Disruption of fresh hydrogen supply for diesel hydrogenation

Stopping the feed when the system pressure falls below a certain value is primarily aimed at ensuring safe operation and preventing accidents. During diesel hydrogenation, the system pressure is a very important parameter, as it reflects the pressure conditions inside the reactor. Firstly, a system pressure below a certain value may cause instability in the system. The hydrogenation reaction needs to take place under certain pressure; when the system pressure falls below this value, it may lead to incomplete reaction, a reduced reaction rate, or even a stop in the reaction. At this point, if feeding continues, it may lead to blockages or other abnormal conditions, causing damage to the equipment. Secondly, too low system pressure can also pose safety risks. The hydrogen generated during diesel hydrogenation is flammable and explosive; if the system pressure is too low, hydrogen leakage may occur, increasing the risk of fire and explosion. To reduce this risk, once the system pressure drops below a certain value, it is necessary to shut off the feed and turn off the engine. In summary, stopping the feed when the system pressure falls below a certain value is done to ensure the stability and safety of the reaction. Through this measure, accidents can be effectively reduced, and the safety of equipment and personnel can be protected. .

May I ask, can low system pressure cause hydrogen leakage? I’m not quite sure

If it’s below 3.0 Mpa, the product quality is definitely unsatisfactory; then why feed it in?

I think it’s because when the pressure falls below a certain threshold, all reactions essentially cease. If feeding continues at this point, the S and N elements in the feedstock cannot react, which leads to carbon deposition on the catalyst, causing it to become deactivated and significantly reducing its service life

From a safety perspective, each unit has its own pressure control range – there is a minimum pressure level that must not be exceeded, as well as a minimum hydrogen partial pressure. It is necessary to maintain stable pressure during production; too low a pressure can result in heat not being able to dissipate, thereby creating a risk of overheating； The reaction rate decreases ； Production fluctuations, and so on. . In the event of a disruption in the supply of fresh hydrogen, the first thing to consider is reducing hydrogen consumption in order to maintain stable system pressure. If the system pressure cannot be maintained, the feed rate should be reduced, along with the temperature at the outlet of the heater. If the system pressure continues to drop and the feed rate is reduced to the minimum level (60%), the system can no longer operate; in such cases, the feed must be stopped and the heater turned off to prevent the furnace tubes from burning out.

When addressing issues, two main factors are considered: one is the safety principle, which refers to actions that must be taken at critical points, such as interlocking and emergency venting. The second is the principle of actual conditions: high-pressure feed pumps have a minimum flow rate limit, while the pumps in the coal system can be tested and operated as usual. But in practice, when it makes no sense to operate the pump, it doesn’t matter whether it’s 3.0 MPa or 4.0 MPa

Too low will result in: a reduced reaction rate；

I think it is mainly due to the following reasons: 1. Low hydrogen partial pressure and low hydrogen-to-oil ratio lead to easy deactivation of the catalyst; 2. At low pressures, the amount of circulating hydrogen is small, which results in a low space velocity as well. This leads to a high degree of reaction, preventing heat from being carried away, and may cause overheating； 3. The circulation rate is low, resulting in easy flow deviation in the reactor bed, which may cause local overheating or excessive temperatures ； 4. If the pressure continues to drop, even if the feed pump is stopped, it will be difficult to push the oil back in the reactor, and overheating may still occur ；

The feed must be stopped, and the heating furnace must be turned off to prevent the furnace tubes from burning out due to lack of fuel. Safety is important.