In the salt chemical production process, process media are generally characterized by high chloride corrosion, wide fluctuations in solid content, and highly continuous operating conditions. As core equipment for material conveying, brine circulation and slurry lifting, centrifugal pumps directly determine production flow accuracy, reaction section stability and equipment service life with their speed stability. Speed fluctuation will not only cause pipeline pressure oscillation, crystallization blockage and reduced product yield, but also accelerate impeller erosion, bearing fatigue and seal failure under long-term operation, greatly increasing the risk of unplanned shutdown.
Based on rich experience in full-scenario working conditions of the salt chemical industry, Changsha Zhonglian Pump Industry provides a full-chain technical solution from five dimensions: power supply, process flow, equipment body, control system and operation & maintenance system. Adopting a systematic engineering approach, it addresses the root causes of pump speed instability and ensures long-term stable operation of the production system.
I.
Power Supply System Optimization: Eliminating Power Input Fluctuations at the Source
Frequent start-stop of high-power equipment and strong impact of grid load in salt chemical plants, coupled with salt spray corrosion that easily degrades electrical connections, make voltage fluctuation and poor contact common triggers of pump speed drift. Governance on the power supply side is the basic prerequisite for stabilizing speed.
- High-reliability Power Supply and Voltage StabilizationFor problems such as grid voltage sag and three-phase imbalance on site, a dual-loop power supply architecture is preferred with a millisecond-level automatic switching device. When a single power supply fails, it switches to the standby loop without disturbance, avoiding sudden speed drop and restart impact caused by short-term power failure. For sections with poor power supply quality, key pumps are equipped with three-phase intelligent online voltage stabilizers to control output voltage fluctuation within ±5%, completely eliminating the impact of grid-side voltage deviation on motor speed. The voltage stabilizer shall be selected to match the starting impact characteristics of pumps, with an overload margin of more than 1.5 times, and a protection rating of IP54 or above adapted to salt spray corrosion environments.
- Full-chain Anti-corrosion and Regular Inspection of Electrical ConnectionsChloride ions in the salt chemical environment will accelerate cable insulation aging and electrochemical corrosion of terminals. Increased contact resistance will cause insufficient terminal voltage and reduced torque of the motor, which eventually manifests as speed fluctuation. A regular inspection mechanism for the electrical system shall be established: test the insulation resistance of power cables every quarter to ensure the resistance is no less than 10MΩ, and replace cables with degraded insulation in time; verify the tightening torque of motor terminals and control cabinet terminals every month, using tin-plated anti-corrosion terminals and anti-oxidation conductive paste to eliminate speed fluctuation caused by poor contact. Outdoor junction boxes shall be equipped with sealed anti-corrosion structures to prevent salt spray intrusion.
II.
Process Flow Adaptation Adjustment: Resolving Load Disturbance from Working Condition Matching
In salt chemical production, material concentration, solid content and system pressure change dynamically with the process. Continuous load fluctuation of pumps is the core working condition cause of speed instability. This problem cannot be solved only by adjusting the pump itself; it requires deep linkage with the process control system to realize dynamic matching of load and output.
- DCS Full-parameter Dynamic Monitoring and PID Closed-loop RegulationEstablish a DCS dynamic monitoring model for the pump system, connecting key parameters such as pump inlet pressure, outlet pressure, medium temperature, flow rate and liquid level into the control system. The opening of the pump outlet valve and operating speed are adjusted jointly through PID algorithm. For sections with frequent working condition fluctuations such as evaporation and crystallization, optimize PID parameter tuning, set pressure fluctuation dead zone and regulation rate limit, so as to ensure rapid speed response to load changes while avoiding oscillation caused by excessive regulation. At the same time, link valves and equipment status of upstream and downstream sections to prevent system pressure build-up and sudden load change caused by pipeline blockage and valve misoperation, reducing the inducement of speed fluctuation from the process side.
- Composite Control Scheme for Scenarios with Fluctuating Solid ContentIn scenarios such as salt slurry and salt mud transportation, the solid content of the medium changes in real time with the production process, which directly leads to large fluctuations in pump load torque. Ordinary constant-speed operation is very prone to speed drop and overload trip. It is recommended to adopt a composite control mode of variable frequency speed regulation + differential pressure feedback: take the inlet-outlet differential pressure of the pump as the core feedback signal to perceive medium concentration and load changes in real time. The frequency converter automatically matches output torque and speed, controlling speed fluctuation within ±1% of the rated value while ensuring stable conveying flow. This mode can also reduce the erosion rate of flow passage components under high solid content conditions and prolong the service life of impellers and pump casings.
III.
Pump Body Structure and Type Selection Optimization: Building a Solid Foundation for Stable Operation
Incorrect pump selection, structural wear and component failure are the root causes of speed instability on the equipment side. Under salt chemical working conditions, the combined effect of corrosion and erosion will accelerate component degradation. It is necessary to balance working condition adaptability and long-term operation stability from the design and selection stage.
- Erosion-resistant Structure and High-quality Core ComponentsFor highly erosive and corrosive media such as salt slurry and brine, the impeller is preferably made of 2205 duplex stainless steel, which combines excellent chloride corrosion resistance and erosion wear resistance. With optimized hydraulic model design, it reduces the impact wear of the medium on blades, maintains stable hydraulic performance after long-term operation, and avoids efficiency decline and speed drift caused by impeller wear. The bearing housing is uniformly equipped with SKF imported heavy-duty bearings, adopting dual lubrication of splash + forced lubrication, matched with double-lip corrosion-resistant mechanical seals to block salt spray and medium from entering the bearing cavity, prolonging the fault-free operation cycle of bearings. Bearing wear is a common internal cause of abnormal pump speed and excessive vibration. High-quality bearing configuration can extend the bearing maintenance cycle by more than 3 times.
- Accurate Selection and Performance Verification Based on Actual Working ConditionsStrictly follow the standard GB/T 3216-2016 Rotary Dynamic Pumps – Hydraulic Performance Acceptance Test Grades. Take the actual operating conditions of the user as the sole basis for selection, and complete comprehensive verification of flow rate, head, power and required net positive suction head (NPSHr) combined with medium density, viscosity, solid content, operating temperature and other parameters. Avoid the deviation of "oversized pump selection": an oversized pump operating far from the high-efficiency zone for a long time will not only cause high energy consumption, but also easily lead to surge and unstable flow, manifested as periodic speed fluctuation. At the same time, avoid insufficient selection margin, which will cause insufficient motor torque and speed drop under high load conditions. Accurate selection ensures that the pump operates efficiently and stably at the rated working point, reducing abnormal speed caused by working condition deviation from the source.
IV.
Control System Upgrade: Achieving Closed-loop Stable Speed with Precise Control
The traditional control mode of simple start-stop and extensive speed regulation cannot meet the speed stability demand of complex working conditions in the salt chemical industry. Through control hardware upgrade and control algorithm optimization, millisecond-level precise speed regulation can be realized to actively offset the impact of load fluctuation.
- Redundant PLC Architecture and Industrial Ethernet CommunicationThe core control system adopts Siemens S7-1200 series redundant PLC modules. The main and standby modules switch without disturbance in case of failure, avoiding control failure and speed out of control caused by single module fault. The whole system adopts PROFINET industrial Ethernet architecture. Compared with traditional bus communication, the data transmission rate is increased by more than 10 times, and the control command delay is less than 10ms, ensuring that speed regulation commands are issued in real time without regulation deviation caused by communication delay. The control system is also connected to equipment condition monitoring data to realize linkage protection of speed, vibration, temperature and pressure, providing early warning and protective regulation under abnormal working conditions.
- High-performance Vector Frequency Converter and Closed-loop Speed ControlThe frequency converter adopts ABB ACS880 series vector control products with direct torque control technology, which can achieve a speed response time of ≤0.5s, quickly compensate output torque when load changes suddenly, and suppress speed fluctuation within a very small range. Configure closed-loop speed control mode, take the encoder feedback signal at the motor end as the verification basis, and correct the output frequency in real time to completely eliminate speed deviation caused by slip. For salt chemical corrosion environments, the frequency converter cabinet adopts IP54 protection rating and anti-corrosion coating design, with built-in anti-salt spray filter device to ensure long-term stable operation of electrical components. At the same time, multiple protection parameters such as torque upper limit and overload protection are set to balance speed stability and equipment safety.
V.
Full-cycle Operation & Maintenance Preventive Measures
The governance of speed instability relies 30% on transformation and 70% on operation and maintenance. Establishing a systematic preventive operation and maintenance mechanism can detect degradation trends in advance, eliminate faults in the bud, and maintain pump speed accuracy for a long time.
- Full Life Cycle Equipment Files and Condition MonitoringEstablish independent full life cycle files for each pump set, recording selection parameters, previous maintenance records, component replacement, fault history and operation data. Perform vibration spectrum analysis once a month, and strictly control the vibration velocity at bearings to no more than 4.5mm/s. Through spectrum characteristics, early faults such as bearing wear, rotor unbalance and misalignment can be identified in advance — these degradation problems often first manifest as abnormal vibration, and further develop into speed fluctuation. Early intervention can effectively prevent fault expansion. Simultaneously monitor the motor current curve, and check load and electrical faults in time when current fluctuation is abnormal.
- Professional Operation and Maintenance Capability CertificationThe operation and maintenance of salt chemical pumps have strong industry particularity, and conventional hydropower operation and maintenance experience cannot fully cover the demand. Front-line technical personnel shall pass the special training of Salt Chemical Pump Operation and Maintenance Certification provided by Changsha Zhonglian Pump Industry, systematically mastering pump structure principle, daily inspection key points, parameter adjustment methods, common fault prediction and treatment specifications, so as to eliminate abnormal speed caused by improper operation and parameter misadjustment. The training also covers industry knowledge such as medium characteristics and corrosion protection to improve the full-scenario problem handling ability of operation and maintenance personnel.
- Preventive Maintenance Agreement with the Pump ManufacturerSign an annual preventive maintenance service agreement with the pump manufacturer, and original factory engineers will regularly conduct professional on-site testing. Services include ultrasonic detection of impeller wear, seal performance detection, bearing condition assessment, electrical parameter verification and other professional items. Components with wear close to the threshold shall be warned and replaced in advance to avoid speed out of control and production shutdown after component failure. The agreement is also equipped with a priority supply channel for spare parts, compressing the fault response time to within 24 hours, minimizing the impact of equipment failure on production.
