【作者】 张立强；

【导师】 马春元；

【作者基本信息】 山东大学 ， 热能工程， 2008， 博士

【摘要】 增强脱硫塔内循环,提高塔内颗粒浓度,是循环流化床半干法烟气脱硫工艺提高脱硫效率、提高钙利用率、降低造价的重要手段。不同位置发生的内循环对脱硫反应的贡献不同,因此提高脱硫塔内循环,并对内循环的有效性进行阐述,组织合理的内循环是需要研究的重要课题。目前循环流化床脱硫工艺主要依靠在塔顶部布置分离器,分离灰在塔内回落来增强内循环。本文首先对脱硫塔顶部物料回流过程进行了冷态试验,分析了物料回流并返混入主流的过程,回流颗粒在下落的过程中被主气流逐渐剥离向塔内扩散,返混沿径向可以分为三个区域:回流区、返混加速区和主流区。在一定的颗粒回流量下,相对最大回落长度与主气流速度基本呈指数型的递减分布;物料在塔内形成了浓度上部高,下部低的分布趋势,有效物料浓度进较低,可以采用外循环灰管的方式将分离物料在塔底送入,以提高利用率。提出了脱硫塔底部采用切向旋流和直流复合流化的方式,在冷态PDA试验台上对研究了表观气速、入口颗粒浓度以及切向旋流风率变化时塔内气固流动以及颗粒内循环特性。表观气速降低到0.68m/s,颗粒沉降作用明显,呈现环核流动特性。在塔底部,形成类似喷动床的流态,最高浓度为最低浓度的80倍,平均浓度比1.34m/s增加了220%。随着表观气速的降低,塔内颗粒逐渐集中于脱硫塔的主反应区域,物料的有效率提高。随着旋流流量的增加,在脱硫塔底部壁面附近区域出现回流区,这增强了气流扰动和气固混合,有利于增强物料的内循环。脱硫塔内高浓度区域集中于0.7R-1.0R之间。当旋流流量为30%时,壁面浓度与中心区域浓度比增加到180。随着旋流流量的增加,边壁高浓度区域也逐渐增大;物料浓度的有效率也逐渐增加,旋流的加入使塔内颗粒逐渐集中于塔的中下部。脱硫塔平均颗粒浓度随入口颗粒浓度的增加逐渐增加,且增加的幅度要大于入口颗粒浓度增加的幅度,塔内颗粒浓度的增加有利于颗粒的团聚,有利于颗粒在离心力作用下被分离而回落,明显增强了脱硫塔的内循环。颗粒粒径的径向分布中心高,壁面低,在0.8R-1.0R之间出现局部高峰。因此沿高度方向颗粒平均粒径逐渐减小,大颗粒的分离和回落现象主要集中于脱硫塔的中下部。提出了强化内循环脱硫塔的结构,底部采用夹层结构实现塔内壁面的旋转流动。研究了脱硫塔的阻力特性,旋流结构的流量分配以及塔内颗粒浓度分布特性。脱硫塔的阻力主要集中于喉口旋流段,占塔总阻力的60-80%,随表观空塔气速和入口颗粒浓度的增加旋流段阻力不断增加。旋流结构同时具有流量调节以及提高负荷适应性的作用,随着旋流入口的关闭,旋流流量逐渐减小,中心直流流量增大,塔内颗粒浓度逐渐降低。当表观空塔气速降低时,旋流流量降低,但颗粒沉降作用明显,塔内平均颗粒浓度得到明显的提高,可关闭部分旋流以满足塔内流态化的要求。将强化内循环脱硫塔应用于140MW机组,增加旋流结构后在塔内下部壁面区域形成了旋转流场,脱硫塔直管段内烟气流速呈现对称分布,脱硫塔内均匀性得到明显的提高。脱硫塔阻力主要集中于脱硫塔入口段,占总阻力的70-80%,增加旋流后阻力增加90-120Pa,占脱硫塔总阻力的20-25%。脱硫塔具有明显的内循环现象:相对于入口灰浓度,机组负荷为120MW,脱硫没投运时时脱硫塔底部壁面处的灰浓度增加了43%;机组负荷将为75MW时,在重力沉降和离心分离的作用下,脱硫塔底部距离壁面50mm和1050mm处灰浓度分别增加了122%和58%。脱硫投运后,颗粒粒径变大,增强了颗粒沉降和离心分离效应,塔内物料浓度得到极大的提高:塔底部距离壁面50mm处颗粒浓度提高了247倍,距离壁面300mm处浓度增加了337%。壁面有明显的物料回流存在,增加了反应的表面积提高了脱硫效率,壁面大量物料的回流和分离不断冲刷壁面,有效壁面了结垢现象。更多还原

【Abstract】 The industry of flue gas desulfurization has large market and expanded space. The CFB-FGD is widely applied with its advantage. Internally circulating of a large number of solid is important in CFB-FGD, which can increase the particle concentration in the bed and increase the desulfurization efficiency and the utilization of the calcium sorbent. There are many methoad to enhence the internally circulating of the particle. Different types of method have different effect to the desulfurization reaction process. One of the important tasks is to discuss the validity of the internally circulating and realize the effective internally circulating of the sorbent.The separator in the outlet of the CFB is mainly used in desulfurization technology. The process of particle flow in the top of the bed is investigated in this thesis. Ways to improve uniformity of CFB-FGD are discussed in cold experimental apparatus. The falling particle is effected by the gas flow. The gas and solid flow in the CFB can be divided three regions: the back flow zone, back mixing and acceleration zone and the main flow zone. The max length of the particle falling decrease in exponential type with the increase of the superficial gas velocity. The pariticle concentration in top of the bed is heigher than the bottom. More solid concentrated in the middle and top of the bed., which decrease the validity of the sorbent to desulfurization reaction. In order to increase the utilization of sorbent, the calcium sorbent should be send to the bottom of the bed.Ways to inprove the validity of pariticle is studied in cold experimental apparatus. When superficial gas velocity decrease to 0.68m/s, the phenomenon of solid sedimentation is obvious. Core-annular flow pattern appears. In the bottom of the bed, the ratio of maximum of the concentration to minimum reach 80. The average concentration increased 220% than the condition of the superficial gas velocity is 1.34m/s. so the validity of the solid invrease with the decrease of the superficial gas velocity.Composite fluidization of tangential swirl-once through flow is put forward to. It adds tangential swirl flow under the once-through fluidized of venturi. This is a valid way to improve the validity of the particle. The characteristics of flow under composite fluidization are studied The characteristics of gas-solid two-phase flow and particle circulation is studied in cold experimental apparatus.With the increase of the swirling flux, reflux appears near the wall. The gas turbulence and the mixing of the gas and the solid is enhenced. In the zone of r/R is 0.7 to 1.0, the solid concentration is higher. In the case of x=30%, the ratio of concentration near the wall to that in the core of the bed is 180. The zone of higher solid concentration become larger with the increase of the swirling flux, thus the validity of solid also increase. When the inlet particle concentration increase, the average concentration of particle also increase. The solid tend to aggregate, and can be easily separated with the centrifugal force. The internally circulating of particle is enhenced. The average particle size in the center is larger than that near the wall. In the area of 0.8R to 1.0R, the particle size peak value appears. Most of the larger particle concentrated in the bottom of the bed.A new internally circulating FGD tower is put forward to based of the experiment. In the bottom of the tower, new type of swirl structure is adopt. The resistance pressure character is studied. The most pressure drop is the venturi throat and the swirl region whose pressure drop is 60%-80% of the all. When shut off part of the swirling inlet, the swriling flow rate decrease. In the case of load of the power plant decrease, the swirling inlet can be shut off to increase the gas velocity in the bottom of the tower.The new internally circulating desulfurization tower was applied in a 140MW power plant. The distribution of the flow and solid concentration is studied in this power plant. The uniformity can be got more quickly. The solid concentration near the wall is 43% higher than that of inlet, when the power load is 120MW. With the decrease of the load, the extend of solid concentration increase become larger. When the desulfurization sytem is running, the size of the particle become larger and the solid concentration improed rapidly.更多还原