (MSW), circulating fluidized bed (CFB) incinerators have been widely adopted in China for incinerating MSW since 1998. In this study, two typical CFB incineration plants (A and B) were investigated for contents and fingerprints of PCDD/F and PCB at different positions downstream their post-combustion zone, aiming to draw a full picture of formation and distribution of these organochlorinated pollutants. Both flue gas and ashes were sampled at five different positions of Plant A, from high-temperature superheater to outlet of baghouse filter, representing a huge range of flue gas temperatures; for Plant B, five ash samples were collected at different positions of the waste heat boiler (from high-temperature superheater to lower economizer). A continuous increase in contents of PCDD/F and PCB in flue gas was observed from superheater to inlet of air pollution control system (APCS) in Plant A, with the most significant rise noticed at air preheater. The load of PCDD/F and dioxin-like PCB in ashes also amplified steadily along the cooling path of flue gas in both plants. Changes in formation pathways are discussed based on homologue and isomer distribution patterns.

Numerical study of slagging trends in the pre-combustion chamber at swirl-burner outlet under different secondary-air temperatures

• The slagging trend of the PCC wall at different T SA is predicted by CFD. • The temperature near the PCC wall increases with increasing T SA . • The relationship between the T SA and slagging trend of the PCCwall is established. • Low T SA is better for protecting the PCC wall from slagging. The swirl burner with the pre-combustion chamber (PCC) has good combustion stability and is usually used in industrial pulverized coal boilers (IPCBs). Due to the limited space of PCC, it is easy to cause slagging on the wall, which affects the operation of the boiler. For different IPCBs, the designed secondary-air temperature ( T SA ) varies widely. Some boilers use outdoor air as SA, thus the T SA is low; other boilers use the air heated by the air preheater as SA, thus the T SA is high. Importantly, the slagging characteristics under different design temperatures are quite different. Hence, for the safe operation of boilers, it is necessary to study the slagging characteristics of PCC walls under different designed T SA , which in turn provides a reference for the design of T SA in IPCBs. In this paper, based on a 29 MW IPCB, the influence of T SA on slagging trends in the PCC is studied by CFD. The relationship between T SA and the slagging trend of PCC walls is established. The higher the T SA , the greater the intensity of pulverized coal combustion, which is more conducive to pulverized coal burnout; meanwhile, the temperature near the PCC wall rises, resulting in the slagging trend increases. This is inconsistent with the results of studies on slagging at burner outlets in coal-fired utility boilers. When T SA is 485K, the slagging trend is about 540 times more serious than that when T SA is 385K. The results of this paper show that the designed T SA should be reduced as much as possible, which is more conducive to protecting the PCC from slagging.

EFFECTS OF EXCESS AIR AND COAL SULFUR CONTENT IN PERFORMANCE IMPROVEMENT OF 660 MW SUPERCRITICAL BOILERS IN TERMS OF ACID DEW POINT TEMPERATURE

The objective of this study was to select an appropriate fuel having different sulfur contents in various coal fuels and optimize the excess air in order to reduce dry flue gas loss, avoid equipment damage due to sulfur dew point corrosion, and reduce maintenance and equipment installation costs. A tri-sector rotary air preheater was employed to exchange heat between dry flue gases and preheat the air (both primary and secondary air). The results showed that coal with 0.6165&amp;#37; sulfur (fuel 2) caused acid dew point temperatures (ADPTs) of 122.38&amp;deg;C and 124.947&amp;deg;C with 15&amp;#37; and 20&amp;#37; excess air, respectively, in a rotary air preheater set at a 30.5&amp;deg; angle, whereas coal with 1.627&amp;#37; sulfur (fuel 1) caused ADPTs of 131.299&amp;deg;C and 133.602&amp;deg;C with 15&amp;#37; and 20&amp;#37; excess air, respectively, in a rotary air preheater set at a 35.99&amp;deg; angle. The experimental results indicate that the use of fuel 2 coal consumption can reduce carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) emission by nearly 4 metric tons (MT)/hour, which is equivalent to a reduction of CO&lt;sub&gt;2&lt;/sub&gt; emission of 3.8 MT/hour.

Features of Replacement of the ТГМП-314 Boiler Heating Installation

Thermal power stations play the main role not only in carrying the base load, but also in ensuring the coverage of peak and semi-peak loads of electricity consumption. Improving the operational maintenance of energy equipment gives a greater economic effect, since the costs of modernization of regenerative air heaters, which improve their density and thermal efficiency, are repaid in a short time. The efficiency and cost-effectiveness of the operation of regenerative air heaters was increased by the reconstruction of the heating installation. The results of the reconstruction of the design heaters of the TГМП-314 boilers with sections of sanitary-technical heaters КФСО -II and КФБО -II with replacement by sections of energy heaters (СО-110) are presented. The improved heating installation is installed in front of each regenerative air heater of the ТГМП-314 boiler and is made of two walls placed sequentially according to the air movement, in each of which 12 sections of reconstructed CO-110 heaters with a downward movement of the heating steam flow are installed. An important advantage of the proposed sequential installation of radiators is an increase in the uniformity of the temperature field in the box in front of the regenerative air heater due to two-stage air heating. Sequential installation of radiator walls increases the heat transfer coefficient approximately 1.6 times compared to parallel connection, which makes it possible to double the air speed in the radiators for the same number of sections. The possibility of formation of stagnant zones of sections of CO-110 heaters is excluded. In this case, it is recommended to reconstruct single-pass radiators with the installation of a pipe board and heating steam condensate removal chambers. The high efficiency of the improved heating installation made it possible to carry out all boiler ignitions with the possibility of supplying flue gases immediately through the RAH.

Modelling a Turbulent Non-Premixed Combustion in a Full-Scale Rotary Cement Kiln Using reactingFoam

No alternatives are currently available to operate industrial furnaces, except for hydrocarbon fuels. Plant managers, therefore, face at least two challenges. First, environmental legislation demands emission reduction. Second, changes in the origin of the fuel might cause unforeseen changes in the heat release. This paper develops the hypothesis for the detailed control of the combustion process using computational fluid dynamic models. A full-scale mock-up of a rotary cement kiln is selected as a case study. The kiln is fired by the non-premixed combustion of Dutch natural gas. The gas is injected at Mach 0.6 via a multi-nozzle burner located at the outlet of an axially mounted fuel pipe. The preheated combustion air is fed in (co-flow) through a rectangular inlet situated above the attachment of the fuel pipe. The multi-jet nozzle burner enhances the entrainment of the air in the fuel jet. A diffusion flame is formed by thin reaction zones where the fuel and oxidizer meet. The heat formed is transported through the freeboard, mainly via radiation in a participating medium. This turbulent combustion process is modeled using unsteady Favre-averaged compressible Navier–Stokes equations. The standard k-ϵ equations and standard wall functions close the turbulent flow description. The eddy dissipation concept model is used to describe the combustion process. Here, only the presence of methane in the composition of the fuel is accounted for. Furthermore, the single-step reaction mechanism is chosen. The heat released radiates throughout the freeboard space. This process is described using a P1-radiation model with a constant thermal absorption coefficient. The flow, combustion, and radiative heat transfer are solved numerically using the OpenFoam simulation software. The equations for flow, combustion, and radiant heat transfer are discretized on a mesh locally refined near the burner outlet and solved numerically using the OpenFoam simulation software. The main results are as follows. The meticulously crafted mesh combined with the outlet condition that avoids pressure reflections cause the solver to converge in a stable manner. Predictions for velocity, pressure, temperature, and species distribution are now closer to manufacturing conditions. Computed temperate and species values are key to deducing the flame length and shape. The radiative heat flux to the wall peaks at the tip of the flame. This should allow us to measure the flame length indirectly from exterior wall temperature values. The amount of thermal nitric oxide formed in the flame is quantified. The main implication of this study is that the numerical model developed in this paper reveals valuable information on the combustion process in the kiln that otherwise would not be available. This information can be used to increase fuel efficiency, reduce spurious peak temperatures, and reduce pollutant emissions. The impact of the unsteady nature of the flow on the chemical species concentration and temperature distribution is illustrated in an accompanying video.

Feasibility Analysis of Coupling Hydrogen-Derived Fuel on a Coal-Fired Boiler for Power Generation

As an alternative to hydrogen, hydrogen-derived fuel (NH3, CH3OH, or CH3OCH3) is considered to be an ideal secondary energy source. The effects of coupling hydrogen-derived fuels with coal on the thermodynamic parameters of a boiler are analyzed through thermal calculations according to the principles of mass and energy conservation. A 300 MW tangentially fired boiler is selected for a case study. The results show that the variations of boiler thermodynamic parameters depend on the properties of hydrogen-derived fuels and coupling mass percentage. After the coupling, the furnace exit flue gas temperature changes, which results in alterations in heat distribution of radiation and convection for the water-cooled walls and the convective heating surfaces. The furnace exit flue gas temperature drops for coupling H2 or NH3 but rises for coupling CH3OH or CH3OCH3 with the growth of the coupling mass percentage. The variations of boiler thermal efficiency with different coupling mass percentages under BMCR load are 0.55% to 0.90% for H2, −0.32% to −1.16% for NH3, −0.22% to −2.03% for CH3OH, and −0.08% to −0.59% for CH3OCH3. The acid dew point rises and then drops as the coupling mass percentage grows. The flow rate of the total flue gas increases at the outlet of the air preheater. Thus, the current forced draft fan could not meet the requirements, and its retrofit should be performed. After the large proportion of cofiring, the coal consumption rate drops. The annual emissions reductions of CO2 are up to 0.734 million tons for H2, 0.231 million tons for NH3, 0.062 million tons for CH3OH, and 0.101 million tons for CH3OCH3 under BMCR load at a 20% coupling mass percentage. The lifecycle CO2 reduction potential should be considered for better illustrating the benefits of cocombustion in future studies.

Experimental Study of Preheated Secondary Air on the Performance of an Updraft Coal Heating Stove.

Although the Chinese government encourages using clean fuels for heating, many households in remote areas still rely on coal as their energy, especially in the Qinghai Tibet Plateau. An updraft coal heating stove was modified to preheat secondary air. The performance of the modified stove was studied compared with a baseline stove. The temperatures in the combustion chamber and near the chimney exit are measured, and the undiluted exhaust concentrations of CO, NO x , and SO2 are obtained. The results indicated that the temperatures and exhaust gas concentrations varied periodically with the coal addition. The oxygen concentration in the flue gas for the modified stove is higher than that for the baseline stove, and the O2 concentration was decreased with the increase in fuel feed rate. The CO concentration peaked 5-15 min after fuel addition and descended quickly toward a baseline with the higher fuel feed rates. It remained almost unchanged at the beginning and then slightly increased when the combustion began to fade with a lower fuel feed rate for the modified stove. The NO x emission for the modified stove is generally lower than that for the baseline stove. The NO x formation during coal combustion mainly comes from prompt NO and fuel NO, while the SO2 emission is mainly related to the sulfur element in the raw coal in the present work. The modified stove is effective in reducing NO x and SO2 emissions. However, the CO emission of the modified stove is higher than that of the baseline stove, especially at the end of the batch.

Biomass energy conversion in a gasifier for injera baking mitad application

The performance of gasification for Injera baking was explored in this study, as well as the effects of moisture content, and primary and secondary airflow rates. Primary air is used in the reactor of a biomass gasifier, which creates syngas that is burned by secondary air on the mitad's bottom side. An average temperature of averaged 185°C at the center and 170°C away from the center was observed; the size of the cone determines the temperature distribution on the metal surface. The reactor's narrower cone diameter allowed for a greater temperature only in the center and a more variable baked Injera eye appearance. The cone diameter has been reduced to 0.15 m of the mitad diameter to improve the temperature distribution on the mitad surface. The gasifier temperature is 800°C when the air/fuel ratio is 5.8 kg/kg and the moisture content of the wood is 16%. Gasification is improved by heating the primary air and changing the air-fuel ratio. The findings revealed that pre-heated air is more efficient for gasification and saves money on baking and fuel. Fuel efficiency (0.45) and time savings (0.12) were discovered in the new gasifier. Between gasification temperatures of 650 and 800°C, an effective Injera baking temperature (170–185°C) on the mitad surface was attained. Following the tests, the average specific wood fuel consumption (1.414 g/kg), char residue (317 g), and average Injera baking time were calculated. For each test of one baking cycle, this was found at the burning rate capability of both stoves, which is 6 kg/hr. Therefore, the fuel consumption and burning rate of fuel are depending on the amount of airflow rate.

A Mathematical Model of Industrial Waste-Derived Fuel Droplet Combustion in High-Temperature Air

The results of a theoretical and experimental study of the processes of ignition and combustion of a single composite liquid fuel (CLF) droplet based on wet coal processing waste and combustible municipal solid waste under radiant and convective heating are presented. Based on the results of a detailed analysis of video recordings and previously obtained experimental data from the ignition and combustion of a single CLF droplet, a mathematical model was developed. The advantage of the developed mathematical model lies in the specification of sequential physical and chemical processes of the high-temperature decomposition of fuel in a high-temperature gaseous medium. A numerical simulation of combustion characteristics was carried out in the Ansys Fluent commercial software for five different CLF compositions. The ignition-delay times were established for fuel droplets that were in a preheated motionless air environment, a temperature in the range of 723–1273 K, and an air flow heated to 723–973 K moving at a velocity of 3 m/s. Using the asymptotic procedure, satisfactory analytical solutions are obtained for the multistage nonlinear problem of ignition and combustion of a single CLF droplet. The possibility for the practical application of the developed program in Ansys Fluent in predicting the characteristics of the ignition processes of CLF droplets is substantiated.

Process optimization and thermodynamic analysis of autothermal coal chemical looping gasification industrial demonstration system

Chemical looping gasification (CLG) is an innovative clean coal conversion technology with industrial application prospects. The technical reliability of coal CLG (CCLG) in an autothermal state remains to be investigated. To clarify the process characteristics of an autothermal CCLG process, a CCLG autothermal operation system was established based on a CLG industrial demonstration unit. Process modeling of the CCLG reactor system and economizer, air preheater, and other heat exchange units was performed, to ensure autothermal operation of the global CCLG process. The optimal operating parameters of the system were established, the optimal heat exchange network was designed, and the source and distribution of thermodynamic irreversibility were clarified. The results showed that the optimal coal feed flow rate, air feed temperature and flue gas circulation temperature were 437.07 kg/h, 550 °C and 450 °C, respectively. The fuel reactor (FR) flue gas circulation was not conducive to system autothermal, resulting in weakened gasification performance. The optimal heat exchange plan allowed the system to operate without an external heat source. The thermodynamic irreversibility mainly originated from the redox process. The system heat efficiency was 81.63 %, the product exergy efficiency was 78.06 %, the total exergy efficiency was 41.10 %, and the total exergy destruction rate was 55.40 %. Additionally, the FR flue gas circulation caused high exergy loss, resulting in reduced system thermodynamic efficiency.

Effect of ammonia co-firing on heat transfer, safety, and economy of coal-fired boilers

Ammonia (NH3) co-firing provides a promising route to reducing CO2 emissions of coal-fired boilers. The thermodynamic calculation model of a 600 MW supercritical coal-fired boiler was established to investigate the effects of NH3 co-firing on the heat transfer, safety, and economy of the boiler. Co-firing 50 % of NH3 (on the lower heat value basis) reduced the emissivity and temperature of the flame, and decreased the heat load of the furnace by 6.2 %-7.1 %. Nevertheless, the heat absorption of both the main steam and reheat steam can still be satisfied by adjusting the ratio of flue gas in two vertical flues without modifications of the heating surfaces. With the NH3 ratio rising from 0 % to 50 %, the temperature of flue gas at the furnace outlet grew by only 7.0 °C. Besides, the tube wall temperatures of the platen superheater and the high temperature superheater increased by < 3.0 °C, ensuring the safety of the heating surfaces. At boiler rated load, low temperature corrosion of air pre-heaters was hardly aggravated by co-firing NH3 of 50 %, but it became more severe at lower boiler loads. Compared with single coal combustion, the temperature of exhaust flue gas rose by 6.2–13.9 °C when NH3 ratio was 50 %, and the boiler efficiency decreased by 0.7 %-1.2 %. The high price of NH3 greatly increased the running cost of the boiler, but a higher CO2 tax can highlight the economic benefits of NH3 co-firing.

Numerical investigation on thermal-hydraulic performance of air preheater equipped with helical inserts

In the present work, a numerical study has been done for the air preheater equipped with different types of helical inserts inside the tubes with segmental baffles in shell. The simulations have been carried out to analyse the heat transfer rate in terms of heat transfer coefficient and friction factor with ANSYS 18.0. The air preheater is divided into two sections shell side and tube side, which contains ambient air and flue gases respectively. The air preheater consists of 34 tubes with a length of 3 m. In the present study, three different types of inserts are investigated with a pitch to diameter ratio (p/d) of 2, 1.7 and 1.4, and the number of turns of 100, 87 and 73, respectively. The insert under study is helical shaped with circular cross-section of diameter 20 mm. Four different values of Reynolds number are used in the range of 4000–24,000. The effects of pressure drop, heat transfer coefficient on different pitch to diameter ratio (p/d) 2, 1.7 and 1.4 of inserts and on the plain tube are discussed in this present work. The results of an air preheater with inserts in tubes get higher value of heat transfer coefficient as compared to the plain tubes. The thermal performance factor of air preheater with inserts of (p/d = 1.4) shows higher factor of 2.31 as compared to the plain tubes at low Reynolds number.

Development of stability criteria for biomass open-top downdraft gasifiers

In the past, few researchers have presented objective criteria that can be applied for the stability assessment of a gasification process for woody biomass. When exploring new operating points, however, an objective rating of the operation must be performed. Therefore, in this paper, a useful stability criterion by comparing different statistical parameters (i.e., standard deviation, relative standard deviation, interquartile range and stability index) for several gasifier variables (i.e., temperatures, pressure loss, air flow, permanent gases, total hydrocarbon content THC and flame front position) is described. Therefore, 124 operating points from different evaluations in a commercial open-top gasifier operated with wood chips were used. These data points include fuel water contents from 2 m% to 21 m%, exhaust gas recirculation, loads within the range of ±20% of the nominal load, water injection and air preheating. By taking this novel approach, three main findings were revealed: (1) The summarized standard deviation of the gasifier temperatures is suitable to rate the process stability; however, the temperature fluctuations showed no influence on the permanent gases. (2) A correlation was found between the standard deviation of the air flow and the absolute value of the THC; this enables an estimation of the gas quality with a cheap air flow sensor. (3) A novel method was developed to identify stable operating timespans during post-processing based on the moving standard deviation. This procedure enables researchers to objectively rate operating points in future gasification development.

Numerical Investigation on the Impact of Exergy Analysis and Structural Improvement in Power Plant Boiler through Co-Simulation

In current power station boilers, fuel burns at a low temperature, which results in low exergy efficiency. This research combined the second law of t with the boiler structure to maximize the efficiency of a 350 MW power plant boiler. A three-dimensional simulation of the combustion process at the power plant boiler is performed. A one-dimensional simulation model of the boiler is then constructed to calculate the combustion exergy loss, heat transfer exergy loss, and boiler exergy efficiency. Under the principle of high-temperature air combustion technologies, this paper also proposes a new structure and improved operating parameters to improve the exergy efficiency of boilers by reducing the heat exchange area of the economizer and increasing the heat exchange area of the air preheater. Simulation results show that the exergy efficiency of the boiler increased from 47.29% to 48.35% through the modified model. The simulation outcomes can instruct future optimal boiler design and controls.

Detailed chemistry modeling of rotating detonations with dilute n-heptane sprays and preheated air

Utilization of liquid fuels is crucial to enabling commercialization of rotating detonation engines (RDE) in the near future. In this study, Eulerian-Lagrangian simulations are conducted for rotating detonative combustion with dilute n-heptane sprays and preheated air. Two-dimensional flattened configuration is used and a skeletal chemical mechanism with 44 species and 112 elementary reactions for n-heptane combustion is adopted. The flow structure, droplet distribution, and thermochemical parameters in the refill zone are first analyzed. It is shown that the mixture in the refill zone is heterogeneous, including evaporating droplets, vapor, and air. When the total temperature is below 950 K, the average equivalence ratio increases with the total temperature. When it is higher than 950 K, the average equivalence ratio is almost constant. Subsequently, the chemical explosive mode analysis is applied to identify the controlling reactions and dominant combustion modes in the fuel refill zone and reaction fronts. Results demonstrate that the initiation reaction (R104: n-C7H16 + O2→ 2-C7H15 + HO2) and low-temperature reaction (R107: RO2→ R'O2H) are dominant in the upstream and downstream of the refill zone, respectively. The intermediate species from low-temperature chemistry, R'O2H, is found to be important for the chemical explosive mode in the undetonated mixture. The influence of species diffusion and dispersed droplets is further analyzed. Results show that vapor autoignition facilitated by droplet evaporation occurs in the refill zone. Finally, the effects of the air total temperature on the detonation propagation speed and RDE propulsion performance are investigated. It is found that the detonation propagation speed and specific impulse increase with air total temperature. The total pressure ratio first increases and then decreases as the air total temperature increases. Moreover, when the total temperature of the preheated air is above 1,300 K, the effects of low-temperature chemistry are negligible.