Study On Smoke And Dust Control Technique For New Type Of Dry-Process Rotary Kilns

In recent years, cement industry has been developed quickly in our country as an important part of national economy. In 2008, there are totally 4350 cement enterprises distributed in 31 provinces/districts/cities with the cement capacity of 18.7 hundreds million tons. Hebei, Shandong and Hubei have the most cement capacity and Hubei province'annual output of cement is larger than that of the whole America. There are 1018 production lines of new type of new dry cement with the cement capacity of 11 hundreds million tons and the lagging cement capacity of 5 hundreds million tons. Others are cement grinding stations and other types of rotary kilns. The kiln head and kiln rear on the new dry cement product lines are the biggest dust pollution source, which can produce 60% of exhaust gas of the total amount. In the process of cement clinker, a lot of dust is produced in the workstage of cmminution, grinding,subsize,burdening,out kiln and pack. Usually, the free silica content is about 1.7-9.0% in clinker, and 1.2-2.6% in finished cement. Long-time inhalation of clinker or cement dust for human body can cause cement pneumonoconiosis. Meeting with water or sweat,cement can generate alkalinity matter such as calcium hydroxide etc., which can irritate skin, causing dermatitis and conjunctivitis and keratitis after entering into eye. In the work area of rotary kiln head,there are hazards such as high temperature and thermal radiation. Hubei Huaxin Cement factory has 21 new type of dry cement produce lines, whose industrial art and technique is in the lead in our country. The writer conducted site survey in Hubei Huaxin Cement factory and Gezhouba Cement factory, finding out that the smoke and dust pollution at clinker kiln head and waste gas emission from the smokestack in kiln end are the main occupational hazard and environment problem. The smoke and dust pollution at clinker kiln head mainly comes from the kiln mouth between the fixed kiln head and rotary cylindrical shell. Therefore, this paper chose smoke and dust control technique for new type of dry-process rotary kilns as a subject, the 4.75 m kiln of Huaxin Cement factory as case study, doing the research in aspects of kiln mouth smoke dynamic characteristics analysis, kiln mouth dust control gravity settling room guidevane, smoke and dust control ventilation system etc.. The main components are followed:Chapter One Introduction. The cement kiln develop stage and new dry cement rotary kiln industrial art were introduced. Combination with the site survey result in Huaxin Cement factory and Gezhouba Cement factory, the current occupational health status in dry cement kiln head of our country and environment protection requests about cement product at home and abroad were discussed, putting forward the essential meaning of this subject. The research status of dry cement rotary kiln mouth seal technique was reviewed, raising the main existed problems of kiln mouth seal. This paper studied on the smoke and dust control theory and measure taking Huaxing 4.74m kiln mouth as a research example and Gezhouba 3.5m kiln mouth as an analogy example, so as to resolve the key technical problem of smoke and dust drain diffusion from kiln mouth seal, to improve occupational health status effectively. At last, the main study content, innovation, research method and technical route.Chapter Two cement kiln mouth smoke and dust dynamic characteristics analysis research. Dust removal mechanism and dust collection device were summarized and Grain diameter definition, particle size distribution(that is degreeofdispersion) concept and Rosin-Rammler particle size distribution foundation were discussed. Kiln mouth smoke granule stress condition was analyzed. The sedimentation model of ringlike passage settle room was established, which divided the settling room into 4 parts, considering the effect of Brown diffusion,turbulence diffusion, gravity settling gravity and turbulent flow throwing power. Based on dimensional analysis, the settling discipline was obtained that showed how different diameter granule settled on the circle passage wall and at the bottom, and further more, the relationship between the top surface settling speed and wall, ground settling speed. The conclusion is that the along with the increase of grain diameter, the granule dimension-settling speed on the wall will decrease and then increase towards to a definite value, and it will increase with the ventilation flow rate increment; at the bottom, along with the increase of grain diameter, the granule dimension-settling speed on the wall will increase and then decrease with less effect of flow rate; the top surface settling speed formula is: (?)Chapter Three cement kiln mouth dust control gravity settling room deflector study. First, gravity settling room deflector was designed initially, including selling room size and structure. The calculation model of deflector was discussed containing calculation area, boundary condition, control formula, mathematical model and its heat transfer rule. Taking Huaxin 4.75m kiln as an example and circle air deflector as a typical numerical example, thorough numeric calculation, it showed that in the condition of air extracting pressure-70kPa, the air extracting pressure doesn't have effect on the inner kiln pressure space, neither on the normal ventilation, the air flow in the seal cover is stable and it will not cause vortex, neither cause dust accumulation in the vortex. The granule with diameter less than 50um will be drawn out. Contrasted with 3.5m kiln, it can be known that wind pressure gradient changes rarely, but because the settling distance minifies, under the condition of settling length unchangeable, the grain diameter is great, which shows that the settling effect is unsatisfactory, and vortex can be formed easily at the air extracting tuyere, thus it can't take grains away, stating that small diameter kiln without air deflector has good settling effect. Though numerical analysis, the following conclusions can be achieved.1.when using circle air deflector in settling room, with the increase of air draft pressure, small granules are taken out, the big granules settling rate increases. However, when the draw pressure is too high, the current drain will raise. So the pressure should be between-70kPa to 50kPa.2.Studied on three types of air deflector settling effect, that is ellipse(a)deflector, ellipse(b)deflector and round deflector. Through the grain diameter distribution at air draft and dust down spouting, it can be known that the settling ability is ellipse(a)deflector expanding type (â…¡) straight trunk type (â… )Chapter Four studied on the ventilation system of dust control. Through the research on the dust settling rules and gravity settling room deflector, big granules can be settled at a time,but the grains with diameter 50um must be collected twice. According to the features of sealed dust control device, it can use curtain to separate dust or unidirectional air flow to draw dust. Considering the effect of high temperature difference, using air curtain needs much more power than using kiln mouth push-pull type to remove dust at current and drawing-in type which would be mentioned later. So this chapter researched on the drawing-in type in detail, including the dust control program and principle, it numeric calculation, which contained the model building and simplify, grids form and optimization, turbulent flow model choosing, boundary condition and initial condition choice and control formula selecting. Then,this chapter studied on the numerical analysis and contrast of different air draft opening number (1,2,4,6,8) and pressure distribution. The whole ventilation system with 6 air draft opening was designed, based on sufficient considering of drawing-in effect, cement dust stratification, flow filed pressure and speed distribution.1.Flow filed speed distribution1)When there are two drawing openings, air till leak from most part of circular arc side even the pressure reaches 1000Pa.2) When there are four drawing openings, the dust control effect can be guaranteed when every drawing opening negative pressure is 800Pa 900Pa.3)When there are six drawing openings, every drawing opening negative pressure is 400Pa, the minimum intake air speed is 2.8m/s,and the speed distribution is balance. So the drawing opening negative pressure 400Pa can be a turning point, that is there are six drawing openings, the dust control requirement can be achieved.4)When there are eight drawing openings, every drawing opening negative pressure is 300Pa, the minimum intake air speed is 2m/s, and the speed distribution is balance which is from 2.0m/s to 4.6m/s. This is a turning point to reach the requirement. As long as the drawing opening negative pressure is not less than 300Pa, dust can be controlled.2.Drawing opening total quality of flowThe opening negative pressure is 350Pa when there are six drawing openings and the speed is from 1.8m/s to 5m/s. The opening negative pressure is 300Pa when there are eight drawing openings and the speed is from 2.8m/s to 4.6m/s. That is to say, the drawing effect is the same when using six drawing openings with the pressure of 350Pa and when using eight drawing openings with the pressure of 300Pa and can assure 2m/s intake air speed at the gap. While the quality of flow is 3.87kg/s when using six drawing openings and 4.74kg/s when using eight, less almost 1kg/s. So using six air openings is suggested.3.Ventilation system design using six drawing openings Based on three-dimensional flow field of negative pressure room, fan's best site, air openings distribution, pipe diameter, angle and connection type are determined when using six drawing openings.