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1.现状
几乎所有的烧结砖厂都是以隧道窑所回收的热量作为干燥室的热源，作为能源的再生利用，这一手段是可取的。但是，由于目前隧道窑回收热量的工艺方法有很多弊端，给产品质量控制及外部环境造成许多问题，因此，深入研究隧道窑热量回收的合理方式，有效的回收隧道窑余热就很有必要。尤其是制砖工业节能环保要求的提升，烧结砖厂应用二次码烧工艺生产空心砌块与保温砌块的生产技术正在全力推广，更显示出解决这一问题的紧迫性。
最为流行的隧道窑热量回收方法是抽取隧道窑尾部的中低温余热作为干燥热源，不足部分抽取高温烟热进行补充，这种余热回收的方式会产生以下弊端：
（1）隧道窑焙烧带前后两端抽力的双重影响，焙烧带火度向前或向后飘逸，隧道窑的运行控制及调节极为困难。
The tunnel kiln firing zone is affected by the pumping force of both the fornt
and rear ends, so the firing zone fire moves forward re backward, and the
operation contorl and adjustment of the tunnel kiln is extremely difficult.
（2）烟气中含有水蒸气，进入干燥室的干燥介质并非干热空气，干燥至某一程度时，制品表面的水蒸气分压与干燥介质中的水蒸气分压达到平衡，导致干燥参与水分较高，达不到2%左右的理想指标，并且，坯体中的水分会在隧道窑预热带进入烟气，湿热烟气又致坯体在干燥室不能彻底干燥，这样的恶性循环对生产过程十分有害。
The flue gas contains steam, and the drying medium entering the drying chamber
is not dry hot air. When it is dried to a certain extent, the pressure of steam
on the surface of the product is balanced with the pressure of steam in the
drying medium, resulting in higher dry residual moisture, which is much higher
than the ideal index of 2%, and the moisture in the bricks will enter the flue
gas in the tunnel kiln prefiring zone, and the hot and humid flue gas will
cause that the bricks cannot be fully dried inthe drying chamber, such a
vicious cycle is very harmful to the production process.
（3）理论上焙烧带过后，制品从最高烧成温度至出窑温度时的热量差值，除去窑体散热，窑车及制品出窑时带走的热量，区域均可回收。但上述隧道窑热量回收的方法未能做到最大限度的回收热量，尤其未能回收高温热量，致使制品出窑温度接近室温才更为合理。这样一方面未能给干燥室提供足够的热量，需要补充约30%的高温烟热，而另一方面窑车与制品出窑时又损失了不少的热量。
Theoretically, after the firing zone is passed, the heat difference form the
highest firing temperature of the products to the temperature at which the
products exiting the tunnel kiln, expcept for the heat removed by heat
dissipation of the kiln, and taken away by the kiln cars and finished products
when exiting the tunnel kiln cars and finished products when exiting the tunnel
kiln, the rest heat can be recovered. However, the above method of heat
recovery in the utmost extent, especially the high, the average temperature
inside and outside the brick stacks is about 150°C, yet it is more reasonable
if the kiln temperature is close to the room temperature. Thus, on the one
hand, it is not possible to provide sufficient heat to the drying chamber and
it is necessary to replenish baout 30% of the high-temperature smoke heat, and
on the other hand, l lot of heat is lost when the kiln cars and finished bricks
leave the tunnel kiln.
（4）这一抽取余热的方法使冷却带温度曲线未能达到工艺要求的合理状态，制品极有可能在中温段出现炸裂。
This method of extracting residual heat makes the cooling zone temperature
curve fail to reach the reasonable state of the process requirments, and
the product is very likely to burst in middle temperature sertion.
（5）大量烟气进入送热管道系统及干燥室。烟气中的酸性气体对干燥车，干燥托盘及风机腐蚀严重，干燥室外溢的含有烟尘及酸雾的气体对钢结构厂房及周围环境构成严重威胁。
A large amount of flue gas enters the heat pipe system and drying chamber. The
acid gas in the flue gas is seriously corrosive to the drying car, the drying
palletes and the fan. The gas containing the dusts and acid mist discharged
from the drying chamber is a serious threat to the steel structure of the plant
and the surrouding environment.
2.冷却带合理的温度曲线
依据隧道窑的工作原理，隧道窑的工作系统分为预热焙烧带及冷却带两部分，这两带应分开工作，互不干扰，分开焙烧带及冷却带最有效的方法是急冷阻隔气幕。冷却带按照冷却速度分为三段。
According to the working principle of the tunnel kiln, the working system of
the tunnel kiln is divided into two parts: the preheating firing zone and
the cooling zone. The two zones should work separately without mutual
interference, and the most effective method for separating the firing zone and
the cooling zone is a quenching air curtain. The cooling zone is
divided into three sections according to the cooling speed.
2.1急冷段
为了将焙烧带与冷却带分开，必须在冷却带开始段设置急冷气幕，首先急冷气幕有效阻隔了保温区域气体流向冷却区域的逆向流动，使得排烟系统的调节更为流畅：同时。急冷使得制品力学性能及制品表观质感得到大幅改善。第三，急冷气体与热制品热交换后产生的高温气体便于高温余热回收。
必须注意的是，急冷段的位置必须是最高烧成温度至800°C左右（部分原料可以降至700°C），这时制品具有很好的弹性，制品的收缩变形为弹性变形而非塑性变形，制品没有爆炸的危险。因此，急冷气幕依据限定的窑内温度值进行自动控制非常重要，对于大断面隧道窑，急冷气幕分若干组布置在窑顶。
In order to separate the firing zone from the colling zone, a quenching air
curtain must be provided at the beginning of the cooling zone, Firstly, the
quenching air curtain effectively blocks the reverse flow of the airflow from
the insulated area to the cooling area, so that the adjustment of the exhaust
system is smoother; meanwhile, quenching results in a significant improvement
in the mechanical properties of the product and the apparent texture of the
product. Third, it is convenient for recovering the high temperature gas
generated after the heat exchange between the quenching gas and the hot product
facilitates.
It must be noted that the location of the quenching section must be between the
highest firing temperature and around 800°C (for some materials-700°C), when
the product has good elasticity ,the shrinkage deformation of the product is
elastic deformation rather than deformation, and there is on danger of the
product bursting. Therefore, it is very important that the quenching air
curtain is automatically controlled according to the defined temperature value
in the kiln. For large-section tunnel kiln, the quenching air curtain is
arranged in several groups(rows) at the top of the kiln.
2.2 缓慢冷却带
制品中的SiO2在573°C由α石英转变为β石英，晶型转变的体积变化率为0.82%。这一低温型的转变体积虽然不大，但是转化速度快，有事在无液相对缓冲的条件下进行转化，因而破坏性极强，若有不慎，就会导致制品炸裂。因此，在500~800°C范围内，不允许采取任何冷却措施，制品冷却必须非常缓慢。换句话说，就是在隧道窑这一段，必须有足够的窑车数量。
The SiO2 in the product was converted form α-quartz to β-quartz at 573°C, and
the volume change rate of the caystal form transition was 0.82%. Although the
low-temperature type has a small transformation volume, the conversion speed is
fast, and the conversion is carried out with-out liquid phase buffering, so
that the destructivepro-perty is extremely strong, and if it is inadvertent,
the product may burst. Therefore, in the range of 500~800°C， no cooling measures are allowed, and
the product coolong must be very slow, In otherwords, in this section of the
tunnel kiln, there must beenough kiln cars.
2.3 加速冷却带
从500°C至产品出窑温度（50°C左右），可以加速冷却制品，一般采取窑尾背压风机向窑内鼓入冷空气的方法。这一冷却过程较长，所以隧道窑这一段必须有足够的长度，加大冷却风量也是一种很好的办法，这样可以给干燥室提供更多的热空气量。
The cooling can be accelerated in the area from 500°C to the temperature at
which the finished products exit the tunnel kiln (500°C)，generally, the pressure balancing fan
at the tail of the tunnel kiln will be used to blow cold air into the kiln.
This cooling process is long, so the length of the tunnel kiln must be of
sufficient length. it is also a good method to increase the cooling air volume,
which can provide more drying air to the drying chamber.
3.冷却带的热量回收模型
综上所述，隧道窑冷却带有两部分热量可以回收，一是急冷气幕产生的高温热量，二是加速冷却产生的低温热量。这两部分热量介质是绝对的洁净干热空气，可以提供给干燥室放心使用。急冷气幕鼓入窑内后，窑内制品内外会产生较大的温差，为了保证窑内温度及制品温度的均匀性，抽出急冷气幕产生的高温气体应逆流抽出，即高温气体抽出口比急冷气体鼓入口更接近隧道窑出车端。
In summary, there are two kinds of heat that can be recoverd in the tunnel kiln
cooling zone, one is the high-temperature heat generated by the quenching air
curtain, and the other is the low-temperature heat generated by the accelerated
cooling. These two parts of the heat medium are absolutely clean and dry hot
air, which can be used safely in the drying room. After the quenching air
cuitain is blown into the kiln, a large temperature difference will occur
inside and outside the product in the kiln. In order to ensure the uniformity
of the product in the kiln and the temperature of the product, the high
temperature gas generated by the quenching air curtain should be extracted counter-currently,
that high temperature gas outlet is closer to the tunnel kiln exit than the
rapid cooling air blowing inlet.
由于窑内抽出的高温气体温度很高，因此，抽风支管必须用耐热钢材制安；同时，抽风支管必须设有配送冷风的特殊阀门，热风总管道也须配有冷风进口阀门，最终进入高温热量回收风机的热空气温度不超过300°C。
加速冷却的大量冷空气又窑尾鼓入窑内，与制品热交换之后从窑顶逐步抽出。进入低温热量回收风机的热空气温度大约在150°C。干燥室要求干燥介质的温度及风量与余热回收风机提供的热空气温度及风量完全不同。所以，要另设置一台干燥室送热风机与隧道窑预热风机串联使用，在两者之间须设立一集风箱，便于高温热空气，低温热空气与掺入的冷空气混合，使得送热风机能向干燥室提供合适的温度与风量的干燥介质。这一过程可以做成全自动控制。同时隧道窑工作系统与干燥室工作系统完全脱开，有利于各自的单独控制与调节。
Because the temperature of the high tempera ture gas extracted from the kiln is
very high, the exhaust branch pipe must be made of heat-resistant steel. At the
same time, the exhaust pipe must be equipped with a special valve for
distributing cold air. The hot air inlet valve. The temperature of the hot air
which finally enters the high temperature heat recovery fan cannot exceed
300°C.
The temperature and volume of the drying medium required by the drying chamber
is totally different from the waste heat recovery fan. Therefore, it is
necessary to set up a drying chamber heating fan to work together with the
heating fan of the tunnel kiln, and to set up an air collecting chamber between
the two fans, so that the high temperature hot air, low temperature hot air and
the cool air can be mixed, and the heating fan can peovide drying medium with
suitable temperature and volume for the drying chamber. This process can be
fully automatic. At the same time, the tunnel kiln working system and the
drying chamber working system are completely disconnected, which is beneficial
to their respective individual control and regulation.
4.隧道窑其他可回收热量
4.1烟热
在隧道窑焙烧带焙烧制品的燃料燃烧产生的大量烟气在排烟风机的作用下向预热带流动，预热坯体，使坯体逐步升温，如果在预热带350°C处抽出高温烟热，势必影响预热带初期烟气对坯体的预热效果。而利用高温烟气的最大坏处是烟气中的酸性气体会对干燥设备带来严重的腐蚀而干燥室溢出气体会危害环境。因此，采用烟热作为干燥介质是不可取的，应使烟气在隧道窑内与坯体充分交换，使其温度降至100~150°C时，由窑内排出，再通过消烟除尘设备集中处理。达到国家标准要求后排放。
4.2窑体空腔换热
过去把窑体空腔换热作为一种窑体保温措施，随着保温材料档次的提升，这种换热方式已逐步淘汰，尤其是窑墙空腔换热。现在有些隧道窑为了降低窑顶吊挂结构温度，保证窑顶安全，在窑顶保温层上表面与吊梁之间仍设有窑顶空腔换热，换热后的热空气温度很低，大约为50°C左右，可以作为干燥介质的补充风量。
4.3窑车冷却后的热风
现代隧道窑均设有车下压力平衡系统。在窑车蓄热最大点位置设置车下冷却风机，向窑车钢结构部分吹风以冷却窑车，热交换后的气体向窑头及窑尾两个方向流动。流向窑头的气体在相应排烟位置抽出以达到预热带上下压力平衡。由于窑车之间密封不是十分严密，所以抽出的气体中会有窜入窑车下的烟气成分，故其一般进入窑炉排烟系统与烟气一并处理。而流向窑尾的气体通过管道进入低温热量回收主管道。
The large amount of flue gas generated by the combustion of the fuel for firing
the bricks flows to the preheating zone ynder the bricks and to gradually
improve the temperature of the smoke exhausting fan to pre-heat the bricks and
gradually improve the temperature of the bricks. If the high temperature smoke
heat is withdrawn at the temperature of 350°C， the brick pre-heating effect of the smoke in the
pre-heating zone will be affected inevitably.
The biggest disadvantage of using high temperature flue gas is that the acid
gas in the flue gas will cause serious coeeosion to the drying equiment and the
gas in the drying chamber will harm the environment. Therefore ,it is not
advisable to use soot as a drying medium, so that flue gas should be fully
exchanged with the blank in the tunnel kiln, and when the temperature is
lowered to 100-150°C，it is discharged from the kiln and then passed through the smoke-removing
and dust-removing equipment. Centralized treatment, discharge after
meeting national standards. The biggerst disadvantage of using high
temperature flue gas is that the acid gas in the flue gas will cause
serious coeeosion to the drying equipment and the gas in the
drying chamber will harm the environment. Therefore, it is not advisable
to use smoke heat as a drying medium. The flue gas should be fully
exchanged with the bricks in the tunnel kiln, and when the temperature is
lowered to 100-150°C；it is discharged from the kiln and then passed through the smoke-removing and
dust-removing equipment for centralized tretment, and then discharge after
meeting national standards.
In the past, the kiln cavity heat transfer was taken as a kind of kiln
insulation measure. With the improvement of the insulation meterial grade, this
heat transfer mode has been gradually eliminated, espe-cially the kiln wall
cavity heat transfer. In order to reduce the temperature of the kiln roof, some
tunnel kiln still has kiln top cavity heat exchange between the upper surface
of the kiln roof insulation layer and the lifting beam , and the hot air
temperature after heat exchange is very low, it is about 50°C and can be used
as a supplemental air volume for drying media.
Modern tunnel kiln has a pressure balance system. the cooling fan under kiln
cart is set uo at the maximum heat storage point of the tunnel kiln carts to
blow cooling air to the steel structure of the kiln carts for cooling the kiln
carts. The air after heat exchanged flows to both the kiln head is withdrawn at
the corres ponding exhaust position so that the pressure above and below the
kiln carts are balanced. Since the seal between the kiln cars is not very
tight, the extracted gas will contain smoke components, which flow into the
lower part of the kiln carts, so it normally enters the kiln smoke exhaust
system and processed toge ther with the flue gas. The gas flowing to the kiln
tail enters the low-temperature heat recovery main pipe through the pipes.
5.结论
（1）通过急冷气幕可以把隧道窑分为两部分，只要隧道窑回收热量与冷却工艺要求相结合，就可以在隧道窑冷却带有效的回收洁净的干热空气作为干燥介质。
（2）经计算和实践检验，由隧道窑冷却带回收的热量可占隧道窑总热耗的35%-45%，能基本满足干燥室的热量需求，例如热耗指标380kcal//kg的隧道窑。回收热量可高达152kcal//kg,干燥室的热耗指标约为1100kcal//kg水，当湿坯水分由20%干燥降至参与水分2%时，需要热量为160kcal//kg,供需基本平衡。
（3）对于内燃隧道窑，只要不是超热焙烧，这一热量回收的方法同样适用，最好内燃比例不要超过80%。
（4）对于二次码烧隧道窑，千万不能抽取烟气作为干燥介质，既不利于隧道窑的焙烧，也不利于环境保护，同时也会对干燥设备及钢结构厂房造成伤害。
The tunnel kiln can be divided into two parts by the quenching air curtan. As
long as the heat recovery of the tunnel kiln is combined with the cooling
process requirements, the clean dry hot air can be effectively recovered as a
drying medium in the tunnel kiln cooling zone.
After calculation and practice test, the heat recovered from the cooling zone
of the tunnel kiln can account for 35% to 45% of the total heat consumption of
the tunnel kiln, which can basically meet the heat demand of the drying room.
For example, in a tunnel kiln with a heat consumption index of 380kcal/kg, the
heat recovery can be as high as 152kcal/kg, and the heat loss index of the
drying chamber is about 1100kcal for one kilogram of water. 160kcal/kg of heat
os needed to reduce the wet billet moisture from 20% to 2% of residual
moisture, and the sipply and demand are basically balanced.
For internal combustion tunnel kiln, as long as it is not superheated, this
method of heat recovery is also applicable. The internal cambustion ratio
should not exceed 80%.
For the two-time stacking and firing tunnel kiln, it is absolutely forbidden to
extract the flue gas as the drying medium, which is not conducive to the firing
of the tunnel kiln, and is not conducive to environmental protection, and also
causes damage to the drying equipment and the steel structure workshop.
-西安博垦特建材科技有限公司/黄永新
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