Discussion on improving the carbon dioxide conversion rate in urea synthesis towers

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1 Overview Theoretically, the synthesis of urea occurs in two steps: first, liquid ammonia reacts with carbon dioxide to form liquid ammonium carbamate, abbreviated as AMM. The reaction equation is as follows: 2NH3(l) + CO2(g) → NH4COONH2(l) ⑴ Subsequently, ammonium carbamate undergoes dehydration to produce urea, with the reaction equation being: NH4COONH2(l) → CO(NH2)2(l) + H2O(l) ⑵ It is well known that the first step, namely the formation of AMM, is easy to carry out; the required reaction conditions are relatively mild, and AMM can be formed from ammonia and carbon dioxide even at normal temperature and pressure. Since methylammonium crystals cannot be dehydrated directly to produce urea, this process can only take place in a liquid phase. The melting point of methylammonium is around 156°C; to remain in a liquid state, certain temperature and pressure conditions are necessary. Therefore, the aforementioned second dehydration reaction must take place in a synthesis tower under high temperature and pressure (180–230°C, 13–25 MPa) in order to proceed toward the formation of urea; sufficient residence time is required to achieve an equilibrium conversion rate. If efficiency is improved merely by extending the residence time of the materials in the synthesis tower, it will inevitably affect the production capacity of the synthesis tower. In existing urea synthesis processes, the following methods are commonly employed to achieve a high carbon dioxide conversion rate. (1) Various internal components are added inside the synthesis tower to enhance the mixing of gas and liquid, thereby minimizing the time and reaction space required for the first reaction mentioned above, while increasing the time and space available for the second reaction. At the same time, the synthesis tower is divided into multiple small sections using these internal components to prevent back-mixing of the materials. For example, Chinese patents such as CN2415033Y, CN2463044Y, CN1157581A, CN2522419Y, CN2675672Y, CN2698786Y, etc., utilize this principle. (2) Improve the conditions under which the material enters the synthesis tower, so that the material is in conditions as favorable as possible for urea production within the tower. For example: Chinese patents CN1224635, CN1157581, etc. The various process and equipment improvements mentioned above, despite differing perspectives and the fact that some process methods draw on one another, share one common feature: all recognize the need to enhance diffusion between the reactants (liquid-liquid, liquid-gas) during the reaction process to ensure thorough mixing. Additionally, it is important to maintain uniformity in concentration, density, temperature, and flow rate across the entire cross-section of the reactor. This not only helps to maintain a proper reaction rate but also prevents separation between the gas and liquid phases, thereby reducing backmixing of materials and ultimately ensuring higher reaction efficiency, that is, a higher conversion rate of carbon dioxide. In fact, when synthesizing ammonium carbamate under high pressure, the issue of liquid-gas mixing has always been a focal point of attention and has also served as a bottleneck hindering the development of this technology. To achieve a higher urea synthesis rate, it is necessary to increase the reaction pressure, extend the process duration, and add high-pressure equipment in order to provide more opportunities and time for the reactants to come into contact under high pressure; all of this comes at the cost of increased investment and higher operating and maintenance expenses. Adding various internal components to the synthesis tower to enhance the mixing intensity and speed of the materials, prevent gas-liquid separation, and avoid back-mixing of the products, as well as ensuring a uniform feed of gas and liquid, all play a role in increasing the urea synthesis rate (i.e., the conversion rate of carbon dioxide). The purpose of various improvement measures in the urea synthesis process is mainly to increase the conversion rate of CO2, a consensus already reached by many technical professionals. Increasing the CO2 conversion rate allows more urea to be produced as the reactants pass through the synthesis tower, thereby reducing the amount of unreacted materials that need to be recycled and achieving higher production efficiency as well as energy savings. Admittedly, there are many factors that affect the CO2 conversion rate. Theoretically, they can be mainly categorized as follows: (1) operating temperature, (2) operating pressure, (3) ammonia-to-carbon ratio (NH3/CO2), (4) water-to-carbon ratio (H2O/CO2), (5) residence time of the reactants, and (6) purity of the reactants. In actual production processes, all of these influencing factors rely on thorough mixing of the materials; without good mixing of the various materials involved in the reaction, the effect of any of these factors cannot be realized. This article discusses the issue of mixing various reactants, which is the most significant factor affecting the urea synthesis rate, namely the conversion rate of carbon dioxide. It aims to draw the attention of experts, scholars, and technical professionals in the industry, so that they can work together to find solutions to improve the urea synthesis rate, or in other words, the conversion rate of carbon dioxide, by addressing the root causes of this problem. 2 Analysis of problems and improvements in the urea synthesis process. The main factors that affect the urea synthesis rate, namely the carbon dioxide conversion rate, are described in detail in various studies. Due to the interference among various influencing factors and the constraints imposed by operating conditions, the theoretical synthetic process conditions cannot be fully realized; in practice, the process parameters are determined after taking all these influencing factors into account. In actual operation, the determination of various operational parameters takes into account factors such as facilitating long-term operation of the production system, ensuring safety, and minimizing operating costs. After the process operation parameters were determined, it became increasingly clear that the reaction processes within the urea synthesis tower (not only the reaction conditions) have a significant impact on the theoretical carbon dioxide conversion rate; this is the underlying reason for the emergence of numerous patented products. Just in terms of enhancing the mixing of gas and liquid, minimizing the time and space required for the ammonium methane synthesis reaction, increasing the time and space available for the dehydration of ammonium methane, preventing back-mixing of liquid and gas, and stopping reversible reactions from occurring, many scientists and engineers have contributed their intelligence and creativity by designing various types of reactor internals and feeding methods, which have indeed played a role in improving the conversion rate of carbon dioxide. However, these internal components of the synthesis towers only improve the already flawed synthesis conditions, without addressing the problem at its root. Here, we conduct a limited analysis based on the working principle of the tower internals. I hope to receive criticism and corrections from industry experts regarding the mistakes. According to the author’s personal understanding, the internals of a synthesis tower can basically be divided into the following three types. ⑴ Baffle type. Specifically, it can be further divided into baffle type and baffle tube type. ⑵ Hood type. They are divided into circular and straight-edge hood types. ⑶ Tube bundle type. The WWS type is a typical representative. The baffle-type tower internals (sometimes also referred to as trays or plates) work by placing these pre-made components within the cross-section of the synthesis tower; this forces the material that would otherwise flow freely to change its path as it passes through these internals. The flow velocity increases as the material passes through the various nozzles provided on these internals, thereby increasing turbulence and enhancing gas-liquid mixing. The working principle of the hood-type internal tray is similar to that of the baffle-type internal tray: the gas-liquid mixture passing through the hood causes more intense disturbances than those created by baffles, and at the same time the hood makes these disturbances more uniform, resulting in a finer division of the tower’s cross-section. It can be said that it achieves better results compared to baffle-type internal trays. The tube bundle tower internals first cause the gas-liquid mixture inside the tower to pass through the rising main pipe and enter the upper mixing chamber, then through the distributor, and finally through the tube bundle to reach the lower mixing chamber. By forcing the mixture to undergo a return process within the synthesis tower, more mixing opportunities are created, which improves mass transfer. Meanwhile, heat transfer also occurs during this return of the material, which helps to reduce the temperature difference inside the tower. This is beneficial for the endothermic dehydration reaction of methylammonium, and it shares certain similarities with the process used in the UTI process. At the same time, another very important point is that, through the use of baffles, the cross-section of the synthesis tower is divided into many small sections; within each of these sections, mixing and reaction occur in a much more uniform and intense manner compared to the entire cross-section of the tower. In principle, the various internal components mentioned above are added to the synthesis tower to transform it from a hollow device into one equipped with internal components. The underlying reason for this is that the way in which the materials enter the synthesis tower results in uneven mixing. The synthesis reaction of methylammonium is theoretically fast, but in practice this is not the case. Adding internal components to the tower is intended to enhance the mixing of gas and liquid, thereby accelerating the completion of the methammonium synthesis reaction and ensuring the necessary time and space for the dehydration of methammonium to produce urea. In the actual operation of the urea synthesis tower, there is another very important issue: due to the limitations of the feeding method, various reaction materials and products cannot remain uniformly distributed across the cross-section of the tower. Although the various internal components of the tower can exert a certain perturbing effect locally, allowing for mixing of the gas and liquid materials in those areas, the distribution remains uneven across the entire cross-section of the tower. As a result, the materials involved in the reaction can only achieve true mixing after passing through multiple trays, at a certain height within the tower. In other words, the synthesis of ammonium carbamate can be essentially completed only at a certain height. After various trays are installed, the synthesis tower can be considered to consist of multiple chambers separated from one another by the trays. The reactants move gradually from bottom to top through each tray; a gas-liquid two-phase system exists in each tray. At the trays, the gas passes through the liquid layer in the form of bubbles, which increases the opportunity for contact between the two phases and thus accelerates the overall progress of the reaction. The tray largely prevents the fluid from the previous chamber from flowing back into the next chamber, thus avoiding mixing of materials and improving reaction efficiency. The greater the number of trays, the more the fluid flow within the tower approaches an ideal plug flow (piston flow). This is the basic starting point for various tray designs, and it is also the fundamental reason why multiple layers of trays are installed. The internals of a packed tower possess the functions mentioned above; moreover, due to the presence of the packing, the cross-section of the tower is divided into separate sections. With the presence of a distributor, mixing also takes place within the tower’s cross-section, which results in better performance. Even so, the synthesis reaction of methylammonium can be truly completed only at a certain height; the fundamental reason is that across the entire cross-section of the tower (at a certain height from the bottom), it is still not possible to achieve complete uniformity in terms of material concentration, density, temperature, and velocity. Therefore, the time and space available for the dehydration of methylammonium to produce urea still need to be reduced to some extent; there is still a certain gap between the carbon dioxide conversion rate in the entire urea synthesis tower and the theoretically designed value. The reaction material entering the synthesis tower, due to the lack of adequate mixing measures, does not distribute evenly across the cross-section of the tower; as a result, the distribution of the products formed is also uneven. In other words, at any cross-section of the tower, the concentration, temperature, density, and velocity of the mixture are inconsistent (at least at a certain height above the bottom of the tower). Comparing the various current urea production processes, in terms of CO2 conversion rate alone, the traditional aqueous solution full-circulation method represents a low-level process route. Of course, the aqueous solution full-circulation method requires only one high-pressure unit, namely the urea synthesis tower, making it relatively cost-effective in terms of equipment investment. The most manufacturers using this process are currently operating in China; according to incomplete statistics, there are around 200 such companies. Technological upgrades to this process can be said to bring good economic and social benefits. Based on existing literature and still focusing on the urea production process using the full aqueous circulation method, this paper further explores and discusses the issue of carbon dioxide conversion efficiency in urea synthesis towers, with the aim of making contributions to this field and prompting further reflection among industry experts through personal insights. 3 Fundamental ways to improve the efficiency of the urea synthesis tower. The above provides a limited analysis of the factors affecting the urea synthesis rate; the preliminary conclusion is that, across the cross-section of the tower, the uniformity of the concentration, temperature, density, and velocity of the mixture (including reactants and products) is the most important factor influencing the urea synthesis rate (i.e., the conversion rate of carbon dioxide), and it also represents the bottleneck hindering an increase in this conversion rate. On this point, technical professionals and industry experts have long reached a consensus; the design and improvement of various tower internals are carried out in line with these principles, yet the results achieved remain limited. 　The three streams that enter the synthesis tower – liquid ammonia, gaseous carbon dioxide, and stage 1 ammonium methoxide – are fed into the tower separately using their own conveying equipment. Their flow rates are very low; once inside the tower, the flow rate becomes even lower due to the increased cross-sectional area, and this is determined by the reaction residence time. Typically, for a synthesis tower with a height of around 30 m, the reaction material needs to flow for 45–60 minutes. This determines the mixing of the materials entering the synthesis tower; the dynamic mixing caused by velocity and velocity differences is minimal, with mixing primarily relying on diffusion between molecules. It is easy to imagine that without trays and various internal components of the tower, the mixing of the three streams through molecular diffusion would be extremely slow; at the high levels in the lower part of the synthesis tower, these three streams would remain separate, and the synthesis reaction of methylammonium might not be completed even by the time the mixture reaches the exit of the tower. The literature states that when the production intensity of the synthesis tower reaches a certain level, the carbon dioxide conversion rate increases as production intensity rises. This is because an increased flow rate of the material entering the tower leads to stronger mass diffusion, thereby enhancing mixing. Additionally, the increased overall flow rate within the tower helps to reduce backmixing of the materials formed in the upper part of the tower, thus minimizing the occurrence of reversible reactions. Theoretically, a synthesis tower could be a hollow container, but in practice this is impossible, as can be concluded from the analysis in this article. However, from a process perspective, the synthesis tower can also be designed as a horizontal structure, which is actually impossible. If designed horizontally, the three streams of material entering the synthesis tower will quickly separate into layers, with the gaseous phase moving to the upper part and the liquid phase to the lower part, making it almost impossible to carry out the synthesis reaction. Even if the interior of the synthesis tower is divided into detailed sections, it won’t make any difference. We base this conclusion on the following facts. In the patented new energy-saving and yield-increasing process for full-circulation urea high-pressure cycles developed by Global Engineering Company, the key equipment, the \"high-pressure ammonium methylate condenser\" (whose operating principle is similar to that of a synthesis tower), was originally designed with a horizontal structure. Theoretically, when gaseous carbon dioxide and liquid ammonia enter the ammonium methanate condenser, they undergo a exothermic reaction to rapidly form ammonium carbamate, generating steam as a by-product thanks to the shell-and-tube structure. During the first engineering verification run at a factory in Shandong in 1999, the mixing requirements between carbon dioxide gas and liquid ammonia were not taken into sufficient account. Coupled with the horizontal design of the high-pressure ammonium methanate condenser, gravity and density caused the gas and liquid to flow separately after entering the condenser, preventing uniform mixing and thus preventing the reaction from taking place. As a result, the ammonium methanate condenser was unable to produce steam as a by-product. Despite a series of measures taken regarding feed parameters and feeding methods, the desired results were not achieved. The successful completion of this process relied on a mixer provided by us, which was used to effectively mix the carbon dioxide gas and liquid ammonia entering the ammonium methoxide condenser through a special atomization device, thereby enabling the condenser to function properly. In subsequent project implementations, Global Engineering Company realized that the mixing of carbon dioxide gas and liquid ammonia is a prerequisite for the operation of the ammonium methoxide condenser; therefore, it designed the condenser in a vertical format and installed a swirl device at the material inlet at the bottom, thereby enabling effective distribution and mixing of the gas and liquid flowing into the tubes of the condenser, thus realizing the initial concept. In short, the key to improving the efficiency of a synthesis tower lies in ensuring good mixing of the gaseous and liquid materials within it. If conditions permit, from the perspective of the structure of the urea synthesis tower, physical stirring to mix gas and liquid seems like a good idea, but in reality this is not feasible. Installing swirl vanes at the feed inlet at the bottom of the tower had some effect, but it was also very limited. Here, we would like to emphasize an important point: regarding the issue of gas-liquid mixing, rather than introducing gas into the liquid medium in the form of bubbles or bringing the liquid into contact with a gaseous medium after it has formed into a film, it is best to atomize the liquid and suspend it in the gaseous medium. This approach ensures uniform mixing on one hand, and maximizes the contact area between the gas and the liquid, thereby achieving the highest mixing intensity and depth, and thus the best mixing results. It can be said that suspending a liquid in a gas medium after atomizing it to achieve gas-liquid mixing is not a new idea, but under normal circumstances, certain conditions are required for this to happen. Firstly, to atomize a liquid, an atomization space is required; that is, after the liquid is atomized, the droplets need to travel a certain distance before they can mix with the gas medium. Conventional atomization methods also require a certain atomization angle, which in turn demands even more space for atomization. Secondly, under high pressure, due to the high density of the gas, the atomized droplets find it difficult to move through the gas medium, resulting in poor mixing. The most important point is that conventional atomization methods use various nozzles to atomize liquids; therefore, to achieve a certain level of atomization quality, the atomization capability of the nozzles is greatly limited. This is the fundamental reason why, in applications such as urea synthesis towers, which feature high pressure, large flow rates, and limited space, no one has ever resorted to atomizing liquid media to achieve mixing. Due to the various reasons mentioned above, the common approach taken at present for mixing the materials inside the urea synthesis tower is to find solutions related to the internal components of the tower; of course, this does not address the problem at its root. It cannot be said that the vast majority of engineering and technical personnel are unaware of the problems identified in the above analysis; they simply lack effective solutions for handling the mixing of liquid and gas under conditions of high pressure, limited space, and high flow rates. The literature states: “The function of the tray is to improve mixing and reduce backmixing.” ……The author believes that a good way to increase the carbon dioxide conversion rate is to complete the reaction between CO2 and ammonia to form methylammonium before the materials enter the urea synthesis tower; after entering the tower, only the reaction of dehydrating methylammonium to produce urea takes place. This approach allows for an increased residence time within the synthesis tower necessary for urea production. ……Add a mixer before the urea synthesis tower,... if this can increase the carbon dioxide conversion rate by 3%–5%......” The literature does not provide clear ideas or solutions on how to design a “mixer”; the main purpose of this paper is to discuss this issue and offer forward-looking answers. The literature has provided a relatively detailed analysis of the operating process of urea synthesis towers, and it also describes the effectiveness of the high-pressure mixer invented by the author. The results of verification experiments conducted at a urea plant in Shandong show that by mixing the CO2 and ammonia (excluding ammonium) before feeding them into the synthesis tower, the conversion rate of CO2 increased from 63%–64% to around 67%, with a maximum value of 67.7%. The results of verification experiments at another urea plant in Shandong showed that: \"By mixing only a portion of CO2 with ammonia (excluding ammonium), and feeding this mixture into the synthesis tower, the conversion rate of CO2 increased by about 3%.\" Achieving such a significant increase in CO2 conversion rate is difficult to accomplish with other methods; moreover, the fact that such an improvement can still be achieved even when tower internals are already in place further underscores the advantages of installing a mixer. Below, following the approach outlined in the literature, we introduce the principle and implementation methods for using a \"high-pressure mixer\" to improve the carbon dioxide conversion rate in urea synthesis towers. As shown in Figure 1, we installed a \"high-pressure liquid-gas tubular rapid mixing reactor\" (invention patent No. 200610065020.2) before the urea synthesis tower. This reactor enables the three streams of material entering the urea synthesis tower – liquid ammonia, gaseous carbon dioxide, and liquid methylamine – to be fully mixed through a special atomization device. Once a uniform liquid-gas mixture is formed, it enters the synthesis tower via the three existing feed pipes in the tower. This will achieve the following effects. Figure 1: Flow diagram of the urea synthesis tower equipped with a mixer. (1) By using a high-pressure liquid-gas type rapid mixing reactor, it is possible to atomize liquid ammonia and ammonium methylate at high pressure (20 MPa) into mist droplets with sizes of 100–250 μm (rather than liquid droplets). These mist droplets are then mixed with gaseous carbon dioxide to form a homogeneous two-phase flow, thereby ensuring that the three materials entering the urea synthesis tower – gaseous carbon dioxide, liquid ammonia, and liquid ammonium methylate – become a completely uniform liquid-gas mixture, thus solving the mixing problem within the tower. ⑵ Since the three materials entering the urea synthesis tower form a perfectly homogeneous liquid-gas mixture, and the materials in the three feed pipes are identical, the flow velocity, concentration, temperature, and overall density of all types of materials (including reactants, intermediates, and products) at any cross-section within the tower will be very uniform. The distribution of gas and liquid is also even, allowing for a true plug flow regime; this eliminates the problem of backmixing caused by differences in material density and temperature. As a result, the requirements for the components inside the tower become less stringent. ⑶ In this scheme, there is essentially no more mixing of materials or formation of methylammonium within the urea synthesis tower; thus, no space or time is required for such mixing and synthesis reactions in the tower. It becomes a true synthesis tower, and its sole function is to convert ammonium carbamate into urea through dehydration. This ensures that there is sufficient time and space for the dehydration of ammonium carbamate to produce urea. This process of dehydrating methylammonium to produce urea **extends the reaction time**, improves the efficiency of the synthesis tower, and ultimately increases the conversion rate of carbon dioxide (theoretically by 3%–6%, or even more, depending on the existing operating conditions of the urea synthesis tower), thereby achieving energy savings and increased production. ⑷ By using a high-pressure liquid-gas tubular rapid mixing reactor, it is possible to reduce the number of feed inlets for the newly designed urea synthesis tower from three to one, thereby solving the problem of providing inlets at the bottom of the urea synthesis tower (especially in smaller towers) and reducing the manufacturing, maintenance, and operating costs of such towers. ⑸ With this approach, the problem of liquid-gas mixing under high pressure is completely resolved. If a suitable urea synthesis tower can be designed in accordance with the conditions for urea synthesis, it will be possible to simplify some of the processes currently in use, reduce the number of high-pressure devices, save costs associated with investment, and lower the maintenance and operating expenses for urea synthesis, all while maintaining the same rate of carbon dioxide conversion. ⑹ With this approach, the mixing of reaction materials and the reaction itself can be concentrated in this key device, reducing the number of parameters that need to be adjusted as well as the number of steps involved. This makes it easier to achieve system equilibrium and stability, facilitating operation and ensuring long-term continuous production. ⑺ The atomization and mixing effects of the special atomization device are not affected by gravity; therefore, there are no requirements regarding its installation orientation, and it can be used in both new systems and those that have been upgraded. Since the high-pressure liquid-gas tubular rapid mixing reactor converts the three materials entering the urea synthesis tower – gaseous carbon dioxide, liquid ammonia, and liquid ammonium – into a perfectly homogeneous liquid-gas mixture, the reaction between carbon dioxide and liquid ammonia to form ammonium occurs very rapidly, releasing a large amount of heat. This ensures a high temperature at the bottom of the urea synthesis tower from the very beginning, thereby creating favorable conditions for the endothermic reaction of ammonium dehydration to produce urea. This is also a prerequisite for ensuring a high urea production rate, and in fact it is the fundamental condition for increasing the conversion rate of carbon dioxide. At the same time, the increase in the bottom temperature of the urea synthesis tower also facilitates leak detection at the bottom of the tower. In the traditional aqueous solution full-circulation process, the temperature of the materials in the three feed pipes at the bottom of the urea tower is low: carbon dioxide is at 100–120°C, liquid ammonia is around 50°C, and ammonium methanate solution is about 90°C. The temperature in the bottom of the tower and in the first section below it is not high; if there are leaks in the linings of these areas, solid crystals will form, which can cause blockages in the leak detection system. Therefore, steam is used for leak detection. The literature proposes installing a first reactor at the inlet of the urea synthesis tower, using the synthesis tower itself as the second reactor, in order to increase the temperature of the material entering the tower; this allows leakage detection at the bottom of the tower to be carried out without the need to introduce steam. Of course, the literature presents this view only in terms of leak detection, without discussing other functions of the first reactor. 4 Conclusions and Discussion on Issues The fundamental principle of the \"high-pressure liquid-gas tubular rapid mixing reactor\" mentioned earlier is to use a special atomization device to address the problem of liquid atomization under conditions of high pressure, limited space, and high flow rates. This allows the liquid to be atomized into droplets with sizes of 100–250 μm within a very short distance (20–50 mm), turning it into droplets rather than liquid particles. These droplets then mix with the gas to form a homogeneous two-phase flow, which is the basis for improving the carbon dioxide conversion rate in urea synthesis towers. In the tubular reactor provided for Dalian \"Dahua Group Co., Ltd.\" for **, this approach is adopted in the special atomization device for liquid nitric acid that we designed, in order to ensure good mixing between liquid nitric acid and gaseous ammonia. Figure 2 shows the results of the laboratory simulation experiments using water as the medium with a special atomization device (the atomization pressure required was 0.4 MPa). http://www.yf116.cn/jishuwang/upload/070227925452048.jpg Figure 2: Experimental results of the special atomization device for tubular reactors at Dahuaxia Group. According to the experimental results, the medium to be atomized is completely atomized at a distance of about 20–30 mm from the end face of the special atomization device; moreover, the area where atomization occurs is almost equal in size to the end face of this device. The water after atomization is no longer in the form of droplets but rather in the form of mist. It is conceivable how complete and uniform the mixture of liquid ammonia, liquid methylamine, and gaseous carbon dioxide will be after these substances are atomized using special atomization devices and then sprayed into the gas phase. Due to such uniform mixing, the synthesis reaction between liquid ammonia and carbon dioxide will be completed very quickly; as a result, the mixture that leaves the mixer and enters the urea synthesis tower will have a much higher degree of uniformity than that achieved by using various tower internals and mixers. In such a homogeneous mixture, the concentrations of various reactants, intermediates, and products are extremely uniform, resulting in a completely homogeneous flow – what is commonly referred to as plug flow. Under such flow conditions, if the effects of the boundary layer caused by the walls of the reactor are ignored, the concentration, density, temperature, and velocity at any point across the cross-section of the reactor will be exactly the same. It is only under these conditions that the reaction processes within the reactor are truly determined by factors such as operating pressure, operating temperature, the ammonia-to-carbon ratio, and the water-to-carbon ratio. At the same time, within the synthesis tower, there is no longer a need to allocate space and time for mixing the reactants and carrying out the reaction. As a result, the process of dehydrating methylammonium to produce urea is **extended**, and the increased temperature at the bottom of the tower creates favorable conditions for this dehydration process. This, in turn, lays the foundation for improving the reaction efficiency of the synthesis tower, that is, the conversion rate of carbon dioxide. This is the conclusion of this article. So far, it’s not the case that what has been discussed above constitutes a perfect solution without any issues; it would be irresponsible to draw such conclusions at this point. From previous experiments, we also identified some problems; the literature has provided detailed analyses of these issues, and discussions on them have also been carried out. Regarding the existing problems, we propose the following solutions, with the aim of implementing them in future engineering applications and achieving the desired results. ⑴ Regarding the issue of high flow rates (at that time, we fed a mixture of carbon dioxide and liquid ammonia into the synthesis tower through the carbon dioxide inlet, while leaving the liquid ammonia inlet unused, which resulted in excessively high flow rates at the carbon dioxide inlet), this problem can be completely resolved by feeding the mixture evenly through the three existing feed pipes in the synthesis tower. ⑵ Regarding the high-temperature issue (at that time, all liquid ammonia and all carbon dioxide were mixed together, with ammonium methanate not being included in this mixture; this caused the temperature of the mixture to rise, leading to the expansion of the fastening bolts on the mixer’s outlet flange and resulting in leakage of the mixture), the modification process described in this article involves introducing ammonium methanate liquid into the mixer at the same time, which helps to alleviate this problem. Additionally, we have designed a control bypass in the liquid ammonia pipeline to regulate the total amount of liquid ammonia that enters the mixer for the exothermic reaction, thereby allowing us to control the temperature of the material at the mixer’s outlet (principally keeping it below 188°C). This approach helps to address the problem of material corrosion under high-temperature conditions. Through the above measures, we believe that, in theory, the approach proposed in this paper to improve the carbon dioxide conversion rate in urea synthesis towers will achieve the desired results and enable stable, long-term operation. We earnestly hope that experts in the industry will provide their opinions on this matter, and that manufacturers will consider the approaches suggested in this paper with a scientific attitude and support their implementation. Together, we can explore new ways to increase the carbon dioxide conversion rate in urea synthesis towers, thereby reviving this established manufacturing process and helping fertilizer plants to save energy, reduce costs, and improve efficiency