What is the cycle pressure control value (gauge pressure)? What should be the outlet temperature of the absorption tower?
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Our facility was among the first to convert from carbon ammonium to the production of 40,000 tons per year of urea of lower grade. After numerous upgrades, including changes from 40,000 tons per year to 60,000 tons, then to 100,000 tons, and finally to 130,000 tons per year, the operational parameters have continued to use those set for the initial 40,000 tons per year production level, despite the significant changes in production capacity and consumption levels. Most of the equipment has also been replaced once or even several times; for example, the current synthesis tower has a capacity of 43 cubic meters, and the four ammonia coolers provide sufficient cooling capacity to meet the production requirements. Medium-pressure decomposition is carried out using a combination of pre-separation, auto-stripping, and a single separation tower, along with flash heaters. The framework follows the general design for small urea plants developed by the Fourth Research Institute in 1986, with a length of 28 meters. However, the diameter of the first absorption tower being 1100 centimeters poses a serious constraint on production. I would like to ask the teachers here: what is the pressure level for one cycle of control (gauge pressure)? What should be the outlet temperature of the absorption tower?
Regardless of the scale of the device, as long as it uses the same process, its specifications remain the same.
I fully agree with the opinion from the second floor. However, I would like to remind you here: the original poster mentioned that \"most of the equipment has been replaced almost once or even several times\"; I wonder if the corresponding pipes have also been replaced? Also, what is the design pressure of the replaced equipment? If production increases significantly while the corresponding pipelines remain unchanged, the resistance between the primary tower and the ammonia cooler will definitely increase. In actual operation, if the original operating pressure (the original medium-pressure pressure measurement point is generally located on the liquid ammonia buffer tank) remains unchanged, the actual pressure inside the devices located further upstream, such as the pre-separator, the first fractionation column, and the first heating unit, may exceed the design pressure. This matter requires great attention. Regarding the outlet gas temperature parameter of a absorption tower, it must remain unchanged; otherwise, overheating will lead to an excessive level of CO2 in the outlet gas.
The cyclic pressure is maintained between 1.7 and 1.75 MPa, and the outlet gas temperature of the absorption tower is kept below 50 degrees; no matter how the equipment is replaced, the process parameters must remain unchanged.
The pressure is below 16–16.7 MPa. I think the threshold of less than 50 degrees mentioned on the 4th floor might be too high; here, CO2 levels start to rise at 48 degrees, so we usually keep the temperature below 46 degrees
After the actual capacity increase, if the pressure in one section is maintained at 1.7 MPa and the temperature of the gas exiting one absorption tower reaches 48 degrees, then after operating for a certain period of time (up to 8 hours), it will be difficult to operate the absorption tower; the exit gas will have an excessive temperature, and the temperature in the upper part of the purification section will be high. At this point, both synthesis and decomposition are working normally; please help analyze the cause again. And why is the ammonia outlet at the inlet of the inert gas scrubber higher than the outlet of the gas phase (tail gas scrubber)? What should be the diameter of the ammonia solution pipeline (130,000 tons per year) from the inerting tank to the absorption tower? What is the diameter of the ammonia return pipe at the top?