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Methanation Catalyst
RK-09D Methanation Catalyst
RK-09D Methanation Catalyst

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1.Applicable scope and usage of product 

RK-09D methanation catalyst is a new titanium rare earth nickel catalyst which is suitable for synthesis ammonia unit or other hydrogen plants, to remove CO and CO2 at low concentration from the hydrogen-enriched raw material and make them to be inert gas methane and water easily removed, thereby achieving the purpose of purifying the gas. This catalyst has unique properties, high strength, large pore volume, high activity and easy unloading. Its operation is obviously higher than that of other catalysts at the high pressure and at high airspeed. Now, it has been widely used in the large, middle and small ammonia synthesis plants and hydrogen plants.

2.Technical requirement

1)The methanation reaction is a strong exothermic reaction, and its main chemical equation is as follows:

CO+3H2=CH4+H2O 

CO2+4H2=CH4+2H2O

Under the general operating condition of methanation system, the adiabatic temperature rise of conversion of each 1% carbon monoxide is 72℃, and the adiabatic temperature rise of conversion of each 1% carbon dioxide is 60℃.

2)Product technical index

Items :Indexes

Initial activity (CO2 content in the outlet gas)    Before heat resistance, 10-6  :≤20

                                                                            After heat resistance, 10-6   :≤25

Anti-crush strength of particle before reduction, N/particle)  Φ4.5-5.5 :≥160

                                                                                                  Φ3.0-4.0 :≥110

Low strength percentage (lower than 90N/particle), % :≤10                         

Wear rate, % :8

3)Physical and chemical properties

Appearance: Φ4-6mm ash black sphere

Bulk density: 0.9±0.05kg/L

Specific surface area: ~100m2/g

Chemical composition: Ni≥14%; Al2O3≥70%; and other few assistants.

4)Packaging and specification 

RK-09D methanation catalyst shall be packaged with the plastic bucket or paper bucket lined plastic film. The quality certificate is attached I the packaging bucket, with the content including: product name, model, batch number, net weight, manufacturer, etc. 

3.Use condition

1) Use condition of RK-09D spherical methanation catalyst

Normal operating temperature, ℃:240~430

Best operating temperature, ℃ :250~430

Pressure, MPa  :≤32.0

Airspeed, h-1:6000~10000

Inlet CO+CO2, V%  :≤0.7

Outlet CO+CO2, ppm :≤10

Total sulfur in inlet gas, ppm :<0.1

Total chlorine in inlet gas, ppm :<0.01

2)Use of RK-09D spherical methanation catalyst

2-1) Filling of RK-09D methanation catalyst

2-1-1)Before filling catalyst, it shall carefully check the reactor, and remove all sundries.

2-1-2) Generally, the methanation catalyst shall be sieved before filling, because it is hard to avoid the dust and fragment in the transportation process, it shall be sieved with 8-10-mesh screen before filling. This catalyst has little dust and fragment due to adopting the static production process, and thus is not sieved, and can be slipped through the chute with hole, so as to avoid damaging the catalyst surface structure and producing the new dust. 

2-1-3) With regard to the filling of catalyst, the upper and lower parts of bed shall be filled with refractory balls, and the stainless steel wire mesh shall be arranged between the refractory balls and catalyst bed. When filling, the cloth bag is taken as the drainage tube, to guarantee that the free falling height of catalyst is not greater than 0.5m.

2-1-4) It shall pay attention to record the weight, volume, batch number and filling height of filled catalyst, and corresponding position of thermocouple, etc.

2-2) Heating of catalyst

After filling, the system shall be purged. In the startup and operation process, it shall pay attention to control the rate of pressure rise and decline in the furnace within 0.2MPa/min, so as to avoid that the catalyst is damaged and pulverized. The reduction pressure of this catalyst is usually controlled at 5.0~6.0MPa. The new catalyst can be heated with nitrogen or process gas, and it shall avoid direct heating with the steam. After heating to 250℃ with nitrogen, it shall be reduced with process gas, and now, most of manufacturers directly heat with process gas. 

2-3)Reduction of catalyst

The reducting medium of RK-09D methanation catalyst can access the pure hydrogen or qualified process gas (CO+CO2≤0.7%) in the circular nitrogen. The current small ammonia synthesis plants mostly adopt the qualified process gas for direct heating reduction.

The starting temperature of reduction of RK-09D methanation catalyst can be controlled at 250~300℃, and gradually increased to the normal reduction temperature (400℃) according to the heating rate in the heating reduction scheme (the hot-spot temperature of reduction is allowed to be increased to 430℃ according to the reduction situation). In the reduction process itself, the significant temperature risen of catalyst bed is not caused, and due to reducing with the process gas, the methanation reaction is started when some nickel metal is generated, therefore, it requires that CO+CO2 in the gas used for reduction shall be less than 0.7%. In special conditions, such as heat source limit, the heat source of methanation furnace can reach 300~320℃, the content of inlet CO+CO2 can be appropriately increased, and the bed temperature can be increased with the reaction heat of CO and NiO and H2. But such operation must be strictly controlled, and it shall strictly prevent that CO+CO2 exceed the standard to cause the soaring of catalyst bed temperature and damage the catalyst activity seriously. As the catalyst is gradually reduced, the methanation reaction heat is given off, and as long as the reduction airspeed reaches above 500h-1 or is 20~50% of full load and the total content of CO+CO2 in the process gas is less than 0.7%, the overtemperature phenomenon will not occur.

When heating reduction, it shall also note that the heating rate shall be controlled at 50~70℃/h when the catalyst bed temperature is lower than 250℃, the heating rate shall be adjusted by virtue of inlet temperature of led process gas, and the gas including CO+CO2 cannot be accessed. Because the partially reduced nickel in methanation catalyst may react with CO at a lower temperature to generate nickel carbonyl which is not only sublimated to enable the active component of catalyst to partially loss, but also is a high-toxicity substance having a big poison to the human body.

Entering the reduction period: the reduction is started after the bed temperature is heated to 250℃, the heating rate can be controlled at 20~30℃/h, and as the reduction is conducted and the bed temperature is increased, the reduction speed is obviously accelerated. When entering the final stage, the inlet temperature is increased above 350℃, and by keeping this condition, it enables the outlet temperature of bed to be close to the hot-spot temperature (430℃) of bed, and keeps for 4-6h, and analyzes that the trace element at the outlet meets the index, then, it can cool to the normal operating temperature, and transfers to the light load production.

The reduced catalyst shall avoid contacting with the air as far as possible, so as to avoid the nickel metal from sharp oxidation for overtemperature.

2-4)Schedule of RK-09D methanation catalyst reduction (for reference only)

Stage

Hot-spot temperature ()

Heating rate (/h)

Estimated time (H)

Cumulative time (H)

Gas composition (H2%)

Heating period

Normal temperature~250

5070

5

5

≥70

Reduction stage

250400

2030

1015

≥70

Reduction stage

400450

30

217

≥70

Constant temperature stage

4500623

≥70

Cooling stage

450250

-50




2-5) Normal operating condition of catalyst

2-5-1) Operating temperature

The methanation reaction is a strong exothermic reaction. Theoretically, it is adverse to the reaction by raising the temperature, but under the ammonia plant condition, the methanation reaction is operated in the state far from equilibrium, and the effect of equilibrium constraint can be ignored. By considering from the dynamics, the reaction can be accelerated by raising the temperature. Generally, the operating temperature of RK-09D methanation catalyst on the middle-high pressure plants is 240~320℃, and if the temperature is too low, its performance cannot be fully played; and if the temperature is too high or it is long-term over-temperature, the reduction of catalyst activity will be accelerated. If the newly reduced catalyst is used at the high pressure, the CO+CO2 content at the inlet shall not be more than 0.05%, and the inlet temperature of bed can be controlled at 240~260℃ to meet the requirement that CO+CO2 at the outlet is not more than 10×10-6; and when it is used at the medium temperature, the CO+CO2 content at the inlet shall not be more than 0.2%, and the inlet temperature of bed can be controlled at 250~270℃ to meet the requirement that CO+CO2 at the outlet is not more than 20×10-6. With the extension of service time and frequent overtemperature, the catalyst at the upper layer is gradually inactivated, and the inlet temperature of methanation furnace can be gradually raised, to guarantee the index of trace element at the outlet.

Overtemperature of methanation furnace is almost caused because a lot of CO and CO2 enter methanation furnace due to the decarburization or the unbalance of methanol system. The bed temperature is not more than 450℃ in a short time, and thus, the influence to the catalyst activity is not big; and if the temperature is more than 450℃ for a long time, the activity and service life of catalyst will be affected. When the methanation furnace has an indication of temperature soaring, the inlet temperature of bed shall be immediately reduced to about 220℃, the process gas shall emptied in front of methanation furnace, the bed shall be purged with refined gas after methanation or nitrogen, a little steam can also be used for cooling if there is no way, but it shall use the steam for cooling as little as possible or avoid using the same, because the steam is weak oxidant, and after cooling, the activity can be recovered by reducing with the qualified process gas again. 

2-5-2)Operating pressure and airspeed

The methanation reaction is a reaction of volume reduction. By increasing the pressure, it is beneficial to the reaction, and also, the partial pressure of reactant is also correspondingly increased to accelerate the reaction, and the airspeed can also be increased correspondingly. The airspeed reflects the ability of catalyst to handle the gas. Under the high-pressure use condition, the use airspeed of RK-09D methanation catalyst can reach 10000 h-1.

2-5-3)Content of inlet CO+CO2

The CO+CO2 content at the methanation furnace inlet shall be controlled within a certain range, and generally, within 0.7%. The CO+CO2 content at the inlet is in proportion to the catalyst load and the temperature rise of methanation furnace. The satisfying activity can still be obtained by operating the catalyst at the higher temperature. But since the catalyst and equipment are operated at the higher temperature for a long time, the catalyst life and equipment are inevitably damaged; and when CO+CO2 content at the inlet is too low, the load of methanation furnace is alleviated, but the methanation reaction speed is declined due to the reduction of methanation, and at this time, to ensure that the trace element of methanation furnace is stable and meets the index, the inlet temperature shall be appropriately raised to guarantee that the catalyst bed temperature is at the economic and reasonable position. Generally speaking, it is normal that the temperature rise of methanation furnace is 20~30℃, and it shall find out the cause if it is too high.

2-6)Influence of poison to catalyst

The poison of methanation catalyst includes sulfur, arsenic, halogen and others. Traces of sulfur, arsenic and chlorine can cause the serious poisoning of catalyst. When RK-09D methanation catalyst adsorbs 0.1% of sulfur and 0.05% hydrogen, most of activity will be lost. Currently, the poison of methanation catalyst is mainly from the decarburization liquid entrainment and sulfur in process gas, and the influence from chlorine is relatively small. Oil also enables the catalyst surface to be covered to be inactivated, therefore, even if the manufacturers adopting the oil-free lubrication shall also arrange the oil-water separator in front of methanation furnace, to avoid the gas entering the methanation furnace from carrying the oil and water to damage the catalyst.

2-7)Shutdown and unloading of catalyst

2-7-1) Shutdown of catalyst 

For the short-term shutdown, the inlet and outlet valves can be shut out, to maintain the furnace temperature and pressure; and for the long-term shutdown, the positive pressure can be maintained with nitrogen or hydrogen-nitrogen after depressurization and cooling. It shall strictly prevent the air contained water and raw material of carbon monoxide from entering the furnace.

While the startup after the short-term shutdown, if the bed temperature is above 200℃, the process gas can be directly led to the surface to pressurize, heat and produce. If the bed temperature is below 200℃, the bed temperature must be risen above 250℃ with nitrogen, and then, it transfers to the normal production. The manufacturers having no nitrogen shall use the qualified process gas (wherein the CO content must be less than 0.5%) to rapidly heat up when heating up below 200℃, to raise the temperature above 250℃ as soon as possible, so as to prevent the generation of nickel carbonyl to cause the loss of active component.

The shutdown before overhaul can be conducted according to the passivation step.

2-7-2) Passivation and unloading of catalyst

Unloading and cooling: after the system is shut down and released the pressure, the furnace gas is replaced with nitrogen until that CO+CO2 is less than 0.5%, and the bed temperature is reduced below 150℃.

Oxygen replenishment and passivation: the initial oxygen replenishment temperature is not greater than 0.3%, and can be appropriately increased according to the temperature conditions, but each increasing amplitude is not greater than 0.5%, the maximum oxygen content is not greater than 6%, and the maximum temperature is controlled to be less than 400℃. Through analysis, the oxygen content of inlet and outlet gas of methanation furnace is basically the same, and the bed also has no temperature rise, but has declining trend. Namely, the passivation of methanation catalyst is finished. 

When replacing the catalyst, the bed temperature can be purged with the steam to 200℃, the bed temperature is reduced to normal temperature with nitrogen or other inert gases, and the catalyst is unloaded by opening the discharge opening. In case of heating phenomenon, it can spray with water to cool.

4.Notes for storage and transportation of catalyst

1) It shall avoid throwing and rolling and collision in the storage, transportation and handling process of catalyst, or will cause the smashing of part of catalysts.

2)The catalyst packaging bucket shall be airtight, and it shall prevent the moisture absorption or contacting wither other gas during the storage and transportation. 

3)The catalyst shall be saved in the dry and rainproof warehouse. The catalyst shall not be stored with the articles doing harm to it.