The evaporative crystallization system is a complete set of equipment organically composed of multiple small units. During the debugging process, various situations are inevitable. Effectively solving and avoiding unstable factors or incorrect operations during debugging can effectively extend the operating cycle of the evaporation system and achieve better economic benefits.
1. Pump tripping phenomenon
Cause analysis ：Pumps play a role in material transfer in the process system. If the pump stops working, the entire system will not be able to operate. During the debugging process, the reasons for pump tripping include: 1. Excessive load, including excessive material viscosity and exceeding the solid-liquid ratio, leading to motor seizure; 2. Foreign objects in the pump cavity, jamming the impeller, etc.; 3. Two-phase power supply is connected incorrectly to the motor.
Solutions :1. In the case of correct motor selection, increase the upper limit of current protection to solve the tripping phenomenon; 2. When the pump is running, listen to whether there is any abnormal noise inside the pump to determine whether there are foreign objects in the pump cavity; 3. Before starting, carefully check the product specifications, model, power, voltage, and current parameters to avoid inconsistencies between wiring and requirements.
2. Material leakage phenomenon
Cause analysis ：During the debugging process, materials may appear in the condensate water, causing material loss and condensate water pollution. The reasons for this include: the liquid level in the crystallizer is too high, the gas-liquid separation space is small, and the material is carried away; the material is severely entrained in the form of mist during evaporation, and the demister does not achieve its working effect, causing the material to be carried away; the system vacuum is too high, exceeding the design range, causing material leakage.
Solutions :1. At the design stage, fully consider the gas-liquid separation space, and strictly control the feed rate. Through liquid level control, avoid the occurrence of high liquid level; 2. Strictly control the material concentration. For conditions with severe mist entrainment, a defoaming device or increased defoaming agent should be designed; 3. Set a pressure transmitter in the separation chamber of the crystallizer to stabilize the vacuum through linkage control.
3. Heat exchanger scaling phenomenon
Cause analysis ：The preheater, evaporator, and condenser in the system all play a role in heat transfer. According to the principle of heat transfer, the thicker the scale layer, the lower the heat transfer efficiency, and the shorter the operating cycle of the heat exchanger. During the system debugging process, the main reason for scaling is that the ions in the material medium combine to form insoluble precipitates, and the precipitation scaling phenomenon becomes serious as the temperature increases.
Solutions :1. Reduce the content of scaling ions in the material as much as possible; 2. The equipment should be cleaned regularly through online chemical cleaning or offline chemical cleaning to ensure that the heat exchanger surface is smooth and free of blockage.
4. Heat exchanger coking phenomenon
Cause analysis ：The heat exchanger separates hot and cold materials through the heat transfer wall. If the heat transfer surface is damaged and the coke layer is increased, the heat transfer of the heat exchanger will fail. During the system debugging operation, the causes of coking include: 1. Material interruption or feed rate less than the sum of the discharge and secondary steam, and steam is not stopped, which will cause the material level to drop, and then the material will hang on the wall, causing the equipment wall to burn dry and coke; 2. Excessive steam pressure, or sudden changes in operating conditions, may cause serious coking on the heat transfer surface.
Solutions :1. Strictly follow the operating manual for start-up and shutdown, and set a flow meter in the feed pipeline to monitor the system and avoid material interruption or insufficient material causing the equipment to burn dry and coke; 2. The steam pipeline needs to be equipped with a steam regulating valve and a pressure regulating valve to control the steam volume, which should not be too high. If the excess is serious, the inlet valve should be cut off as soon as possible, and the amount of cold material should be increased to absorb the residual heat.
5. Automatic control failure of electrical components
Cause analysis ：At present, the evaporative crystallization systems used in engineering applications have all achieved automatic control. Among them, regulating valves, liquid level sensors, temperature transmitters, and pressure transmitters play a decisive role in the interlocking control. If they fail, it will affect the system from minor control imbalance to major system damage. The reasons for failure include: 1. The regulating valve positioner fails and cannot be remotely adjusted; 2. The liquid level meter fails, and the real-time liquid level cannot be determined. The reason may be a wiring error in the liquid level meter itself, or it may be foaming of the material causing a false liquid level; 3. Temperature and pressure changes fail, and cannot provide real-time feedback on the system temperature and pressure. The temperature probe may contact the wall, and the pressure change probe hole may be blocked, causing it to fail.
Solutions :1. Once the regulating valve is damaged, it should be returned to the factory for repair in time, and inspection and testing should be carried out before leaving the factory. After passing, it should be sent to the site. If it cannot be solved in time, a backup plan can be used for local operation, but experienced operators are required; 2. Different types of liquid level meters should be installed strictly according to the installation instructions. If the liquid level probe is too long, consider the impact of material flow, whether it will cause measurement failure. If false liquid level is caused by material foaming, defoaming agent should be added in time or a defoaming device should be set; 3. For temperature and pressure changes, the wiring problems should be ruled out first. If there is no error, check whether the probe is wrapped or damaged. Local instruments should be set in the system, which can be compared and corrected with the sensor.
6. Pipeline blockage phenomenon
Cause analysis ：In the system crystallization process, the pipeline for transporting crystal slurry may cause different degrees of blockage due to valve settings and temperature control factors. The main reasons for blockage include: 1. Some crystallized materials will quickly crystallize on the inner wall of the pipe as the temperature decreases, causing pipeline blockage; 2. Valves play a role in cutting off in the pipeline system. When the valve is closed, the material will be cut off. When the valve is fully open, the material will flow. Some valves will also have mechanical dead corners in the fully open state, causing crystal grains to accumulate. Under long-term working conditions, it will cause pipeline blockage.
Solutions :1. In order to prevent large temperature changes during pipeline transmission, insulation measures or heating devices can be designed to ensure that the material does not crystallize in the pipeline and cause pipeline blockage; 2. Valves are generally selected according to the standards of simple structure and large flow area, such as ball valves, and try to avoid using globe valves or butterfly valves. In the pipeline setting, try to set one valve for each pipeline, which is convenient for disassembling the pipeline when the pipeline blockage is serious.
Disclaimer: The content is from the Internet. We remain neutral on the views in the text and provide it for reference and exchange purposes only. The copyright of the reprinted articles and pictures belongs to the original authors and institutions. If there is any infringement, please contact us for deletion!
