The Computational fluid dynamics (CFD) code PHOENICS is applied to simulate and evaluate the combustion process within the furnace of a 1,000 MW dual circle tangential firing single furnace lignite-fired ultra supercritical (USC) boiler. The dependence on overfire air (OFA) positioning on the combustion process is studied. The results show that the highest temperature appears on the upside of the burner zone close to the front wall, and the high temperature zone rises with elevated OFA positions. However, the temperature field distributions are similar despite differing OFA positions. The char content near the rear wall is higher than that near the front wall, and below the furnace arch, coal particles concentrate towards the front wall. Also with elevated OFA positions, nitrogen oxide (NO x ) concentrations at the outlet fall, but char content increases. In regard to NO x emission and char burnout, the suggested optimal distance from the OFA center to the center of the uppermost primary air nozzle should be 6 meters.
The FLUENT computational fluid dynamics software package was used to model outlet velocity and temperature inhomogeneity in a 1000 MW dual circle tangential firing single furnace ultra-supercritical boiler. These computations allowed a theoretical analysis of thermal deviations at the furnace outlet and suggested means of reducing such deviations. This work involved study of radiative and convective heat transfer of the upper furnace platen superheaters, the radiative-convective heating surfaces above the furnace nose and the convective heating surfaces in the horizontal flue. The results demonstrated that the radiant heat load of the heating surfaces of the platen superheaters is related to the sectional dimensions of the furnace and exhibits a bimodal distribution in the boiler modeled during this work. It was also determined that a large recirculation zone is formed in the central section of the horizontal flue owing to velocity superposition. After establishing the thermal load distribution characteristics and the causes of thermal deviations at the various heating surfaces, further modeling was performed to assess the extent to which thermal deviations could be reduced by decreasing residual rotation at the furnace outlet via horizontally swinging the over fire air (OFA). The effects of OFA swing angles on velocity and temperature inhomogeneity at the furnace outlet were subsequently analyzed, and an OFA swing of À10 was found to be optimal based on considerations of thermal deviations at the furnace outlet, the airflow field in the furnace, and safe operation of the boiler.
A test loop system with adjustable spoiler function and visual structure was built in this paper. A PIV test system was adopted to investigate the influence of the uniformity of the inlet flow field on the performance of a nuclear main pump scale model, and the NUMECA software was used to numerically simulate the test cases. The research results show that when the rotation direction of the spoiler blade is opposite to that of the impeller, the greater the deviation of the spoiler blade from the axial angle, the more the pump efficiency and head drop; proper positive pre-rotation will not reduce the pump efficiency, but will increase the pump head; for the same spoiler blade deflection angle, when its structure produces irregular flow field disturbances under non-centrosymmetric conditions, the flow field downstream of it will not produce clear swirling flow, and it will not have more impact on the performance of the pump; the axial velocity distribution uniformity δ and the velocity weighted average angle θ, θ’ have obvious direct effects on efficiency, and in the δ interval of each working condition in this paper (the difference between the maximum value and the minimum value of δ is 0.093), the speed weighted average angle has a greater impact on efficiency. Nomenclature. Q Rate of flow δ Axial velocity distribution uniformity θ Weighted average angle parameter of velocity θi Absolute axial velocity angle θ′ Weighted average angle parameter of velocity η Efficiency H Head
The mechanism for phosphate cement hydraulic reaction is determined. The microscopic process is described by means of scanning electronic microscope, X-ray diffraction analysis,infrared spectrophotometry and differential heat analysis. The results show the three main phases are present, i.e. hydromagnesium phosphates, Mg (OH)2and MgO phase. The type, structure, and amount of every phase play an important role in phosphate cement properties. Hydromagnesium phosphate phase structure has a close relation to phosphate cement setting and hardening. The development of strength has much to do with the formed crystalline directing.
In this paper, the characteristics of the flow field in the gas turbine under different catalyst particle concentrations are simulated and analyzed by FLUENT software. The influences of catalyst particle concentration on the high-temperature smoke flow field, the movement track of catalyst particles and the erosion of the moving blade are studied in detail. The results show that the change of particle concentration has no obvious influence on the high temperature smoke flow field. The erosion wear of moving blade mainly occurs near the leading edge and trailing edge of the blade. The possibility of erosion wear at the leading edge is obviously greater than that at the trailing edge. The concentration of catalyst particles has a great influence on the erosion wear of moving blade. The erosion wear will be aggravated with the increase of catalyst particle concentration.
The composition and properties of phosphate cement, the requirement of its materials needed are discussed. Its compositional materials are heavy burnt magnesia and polyphosphatic solution. The effect of features, the amount of magnesium oxide and phosphate on the cement properties are described. It can be used in large fabrication repairing and in industrial waste disposal.
The Computational Fluid Dynamics (CFD) code PHOENICS was applied to evaluate the combustion process in the furnace of a 1000MW dual circle tangential firing single furnace lignite-fired Ultra Supercritical (USC) boiler. The influence of different primary air ratios (35%, 39% and 43%) on the flow and mixing characteristics of the gas-solid two-phase flow and the combustion process in the furnace was focused on. The results indicate that in the furnace with double tangential firing, the flow field shows two well-symmetrical ellipses at different primary air ratios. The surface temperatures of the burners at which, the long axis of the ellipses pointed, are much higher than those in the other four corners. Thus the phenomena of 'Hot corners' and 'Cold corners' arise. In practical operating, the flow erodes the walls in the hot corner which may lead to high temperature corrosion and slagging. With the increase of primary air ratio, the average concentration of NO x at the outlet of furnace rises while the char distributions in the furnace are similar. By the comparisons of the characteristics of the airflow, the temperature distributions, the NO x formation amounts and the char burnout rates, the situation with the 35% primary air ratio is preferable. The results of this paper have great value because of the support they lend to the design of USC lignite-fired boilers.
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