Showing papers on "Secondary air injection published in 2017"

Suppression of thermo-acoustic instability using air injection in horizontal Rijke tube

Abstract: The thermo-acoustic instability arising out of coupling between the pressure fluctuation and the unsteady heat release, when grows sufficiently, is known to cause serious structural damage thereby reducing the life span of systems having combustor for example, jet engines, gas turbines and industrial burners. The present work involves experimental study of thermo-acoustic instabilities occurring in a Rijke tube and their suppression by means of diverting a very small fraction of the incoming air flow in the form of radial injection from the wall of the tube through micro jets. A horizontal quartz tube with pre-mixed burner is used as the test model of Rijke tube. The coefficient Rayleigh Index (RI) is estimated from simultaneous measurement of chemiluminescence using a PMT and pressure in the plane of burner head. Experiments were carried out at the equivalence ratio of Φ = 1 for a range of the burner position inside the tube, velocity of micro jets, and total mass flow rate through the tube. The control technique of micro jets was found to completely suppress the thermo-acoustics in a range of jet velocity depending on the burner position and the total air mass flow rate. For complete suppression of the thermos-acoustics, the phase difference between the pressure and chemiluminescence waves was found to significantly increase and the RI was found to reduce to nearly zero. In such case, the flame luminescence was observed to significantly reduce. The proposed technique of air injection into the flame through radial micro jets is simple yet very effective in controlling the thermos-acoustic instability.

Stirring-type drying device for cereal

Abstract: The invention discloses a stirring-type drying device for cereal. The stirring-type drying device for cereal comprises a shell, wherein an upper cover is arranged at the upper end of the shell; a feed pipe, a rotating baffle plate, a stirring shaft, an air pump and a motor are arranged on the upper cover; stirring fan blade rods, a stirring fan blade and a rotating bearing are arranged on the stirring shaft; a discharge pipeline and a circulating air outlet pipeline are arranged on the right wall of the shell; a circulating air inlet pipeline is arranged on the left wall of the shell; an air exhaust cylinder is arranged on the rear side of the shell; a unidirectional air inlet pipe, a unidirectional air outlet pipe, a piston block, an electric push rod, a heating pipe and an inclined block are arranged on the air exhaust cylinder; and a supporting rod and a supporting bottom plate are arranged at the bottom of the shell. According to the stirring-type drying device for cereal disclosed by the invention, through the hollow stirring shaft and the stirring fan blade rods, air injection and stirring are performed, and cereal is dried; and the air exhaust cylinder which is capable of heating is matched to perform circulating air exhaust and air injection and at the same time, the air is heated, so that the movement of the cereal in the shell can be promoted, water vapour can be removed and the drying efficiency can be improved.

Effects of Fuel Staging on the NO Emission Reduction during Biomass–Biomass Co-combustion in a Fluidized-Bed Combustor

Abstract: Fuel-staged co-combustion of sunflower shells (as a base fuel) and coconut coir dust/moisturized rice husk (as a secondary fuel) was studied on a 205 kWth fluidized-bed combustor with bottom air injection. During the experiments, the energy fraction of both secondary fuels in the total heat input to the reactor was varied from 0 to 0.22, while the amount of excess air ranged from ∼20% to ∼80% for each co-firing option. Temperature and gas concentrations (O2, CO, CxHy, and NO) were measured along the reactor centerline, as well as at stack, to evaluate the emissions and combustion efficiency of the combustor for the specified operating parameters. The experimental results revealed significant effects of excess air on the combustion and emission characteristics of the reactor, whereas the influence of fuel staging on these characteristics was moderate. An optimization method minimizing “external” costs of the co-firing was used to quantify the optimal energy fractions of the co-fired fuels and optimal amoun...

Aerodynamic Optimization of a Single-Stage Axial Compressor with Stator Shroud Air Injection

Abstract: The effects of stator shroud air injection on aerodynamic performance were investigated for a single-stage axial compressor. Multiobjective optimization of the air injector was performed to maximiz...

Numerical investigation of the air injection effect on the cavitating flow in Francis hydro turbine

Abstract: At full and over load operating points, some Francis turbines experience strong self-excited pressure and power oscillations. These oscillations are occuring due to the hydrodynamic instability of the cavitating fluid flow. In many cases, the amplitude of such pulsations may be reduced substantially during the turbine operation by the air injection/ admission below the runner. Such an effect is investigated numerically in the present work. To this end, the hybrid one-three-dimensional model of the flow of the mixture “liquid−vapor” in the duct of a hydroelectric power station, which was proposed previously by the present authors, is augmented by the second gaseous component — the noncondensable air. The boundary conditions and the numerical method for solving the equations of the model are described. To check the accuracy of computing the interface “liquid−gas”, the numerical method was applied at first for solving the dam break problem. The algorithm was then used for modeling the flow in a hydraulic turbine with air injection below the runner. It is shown that with increasing flow rate of the injected air, the amplitude of pressure pulsations decreases. The mechanism of the flow structure alteration in the draft tube cone has been elucidated, which leads to flow stabilization at air injection.

Evaluation of Sulfide Control by Air-Injection in Sewer Force Mains: Field and Laboratory Study

Abstract: Chemical and biological processes consume dissolved oxygen (DO) in urban wastewater during transportation along sewer systems. Anaerobic conditions (DO < 0.2 mg/L) are easily reached, leading to sulfide (S2−) generation. Release of free sulfide, hydrogen sulfide gas (H2S), from the liquid to the gaseous phase, causes odor, corrosion of pipes and supposes a risk for health of people working in sewers. These issues get worse in force mains, due to inability to take oxygen from the gaseous phase of pipe. Air injection is a suggested practice to control H2S emission in force mains. That technique aims to keep aerobic conditions in wastewater in order to avoid sulfide generation and favor a decrease of Biochemical Organic Demand (BOD). However, several force mains with air injection are not achieving their goals due to a limited oxygen transfer. Field measurements of dissolved oxygen in urban wastewater are presented in an existing force main with air injection during the summer of 2014 in the southeast of Spain. A laboratory scale model is constructed to quantify two-phase flow conditions in pipe due to air injection for different incoming flows rates of water and air. Particularly, for the case of plug flow, also known as elongated bubble flow. Velocity field measurement of water phase in laboratory allows estimating turbulent diffusivity of oxygen in the water, Em, and inter-phase mass transfer coefficient KL(T). In the laboratory, flow and air depth, bubble length, water velocity field, pressure inside force main and water and airflow rates are determined experimentally. These variables are used to assess DO in water phase of force main by comparison with those obtained from field measurements. This work allows assessing air injection efficiency in wastewater, and, therefore, to predict DO in wastewater in force mains.