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1.現(xiàn)狀
幾乎所有的燒結(jié)磚廠都是以隧道窯所回收的熱量作為干燥室的熱源，作為能源的再生利用，這一手段是可取的。但是，由于目前隧道窯回收熱量的工藝方法有很多弊端，給產(chǎn)品質(zhì)量控制及外部環(huán)境造成許多問題，因此，深入研究隧道窯熱量回收的合理方式，有效的回收隧道窯余熱就很有必要。尤其是制磚工業(yè)節(jié)能環(huán)保要求的提升，燒結(jié)磚廠應(yīng)用二次碼燒工藝生產(chǎn)空心砌塊與保溫砌塊的生產(chǎn)技術(shù)正在全力推廣，更顯示出解決這一問題的緊迫性。
最為流行的隧道窯熱量回收方法是抽取隧道窯尾部的中低溫余熱作為干燥熱源，不足部分抽取高溫?zé)煙徇M(jìn)行補(bǔ)充，這種余熱回收的方式會(huì)產(chǎn)生以下弊端：
（1）隧道窯焙燒帶前后兩端抽力的雙重影響，焙燒帶火度向前或向后飄逸，隧道窯的運(yùn)行控制及調(diào)節(jié)極為困難。
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）煙氣中含有水蒸氣，進(jìn)入干燥室的干燥介質(zhì)并非干熱空氣，干燥至某一程度時(shí)，制品表面的水蒸氣分壓與干燥介質(zhì)中的水蒸氣分壓達(dá)到平衡，導(dǎo)致干燥參與水分較高，達(dá)不到2%左右的理想指標(biāo)，并且，坯體中的水分會(huì)在隧道窯預(yù)熱帶進(jìn)入煙氣，濕熱煙氣又致坯體在干燥室不能徹底干燥，這樣的惡性循環(huán)對(duì)生產(chǎn)過程十分有害。
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）理論上焙燒帶過后，制品從最高燒成溫度至出窯溫度時(shí)的熱量差值，除去窯體散熱，窯車及制品出窯時(shí)帶走的熱量，區(qū)域均可回收。但上述隧道窯熱量回收的方法未能做到最大限度的回收熱量，尤其未能回收高溫?zé)崃?，致使制品出窯溫度接近室溫才更為合理。這樣一方面未能給干燥室提供足夠的熱量，需要補(bǔ)充約30%的高溫?zé)煙?，而另一方面窯車與制品出窯時(shí)又損失了不少的熱量。
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）這一抽取余熱的方法使冷卻帶溫度曲線未能達(dá)到工藝要求的合理狀態(tài)，制品極有可能在中溫段出現(xiàn)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）大量煙氣進(jìn)入送熱管道系統(tǒng)及干燥室。煙氣中的酸性氣體對(duì)干燥車，干燥托盤及風(fēng)機(jī)腐蝕嚴(yán)重，干燥室外溢的含有煙塵及酸霧的氣體對(duì)鋼結(jié)構(gòu)廠房及周圍環(huán)境構(gòu)成嚴(yán)重威脅。
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.冷卻帶合理的溫度曲線
依據(jù)隧道窯的工作原理，隧道窯的工作系統(tǒng)分為預(yù)熱焙燒帶及冷卻帶兩部分，這兩帶應(yīng)分開工作，互不干擾，分開焙燒帶及冷卻帶最有效的方法是急冷阻隔氣幕。冷卻帶按照冷卻速度分為三段。
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
為了將焙燒帶與冷卻帶分開，必須在冷卻帶開始段設(shè)置急冷氣幕，首先急冷氣幕有效阻隔了保溫區(qū)域氣體流向冷卻區(qū)域的逆向流動(dòng)，使得排煙系統(tǒng)的調(diào)節(jié)更為流暢：同時(shí)。急冷使得制品力學(xué)性能及制品表觀質(zhì)感得到大幅改善。第三，急冷氣體與熱制品熱交換后產(chǎn)生的高溫氣體便于高溫余熱回收。
必須注意的是，急冷段的位置必須是最高燒成溫度至800°C左右（部分原料可以降至700°C），這時(shí)制品具有很好的彈性，制品的收縮變形為彈性變形而非塑性變形，制品沒有爆炸的危險(xiǎn)。因此，急冷氣幕依據(jù)限定的窯內(nèi)溫度值進(jìn)行自動(dòng)控制非常重要，對(duì)于大斷面隧道窯，急冷氣幕分若干組布置在窯頂。
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 緩慢冷卻帶
制品中的SiO2在573°C由α石英轉(zhuǎn)變?yōu)?/span>β石英，晶型轉(zhuǎn)變的體積變化率為0.82%。這一低溫型的轉(zhuǎn)變體積雖然不大，但是轉(zhuǎn)化速度快，有事在無液相對(duì)緩沖的條件下進(jìn)行轉(zhuǎn)化，因而破壞性極強(qiáng)，若有不慎，就會(huì)導(dǎo)致制品炸裂。因此，在500~800°C范圍內(nèi)，不允許采取任何冷卻措施，制品冷卻必須非常緩慢。換句話說，就是在隧道窯這一段，必須有足夠的窯車數(shù)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 加速冷卻帶
從500°C至產(chǎn)品出窯溫度（50°C左右），可以加速冷卻制品，一般采取窯尾背壓風(fēng)機(jī)向窯內(nèi)鼓入冷空氣的方法。這一冷卻過程較長(zhǎng)，所以隧道窯這一段必須有足夠的長(zhǎng)度，加大冷卻風(fēng)量也是一種很好的辦法，這樣可以給干燥室提供更多的熱空氣量。
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.冷卻帶的熱量回收模型
綜上所述，隧道窯冷卻帶有兩部分熱量可以回收，一是急冷氣幕產(chǎn)生的高溫?zé)崃?，二是加速冷卻產(chǎn)生的低溫?zé)崃俊＿@兩部分熱量介質(zhì)是絕對(duì)的潔凈干熱空氣，可以提供給干燥室放心使用。急冷氣幕鼓入窯內(nèi)后，窯內(nèi)制品內(nèi)外會(huì)產(chǎn)生較大的溫差，為了保證窯內(nèi)溫度及制品溫度的均勻性，抽出急冷氣幕產(chǎn)生的高溫氣體應(yīng)逆流抽出，即高溫氣體抽出口比急冷氣體鼓入口更接近隧道窯出車端。
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.
由于窯內(nèi)抽出的高溫氣體溫度很高，因此，抽風(fēng)支管必須用耐熱鋼材制安；同時(shí)，抽風(fēng)支管必須設(shè)有配送冷風(fēng)的特殊閥門，熱風(fēng)總管道也須配有冷風(fēng)進(jìn)口閥門，最終進(jìn)入高溫?zé)崃炕厥诊L(fēng)機(jī)的熱空氣溫度不超過300°C。
加速冷卻的大量冷空氣又窯尾鼓入窯內(nèi)，與制品熱交換之后從窯頂逐步抽出。進(jìn)入低溫?zé)崃炕厥诊L(fēng)機(jī)的熱空氣溫度大約在150°C。干燥室要求干燥介質(zhì)的溫度及風(fēng)量與余熱回收風(fēng)機(jī)提供的熱空氣溫度及風(fēng)量完全不同。所以，要另設(shè)置一臺(tái)干燥室送熱風(fēng)機(jī)與隧道窯預(yù)熱風(fēng)機(jī)串聯(lián)使用，在兩者之間須設(shè)立一集風(fēng)箱，便于高溫?zé)峥諝?，低溫?zé)峥諝馀c摻入的冷空氣混合，使得送熱風(fēng)機(jī)能向干燥室提供合適的溫度與風(fēng)量的干燥介質(zhì)。這一過程可以做成全自動(dòng)控制。同時(shí)隧道窯工作系統(tǒng)與干燥室工作系統(tǒng)完全脫開，有利于各自的單獨(dú)控制與調(diào)節(jié)。
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.隧道窯其他可回收熱量
4.1煙熱
在隧道窯焙燒帶焙燒制品的燃料燃燒產(chǎn)生的大量煙氣在排煙風(fēng)機(jī)的作用下向預(yù)熱帶流動(dòng)，預(yù)熱坯體，使坯體逐步升溫，如果在預(yù)熱帶350°C處抽出高溫?zé)煙?，?shì)必影響預(yù)熱帶初期煙氣對(duì)坯體的預(yù)熱效果。而利用高溫?zé)煔獾淖畲髩奶幨菬煔庵械乃嵝詺怏w會(huì)對(duì)干燥設(shè)備帶來嚴(yán)重的腐蝕而干燥室溢出氣體會(huì)危害環(huán)境。因此，采用煙熱作為干燥介質(zhì)是不可取的，應(yīng)使煙氣在隧道窯內(nèi)與坯體充分交換，使其溫度降至100~150°C時(shí)，由窯內(nèi)排出，再通過消煙除塵設(shè)備集中處理。達(dá)到國家標(biāo)準(zhǔn)要求后排放。
4.2窯體空腔換熱
過去把窯體空腔換熱作為一種窯體保溫措施，隨著保溫材料檔次的提升，這種換熱方式已逐步淘汰，尤其是窯墻空腔換熱。現(xiàn)在有些隧道窯為了降低窯頂?shù)鯍旖Y(jié)構(gòu)溫度，保證窯頂安全，在窯頂保溫層上表面與吊梁之間仍設(shè)有窯頂空腔換熱，換熱后的熱空氣溫度很低，大約為50°C左右，可以作為干燥介質(zhì)的補(bǔ)充風(fēng)量。
4.3窯車?yán)鋮s后的熱風(fēng)
現(xiàn)代隧道窯均設(shè)有車下壓力平衡系統(tǒng)。在窯車蓄熱最大點(diǎn)位置設(shè)置車下冷卻風(fēng)機(jī)，向窯車鋼結(jié)構(gòu)部分吹風(fēng)以冷卻窯車，熱交換后的氣體向窯頭及窯尾兩個(gè)方向流動(dòng)。流向窯頭的氣體在相應(yīng)排煙位置抽出以達(dá)到預(yù)熱帶上下壓力平衡。由于窯車之間密封不是十分嚴(yán)密，所以抽出的氣體中會(huì)有竄入窯車下的煙氣成分，故其一般進(jìn)入窯爐排煙系統(tǒng)與煙氣一并處理。而流向窯尾的氣體通過管道進(jìn)入低溫?zé)崃炕厥罩鞴艿馈?/span>
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.結(jié)論
（1）通過急冷氣幕可以把隧道窯分為兩部分，只要隧道窯回收熱量與冷卻工藝要求相結(jié)合，就可以在隧道窯冷卻帶有效的回收潔凈的干熱空氣作為干燥介質(zhì)。
（2）經(jīng)計(jì)算和實(shí)踐檢驗(yàn)，由隧道窯冷卻帶回收的熱量可占隧道窯總熱耗的35%-45%，能基本滿足干燥室的熱量需求，例如熱耗指標(biāo)380kcal//kg的隧道窯。回收熱量可高達(dá)152kcal//kg,干燥室的熱耗指標(biāo)約為1100kcal//kg水，當(dāng)濕坯水分由20%干燥降至參與水分2%時(shí)，需要熱量為160kcal//kg,供需基本平衡。
（3）對(duì)于內(nèi)燃隧道窯，只要不是超熱焙燒，這一熱量回收的方法同樣適用，最好內(nèi)燃比例不要超過80%。
（4）對(duì)于二次碼燒隧道窯，千萬不能抽取煙氣作為干燥介質(zhì)，既不利于隧道窯的焙燒，也不利于環(huán)境保護(hù)，同時(shí)也會(huì)對(duì)干燥設(shè)備及鋼結(jié)構(gòu)廠房造成傷害。
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.
-西安博墾特建材科技有限公司/黃永新
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