Why is the vent volume high for the synthesis unit?

With a methane content of 3.0 in the fresh gas, it’s no wonder that the amount of off-gas is low. I’m not familiar with your production process; I suggest investigating further to find out the reason. Personally, I think that a methane level this high in the refined gas indicates a leak somewhere in the preceding equipment, such as the heat exchangers in the conversion system or the heat exchangers for raw gas/converted gas. If the refining process involves methanation, then it’s necessary to check the conversion and decarburization systems upstream.

Reducing the vent volume causes pressure to rise rapidly, methane levels to increase quickly, and ammonia production to drop significantly. From the above, it can be seen that the gasification operation in the previous section was not proper; it is estimated that your plant uses fixed-bed intermittent gasification. Recently, there have been changes in the quality of the raw coal, and furthermore, the operation of the gasifier is not optimal.

Such a high level of methane mainly comes from the previous process stage; it is necessary to check that stage. Check the changes in the previous process stages! First: in the methanation reaction section, check whether there are any signs of a significant increase in bed temperature, and whether the cooling bypass is open to a greater extent than normal! Secondly: Analyze whether there are any signs of a significant increase in carbon dioxide emissions from the decarbonization process! Once again: check the transformation section to see if the carbon monoxide level at the outlet is above the limit. Reasons for exceeding the standard: 1. It may be due to poor activity of the catalyst in the middle and later stages, resulting in the excess level. Increase the bed temperature and replace the catalyst! 2. Insufficient water vapor ratio. Increase the water vapor ratio! Check the carbon monoxide and carbon dioxide levels at the inlet and outlet of each heat exchanger; if these levels are low, and the order of reaction is reversed compared to the levels at the inlet and outlet, it indicates that there is a leak in the heat exchanger. Stop the operation immediately to address the leak! This post was last edited by snowdfr on 2009-2-28 08:45]

The high methane content is mainly due to the quality of the coal; bituminous coal has a high volatile content, so it is recommended to focus on improving the coal quality.

If the hydrogen and nitrogen purification is carried out using a methanation process, there are two reasons for this: 1. High levels of trace substances (excess amounts of carbon monoxide and carbon dioxide)； 2. The composition of the gas used for gas production is poor. If the copper washing refining process is used, then the composition of the gas used for gas generation is poor.

In my opinion, there are two scenarios: one is that the methane content in fresh gas is high, and we keep it between 1 and 2, but most of the time it is at the lower limit. Also, is it because the catalyst has been in use for a long time, entering its later stages? It will also result in a large amount of air being released.

Check the process flow to see if the valves that should be closed aren’t closed; air from the upstream system is leaking directly into the synthesis circuit.

3.0 for methane is indeed high; we use a hydroformylation process along with copper-based refining, and changes in the type of coal used as raw material have a significant impact on the gas properties, sometimes preventing it from being reduced to the desired level. I’m not sure what process LZ refers to; if it’s similar, it’s better to check the coal type and its properties first. Due to the catalyst, there should be a process for it to make sense.

There are many reasons for high methane levels, primarily stemming from the previous processing stages. 1. The vaporization temperature in the gas generation plant is low, or the operation is unstable; frequent adjustments and furnace changes result in the raw gas having unsuitable composition, with high levels of carbon dioxide, oxygen, and inert gases. 2. In the methanation reaction section, is there any significant change in the bed temperature, or is the methanation catalyst poisoned? 3. Has the carbon dioxide content increased due to decarburization? 4. Changing the processing section results in a poor transformation effect, with excessive levels of carbon monoxide. (Poor catalyst activity, insufficient water vapor ratio, low operating temperature, large fluctuations in load, etc.) 5. The high trace content in the purified gas affects the activity of the synthesis catalyst, resulting in high pressure in the synthesis system. 6. High ammonia levels at the inlet of the synthesis tower increase system pressure and deteriorate the reaction. 7. Poisoning of synthetic catalysts

Our company deals with coked gas; the CH4 content in the refined gas is generally around 0.8–1%. About 3% of your company’s output is likely from natural gas conversion or lignite gas production, and there are issues with the CH4 conversion process ； In the case of a high-pressure alcohol alkylation purification process, it may be that the control of CO or CO2 at the alkylation inlet is too strict (due to high levels of CO/CO2 in the alkylation process and low conversion rates resulting from catalyst aging), which leads to high levels of CH4 at the alkylation outlet and excessive hydrogen consumption; it is necessary to check the issues prior to this stage. If the inlet CH4 level is not reduced, methane will accumulate too rapidly in the system’s recycle gas, resulting in a decrease in the net amount of ammonia produced. The system pressure will rise as well, which in turn will lead to an increase in the raw material gas consumption and electricity usage in the ammonia synthesis system. Production will drop significantly, leading to substantial losses. This post was last edited by FEIJING on 2009-3-2 17:20]

Thank you all. As a supplementary point, our company uses a fixed-bed batch coal rod gas generation process. Recently, in order to test local coal varieties, we added 20% bituminous coal to the white coal; as a result, the CH4 content in the semi-water gas was only 2.6%, but the amount of gas released during synthesis increased significantly, leading to a decrease in production. The volatiles content in the coal rods is 8.8%

Our company uses a fixed-bed batch coal rod gas production process; the raw coal contains 20% bituminous coal, with a volatility content of around 8.8% in the coal rods. The methane content in the semi-water gas is about 2.6%, while in the shift gas it is around 2.4%. CO2 is removed using a shift gas-based alkali production process; however, the CH4 content in the dual-methane feedstock is as high as 3.5–4.5%, and that in the synthesis make-up gas is 3.5–4.0%. As a result, there is a large amount of waste gas generated, leading to low production levels and high consumption. When producing gas from lump carbon, the proportion of synthetic make-up gas CH4 is around 2.0%, and that of semi-water gas CH4 is about 1.8%. So why is there such a large change at present? Please give me some advice, thanks!