Carbon dioxide stripping method, control of gas-liquid phase temperatures in the high-efficiency scrubber
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Hello everyone! I am an operator in a plant that produces 300,000 tons of urea, and we use a carbon dioxide stripping process. I have been driving the production machine for 1 year now, and there are still some issues that haven’t been resolved. Problems such as high ammonia consumption and a high urea content in the hydrolysis waste liquid. I mainly want to ask about high pressure issues at the moment; I believe that high-pressure conditions have a direct impact on ammonia consumption, and it is of utmost importance. I would like to ask: when there is a dehydrogenation reactor in use, what temperature should be maintained for the gas washer’s ambient temperature? Our team isn’t willing to lower the temperature; it is usually kept above 138 degrees. The batch production volume is 380 tons (about 6 tons of dust), with an ammonia consumption of 600, excluding the dust. Could high ammonia consumption be due to too much being carried away by the weather in the scrubber zone?
Without dehydrogenation, the high-wash unit should not absorb excessively. The gas phase temperature of the high-scourer is controlled by a high-pressure temperature regulator. Adjust the warm water inlet temperature to 130°C and the outlet temperature to 140°C according to the design values of the old unit; these values should not be reduced easily.
The control of the meteorological temperature in high-scourers is influenced by several factors: 1. System pressure； 2. Crystallization temperature ； 3. The gas-phase components are non-explosive. It is recommended to analyze the gas-phase components; if they are far from the explosion limit, considering appropriate cooling may be advisable.
I believe the main issue causing high ammonia consumption is abnormal operation of the low-pressure absorption tower and the low-temperature methanol cooler; your high gas washing temperature is relatively normal, so its impact is not significant.
First, what you need to do is figure out where this extra ammonia is going – whether it’s due to inaccurate measurement units or because it’s being carried away through some type of drainage. Once the cause is identified, it won’t be difficult to solve the problem
The gas phase temperature of the high-pressure washer should be reduced to around 115°C
Thank you all for your comments. Identifying the cause is key, but we haven’t actually found the main one. There’s another issue: our low-pressure system keeps experiencing overpressure; the relief lines connected to the meteorological system are hardly ever closed, and in many cases it’s necessary to use emergency relief valves. I think there are probably many things that can escape from this place, so I would like to ask: is fresh ammonia required for low pressure? Because there is an ammonia pipeline in this area, but it has never been used.
If the vent line has never been closed, it is recommended to use fresh ammonia for debugging.
How much ammonia is there at each vent point? If there is an excess, analyze the related pipelines until the cause of the low or high pressure is identified. You haven’t mentioned a single parameter – how can we help you analyze it then?
Hello, everyone! I’m here again. Since we have many questions, I’ve come to ask you for your advice once more. Our plant produces around 380 tons of urea per shift, with an ammonia consumption of over 590 tons. Since there aren’t many parameters available for analysis, I’ll try to provide as much detail as possible in the hope of getting some help. First, under what we consider normal high-pressure conditions, the low pressure can overpress at irregular intervals. For example, the high-pressure level is around 14.2 MPa, the liquid level in the stripping tower is about 70%, the temperature of the liquid exiting the tower is 167–168 degrees, the pressure in the high-pressure vessel is 1.88–1.91 MPa. The volume of the reflux liquid is around 9 cubic meters, with a temperature of 52–60 degrees. The low-pressure feed lines are fully open, which causes the low pressure to overpressurize from time to time; this must be maintained by activating the emergency venting system. I wonder why? Also, the urea content in our treated wastewater is very high, reaching over 6,000 PPM at its peak. The steam used for hydrolysis is saturated steam at 2.2 MPa (the steam pressure cannot be changed temporarily); the hydrolysis pressure is usually 1.8–1.9 MPa, and the temperature of the liquid product is around 200 degrees. The exhaust temperature is over 150 degrees.
Also, the urea content in our treated wastewater is very high, reaching over 6,000 PPM at its peak. The steam used for hydrolysis is saturated steam at 2.2 MPa (the steam pressure cannot be changed temporarily); the hydrolysis pressure is usually between 1.8 and 1.9 MPa, while the temperature of the output liquid is around 200 degrees. The exhaust temperature is over 150 degrees. Our hydrolysis tower is vertical, with 24 trays inside. The level gauge is located above the top tray, at a height of 60 centimeters. I would like to ask why our waste liquid is in this condition. Our class produces around 380 tons, and 33 cubic meters of ammonia are needed to keep things balanced. If it’s in such a state, a large amount of ammonia nitrogen must be discharged!