Question regarding the exhaust temperature of the chimney in the sulfur recovery unit

If the exhaust temperature from the sulfur recovery unit is too low, water vapor condensate reacts with sulfur dioxide to form sulfurous acid, which can cause corrosion to the equipment. Also, elemental sulfur will crystallize, causing blockages in the pipes.

The flue gas temperature is generally controlled between 250 and 450°C; too low a temperature can lead to dew point corrosion at the top of the chimney.

The specific temperature to be controlled is related to the height of the chimney; generally, the temperature at the chimney outlet should be kept above 150°C to prevent dew point corrosion caused by SO2. If the chimney of our facility is 130 meters high, and assuming that the temperature of the flue gas decreases by 1°C for every 1 meter of height increase, the temperature of the flue gas should be kept at least at 280°C. Therefore, under normal circumstances, we keep the temperature of the flue gas in our facility around 300°C.

In fact, the main goal is to keep the temperature of the flue gas exiting the chimney at least at 150 degrees. However, if the flow rate of the flue gas is low or there are issues with the insulation lining of the chimney, the temperature of the flue gas may drop by much more than 1 degree per meter. Therefore, it is recommended to install thermometers on the chimney platform to monitor the flue gas temperature. By calculating the difference between the temperature of the flue gas as it leaves the furnace and the temperature on the platform, along with the length of that section of the chimney, it is possible to determine the appropriate control temperature for the flue gas, which should generally be around 350 degrees.

The chimney is not only the final outlet of the exhaust gas incinerator but also the final outlet of the sulfur recovery unit, with its emissions being discharged directly into the atmosphere. Its structure can be either steel or concrete-finished ； Steel chimneys have linings that serve to insulate them and protect them from corrosion. It is generally cylindrical in shape. It mainly consists of the chimney body and supports. Its function is to discharge sulfur recovery exhaust gases and minimize pollution of the atmosphere. For chimneys made of metal, the main concern during operation is to prevent dew point corrosion, especially at the top of the chimney. Due to the low temperature here, low-temperature dew point corrosion is highly likely to occur. At the same time, due to limitations imposed by the metal material, the high-temperature gases generated after combustion cannot be discharged directly into the chimney; they must be cooled first before being released. Taking both factors into account, the exhaust gas temperature is generally controlled between 250 and 350°C. Additionally, during operation, it is also necessary to prevent sulfur buildup at the bottom of the chimney.

The flue gas emission temperature of our equipment is relatively high, exceeding 400°； It feels like too much of an energy waste. What’s the current status of your device? Let’s discuss it – what is the lowest temperature that can be reached?

Are there any official documents or guidelines regarding the control of this temperature at present? Does anyone know?

The specifications do not specify this explicitly; typically, the design institute designs it based on the requirement that the temperature of the flue gas throughout the flue remains above the dew point temperature.

This is mainly due to the differences in the processing conditions of various devices. We mainly use the Claus and Scott reactions; however, when the equipment was designed, the chimney material used was iron, with a melting point of around 350 degrees Celsius. Since the area where the device is located is cold in winter, this is to prevent dew point corrosion. We usually keep it between 300 and 350. In terms of the maintenance results, sulfur deposition still occurs at the upper part of the chimney.