Discussion on the 5 New Urea Technologies Series, Part 2 (Japanese Modified C Method)
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On January 31, 2009, jindin312 reported on the news that “for the first time in the world, 5 technologies were successfully applied in a urea project” (see the Chemical Industry News of January 16). This news is certainly very encouraging for the nitrogen fertilizer industry; if this \"world-leading high-tech technology\" proves to work successfully in actual production, it can be regarded as a major advancement in urea technology. Regarding these 5 technologies, I believe that most users working with urea are not very familiar with them. Therefore, I suggest that we discuss each of these technologies in detail, based on the information we have, so that we can all gain a deeper understanding of these 5 technologies and work together to improve our skills. This post focuses on the second technology: what technologies might have been used, which could be the “Japanese modified C method”? We welcome everyone to participate actively, with extra rewards for in-depth discussions. This post was last edited by lxq700918 on 2009-2-11 17:52.]
Personal opinion: Adopt modified Condition C for the reaction: In the modified C method, the N/C ratio is high, while the H/C ratio is low; the reaction pressure and temperature are high, resulting in a high conversion rate, with less air required for corrosion prevention. The urea synthesis tower is a high-pressure vessel lined with titanium plates of 5 mm, 4 mm, and 3 mm thickness. It has an outer diameter of 2170 mm, a height of 29100 mm, and a volume of 100 m3. There are 76 leak detection holes on its top and bottom heads as well as on its outer walls. There are thermometer sleeves at the top and bottom, with three temperature measurement points on the outer wall. The synthesis tower must have sufficient mechanical strength to withstand high pressures and high temperatures. For the full-cycle process of ordinary solutions, the pressure in the synthesis tower is around 20 MPa, and the temperature is around 180–200°C. The synthesis pressure under the modified \"C\" method is as high as 25–26 MPa, with a temperature of 195–200°C. In the synthesis tower, the NH3/CO2 ratio is around 4:1. This is mainly because the synthesis tower operates in a state of self-heating equilibrium; the presence of an excess amount of ammonia not only facilitates the production of urea but also helps to reduce corrosion of the lining and the pipelines leading out of the tower. It also serves as a key means for regulating temperature. In the synthesis tower, the H2O/CO2 ratio is around 0.37, mainly to take into account the recovery of CO2 and the proper operation of the methanamide pump. In production, the amount of water fed into the tower should be minimized to facilitate urea synthesis and reduce corrosion of the tower lining as well as the occurrence of side reactions. In the future, better materials will be available and can be used in place of the current ones, such as the duplex steel currently in use. This post was last edited by Slip in with the wind on 2009-2-12 at 16:21.]
Advantage 2 of the modified C method: Granulation by crystallization results in low levels of biuret, allowing urea to be used by customers with low Bi requirements. There are several methods for the process of evaporating and concentrating a urea solution to obtain a molten state followed by granulation: 1. Evaporate and concentrate the urea solution to a molten state with a concentration of over 99.7%, and then granulate it – this method is known as evaporation granulation and is the most widely used approach at present. 2. The urea solution is evaporated and concentrated to 80%, after which urea is crystallized in a crystallizer at 40°C; this method is known as the crystallization method. 3. First, the urea solution is concentrated and crystallized; then the crystalline urea is dried and rapidly melted and granulated. This method is known as the crystallization granulation method. The Mitsui Toyo Press improved C method utilizes this approach, and the urea produced by this method has a biuret content of less than 0.3%, whereas the urea obtained through the evaporation granulation method has a biuret content ranging from 0.8% to 0.9%.
Please slip into the sea with the wind. When replying, make sure to do so in line with the theme of the original post – don’t answer off-topic! I think the high-pressure system of Japan’s improved C method has a high operating pressure, and I guess people aren’t interested in it. What is worth learning from this technology is its low-decomposition recycling method; I wonder if everyone shares this view. As for the specific technologies, I encourage everyone to actively participate in the discussions and share their valuable insights.
The medium and low-pressure decomposition system makes full use of hierarchical utilization of thermal energy, enabling the temperature in the condensation storage tank to be reduced to 60 degrees.
In the improved \"C\" process, the decomposition of unreacted substances in the molten urea can be carried out by methods such as reduced pressure, elevated temperature (in high-pressure decomposition systems), and gas stripping (in low-pressure decomposition using CO2 for stripping, with a gas separator using exhaust air for stripping). For low-pressure decomposition: The solution coming out of the bottom of the high-pressure decomposition tower is depressurized to 0.25 megapascals via a level control valve and then fed into the upper part of the low-pressure decomposition tower. In the upper part of this tower, sensible heat is used to vaporize some of the ammonia and carbon dioxide; thereafter, these gases enter a heat exchanger and a reboiler simultaneously before returning to the packing section at the lower part of the low-pressure decomposition tower, where they come into countercurrent contact with the rising carbon dioxide gas to facilitate gas lift, thereby further decomposing methammonium into ammonia and carbon dioxide.