Hot spot temperature issue in the synthesis tower

Key factors: production load (CO content), space velocity, purity of the feed gas, and operating time. As the CO content increases, the driving force for the reaction in the upper portion increases; the hot spot generally remains in the same position, but the temperature difference along the axial direction (in the direction of the gas flow) increases ； The hot spot of increased airspeed generally moves downward ； As usage time increases, the poisons affecting the catalyst coefficient in the upper layer also increase, the catalyst lattice grows larger, its activity declines, and the hot spots shift downward over time, ultimately leading to a decrease in the outlet conversion rate and the need to replace the catalyst.

That’s more or less it! Over time, its lifespan becomes shorter and shorter, until it eventually needs to be replaced~~ That’s all there is to it!

The reason for incomplete catalyst activation is external interference affecting the thermometer thermocouple

In a synthesis tower, the hotspot temperature generally increases as the catalyst activity decreases. The hotspot temperature is divided into early, middle, and late stages; the temperature is lowest in the early stage and highest in the late stage. The hot spot also gradually moves downward as its temperature increases. Under normal circumstances, the maximum operating temperature for copper-based catalysts is 290 degrees.

Our plant has five catalyst temperature measurement points, located at the inlet of the synthesis tower, two in the insulation layer, and two at the outlet. Initially, it was around 185 at the inlet, around 192 for the insulation layer, and 214 at the outlet. With a gas holder pressure of 2.0 MP, the values were 198 at the inlet, 196 and 200 for adiabatic conditions, and 234 at the outlet after two years of use. At a gas holder pressure of 2.6 MP, due to the H2S concentration remaining around 0.1 PPM, coupled with thermal aging, the temperature at the catalyst hot spots decreased significantly

What are the sulfur control targets you require? Two years of usage can be considered a relatively long period of time

The sulfur control limit in our factory is <0.1 ppm, and the catalyst has been in use for over two years now!

1. What is hotspot temperature? Why is it necessary to control the hotspot temperature? Hot spot temperature refers to the temperature at the highest point within the catalyst layer. Although the hotspot temperature refers to the temperature at a specific point within the catalyst layer, it provides a comprehensive indication of the temperature conditions, so it needs to be strictly controlled. The hotspot temperature should vary depending on the different catalyst models, the activity of the catalyst at various times, and the operating conditions at that time. If the catalyst has good initial activity, the hotspot temperature can be kept lower, with the hotspot located in the upper part. As the catalyst ages and its activity declines, the hotspot temperature increases accordingly to accelerate the reaction rate, while the catalyst temperature gradually decreases. For the C207 catalyst, the initial hot spot temperature can be maintained at 220–235°C, and it can increase to around 255°C in the later stage. In practical operation, and while maintaining operational stability, keep the hotspot temperature as low as possible. This is because: (1) the hotspot temperature is low, which is favorable for the equilibrium of the methanol reaction ； (2) It can extend the service life of the catalyst ； (3) High temperatures can easily degrade the mechanical properties of metals and accelerate chemical corrosion, causing more significant damage to the internal components; therefore, low temperatures can protect these components from damage. According to reaction theory, the ideal temperature distribution of a catalyst is high at first and then low, meaning that the hot spot should be located in the upper part of the catalyst. 2. Why does the hotspot temperature drop? A. The catalyst remains at high temperatures for long periods or experiences large temperature fluctuations, resulting in a decrease in its activity ； B. The effect of toxins reduces the activity of the upper catalyst layer, causing the hot spots to shift downward ； C. Damage to the upper part of the internal components causes air leakage, with the hot spot shifting downward ； D. Poor catalyst reduction, lower activity of the upper layer of catalyst, shift of hot spots downward ；