Discussion on the shutdown accident of downstream equipment caused by catalytic waste heat boiler steam paralleling
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A refinery started operation after repairing the catalytic hood. Steam was generated in the steam production system and the pressure reached 3.7MPa. The steam drum was about to be overpressured and required to be merged into the system. At this time, the pressure of the system was 1.7MPa. After the rapid merge, the steam carried a large amount of water, causing the shutdown of key downstream devices (the steam turbine suffered severe water hammer and emergency shutdown. It was lucky that the blades were not broken, but it is estimated that there was damage). My analysis of this issue is as follows: 1. The catalytic drum is in a saturated state of 3.7Mpa at this time, and the saturation temperature is 246°C. It is suddenly merged into the 1.7Mpa system, and the pressure drops sharply, causing the water in the drum to be in a supersaturated state and vaporize rapidly. The saturation temperature of 1.7Mpa steam is 204℃. The water in the 3.7Mpa steam drum is seriously supersaturated, and the supersaturation temperature difference reaches 42°C. It expands rapidly, causing the liquid level in the steam drum to rise sharply, and may be full, and the steam brings a large amount of water into the system. After the boiler water is vaporized, the liquid level in the steam drum drops sharply, causing the water supply to be unable to keep up and the pressure of the feed water pump to decrease. This is the main cause of problems. You can check the drum pressure changes and liquid level change trends, and the problem will be clear. Historical trends If the pressure drops rapidly and the liquid level rises sharply to reach the full liquid level (steam carries a lot of water), and then the liquid level drops rapidly, it can explain the problem. 2. Since the steam supply of the power boiler cannot guarantee the start-up of the catalytic condensing compressor, in order to start the catalytic operation, the catalytic steam must be overheated by the waste heat boiler and then merged into the medium-pressure steam system. At this time, the waste heat boiler should be connected to the system (the secondary line valve should be opened or the main line must be opened to a certain degree). Such benefits: 1) The working pressure of the catalytic drum is consistent with the system, so that there will be no large pressure difference and the problem of blocked catalytic back path. This will prevent the problem of serious insufficient steam pressure in the system. If the catalytic system and the power steam system are disconnected, there are two pressure systems. The power steam pressure system is controlled by someone, but the pressure control of the catalytic steam production system is insufficient, and the steam is not removed or vented, which will inevitably increase the difficulty and risk of operating the catalytic drum. 2) Steam passes through the residual furnace, which protects the furnace tube. At this time, adjusting the flue gas bypass and main line regulating valve can absolutely ensure that the steam generated by the catalytic drum is superheated into superheated steam through the residual furnace without water. 3) The system is connected and flowing, which can reduce the accumulation of condensed water between the saturated steam of the catalytic drum and the waste heat boiler. 4) By adjusting the opening of the waste heat boiler bypass and main flue gas baffles, the temperature of the steam and flue gas sides of the waste heat boiler can be controlled. The company is in a special situation. The saturated steam produced by catalysis is not overheated by the waste heat boiler and incorporated into the system. The medium-pressure steam cannot guarantee the start-up of the steam turbine of the condensing pneumatic unit. Therefore, there are also problems with the operation of cutting out the waste heat boiler from the system (I personally do not agree with cutting out the waste heat boiler. Cutting out increases the workload and increases the difficulty of system operation. Moreover, it must be integrated into the system to ensure the use of steam for catalytic start-up). Discuss, everyone. Discuss it clearly to avoid it happening again. This post was last edited by Qin Yu on 2009-2-24 23:07 ]
There are many such things. The remaining boiler of our catalytic unit produces 1.0 MPa superheated steam, which is used for reaction stripping steam, nozzle atomization steam, and fractionation stripping steam. At that time, the exhaust was small and anxious during steam merging, causing catalyst sludge. For equipment, I personally think that the most problems arise during start-up and shutdown, so you must not be too quick.
The maintenance of the hood should be in standby operation. There is still a certain amount of medium-pressure steam in the standby operation to ensure the normal operation of the catalytic turbine. Why is the system pressure 1.7MP? The remaining pot is removed? Do their steam turbines still use external grid medium pressure steam?
:):):):):):):):)
Doesn’t the catalytic self-generated steam have a dedicated line connected to the steam pipe network? Why do we have to wait until the pressure is 3.7MPa before we start steam merging? The superheated steam produced by the waste heat boiler should be divided into two lines. One line goes to the catalytic self-produced steam line and can be merged into the pipeline network. The other line is merged with the dedicated steam turbine line for industrial steam turbines. Once the turbine steam temperature is raised, the start-up adjustment must be slow and coordinated. Otherwise, it will cause the steam pipeline to buckle and cause the risk of shutdown.