The external heat absorption capacity has decreased
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The 70,000-ton small catalytic unit in the north uses an external circulation system for heat extraction; it has been operating normally for 7 years. After being shut down for 2 months during winter, it was restarted in February, and it was found that the maximum water supply rate achievable was only 2.3 tons per hour, with a limited range of adjustment possible. The fluidization was normal, as was the loose-air supply； Under normal conditions, the maximum water supply rate was 3.2 tons per hour, with good sensitivity in adjustment; so, can the fluidization issue be ruled out? What could be the problem at some stage?
Reply 1# hwh333: The fluidization issue cannot be ruled out. Pay attention to the density, reserves, and temperature distribution of the external heat exchanger, and conduct a comparative analysis with previous recorded parameters to identify the causes.
Three possibilities: 1. A change in the heat exchange condition of the waste heat system reduces the temperature of the water supplied, affecting the steam generation capacity； Check the parameters of the economizer in the waste heat boiler. 2. External heat flux fluidization problem ； Check the external heat extraction density and temperature parameters to confirm. 3. Phosphate hiding ； Dissolve under reduced load, or clean the furnace tubes.
Reasons for the low heat extraction load of the external heat exchanger: 1. As mentioned by the two people before, it is necessary to check whether there are any issues with fluidization, as well as to examine the temperature and density at the inlet of the external heat exchanger barrel, along with the density of the barrel itself and that of the return pipe； 2. Check the bottom of the outer heat exchanger cylinder for any loose points from which catalyst can be discharged; by observing whether hot catalyst is released, it is possible to determine whether the cylinder or its bottom is blocked by materials such as linings or other foreign objects, which could reduce the flow area (be careful when discharging catalyst) ； 3. Check whether the flow rates of the fluidization air and lift air in the external heat exchanger are accurate.
First, rule out instrument-related issues; this problem has also occurred in our equipment. If there is no problem with the instrument control valve, then it’s likely that the external heat extraction circuit is not functioning properly!