Nexisense Pipeline Tuning Fork Density Meter Application Practice in Coal Slurry Concentration Monitoring in Coal Washing Industry

In the coal washing and preparation production process, coal slurry concentration is the core process parameter that affects heavy medium separation efficiency, flotation reagent dosage and filter press dewatering effect. Traditional measurement methods are affected by pipe diameter limitations, flow velocity impact and strong electromagnetic interference on site, making it difficult to meet the needs of continuous and stable operation of coal washing plants. Nexisense developed a dedicated solution for pipeline tuning fork density meter based on the actual working conditions of a coal washing plant in Shanxi. Through bypass installation, fluid optimization design and anti-interference technology, it effectively solved the problem of high-precision online density monitoring under small pipe diameter, high flow velocity and strong vibration environment, providing a reliable technical path for system integrators and engineering companies.

Project Background and On-site Working Condition Analysis

The coal washing plant is located in Shanxi and mainly processes local thermal coal. The core processes include heavy medium cyclone separation and flotation. The coal slurry concentration monitoring point is located in the cyclone feed pipeline, with a pipe inner diameter of only DN80, normal flow velocity as high as 2.8–3.5 m/s, and dense motor groups on site with significant electromagnetic interference. Traditional differential pressure or γ-ray density meters have the following prominent problems under this working condition:

• High flow velocity causes serious sensor erosion and short maintenance cycle;

• Direct installation in small pipe diameter easily produces bubble retention and fluid impact, resulting in large measurement fluctuations;

• Strong motor interference reduces signal stability, making it difficult to access the DCS system.

The system integrator clearly required during the project evaluation stage: the sensor must support bypass installation, have erosion resistance and anti-interference capabilities, and ensure that the measurement accuracy meets the requirements of automatic control of flotation reagent addition.

Nexisense Pipeline Tuning Fork Density Meter Technical Solution

Nexisense pipeline tuning fork density meter is based on the high-frequency resonance principle and has been targetedly optimized for the special working conditions of the coal washing industry, forming a complete on-site application solution.

1. Bypass installation method reduces the influence of flow velocity
To avoid the direct impact of high flow velocity in the main pipeline on measurement accuracy, the solution adopts bypass installation mode. Part of the coal slurry is introduced into the bypass measurement section through a variable diameter pipeline, controlling the bypass flow velocity within 0.8–1.5 m/s. This not only ensures representative sampling but also significantly reduces the risk of fork body erosion. The bypass design reserves shut-off valves and sewage outlets, supporting online maintenance without stopping production, greatly reducing the construction difficulty and later operation and maintenance costs for system integrators.

2. Horn transition structure optimizes fluid dynamics
A progressive horn transition design is adopted between the measurement pipe section and the on-site main pipeline. This structure effectively avoids retention areas of medium and gas, while converting the direct impact of fluid on the fork body into smooth bypass flow, reducing the influence of dynamic pressure fluctuations on the resonant frequency. Actual test data shows that after adopting the horn design, the density measurement fluctuation amplitude is reduced by about 65% compared with traditional straight pipe installation.

3. Built-in anti-interference module copes with strong electromagnetic environment on site
Aiming at the characteristics of dense motors and numerous frequency converters in coal washing plants, Nexisense integrates a high-performance anti-electromagnetic interference module inside the density meter and performs multi-layer shielding treatment on the signal acquisition circuit. At the same time, the sensor adopts high-frequency resonance working mode (far higher than the mechanical vibration frequency of industrial sites), effectively filtering motor vibration and electromagnetic noise to ensure the stability of the output signal. Measured data shows that when the on-site motor group operates simultaneously, the density reading fluctuation is controlled within ±0.0003 g/cm³.

4. Full temperature compensation and high wear-resistant wetted material
Coal slurry temperature fluctuates significantly with seasons and processes. Nexisense density meter has a built-in multi-point temperature compensation algorithm, which can correct the relationship curve between medium density and temperature in real time to ensure measurement accuracy. The wetted part adopts high-density reinforced 316L stainless steel, and optional tungsten carbide hard alloy coating is available to effectively resist the erosive wear of sharp gangue particles in coal slurry and significantly extend the service life of the instrument.

5. Design with online cleaning interface
To cope with the problem of coal slurry hanging, the sensor measurement section is designed with a dedicated cleaning interface. During shutdown or maintenance, online flushing can be performed with high-pressure water or steam without disassembling the instrument, reducing the on-site maintenance workload for system integrators.

Project Implementation Effect

Since the solution was put into operation, it has been running continuously and stably for more than 14 months. System integrator feedback:

• Density measurement repeatability is better than ±0.0005 g/cm³, meeting the accuracy requirements of the flotation reagent automatic control system for concentration signals;

• The bypass installation method reduces the main pipeline modification workload by more than 70%, and the construction period is greatly shortened;

• The application of anti-interference and temperature compensation technology makes the instrument availability under complex working conditions reach 99.3%;

• The online cleaning interface effectively solves the problem of coal slurry hanging, and the maintenance frequency is reduced by 60% compared with traditional solutions.

At present, the coal washing plant has connected the density data to the DCS system, realizing closed-loop linkage control with reagent dosing quantity. The reagent unit consumption has decreased by about 9.8% compared with before the transformation.

FAQ

Q1: When the coal slurry flow velocity is high, how does the pipeline tuning fork density meter ensure measurement accuracy?
A1: The flow velocity of the measurement section is controlled within 0.8–1.5 m/s through bypass installation, and the horn transition structure is used to reduce fluid impact and bubble retention. Combined with the built-in dynamic pressure compensation algorithm, it can effectively eliminate measurement deviations caused by high flow velocity and meet the accuracy requirements of the flotation process for concentration signals.

Q2: The on-site motor interference is strong. Is the tuning fork density meter signal easily affected?
A2: Nexisense density meter adopts high-frequency resonance working mode and integrates multi-layer electromagnetic shielding and anti-interference modules. The signal acquisition circuit has undergone special filtering processing. In dense motor environments, the output signal fluctuation can be controlled within ±0.0003 g/cm³, ensuring stable data access to PLC or DCS systems.

Q3: The coal slurry contains many coarse particles. Is the fork body prone to wear?
A3: The wetted part adopts reinforced 316L stainless steel and optional tungsten carbide hard alloy coating, significantly improving erosion resistance. Actual project data shows that under high-wear working conditions, the instrument service life can reach more than twice that of traditional solutions.

Q4: Will bypass installation affect the normal production of the main pipeline?
A4: The bypass design reserves shut-off valves and bypass pipelines, allowing instrument installation, maintenance and calibration to be completed without stopping production. System integrators can flexibly select bypass caliber according to the on-site pipe diameter to minimize the impact on the main process flow.

Q5: When temperature changes have a large impact on coal slurry density measurement, how to ensure accuracy?
A5: 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 preset density-temperature characteristic curve. In actual applications, when temperature fluctuates ±15℃, the compensated density measurement error is controlled within ±0.0004 g/cm³.

Q6: When coal slurry is easy to hang, how is the instrument maintained?
A6: The measurement section is designed with a dedicated online cleaning interface, supporting flushing with high-pressure water or steam during shutdown. At the same time, the sensor has a built-in hanging diagnosis function. When the frequency characteristics are abnormal, it will issue a reminder through the cloud platform or on-site display screen to facilitate timely handling by operation and maintenance personnel.

Q7: How does this solution interface with the existing DCS or PLC system?
A7: It supports two output methods: 4-20mA+HART and RS485 Modbus RTU, and can be directly connected to most mainstream DCS/PLC systems. Nexisense provides complete communication protocol documents and test tools. System integrators can usually complete data docking and function verification within 2–3 days.

Summary

Nexisense pipeline tuning fork density meter provides multiple targeted measures such as bypass installation, fluid optimization, anti-interference design and online maintenance for typical working conditions in the coal washing industry such as small pipe diameter, high flow velocity and strong interference. This solution has been verified in Shanxi coal washing projects and provides a reliable and efficient technical path for online coal slurry concentration monitoring for system integrators and engineering companies.

For integrators and engineering companies that are promoting intelligent transformation of coal washing plants, choosing a mature industrial-grade density monitoring solution can not only reduce project implementation risks but also provide a stable and reliable data foundation for subsequent process optimization and data analysis. If you need customized solutions for specific pipe diameters, coal quality characteristics or system integration requirements, please contact Nexisense industrial application engineers. We will provide detailed technical selection support, installation guidance and on-site debugging services to help projects land efficiently.