The Modeling Study On Material Cycling System Of Circulating Fluidized Bed Boiler

Circulating fluid bed technology is a kind of new clean coal combustion technology developed in recent years in the global world. Due to the advantages of high efficiency, low pollution and wide adaption of coal, it has received an universal attention by scholars around the world which made it to be one of the leading direction of clean coal combustion technology currently. Circulating fluid bed boiler is based on the gas-solid two phase flow combustion technology which contains combinations of gas-solid flow. Material is flowing and burning circularly in the gas-solid fluidization which is the process that material working. Material circulation process includes outside loop and inner loop. Outer loop is the process that material passes the furnace, segregator and return valve, finally gets back to the boiler. The concentration distribution of material is an important aspect of inner loop. Material concentration distribution is an important aspect. It reflects the dynamic characteristics of the circulating fluidized bed. Material concentration directly affects the key problem of motion characteristics, heat transfer and abrasion of heating surface. Therefore, establishing the model of material cycling system of circulating fluidized bed boiler to study the material concentration distribution has a certain practical significance.At first, the article simply introduces the research status, operating principle and composition of material cycling system of circulating fluidized bed boiler. Then, the article adapts cell model which divides the furnace into dense-phase zone, transition zone and the dilute phase zone. And at the three regions, establish the corresponding material dynamic mass balance equation. Unlike previous papers, the article is not only considering the gas-solid two phase flow, but also considering the process of combustion and material dynamic mass balance equation. Finally, establish the model of material concentration containing gas-solid flow and combustion on the basis of previous experimental formula. Because of the complex physical process and chemical process in the furnace, so we simplify the model properly.Because of the complexity of the boiler operation and the limit of test condition, we can't collect parameter of material concentration in the power plant. So in this article, we choose a kind of new numerical simulation software FLUENT to replace the power plant. Many scholars make a lot of research on flow, combustion and heat transfer which prove the feasibility of FLUENT. In the article, author adapts FLUENT to simulate the distribution of material concentration at different time based on the EULER two-fluid model. The simulation results show that: generally, in the upper part, the material concentration is low, and in the bottom part, the material concentration is high. Over the secondary tuyere, the concentration typically shows core-annulus flow structure. In addition, when change the fluidization air velocity and circulating rate, the particle concentration is changed obviously on the axes at the bottom and middle part, and in the upper part, the particle concentration is obviously changed in the side wall in the radical direction.Finally, the author derived data about material concentration on the axes by FLUENT. And compare the data between FLUENT and mechanism model, in addition, prove the correctness of the mechanism model. This method provides a new thought of study on material concentration system of circulating fluidized bed boiler.