馏分循环对延迟焦化加热炉管结焦规律影响的实验研究

结合克拉玛依石化公司延迟焦化工艺,就馏分循环对焦化加热炉受热结焦规律进行实验研究,主要考察采用不同类型馏分油循环、不同循环比时炉管中结焦趋势的变化规律,并进一步研究循环物流所携带焦粉对炉管结焦的影响规律。结果表明,不同焦化原料的性质(如密度、粘度、残炭等)和组成差别都较大;相对于减压渣油而言,加热炉进料的结焦诱导期较长,表明采样期间的循环焦化方案利于抑制焦化加热炉炉管的结焦。深入研究发现,不同循环馏分都可不同程度抑制炉管结焦,尤其以分馏塔焦化循环油加入后的结焦诱导期最长;随着循环比的增大,结焦诱导期不断延长,但循环比在0.6以上时的影响变化不大;循环馏分携带来的焦粉对加热炉炉管中的结焦具有一定促进作用。

EXPERIMENTAL STUDY ON THE EFFECT OF FRACTIONS CIRCULATION ON THE COKING OF FURNACE TUBE IN DELAYED COKING UNIT

Premature coking inside the furnace tube is a main factor affecting the operation period of delayed coking. On account of this important issue, the effect of fractions circulation on the coking of furnace tube was studied in the laboratory using feedstocks from the delayed coking unit of Karamay Petrochemical Company. The influences of various circulating fractions, circulation ratio and the amount of entrained coke breeze in circulating stream on the coking of tube were investigated. Results showed that the properties (such as density, viscosity, carbon residue and etc.) and compositions of various coker feedstocks were varied significantly; the coke-induction period of furnace feedstock was longer than that of vacuum residue, which indicated that the existing circulating scheme was favored in inhibiting the coking of tube. Although inhibition of the coking of tube was observed with various circulation fractions, when using the cycle oil of fractionator as circulating fraction the longest coke-induction period was obtained. The coke-induction period increased with the increase of circulation ratio till the ratio reached 0.6, then without significant increase. However, the entrained coke breeze in circulating stream could promote the coking of tube.