METHOD FOR PRODUCING A COKING ADDITIVE BY DELAYED COKING

Abstract

This invention relates to the field of oil refining and, in particular, to a delayed coking process that produces coke with a volatile substances content of 15-25% for use as a coking additive in a coal coking charge in the production of metallurgical coke. The invention is directed towards increasing the content of volatile substances in coke and increasing the efficiency of a plant. The method comprises preheating a primary raw material, mixing the latter with recycle in a tank in order to form a secondary raw material, heating the secondary raw material to 455-470° C. and supplying the latter to a coking chamber, and coking to form a coking additive. It is expedient to feed an antifoaming additive into the coking chamber 3-5 hours before coking is finished. It is preferable to feed in the antifoaming addition agent at two-four points around the perimeter of the coking chamber.

Description

This invention relates to oil refining, in particular to delayed coking that produces coke containing 15-25% of volatiles substances, which can be used as a coking additive in a coal coking charge for metallurgical coke production.

Oil coke with more than 14% but less than 25% volatiles is capable not only of replacing the K-brand (coking) coal, which is in short supply, in coal coking charges, but also of improving the quality of metallurgical coke (Russian Federation Patent 2355729, C10B57/04, published on 20 May 2009).

There exists technology for forming oil coke by delayed coking of oil residues. This method includes slowly heating raw materials to 490-515° C. in a tubular furnace, mixing the raw materials with a recirculant, presenting the coking distillate products formed inside the coking chamber, in a rectification column, which produces bottoms, supplying the bottoms as the secondary raw materials to the coking chamber at 485-495° C. and carrying out coking, which results in the formation of coke (Z. I. Syunyaev, “Forming, Refining and Using Petroleum Coke”, Moscow: Khimiya: 1973, p. 95).

The drawback of this method is that the coke formed by its application has a high strength and low concentration of volatiles (up to 9% by mass).

It is possible to increase the concentration of volatiles in coke by reducing the temperature of the raw materials at the inlet into the coking chamber. However, reducing that temperature and coking at low temperatures results in excessive foaming and, consequently, it increases the probability of the foam getting into the rectification column, then into the furnace, which might result in the plant becoming coked up, shortening the spans between overhauls.

A delayed coking method, capable of guaranteeing that no direct contact would occur between the primary charge and the vapours reaching the rectification column from the coking chamber during the formation of the secondary charge, can prevent coke foam finding its way inside the reaction spiral tubes of the furnace, the coking up of the plant and thus lengthen the spans between overhauls.

The technology nearest to the proposed invention is the delayed coking of oil residues, which includes heating the original raw materials to 340-380° C., mixing them with a recirculant—heavy coking gasoil (pyrolisis resin, heavy catalytic cracking gasoil)—in a mixing tank where the secondary charge forms, heating the secondary charge, i.e. the heavy residues formed in the mixing tank, transferring this into the coking chamber at 485-505° C., and coking to form coke (Russian Federation Patent No. 2206595, class C10B 55/00, published on 20 Jun. 2003).

The drawback of this invention is the low concentration of volatiles in the final product due to the high coking temperature (485-505° C.) and the low efficiency due to extensive foaming, and consequently to not being able to use the coking chamber to its full capacity.

This invention aims at increasing the concentration of volatiles in the coke and improving the efficiency of the plant.

This aim is achieved because this method of delayed coking of a coking additive includes preheating of the primary raw materials at 270-350° C., mixing the primary raw materials with the recirculant in the tank for the production of secondary charge, heating the secondary charge, transporting it to the coking chamber, and coking to form the target product. In this invention the secondary charge is heated at 455-470° C. before it reaches the coking chamber.

Moreover, to prevent foaming, an anti-foaming dope is introduced into the coking chamber 3-5 hours before the end of coking.

Moreover, taking into consideration that the foam developed in low-temperature coking forms a thick layer, the anti-foaming dope is introduced in two to four areas around the perimeter of the coking chamber, so that it covers the entire surface of the foam.

Coking carried out at low temperatures, because the raw material is charged into the coking chamber at a low temperature, produces coke with a concentration of volatiles of 15-25% to be used as a coking additive.

Introducing the anti-foaming dope during the last 3-5 hours of the coking process not only reduces the amount of foam forming in the coking chamber but also makes the process more efficient with respect to the primary raw materials.

The diagram shows the main parts of the plant for carrying out the proposed method for production of a coking additive by the means of delayed coking.

The proposed method of production of a coking additive in delayed coking works as follows.

The original raw materials, such as tar, de-asphalting asphalt, oil production extracts, heavy gasoil of catalytic cracking or any mixtures of the above, are heated in a tubular furnace 1 to 270-350° C., then discharged into the mixing tank 2 connected in pairs to the rectification column 3. Heavy coking gasoil, used as the recirculant, is also charged into the rectification column 3. It is discharged from column 3 as a side fraction.

The mixture of the primary raw materials and recirculant, which becomes the secondary charge, is heated to 455-470° C. in the tubular furnace 4, then fed into the alternately working coking chambers 5 where a coking additive with 15-25% volatiles is gradually accumulated. The distillate coking products, formed in the coking chamber 5, are discharged into the rectification column 3, where they are resolved into a gas, benzene, light and heavy coking gasoil and the bottoms.

Vapour-like products leave the plant through the top of the column 3, light and heavy gasoils are discharged from the middle part of the column, while the bottoms are removed from the bottom part. To reduce foam formation, the anti-foaming dope 6 is introduced in four areas around the perimeter of the coking chamber.

The suggested technology is illustrated with the following four examples: 1-4.

A mixture of raw materials, comprised of a vacuum visbreaking residue, tar oil and heavy gasoil of catalytic cracking in the ratio of 15:75:10 was coked, using an industrial delayed coking plant. The mixture had the following characteristics: density 1.055 g/cm³, cokeability 25.8% and sulphur content 3.8%. The primary charge was heated in a convection furnace to 320° C., then it was mixed with a recirculate: heavy coking gasoil, discharged from the rectification column as a side fraction. The produced secondary charge was heated in a tubular furnace, then it was fed into the coking chamber to produce a coking additive. When coking was over, the coke was steamed out, water-cooled and discharged by hydraulic means. In Examples 2 and 4, an anti-foaming dope was introduced into the coking chamber 4 hours before the end of the process—to prevent foam formation.

Coking conditions and results in Examples 1-4 are shown in the Table.

For comparison, the same charge as in 1-4 was coked, using the technology of the prototype of this invention. The temperature of the secondary charge at the inlet of the coking chamber was 485° C. No anti-foaming dope was used. The result was ordinary electrode coke with a concentration of volatiles of 10.8%. The conditions and results are also presented in the Table.

TABLE
Comparative Data on Coking of Raw Materials
	Example
	Invention technology	Prototype
Characteristics	1	2	3	4	5
Plant efficiency	96	100	96	98	95
with respect to
primary charge,
m3/h
Plant efficiency	106	110	110	112	105
respective the
secondary charge,
m3/h
Secondary charge	468	468	456	456	485
temperature at the
coking chamber
inlet, ° C.
Coking duration, h	16	16	16	16	16
Coke level in the	19.0	20.5	19.5	21.0	19.0
chamber, m
Concentration of	15.1	15.5	21.8	22.4	10.8
volatiles in coke, %
Anti-foaming dope,	No	Yes	No	Yes	No
yes/no

As can be seen from the Table, the coking method suggested by this inventor produces coke that can be used as a coking additive, with a concentration of volatiles higher than 15%. Introducing it into the coking chamber at 456° C. is not practicable because bitumen is likely to form, and it would make the steaming out and cooling down of coke difficult. On the other hand, a charge introduced at a temperature above 470° C., will produce coke that contains less than 15% of volatiles.

Introduction of the anti-foam dope into the top part of the coking chamber reduces the amount of foam that forms during coking, which improves the working efficiency of this technology with respect to the original raw material.

Claims

1-3. (canceled)

4. A method of producing a coking additive in delayed coking, comprising:

heating a primary charge to 270-330° C.;

mixing the primary charge with a recirculate in a tank to form a secondary charge;

heating the secondary charge and introducing it into a coking chamber; and

coking to form a target product;

wherein the secondary charge is introduced into the coking chamber at 455-470° C.

5. The method according to claim 4, further comprising introducing an anti-foaming dope into the coke chamber 3-5 hours before the end of coking.

6. The method according to claim 5, wherein the anti-foaming dope is introduced into 2-4 areas around a perimeter of the coking chamber.