How to control the hydrogen-nitrogen ratio in fixed-bed intermittent gas generation
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The method of controlling the H/N ratio is by adding or subtracting nitrogen during the blowing or up-and-down blowing stages. The operation of adding and subtracting nitrogen is achieved by adjusting the upper and lower nitrogen blowing time and the second blowing recovery time. In this way, the H/N ratio is controlled to be stable at a certain optimal point. However, due to the large number of equipment, long pipelines, and long routes between gas generation and synthesis, and chemical reaction devices installed in each link, control is difficult. The pure lag time is long, and it usually takes 20 to 50 minutes from gas creation to synthesis. System response time is slow. There are many interference factors, such as media, production conditions, conversion efficiency of conversion, compressor start and stop, total steam pressure, production load addition and subtraction, etc. H/N control has many interfering factors, so H/N ratio adjustment has always been a difficult problem. Generally, the parameters that can be used as control quantities for gas production are:: There is a time difference between the fluctuations in the four hydrogen values of desulfurized hydrogen, converted hydrogen, replenished hydrogen and circulating hydrogen. How to control the hydrogen-to-nitrogen ratio?
We adjust the hydrogen ratio by adding or subtracting the blowing air recovery time. As the poster said, there are many influencing factors, which is also a question we often discuss. To stabilize the hydrogen ratio, first of all, the entire production must be stable. Transformation, decarbonization, synthesis of vent volume, compressor start and stop, addition and subtraction. Then there is the influence of the gas production section, changes in ballast quality, and furnace temperature, which also have a great impact on hydrogen.
There are no major fluctuations in production, such as starting and stopping compressors, tripping, etc. It's very controllable. We connect the trend curves of desulfurized hydrogen, converted hydrogen, replenished hydrogen and circulating hydrogen to the gas generation control microcomputer screen, which can be easily controlled.
How to determine the lag time for hydrogen to nitrogen ratio adjustment
In daily production, the hydrogen content of the conversion gas is generally used as a reference, and the proportion of hydrogen content in the synthetic circulating gas is used as the basis for adjusting the hydrogen-to-nitrogen ratio. Specific method for adjusting hydrogen-to-nitrogen ratio: It is advisable to relatively fix the air stage time, up-blowing nitrogen adding time and nitrogen adding air adjustment valve, and use methods to increase or decrease the recovery time at the end of the blowing stage of each furnace to achieve effective adjustment of the hydrogen-to-nitrogen ratio. The theoretical basis and specific operations for adjusting the hydrogen-to-nitrogen ratio using the above methods: ①Extend the up-blowing nitrogen addition time to the maximum capacity (based on ensuring safety) to ensure that the decrease in the temperature of the gasification layer during the gas production stage is reduced and relatively stable. ②If excessive nitrogen addition occurs, appropriately reduce the opening of the nitrogen addition handwheel and reasonably adjust the amount of nitrogen addition air. ③Find out the appropriate opening of the nitrogen handwheel, choose a gas furnace combined with a fan, and set a more appropriate recovery time at the end of the blowing stage, generally between 2% and 4%. ④Simply increasing or decreasing the amount of nitrogen air blown up and down to adjust the hydrogen-to-nitrogen ratio is the opposite of the nitrogen recovery effect of using the blowing stage, so it is not recommended to be used. ⑤Using a microcomputer to create a program for self-adjusting the hydrogen-to-nitrogen ratio can also be applied to the above ideas for reasonable configuration. 1#shiguomiao
There happens to be a case where I would like to share the story of a high-pressure accident involving circulating hydrogen.: At about 10 o'clock in the morning during the day shift on the day of the year, Fan, an operator at the synthesis post, saw that the hydrogen in the synthesis cycle had increased to 61%, so he called the gas production post to add nitrogen and pressurized hydrogen. Zhang, the gas production operator, was afraid that too much nitrogen would cause high nitrogen levels in the later period, so he went as he had done in the past. * It is customary to stop adding nitrogen when the hydrogen in the semi-water gas drops to 38%. A few minutes later, the hydrogen in the semi-water gas rises to about 41%. Zhang adds nitrogen again, and so on. During this period, the synthesis operator and the dispatcher notified the gas production station many times to add nitrogen and pressurized hydrogen, and by 13 noon: In 30 minutes, the synthesized circulating hydrogen reached a high of 83%, the system pressure soared, the temperature of the catalyst layer dropped, the hot spot moved downward, the plane temperature difference increased, and the machine was forced to reduce the machine to vent the live production. until 15: It gradually returned to normal around 00. Cause of accident: 1. At that time, there were few startups, the system gas operation cycle was long, and the circulating hydrogen reaction was quite lagging. When the circulating hydrogen reaction was high, the front section, including the entire gas cabinet, was already full of high hydrogen gas. The gas generation operator Zhang only controlled based on desulfurized hydrogen, and lacked comprehensive judgment on the startup situation and the growth trend of circulating hydrogen. 2. The gas volume is small and the gas cabinet is high. When nitrogen is added, the gas cabinet is emptied and part of the effective gas is lost. The micromachinist did not stop the furnace in time to properly lower the gas cabinet and add nitrogen to pressurize the hydrogen, resulting in the feeling that the hydrogen pressure is getting higher and higher and cannot be suppressed. 3. After the desulfurization hydrogen meter was replaced in May, the operators lacked exploration and relied on previous experience, resulting in the actual hydrogen control being always on the high side.
As mentioned on the 6th floor, the circulating hydrogen should be stopped and reduced when it reaches 83. This is not possible here. The circulating hydrogen index is 54-60. If the synthesis is not well controlled, the amount will be reduced if it exceeds 60. If it is well controlled, it cannot exceed 63. In short, as long as it exceeds 60 or is lower than 54, the reduction is considered to be gas production. Therefore, the gas generator operator is under a lot of pressure when working, and the mental pressure of the previous shift was high. Regarding how to adjust the hydrogen to nitrogen ratio, I think we should start from the following aspects.； First of all, we should start from our own aspects, that is, we should have a good grasp of the furnace conditions, and judge the changes in coal quality based on the gas production. This requires more observation of the coal entering the furnace and the furnace conditions. In addition, when shutting down the furnace when the gas volume is sufficient, pay attention to the status of the stopped furnace, its nitrogen addition time, etc., to prevent temperament fluctuations caused by shutting down the furnace. , in short, do a good job in the details to prevent temperament fluctuations caused by gas production. Secondly, in normal production, you should master the effective time of the adjustment. The specific method can be as follows. If the adjustment is to make the hydrogen increase, you can reduce it more appropriately, pay attention to the short time, and then add it to what you think is normal. time, write down the specific time of the adjustment to see when it rises. It is the effective time of the adjustment. Sometimes, in order to be clear, we adopt the method of forcibly recovering or fetching water and gas. After once again mastering the effective time of the adjustment, we artificially divide it into 3-4 time periods. One-third of the time is used to increase the time for the hydrogen to increase, and one-third is used. Add a period of time for hydrogen to stabilize, and a third of the time period for hydrogen to drop. The initial adjustment can be larger, but it must be ensured that the pressure will rise and the pressure will fall. Repeat several times to lock in the target piecemeal. In short, use the fluctuation adjustment method to determine the correct recovery amount. Finally, work hard to learn on the premise of doing your own work well. * Understand the impact of the reduction in the rear section on the hydrogen-to-nitrogen ratio and adjust it as soon as possible. In addition, we should strengthen contact with the rear section and adjust in advance to ensure that the hydrogen-to-nitrogen ratio is within the target. To sum up, synthetic ammonia production is a continuous process. In order to stabilize the temperament, the carbon monoxide control volume and other indicators in the rear section must also be It must be stable. In addition, it should be noted that if the quantity is small and the reaction time is long, the time period must be divided into 5-10 parts for adjustment. This will prevent long-term impact on production and make it easy to grasp the specific recovery quantity. In short, only the cooperation of all aspects and the careful operation of the gas generator can the temperament be stabilized.