The problem of oxygen content in one stage furnace
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Experts in natural gas ammonia synthesis equipment would like to ask for advice.: The online analysis of the central control of the oxygen content in one section of the furnace showed that the oxygen content was low, and the fuel gas consumption was higher than the designed value. The temperature measurement points of the flue gas were obviously overheated. However, on the contrary, manual analysis showed that the oxygen content was obviously too high, and the temperature of each coil in the convection section did not reach the design value. The company invited Xi'an Jiaotong University to conduct an energy evaluation last year. , also unanimously concluded that the first stage of the furnace is obviously oxygen-rich combustion, and part of the heat is wasted in the form of exhaust smoke. Now the department leaders, especially the leaders in charge of the process, are having a headache and don’t know how to solve the problem. It is certain that the oxygen content is high, but I don’t know how to explain the problem of the ultra-temperature and low oxygen content of the flue gas in the online analysis. (Note: "There is no problem with the online analysis instrument." Please give me your advice.
Recheck the online analysis instrument and check the manual analysis results and the online analysis results.
I guess you are talking about a new device, so I will talk about the new device first.: 1. Check the tail length of the thermometer used to measure the temperature. In the furnace, some thermometers are not long enough and are at the edge of the refractory layer. Some are longer, and the measured temperature difference will be larger. ； 2. While measuring the amount of peroxygen, trace CO should be measured. If it is high, it should be insufficient oxygen. ； 3. To measure the amount of peroxygen, you should use a pump to extract it. Because the furnace is under negative pressure, it is easy to draw air outside the furnace into it, so the measured amount of peroxygen is not the actual amount inside the furnace. ； 4. The measuring points must be consistent ； 5. Strictly speaking, if there is more gas and more air, the total amount will be more. A high temperature in the transition section means that the total heat energy is high. If the total heat energy is high, the temperature of the coil in the convection section should be high after heat exchange. Otherwise, the heat exchange situation is very good. Let me tell you my opinion: The combustion in your furnace is post-burning due to lack of air. 1. Try it. When you lower the gas, the temperature in the transition section should drop. ； 2. Or if you add more air, the temperature in the transition section should also drop. ； 3. The proportion of gas and air is out of balance, and combustion is not complete. When the transition section is reached, the combustible gas inside leaks in due to negative pressure due to lax sealing such as viewing holes, and the transition zone is used as the combustion zone, so the temperature in the transition section is high. ； 3. Since the total air volume is not high and the total heat energy is not enough, the temperature in the convection section is low. That's all. You try it. If the phenomenon is consistent with what I said, we can discuss how to adjust and improve it. ； If there are differences, we can also communicate further. If it is not resolved, many problems will arise in the future.
What type of furnace does your factory have? Is the combustion air used from gas turbine exhaust or preheated air? Is there a problem with uneven airflow distribution? The amount of information provided by the poster is difficult for people to judge. It is recommended to conduct several more flue gas analyzes at different positions of the furnace.
Our plant's ammonia synthesis plant is a typical Kellogg process, and the first stage furnace is a Kellogg top-fired box furnace. The combustion air uses 101-BC preheated air. Now it is judged that there may be a reason for the uneven distribution of combustion air, because the oxygen content was found to be low when sampling from the radiant section, but the oxygen content was obviously high when sampling from the outlet of the induced draft fan (exhaust fan), that is, the chimney. All preliminary judgments indicate that secondary combustion may occur in the convection section, causing the furnace outlet temperature to fail to rise, and on the contrary, the flue gas temperature rises. Because my equipment is second-hand equipment imported from Canada, during operation, the transition section of the furnace once burned red and the insulation material fell off. The current analysis is that a large amount of air may have leaked into the transition section, but it is difficult to find out where the leakage is. What a headache!
The analysis above is correct, but our device is foreign equipment from the 1960s. As mentioned above, air may leak in. We thought about this, but we were not sure where the air leakage point was because the fire viewing hole and the air duct were closed during normal operation. The situation analyzed above is exactly what happens to us all the time. The following is an analysis of the flue gas oxygen content data we collected. I don't know if there is any good solution upstairs. Flue gas data statistics project 101B Flue gas A6 (design value 2.98) Auxiliary pot flue gas A7 (design value 3.19) Heating furnace flue gas A06 (design value 2.50%) Date O2% (manual analysis of dry gas) O2% (manual conversion of dry gas into moisture) O2% (online analysis of moisture) O2% (online conversion of moisture) For dry gas) O2% (manual analysis of dry gas) O2% (manual conversion of dry gas into moisture) O2% (online analysis of moisture) O2% (online conversion of moisture into dry gas) O2% (manual analysis of dry gas) O2% (manual conversion of dry gas into moisture) O2% (online analysis of moisture) O2% (online conversion of moisture into dry gas) Sampling 1 Original point (sample at the fire viewing hole, the rod is deep into the furnace, and the fire viewing hole cover is open) 2008.4.16.08:302.251.851.021.2415.1412.413.364.1010.258.416.137.482008.4.16.16:3 02.321.901.021.248.476.953.324.056.395.246.237.602008.4.17.08:302.011.651.121.37 5.524.533.273.996.315.176.057.382008.4.17.16:301.221.000.941.159.778.013.654.456 .315.176.317.702008.4.18.08:302.512.061.071.3112.3610.144.375.337.786.386.347.73 2008.4.18.16:302.912.390.961.178.987.364.956.047.275.966.197.552008.4.19.08:302. 452.010.931.136.745.533.664.479.247.585.967.272008.4.19.16:301.941.591.081.3210. 979.003.724.5411.489.416.908.422008.4.20.08:302.712.221.601.9510.438.556.227.597 .516.165.506.712008.4.20.16:303.332.731.591.948.607.054.605.617.806.406.107.44 Sampling 2 Improve the sampling point (sample at the fire viewing hole, the rod goes deep into the furnace, and the fire viewing hole is blocked with cotton gauze) 2008.12.10.14:502.031.661.912.335.904.846.698.165.824.775.837.112008.12.11.11:302.532.071.021.249.067.438.3310.16 0.00 0.002008.12.12.11:003.392.782.112.578.647.088.4010.257.125.846.207.562008.12.15.11:301.731.421.541. 884.293.524.725.766.585.46.027.342008.12.19.14:001.881.541.411.725.944.875.286.446.395.246.277.65 Sampling 3 Improved sample point (sealed welded pipeline leads to the ground, similar to sampling 2) 2009.1.9.11:007.005.741.892.317.025.766.257.63 2009.1.12.16:307.586.221.652.018.506.975.336.50 2009.1.14.14:005.904.841.541.887.005.744.675.70 2009.1.15.11:006.275.141.802.206.485.313.103.67 2009.1.19.14:206.625.431.912.3310.568.663.013.67 0.00 0.002009.1.19.16:306.285.151.902.3211.839.703.424.17 0.00 0.002009.1.20.8:306.345.201.842.2410.668.744.575.58 0.00 0.00