Coking cycle ratio

Circulating oil = Total radiation flow rate – Amount of fresh material. Circulation ratio = ———————————— Amount of fresh material. Last edited by Hongru on 2009-3-30 11:13.]

A calculation formula module can be installed on the DCS to monitor changes in the circulation ratio at any time. This is quite simple; the instrument operator can handle it!

The ratio of the circulating oil to the delayed coking feed oil entering the fractionation tower is called the circulation ratio. The cyclic comparison device has a significant impact on the processing volume, output, as well as the distribution and properties of the coking products. The design value for the circulation ratio in conventional delayed coking units is 0.2 to 0.4. As the circulation ratio increases, the yield of delayed coker product rises, while the yield of coker residue decreases; the yields of coker light oil and gases remain essentially unchanged. Operating a delayed coking unit with a high circulation ratio helps to increase the production of ethylene feedstock and diesel. Some delayed coking units, in order to expand their production capacity at the lowest cost, use a low circulation ratio or even a zero circulation ratio, which results in an increased amount of coker wax oil of lower quality.

Extracted from the technical specifications I prepared; I hope it will be helpful: The circulation ratio is a very important operating parameter in the coking process, and it is a key factor affecting the product distribution and operational costs. At a constant furnace flow rate, increasing the circulation ratio significantly reduces the processing capacity of the unit. A decrease in the recycle ratio means that the final boiling point of the wax oil separated from the fractionation tower increases; fewer heavy hydrocarbons are returned to the coke furnace for secondary cracking. As a result, the production of light hydrocarbons and coke decreases, while the yield of intermediate fractions increases, allowing for more efficient utilization of the hydrogen in the feedstock. The smaller the recycle ratio, the higher the liquid yield, while the yields of gas and coke are lower. Therefore, to increase the yield of the liquid product, it is necessary to operate at a low recycle ratio. Practice has shown that when the circulation ratio is too low and the feed to the heating furnace resembles the properties of the raw material, it can easily lead to coking in the heating furnace, affecting its operation over extended periods. The recycle ratio decreases, while the final boiling point, residue, and heptane-insoluble matter of the heavy paraffin oil increase. Therefore, determining an appropriate circulation ratio requires considering not only the economic efficiency of the coking unit but also, more importantly, the processing capacity of the downstream processing units. When producing fuel-grade coke, it is advantageous to operate the delayed coking unit under as low a recycle ratio as possible, provided that the downstream processing units are capable of handling wax oils with higher levels of dry points, residue, heavy metals, and sulfur and nitrogen content. Therefore, with the current approach, there are limits to reducing the cycle ratio. Currently, the cycle ratio for delayed coking is usually in the range of 0.2 to 0.4. When producing electrode coke, the circulation ratio can reach 0.8; if the circulation rate (relative to the feed) is reduced by about 10%, the coke production decreases by approximately 1.2% (relative to the feed). Sometimes, due to process requirements, it is necessary to increase the recycle ratio in the following situations: 1) To reduce the production of coker wax oil according to the refinery’s needs. 2) Further improve coke quality. 3) Improve the quality of wax oil and protect older or overloaded hydroprocessing or hydrocracking units downstream. 4) Prevent the formation of shot coking to ensure safe production in coking removal. 5) Reduce coking in the heating furnace tubes and stabilize the operation of the heating furnace.

(Radiation total flow – amount of fresh feed) Cycle ratio = ———————————— Amount of fresh feed. When the cycle ratio is greater than 1, the yield of light oil (conversion rate) changes little, but energy consumption and coke production increase significantly.

 The cycle ratio is a key factor affecting product distribution and operating costs. At a constant furnace flow rate, increasing the circulation ratio significantly reduces the processing capacity of the unit. A low recycle ratio means that the final boiling point of the wax oil separated from the fractionation tower increases; as a result, fewer heavy hydrocarbons are returned to the coke furnace for secondary cracking. This leads to a decrease in the production of light hydrocarbons and coke yield, while the yield of intermediate fractions increases. The hydrogen present in the feedstock is thus utilized more effectively. Calculation formulas: Circulation ratio = Recycled oil / Fresh feed oil. Combined circulation ratio = Furnace flow rate / Fresh feed oil = (Fresh feed oil + Recycled oil) / Fresh feed oil = 1 + Circulation ratio. The rule is that the lower the circulation ratio, the higher the liquid yield, while the yields of vaporized product and coke are lower; therefore, to increase the yield of products, it is necessary to operate with a low circulation ratio. Practice has shown that when the recycle ratio is reduced to 0.25, the temperature in the distillation column rises above 400 degrees; at this point, cracking and condensation reactions occur at the bottom of the column, which can easily lead to coking in the distillation column. It affects long-term operation; therefore, with the current approach, reducing the cycle ratio is limited.

According to your formula, what is calculated is the cycle ratio; but if it is greater than one, then it should be the combined cycle ratio. If the amount of recycled oil is greater than the amount of fresh feed, then this coking process is absolutely absurd

What is the total radiation flux becquerel? Calculated? Is the amount of fresh raw material calculated, or is it the feed rate to the fractionation tower? I would like to ask the teacher. Thank you

The general process is for the residue to first enter the convection chamber of the heater, then the distillation tower, and finally the radiation chamber of the heater. The total radiation flow rate is the sum of the values shown for each branch in the furnace’s radiation chamber, while the amount of fresh feedstock is the quantity of residue oil fed into the unit. I’m not sure if this can help you.

(Total radiation * 0.85 – amount treated) / amount treated=

Is it a volume ratio or a mass ratio? They are different; please advise! Typically, DCS displays volumetric flow rate.

An increased circulation ratio reduces coking in the furnace tubes – why is that?