Talk about cooling through urea pellet rate

Have you all switched to fluidized beds and the temperature still doesn’t drop?

Can it be ensured that the finished product will not clump together after being stored for 10 days when the temperature inside the bag is 50 degrees Celsius? After adopting the fluidized bed, the temperature of the product inside the bags in summer is generally above 50 degrees.

Factors affecting the bed temperature in granulation machines and countermeasures 1) Temperature of the urea solution. During normal production, the temperature of the urea solution being evaporated is controlled at 128–130 °C. As the temperature of the urea solution increases, the temperature of the bed in the granulator also rises; similarly, when the temperature of the urea solution decreases, the temperature of the bed in the granulator decreases as well. Since the evaporation temperature has a significant impact on two very important quality parameters of urea products – moisture and biuret – it should be adjusted within the factory-controlled range based on the actual moisture and biuret levels in the product. As long as the moisture content remains within acceptable limits, if the biuret content is high, the temperature should be kept at the lower end of the specified range; conversely, the temperature can be increased slightly, as too low a temperature makes it difficult to maintain the proper moisture level in the product. Of course, there are many other factors that affect the moisture content in urea products, including the vacuum level during evaporation. 2) Vacuum level of evaporation. It is well known that vacuum evaporation is highly effective for concentrating urea solutions; when the evaporation pressure is reduced, the same level of evaporation can be achieved at lower temperatures. The selection of evaporation conditions is based on achieving the highest possible vacuum level during evaporation at a certain temperature (determined by the levels of biuret and moisture in the urea product), while ensuring that the urea solution does not enter a saturated state and thus avoid the risk of crystallization. After taking into account a certain safety factor, the vacuum level for evaporation generally corresponds to the temperature of the liquid being evaporated, which enables the most economical use of energy. According to the vapor pressure diagram of urea aqueous solutions, a urea solution with a concentration of 96% can be obtained at a temperature of 130 °C when the evaporation vacuum (absolute pressure) reaches 34 kPa. Therefore, the design vacuum for urea evaporation in the first-phase fertilizer plant is 29 kPa, the design temperature is 128–133 °C, and the normal operating temperature is 130 °C. The design vacuum degree for urea evaporation in the second-phase fertilizer plant is 25 kPa, and the design temperature is 135 ℃. Under the same load and other conditions, the higher the vacuum level for evaporation, the higher the concentration of the urea solution, and the temperature of the granulator also increases accordingly. Conversely, the temperature of the granulator also decreases as the evaporation vacuum level drops. 3) Flow rate of the fluidized air. With all other conditions unchanged, increasing the volume of air used for fluidization results in more heat being removed as the urea crystals release heat, which in turn lowers the temperature of the granulator. Conversely, reducing the volume of air used for fluidization causes the temperature of the granulator to rise. Due to the location in Hainan, an area with high temperatures and little rainfall throughout the year, the air temperature is high; as a result, the dampers of the fluidization fans are kept fully open most of the time. Only when both the granulation load and air temperature are low, and there is a shortage of low-pressure steam, can the dampers for the fluidization air be adjusted slightly to lower them, in order to maintain the temperature of the granulator. 4) Fluidized air temperature. The temperature of the fluidized air is the normal room temperature during normal operation. Under normal circumstances, the fluidized air is not heated. However, in particularly cold weather or during heavy rain, a fluidized air heater is used to ensure that the temperature of the granulator remains within the normal range. 5) Atomized air temperature. As the temperature of the atomized air rises, the temperature of the granulator also increases; conversely, when the temperature of the atomized air drops, the temperature of the granulator decreases as well. During normal production, it is advisable to control the temperature of the atomized air at the same level as the temperature of the urea solution being evaporated. Since the atomized air is the first to come into contact with the urea solution, a large temperature difference can cause the urea solution to cool down or heat up, and both of these types of heat transfer are unfavorable. If the temperature is too high, heating the urea solution will increase the content of biuret in the product; if the temperature is too low and the urea solution cools down prematurely, it will lead to an increase in dust levels in the granulator. During actual operation, it is necessary to frequently check whether the on-site temperatures of the urine and the atomized air before the granulator are the same. 6) Air humidity. When it is raining or the air humidity is high, there is a large amount of moisture in the air; when this moisture evaporates inside the granulator, it takes away a lot of heat, causing the temperature inside the granulator to drop. In such cases, a fluidized air heater should be activated promptly. 7) Material level in the granulator. Controlling the level of material in the granulator also plays a role in regulating its temperature. When the temperature of the granulator is too high, it is possible to reduce the material level in the granulator accordingly; this shortens the time that the urea particles spend inside the granulator, allowing some of the heat contained within those particles to be transferred to the cooler for removal. Conversely, when the temperature of the granulator is too low, it can be adjusted by appropriately increasing the material level in the granulator. The level of material in the granulator has a limited impact on the extent to which the granulator’s temperature can be adjusted; generally, it is only used when other adjustment methods have failed to produce the desired effect. 8) Air volume in each chamber of the granulator. The distribution of air volume among the various chambers of the granulator also matters; if this distribution is not appropriate, it can affect the temperature of the granulator, which in turn impacts the quality of the urea product. The designed flow rate of fluidizing air for the first 5 chambers of the second-stage granulator is as follows: 75 t/h for the first 3 chambers, and 69 t/h for the last 2 chambers. In actual production, the air volume in each chamber can be adjusted appropriately according to the load of each chamber in the granulator; however, since adjusting the air valves is not very convenient, such adjustments are generally not made frequently. 9) Granulation load. When the load on the granulator is low, the heat brought into the granulator due to the evaporation of urine is relatively reduced; as a result, the temperature of the granulator drops under the same weather conditions. To ensure that the water in the urine can evaporate properly, a fluidized air heater should be used as needed to raise the temperature of the fluidized air, thereby keeping the temperature of the granulator within the normal range and ensuring the quality of the product. For example, before starting granulation, a fluidized air heater must be used to raise the temperature of the granulator to 70 ℃–80 ℃. As the load on the granulator gradually increases, the temperature of the fluidized air can be lowered step by step until heating is stopped. It should also be noted that due to the low evaporation load, the urea solution stays in the evaporation zone for a longer period of time, resulting in a higher content of biuret. Therefore, the temperature of the urea solution should be kept at the lower limit set by the design specifications; even if the temperature of the granulator is low, it is not appropriate to adjust this by raising the temperature of the urea solution. When the granulation load is high, the temperature of the granulator rises due to the large amount of heat introduced by the urea solution into the granulator. During the summer when temperatures are high and the system’s load is particularly high, it is most difficult to keep the temperature of the granulator within the normal range. As mentioned earlier, process operators should take into account all the factors outlined in this text in order to make the necessary adjustments. From June to July 2007, failures in the offshore platform led to multiple shutdowns of the urea granulation unit in Phase 2. Meanwhile, the fertilizer plant in Phase 2 had to process the liquid ammonia supplied by the fertilizer plant in Phase 1, which kept the load on the urea granulation unit in Phase 2 at a high level. How to extend the operating cycle of granulators under high load during hot seasons is a major challenge that urea production staff in the current second phase must face.

This is a completed chapter of a paper titled \"Temperature Control of Fluidized Bed Granulators\" by Wang Youquan from CNOOC Petrochemical Co., Ltd., Dongfang, Hainan 572600. Abstract: It outlines the key aspects of temperature control for the Hydroturf large-grain urea fluidized bed granulators in CNOOC Petrochemical Co., Ltd.’s second-phase fertilizer production facility, as well as the precautions to be taken in terms of operation and control. Keywords: fluidized bed, granulation, temperature, evaporation. The design production capacity of the second-phase fertilizer plant of CNOOC Petrochemical Co., Ltd. is 450 kt of synthetic ammonia and 800 kt of urea per year; it was officially completed and put into operation at the end of September 2003. The granulation process used by this facility to produce large-grained urea relies on Hydril’s fluidized bed technology from Norway. The first application of this technology in large domestic urea plants was in the first-phase fertilizer plant of CNOOC Petrochemical Co., Ltd., which came online in 1996. The granulator is the core equipment in the entire large-particle granulation system; its operating performance directly determines the quality of the urea product. Moreover, the operating conditions of the granulator also influence the cycle time for urea granulation. There are many factors that affect the operating conditions of granulators, among which the bed temperature of the granulator directly influences product quality parameters such as the particle resistance to crushing strength of urea, biuret content, and moisture level. Since there are not significant differences in the processes of the two sets of large-particle granulation units, this paper focuses solely on the temperature control of the fluidized bed granulator in the second-phase fertilizer granulation unit. 1 Working principle of the granulator. The granulator is essentially an empty container that contains a fluidized bed layer in which urea particles are formed. It consists of components such as a porous plate, lower housing, nozzle, and upper housing; the upper housing is divided into 6 chambers by partitions. In the granulator, the urea solution with a concentration of around 96% supplied from the evaporation system and the additive UF solution are evenly mixed; thereafter, this mixture is atomized by air through 312 nozzles and sprayed onto the seed crystals, where it accumulates to form urea particles. Seeds are small particles of urea and large particles of crushed urea that are screened out from the system after granulation and returned to the granulator; these urea particles acting as seeds are agitated by the flowing air in the granulator, creating a bubbling effect. The urea particles of varying sizes produced in the first 3 chambers pass through the cooling in the latter 3 chambers under the action of fluidized air, then enter the first fluidized bed cooler for further cooling, before proceeding to subsequent processing steps. The temperatures in the 6 chambers of the fluidized bed granulator vary; under normal conditions, the temperature in the second chamber (TI3532) is the highest, with a designed temperature of 104–108°C. In the first chamber, due to the addition of seeds at a lower temperature, its temperature (TI3531) is 2–4°C lower than that of the second chamber. In the third chamber, as a result of the return of some cooled material from the fourth chamber, its temperature (TI3533) is also 2–4°C lower than that of the second chamber. As for chambers 4, 5, and 6, since no urea solution or atomized air is added and only fluidized air is used for cooling, the temperatures in these three chambers are typically around 102°C, 100°C, and 95°C respectively. During normal production, the temperature of the granulator is controlled based on the temperature of the second chamber. The importance of temperature control is based on the following factors: 1) Excessively high temperatures have the following direct negative consequences: ① Excessive dust. Due to the excessively high temperature control inside the granulator, many of the atomized urea droplets evaporated and solidified before they could come into contact with the seed crystals. These excess urea dusts increase the load on the washing and recovery systems as well as the evaporation system, thereby raising the energy consumption per unit of urea produced. ②Excessively high temperatures inside the granulator can cause some urea particles to melt on the porous plate, forming flaky urea, which can severely clog the nozzles. ③The moisture content in the product is low, resulting in a reduced resistance of urea to crushing. 2) When the temperature is too low, the direct negative consequences are as follows: ① The urea droplets in the mist condense prematurely or partially; these prematurely solidified urea droplets do not adhere well to the seed crystals, resulting in a reduced resistance of the product to crushing. ②The moisture content in the product exceeds the specified limit. 2 Factors affecting the layer temperature in granulation machines and countermeasures 1) Temperature of the urea solution. During normal production, the temperature of the urea solution being evaporated is controlled at 128–130°C. As the temperature of the urea solution increases, the bed temperature of the granulator also rises ； Similarly, as the temperature of the urea solution decreases, the bed temperature of the granulator also decreases accordingly. Since the evaporation temperature has a significant impact on two very important quality parameters of urea products – moisture and biuret – it should be adjusted within the factory-controlled range based on the actual moisture and biuret levels in the product. As long as the moisture content remains within acceptable limits, if the biuret content is high, the temperature should be kept at the lower end of the specified range; conversely, the temperature can be increased slightly, as too low a temperature makes it difficult to maintain the appropriate moisture level in the product. Of course, there are many other factors that affect the moisture content in urea products, including the vacuum level during evaporation. 2) Vacuum level of evaporation. It is well known that vacuum evaporation is highly effective for concentrating urea solutions; when the evaporation pressure is reduced, the same level of evaporation can be achieved at lower temperatures. The selection of evaporation conditions is based on achieving the highest possible vacuum level during evaporation at a certain temperature (determined by the levels of biuret and moisture in the urea product), while ensuring that the urea solution does not enter the saturated zone and thus avoid the risk of crystallization. After taking into account a certain safety factor, the vacuum level for evaporation generally corresponds to the temperature of the liquid being evaporated, which ensures the most economical energy consumption. According to the vapor pressure diagram of urea aqueous solutions, a urea solution with a concentration of 96% can be obtained at a temperature of 130°C when the evaporation vacuum (absolute pressure) reaches 34 kPa. Therefore, the design vacuum for urea evaporation in the first-phase fertilizer plant is 29 kPa, the design temperature is 128–133°C, and the normal operating temperature is 130°C. The design vacuum degree for urea evaporation in the second-phase fertilizer plant is 25 kPa, with a design temperature of 135°C. Under the same load and other conditions, the higher the vacuum level for evaporation, the higher the concentration of the urea solution, and the temperature of the granulator also increases accordingly. Conversely, the temperature of the granulator also decreases as the evaporation vacuum level drops. 3) Flow rate of the fluidized air. With all other conditions unchanged, increasing the volume of air used for fluidization allows more heat to be removed as urea crystals are discharged, which in turn lowers the temperature of the granulator. Conversely, reducing the volume of fluidizing air raises the temperature of the granulator. Due to the location in Hainan, an area with high temperatures and little rainfall throughout the year, the air temperature is high; as a result, the dampers of the fluidization fans are kept fully open most of the time. Only when both the granulation load and air temperature are low, and there is a shortage of low-pressure steam, can the dampers for the fluidization air be adjusted slightly to lower them, in order to maintain the temperature of the granulator. 4) Fluidized air temperature. The temperature of the fluidized air is the normal room temperature during normal operation. Under normal circumstances, the fluidized air is not heated. However, in particularly cold weather or during heavy rain, a fluidized air heater is used to ensure that the temperature of the granulator remains within the normal range. 5) Atomized air temperature. As the temperature of the atomized air increases, the temperature of the granulator also rises; conversely, when the temperature of the atomized air decreases, the temperature of the granulator decreases as well. During normal production, it is advisable to control the temperature of the atomized air at the same level as the temperature of the urea solution being evaporated. Since the atomized air is the first to come into contact with the urea solution, a large temperature difference will cause the urea solution to cool down or heat up, and both of these types of heat exchange are unfavorable. If the temperature is too high, heating the urea solution will increase the content of biuret in the product ； If the temperature is too low and the urea solution cools down prematurely, it will cause a significant increase in dust in the granulator. During actual operation, it is necessary to frequently check whether the on-site temperatures of the urine and the atomized air before the granulator are the same. 6) Air humidity. When it is raining or the air humidity is high, there is a large amount of moisture in the air; when this moisture evaporates inside the granulator, it draws away a significant amount of heat, causing the temperature inside the granulator to drop. In such cases, a fluidized air heater should be activated promptly. 7) Material level in the granulator. Controlling the level of material in the granulator also plays a role in regulating its temperature. When the temperature of the granulator is too high, it is possible to appropriately reduce the material level in the granulator; this shortens the residence time of the urea particles inside the granulator, allowing some of the heat contained within those particles to be transferred to the cooler for removal. Conversely, when the temperature of the granulator is too low, it can be adjusted by appropriately increasing the material level in the granulator. The level of material in the granulator has a limited impact on the extent to which the granulator’s temperature can be adjusted; generally, it is only used when other adjustment methods have failed to produce the desired effect. 8) Air volume in each chamber of the granulator. The distribution of air volume among the various chambers of the granulator also needs to be carefully managed; if this distribution is not appropriate, it can affect the temperature of the granulator, which in turn impacts the quality of the urea product. The designed flow rate of fluidizing air for the first 5 chambers of the second-stage granulator is as follows: 75 t/h for the first 3 chambers, and 69 t/h for the last 2 chambers. In actual production, the air volume in each chamber can be adjusted appropriately according to the load of each chamber in the granulator; however, since adjusting the air dampers is not very convenient, such adjustments are generally not made frequently. 9) Granulation load. When the load on the granulator is low, the heat brought into the granulator due to the evaporation of urine is relatively reduced; as a result, the temperature of the granulator drops under the same weather conditions. To ensure that the water in the urine can evaporate properly, a fluidized air heater should be used as needed to raise the temperature of the fluidized air, thereby keeping the temperature of the granulator within the normal range and ensuring product quality. For example, before starting granulation, a fluidized air heater must be used to raise the temperature of the granulator to 70°C–80°C. As the load on the granulator gradually increases, the temperature of the fluidized air can be lowered step by step until heating is stopped. It should also be noted that due to the low evaporation load, the urea solution stays in the evaporation zone for a longer period of time, resulting in a higher content of biuret; therefore, the temperature of the urea solution should be kept at the lower limit set by the design specifications. Even if the temperature of the granulator is low, it is not appropriate to adjust this by raising the temperature of the urea solution. When the granulation load is high, the temperature of the granulator rises due to the large amount of heat introduced into it by the urea solution. During the summer when temperatures are high and the system’s load is particularly high, it is most difficult to keep the temperature of the granulator within the normal range. As mentioned earlier, process operators should take into account all the factors cited in this text in order to make the necessary adjustments. From June to July 2007, failures at the offshore platform caused multiple shutdowns of the urea granulation unit in Phase 2. Meanwhile, the fertilizer plant in Phase 2 had to process the liquid ammonia supplied by the fertilizer plant in Phase 1, which kept the load on the urea granulation unit in Phase 2 at a high level. How to extend the operating cycle of granulators under high load during hot seasons is a major challenge that urea production staff in the current second phase must face. 3 Example: The comparison of operational data before and after adjustments to the granulation system is shown in Table 1. As can be seen from Table 1, the evaporation load has reached 137.1543 t/h, which exceeds the design load of 134.8 t/h. Although the damper of the fluidization fan was set to its maximum position, the air temperature at the inlet of the fluidization fan was 33.7°C due to the high ambient temperature. At this point, increasing the volume of air used for fluidization in the granulator was no longer sufficient to lower the temperature of the fluidized bed in the granulator, which remained as high as 112.7°C. This temperature **exceeds the design temperature of the granulator; as a direct result, the resistance of the urea product to crushing is reduced, and there is an increase in urea dust within the product. The amount of urea dust in the finished product storage areas also increases significantly. The levels of biuret and moisture in the product are both below the factory-controlled limits. By reducing the evaporation temperature and vacuum level, as well as the material level in the granulator, the temperature of the granulator dropped by about 2.4°C. Based on the analysis of the finished product storage, the dust content in urea also decreased. However, the two quality parameters related to urea products – namely the biuret content and moisture content – remained **below the standards required for top-quality products. By comparing the data from the first phase of evaporation, it is possible to further reduce the evaporation temperature and vacuum level under such high loads, while still ensuring product quality; in other words, the temperature of the granulator can be lowered further. 4 Conclusion The temperature control of granulators may seem simple, but in reality, it is quite challenging to keep it within an appropriate range under different operating conditions; it is especially difficult to control under conditions of high load and high temperatures. Since there are many factors that affect the temperature of the granulator, these factors, together with the granulator’s temperature, directly influence the quality of the urea product. Many process parameters in the system are established to ensure that product quality does not exceed specified limits; therefore, the adjustment of the granulator temperature should also be carried out in close alignment with the quality criteria for urea products. The design values of various process parameters serve as the basis for adjustment, but under different conditions they should also be optimized according to actual circumstances. If necessary, it is possible to go beyond the limits set by factory control specifications in order to overcome unfavorable environmental factors and ensure that the product quality meets top-grade standards.

This post was last edited by zhanghouqing on 2010-5-7 15:09. Powder flow heat exchangers in Canada are very suitable for cooling both large-particle and small-particle urea. Currently, over a dozen powder flow heat exchangers are in use for powder heat exchange processes in China. Over twenty years ago, powder flow heat exchangers were applied in the fertilizer industry. This is a new type of equipment for cooling solid particles, and it is highly suitable for cooling both large and small urea particles. The powder flow heat exchanger is an effective alternative to fluidized bed and drum coolers, meeting industry standards. By reviewing over 40 applications of powder flow heat exchangers in the fertilizer industry, this article outlines the key design principles for cooling large-particle and small-particle urea. Introduction to the Powder Flow Heat Exchanger: The powder flow heat exchanger is a device with a simple concept; as its name suggests, it is a heat exchanger used for handling powder flows. The heat exchange section is a plate pack composed of hollow stainless steel plates arranged vertically and closely together. The powder flow moves slowly between the heat exchange plates in a dense-phase transport mode under the influence of gravity. As you would expect, the water flow and the product flow are in opposite directions. The discharge device at the lower part of the heat exchange plate controls the flow of powder through the heat exchanger. This design concept is the same as that of traditional shell-and-tube heat exchangers, but in this case, granular material flows through one side of the heat exchanger, which presents the following challenge: solid particles are poor conductors of heat, so a long residence time is required to achieve adequate cooling. Solid particles pass through the heat exchanger entirely in a thin layer (compared to the turbulence in most liquid or gas phase heat exchangers). The starting point of the design is to ensure that the solid particles pass through the cooler in a \"dense-phase transport\" manner. Slurry transport: The principle of slurry transport was discovered by Jenike and Johansen in the 1860s. They developed a characteristic theory for powder flows and predicted their flow capabilities, enabling bins and silos to be designed for free discharge while avoiding dead zones and material buildup. A typical dense-phase conveying bin has steel walls and a discharge cone. When a small amount of material passes through the dense-phase conveying bin, all the material in the bin moves. The principle of dense-phase conveying is a key aspect in the design of powder flow heat exchangers. To achieve a uniform cooling effect, the material must pass through the cross-section of the cooler at a uniform speed. To achieve dense-phase transport, we must install a feeding device at the bottom of the heat exchanger that can provide uniform flow. Uniform flow at the bottom allows the material to pass evenly through the cross-section of the cooler’s plate pack. The natural cone formed by the feed bin distributes the material between the heat exchange plates. At the same time, the discharge device controls the material through a heat exchanger. For applications in the fertilizer industry, we have designed two types of feeding devices: a vibrating disc feeding device. The entire cross-section of this feeding device vibrates at a high frequency (30–60 Hz) and with a small amplitude (0.5–1.0 mm). Flow rate is controlled by adjusting the frequency. For gate-type dense-phase conveying silos, the dual “V”-shaped discharge hoppers adjust their flow rate by changing the cross-sectional area. Cooling of large particle urea: In typical fluidized bed granulation plants, the discharge temperature from the granulator is between 90 and 100°C. The optimal storage temperature is around 40°C to prevent caking (this temperature may vary depending on the factory’s location and the parameters set by the process supervisor or owner). According to process requirements, the cooler can be designed as single-stage or two-stage, with the two-stage version consisting of a primary stage and a secondary stage. Screening is performed before entering the cooler, and it is returned to the granulator. To date, there has been a tendency to install the powder flow heat exchanger as a secondary cooler; however, tests and pilot installations in the Toyo process have shown that it can successfully serve as a primary cooler, or even be used as a single-stage cooler. But we focus on using it as a secondary cooler. Typical operating conditions for the second-stage heat exchanger: Product processing capacity of 62,500 kg/h (1,500 t/day); product inlet temperature of 60°C; product outlet temperature of 40°C; specific heat of 0.42 kcal/kg·°C; cooling water temperature of 30°C; particle size d50 of 3.5–5.0 mm; environmental conditions of 35°C or relative humidity of 70% (in summer). Design concept: Two plate packs in series enable this specific unit to be installed within a single piece of equipment. The material of the heat exchange plate is 316L stainless steel, while the material of the housing is 304L stainless steel. Through the compensation of the lower plate group by the upper plate group, the heat exchange efficiency of the double-plate group heat exchanger is very high. Cooling water: The circulating water from the factory’s standard cooling towers can be used. The cooling water passes through the two sets of plate assemblies in series. Based on a cooling water temperature rise of 6°C, the designed flow rate for the cooling water should be 88 m3/h ； At this flow rate, the pressure drop across the two-stage plate pack is around 1.5 bar. As a principle, the chloride ion content must be less than 200 ppm to reduce the risk of stress corrosion cracking in stainless steel heat exchange plates. Dry air purging: In areas with high temperatures and high relative humidity during summer, there is a risk of condensation between the heat exchange plates. Moisture on the heat exchange plate can cause the product to clump, reducing the cooling effect, and may also lead to blockages in the heat exchanger. To prevent condensation, dry air is used for purging in order to lower the dew point of the air in the heat exchanger, keeping it below the temperature of the cooling water. The typical injection rate for dry air is 250 Nm3/h. Discharging device: Vibration discharging device or gate-type dense-phase conveying discharging device. Recently, most customers have chosen vibration feeding devices because they offer a wide range of effective feeding speeds and greater operational flexibility. Maintenance access: There is a large hinged door at the back of the cooler, which provides sufficient access if the plates in the panel assembly need to be cleaned. Cooling of small-grained urea: In most small-grained urea plants, there is no separate cooler after the granulation tower. Therefore, in the early designs of small-scale urea granulation plants, sufficiently tall granulation towers provided ample air for cooling, in order to achieve an appropriate temperature before the product was stored. These days, things have changed as workshop production capacities have generally improved, and many advanced technologies are being used to increase the output of urea production facilities, such as those provided by UREA CASALE. As production increased, the manufacturing process in the urea plant’s granulation tower encountered bottlenecks, as the cooling capacity of the tower relies primarily on its height. A powder flow heat exchanger can solve this problem, as it is capable of cooling the output from the granulation tower before the products are stored. Typical process conditions for specifying the cooling load: Product processing capacity: 83,300 kg/h (2,000 t/day); Product inlet temperature: 85°C; Product outlet temperature: 50°C; Specific heat: 0.42 kcal/kg·°C; Cooling water temperature: 35°C; Particle size d50: 2.0 mm; Environmental conditions: 35°C or relative humidity of 70% (in summer). Design concept: Installation – The powder flow heat exchanger is installed at the rear of the granulation tower. The discharge height of the granulation tower is low, so rakes and conveying devices are generally required. At the same time, a bucket elevator is required to feed the heat exchanger. Lumps occasionally form on the walls of the granulation tower, rakes, conveyors, and other such components. Therefore, it is important to install a small vibrating screen at the inlet of the heat exchanger to prevent lumpy materials from entering it. Plate pack: In the case of large-grain urea heat exchangers, two sets of heat exchange plate packs are installed in series within a single unit to achieve the desired heat exchange capacity. Cooling water: Regular workshop cooling water from the cooling tower can be used. It is also feasible to specify the use of seawater as cooling water. It is not wise to use seawater that enters the heat exchange plates directly, as titanium or Hastelloy materials are required for these plates, and using a large surface area makes things very expensive. A better solution is to use a closed-loop circulating cooling water system, with a heat exchanger at the primary end to exchange heat with seawater. Plate heat exchangers are the best choice for cooling closed-loop water, as their high heat exchange efficiency allows for a relatively small plate area. Using a plate heat exchanger, it is easy to achieve around 2°C. Dry air purging: Dry air purging is required ； The evaluation is the same as for dry air applications of large-grain urea. Ventilation equipment: The mechanical strength of small-particle urea is lower than that of large-particle urea ； This will result in more dust in the product. A high dust content increases the risk of clogging in the heat exchanger, and a well-designed ventilation system in the feed bin of the heat exchanger can effectively reduce dust levels and improve its performance. Discharge device: Vibration discharge device or gate-type dense-phase conveying discharge device. The evaluation is the same as that for the use of large-grained urea. Maintenance access: A large hinged door is installed at the rear of the cooler, providing sufficient access if the plates in the panel assembly need to be cleaned. Note: Stress corrosion cracking of austenitic stainless steels is a complex phenomenon influenced by various factors, including temperature. The chloride ion content of 200 ppm indicated in the text does not guarantee that stress corrosion cracking will not occur again ； However, experience shows that the risk is low at the specified process temperature. For more information, please refer to: http://www.chemequip.net/huanreqi.html