Commissioning of the gas separation unit

a) Establish reasonable driving procedures, schedules, and necessary preventive measures； Prepare the necessary raw materials as well as supplies of water, electricity, and steam ； Assign the necessary staff and complete the relevant training, etc. b) At this point, the structure of the tower must meet the design requirements; it should be clean, free of any solid debris or blockages, and all substances that are not allowed to be present there must be removed. For example, the oxygen and moisture content within the tower must be within specified limits ； The pumps and instruments are functioning properly after calibration ； The safety measures have been adjusted. c) Pressurize and depressurize the tower to reach the normal operating pressure. d) Heat and cool the tower to bring it close to the operating temperature. e) Add the raw materials to the tower. f) The heat source for starting the tower top condenser and the reboiler as well as various heaters, and the cold source for various coolers. g) Gradually adjust the operating conditions and parameters of the tower, so that the tower’s load and product quality can reach the normal operating values as quickly as possible, thereby enabling normal operation to be resumed. Due to the great differences in the properties of the materials processed by each distillation column, operating conditions, and their roles within the entire production facility, the specific operating procedures are likely to vary. It is important to pay attention to the characteristics of the specific tower and carefully determine the startup steps.

Actually, I just want to ask about the general steps for starting up a distillation tower. Recently I used a simulation system to start up a gas separation unit, and I’m curious to see what it’s like in an actual factory. I’ll ask a specific question instead: When starting up a distillation column in a cold state, it should first be stabilized with full reflux. That means feeding material in first, gradually heating the bottom of the column, and allowing condensation at the top. Once there is a certain level of liquid in the reflux tank, this liquid is sent back into the column. After the bottom of the column reaches a certain liquid level, the feed valve is closed; once stability is achieved, feeding and discharging can begin. Is that so?

Purge, introduce nitrogen for displacement, ensure airtightness, introduce hydrocarbons, conduct sampling – results are satisfactory; introduce a heat source to activate C1, establish reflux, control pressure, conduct sampling – results are satisfactory, then activate C3; send the sample to the qualified filling facility once the sampling results are satisfactory.

1. Depropanization tower system: 1) Open the pressure gauge and level gauge lead valves, activate the instrument control system, and open the relevant pipelines at the appropriate times as required by the process； 2) Purging: Fuel gas is introduced into the depropanization tower system for purging; purging stops when analytical testing shows that the nitrogen content in the system is less than 1%. The system is then pressurized with fuel gas, and the non-condensable gas line is closed once pressure equilibrium is achieved. 3) Control the raw material valve assembly to ensure that the flow rate of liquid hydrocarbons entering the buffer tank is not too high; when the liquid level in the buffer tank reaches 70%, open the inlet and outlet valves of the feed pump to equalize the pressure between the raw material system and the depropanization tower system, and then start the pump to feed material. 4) Before feeding, less heat source or circulating water should be supplied to the raw material preheater, bottom heater, and cooler. 5) When the liquid level at the bottom of the tower is 70%, an appropriate amount of steam is supplied to the reboiler at the bottom of the tower; the rate of temperature increase is strictly controlled, with the temperature and pressure rising at a rate of 10–15°C per hour. At the same time, attention is paid to adjusting the feed rate in order to maintain the liquid levels in the reflow tanks at the bottom and top of the tower. 6) At a tower pressure of 1.0 MPa and at the normal operating pressure, maintain a constant pressure respectively to check for any leaks in the equipment. 7) When the liquid level in the top reflux tank reaches 70%, start the pump to initiate reflux; manually control the reflux flow control instrument to enable full reflux operation of the propane column. 8) Adjust the temperature and pressure to meet the requirements of the process. Once operation is stable, automatic control can be applied to the bottom temperature and pressure. When analytical tests show that both the products at the top and bottom of the tower meet the specified criteria, the material from the bottom of the tower is sent to the pentane removal tower, while the product from the top of the tower is sent to the ethane removal tower. 9) While feeding the depropanization tower, close attention should be paid to changes in the liquid level of this tower; the liquid level at the bottom of the tower should be maintained at 60-70%. At the same time, temperature and pressure must be adjusted to minimize the disruptions caused by the increased feed rate. 2. Deethanizer tower system: 1) Open the fuel gas valve and use fuel gas to pressurize the system; after pressurization, close the fuel gas valve and release air from the low-pressure pipeline. Once the pressure stabilizes, close the low-pressure valve, then pressurize again using high pressure. Repeat this process several times. Once the analysis shows satisfactory results, pressurize the system with fuel gas, and after completion, close the valve of the high-pressure pipeline. 2) After analytical testing shows that the nitrogen content in the deethanizer system is below 1%, close all flare valves and overhead vent valves of the deethanizer system, stop the purging process, and pressurize the system with fuel gas; once pressure equilibrium is achieved, close the non-condensable gas line. 3) Once the load operation of the depropanization column is normal, preparations can be made to pressurize and feed material into the deethanization column. 4) Before feeding, open the pressure gauge of the deethanizer system and the level gauge lead valve; supply a small amount of heat source or circulating water to each heat exchanger and cooler. 5) Feed the raw material into the deethanizer; make sure to maintain the liquid level in the reflux tank at the top of the depropanizer between 60-70%, and activate the temperature control instruments. 6) When the liquid level at the bottom of the tower is 70%, adjust the reboiler at the bottom of the tower and the steam flow rate; activate the steam flow control valve to ensure that the heating rate does not exceed 20°C per hour during the process of heating and increasing pressure. 7) When the liquid level in the top reflux tank reaches 70%, start the reflux pump to establish top reflux and maintain a stable liquid level in the top reflux tank. 8) When the pressure rises to 1.5 MPa and the pressure required by the process, check for leaks in all areas at a constant pressure; if there are no issues, proceed to the next step. 9) After adjusting the temperature and pressure to meet the process requirements and ensuring stable operation, the bottom temperature and tower pressure can be placed under automatic control. 10) Once the compositions at the top and bottom of the tower meet the control specifications as determined by analytical testing, the crude propylene tower can be replaced. 3. Crude propylene and refined propylene column systems: 1) Purging: The deethanization operation proceeds normally, and the compositions at the top and bottom of the columns are within acceptable limits; purging can be carried out once all nitrogen in the deethanization column has been removed as much as possible before it enters the crude propylene column. 2) The ignition fuel gas is used to purge the crude propylene and refined propylene columns, pressurize them; the heater provides a small amount of heat, while the column top cooler supplies circulating water. 3) Open the feed valve of the crude propylene column to purge the crude propylene and refined propylene columns. 4) Once the nitrogen content in the crude propylene and refined propylene column systems is less than 1%, close all flare valves and vent valves. Fill the system with fuel gas; after pressure equilibrium is achieved, close the fuel gas valve and fill it with the medium from the bottom of the deethanizer. 5) Before replacement, open the pressure gauge and level gauge lead valve of this system. 6) When the liquid level at the bottom of the crude propylene column reaches 70%, introduce the heat source to the reboiler as normal, and activate the manual reboiler control valve. Ensure that the temperature rise at the column bottom does not exceed 20%; adjust the steam flow accordingly to maintain the liquid level at the bottom of the column. 7) When the liquid level at the bottom of the refined propylene column reaches 50%, the reflux pump for the crude propylene column can be started to establish reflux at the top of that column. 8) When the liquid level in the reflux tank at the top of the purified propylene column reaches 70%, start the reflux pump for the purified propylene column to establish reflux at the top of the column, making sure to maintain a stable liquid level in the reflux tank. 9) Once the liquid levels in the crude propylene tower, refined propylene tower, and top reflux tank are normal, switch the control instruments to automatic mode. 10) When the crude propylene and refined propylene column systems are operating properly and the products from the bottom of the crude propylene column and the top of the refined propylene column meet the specifications, connect the propane and propylene outlet systems of the plant.

Simulation is merely a flow simulation of the programmed process; it differs significantly from actual operation of the equipment. To gain a thorough understanding, it is best to spend some time working with the actual equipment. For a simple multi-component distillation process, the principles and operations are not complicated, but it still takes time to master and control the quality of the products at the top and bottom of the tower – much of this comes from experience gained over time.