How to deal with the issue of excessive flue gas emission temperature in the waste heat boiler used for blowing air?
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Our company uses briquette gas generation, and we have a flue gas recovery system in place. However, the temperature of the flue gas is always above the specified limit; the required temperature range is 120–150, while the actual temperature is usually above 170. The oxygen content in the flue gas is relatively normal, ranging between 5% and 6%. The exhaust fan is run at full capacity, the blower is set to level 5 out of 6, and the air distribution valves are also open at full capacity. I would like to ask for advice on how to address this issue
It can be sent to the waste heat boiler for recovery to generate steam； A heat exchange station can also be added to recover waste heat.
A soft water heater is installed after the high-temperature air preheater, using the flue gas to heat the water. The water intended for the boiler first passes through the soft water heater, where some of the heat is recovered before it enters the waste heat boiler. This helps to reduce the temperature of the flue gas, increase the temperature of the water entering the boiler, and thereby increase the steam production.
Personal opinion: Based on what the original poster mentioned, my analysis is that the problem likely lies in the technical calculations and process settings of the equipment; the heat generated by the combustion of the blowing air is not fully utilized, which results in excessively high exhaust temperatures. In other words, even after passing through the steam superheater, high-temperature air preheater, waste heat boiler, soft water heater, and low-temperature air preheater (the exact components may vary depending on the process setup), some of the heat from the burned blowing air still remains unutilized. If this is true, the only way to resolve this issue is by improving the processes or equipment; the opportunity of a major overhaul can be used to add a set of soft water heaters (in the form of heat pipes) or to increase the surface area of other heat exchangers. Under normal conditions, the smoke exhaust temperature should not exceed 120 degrees; at 170 degrees currently, modifications are necessary to meet the design specifications and achieve maximum energy savings and reduced consumption. This post was last edited by zjyang168168 on 2007-11-27 14:47.]
It’s quite difficult to carry out technical upgrades at the moment. Is it possible to make adjustments to the manufacturing process? For example, adjusting the opening degrees of the exhaust fans and blower fans. I have summarized the reasons as follows: 1. The entire system for blowing air may accumulate dust, resulting in a reduced heat exchange rate. 2. There is a lot of scale in the waste heat boiler, which prevents full utilization of the heat. Solutions: 1. Increase the frequency of soot blowing. 2. Enhance boiler sludge removal and chemical dosing. I wonder if anyone else has any good suggestions! Thank you
Original poster, the flue gas temperature of your boiler is more than 20 degrees higher than the designed value, which results in a reduction in the boiler’s efficiency by over 1%. It’s difficult to resolve this issue without carrying out major repairs. I’m not sure what the feedwater temperature of your boiler is; if it’s low, you could consider adding a water-to-water heat exchanger at the economizer. This would not only increase the feedwater temperature but also reduce the flue gas temperature, although the main steam temperature and the boiler’s load will be affected to some extent. Additionally, it is recommended that you reduce the oxygen content in the boiler and lower the wind speed; this will decrease the outlet temperature of the furnace as well as the flue gas temperature. This is for reference only.
If the pressure has been at 170 since the boiler started operating, this indicates a design flaw; it is recommended to install a soft water heater. If this issue develops gradually after the boiler has been in use for some time, check for dust accumulation in the system or whether there is scaling on the pipe heat exchangers. Also pay attention to the water quality and the amount of gas produced by the boiler. If the furnace isn’t under excessive pressure, reducing the draft rate can help shift the heat focus in the system toward the front end, and lowering the oxygen content by 4% should also help
The combustion exhaust gas passes through the steam superheater, high-temperature air preheater, waste heat boiler, soft water heater, and low-temperature air preheater; I work in the field of heat pipe exchangers