Temperature control of the gas distribution bed in an axially variable reactor
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Question: When using a Shell gasifier to supply water gas at low load to an axial one-stage reactor, the catalyst bed of the one-stage reactor often experiences overheating, with temperatures sometimes reaching around 500°C. Is there always an over-temperature issue with the gas flow in the first converter after Shell gasification? How to control overheating during gas guidance?
Shell gasification inherently has a low water vapor ratio; therefore, overheating of the shift reactor catalyst bed is quite normal. The methods for dealing with overheating in the coal powder catalyst bed are as follows: 1. Due to the low water vapor ratio, steam is added before the shift reactor (saturated steam, or water can also be used). . . ), increasing the water vapor ratio. 2. When introducing gas, keep the inlet temperature as low as possible; 10 degrees above the saturation temperature is sufficient. 3. When the temperature rises too rapidly during gas introduction, it is necessary to quickly increase the air flow rate to stabilize the inlet temperature (at a level comparable to that specified in point 2); if needed, nitrogen can be used to lower the temperature. 4. If it cannot be controlled, increase the gas flow by raising the gas supply volume; boost the gas flow significantly to rapidly lower the bed temperature. Basically, with 4 units in use, overheating is almost never an issue.
1. Control the gas-to-gas ratio. 2. Pre-warm the pipes before starting up the converter
It’s difficult to operate when adding steam during gas guidance, and the temperature tends to rise very quickly; the best approach is still to follow your suggestions in points 3 and 4
The summary is accurate; the described operation method is the same as that used in Sinopec Zhijiang Fertilizer Plant’s 30-52 project: ① For the initial introduction of gas, ensure that the inlet temperature is 10–20°C higher than the catalyst activation temperature, and introduce the gas slowly (the gas flow rate should not be too high at the beginning to prevent temperature fluctuations in the bed)； ②As the temperature of each layer of the bed rises (i.e., due to the exothermic reaction), the amount of air supplied should be increased gradually. Once the temperature of the lowest layer starts to rise, the air supply should be increased further; at this point, it is the space velocity that controls the bed temperature. It is recommended to also introduce nitrogen simultaneously – this helps to lower the temperature and dilute the CO concentration, thereby reducing the heat generated by the reaction – in order to prevent excessive temperature rises. This approach is more gentle, and the system will reach equilibrium quickly, saving time and effort ；
If it is high-CO powder gasification, and gas is guided using the method you mentioned, the temperature will soar out of control! You are correct only in stating that nitrogen can be supplied simultaneously, but many factories do not have the facility for medium-pressure nitrogen.
This post was last edited by shuker666 on 2019-6-6 at 11:07. For dry powder gasification, nitrogen of various grades is necessary; for the transportation of dry coal powder, high-pressure nitrogen is required first (for devices that need a certain grade of nitrogen, the pressure can be reduced accordingly), so the operation can indeed be carried out. If nitrogen is not connected to the conversion process, technical modifications can be carried out; lessons can be learned from Project 30-52 at Hubei Zhijiang Fertilizer Factory ； At around 18:00 on March 1, 2013, a crack occurred at the midline position on the side of the elbow in the outlet pipeline of the reformer (on the north side), resulting in a leak of process gas that caught fire. At that time, the reforming unit was undergoing startup and shutdown procedures. I had trained 8 employees for three months, teaching them the actual methods of operation. My advice is that you should consider visiting the site or consulting their technical staff. It should be emphasized again that in any coal chemical process that uses pressurized gasification, regardless of the specific gasification technique employed, there is low-pressure and medium-pressure nitrogen available from the associated air separation unit. Additionally, since the amount of nitrogen required for gas formation during the initial stages of conversion is small, it has no impact on the system, and the requirements can be fully met.
Yes, but many companies are unable to use nitrogen for cooling. Nitrogen cooling is indeed the most direct and effective method.