Catalytic slurry as a feedstock for coking

When catalytic slurry is mixed with residue for coking, attention must be paid to the issue of excessive metal content in the catalytic slurry, as this can significantly affect the quality of petroleum coke and also cause unnecessary fluctuations in the production process

The catalyst particles in the slurry wear the furnace tubes.

Many plants have conducted experiments on feeding catalytic cracking slurry into delayed coking, and quite a number of them are still reprocessing this slurry. Theoretically, catalytic slurry contains a high amount of aromatics; at typical coking and cracking temperatures, it is difficult for significant cracking reactions to occur. As a result, most of the slurry ends up in the coking wax oil fraction and returns to the catalytic unit (some of this coking wax oil may need to be hydrogenated), which increases the difficulty of cracking within the catalytic unit. This cycle of back-and-forth movement of catalytic slurry between catalytic and coking units leads to higher energy consumption in processing； On the other hand, the addition of catalytic slurry reduces the viscosity of the feedstock used in delayed coking, thereby increasing the flow rate of the oil through the heating furnace and reducing the tendency for coking in the furnace tubes. However, due to the high content of solid substances in the slurry, the bottom circulation filters and radial filters in the distillation tower become severely clogged. Therefore, based on the current processing methods, it is not very suitable for processing catalytic slurry, unless the main goal is to produce needle coke, or the issue of catalyst being carried along in the catalytic slurry is resolved fundamentally.

(1) It is uneconomical to use catalytic slurry in delayed coking units. Both industrial practice and laboratory studies show that the oil slurry itself yields at least 40% coke in coking reactions, with some cases showing yields higher than 50% ； The yield of gasoline and diesel is only around 20%. Under the selected oil price system, the value of the slurry as a product of coking processing is even lower than its cost; coupled with the operating expenses of the coking unit, the overall economic efficiency is extremely poor. (2) The distribution of the product structure of the oil slurry in coking processing is determined by its chemical properties. Since the oil slurry is a product of catalytic cracking units, its four component types mainly consist of condensed aromatic hydrocarbons with no side chains, few side chains, and short side chains. During the coking reaction, they rarely convert into gasoline and diesel fractions with high added value; instead, they mainly undergo dehydrogenation and condensation to produce gases and coke. In the residue products, the yields of coke and gas are high, while the yields of gasoline and diesel are low. After coking the oil slurry, it also increases the ash content of the coke, and the quality of the wax oil deteriorates as well. (3) Since the oil slurry also contains 0.5%–1.0% of catalyst solid particles, upon entering the coking unit for processing, these catalyst particles adsorb inorganic salts, gelatinous asphaltenic molecules, and foam coke particles to form precursors for coke formation. This accelerates coking in the tubes of the coking furnace; moreover, it facilitates deposition and coking in the dead zones of the distillation tower, bottom pump, radial feed pump, and pipelines of heat exchange equipment. Prolonged use of such oil slurry can cause wear on the pump impellers and control valve spools due to the catalyst. The above situations will significantly shorten the operating cycle of the heating furnace and the long-term safe operation of the distillation column bottom system. Given the factors mentioned above, delayed coking units are not suitable for processing catalytic cracking slurry. And this is because of the low viscosity of the slurry. Due to its high content of aromatic hydrocarbons, it can be used as a major component in the formulation of low-viscosity fuel oils, or as a raw material for needle coke, provided that the necessary post-treatment is carried out. And achieve certain economic benefits.

Are there any requirements for using slurry as quench oil? Is there any refinery that uses it? If there are any, we can also go and take a look.

It’s probably not very good; one needs to weigh the pros and cons, but there shouldn’t be any principled issues

The catalytic slurry can be fed into the VRDS unit as a raw material after filtration, with good results.

Personally, I think that if the solid content in the catalyzed slurry is low, it can be fed into the vacuum section of the atmospheric and vacuum distillation unit to recover wax oil. Additionally, the fuel oil can also be adjusted before leaving the factory.

Catalytic slurry, after filtration, is an excellent raw material for producing needle coke. However, in China, the technology for producing needle coke is not yet well-developed; two attempts were made at the Shandong Haihua Petrochemical Plant, both of which ended in failure. If it goes directly to coking, can the pipelines designed for coking handle the wear and tear caused by the catalyst? Changes in the properties of the feed oil have a significant impact on production. Less is better.

I think it’s not possible. I. The properties of the slurry in the catalytic cracking unit determine ； II. The inclusion of oil slurry in coking feedstock affects the yield; most of it ends up as coke, so economic benefits will surely increase, making it better to simply blend it with fuel oil and sell it as such. III. Consider whether the crude oil used by the company is of paraffin grade. If so, a test can be conducted to see whether adding it in appropriate amounts can increase the coking yield

Given the compositional characteristics of the slurry (high metal content and high hydrocarbon ratio), it is clearly unsuitable as feed for coking units.

We have done atmospheric and vacuum distillation processes; what about coking?