JPS6310755B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing olefins using heavy oil as a raw material using a coke heating medium circulation fluidized bed, in which nitrogen oxides are reduced and removed using ammonia and high-temperature coke produced as by-products from the raw material heavy oil. In a method (hereinafter referred to as coke heating medium method) in which a coke heating medium circulating fluidized bed is formed between a reaction tower and a heating tower and heavy oil is thermally decomposed in the reaction tower to produce olefins, crude oil or crude oil is added to the pyrolysis feedstock oil. Heavy oil such as distillation residue oil is used. These heavy oils have a high nitrogen content, ranging from 0.05 to 1.0% by weight. Therefore, the nitrogen content in heavy oil produced as a by-product of decomposition is often about 0.1 to 2.0% by weight. In the coke heat transfer method, this cracked heavy oil is used as fuel for the external combustion furnace of the heating tower, so a large amount of so-called fuel NOx is generated. Furthermore, the cracked gas contains a considerable amount of ammonia produced by decomposition based on the nitrogen in the feedstock, and the ammonia production yield is, for example, 10 to 20% of the nitrogen in the feedstock. The ammonia produced is largely dissolved in the so-called process condensate water and removed in a condensate steam stripper, and the ammonia-containing acid gas is combusted in a combustion furnace. However, when ammonia is burned, almost NOX is produced.
Nitrogen oxides generated in the above process, that is, those generated in the external combustion furnace and acid gases in the combustion furnace, place a large load on the denitrification equipment. Accordingly, the present invention provides a method for producing olefin using such a coke heat transfer method, in which ammonia, which is a byproduct of decomposition from raw material heavy oil, is passed through a coke heating tower, where high-temperature coke and the reducing ammonia gas are By reducing and removing the nitrogen oxides generated and flowing in from the external combustion furnace attached to the heating tower, and at the same time consuming the ammonia in the nitrogen oxide reduction reaction, the heating tower exhaust gas, etc. is combusted from ammonia in the re-combustion furnace. The present invention relates to a method for reducing nitrogen oxides. That is, to summarize the present invention, the present invention provides two fluidized beds of coke particles, a reaction tower and a heating tower, circulates coke particles between the two towers, and in the heating tower, an external combustion furnace attached thereto is installed. When producing olefin by heating the coke particles with high-temperature combustion gas from the feedstock and pyrolyzing heavy oil using the heated coke particles as a heat medium in a reaction tower, the coke particles are produced as a by-product from the raw material heavy oil. This is a method in which ammonia is passed through a heating tower, where nitrogen oxides generated and flowing from an external combustion furnace are reduced and removed by high-temperature coke and the reducing ammonia gas. In the coke heat transfer method, two coke particle fluidized beds, a reaction tower and a heating tower, are installed, the coke particles are circulated between the two towers, and the fuel and, if necessary, part of the coke particles are combusted in the heating tower. By heating the coke particles, the heated coke particles in the reaction tower are used as a heat medium to heat heavy oil such as crude oil or its distillation residue oil to approximately 700 ml.
It is thermally decomposed in the presence of water vapor at a temperature of ~850°C to produce olefins such as ethylene and propylene. An external combustion furnace that burns fuel installed on the side of the heating tower burns the distillation residue, which is a liquid byproduct of thermal decomposition. In the coke heat transfer method, the above-mentioned heavy oils are used as pyrolysis feedstocks, and these feedstocks have a high nitrogen content, so that the distillation residue of the by-product liquid product of external combustion furnace fuel has a high nitrogen content. According to the analysis results, the nitrogen content is approximately 0.1 to 2.0% by weight, and the nitrogen oxide concentration in the external combustion furnace exhaust gas is also high, 400 to 600 ppm.
(based on dry exhaust gas). The hot exhaust gas of the external combustion furnace is passed into the circulating coke fluidized bed and heats the coke to 750-850°C. Here, it was confirmed that the nitrogen oxide concentration in the heating tower exhaust gas was slightly lower by 200 to 500 ppm than the nitrogen oxide concentration in the combustion exhaust gas passing through the heating tower. It is a well-known fact that some nitrogen oxides are catalytically reduced in high-temperature coke [for example, Japan Fuel Association Journal, Vol. 54, No. 581, 766-773].
(1975)], also in the coke heat transfer method, denitrification reactions occur partially through catalytic reduction using high-temperature coke. In the single coke heat transfer method, a considerable amount of ammonia is present in the cracked gas. For example, in the case of vacuum residue with a nitrogen content of 0.4 to 0.5% by weight as a pyrolysis feedstock,
The amount of ammonia produced when the flow rate to the reaction tower is 100T/hour is
100-150Kg/hour. A considerable amount of this by-product ammonia is dissolved in the steam condensed water used in the process, which is condensed in the top system of the first fractionating column. The ammonia dissolved in the condensed water is steam stripped with gases such as hydrogen cyanide and hydrogen sulfide, and the gases are then combusted. Here, the amount of stripping ammonia gas is 50 to 100 kg/hour in the above case, and when the ammonia-containing stripping exhaust gas is passed through the heating tower, ammonia and high-temperature coke are discharged from the external combustion furnace attached to the heating tower. of nitrogen oxides
It was found that 70-98% of the nitrogen content was very effectively denitrified by catalytic reduction. Further, although the ammonia-containing steam stripping exhaust gas was subjected to combustion treatment, in the above method, ammonia was used and consumed in the denitrification reaction, so the amount of nitrogen oxides produced by combustion from ammonia in the reburning furnace was reduced. Furthermore, it was possible to reduce the load on the subsequent denitrification catalyst that denitrates these exhaust gases. If the pyrolysis feedstock has a low nitrogen content, such as crude oil or atmospheric residual oil, it has become possible to discharge the subsequent exhaust gas without passing it through a denitrification treatment facility. Next, the present invention will be specifically described with reference to the accompanying drawings. The accompanying drawing is a system diagram of an apparatus for explaining an embodiment of the present invention and a comparative example. 1 is a reaction column, and 2 is a heating column. A fluidized bed of coke particles is formed in each column, and the coke particles are circulated between the two columns via a line 16. 1
5 is an external combustion furnace of the heating tower, 17 is a combustion air supply line, and 18 is a line for supplying the combustion exhaust gas to the heating tower. Raw material heavy oil is supplied to the reaction tower 1 from line 3, and is thermally decomposed by coke particles.
line 4, cyclone 5, line 7, quencher 8,
It is introduced into a first fractionator 11 via a line 10. The cracked heavy oil obtained from the bottom of the tower is line 1
4 and the residue is fed via line 13 to an external combustion furnace 15. On the other hand, the top component is cracked gas 1
2. Separated into cracked gasoline 32 and condensed water 19,
The condensed water is introduced into a condensed water stripper 31. Condensed water stripper 3 for ammonia-containing exhaust gas
1, it is stripped by a stripping steam 30 and passed through a line 20 to a heating tower 2.
Nitrogen oxides in the combustion exhaust gas 18 of the external combustion furnace 15 are denitrified by the ammonia-containing exhaust gas introduced from the circulating high-temperature coke 33 and 20, and are discharged from the heating tower via a cyclone 21 and a line 23. On the other hand, the coke separated by the cyclone 21 passes through the dipleg 22 and returns to the fluidized bed. The ammonia-containing exhaust gas 20 was previously combusted in the reburning furnace 24 from the line 29 and became a source of nitrogen oxides. However, in the present invention, ammonia is consumed in the denitrification reaction in the heating tower 2, and unreacted ammonia is burned in the reburning furnace. Therefore, the nitrogen oxides generated and flowing into the external combustion furnace 15 are denitrified, and the nitrogen oxides generated in the reburning furnace are also reduced, so that the amount of nitrogen oxides in the combustion exhaust gas 28 of the reburning furnace 24 becomes extremely small. In addition, 2 of the reburning furnace 24
6 is water supplied to the boiler, 27 is the generated steam, and 25 is combustion gas. Further, 9 is a supply line for the quenching oil in the quencher 8, and 6 is a line for returning the coke particles separated by the cyclone 5 to the reaction tower. Next, examples of the present invention will be shown, but the present invention is not limited thereto. Example 1 Atmospheric residual oil produced in the Middle East was supplied to the reaction column 1 of the apparatus configured as shown in the attached drawing, and thermally decomposed at a temperature of 750°C and a weight ratio of diluted steam to feedstock oil of 1.0. 49% by weight, by-product light oil (boiling point 80
~200℃) 11% by weight, by-product residue (boiling point 200℃ or higher)
32% by weight and 8% by weight coke. 70% of this by-product residue was supplied to an external combustion furnace installed on the side of the heating tower, and 20% by weight of steam for atomization was blown into the by-product residue to combust it with the theoretical amount of air.
In addition, 270 kg/hour of gas at 53°C, stripped by a condensed water stripper 31, is supplied from a nozzle 20 installed at the bottom of the heating tower below the combustion gas inlet.
It passed through a heating tower at 790°C. The composition of the stripping gas was as follows. H ₂ S 69% HCN 4 NH ₃ 21 Others 6 The amounts of nitrogen oxides at the outlet of the external combustion furnace, heating tower, and reburning furnace are summarized in Table 1 below, along with the results of each example below. Example 2 The same procedure as in Example 1 was carried out except that vacuum residual oil with a nitrogen content of 0.58% by weight was supplied as the feedstock oil to the reaction column. Table 1 shows the results of the amount of nitrogen oxides at each point. Comparison Column 1 The same operations as in Example 1 were carried out except that the entire amount of the condensed water stripping exhaust gas was introduced into the reburning furnace through line 29 and subjected to combustion treatment. Table 1 shows the results of nitrogen oxides at each point in this case. Comparative Example 2 The same operations as in Example 2 were carried out except that the entire amount of the condensed water stripping exhaust gas was introduced into the reburning furnace through line 29 and subjected to combustion treatment. Table 1 shows the results of nitrogen oxides at each point in this case.

[Table] As is clear from the values in Table 1 above, according to the present invention, the amount of NOX in the exhaust gas introduced from the external combustion furnace to the heating tower can be reduced to 30% or less of the conventional method. Ta. Therefore, the effect is significant.

[Brief explanation of the drawing]

The accompanying drawing is a system diagram of an apparatus for explaining an embodiment of the present invention and a comparative example. 1: Reaction tower, 2: Heating tower, 12: Cracking gas, 1
5: External combustion furnace, 19: Process condensate water, 20:
Stripping acid gas, 24: Reburning furnace, 2
9: Acid gas combustion line, 31: Condensed water stripper.

Claims (1)

[Claims] 1. Two coke particle fluidized beds, a reaction tower and a heating tower, are installed, the coke particles are circulated between the two towers, and the coke particles are heated in the heating tower by high-temperature combustion gas from an external combustion furnace attached to the heating tower. At the same time, when producing olefins by thermally decomposing heavy oil using heated coke particles as a heat medium in a reaction tower, ammonia, which is produced as a by-product from the raw material heavy oil, is passed through the heating tower, where it is heated to a high temperature. A method of reducing and removing nitrogen oxides generated and flowing from an external combustion furnace using coke and the reducing ammonia gas.