Precautions for operation and adjustment of plate tower and packed tower
The normal operation and adjustment of the plate tower and the packed tower should be the same, but the packed tower should pay attention to the following points:
Packed columns have a smaller operating range and are especially sensitive to changes in liquid load. When the liquid load is small, the packing surface cannot be well wetted, so the mass transfer effect drops sharply, otherwise, liquid flooding is easy to occur.
Packed towers are not suitable for handling materials that are easy to polymerize or contain suspended solids.
For systems that are prone to foaming, packed towers are more suitable because of the confinement and fragmentation of the foam.
Heat-sensitive substances are easy to use packed towers, because the liquid holding capacity is less than that of plate towers, and the residence time of materials in the towers is shorter.
The packed tower is more suitable for the operation of the negative pressure tower, the pressure drop is smaller than that of the plate tower, and the energy loss is less.
In terms of equipment installation and maintenance, the cost of packing is higher than that of trays, the installation period is shorter, and the maintenance is not as convenient as trays. And the installation is more demanding than the tray. Especially the level of the distributor, it can be said that whether a packed tower can be successfully driven largely depends on the design and installation of its distributor.
Original start-up operation technology of rectification column
Check and check one by one according to the installation process flow chart.
blow off and clear
In the newly built or overhauled tower system equipment and pipelines, there are often dust, welding rod iron filings and other sundries during the installation process. In order to prevent this debris from blocking the pipeline or jamming the valve during driving, it must be blown or cleaned with compressed air.
Before blowing off, the flanges connected to the equipment and valves should be dismantled in sequence according to the gas-liquid process, and the blown-off substances should be discharged from here. When blowing, use high-speed compressed air to blow off in sections and lightly tap the outer wall with a wooden hammer. After blowing out a section, install the flange immediately. The purging process should be blowing from a high place to a low place of the equipment.
System hydrostatic test and air tightness test
In order to check the compactness and mechanical strength of the weld seam of the equipment, a hydrostatic test is carried out before use. The hydrostatic test is generally carried out according to the requirements on the design drawings. The water pressure test should use clean water at normal temperature, and it should be injected from the lowest point of the equipment so that the gas in the equipment can be exhausted from the top.
In order to ensure that the gas does not leak from the flanges and welds during start-up, and to ensure continuous and stable operation of the tower, a system airtightness test must be carried out. The test method is to use a compressor to send air into the system, and gradually increase the pressure to 1.05 times the operating pressure.
Then apply soapy water to all equipment, welds on pipelines and flanges one by one to check for leaks. If a leak is found, mark or record it well, and deal with it after the pressure is released. If there is no leakage, keep the pressure for 30 minutes, and if the pressure does not drop, it is qualified, and finally vent the gas
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Stand-alone test run and linkage test run
The stand-alone test run is to confirm whether the rotating and to-be-rotating equipment (such as air compressors and centrifugal pumps, etc.) are easy to use and whether they are loaded with relevant technical specifications. The stand-alone test run is carried out without materials and without load. First, disconnect the coupling, start the motor alone, run for 48 hours, and observe whether the motor is hot, vibrating, whether there is noise, whether the direction of rotation is correct, etc.
A linkage test run is a kind of test run simulating a production state in which water or other materials similar to production materials are used instead of production materials. The purpose is to test the ability of the production device to pass through the material continuously. Heat the water during the linkage test run, and observe whether the instrument accurately indicates the data such as the flow rate, temperature and pressure passed through, and whether the equipment is operating normally.
In industrial production, most of the separated substances are organic substances, which are flammable and explosive. If the air in the equipment is not driven out before the equipment is put into operation, it is easy to form an explosive mixture with the organic substances. Therefore, before sending the mixture into the system, the air in it should be replaced with an inert gas (nitrogen) so that the oxygen content in the replacement gas is not more than 0.5%.
After the system replacement is qualified, the system can be started.
Operation Technology of Normal Opening and Shutdown of Distillation Column
After the replacement of the system device is qualified, the normal start-up of production can be carried out. The normal driving of rectification operation is divided into driving after short-term parking and driving after long-term parking.
a. Driving after short-term parking
Check the inventory of raw materials, select the amount of feed, and feed to the tower kettle. When the liquid level is seen, the temperature is raised slowly. In the process, with the rise of the tower pressure, the inert gas in the tower is gradually discharged. At this time, the condensate should be gradually increased accordingly, and the total reflux operation is carried out.
When the liquid level of the tower kettle is controlled at 1/2 to 2/3, the feeding can be started. When the tower has turned to normal with the heating process, stop feeding and let the tower circulate by itself. After the reflux liquid analysis is qualified, start mining. Produce products, and continue feeding production.
In the self-circulation process, it is a total reflux operation. When continuous feeding and continuous production are achieved, it is a successful start-up.
When the empty tower feeds just heating up, the temperature rise rate should be slow, because there is no liquid reflux at this time, and there is no gas-liquid contact and material exchange on the tray, so the gas rise rate is faster than the normal operating speed.
As the temperature rises, the gas evaporated from the top of the tower is condensed, and then flows back to the top of the tower and flows down the tray, gradually forming a liquid layer on the tray, and the process of mass transfer and heat transfer will be carried out in the tower. If this operation is not followed, the less volatile components will be taken to the top of the tower, and the produced products will be unqualified.
b. Driving after long-term parking
Driving after long-term parking generally refers to driving after maintenance. First check whether all equipment, pipelines, valves, sampling points, electrical appliances and instruments are in good condition; then carry out blowing, cleaning, strength and air tightness tests on the system, and replace the system. Carry out the driving operation steps.
In chemical production, the parking method is related to the state before parking. Generally, there are three ways:
a. Normal parking
After a period of production, the equipment needs to be inspected or overhauled and the planned shutdown is called a normal shutdown. This kind of shutdown is to gradually reduce the addition of materials until the addition is completely stopped.
After the material is steamed, stop the air supply to heat, cool down and remove the system pressure, then stop the water supply, and drain the solution in the system (to the solution storage tank).
Open the system vent valve and clean the system. If the raw material gas contains flammable and explosive gases, the system should be replaced with inert gas.
After parking, for some equipment that needs to be overhauled, it is necessary to use a blind plate to cut off the material pipeline on the equipment to avoid accidents caused by the leakage of combustibles.
b. Emergency stop
Parking under some unimaginable special circumstances in production is called an emergency stop. For example, if some equipment is damaged, the power supply of some electrical equipment fails, one or more instruments fail, etc., all of them will cause the emergency stop of the production device.
In the event of an emergency shutdown, first, stop feeding, adjust the amount of heating steam and condensate output in the tower kettle, and keep the equipment in a state of waiting for production. At this time, it should be actively repaired and troubleshoot. To resume production.
c. Full emergency stop
When there is a sudden power outage, water outage, gas outage or major accident in the production process, a comprehensive emergency shutdown is required.
In order to prevent full-scale emergency shutdown, general chemical plants all have backup power supplies. When the first power supply fails, the second power supply should send power immediately.