System Startup (IX) – Catalyst Heating and Reduction
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System Startup (IX) – Catalyst Heating and ReductionI. Basis for Preparation
1. “Specifications for Catalysts and Reactor Packings”
2. Final synthesized PID flow diagram
II. Scope of Application
This procedure specifies the operating methods for reducing methanol synthesis catalysts. III. Preparation Work and Required Conditions 1. All installations and associated works have been completed in accordance with the design specifications (including any design changes); the quality of the work meets the required standards, and all projects have passed the handover inspection. 2. All process pipelines and equipment have passed strength tests successfully; after the catalyst was loaded, the catalyst powder was blown out of the synthesis tower using air (or nitrogen). The equipment and pipelines have undergone airtightness tests and been confirmed to be qualified. 3. The syngas compressor has been tested and is operating normally. 4. The catalyst loading in both the synthesis tower and the protection bed has been completed. 5. The synthesis steam drum firing and system water circulation have both been completed. 6. Water, electricity, steam, instrument air, plant air, nitrogen, and other utilities for public works can be supplied as per the design specifications. 8. The electrical equipment, instruments, and meters of the synthesis system have been tuned properly, and the meters have been calibrated. The set values for alarm and interlock functions have been verified to be accurate and functional through static testing (the temperatures and pressures at the inlet and outlet of the synthesis tower, as well as the flow meters in the synthesis circuit, must be strictly calibrated). 9. The laboratory analysis work is ready: the sample gas for the automatic analyzers has been prepared and is on standby; the analysis sampling points have been determined. It is now possible to promptly and accurately analyze the concentrations of various components such as CO, H2, O2, and CO2, as well as water vapor concentration, at both the inlet and outlet of the synthesis reactor. It can accurately analyze hydrogen content, especially at low hydrogen levels (0–2%) and high hydrogen levels (5–15%). 10. Conditions for the stable supply of reducing gases CO+H2 are available. 11. Contact the plant control room to submit a request for a large quantity of nitrogen, ensuring that its purity is >99.9% (V%). 12. The temperature-raising reduction operation for the synthetic methanol catalyst is carried out according to Table 2, and the curve graph of the temperature-raising reduction operation is drawn based on Table 2. 13. Prepare the measuring tools for the amount of reduced water. The record forms are ready. We have communicated with the catalyst manufacturer, and the heating-reduction plan has been approved. The temperature rise reduction curve graph and various confirmation forms for the report have been prepared. IV. Preparation of hydrogen for reduction Plan 1: Pure hydrogen 1. Standards for pure hydrogen 1.1 Hydrogen purity: 99.9% – this is the standard for industrial hydrogen, free from sulfur and chlorine elements. 1.2 Operating pressure: 10 kg. 1.3 Hydrogen consumption and time. Option 2: Process gas 1. Standards for process gas 1.1 The process gas coming from the purification unit must meet the plant’s control specifications; any exceedance of these standards is strictly prohibited. 1.2 The valves on the synthesis heating and reduction pipeline must be reliable and functional. V. Detailed Rules for Temperature-Induced Reduction 1. Overview Copper-based catalysts for methanol synthesis must be reduced to become active. The reduction reaction is a highly exothermic reaction, with the reaction equation as follows: CuO + H2 ==== Cu + H2O + 86.7 KJ/mol. Therefore, it is essential to carefully control the temperature of the catalyst bed during the reduction process, in order to prevent the catalyst from overheating and causing the copper particles to sinter, which would damage the catalyst’s activity. The reversing operation is a very important step during driving. The level of catalyst activity per batch depends not only on the production quality and filling quality of the catalyst itself, but also to a large extent on the quality of its reduction process; this has a long-term impact on the production capacity of the facility. Therefore, the reduction process must be carried out strictly, meticulously, and carefully. 2. Introduction to the catalyst: The catalyst is used to facilitate the reaction between hydrogen and carbon monoxide to produce methanol. Dimensions: 6mm*4mm Chemical composition: Cu, >43% ； Zn, 20±3% ； Al, 5±1% axial compressive strength, >220 kg/cm2 ； Fill density: 1 kg/L. Catalyst service life: A service life of over 3 years under normal operating conditions. 3. Catalyst Reduction Schedule Table 2: Catalyst Reduction Schedule Table (to be revised and improved)
Reduction Stage | Temperature Range (°C) | Heating Rate (°C/h) | Time Required (h) | Cumulative Time (h) | Hydrogen Content (10-2) atm
--- | --- | --- | --- | --- | ---
Heating | Room temperature ~ 120 | ≤50–60 | 2 | 2 | 0
| 120 ~ 170 | ≤30 | 4 | 6 | 0
Initial Stage | 170 | 0 | 1–2 | 8 | 0.2–0.5
| 170 ~ 180 | 2–3 | 4 | 13 | 0.5–1
Main Stage | Up to 180 | 0 | ≥33 | 46 | 0.5–1
| 180 ~ 190 | 1–2 | 5 | 51 | 1.5–2
| 190 ~ 200 | 2–3 | 4 | 55 | 1.5–2
Later Stage | 200 ~ 220 | 5 | 4 | 59 | 2
| 220 ~ 230 | 5–10 | 2 | 61 | 2
| 230 | 0 | 1–2 | 62 | 5
| 230 | 0 | 1–2 | 64 | 10
| 230 | 0 | 1–2 | 66 | 15
Cooling | 210 | 10 | 2 | 68 | /
4. Procedure for Heating and Reducing the Catalyst
1) Nitrogen purging of the synthesis system and establishment of nitrogen circulation
① Activate the loop water cooler.
② Start the compressor to purge the synthesis loop with N2 gas; this includes the methanol flash tank in the low-pressure section, liquid methanol pipelines, and hydrogenation pipelines used during startup. Each pipeline must be thoroughly purged until the residual oxygen content at all sampling points, discharge ports, and drain valves in the system is ≤0.1%, at which point the purging can be considered complete. ③ The complete replacement with nitrogen is particularly important for the startup of the synthesis system. The drain or sewage outlets at various locations should be opened one by one for on-site venting, but great care must be taken regarding safety when performing this task; an oxygen respirator must be worn, and at least two people should work together. ④ Establish a nitrogen circulation in accordance with the compressor operating procedures. Gradually adjust the outlet pressure of the circulation section to around 0.6 Mpa, and increase the circulation rate to its maximum. The inlet pressure of the synthesis tower is maintained at a constant level of 0.7 Mpa by adjusting the amount of nitrogen added and controlling the amount of vented gas, thereby enabling the heating and reduction process to proceed. 2) Procedure for heating and reducing the catalyst: 1. O2 < 0.1×10-2, S < 0.1×10-6, Cl < 0.01×10-6, NH3 < 10×10-6. 2. Free from harmful impurities such as heavy metals, with extremely low levels of unsaturated hydrocarbons and oil mist. 3. The reduction conditions are: ① Pressure of 0.7 MPa (gauge pressure); ② Temperature up to 230°C. ③ The air velocity should be greater than 250 h-1. (Circulation rate: should be greater than 10,000 Nm3 h-1) ④ The reducing gas is a mixture containing 1×10-2 H2 (or CO+H2) and N2. ⑤ The entire heating and reduction process takes approximately 70 hours. 3) Synthetic drum operation: The inlet temperature of the synthetic tower bed is used as the reduction control temperature. The hot spot temperature in the synthesis tower bed is an important monitoring temperature. If the temperature rises, prioritize opening the steam valve and use the vent valve as a supplement. The operation of the steam drum is based on the table showing the relationship between steam pressure and temperature. 4) During the reduction process, the analysis frequency of the gases entering and leaving the tower is required to be once every 0.5 hours; nitrogen and H2 (or CO+H2) gases are sampled and analyzed at regular intervals as needed. Drain the water every half hour and measure it. Operational data is recorded every half hour. Sampling point locations: Sampling points on the inlet pipeline of the syngas tower, sampling points on the outlet pipeline of the synthesis tower; Analysis contents: Comprehensive analysis of inlet and outlet gases, water vapor concentration. 5) Heating and reduction process: ① Heat the temperature of the reaction bed to 120°C at a heating rate of ≤50–60°C/h, and then maintain the heating rate at ≤30°C/h. When the hotspot temperature inside the tower rises above 40°C, monitor the separator level promptly. When the liquid level rises, water is drained via the crude alcohol filter drain, with measurements taken every half hour. ② Maintain a constant temperature of 170°C for 1–2 hours; once the liquid level in the methanol separator stops rising, it can be considered that almost all physical water has been removed. Drain the water from the separator; close the valve only after nitrogen has been released. Drain it again every 2 minutes until all the water is removed. ③ Contact the dispatcher to supply hydrogen to the synthesis loop via the main valve at the inlet of the heating and reduction pipeline; introduce H2 (or CO+H2) into the synthesis loop slowly and carefully in intermittent amounts. The concentration of H2 (or CO+H2) in the inlet gas of the synthesis tower should be 0.2–0.5% (v%), and samples should be taken for analysis immediately. Carefully monitor the bed temperature; if it rises suddenly, the reducing gas should be cut off. When the (H2+CO) concentration decreases, H2+CO can be replenished through the valve until the hydrogen concentrations at the inlet and outlet of the methanol synthesis tower are equal. Maintain the (H2+CO) concentration at 0.5–1%, gradually increase the opening degree of the steam injector valve to raise the steam flow rate, and reduce the catalyst at a rate of 2–3°C/h. Before each temperature increase, the hydrogen concentrations at the inlet and outlet of the methanol synthesis tower must be equal, to ensure that the catalyst is fully reduced at each temperature level. ④ Continue to increase the temperature according to the heating schedule, and gradually raise the concentration of H2 (or CO+H2) fed into the reactor to 0.5–1%, until the hydrogen concentration at the outlet of the reactor is less than 0.3%; this indicates that the catalyst has entered the main reduction phase. At this point, the bed temperature is controlled at around 180°C, and reduction continues under these conditions. ⑤ When the bed temperature is around 180–190°C, the catalyst reduction rate begins to level off; at this point, the concentration of H2 (or CO+H2) can be gradually increased to 1.5–2%. ⑥ After entering the main reduction phase, CO2 accumulates rapidly in the system; it is necessary to keep the CO2 concentration below 5% (based on the gas leaving the tower). The CO2 level can be controlled by venting and adding nitrogen. ⑦ Continue heating according to the heating schedule until 230°C, then increase the concentration of H2 (or CO+H2) to 5%, 10%, and 15% respectively, and carry out reduction at each corresponding concentration for about 1–2 hours. ⑧ When the hydrogen concentrations at the inlet and outlet of the synthesis reactor are essentially equal (CO+H2≤0.1%), the amount of reduced water discharged is close to the calculated amount of reduced water, and almost no more water is generated; furthermore, the temperatures at various points throughout the bed are basically the same. Under these conditions, it can be considered that the reduction has reached its endpoint and the reduction process is complete. Stop feeding H2 (or CO+H2) gas, and blind-seal the H2 (or CO+H2) gas feed line and the nitrogen feed line. Lower the catalyst bed temperature to 210°C and wait for feeding. 5. Precautions for the reduction process: 1. During the reduction process, the bed temperature is controlled by regulating the temperature at the inlet of the synthesis tower and the amount of H2 (or CO+H2), to keep it below 230°C. 2. The key to the reduction process is controlling the rate of the reduction reaction, and the reaction rate is primarily related to hydrogen concentration and reaction temperature. Therefore, it is required that the hydrogen concentration analysis be accurate, the temperature increase must be gradual, and the hydrogen supply rate as well as the water output rate of the catalyst must be strictly controlled to ensure a smooth progress of the entire reduction process. 3. During the reduction process, the principle of \"increasing hydrogen flow without raising temperature, and increasing temperature without increasing hydrogen flow\" should be followed. Understand and master the “three” principles. Three lows, three stabilities, three prohibitions, three controls. (Three lows – low-temperature effluent, low-hydrogen reduction, and a low-load production period after reduction) ； Three stabilities – temperature stabilization, hydrogen supplementation stabilization, and water output stabilization ； Three prohibitions – heating and hydrogen introduction are not allowed simultaneously, and moisture is not permitted to enter the tower ； Do not allow water to flow at high temperature for long periods of time ； Three controls – controlling the hydrogen addition rate, controlling the CO2+H2 concentration, and regulating the hourly water output; the maximum water output must be strictly kept within the range of 300–350 kg/h. 6. Accident handling plan: 1) During the catalytic heating and reduction process, if the centrifugal compressor stops operating due to a fault (lack of water, power failure, lack of instrument air, problems with the lubrication system, or other accidents), it is necessary to immediately close the valve supplying the reducing gas, reduce the amount of medium-pressure steam sent to the steam drum, quickly open the vent valve, and purge the entire system with nitrogen. 2) In the event of an H2 interruption, promptly close the reducing gas valve; keep the centrifuge running, and supply nitrogen through a nitrogen charging valve as appropriate to maintain stable system pressure. Keep CO+H2 participating in the reduction process within the system; when the temperature shows a downward trend, slightly open the steam valve to maintain a constant temperature of the catalyst. 3) During the reduction process, it is necessary to closely monitor changes in the bed temperature. If the bed temperature rises sharply, the reduction gas must be immediately cut off and the startup steam stopped. If there is no sign of a decrease in temperature or if the temperature is too high (operating temperature < 290°C), measures such as venting the system to reduce pressure and purging the entire system with nitrogen can be taken. 7. Driving 1) After the reduction is complete, lower the temperature of the reactor bed to 210–220°C. Once the temperature of the entire bed has stabilized at 210–220°C, introduce syngas, controlling the rate of pressure increase per hour at 10% of the design pressure (as required for the synthesis loop). For catalysts, other different pressure increase rates are also acceptable; generally, the pressure can be increased more rapidly up to 3.0 Mpa. 2) During the pressure increase process, pay attention to changes in the temperature of the catalyst bed in the synthesis tower, and adjust the flow rate of the startup steam as needed to prevent a rapid rise in bed temperature, which could cause the Cu grains in the catalyst to sinter. 8. Parking 1. Short-term parking: The parking period is within 24 hours, and it does not affect the synthesis loop; the procedure is as follows: (1) Stop the supply of syngas. (2) Continue to run the cyclical compressor until the reaction of CO and CO2 in the system is complete; the amount of CO+CO2 in the system