Diesel hydrogenation water injection location
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Our diesel hydrogenation unit has three water injection points in the high-pressure heat exchanger: pre-injection, mid-injection, and post-injection. These are located at the inlet of one heat exchanger, the outlet of that same heat exchanger, and the outlet of the next heat exchanger. What I would like to know is what are the differences between these three injection points?
Inject water at the front to induce crystallization in the first unit, use the middle part to prevent crystallization in the second unit, and boil water at the back to avoid air-cooled crystallization! The crystals are divided into chlorides and sulfides; the former crystallizes at around 180 degrees, while the latter crystallizes at 120 degrees
Can’t that prevent all water injection at the first point? What are the conditions for switching between points?
Under normal circumstances, water is injected before air cooling during normal production. When the heat exchange efficiency is poor due to process parameters, the water injection can be changed to mid-flow injection for two hours, after which it can be resumed. To prevent salt buildup in the heat exchanger from blocking the pipelines during shutdown, when the temperature behind the heat exchanger drops to around 180 degrees, the water injection method is changed back to the previous one
If water injection is carried out before normal production, it can prevent salt formation and blockages, but the heat exchange temperature will be lower, leading to stripping and a lower temperature at the distillation inlet. To compensate for this lower temperature, more energy must be used, which is not worth it. Additionally, the temperature of the water injected before the heat exchanger is usually higher than the temperature at which salt forms; even if there is slight salt formation, changing the point of water injection intermittently is sufficient!
Continuous water injection and intermittent water injection are arranged according to the salt formation situation. . .
Salts clog pipelines and heat exchanger tubes; water is used to dilute these salts. There are amine chlorides, amine sulfides, etc., and due to their different crystallization temperatures, or because the injection points change when the temperature rises or falls during startup and shutdown