Pressure drop across the catalyst bed in the hydrogenation unit
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The pressure difference across the catalyst beds in the diesel hydrogenation unit is increasing, with an increase in each bed. Recently, the upstream coking units have been shut down and started up, with direct feeding. But I don’t know what the specific reason is?
It may be that the direct feeding after the coking unit was shut down led to unstable raw material quality, blockage of the catalyst bed, or accumulation of contaminants, resulting in an increase in pressure difference. It is necessary to check the quality of raw materials and the condition of the catalyst bed. .
An increase in the pressure drop across the catalyst beds in the diesel hydrogenation unit, with an increase in each bed, may be related to various factors. Considering the recent start-ups, shut-downs of upstream coking units and the situation with direct feed, here are some possible reasons: Issues with crude oil: The start-ups and shut-downs of upstream coking units can lead to changes in the properties of the crude oil, such as an increase in its density and viscosity. Such changes can result in an increase in reactor pressure drop, thereby affecting the pressure difference across the catalyst bed. High feed impurities: The direct feed from upstream coking units may contain many impurities, which can deposit on the catalyst as it passes through the catalyst bed, leading to an increase in the pressure drop across the bed. Catalyst issues: Problems such as coking, crushing, and local collapse of the catalyst can also lead to an increase in the pressure difference across the bed. Furthermore, if the catalyst's activity decreases, it may also affect the pressure drop across the bed. Operational issues: Abnormal filter operation, scaling at the top of the reactor, etc., can also lead to an increase in the pressure difference across the bed. Changes in system pressure drop: Factors such as the activation of emergency pressure relief valves or safety valves for the cold high-pressure section, an increased processing volume that leads to a rise in reactor pressure drop, or a high flow rate of recycled hydrogen that also results in an increase in reactor pressure drop, can all affect the pressure difference across the beds in the entire hydrogenation unit. To address this issue, the following measures can be considered: improving the management and testing of crude oil to ensure that its properties meet the requirements of the facility. Strengthen the maintenance and operation of filters, and use as many filters as possible to minimize the impact of impurities on the catalyst. Enhance temperature monitoring of the catalyst bed to prevent coking in the bed. If the processing volume is too high, you can contact the scheduler to reduce the device’s processing volume. If it is a problem with the crude oil, you can contact the dispatch team to adjust the proportion and properties of the raw materials. If the problem is caused by a high flow rate of recycled hydrogen, the speed of the recycler can be reduced to lower the flow rate of recycled hydrogen.
Control the properties of the feed oil to meet the requirements of the plant, and install filters to prevent coking in the bed. Load of the control device. Reduce the flow rate of recycle hydrogen.
It’s quite likely, but the question is whether each bed layer rises as well.
If other operating conditions remain largely unchanged and every bed layer rises, it is likely related to changes in the feed composition. Generally speaking, if an increase in pressure drop is caused by catalyst carbon deposition or mechanical impurities, it should be manifested as a rapid increase in the pressure drop across one bed layer ； However, problems with the internal components and collectors between the lower bed layers, as well as localized collapse of the catalyst caused by the accumulation and blockage of ceramic balls, are less likely. If the raw materials change and the composition of the feed becomes heavier, as well as the amount of feed increasing, the pressure drop across each bed layer will increase as well; this varies depending on the operating parameters. Additionally, we have a diesel hydrogenation unit; the pressure at the outlet of the circulator is continuously rising, while the pressure difference in the reactor is normal. It is currently assumed that the point of pressure buildup is at the reaction products/raw oil and the hydrogen mixing heat exchanger, with the raw oil flowing through the shell side, and there is a cold oil control valve in place. I wonder if that device has experienced such a phenomenon?
I have experienced the phenomenon you mentioned; at that time, the pressure difference in the raw material section increased, while there was no change in the pressure drop across the bed. We tried running two circulating hydrogen compressors and using flow rate variations to flush the bed layer, but that didn’t work; we had to shut down the operation. Later, we added scale inhibitors in other areas, and the problem did not occur again.
Our scale inhibitor injection point is at the outlet of the raw material tank. Where and to where has your scale inhibitor injection point been changed? How do you handle shutdowns? We might also have to suspend work, but the key solution has not been found yet.
Pay special attention to the side of the heat exchanger where circulating hydrogen flows; the baffle plates in this heat exchanger are damaged, which causes blockage at the outlet of the shell side, and the blockage worsens over time, leading to an increasing pressure at the compressor outlet. If there is a bypass, using it for testing will make it clear.