【文章翻譯】廢氣鍋爐失火類型與預防辦法 Types of Exhaust Gas Boiler (EGB) Fires and Ways to Prevent Them

An Exhaust Gas Boiler is a type of heat recovering system on ships which allows the exhaust heat of the main engine to produce steam while going out in the atmosphere.

廢氣鍋爐是一種船用廢熱回收系統，利用主機的廢氣在排出大氣層前製造蒸氣。

Every system, which is operated at high temperature, always has a risk of fire. This applies to EGB which has the inlet temperature of exhaust gases @ 300-400 deg. C. The most common type of Exhaust Gas Boiler (EGB) used on ships are water tube boilers.

任何一種在高溫工作的系統都有機會失火，這句話也適用在廢氣鍋爐，因為它的進口溫度高達300-400度。其中最常見的廢氣鍋爐種類就是水管式鍋爐。

In water tube type of arrangement, the water passes through tube stack, which is arranged in the path of exhaust gas inside the exhaust gas trunking of the main engine. The exhaust gas flows over the tube stacks and heats the water, thus producing steam.
在水管精密的排列下，鍋爐水會通過在主機排氣管道內的水管群，而廢氣通過水管間來加熱鍋爐水進而產生蒸氣。

The main constituent of the soot deposit is particulates but in addition, some unburnt residues of fuel and lubricating oils may be deposited in the boiler.

煙灰沉積物主要的成分為灰塵微粒，但未完全燃燒的燃油和滑油可能也會沉積在鍋爐當中。

Soot deposit and fire in the EGB can be-

煙灰沉積與廢氣鍋爐失火可能由下列幾點造成：

1. 主機燃油燃燒不完全 Due to the poor combustion of fuel in the main engine
2. 減速航行時間過長 Due to prolong slow steaming
3. 船舶主機的長時間運轉 Long maneuvering of the ship
4. 頻繁啟動、停止引擎 Frequent starting and stopping of the engine
5. 燃油、汽缸油品質過低 Poor grade of fuel oil/ cylinder oil
6. 廢氣流動速度過低 Low exhaust gas velocity passing the EGB
7. 鍋爐水流動速度過低 Low water inlet velocity in the water tubes
8. 鍋爐水流動率過低Low circulation water flow ratio*1

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For a better understanding, it is better to distinguish the EGB fire in stages rather than in types. EGB fires can be differentiated in two or three stages depending upon the intensity of the fire.

為了方便理解，我們利用等級來區分廢氣鍋爐失火，而不是以類型區分。
廢氣鍋爐失火可以依據火焰的溫度來區分為三個等級：

        等級一：普通煙灰火 Normal Soot fire

        等級二：氫氣火 Hydrogen Fire

        等級三：鐵火 Iron Fire

等級一：普通煙灰火 Normal Soot fire (比較常見的小火災)

Soot is deposited in the water tube of the exhaust boiler. When the ship is at slow speed, the exhaust temperature of the main engine may vary from 100 to 200 deg C. This temperature is enough to ignite “wet soot” whose ignition temperature is around 150 deg. C.

煙灰會沉積在排氣鍋爐的水管表面上，當船舶以低速前進時，排氣的溫度大概介於100-200度之間，這溫度足夠點燃”濕煙灰”，它的燃點大約是150度。(未完全燃燒的燃油或滑油)

If the soot is “dry”, it will not get ignited at such low temperature (150 deg. C) but when the engine is running at higher speed and the temperature of gases reaches to above 300 deg. C, then in the presence of excess oxygen the deposits of combustible materials will liberate sufficient vapor, which can be ignited by a spark or a flame.

如果煙灰是”乾”的，那它將不會在低溫被點燃(150度)，但主機高速下排氣溫度提升到300度以上時，將會釋放出足夠的可燃氣體，此時若足夠的氧氣存在就會很容易被火花或火焰點燃。

The above soot fires are called small or normal soot fire because the heat energy is conducted away by the circulating boiler water and steam. Also, the sparks remain inside the funnel or diminish while passing through the flame arrestor in the funnel top.

上述的煙灰火被稱作小失火或普通煙灰火，因為熱量會被循環水和蒸氣吸收帶離，同時火花也只留在煙囪內或者被煙囪頂部的阻火器減弱。

等級二：氫氣火 Hydrogen Fire(到這邊可以準備棄船了)

Hydrogen fire in an EGB occurs when the chemical reaction of dissociation of water takes place at a temperature above 1000 deg. C. This leads to the formation of Hydrogen (H2) and Carbon mono-oxide (CO) which are both combustible in nature.

氫氣火發生在廢氣鍋爐達到1000度以上時，發生化學作用使水解離。這導致氫氣(H2)和一氧化碳(CO)的形成，它們都是極易燃的可燃氣體

2H2O= 2H2 + O2 [水解離形成氫氣 (Dissociation of water Leading to formation of hydrogen-H2)]

H2O + C =H2 + CO [水和炭反應形成氫氣和一氧化碳 (Reaction of water with carbon deposit leading to formation of carbon monoxide-CO)]

等級三：鐵火 Iron Fire(要到這邊不容易)

At this stage, the chain reaction of oxidation of iron metal starts at a high temperature of 1100 deg. C which means at such high temperature the tube will start burning itself, leading to complete meltdown of tube stacks.

在這個階段，在1100度的高溫下促使鐵金屬氧化的連鎖反應，也就是說在這麼高溫下管路會開始燃燒自己，導致管線完全熔毀崩壞。

2Fe + O2 =2FeO+ heat

It is strictly advised not to use water or steam at this stage to fight the fire because the overheated iron will react with water to continue this reaction.

嚴格建議不要在這個階段使用水或蒸氣滅火，因為過熱的鐵會和水反應來助長火勢。

Fe + H2O =FeO+ H2 + heat

預防火災的措施 Steps for Prevention of Fire

1.  Avoid slow steaming of the main engine
   避免主機減速航行
2. Ensure good fuel combustion in the main engine
   確保燃油燃燒完全 
3. Ensure fuel is treated and is of good quality while supplying to the engine
   確保燃油完善處理，品質良好的被送入引擎
4. Do regular soot blow of boiler tubes
   定期對鍋爐管道吹灰
5. Do water washing in ports at regular interval
   每一段時間在港口做水洗作業 
6. Ensure design of exhaust trunk to be such to provide uniform heat to complete tube stack
   確保煙囪設計良善，可以均勻地加熱水管群
7. Pre-heated circulating water to be supplied to boiler mainly at the time of startup
   預熱供應至鍋爐的循環水，特別是在啟動的時候 
8. Circulating pump should not be turn off at any time while the main engine is running
   循環泵不可以在主機運行時關閉
9. Do not stop circulating pump for at least two hours after the main engine is stopped
   主機停止後兩個小時禁止關閉循環泵
10. Start circulating pump prior to 2 hours before starting the main engine
    主機啟動前兩個小時預先啟動循環泵

How to Tackle EGB Fire?

如何處理廢氣鍋爐失火

The response for tacking EGB fire will be different for different stages.

廢氣鍋爐失火會因階段不同而有不同處理方式。

When there is stage 1 fire, i.e. normal soot fire:

若是階段一的火災，也就是普通煙灰火：

1. Stop the main engine, and thereby the oxygen supply to the fire
   停止主機，藉以停止氧氣供應至火源
2. Continue operating the water-circulating pump. Never stop the pump
   持續運作循環泵，不要停止
3. Never use soot blowers for firefighting whatever type it is – Steam or Air as both will accelerate the effect of fire
   不要使用吹灰器不論是哪種類型的火災，蒸氣或空氣都會助長火勢
4. Ensure all the exhaust valves in the stopped Main engine are in closed position so as to cut any chance of air supply to the soot fire
   確保所有主機的排氣閥處於關閉位置，以避免空氣提供至煙灰火中
5. Cover the filter of turbocharger
   遮蓋渦輪增壓器的入口(防止空氣進入)
6. Water washing, if fitted, may be used to extinguish the fire. This is normally connected to the ship’s firefighting water system
   使用水洗設備進行滅火，通常都會連結至消防水系統
7. External boundary cooling can be done
   可以進行煙囪外殼冷卻(噴水在煙囪外面降溫)

For Major Fire

若是大火：

1. Stop the main engine, if it is not stopped already
   停止主機，若它還沒停止
2. Stop the circulating water pump.
   停止循環泵
3. Shut all the inlet and outlet valves on the water circulation line
   關閉循環水管線的所有進口、出口閥
4. Discharge the (remaining) water from the exhaust gas boiler sections by draining
   利用疏水閥釋放廢氣鍋爐中(剩餘的)水
5. Cool down with plenty of splash water to boundary cool the heart of the fire
   (Take care not to splash water in other parts as water can accelerate the reaction)
   利用大量飛濺的水直接對煙囪外殼冷卻
   (注意不要使水飛濺到其他部分，以免加速反應增大火勢)

原作者：About Anish

來源：http://www.marineinsight.com/tech/types-of-exhaust-gas-boiler-egb-fires-and-ways-to-prevent-them/

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單字筆記：

阻火器 flame arrestor

譯者心得：

船上通常會定期清洗鍋爐，主要就是把管壁上的煙灰與油漬清除。若主機運轉狀況異常，造成煙囪有大量油垢累積，又缺乏清潔就很容易發生小火災摧殘水管群，狀況不好就會開始漏水。要像作者說等級２等級３那種超級大火機會不大，但是也不是不無可能，重點還是要定期清洗，然後燃油不要用太劣質的，哈！

***最後更新2020/09/28

*1流動率概念(待補)