回转窑焚烧炉窑内结圈的原因分析 analysis of ring formation in rotary kiln incinerator

June 11, 2020
回转窑焚烧炉窑内结圈的原因分析
由于国内环保要求越来越严格,处置成本越来越高,因此外送危废处置中心的废弃物一般都尽量浓缩,致使此
 
类废弃物特别是固废和蒸馏残渣的热值普遍较高,多数情况下在3,000~5,000Kcal/kg之间。为了保持较好的燃
 
烬效果,回转窑普遍在950~1,150℃之间运行,而危废灰渣的熔点普遍在1,000~1,200之间。加上送入回转窑的
 
物料一般都较为复杂、热值波动较大、物料进料不均匀,且物料在窑内停留时间较长(一般在60~90分钟),比
 
较难做到及时调整燃烧过程,因此窑内温度一般都会有一定的波动,不可避免会出现窑内局部温度过高导致灰
 
渣熔融,进而粘附在回转窑内壁上。随着转窑的转动及由于内衬的温度呈梯度分布,部分熔融的灰渣可能会在
 
内衬材料上凝固下来,形成新的窑皮。随着窑的转动,部分灰渣可能会被再次熔融,并达到一定的平衡,这样
 
窑皮就不会增厚。但是如果没有达到平衡,掉落下来的灰渣少,窑皮就会逐步增厚,达到一定程度后就形成结
 
圈.:
 
analysis of ring formation in rotary kiln incinerator
 Since domestic environmental requirements are becoming more stringent and disposal costs are 
 
increasing, waste from hazardous waste disposal centres is generally concentrated as far as 
 
possible, resulting in a generally high calorific value of such waste, especially solid waste and 
 
distillation residues, in most cases between 3,000~5,000 Kcal/kg. To be a good burning effect, 
 
rotary kilns generally operate temp between 950~1,150℃, while the melting point of hazardous 
 
waste ash is generally between 1,000~1,200. Add into rotary kiln materials are generally more 
 
complex, calorific value fluctuation, material feed uneven, and materials in the kiln stay longer 
 
(generally in 60~90 minutes), it is more difficult to adjust the combustion process in time, so 
 
the kiln temperature will generally have a certain fluctuation, it is inevitable that the kiln 
 
local temperature too high lead to ash melting, and then adhere to the inner wall of rotary kiln. 
 
With the rotation of the rotary kiln and the gradient distribution of the temperature of the 
 
lining, the partially melted ash may solidify on the lining material to form a new kiln skin. As 
 
the kiln rotates, part of the ash may be melted again and reached a certain balance so that the 
 
kiln skin does not thicken. But if the balance is not reached and the ash falls down less, the 
 
kiln skin will gradually thicken, to a certain extent after the formation of a ring.
 
 
形成结圈的主要原因有如下几点:
1.回转窑的操作模式
根据操作温度的不同,回转窑有两种操作模式:干渣模式和熔渣模式。干渣操作模式在危废焚烧中最为常见,
 
也被证明是最为可靠的一种操作模式,常规一般认为925℃以下为干渣模式,正常配伍可以保证灰渣不会熔融,
 
此种操作模式结圈的可能性比较小。另外一种模式是熔渣模式,回转窑会在较高的温度运行,使得焚烧后形成
 
的灰渣融化成液态,常规的熔渣模式操作温度大于1,200℃,此种模式由于灰渣处于熔融态,一般也较难结圈。
 
如果操作温度运行在950~1,200℃之间,其操作正好介于干渣和熔渣操作模式中间,可以称为半熔融态操作模式
 
,比较容易产生部分熔融,但又不能完全熔融的工况出现,进而随着温度变化及波动,造成部分熔融的渣凝固
 
在转窑内衬上,同时包裹一些高熔点灰渣,窑皮逐渐加厚,进而造成结圈。
 
The main reasons for the formation of the ring are as follows:
 1. operation mode of rotary kiln
 According to the different operating temperature, there are two operating modes in rotary kiln: 
 
dry slag mode and slag melting mode. dry slag operation mode is the most common in hazardous 
 
waste incineration, and it has also been proved to be the most reliable operation mode. it is 
 
generally considered that below 925℃ is the dry slag mode, and the normal compatibility can 
 
ensure that the ash will not melt, and the possibility of such operation mode is relatively 
 
small. Another mode is slag melting mode, the rotary kiln will operate at a higher temperature, 
 
so that the ash formed after incineration melts into liquid, the conventional slag mode operation 
 
temperature is more than 1200℃, this mode is generally difficult to circle because the ash is in 
 
the melting state. When the operating temperature is between 950~1,200℃, the operation is just 
 
between dry slag and slag operation mode, which can be called semi-melting operation mode.
 
2.回转窑进料的及配风稳定性
危险废弃物包括液态、固态和半固态,特别是固废成分、形态比较复杂。一般占主导地位的回转窑固废进料以
 
抓斗+推料机或者溜槽等间歇进料为主,部分转窑还间歇处理一些直接入炉的低闪点的桶装特殊废液。由于间歇
 
进料会造成物料焚烧的大幅波动,以及会影响配风的稳定性,造成回转窑温度的波动较大,这也成为导致回转
 
窑窑内结圈的重要原因之一。
 
2. rotary kiln and air distribution stability
 Hazardous waste includes liquid, solid and semi-solid, especially the composition and morphology 
 
of solid waste. In general, the main solid waste feed of rotary kiln is intermittent feed such as 
 
grab push machine or chute. Some rotary kilns also intermittently treat some special barreled 
 
waste liquid with low flash point directly into the furnace. Because of the large fluctuation of 
 
material incineration caused by intermittent feeding and the influence on the stability of air 
 
distribution, the temperature fluctuation of rotary kiln is large, which is also one of the 
 
important reasons leading to the ring formation in rotary kiln.
 
3.灰渣的化学组分及灰熔点
回转窑底部灰渣的主要成分是一些无机氧化物,如SiO2、Al2O3、FeOx及CaO,另外由于部分危废高含盐,也普
 
遍含有一定量的低熔点碱金属盐如Na/K盐。若碱金属组分含量较高,由于其熔点低,因此入炉废料如果含盐量
 
较高,很容易在窑内浓缩,导致窑内结圈。而根据文献的实验研究结果,当分别提高SiO2、Al2O3及CaO的含量
 
时,其灰熔点温度都有不同程度的上升,因此底渣的成分对于灰渣软化温度有较大的影响。根据现场操作经验
 
,在此情况下,即使回转窑在较低温度运行时(比如850~950℃),窑内也可发现较多的熔融物。
 
3.Chemical composition of ash and ash melting point
 The main components of ash at the bottom of rotary kiln are some inorganic oxides, such as SiO2
 
、Al2O3、FeOx and CaO,. In addition, because of some dangerous waste high salt, there is also a 
 
certain amount of low melting point alkali metal salt such as Na/K salt. If the content of alkali 
 
metal components is high, because of its low melting point, so the waste into the furnace if the 
 
salt content is high, it is easy to concentrate in the kiln, resulting in the kiln ring. The 
 
temperature of ash melting point increases in different degrees when the content of SiO2、Al2O3 
 
and CaO increases, so the composition of bottom slag has great influence on the softening 
 
temperature of ash. On the basis of field operation experience, in this case, even if the rotary 
 
kiln operates at a lower temperature (e.g .850~950℃), more molten matter can be found in the 
 
kiln.