Secondary reforming catalyst RK-11-4 is suitable for the reforming plant for secondary reforming, oxygen-enriched reforming, pure oxygen reforming, and methanol preparation based on coke-oven gas of the ammonia plant which takes natural gas, oil field associated gas and light oil as raw materials. Generally, secondary reforming catalyst RK-11-4 is used together with thermal protective catalyst RK-11-3.
1.Physical properties and chemical components of catalyst
1) Composition: nickel is the active component, and alumina with special additives is the carrier.
2)Appearance: ring
Specification (outer diameter * inner diameter * length): φ19*9*19mm
Bulk density: 0.80-1.20 Kg/L
Side crushing strength: ≥500N/p
Burn weightlessness: ≤5%
3)Operation condition
Pressure: normal pressure -5Mpa
Temperature: ＜1250℃
Water/carbon ratio: ≥2.5
Air speed: ≤6000h-1
4)Heat-resisting performance: it will not melt and deform by calcining for 4h at 1450℃, and operate for a long time at 1200℃. Moreover, in the operation process at high temperature, the structure is stable, the strength is good, and the catalyst will not break.
2.Storage and loading/unloading of catalyst
1) RK-11-4 catalyst packed in plastic bag well shall be placed in an iron drum, and placed in a dry and clean place without freezing, and it shall be prevented from falling from the place of 0.5m and above as well as impacting at any time. Moreover, the catalyst shall be prevented from the pollution caused by sulfur or other soluble salts.
2)Before feeding into the furnace, the catalyst shall be sieved to remove a small amount of powder therefrom, and the blocking condition for the interior of furnace and supporting grid shall be inspected. When the catalyst is fed into the furnace, the operation of blowing down shall be carried out with air.
3)Loading of catalyst in secondary reformer
In the loading process, the catalyst shall be leveled, which means it shall not be piled before leveling, and the operation can enter into the furnace when necessary, but he/she shall not walk and trample directly on the catalyst.
Generally, the upper part of RK-11-4 layer shall be provided heat resisting catalyst RK-11-3 of 20-25% of the whole furnace.
4) Passivation treatment shall be carried out as required when the catalyst shall be removed.
3.Driving of reforming plan
1)Generally, the catalyst of the first and second sections will be subject to the temperature-rising reduction at the same time. The primary reformer can use air as heating medium (the best heating medium is nitrogen gas (if possible)) at 200℃. When the temperature is 200℃, the operation temperature can be realized with steam, but the temperature of secondary reformer shall be reached to 150℃ and above herein. When the reduction operation of the primary reformer is started, the reforming catalyst of the second section will start the reduction. When the temperature of the secondary reformer is 650℃ and above, a small amount of air can be added into the secondary reformer, and then add the air slowly to the designed value after confirming the success (analyzed and judged from furnace temperature and composition of exhaust gas) of automatic ignition based on the air fed.
2)Main condition of temperature-rising reduction
①When the temperature-rising speed is 100℃/h and below, there is no adverse effect to the various properties of CN-20 catalyst. The actual temperature-rising speed is limited by furnace equipment and materials. During the temperature-rising process, the constant temperature stage shall be noted: the purpose of constant temperature is to homogenize the temperature of catalyst bed; the purpose of constant temperature before starting reduction is to reduce the temperature difference of catalyst bed and realize consistent reduction speed; and the purpose of constant temperature after the completion of reduction is to thoroughly eliminate a small amount of poison in the catalyst and stabilize the structure of the catalyst further, which is favorable to improve the activity.
②Generally, the catalyst is simultaneously reduced together with that of the first section. The reduction medium of the primary reformer can be the water vapor with ammonia or hydrogen nitrogen, or the water vapor matched with a certain proportion of raw material natural gas. Herein, H2O/C shall be 5 to 7 as required.
③Reduction temperature: 650～800℃;
④Reduction pressure: 0.20～0.70 Mpa (gage pressure);
⑤Reduction air speed: 200～600h-1;
⑥ Reduction time: the reduction time shall be less than 8h after reaching to the reduction temperature specified.
3)After starting reduction, the catalyst shall not be contacted with oxidation gas.
4.Notes in operation
1)The requirements on harmful toxins shall be follows:
Generally, the content of sulfur in raw material gas and process air shall be less than 0.5ppm (the best condition is that the content of sulfur is less than 0.2ppm), and the content of chlorine thereof shall be required strictly. The gas mentioned above shall contain arsenic, lead, phosphorus, etc.
In addition to chloride, arsenic and other toxics, the water vapor shall not include condensate and other chemical poisons.
2)In the operation, it shall be ensured that the water/carbon ratio is not less than the design value at any time, and the water vapor shall be added before the raw material gas while increasing the load, and the raw material gas shall be reduced before the water vapor while reducing the load.
5.Shutting down
1)Generally, the air of secondary reformer can be cut off in case of short-term shutting down while keeping the catalyst, then the raw material gas of the first section shall be closed, the water vapor fed to the primary reformer can be continued, and the fuel gas shall be closed to cool. When the temperature is reduced to the point above the dew point of water vapor for about 50℃, the water vapor within the system shall be blown off with nitrogen (or air), so as to ensure that the temperature will be reduced to normal condition while keeping the pressure.
2) In case of long-term shutting down or replacement of catalyst, the catalyst shall be subject to passivation treatment, so as to prevent from vigorous oxidation, wherein the passivation medium shall be water vapor. The passivation for the catalyst of the second section is generally carried out together with that of the first section, in which the air of the secondary reformer can be cut off, then the raw material gas of the first section shall be closed, the water vapor fed to the primary reformer can be continued for 6-8h, until the outlet gas of the secondary reformer does not include non-condensable gas, which can prove that the catalyst has been passivated basically. At this point, the fuel gas of the primary reformer can be closed, the water vapor fed to the primary reformer can be continued; when the cooling speed is about 50℃/h and the temperature is higher than the dew point for about 50℃/h, the water vapor within the system shall be blown off with nitrogen (nitrogen can be replaced with air in the place without conditions), until the temperature is less than 50℃, the plant can be stopped and opened to remove catalyst.
3)To give full play to the use of the catalyst, prolong its service life, the catalyst shall be prevented from long-term contacting with excessive water vapor at high temperature. The cooling temperature of RK-11-4 catalyst shall be mainly considered from the process equipment.
6.Poisoning of catalyst
1)When the reaction temperature is relatively high, nickel catalyst poisoned sulfur is reversible, the water/carbon ratio operation can be increased properly by infusing the raw material gas of which the sulfur content is lower than the value specified in case of sulfur poisoning, and then the activity of the catalyst will gradually recover. But it shall be pointed out that the activity cannot be recovered completely, and there are still some adverse effects to the catalyst.
2) The poison of catalyst to chlorine is reversible, but the removal regeneration is more difficult, which means replacement of catalyst is better than regeneration, so that the possibility of chlorine entering into reformer shall be eliminated.
3) The poison of catalyst to arsenic is irreversible, and therefore arsenic entering into the reforming system must be prevented strictly.
7.Carbon deposition process of catalyst
In case of small amount of carbon deposition of the catalyst, the natural gas can be reduced, the water/carbon ratio can be increased, the outlet temperature shall be kept at 650～800℃ and maintained for a period of time, and the change in CO2 content in outlet gas shall be observed. When the CO2 content is normal, it can be regarded that carbon deposition process is completed.
When the carbon deposition of catalyst is serious, the general treatment effect is bad, and the suggestion is to replace the catalyst.
8.Overtemperature
When the operation of mixer in the secondary reformer is abnormal, it will cause the intense overtemperature of catalyst layer in the secondary reformer, and even the catalyst will fused into pieces. As the position of temperature measuring point of the secondary reformer cannot reflect the temperature distribution and change of catalyst layer normally and timely, the small changes to the furnace temperature shall be noted carefully, and then the overtemperature condition shall be judged by combining with the composition of reforming gas in the second section. In case of the overtemperature phenomenon, the various measures shall be taken until stopping for checking.
Description: the starting condition and accident treatment for the catalyst are the main principle of the instruction, and the starting, operation and other conditions of specific plant shall be carried out according to the specific operation provisions provided by design department.
