How to improve the conversion rate of the urea synthesis tower

1. It requires a relatively high operating temperature for the synthesis tower; for the aqueous solution full-circulation method, this temperature is 188 ℃±2 ℃； For synthesis towers lined with industrially pure titanium, the operating temperature of the synthesis tower can be appropriately increased ； For the CO2 stripping process, it is between 180 ℃ and 185 ℃. 2. Control the ammonia-to-carbon ratio (NH3/CO2 molecular ratio); the presence of excess ammonia can increase the conversion rate of urea synthesis. NH3/CO2 molecular ratio 2 3 4 Conversion rate % 40 54 67.5 For every increase of 0.2 in the NH3/CO2 ratio, the conversion rate increases by 1.0%–1.5%. However, the ammonia-to-carbon ratio should not exceed 4.5. For the full-circulation process in aqueous solution, the optimal ammonia-to-carbon ratio is 4.0 ； For the NH3 or CO2 stripping process, it is 3.0–4.0. 3. Minimize the water-to-carbon ratio (H2O/CO2 molecule ratio). For every 0.1% increase in the water-to-carbon ratio in the feed to the urea synthesis tower, the conversion rate of urea synthesis decreases by about 1%. Urea production always strives to minimize the water-to-carbon ratio. For the full-circulation aqueous solution method, the water-to-carbon ratio should be controlled at

The 60/104 large-scale fertilizer project of Ordos United Chemical Co., Ltd. employed Stamicarbon pool condenser/pool reactor technology to design a new high-pressure unit, thereby expanding the original two sets of plants based on Japan’s TEC (Toyo Engineering Corporation) full-circulation improved C process with a capacity of 1,500 tons per day to a capacity of 3,500 tons per day. Hello there! It seems you’re quite familiar with the technical features of our company! Thank you!

Minimize the water-to-carbon ratio (the ratio of H2O to CO2 molecules). For every 0.1% increase in the water-to-carbon ratio in the feed to the urea synthesis tower, the conversion rate of urea synthesis decreases by about 1%. Urea production always strives to minimize the water-to-carbon ratio. For the full-circulation aqueous solution method, the water-to-carbon ratio should be controlled at

Because I visited your company for a study tour, I gained a lot from it! Thank you for the correction. There was a decimal error in the H2O/CO2 ratio, and it has been fixed. This post was last edited by zhanghua on 2007-11-30 19:35]

Factors that affect the conversion rate include temperature, pressure, residence time, N/C, H/C, and the purity of the feed gas; these are controlled through operational adjustments. Furthermore, in terms of technical upgrades, consideration should be given to modifying the trays in the synthesis tower as well as the medium and low pressure absorption systems, in order to improve the efficiency of the material reactions and reduce the amount of water carried by the subsequent systems.

Does a high conversion rate necessarily lead to more urea production? I don’t think so; under different loads, more attention should be paid to the relationship between \"capital utilization and turnover rate.\" Especially when choosing H/C, it’s important to consider which is more cost-effective: the maximum turnover rate of methylamine or the utilization rate of CO2. Of course, this doesn’t mean that conversion rate should be ignored.

In terms of the stripping process, it is one-sided to pursue excessively high conversion rates; the stripping efficiency must also be taken into account, as the composition data from the high-pressure system represents the ultimate criterion for optimizing the operation of the plant. This post was last edited by Xu Xu on 2007-11-30 23:39]

Using high-efficiency trays seems like a good idea!

8.1 Parallel Method The first facility to adopt the parallel method and achieve good results was the Luxi Fertilizer Plant. In this approach, NH3, CO2, and ammonium methanate are each fed separately into two urea synthesis towers; the products resulting from synthesis then enter a medium-pressure decomposition system together. The synthesis towers utilized innovative tray designs. Although this approach was adopted in 1995, it was relatively conservative in nature, yet both urea synthesis towers achieved high conversion rates. Thereafter, Ningyang Fertilizer Plant operated two towers of 20m3 and 23m3 in parallel, controlling the material volume at a production intensity of 13; at NH3/CO2=4.1 and H2O/CO2=0.65, the conversion rate of both towers was 66.5%. 8.2 Combined method: This method was proposed by both Casali in Switzerland and the Fertilizer Center. Following the principles of simplicity, convenience, minimal modifications, and low investment, we adopt a two-tower operation system; the high-pressure section remains unchanged, while only the medium-pressure system is modified, thereby achieving the goals of increased production and energy savings. During operation with two towers, ammonium methylate does not enter the first synthesis tower; the ratio of NH3/CO2 is 3.8, and the ratio of H2O/CO2 is around 0. In this case, the equilibrium conversion rate is 80%, while the actual conversion rate reaches 75.2%. The second synthesis tower receives NH3, CO2, and ammonium methylate, with a production load of 40%; the feed ratio of NH3/CO2 is 4.4, and the ratio of H2O/CO2 is 1.2–1.3. The equilibrium conversion rate in this case is 66.8%, and the actual conversion rate can reach 63.5%. The overall ratio of NH3/CO2 for both towers combined is 4.05, and the ratio of H2O/CO2 is 0.55; thus, the overall conversion rate is 70.5%. 8.3 Series method: Recent in-depth studies suggest that this method does not involve all the materials entering the first synthesis tower, with the reaction products emerging from the second synthesis tower. Although it is more complex to operate, it is also a method that allows for a higher conversion rate; moreover, it can achieve near-isothermal operation similar to the UTI process

A CO2 compression dehydrogenation unit is used to reduce the amount of inert gas entering the tower, thereby increasing the purity of carbon dioxide as much as possible. By taking into account the overall condition of the equipment, appropriate operating parameters for this system are established, the system load is determined, and the conversion rate of the urea synthesis tower is improved.

Actually, many of you upstairs have already discussed in great detail the ways to improve the conversion rate of the synthesis tower, and those discussions were quite comprehensive. I would like to briefly share my own thoughts here. In the entire system, there is one factor that cannot be ignored, and that is the professional competence of the staff. For example, if there are four operation shifts, and the professional competence of the chief operators in three of these shifts is high, while that of the chief operator in one shift is slightly lower, then during routine adjustments, it is easy for the shift with lower competence to make slower adjustments and use larger amplitudes, which in turn affects the stable operation of the entire system.

A hydrogen peroxide anti-corrosion device is added to the urea high-pressure system, which reduces the amount of anti-corrosion air introduced into the CO2 gas and increases the purity of CO2, thereby being highly beneficial for the conversion rate in the urea synthesis tower.

To increase the conversion rate of urea synthesis towers, there is another technique available: the use of a dual-phase stainless steel recently developed by Sandvik for lining urea synthesis towers or for manufacturing pipes in high-pressure systems (this material is already being used by customers in China). It is said that by not adding anti-corrosion air to the CO2, its purity can be increased from around 96% to over 98.5%, which will certainly help to raise the conversion rate of urea synthesis towers. Unfortunately, this technology is monopolized by foreign countries and has not yet been widely used in China. However, it’s likely not much longer before that happens.

Regarding the material residence time, since a longer residence time leads to a higher conversion rate but a lower production intensity (output), it is not appropriate to focus solely on the conversion rate! A optimal balance should be sought between conversion rate and production intensity to achieve the highest economic benefits! Even if the conversion rate is slightly lower, it is more valuable as long as the cycling and desorption & hydrolysis processes can handle it effectively, thereby increasing production.

For the CO2 stripping method, it is quite important to control the N/C and H/C ratios of the system for achieving high conversion rates.

As mentioned on floor 15, as the system load continues to increase, the system’s conversion rate will definitely decrease. The extent of this decrease is closely related to the system’s ability to adjust itself. When increasing the load on the system, experienced operators can do so in just one step, while operators with less technical skill may also be able to increase the load in one step, but the system’s conversion rate in such cases tends to be lower. This necessitates further fine-tuning of the system by those in charge of the process.

Here, we have three towers connected in parallel; two sub-towers are used, and the conversion rate is quite good

Add hydrogen peroxide for preservation, reduce preservative air, lower the vapor pressure, and increase the conversion rate.

It is feasible to use this material for new installations, but it is likely impossible to replace the high-pressure equipment and pipelines in existing installations with this material.

The best way is to control the N/C, H/C, inert gas content, and residence time within the system. But does controlling the high-pressure coil alone to improve the conversion rate have an impact on the overall energy consumption of the entire system? In my opinion, optimizing the operation of other sections can also increase the CO2 conversion rate.