关于在线清焦？ 延迟焦化炉在线清焦技术可以实现在不停炉的情况下对炉管内结焦进行有效清除，可以使延迟焦化炉的操作周期得到大幅度延长。采用在线清焦技术的焦化炉一般应采用4管程或6管程，以避免在线清焦时对后续设备操作造成太大的影响。操作时对其中一管程通入蒸汽，通过对炉管恒温或变温操作达到清除管内结焦的目的，而其余三管程或五管程正常操作，在线清焦用的蒸汽及清除的焦炭与其他管程的油品一同进入焦炭塔． 在线清焦技术较好，最高能够降低管壁温度达到100℃。 2008年燕山使用了在线清焦技术，进行清焦取得较好的效果。 下文为关于介绍在线清焦技术、空气烧焦技术和机械清焦技术的介绍： eater decoking options steam-air decoking (steam & air burn) ? performed when heater is off-line ? heater box temperature is reduced/cooled mechanical (pigging) ? performed when heater is off-line ? heater box temperature is cooled on-line spalling ? performed while heater is in service ? 1 pass is taken out of service while other passes remain on-line steam-air decoking methodology ? coke is burnt off the heater tubes by firing the furnace in a controlled decoking process by circulating a steam-air mixture at elevated temperatures. ? air is used to burn the coke off the tubes. ? steam is used to keep the burning temperatures low such that they do not exceed the maximum tolerable temperatures. ? typical decoking time 24 to 48 hours per pass depending on amount of coke in tubes. mechanical decoking methodology (“pigging”) ? coke is removed from the heater tube by pumping a metal studded foam or plastic “pig” with water. the metal studded “pig” rotates such that it scrapes the coke off the inside of the heater tube. ? different size and abrasiveness “pigs”are used in the decoking process. “pigs” are slightly smaller than the inside diameter of the heater tube. ? usually “pigs” are pumped through heater several times forward and backward until overall differential pressure across the tube (inlet to outlet) is restored to its original “unfouled” condition. ? typical decoking time is 18 to 24 hours per heater depending on setup time. on-line spalling methodology ? procedure basis was originally developed by the late mr. lloyd langseth and has been further developed by foster wheeler. ? coke is removed from the heater tube by varying the steam or condensate flowrate on the fouled tube such that a thermal shock is created that breaks off the coke from the tube. ? the spalling medium will transfer the coke particles into the heater effluent where it will be collected in the downstream coke drum. ? one pass is spalled while the other coils of the heater remain in normal hydrocarbon service. ? typical decoking time is 16 to 24 hours per heater pass. steam-air decoking ? advantages: – removes almost all coke from the inside of the tubes – heater firebox does not need to be fully “cooled” – can be performed by unit operators- no outside vendor needed ? disadvantages: – time & cost (maintenance & unit loss production) – environmental concerns on venting to atmosphere – disposal of water/coke mixture – potential tube rupture – not found to be effective on crude slates containing inorganic material (i.e. canadian crudes, some crude flow improvers) mechanical decoking (“pigging”) ? advantages: – all coke is removed from the inside of the tubes – more environmentally safe than s.a.d. – no venting to atm. – “pigs” do not score inside of tubes – usually performed faster than s.a.d. – clients have reported longer run lengths than s.a.d. – requires outside vendor to perform decoking procedure- unit operators can spend more time on turnaround activities ? disadvantages: – requires heater to be taken fully out of service – disposition of “dirty” water required – downtime is 1 to 3 days/heater – cost - specialized decoking vendor needed on-line spalling ? advantages: – heater remains in service during procedure, one pass at a time – immediate feedback on effectiveness once pass is back in service – allows extended heater run length before “pigging” is required – coke is collected in downstream coke drum – regular decoking program can be developed by refiner ? disadvantages: – may not get all coke off a particular tube section-still need to eventually fully decoke – potential tube damage due to tube expansion/contraction – potential u-bend corrosion/erosion – potential coke blockage of tube – “pigging” required – can only be performed on 3 or 4 pass heaters with individual pass firing [ ]查看更多
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