Experimental Research On The Atomization Characteristics Of Air-blast Spray Nozzles For Selective Non-catalytic Reduction System

Nitrogen oxides (NO_x) released by the fuel electric plants are frequently concerned in the recent thirty years. SNCR (Selective Non-Catalytic Reduction) technology is a developed NO_x control technology and already widely brought into commercial service abroad. The spray nozzle which is a crucial apparatus ejecting the reducing solution in SNCR system can effect the efficiency of NO_x control directly.Firstly, this paper introduces the development and recent situation of NO_x control technology, especially the SNCR technology. Then some common performance indicators for spray nozzles are introduced, such as the flow-rate characteristics, the atomizing angle, SMD (Sauter Mean Diameter) and its distribution, velocity of droplets, AWR (Air Water Ratio) and so on. The paper also gives some examples of nozzles already applied home and abroad, including their structures and spray characteristics.Secondly, the paper presents the composition of experimental system and the experimental procedures, and also the relevant apparatuses, including the LS-2000 laser particle analyzer and HAAKE rotary viscometer. Experiments research on the flow-rate characteristics, pressure, the atomizing angle, SMD and its distribution in transversal and lengthwise direction.At the first stage of experimental research, a pressure-type nozzle and an air-blast nozzle are developed and compared, and the latter one is proved to be much better. Therefore different kinds of fan-shaped air-blast nozzles are developed subsequently at the second stage, including the rectangular nozzles, olive-shaped nozzles and nozzles with mixing section. With thorough analysis and comparison, it comes out that the olive-shaped nozzles and nozzles with mixing section are the better ones, and further researches are carried out on them.These fan-shaped air-blast nozzles have a weakness that even the pressures of liquid and pressurized-air are lifted up, AWR is still a bit low and makes droplets a little bigger. On the basis of fan-shaped air-blast nozzles, by adding external-mixing passages, different kinds of partial internal-mixing nozzles are developed. Because of the existence of external-mixing passages, AWR becomes higher, and droplets become smaller. On the basis of researches on nozzles all above, a simple new-style nozzle with their merits are developed and applied in practical project at the end of chapter 4.Because of the limitation of experimental system, the velocity of droplets can't be measured; thereby the velocity field of spray can't be well understood. Numerical simulation of atomizing process is tried by using Fluent software. First step of simulation is to build the mesh pattern with similar structure and size of real nozzle, and then the boundary conditions and initial conditions are set, and then start the iteration by using VOF (Volume of Fluid) multiphase model. It is a good make-up to the experimental research.