焦化加热炉对流段结焦的原因分析与对策

Analysis of Causes of Coke Deposition in Convection Section of Coking Furnace

中国海油惠州炼油分公司420×104t/a延迟焦化装置采用"两炉四塔"工艺技术,设计加工减压渣油,正常在线清焦周期在4～6个月。2010年6月,该装置掺炼催化油浆,在不到2个月的时间内焦化加热炉对流段与对流入口严重结焦,导致装置分炉进行机械清焦。通过对焦块取样化验分析并从工艺角度进行综合分析,得出了加热炉结焦的主要原因是:催化油浆含有0.5%～1.0%的附着有铁、镍、钒、钙等重金属和焦炭的催化剂固体颗粒,极易吸附从焦炭塔带来的泡沫焦焦粉颗粒和塔底油中的沥青质和胶质分子,形成更多的结焦母体,进一步强化了结焦作用;此外,由于采用单点注水,注水与柴油换热后温度偏低(180～200℃),导致减压渣油中的沥青质析出挂在管壁上,产生缓慢积焦。提出了清焦后的技改措施:及时投用第二点注水;加强对焦化原料与底循油的分析,原料易结焦时取大循环比操作;平稳操作,减少辐射进料携带入炉管的焦粉量;停炼催化油浆。

CNOOC Huizhou Refinery′s 420×104t/a delayed coking unit uses a two-furnace,four-column process and is designed to process vacuum residuum.Its normal inline coke removing cycle is 4-6 months.In June 2010,the unit began to process oil blended with FCC slurry oil.In less than two months,serious coke deposition took place at the convection section and the convection inlet of the coking furnace and the company had to carry out mechanical decoking.By assaying coke samples and analyzing the process,the company found out the main reasons for the coke deposition in the coking furnace.The FCC slurry oil contained 0.5%-1.0% solid catalyst particles on which heavy metals(iron,nickel,vanadium and calcium) and coke deposited.These particles could easily adsorb foam coke powder particles from the coking column as well as asphaltene and colloid molecules in column bottom oil,thus forming more coking matrixes and further intensifying coke deposition.In addition,as water was injected at a single point,the temperature of the water injected was too low(180-200℃) after exchanging heat with diesel fuel,resulting in the asphaltene in the vacuum residuum separating out and hanging on the wall of the tube,in turn leading to slow coke deposition.This article proposes measures to improve the process after decoking,including injecting water at a second point,strengthening the assay of coking feedstock and bottom circulating oil,using large-circulating-ratio operation when feedstock is prone to coking,maintaining steady operation to reduce the amount of coke powder carried by radiation feed into furnace tubes,and stopping processing FCC slurry oil.