This really isnt my area of expertise but my guess would be that the draft in the vaporizer is such that the heat from the burner(s) is pretty much bypassing the vaporizer coils and damaging the economizer. The solution would seem to be to slow the passage of the combustion products down and/or increase their contact rate with the coils. As a result of this situation, there also may be an excess of air. I would suggest increasing the retention time by adding an exhaust damper and at the same adding angled inlet dampers to increase the swirl inside of the combustion chamber to increase the contact rate of the flame with the coils. Increasing the fuel rate or steam injection may be used to reduce flame temperature and limit NOx while maintaining adequate heat to provide the required vaporization rate.
Patrick Richards, sr. instrument designer
Fluor Canada, Saint John, N.B.
Our fractionating column is notorious for its problems. Oil is injected into heated feed to separate an impurity (Figure 2). This approach eliminates the impurity well, perhaps too well. A sludge collects in the bottom of the reboiler feed tank, clogs the sieve column and plugs the reboiler and pre-heater. There is some concern that separation efficiency is affected by plugging of the trays but the main problem is frequent fouling of the heaters, which have fixed heads and are difficult to bore out. The reboiler pump fails often and we must call in a vacuum truck frequently and unexpectedly to clean out the reboiler feed tank. Start-up is often a problem because the steam plant is far away. The oil frequently burns, which adds to our fouling woes. What can you recommend to reduce sludge build-up in the trays, heaters and reboiler feed tank?
Figure 2. A variety of problems lead to excessive downtime.
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