Impact of operating without H2 on the system
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Our plant's urea unit is a Stam CO2 gas process. A new H2 removal system was added last year. It has not yet been put into use. It will be put into operation after the natural gas enters the plant in July. Anyone who has this device can tell me what impact it will have on the system after running without H2? Includes compressor. Also explain: We are now providing CO2 as the raw material for coal gasification drive. That's what the 5th floor said. . . This post was last edited by HGLT2007 at 2009-3-9 11:21 ]
The setting of the H2 removal system is beneficial to the safe operation of the urea unit, mainly reflected in the following: 1. After dehydrogenation is set up, the hydrogen carried in the raw material CO2 can be removed. Due to the wide explosion limit of hydrogen, the formation of explosive gas in the high-pressure coil tail gas can be avoided. 2. After dehydrogenation is set up, the hydrogen carried in the raw material CO2 is converted into water, which can improve the purity of CO2 and help increase the CO2 conversion rate. 3. I don’t know whether your dehydrogenation device is installed at the final outlet of the CO2 compressor or between stages. If it is at the final stage outlet, it will have no impact on the CO2 compressor. In fact, even between sections, there is no big impact. Since the dehydrogenation reaction is an exothermic reaction, it only increases the load of the corresponding inter-section cooler at the next stage (if it is set separately, there will be no impact).
Our factory uses a separate system to remove H2 after the final stage of the compressor, which is good for the process system. As mentioned above, the heat of the high-temperature water can be moved to the evaporation stage to heat the urine. There is a very important issue here, that is, the O2 required to remove H2 is added from the inlet of the compressor section. Our factory used natural gas for production for more than half a year in 2006. At that time, the H2 content in CO2 was about 0.8. The purity of CO2 at the inlet is reduced, which may have an impact on the operation of the compressor.
I don’t know if you are using the catalytic combustion method. If so, let’s briefly talk about its impact and the advantages of the catalytic combustion method.: (1) In the high-pressure ammonium methane condenser, NH3 and CO2 are almost completely condensed under high pressure, and the NH3 consumption is low. (2) NH3 and CO2 are condensed under the same synthesis pressure, with low power consumption. (3) The medium-voltage system is cancelled, making the operation simple and convenient. The disadvantage is: (1) The water generated by combustion causes H2O/CO2 to rise, and the CO2 conversion rate decreases slightly. ； (2) The catalyst is not resistant to sulfur and is easily poisoned. ； (3) When dehydrogenation is abnormal, the high-pressure exhaust gas becomes explosive gas and may explode.
The author's concern is correct. The O2 from anti-corrosion and hydrogenation reactions will reduce the purity of CO2. If the O2 required to remove H2 is also added from the inlet of the compressor section, it is easy to overpressure and it is difficult to carry a high load. suggestion: Add a small air compressor to add air directly to the dehydrogenation device. There is still a little doubt: “Is "Stam CO2 gas process" a clerical error by the poster? Snam refers to the NH3 gas stripping process, and the CO2 gas stripping process is from Stamicarbon, right? Please also make it clear.
The fifth floor is right. The dehydrogenation reaction consumes oxygen. Oxygen is generally provided by air. The addition of air will cause the purity of carbon dioxide gas to decrease, the conversion rate will decrease, and the high-pressure venting amount will increase. For the water produced by the dehydrogenation device, a gas-water separator can be set up to drain the water in time to avoid affecting the operation of the compressor. The main purpose of dehydrogenation is to reduce the hydrogen content in carbon dioxide gas to less than 50 ppm, reduce the explosion range of high-pressure exhaust gas, and ensure the operation safety of high-pressure equipment.
In fact, after the dehydrogenation system is operated, the purity of the gas entering the high-pressure system will generally decrease, and the synthesis conversion rate will decrease. The purpose of putting dehydrogenation into operation is mainly for safety and protection of the high-pressure scrubber. It can safely reduce the temperature of the high-pressure water and increase the condensation capacity of the high-pressure scrubber.
The dehydrogenation process is generally located at the outlet of the second or fourth stage of compression for the purpose of adding air. 1. Participate in dehydrogenation reaction. 2. Passivation of high-voltage system. 3. Ensure that the inert gas of the high-pressure scrubber does not enter the explosion limit. The disadvantage is that the carbon dioxide concentration is reduced and the compressor power consumption is increased. Excuse me: 1. Which company uses a small compressor to add air to the four-stage outlet? 2. Which company has installed a steam-water separator after dehydrogenation? Please express thank you! ! This post was last edited by Boating Five Lakes on 2009-3-9 02:08 ]
The small compressor solution is beneficial to the operation of the CO2 compressor, but if the design is based on the purity of the dehydrogenated CO2, it would be best to reduce the number of compressors. Because small high-pressure compressors often malfunction according to our operating conditions, and if there is a problem with adding air, the impact on the system will be fatal.
How much oxygen can be added by dehydrogenation? Basically, it is just a slight change in molecular weight, which has no effect on the compressor at all. In addition, it is okay if you add it to the four-stage outlet, but you must pay attention to whether the temperature can be reached. If it is added between sections, the impact of the pressure difference on the compressor must also be considered. There will be an increase in water and temperature rise after dehydrogenation, and the design margin of the downstream separator and cooler must be considered.
Those above beg to differ. The oxygen added by dehydrogenation has a great impact on the compressor, at least in our factory, because the compressibility of air is * * Less than CO2, the work done by compressing 100 cubic meters of air is equivalent to several hundred cubic meters of CO2 (I don’t know the specific data). It would be great if someone who specializes in compression can explain this issue. This post was last edited by cthlj2007 on 2009-3-9 23:10 ]