Methanol synthesis

This post was last edited by sxtblo on 2010-5-23 at 23:41. Original startup procedures for the methanol synthesis plant: Preparations to be completed before startup: Check whether the equipment, pipelines, and valves are installed correctly and completely. Check whether the opening and closing status of each blind flange in this process is correct: the equipment and pipelines have been properly purged, the individual pumps have passed their trial runs, and the shell side of the methanol synthesis tower as well as the drum have been cleaned and leak-tested. The catalyst has been loaded. The system’s airtightness test passed. The safety valves, instruments, and safety interlock systems within the system have been properly calibrated and are functioning normally. Check whether safety facilities such as fire-fighting and gas protection equipment are complete and in good working condition. Utilities (cooling water, demineralized water, high-pressure seal water, N2, high-pressure superheated steam, instrument air, electricity) have been supplied as required. Notify the quality inspection center to prepare all necessary analytical tasks prior to starting up the synthesis process. Prepare a 5% (wt.) Na3PO4 solution for use. 2. N2 purging of the high and low pressure systems; 3. Catalyst heating for reduction; 4. In the synthesis gas generation system, operation is carried out at 50%–60% load for 2 days, then at 80% load for one month, and finally at full load. For long-term parking, the 1-hydrogen recovery unit is shut down following normal procedures, and the vent gas scrubber is taken out of service. 2. Contact the dispatch team to stop the supply of fresh gas; keep the circulation gas compressor at its original circulation rate. Allow circulation for about 30 minutes. Once the percentage of (CO+CO2) in the circulation gas is ≤0.2%, reduce the pressure in the synthesis vapor drum, increase the amount of wastewater discharged and the volume of cold boiler water used for replacement, and control the cooling rate at ≤20°C/h. Once the hot spot temperature in the synthesis tower drops to 100°C, stop the recycle gas compressor. 3. Reduce the pressure in the synthesis system to 1.0 Mpa (with a pressure reduction rate of ≤0.1 Mpa/min). Once the liquid levels in the separator and expansion tank are stable, close the shut-off valves located before and after the liquid level control valves of these two devices. 4 If maintenance is required for the synthesis system, depressurize the system to 0.1 Mpa and then close the pressure relief valve. Reverse the flow in the N3 pipeline and install a blind flange between the nitrogen filling valves; fill the system with nitrogen until the pressure reaches 0.45 MPa, after which depressurize it to 0.1 MPa. Repeat this process several times. When the (H2+CO) content in the circulation loop is <0.1%, the system can be maintained at pressure using 0.3 MPa of nitrogen. 5 If it is necessary to remove the catalyst, it must be passivated with air according to the specified procedure, in order to prevent oxidation and heat release of the catalyst during removal, which could lead to accidents. 6 Close the inlet and outlet valves on the water cooler; when shutting down the system in winter, pay attention to draining water to prevent freezing.

(1) Inform the recycle gas compressor to make all necessary preparations. (2) Coolant is introduced into the water cooler, and it is checked that the water temperature, pressure, and flow rate are normal. (3) Set the drum to automatic operation at 50% to maintain a stable liquid level and analyze water quality. (4) Allow slight continuous discharge of wastewater, at a rate of about 5% of the water inflow amount; adjustments can be made based on the analysis of water quality. (5) When the drum pressure is set at 2.5 MPa, automatic mode is activated and the steam is fed into the steam network. (6) Start the recycle gas compressor to circulate N2 in the synthesis system, maintaining a pressure of 0.5 MPa; add more N2 if the pressure is insufficient. (7) Slightly open the fresh gas valve, adding to the synthesis system in amounts of about 5% of the total load each time; there must be a 30-minute interval between two additions. (8) During the gas guiding process, pay close attention to the temperature of the synthesis tower; adjust the amount of steam supplied by the ejector as well as the circulation rate in order to maintain the outlet temperature of the synthesis tower at 210–220°C. (9) As fresh gas is added, the pressure continues to rise. As the synthesis reaction speed increases and more heat is released, the amount of steam supplied to the injector can be gradually reduced. (10) When the injector nozzle is fully closed, steam should be gradually introduced into the pipeline network depending on the drum pressure and the conditions of the steam pipeline system. (11) When the system pressure approaches 4.0 MPa, slightly open the purge valve to prevent too rapid pressure increase; throughout the entire pressure-raising process, the rate of pressure increase should be controlled at 0.5 MPa/h. (12) When the gas flow rate load is increased to 50%, production shall be maintained for one week to ensure complete reduction. (13) Sample analysis is conducted at the outlet of the synthesis tower; the gas composition is analyzed at the inlet of the synthesis tower, and the H/C ratio is calculated to determine the appropriate vent volume. (14) When the system pressure reaches 4.9 MPa, adjust the blowdown gas volume to maintain system stability. (15) After operating at half load for one week, the load can be gradually increased until it is at full capacity; at the same time, attention should be paid to adjusting the cooling water volume and increasing the circulation rate. (16) At the beginning of production, crude methanol contains many impurities, which are discharged into waste oil tanks through temporary pipes. Samples must be taken regularly for analysis during this discharge process; discharge should be stopped once the product becomes clear and transparent with no abnormal odors, after which the backflow valve should be closed and the cut-off valve opened. The liquid level in the separator is set at 50% to enable automatic operation. (17) When the liquid level in the methanol expansion tank reaches 30%, notify the distillation section to get ready for reception; open the shut-off valve on site, and switch to automatic control at a liquid level setpoint of 50%.

Parking steps: After receiving the dispatch instructions and coordinating with the upstream and downstream units, (1) close the main valve for fresh gas. (2) Shut off after purging, and maintain pressure in the synthesis system. (3) Gradually reduce the circulation volume until the reaction ceases, reducing it until finally shutting down by closing the inlet isolation valve. (4) After the separator level has been drained, close the shut-off valve. (5) Close the drum continuous blowdown valve. (6) Maintain pressure in the system while activating the ejector to keep the outlet temperature of the synthesis tower at ≥210°C.

What are the precautions for catalytic reduction and its use? Answer: (1) During the reduction process, it is necessary to closely monitor the temperature at the outlet of the synthesis tower; when the temperature rises sharply, it is essential to immediately stop or reduce the amount of reducing gas supplied, as well as decrease the flow rate of the steam nozzle. (2) Strictly control the effluent rate; the hourly effluent volume shall not exceed 2 kg per ton of catalyst. (3) Determination of the reduction endpoint: When the concentration of CO + H2 in the gas exiting the reactor, as determined through multiple analyses, becomes identical to the inlet concentration, it indicates that the catalyst is no longer consuming CO + H2 and that the liquid level in the separator is no longer rising; at this point, it can be considered that the catalytic reduction has reached its endpoint. (4) After the reduction is complete, reduce the system pressure to 0.15 MPa, maintain the temperature of the synthesis tower at no less than 210°C, and replace the N2 in the system with fresh gas until its concentration is below 1%, after which methanol synthesis can be initiated. (5) When using synthetic pressure rise, the pressure increase rate must not exceed 0.5 MPa/h to prevent the catalyst from being damaged due to excessive temperature rise. (6) The operation of the new catalyst involves maintaining a certain production level, followed by gradual pressure increase, increased circulation rate, increased CO content, and gradual temperature rise. During the first start-up with the new catalyst, the exit temperature of the synthesis tower gradually increased from 220°C to 230°C. (7) The sulfur content and chloride content in the syngas should both be less than 0.1 ppm; trace amounts of oxygen, heavy metals, water vapor, and carbonyl compounds must not be introduced into the tower. (8) During the methanol synthesis process, the conditions must be strictly controlled; the temperature of the catalyst bed should not fall below 210°C. Sudden changes in catalyst temperature are strictly prohibited, and an optimal space velocity for using the catalyst is 6000–10000 h-1. (9) In the event of a stoppage during operation due to certain reasons, for a short-term stoppage within 24 hours, the fresh gas supply can be cut off to continue the circulation. Until the CO + CO2 reaction in the system is complete, the catalyst bed is maintained at above 210°C. (10) If the parking time exceeds 24 hours, the normal procedure can be followed: after parking as described in (9), reduce the pressure and temperature, replace the gas with N2, and maintain the system pressure at 0.5 MPa.