The issue of the lowest pressure increase temperature during the first start-up of the hydrogenation reactor
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The hydrogenation reactor is made of 21/4Cr-1Mo steel, with a design pressure of 11.14 MPa; difficulties were encountered during its commissioning. Some people say that the temperature must first be raised to 135 degrees before the pressure can be increased to the operating level, in order to avoid temper brittleness. Others, including highly renowned hydrogenation experts in China, say that no minimum pressure-raising temperature is required for the first start-up, as the reactor undergoes a hydrostatic test at 16 MPa after heat treatment. I would like to ask the experts: is there any minimum heating temperature requirement for the first start-up of a reactor made of 21/4Cr-1Mo steel? Thank you!
There is no temperature requirement for the first voltage increase; you can simply ask the design institute or the manufacturer to provide you with the relevant information. As long as such information is available, any problems that arise are their responsibility
In principle, no restrictions are required for the first start-up. Based on past experience, hydrogen will penetrate into the 21/4Cr-1Mo steel during operation; therefore, during shutdown, the pressure must be reduced first and then the temperature lowered to allow the hydrogen to escape, while during start-up, the temperature must be increased first and then the pressure raised. At present, given the current level of material manufacturing, it seems there is no explicit requirement for this, but we still use it based on this experience
Generally speaking, the minimum pressure increase temperature for the first start-up of a hydrogenation reactor, as well as for subsequent start-ups, is specified by the design team. Different material types require different minimum pressure increase temperatures, and the value for the first start-up is higher than that for subsequent start-ups. Although I personally believe that no restrictions are necessary for the first start-up, it is still advisable to follow the design specifications.
Generally not, but it’s good to be cautious – after all, it’s critical equipment
Our hydrogenation reactor is designed for a pressure of 16 MPa. At the time of its initial operation, it was specified that as long as the temperature at any point within the reactor did not exceed 51 degrees, the inlet pressure to Reactor 1 must not be greater than 4.125 MPa, which is in other words, no more than one-quarter of the reactor’s design pressure.
During the shutdown process, pressure must be reduced first and then temperature lowered to allow hydrogen to escape; during the startup process, temperature must be increased first and then pressure raised.
If the design institute demands this, there must be a reason for it; following those requirements will not lead to any mistakes.
Ordinary equipment undergoes heat treatment before leaving the factory. The poster can check the documentation that comes with the equipment to find out, and it also needs to be done in accordance with the design requirements
The temper embrittlement of chromium-molybdenum steel is a phenomenon in which the fracture toughness of the material deteriorates when it is maintained at temperatures between 325 and 575°C for an extended period of time (some suggest 371–593°C, 354–565°C, or 400–600°C, etc.), or when it is cooled slowly from such temperature ranges. It is caused by the segregation of impurity elements and certain alloying elements in the steel toward the original austenite grain boundaries. When starting up, pay attention to the rate of voltage increase, and follow the temperature and voltage rise curve strictly.
For our hydrogenation unit, it was specified at the time of its initial commissioning that, as long as the temperature at any point in the reactor did not exceed 135 degrees, the inlet pressure to Reactor 1 must not be greater than 4.5 MPA. So it is essential to follow the manufacturer’s instructions and the design provided by the design institute; operating in accordance with the procedural guidelines and commissioning plans will definitely ensure no problems. What well-known experts say can be used as a reference for discussion.
The hydrogenation reactor is made of 21/4Cr-1Mo steel; to prevent temper embrittlement, there is also a minimum temperature requirement for pressure increase during the first start-up, although this temperature is likely to be below 135 degrees.
Our heating rate is 50C–70C/h, which is the limit for the expansion of steel
Generally, at pressures below 4.0 MPa, no specific temperature requirement exists; whereas at pressures above 4.0 MPa, the temperature may be either 95 degrees or 120 degrees, with different requirements in each case.
1. For the first use, when the temperature at any point on the reactor surface is below 50 degrees, the reactor pressure must not exceed 25% of its design pressure; in other words, when the pressure approaches 25% of the design value, the reactor temperature must be above 50 degrees. This is why during the initial cold-pressure leak test of the system, the pressure can only be raised to 4.0 MP – for higher pressures, the reactor heating furnace must be used to conduct a hot-pressure test； 2. After one cycle of use of the reactor, this limit temperature rises to 93 degrees; that is, if the reactor pressure exceeds 25% of the design pressure, the temperature at any point on its surface must be greater than 93 degrees. 3. These principles must be observed during startup and shutdown.
Hello, are there any written regulations regarding this? Could you let me know!
The requirements in this regard are the result of decades of experience accumulated by those who came before us; they are essentially empirical values, and there are no written rules. Nevertheless, everyone should abide by what our predecessors have left behind
During the start-up process, before the lowest temperature of the reactor wall (measured by surface thermocouples) reached 93°C – whereas our initial start-up plan specified that it should be below 50°C – the operating pressure was not allowed to exceed 1/3 of the design pressure. Only after the lowest temperature on the vessel wall reaches 93°C is it permissible to gradually increase the operating pressure to the normal operating level. During shutdown, before the lowest temperature of the reactor wall (measured by surface thermocouples) reaches 93°C, the operating pressure must be reduced to less than 1/3 of the design pressure.
Our reactor design: 19.3; operations: 18.3. For the first start-up, the reactor wall angle is greater than 93°