Weekly Topics on Synthetic Ammonia； Reasons for high methane content at the outlet of the two-stage furnace and solutions (August 29–September 4)

Once it is ensured through the process that the raw gas has been properly desulfurized, the key points to check are whether the carbon-to-water ratio in the first furnace and the furnace temperature are too low, and whether insufficient process air is being supplied to the second furnace. If there are no issues with these aspects, then the catalyst activity needs to be examined. First, the pressure difference between the first and second furnaces is checked to determine whether there is any catalyst degradation. Then, it is analyzed whether the process steam used in the first furnace meets the required standards; the presence of liquid or salts in this steam can easily lead to catalyst poisoning. It is also important to check whether excessively high furnace temperatures in the early stages caused carbon deposition...； There isn’t much that can be checked on the device; there are probably few issues that can arise ； For instrument-related issues, you can contact them for troubleshooting ； Generally, on the premise of maintaining the hydrogen-to-nitrogen ratio in the synthesis tower within an optimal range, the water-to-carbon ratio, the exit temperature of the first stage, and the amount of air supplied to the second stage furnace are appropriately increased. If the equipment breaks down, maintenance must be halted; whether production needs to stop depends on the severity of the issue.

1. High methane content in the first stage of output (catalyst aging, pulverization, or insufficient temperature in the first stage)； 2. The amount of air supplied is insufficient ； 3. Aging or pulverization of the second-stage catalyst ； Make appropriate adjustments to reduce the methane content in the exhaust stream, either by adding air or by reducing the load. If that really doesn’t work, then replace the catalyst.

Reply to 3# liuchao7324835: Has no one considered the possibility that the data analysis is incorrect? There are also equipment-related reasons (related to the internal components of the two-stage furnace); what about system-related reasons? Fluctuations in total carbon in natural gas! What else? Who can come up with a more comprehensive list? There are basically a dozen items or so, hehehe

Generally, by examining the temperature of the second-stage furnace bed, the outlet temperature, as well as the pressure difference in the subsequent synthesis tower and the reaction conditions, along with the ammonia production volume and the amount of CO2 produced as a by-product, it is possible to get an idea of the situation. To be honest, I don’t really trust the test analysis data. The structure of the two-stage furnace is relatively simple, and the part that is most prone to damage is the air mixer. Changes in natural gas composition can be observed by comparing CO2 levels with ammonia production amounts; there is also analysis of this feed gas composition, though it is conducted less frequently. Of course, there are also the analysis results from online analyzers.

The central burner and air distributor are also known as mixers; they are the same thing.

Reply to 6# julius6054: Regarding the issue of catalysts, there are likely many reasons: 1. Aging, due to prolonged use beyond its service life ； 2. The catalyst becomes pulverized; the temperature in the two-stage furnace is very high, and a layer of heat-resistant catalyst covers the surface when the catalyst is loaded ； 3. Poisoning, H2S, etc ； 4. High-temperature sintering leads to uneven distribution of process gas and airflow short circuits ； 5. Insufficient or improper catalyst loading, which leads to layer collapse issues. 6. The support structure at the bottom of the catalyst is damaged; severe cracks were detected during our maintenance checks. These are issues related to the catalyst, and they need to be addressed. Possible solutions include reducing the load, increasing the water-to-carbon ratio, adding air, and replacing the catalyst during shutdown for maintenance. Everyone is welcome to discuss this topic. This question can be used as a skill test for junior, intermediate, and senior technicians; different technical levels require more comprehensive consideration of the answers, including analysis of the upstream systems as well

Regarding catalysts, their performance can be analyzed based on the parameters mentioned earlier. The standard approach is to enlist professionals to conduct evaluations of catalyst performance; after all, there are many factors to consider before deciding whether a catalyst needs to be replaced, and the most straightforward indicator is the performance of the chemical reaction process.

This post was last edited by Mojin2 on 2011-8-30 09:54. From a process operation perspective, it is also necessary to monitor furnace temperature control, whether the methane level at the outlet exceeds the specified limits, as well as the ratio of HN; moreover, catalyst aging in stage one and stage two needs to be taken into account ==:lol

1. If the conversion in the first reactor is inadequate, increasing the steam supply and raising its outlet temperature can help, provided the catalyst is in good condition. 2. Increasing the air and steam supply to the second reactor can raise the conversion temperature. 3. If there is an incorrect indication of temperature in the second reactor, it is necessary to consult the instrumentation team to make adjustments as appropriate. 4. When the H/N ratio is appropriate, the methane level can be determined based on the pressure and temperature differences in the synthesis tower. 5. Aging of the catalysts in both reactors. 6. Flow imbalances. 7. Problems with the burners

Reply to 10# WindShadow1: A high pressure difference could be caused by problems with the molecular sieve at the outlet of the first stage of the compression compressor, it might also be due to poor cryogenic separation performance, or it could be because too much air was added, etc. It is recommended to discuss these issues in more detail.