【Q&A Question 223】November 29, 2016
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This post was last edited by liuquan1100 on 2016-11-29 08:03. [Q&A Question 223] 2016.11.29: How to determine whether the furnace tube is coked? A reference ** will be shown after responding; scoring is achieved by answering the key points. Coking in the furnace tubes can be determined from the following aspects: (1) With the feed rate remaining constant, check whether the pressure difference between the inlet and outlet of the furnace tubes increases; if there is such a change, the reasons should be analyzed promptly. (2) Observe whether the surface of the furnace tube turns red; due to the increased thermal resistance caused by coking inside the tube, heat has difficulty being transferred, which leads to a rise in the local temperature of the tube wall and causes it to turn red. (3) The processing capacity remains unchanged while the furnace outlet temperature drops or the fuel volume increases. (4) The slow response of the furnace exit temperature indicates coking at the thermocouple sheath. Summary post of Q&A from 2016 (updated as of November~~~~) http://bbs.hcbbs.com/thread-1597792-1-1.html Seeking sponsors for the “2016 Haichuan Top 10 Members Selection Contest” http://bbs.hcbbs.com/thread-1628108-1-1.html (Source: Haichuan Chemicals Forum)
1) The pressure difference at the furnace outlet increases, causing the furnace pressure to rise. 2) The thermocouple at the furnace outlet indicates a low temperature, with slow response. 3) With unchanged operating conditions, the furnace temperature rises significantly, while the temperature at the furnace outlet fails to increase.
Reference ** (1) In a bright furnace chamber, if dull spots are seen on the furnace tubes, it indicates that coking has occurred in those areas of the tubes. (2) The processing capacity remains unchanged, while both the furnace temperature and the pressure entering the furnace increase. (3) The slow response of the furnace exit temperature indicates that coking has occurred at the thermocouple sheath.
(1) Has the pressure difference at the inlet and outlet of the furnace tube increased? (2) The furnace outlet temperature drops, and it is difficult to raise the temperature even by increasing the fuel supply. (3) Check whether there is any redening on the surface of the furnace tube and the wall of the tube.
(1) Poor combustion in the burner causes the flame to direct toward the furnace tubes, resulting in localized overheating of those tubes. (2) Dry burning is caused by too low oil flow rate inside the furnace tube, excessive residence time of the medium, or interruption in feed. (3) Malfunctioning instruments fail to reflect the temperature at various points in a timely and accurate manner, resulting in overheating of the pipe walls.
1) The pressure difference at the furnace outlet increases, causing the furnace pressure to rise. 2) The furnace outlet thermocouple indicates a low reading, with slow response. 3) With unchanged operating conditions, the furnace temperature rises significantly, while the outlet temperature fails to increase. 4) The furnace tubes gradually change from pink to black, and even develop peeling and spots; the refractory brick hangers in the furnace chamber change from a warm red color to white. 5) Increased fuel consumption.
(1) With the feed rate remaining constant, check whether the pressure difference at the inlet and outlet of the furnace tube increases; if there is any change, analyze the reasons promptly. (2) Observe whether the surface of the furnace tube turns red; due to the increased thermal resistance caused by coking inside the tube, heat has difficulty being transferred, which leads to a rise in the local temperature of the tube wall and causes it to turn red. (3) The processing capacity remains unchanged while the furnace outlet temperature drops or the fuel volume increases. (4) The slow response of the furnace exit temperature indicates coking at the thermocouple sheath.
1) The pressure difference at the furnace outlet increases, causing the furnace pressure to rise. 2) The furnace outlet thermocouple indicates a low reading, with slow response. 3) With unchanged operating conditions, the furnace temperature rises significantly, while the outlet temperature fails to increase. 4) The furnace tubes gradually change from pink to black, and even develop peeling and spots; the refractory brick hangers in the furnace chamber change from a warm red color to white. 5) Increased fuel consumption.
1. Observe the change in the pressure difference between the inlet and outlet of the furnace tubes; a significant increase in this pressure difference indicates possible coking. 2. Check the heat exchange efficiency of the heating furnace; a noticeable decline in efficiency suggests coking may be present. 3. Examine the gas consumption under the same load and temperature conditions; an increased consumption indicates possible coking. A change in just one parameter alone cannot confirm coking; it is necessary to consider all three factors together to make a judgment
It can be determined by the different colors of the furnace tube surface. In areas where coking occurs, the low heat transfer coefficient due to carbonaceous scale results in a higher surface temperature of the furnace tube, giving it a dark red color or some grayish spots, while the rest of the furnace tube is black.