CN105950207B - A kind of method for suppressing hydrocarbon fuel cracking furnace pipe tube wall coking - Google Patents

Abstract

The invention relates to a method for suppressing the coking of the pipe wall of a hydrocarbon fuel cracking furnace. Any one or more of pure water, monohydric alcohol or phosphotungstic acid is blended with the hydrocarbon fuel to form a fuel mixture, and then the obtained The fuel mixture is input into the cracking furnace tube for cracking.

Description

A method for suppressing coking on the tube wall of hydrocarbon fuel cracking furnace

technical field

The invention belongs to the field of maintenance operation of hydrocarbon fuel cracking furnace tubes, and in particular relates to a method for suppressing coking of the tube walls of hydrocarbon fuel cracking furnaces.

Background technique

During the thermal cracking process of hydrocarbon fuel, coking occurs along with polymerization and condensation, which reduces the heat exchange efficiency of the metal surface, blocks the nozzle and reduces the oxidation resistance of the metal material. It increases the loss of metal materials. How to effectively suppress the appearance of solid coke at high temperatures is the key to designing high thermal stability aviation fuels. At present, the methods to solve this problem include adding coking inhibitors, supercritical extraction, modifying the surface of materials, steam reforming, etc. From the overall research results, adding coking inhibitors to hydrocarbon fuels is recognized as a more effective method, and steam reforming is considered to be one of the most promising methods.

Patent CN 103421531 B provides a method for alleviating coking of cracking furnace tubes, including coating an anti-coking coating on the inner surface of cracking furnace tubes, and adding coking inhibitors to cracking raw materials. Coking inhibitors include dimethyl disulfide, hydroquinone, methylnaphthalene, tributyl phosphate, dimethylquinoline, magnesium alkyl salicylate, and propylenediamine disalicylate. Among them, the contents of dimethyl disulfide and dimethylquinoline are relatively high, both being 30-50 parts. However, dimethyl disulfide is easy to corrode the inner wall of the metal furnace tube, and dimethyl quinoline is heated to decompose and release toxic nitrogen oxide fumes, which pollute the environment, and both of them will cause human eyes, respiratory system and skin. Stimulating effect, cannot be used as an environmentally friendly inhibitor. Existing coking inhibitors have certain defects in the use process, such as sulfur and phosphorus compounds have a greater corrosion effect on metals; boron compounds need to use additional organic matter as a solvent during use, which increases the side reactions of the cracking reaction ; Alkali metal compounds inhibit coking by catalyzing the reaction between coke and water vapor, but the dispersibility of such additives in fuels is poor, and their service life as catalysts is limited.

Hydrogen produced by steam reforming of hydrocarbons is an efficient and clean energy source. Combustion of 1 kg of hydrogen can produce 1.25×10 ⁶ kJ of heat, which is equivalent to the heat released by the complete combustion of 3 kg of gasoline or 4.5 kg of coke. In addition, the water produced by hydrogen combustion is environmentally friendly and non-polluting, and is a precious resource. Patent CN 105366640 A discloses a method and device for producing hydrogen based on steam catalytic reforming of biomass gasification primary gas. The primary gas is fully mixed with water vapor after preheating, and hydrogen is obtained after catalytic reaction purification. The sensible heat of the gas after catalytic reforming is used to preheat the biomass primary gas, which realizes the utilization of waste heat, reduces the energy consumption of the device, and improves the efficiency of catalytic reforming. Patent CN 105087044 A discloses a method for online treatment of the inner surface of the hydrocarbon cracking furnace tube. The method is to place the inner surface of the cracking furnace tube in a mixed gas atmosphere for high-temperature gasification and oxidation treatment. The mixed gas is hydrogen and aqueous solution gasified A mixed gas, water vapor is added to the mixed gas. High-temperature gasification refers to the reaction of carbon remaining on the inner surface of the furnace tube with water vapor under the catalysis of the solute, and oxidation treatment refers to the reaction of water vapor with Cr and Mn elements in the furnace tube matrix alloy. When water vapor accounts for about 15% of the volume of the gasified mixed gas, the coking inhibition rate is as high as 82% after the furnace tube is subjected to 5 cycles of pyrolysis and coking under the same conditions. It can be seen that water vapor plays an obvious role in promoting coke cleaning.

Contents of the invention

The present invention aims to overcome the problems of poor dispersibility of the original coking inhibitor in the fuel and the relatively large corrosion effect on metals, etc., and uses steam reforming of hydrocarbon fuels as a technical approach to improve fuel utilization while reducing the coke content.

The present invention solves the above problems through the following solutions:

A method for suppressing coking of the pipe wall of a hydrocarbon fuel cracking furnace, blending any one or several of pure water, monohydric alcohol or phosphotungstic acid with the hydrocarbon fuel to form a fuel mixture, and then mixing the fuel mixture Input into the cracking furnace tube.

In a specific embodiment, the consumption of the pure water is 0.1-10% of the fuel mixture weight; the consumption of the monohydric alcohol is 0.1-15% of the fuel mixture weight, and the consumption of the phosphotungstic acid is the fuel mixture weight 0.01 to 0.5% of the total.

Preferably, the monohydric alcohol is any one of methanol, ethanol or propanol.

Preferably, the hydrocarbon fuel and the pure water are gasified separately and then mixed, and the mixing method is realized by two feed pumps, one for delivering fuel and the other for delivering high-purity water, the purpose of which is to improve the fuel and pure water degree of mixing.

Preferably, the cracking conditions of the hydrocarbon fuel are: cracking temperature 650-800° C., fuel flow rate 0.5-16 g/s, system pressure 0.3-10 MPa.

In a specific embodiment, the cracking furnace tube is made of alloy, and its inner wall is coated with a perovskite coating.

In a specific embodiment, the amount of phosphotungstic acid is 0.1% by weight of the fuel mixture.

In a specific embodiment, the ethanol is used in an amount of 5% by weight of the fuel mixture.

Beneficial effects of the present invention:

1. In the embodiment of the present invention, two delivery pumps are used to feed materials, one to deliver hydrocarbon fuel, and the other to deliver high-purity water. The purpose is to slowly deliver high-purity water so that the water and fuel are in stable contact.

2. The method for suppressing the coking of the tube wall of the hydrocarbon fuel cracking furnace of the present invention is simple, and the effect of reducing the average carbon deposit on the inner wall of the tube wall of the cracking furnace is very obvious. The method is simple, easy to implement, environmentally friendly and low in cost, and can prolong the operation cycle and service life of the cracking furnace tube.

3. The reforming reaction of hydrocarbon fuel and water vapor of the present invention belongs to an endothermic reaction, which can effectively reduce the temperature of the cracking reaction device; the reformed final product _H2 has a high calorific value and is a clean and environmentally friendly new energy source;

4. The water vapor added in the present invention can catalyze the reaction with the coke attached to the inner wall of the cracking reaction furnace tube, and play the role of coke cleaning.

5. The purpose of adding pure water is to use steam reforming of hydrocarbon fuels to generate efficient and clean energy H ₂ , and at the same time use the reforming endothermic process to absorb excess waste heat in the reactor. The dehydration of monohydric alcohols under low temperature conditions can produce the same effect as pure water. As a catalyst, phosphotungstic acid can catalyze the chemical reaction between coke and water vapor at high temperature, and reduce the content of coke attached to the inner wall of the furnace tube.

Description of drawings

Fig. 1 Example 1 Cracking furnace tube wall temperature and carbon deposition distribution along the tube length.

Fig. 2 Condenser pressure difference comparison between embodiment 1 and embodiment 3.

Fig. 3 Comparison of the average carbon deposition on the tube wall of the pyrolysis furnace in Examples 1 to 4.

detailed description

In a specific embodiment, the steps are as follows:

(1) Pretreatment of superalloy tubes

Use a peristaltic pump to drive the reagent into the superalloy tube, and circulate the flow to clean the tube wall. The cleaning time for each reagent is 10-60 minutes. The order of injecting reagents is as follows: methylene chloride, water, ethanol, wherein the function of methylene chloride is to wash off the organic impurities on the inner wall of the tube, and the function of ethanol is to wash away excess methylene chloride. After cleaning, purge the inner wall of the tube with high-purity nitrogen for 5-30 minutes, then dry it at 80-120°C for 1-3 hours, and finally seal both ends of the tube with PTFE tape for future use.

(2) Coating preparation and coating

The inner wall of the superalloy tube is coated with perovskite coating. The specific preparation process and coating process are detailed in the patent "A Composite Coating for Inhibiting Furnace Tube Coking, Its Preparation Method and the Composite Coating Made from It", Application No. : 201610453604.0.

(3) Experimental grouping

(4) Prepare the mixed solution of additives and fuel

Experiment 1: No preparation required.

Experiment 2: No preparation required.

Experiment 3: First, add a certain amount of monohydric alcohol to a small amount of kerosene, and stir evenly to obtain mixture A; secondly, according to the amount used in the experiment, pour mixture A into barreled kerosene, stir evenly, and seal it for storage.

Experiment 4: First, dissolve a certain amount of phosphotungstic acid into monohydric alcohol solution to obtain mixture B; secondly, add mixture B to a small amount of kerosene and stir evenly to obtain mixture C; thirdly, according to the experimental dosage, mix mixture C Pour it into barreled kerosene, stir evenly and seal it for storage.

(5) Experimental conditions

Cracking temperature: 700°C, fuel flow rate: 1g/s, system pressure: 4MPa.

(6) Lysis experiment

Hydrocarbon fuel cracking experiments were carried out on a high-pressure thermal cracking experimental device.

(7) Detection of carbon deposition on the pipe wall

The amount of coking in the tube wall of the cracking furnace is detected by a CO ₂ infrared detector.

Embodiment 1 (comparative example)

(1) Carry out the cracking experiment of hydrocarbon fuel on the high-pressure thermal cracking experimental device, and use a feed pump to transport kerosene alone, without additives;

(2) On-line monitoring of the pressure difference between the reaction tube and the condenser;

(3) After the reaction is finished, the reaction tube is removed, and the amount of carbon deposited in the tube is detected by a CO ₂ infrared detector. Through calculation, the average amount of carbon deposited on the inner wall of the cracking furnace tube is obtained to be 1.90 mg/cm ² . Figure 1 shows the distribution of the tube wall temperature and coking amount along the length of the cracking furnace tube. The closer to the cracking furnace tube outlet, the higher the wall temperature and the more carbon deposits.

Embodiment 2 (high pure water)

(1) Carry out the cracking experiment of hydrocarbon fuel on the high-pressure thermal cracking experimental device, using two feed pumps, one conveys kerosene, and the other conveys high-purity water, wherein the weight percentage of high-purity water and kerosene is 1:19, that is, high-purity water is in the fuel The proportion in the mixture is 5%, and the two are gasified separately and then mixed;

(2) On-line monitoring of cracking furnace tube and condenser pressure difference;

(3) After the reaction is finished, the cracking furnace tube is removed, and the amount of carbon deposited in the tube is detected by a _CO2 infrared detector. By calculation, the average amount of carbon deposited on the inner wall of the cracking furnace tube is obtained to be 0.83 mg/cm ² .

Embodiment 3 (ethanol)

(1) Add ethanol to a certain amount of kerosene, mix well, and then add it to the barreled kerosene. Wherein, the percentage by weight that ethanol accounts for in the fuel mixture is 5%;

(2) Carry out the cracking experiment of hydrocarbon fuel on the high-pressure thermal cracking experimental device, and use a feed pump to deliver the fuel mixture;

(3) On-line monitoring of pressure difference between cracking furnace tube and condenser. Comparing Example 1 with Example 4, it was found that the pressure difference of the condenser containing 5% ethanol additive was slightly higher than that of the blank group, and the fluctuation range of the pressure difference was stable within 0.04MPa, which did not affect the experiment. The result is shown in Figure 2;

(4) After the reaction is finished, the cracking furnace tube is removed, and the amount of carbon deposited in the tube is detected by a _CO2 infrared detector. Through calculation, the average amount of carbon deposited on the inner wall of the cracking furnace tube is obtained to be 0.79 mg/cm ² .

Embodiment 4 (phosphotungstic acid and ethanol)

(1) Dissolve phosphotungstic acid in ethanol solution, mix it evenly and add it to a certain amount of kerosene, and mix it evenly again, then add it to the barreled kerosene. Finally, the percentage by weight of phosphotungstic acid in the fuel mixture is 0.1%, and the percentage by weight of ethanol is 5%;

(2) Carry out the cracking experiment of hydrocarbon fuel on the high-pressure thermal cracking experimental device, and use a feed pump to deliver the fuel mixture;

(3) On-line monitoring of cracking furnace tube and condenser pressure difference;

(4) After the reaction is finished, the cracking furnace tube is removed, and the amount of carbon deposited in the tube is detected by a _CO2 infrared detector. By calculation, the average amount of carbon deposited on the inner wall of the cracking furnace tube is obtained to be 0.76 mg/cm ² .

Claims (8)

1. a kind of method for suppressing hydrocarbon fuel cracking furnace pipe tube wall coking, it is characterised in that be total to phosphotungstic acid with hydrocarbon fuel Mixed fuel mixture or phosphotungstic acid are blended into fuel mixture with pure water and/or monohydric alcohol with hydrocarbon fuel, then will be described Fuel mixture is input in the cracking furnace pipe.

2. according to the method described in claim 1, it is characterised in that the consumption of the pure water is the 0.1 of fuel mixture weight ~10%；The consumption of the monohydric alcohol is the 0.1~15% of fuel mixture weight, and the consumption of the phosphotungstic acid mixes for fuel The 0.01~0.5% of thing weight.

3. according to the method described in claim 1, it is characterised in that wherein described unary alcohol is in methanol, ethanol or propyl alcohol Any one.

4. according to the method described in claim 1, it is characterised in that the cracking furnace pipe material is to be coated on alloy, its inwall There is perovskite coating.

5. according to the method described in claim 1, it is characterised in that after the hydrocarbon fuel and the pure water gasify respectively again Mixed.

6. according to the method described in claim 1, it is characterised in that hydrocarbon fuel cracking condition is：Cracking temperature 650~800 DEG C, 0.5~16g/s of fuel flow rate, 0.3~10MPa of system pressure.

7. according to the method described in claim 1, it is characterised in that the consumption of the phosphotungstic acid is fuel mixture weight 0.1%.

8. method according to claim 3, it is characterised in that the consumption of the ethanol is the 5% of fuel mixture weight.