【Q&A Question 079】March 20, 2018
Thread Content
【Q&A Question 079】March 20, 2018: Briefly explain the significance of controlling the oxygen content in flue gas ① Reduce heat loss. ② Prevent the accelerated oxidation of the metal pipe wall due to excess oxygen. ③Increase the heat rate of the furnace. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) Due to the limitations on the number of posts in the “One Question per Day” section, “One Image per Day” has been moved to the registered devices section; you can access it through the directory I posted. For management purposes, if you need to access content from a few days ago, please go to the summary post below to enter the “My Registration Season” event – (Note: This event is currently ongoing in the Chemical Engineering section). https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=18978 For the daily questions section related to chemical engineering technology training in 2018: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1888971 For the daily image summary section related to registration equipment in 2018: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1888970 For the Q&A section related to hydrogen production and hydrogenation technologies in 2018: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1888968 For the daily questions section related to LNG technology in 2018: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1888973 For the Q&A section from 2017 (updates have started): https://bbs.hcbbs.com/thread-1657793-1-1.html For the daily questions section from 2017 (updates have started): https://bbs.hcbbs.com/thread-1657794-1-1.html For the daily image summary section from 2017: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1875160 For the list of daily questions related to LNG in 2017: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1804162 For the Q&A section from 2016 (updates are complete): https://bbs.hcbbs.com/thread-1597792-1-1.html
① Reduce heat loss. ② Prevent the accelerated oxidation of the metal pipe wall due to excess oxygen. ③Increase the heat rate of the furnace.
The oxygen content in the boiler flue gas is a key indicator to measure the efficiency of the combustion process. Flue gas oxygen content control maintains the oxygen level within an optimal range by adjusting the air-fuel ratio, with the main method being the coordinated control of fuel supply and air supply. The key to controlling the oxygen content in flue gas lies in having an oxygen analyzer with good dynamic performance and stable, reliable operation.
Reduce heat loss； Prevent accelerated oxidation of the metal pipe wall due to excess oxygen ； Increase the heat rate of the furnace.
Answer: ① Reduce heat loss. ② Prevent the accelerated oxidation of the metal pipe wall due to excess oxygen. ③Increase the heat rate of the furnace.
1. Ensure complete combustion of the fuel gas, improve the thermal efficiency of the furnace, and save fuel gas. 2. Reduce nitrogen oxide emissions.
Low oxygen content leads to incomplete combustion, with the fuel gas being carried away through the chimney; high oxygen content results in a large excess air coefficient, facilitating secondary combustion and causing damage to the equipment
The use of an oxygen probe for automatic analysis of the oxygen content in boiler flue gas is intended to continuously monitor the quality of combustion, so as to control the ratio of fuel to air in a timely manner and maintain combustion in an optimal condition. In order to ensure complete combustion of the fuel without excessively increasing exhaust volume or lowering the combustion temperature, it is first necessary to control the ratio of fuel to air, keeping the excess air coefficient α within a certain range.
The oxygen content in the furnace is an essential element in the combustion process, and its level can be determined based on the following factors: 1. It is necessary to meet the oxygen demand of the fuel during combustion; insufficient burning in the furnace leads to fuel waste and reduced efficiency, and in severe cases, it can even cause production accidents； 2. The flue gas generated by combustion contains a large amount of heat, which is ultimately released into the atmosphere through the chimney. The higher the oxygen content, the more heat can be carried, which in turn is not conducive to the efficiency of the furnace ； 3. Excessively high oxygen content in flue gas can exacerbate dew point corrosion in low-temperature areas such as the preheating system and the inlet of the induced draft fan ； 4. Excessively high oxygen levels in the furnace chamber also accelerate the rate of high-temperature oxidation on the surface of the furnace tubes ； Therefore, taking all the above conditions into account, the oxygen content in the flue gas should be maintained at an optimal level, which is usually expressed by the excess air coefficient. For heating furnaces of different types, this coefficient is generally kept between 1.05 and 1.25 for gas-fired furnaces, while it can be increased slightly for oil-fired furnaces ；
The quality of combustion in coal-fired boilers is directly related to the fuel consumption rate. Measuring the oxygen content in the flue gases serves to prevent excess air from entering the furnace and thereby reducing physical heat losses, as well as to avoid increased heat losses due to incomplete chemical combustion resulting from insufficient oxygen levels. A low oxygen level in the flue gas indicates a lack of oxygen, which leads to incomplete combustion of the gases; as a result, large amounts of carbon monoxide are released into the furnace. When the oxygen content in the flue gas is high, it indicates that the excess air coefficient is too large; this leads to an increased amount of exhaust gas, and as a result, a large amount of thermal energy is carried out of the furnace, resulting in waste.
The oxygen content is too high; there is an excess of air. Under normal circumstances, an oxygen level of 6-7 is considered quite good! ! The oxygen level is too high: 1. There is excessive air supply, or there is a severe air leakage issue. 2. Incomplete combustion: a large amount of gas is released directly without participating in the combustion process!