Advanced Materials Research Vols. 614-615

Abstract: High-density circulating fluidized beds (CFB) differ in several respects from low-density CFB systems. In high-density CFB risers, solids move upward throughout the entire riser cross-section, and the net downflow of particles at the wall, a commonly observed feature of fast fluidized beds, is absent. Hence there exists a transition regime from the low density to high density CFB where the net particle motion in the vicinity of the wall is changing from downwards to upwards. This was confirmed by experiments carried in a dual-loop high-density CFB facility with concentric-tube heat exchanger installed in the riser. Local suspension-to-wall heat transfer coefficient and suspension temperature distribution below and above the heat exchange section were measured. Experimental results elucidated that particles move both upwards and downwards in the vicinity of the wall for the operation conditions studied. This alternation of direction leads to higher heat transfer coefficients at both ends of the heat exchange.

Abstract: According to the phenomenon that large lagging and the fluctuation of the fuel regulation of the supercharged boiler, the dynamic behavior of the steam pressure is simulated to study the internal pure delaying in this paper. The flame detector system was used to collect the real-time picture of the flame in the boiler furnace, and the radiant energy signal was introduced into the combustion control system. A combustion auxiliary duct pilot was added and some stimulation is studied. The results shows that with the change of the radiant energy signal, the new control system can change the supply of the fuel in 20 seconds and wipe off all the disturbance in 30 seconds and the amplitude of fluctuation is dramatically reduced.

Abstract: For Marine pressurization boiler dynamic system, when the boiler provide steam for air storage, boiler drum pressure and steam pressure will have produced a wave phenomenon; In order to research this a wave phenomenon, considering similar principles , establish the model experiments to simulate the wave process. Due to boiler provide steam for air storage that involves in many complex physical processes, including two phase flow, heat transfer, braising physical phenomena. By a simple analysis, to be completely similar to the model, model must be the same as the real situation; it will lose the small model experimental significance. According to this problem, we consider use approximate modeling method which usually used in engineering, seize the pressure fluctuations of the main contradictions; Put forward in the process of considering only reflect pressure fluctuations of local fluid dynamic field project of similar approximation, Finally we get the fluctuation relationship of the actual conditions and small model experiment of main steam pressure.

Abstract: Based on the thermal calculation, the paper makes a contrastive analysis on the parameters of flue gas, and convection heat properties of the coal-fired boiler under atmospheric air combustion, atmospheric oxy-fuel combustion and pressurized (6MPa) oxy-fuel combustion conditions. It takes a 300MW pressurized(6MPa) oxy-fuel combustion boiler as research object, the result indicates that: compared to the coal-fired boiler atmospheric air combustion, the flue gas volume flow in the pressurized oxy-fuel combustion has a decrease of 98.79%; convective heat output has a decrease of 24.69% with the same difference in temperature. In the pressurized oxy-fuel combustion, both the flue gas convective heat transfer coefficient and the pressure drop are greater than the atmospheric oxy-fuel combustion, flue cross-sectional area is smaller than conventional boiler, and heating surface area is less than atmospheric oxy-fuel combustion. With a method named dynamic minimization of costs the best flue gas velocity in this paper is 1.07m/s

Abstract: Combustion characteristics of three types of lignite (coming from Indonesia, Ximeng, Hami), and a bituminous coal from Shenfu were studied by thermogravimetric analysis (TGA). Combustion parameters including characteristic temperatures, maximum rate of combustion, combustion performance index and activation energy of samples were analyzed. Kinetic parameters of samples were calculated using Jander model. The results showed that the characteristic temperatures of lignite samples are lower than that of bituminous coal. Indonesian lignite has the best combustion performance and the lowest activation energy. It indicates that high quality lignite such as Indonesian lignite has good combustion performance, even better than some bituminous coal, which makes it possible to use lignite by bulk combustion.

Abstract: The comparative experiments on CaCO₃ crystallization fouling on brass, copper and stainless steel 304 and 316 at different pH at 35°C were carried out. The growing curves of fouling were got by direct weighing after static reaction experiments, and the morphology of crystals at different conditions was obtained by scanning electron microscope (SEM) and the parameters such as polymorphism, crystal size and so on were got, so the growing characteristics of CaCO3 crystallization fouling were known. The experimental results show the mass of crystallization fouling on stainless stee_{Subscript text}l surfaces are almost equal and increasing a little when pH increased, but the mass of fouling on brass and copper surfaces are close and far less than on stainless steel and increasing a lot when pH increased; not only the homogeneous nucleation rate in bulk solution and heterogeneous nucleation rate on metal surface are increased to generate more new crystal nuclear but also square aragonite and calcite are formed more by higher pH, so the mass of metal surfaces is more and the phenomenon is more obvious that single crystal has a size extremum by higher pH.

Abstract: Combined cooling, heating and power ( CCHP ) system provides three different energy level products. This paper presents four thermodynamic evaluation indexes, such as primary energy rate, exergy efficiency, energy saving rate and energy cascade utilization efficiency. These thermodynamic evaluation indexes are adopted to evaluate four redesign system schemes based on an actual hospital in this paper. Analysis results show that exergy efficiency and energy cascade utilization efficiency, which take exergy value into account, are more reasonable than the others.the others.

Abstract: Study on the combustion behavior and pollutant emission properties of the different types and different ratio of blending coal have been done. The influence of the ratio of brown-blending coal on the combustion efficiency and NO_x emission have been researched and concentrated ratio and method of pulverized coal have been get. The thermal-load distribution along the height of furnace and the control of the flue gas temperature at the exit of the combustion chamber have been discussed and the retrofit schema has been put forward. By reasonably blending coal, combustion efficiency increases and NO_x emission goes down.

Abstract: In this work, a series of combustion experiments for oil shale semi-coke , rice straws as well as their mixture were conducted by the thermogravimetric analyzer at different heating rates (10, 20 and 50 K/min) under atmospheric pressure. Combustion characteristic curves and combustion characteristic parameters were acquired. The results showed that the combustion process of blends can be broadly separated into three stages: combustion of the volatile matter, combustion of fixed carbon and combustion of difficult decomposition substance. The point of ignition and burnout shifted to higher temperature with increasing the heating rates. Furthermore, kinetics parameters were analyzed in the second stage. The result showed feasibility of using the reaction model to solve the kinetic parameters of biomass combustion. Finally, the obtained DTG curves were separated by Gaussian Fitting method. The result showed that the derivative thermogravimetry (DTG) curve displays an overlapping peak consisted of three sub-peaks at 645–900K under heating rate of 20K/min.