Problems with starting up the first-stage ammonia synthesis furnace

No, the oxygen content in the air is too high, and temperatures above 200 degrees will damage the catalyst. Using air to heat up is also a last resort. Because the natural gas ammonia plant has no source of nitrogen. In principle, when the temperature is higher than the dew point, switch to steam heating as soon as possible.

Thanks for helping solve the problem. “The oxygen content in the air is too high, and temperatures above 200 degrees will damage the catalyst." Is there any reaction at a certain temperature? What will be generated? Can the experts provide more details?

These are the startup regulations for the original KELLOGG ammonia synthesis unit. There may be different regulations for different units and different catalysts.

It is generally believed that 204 degrees is the combustion point of carbon in the catalyst. The earliest catalyst temperature rise, including medium-temperature catalysts, stipulates that the air temperature rise is less than 204 degrees. In fact, most catalyst factories no longer require this (basically no activated carbon is included), but users still require this for insurance purposes. (I am responsible for preparing the driving, heating and restoration plans)

Floor 5 is right. The current natural gas first-stage furnace catalyst uses dry gas such as air, nitrogen, carbon dioxide, hydrogen, ammonia, etc. to heat the catalyst to above 350°C, with a minimum of not less than 250°C. Then, superheated steam is introduced, and the superheated steam is used to continue heating.

Basically, according to the original design or the requirements of the catalyst manufacturer, circulating N2 is used to raise the temperature to 300 degrees. However, considering the cost of circulating N2 compressor equipment and maintenance (it is really wasteful to use it only once after stopping for a long time), so... of course, it is the most cost-effective to use air. Our factory has been using air to raise the temperature to 300 degrees for 30 years. We have not had any problems before switching to superheated steam. OK~~~ And if you use superheated steam from the beginning, the temperature will rise too fast. Because the furnace is opened for maintenance, some water vapor will escape into the furnace. It is better to follow the program to raise the temperature... The above is for your reference. I hope it will be helpful to the poster~~ :)

Thanks for your help in resolving the issue. Really appreciate it :'( :'(

Graphite is used in the manufacturing process of oxidation catalysts, but it is generally consumed during the calcination process. Therefore, the requirements for air temperature are not high. As long as it is higher than the dew point, it is sufficient, but subsequent catalyst issues need to be considered. Since the passivation of reduced catalysts will not be complete, air heating is generally not allowed.

We no longer use the method of heating the air. Instead, using N2 to increase the temperature is safer for the catalyst and easier to operate. As for the temperature rise to 204, pour the steam to heat up. This is mainly to prevent the catalyst from soaking in water and raise the temperature to higher than the saturated steam pressure.

Generally, there will be no problem if the air is heated again after steam passivation. The small factory does not have a nitrogen generating device, so it has to use air to heat it.

Generally speaking, the first and second stages of temperature rise together. According to the requirements, as long as the air temperature rises above 150 degrees, why should we choose 200 degrees? One of the purposes is to drive the second stage to rise above 150 degrees to avoid soaking in water. Furthermore, if it rises above 204, it will damage the catalyst in the first stage. Most factories now have nitrogen-making equipment. It is of course best to use nitrogen to heat up.

We first raise the temperature of nitrogen to 420 degrees, then raise the temperature of steam to 760 degrees, and finally mix the raw gas. I have never seen one that uses air to heat up.