Summary of Urea Particle Cooling Project
The 600,000 t/a synthetic ammonia and 800,000 t/a urea project of Hebei Zhengyuan Hydrogen Energy Technology Co., Ltd. (referred to as Zhengyuan Hydrogen Energy) has reached the designed capacity and standards since its startup in 2015. However, there were also some problems, such as high temperature of particles entering the urea bulk warehouse. The maximum temperature exceeded 70℃ in July and August from 2016 to 2018. Moreover, due to the high humidity in summer at the plant's geographical location, attrition and caking in the bulk warehouse were relatively serious. In response, Zhengyuan Hydrogen Energy implemented a new cooling design for urea particles from the prilling tower. Since its commissioning in the summer of 2019, the cooling project has achieved ideal operation results.
1 Process Design and Flow
Urea products from this facility are mainly supplied to industrial users. No formaldehyde is added to the urea melt in the urea evaporation system, resulting in low strength of urea particles. The temperature of urea particles in the bulk warehouse was as high as above 70℃, and pulverization and moisture absorption were serious, affecting product quality.
In this cooling project, urea particles from the outlet of the prilling tower enter the belt trestle. A plow discharger is set at an appropriate height and position, and the particles enter the urea particle solid cooler. After indirect cooling by circulating water, they fall into the bucket elevator. The bucket elevator lifts the cooled urea particles back to the original belt trestle, which then conveys them to the packaging workshop. To prevent particle caking, air is introduced at the bottom of the cooler. Baghouses are installed at the top and bottom of the cooler.
This cooling process does not change the original belt conveying system. In spring, autumn and winter, the original belt system flow is still followed. In summer, a plow discharger is adjusted to force urea prills into the cooling system. The transformation has a short process flow and low cost.
2 Automatic Control System
The control system of the urea particle cooling system is mainly divided into material level control, pneumatic vibrator control, outlet water temperature control and peripheral logic control. The automatic control of the material level of the urea cooler is realized through the interlock between the material level of the inlet hopper and the opening of the discharger. Pneumatic vibrators are controlled by solenoid valves. The outlet water temperature is controlled by the demineralized water feed regulating valve. Interlocks are also be set between the bucket elevator and the plow discharger, as well as between the urea cooler material level and the plow discharger, to keep the material levels of the bucket elevator and the cooler within a reasonable range.
3 Project Outcomes
Since its commissioning in May 2019, the urea particle cooling system has operated well without any problems. The maximum inlet temperature of the urea cooler reaches 75℃, and the urea temperature is as low as 45℃ after cooling. The feed temperature of demineralized water is 25℃, and the return water temperature is 45℃, meeting the design requirements. The product quality meets the national standard requirements.
4 Conclusion
After implementation, the project has achieved expected results, ensuring the stable operation of Zhengyuan Hydrogen Energy's urea unit in high-temperature summer and the improvement of product quality. Meanwhile, the project features short process flow, reasonable equipment design and compact layout, makes full use of the space under the trestle, and has small footprint and low investment. It is very suitable for the transformation of urea cooling systems in North China and regions to the south.