Comparison of the performance of evaporative water coolers and shell-and-tube water coolers in ammonia synthesis and urea production plants

Evaporative water coolers indeed perform well, mainly because of the high quality of the water, which prevents scaling; shell-and-tube water coolers, on the other hand, are greatly affected by the quality of the circulating water.

Feasibility analysis of soft water closed-loop circulation technology in CO2 stripping urea plants. 1. Impact of process material leaks on the soft water closed-loop circulation system: In the CO2 stripping urea production process, apart from the carbon dioxide compression unit, there are 22 heat exchange units, including 4 surface condensers in the evaporation system, all of which operate under negative pressure ； There are 2 units in the low-pressure desorption and absorption system; the reflux condenser has a U-tube structure, with cooling water flowing inside the tubes and the desorbed gas flowing outside them ； 7 steam condensate (including low-pressure steam) coolers ； 1 high-pressure CO2 cooler, of the U-tube type, with water flowing inside the tubes and CO2 gas flowing outside the tubes ； One atmospheric-pressure wastewater cooler. Based on the configuration of the process equipment, it is impossible for there to be any leakage of process materials into the soft water with 4 negative pressure units in use ； Even if there is a leak in the steam condensate cooler, it does not affect the water quality of the soft water closed-loop system ； The atmospheric pressure wastewater cooler is a device that operates at normal pressure; as long as the desorption-deep hydrolysis system is functioning properly, even if wastewater leaks into the soft water closed-loop system, it will not have a significant impact on that system ； The only equipment leakage that can affect the water quality of a closed-loop system is that of the cooling equipment in the low-pressure desorption system: under normal conditions, the operating pressure in this system is 0.3 MPa, while the supply pressure for the circulating cooling water is around 0.4 MPa. Due to the differences in elevation resulting from the layout of the equipment, it is possible for the fluid from the low-pressure absorption cooler to leak into the soft water circulation system. Under normal design conditions, the low-pressure absorption cooler is used primarily to cool process condensates, which are dilute ammonia solutions and have relatively low corrosivity; therefore, 304L material is used for this equipment. The reflux condenser is made of 316L material, and since the process fluid in question is a dilute methylammonium solution, its corrosivity is also lower. Compared with the full-circulation method using aqueous solutions, cold exchange equipment does not involve heat exchange with the medium-pressure material system, thereby **reducing the likelihood of materials leaking into the circulating water**. Therefore, it is unlikely that process materials from the urea production process will leak into the circulating soft water system. 2. Process adaptability analysis: Under normal design conditions, high-pressure CO2 coolers and shell-and-tube condensers are of the U-tube type, with cooling water flowing inside the tubes; if conventional open-loop circulating cooling water is used, it becomes very difficult to clean the heat exchangers. By using a soft water closed-loop system, the aforementioned cooling equipment is not affected by production disruptions or the need for shutdowns for cleaning due to scaling in the circulating cooling water or sludge blockages. By using a soft water closed-loop system, the heat exchange efficiency of the cooling equipment is **improved**. Under normal conditions, the cooling equipment will not experience a decline in heat exchange efficiency or require shutdown for cleaning due to scaling or sludge buildup, thereby **extending** the operational cycle of the system. For chemical processing units, an improvement in heat exchange efficiency ensures that the process parameters during operation as well as the emissions of process exhaust gases are all maintained in accordance with the design specifications; the indirect economic benefits resulting from this are immeasurable. Although the carbon dioxide stripping method is a sophisticated process, due to the large size of the high-pressure synthesis system, the losses incurred during each shutdown are 2 to 3 times higher compared to those in plants using the aqueous solution recirculation method. Reducing the number of shutdowns will **lower costs and improve the economic efficiency of the enterprise. 3. Improved safety of the equipment: The equipment, fittings, and valves used in the urea production process are generally made of stainless steel of grade 304L or higher. If soft water leaks into the process equipment, its low Cl—content reduces the stress corrosion phenomenon that can occur in stainless steel. At the current stage, urea process design requires that the Cl— content in circulating cooling water be less than 30 PPm; it is difficult for open-loop circulating water systems that use liquid chlorine as a disinfectant to meet this requirement. IV. Disadvantages of soft water closed-loop circulation technology: Investigations show that the investment in soft water closed-loop circulation systems is about 15% to 20% higher than that of open-loop circulating cooling water systems.

Evaporative types are better; shell-and-tube types are prone to blockages and other issues.

Evaporative types are better, but attention must be paid to the corrosion of the heat exchange tubes; stainless steel corrugated tubes are the best choice. Shell-and-tube types are prone to problems such as blockages and tube sheet leaks.