Nexisense Tuning Fork Density Meter Dedicated to Urea Production: Application Practice in High-Temperature and Bubble-Prone Media Conditions

In the urea production process, the density of synthesis tower discharge, circulating liquid and urea solution is a key process parameter that affects reaction conversion rate, evaporation energy consumption and product quality. Traditional measurement methods often face problems such as large measurement fluctuations, serious material hanging and high maintenance frequency when dealing with high-temperature, bubble-prone and easy-scaling media. Nexisense developed a dedicated pipeline tuning fork density meter solution for the actual working conditions of an isotope urea production workshop in Datong, Shanxi. Through fluid dynamics optimization, steady flow design and online maintenance functions, it effectively solved the problem of online density monitoring under special media conditions, providing reliable technical support for system integrators and engineering companies.

Project Background and Working Condition Challenges

The urea production workshop adopts the CO₂ stripping process. The density measurement points are mainly located in the high-pressure synthesis tower discharge pipeline and the medium-pressure circulation section. The medium temperature is usually 120–150℃, with high pressure. The urea solution is easy to decompose and produce trace gases, and has certain adhesion, which is easy to scale on the pipeline and sensor surface. Traditional insertion-type or straight-pipe density meters face the following prominent problems under this working condition:

• High temperature causes bubble precipitation, seriously interfering with measurement stability;

• Medium adhesion makes the sensor response sluggish and accuracy decreases;

• Conventional pipeline structure easily forms dead zones, causing local concentration deviation;

• Frequent shutdown and disassembly are required during maintenance, affecting the long-cycle operation of the unit.

The system integrator clearly proposed during the preliminary technical exchange: the sensor must have customized pipeline design, steady flow capability, online cleaning function, and be able to adapt to high-temperature and high-pressure environments, while ensuring that the measurement data can be directly connected to the existing DCS system.

Nexisense Urea Dedicated Tuning Fork Density Meter Technical Solution

Nexisense tuning fork density meter based on high-frequency resonance principle has been targetedly optimized in combination with the characteristics of urea production process, forming a complete dedicated solution.

1. Customized pipeline structure reduces flow velocity at the probe
According to the on-site medium flow rate, Nexisense designed a specially enlarged measurement pipeline section. By reasonably increasing the diameter of the measurement pipe section, the flow velocity in the area where the probe is located is controlled at 0.6–1.2 m/s, effectively reducing the impact of fluid on the fork body, while reducing the probability of bubbles passing through the probe area with high-speed fluid, and improving measurement repeatability.

2. Front and rear straight pipe section design improves flow stability
Straight pipe sections of no less than 10D length (D is the inner diameter of the measurement pipe) are set at the front and rear ends of the tuning fork body respectively to ensure that the medium flow state is fully developed before entering the measurement area, eliminating turbulent interference caused by local resistance parts such as upstream elbows and valves, so that the density measurement is in a stable laminar flow or weak turbulent flow state.

3. Upper and lower valve configuration realizes flow velocity control and convenient maintenance
A high-reliability shut-off valve is installed at the upper and lower ends of the measurement pipeline, which can not only accurately adjust the bypass flow during normal production, but also quickly cut off the medium when maintenance or calibration is required, realizing maintenance without stopping production, significantly reducing the on-site operation risk and downtime loss of engineering companies.

4. Online cleaning interface solves medium adhesion problem
The sensor measurement section is designed with a dedicated external pressure flushing interface, supporting regular introduction of high-pressure water or steam for online flushing of the tuning fork body. Combined with the self-cleaning characteristics of the tuning fork's own high-frequency micro-vibration, it can effectively remove surface attachments, maintain long-term measurement accuracy, and reduce unplanned downtime.

5. Full temperature compensation and high-temperature resistant material selection
The instrument has a built-in multi-point temperature compensation algorithm that collects medium temperature in real time and automatically corrects it according to the urea solution density-temperature characteristic curve. At the same time, the wetted part adopts high-temperature resistant reinforced 316L stainless steel, and Hastelloy material is optional to ensure long-term stable operation in 150℃ high-temperature environment.

Project Implementation and Operation Effect

Since the solution was put into operation, it has been running continuously and stably for more than 10 months. System integrator feedback:

• Density measurement repeatability is better than ±0.0006 g/cm³, meeting the accuracy requirements of the synthesis process for concentration control;

• Customized pipeline and straight pipe section design greatly reduces bubble interference, and signal fluctuation is reduced by about 70% compared with traditional solutions;

• The online cleaning interface combined with regular flushing procedures effectively controls the medium adhesion problem, and the maintenance cycle is extended from the original once a month to once a quarter;

• The data is stably connected to the DCS system through RS485 Modbus RTU protocol, realizing linkage optimization with evaporation load and circulating pump speed.

The project leader said that this solution significantly improves the reliability of urea solution density data and provides solid support for process parameter optimization and long-cycle operation of the unit.

FAQ

Q1: Urea solution is prone to bubbles at high temperature. How does the tuning fork density meter ensure measurement stability?
A1: The flow velocity at the probe is controlled at 0.6–1.2 m/s through a specially enlarged pipeline section, and sufficient length straight pipe sections are set before and after the tuning fork body to ensure stable flow state. Combined with the instrument's built-in dynamic bubble compensation algorithm, it can effectively filter out the interference of bubbles on the resonant frequency. In actual operation, the signal fluctuation is controlled within ±0.0006 g/cm³.

Q2: When the medium is easy to adhere and scale, how does the density meter maintain long-term measurement accuracy?
A2: The sensor is designed with a dedicated online cleaning interface, supporting regular external pressure flushing. At the same time, the high-frequency micro-vibration of the tuning fork has a self-cleaning effect. The combination of the two can effectively remove surface attachments. Integrators can set the cleaning cycle according to the medium characteristics, significantly extending the instrument maintenance-free time.

Q3: When the on-site pipeline flow is large, will the customized pipeline affect the main process flow?
A3: The measurement pipe section adopts parallel bypass design. The upper and lower valves can accurately adjust the bypass flow, with minimal impact on the main pipeline pressure loss. System integrators can flexibly adjust the bypass diameter according to the actual flow to ensure that the measurement requirements are met without affecting the normal production of the unit.

Q4: How to ensure the reliability of instrument material and sealing in high-temperature environment?
A4: The wetted part adopts high-temperature resistant reinforced 316L stainless steel or Hastelloy material. The sealing structure has passed 150℃ high-temperature cycle test. The temperature compensation algorithm can correct the change of medium density with temperature in real time to ensure measurement accuracy in the full working condition range.

Q5: How does this density meter achieve data docking with the existing DCS or PLC system?
A5: It supports two output methods: 4-20mA+HART and RS485 Modbus RTU, and can be directly connected to most mainstream control systems. Nexisense provides complete protocol documents, mapping tables and test tools. System integrators can usually complete docking and debugging within 2–4 days.

Q6: How to verify the density measurement accuracy during project acceptance?
A6: Standard density bottle sampling + laboratory analysis method can be used for comparison with online instruments, and the full curve of the instrument's original frequency, temperature and compensated density can be recorded at the same time. Nexisense can cooperate with third-party metrology institutions to issue verification reports to meet the acceptance requirements of engineering companies.

Q7: Does it support further customized development in batch projects?
A7: Supported. According to the pipe diameter, flow rate, medium characteristics and control system requirements of different urea units, the measurement pipe section size, valve specifications, cleaning interface form and communication protocol fields can be customized. The standard customization cycle is 4–6 weeks, with sample verification provided before batch supply.

Summary

Nexisense tuning fork density meter dedicated to urea production effectively solves the problem of online density monitoring under high-temperature, bubble-prone and easy-adhesion media conditions through technical measures such as customized pipeline structure, straight pipe section steady flow design, valve control and online cleaning interface. This solution has been verified in the urea production workshop in Datong, Shanxi, providing system integrators and engineering companies with a reliable density monitoring technical path suitable for special chemical processes such as urea.