Learn - Nov. 19, 2024
In a complete evaporation crystallization application, it is often necessary to utilize various types of pump equipment, including chemical axial flow pumps (also known as forced circulation pumps or evaporation circulation pumps), chemical mixed flow pumps, chemical centrifugal pumps and vacuum pumps. The professional selection of pump equipment according to the suitable evaporation crystallization conditions is crucial for enhancing the overall performance and economic benefits of the evaporators.
The primary functions of pumps in the evaporation systems are as follows:
Material handling
Pumps play a crucial role as power sources in evaporative crystallization applications, facilitating the transportation of raw material liquids, intermediates, condensate or finished concentrates between containers and pushing liquids through heaters, heat exchangers, and other equipment.
Circulation and Agitation
In certain evaporative crystallization processes (e.g., forced-circulation evaporators), pumps are utilized to maintain a continuous flow of solution, ensuring even distribution of heat, preventing localized overheating, and promoting uniform crystal growth.
Flow and Pressure Control
By adjusting the speed of the pumps or opening of discharge valve of the pumps, precise control over the flow into the evaporator and pressure within the system can be achieved. This is essential for maintaining a stable evaporation rate and optimal crystallization conditions.
The selection of a pump for an evaporator crystallization system should take into consideration the following aspects:
Flow and head
Accurately calculate the required pump's flow and head based on the specific needs of the evaporator to avoid inefficient operation, which can impact energy consumption and efficiency.
Corrosion resistance and material
Since evaporation crystallization processes often involve corrosive medium such as acids, alkalis, and salts, it is crucial to select a pump with materials that can resist corrosion from these chemicals. Commonly used materials include various stainless steels, titanium, nickel alloys, Hastelloy steel or non-metallic materials like PVDF, PFA or PTFE linings.
High temperature and high pressure resistance
The evaporation crystallization process may involve high temperatures and certain pressures. Therefore, it is important to choose a pump with design temperature and pressure levels higher than the actual operating conditions to ensure safe and reliable operation.
Wear resistance
Solid particles may be present during the crystallization process, requiring enhanced wear resistance in the pump's wetted parts. During the pump selection, please consider whether its structural design can reduce wear by utilizing features such as open impellers or wear-resistant bushings.
Self-priming ability and anti-cavitation ability
Some processes may require pumps with good self-priming abilities, especially when frequent starting/stopping occurs or when cavitation is likely. In such cases, opt for pumps with sufficient self-priming height.
Shaft sealing
Consider medium characteristics and environmental protection requirements when choosing an appropriate sealing configuration, for example single mechanical seals, double mechanical seals or magnetic drive pumps, to prevent leakage.
Maintenance and cleanup
The selection of pumps for evaporation crystallization equipment should also consider the maintenance cycle and cleaning requirements. It is advisable to choose a pump type that is easy to disassemble, maintain and clean.
Energy efficiency
To reduce operating costs and align with the industrial trend of energy conservation and emission reduction, it is recommended to select high-efficiency pumps that meet or exceed relevant energy efficiency standards.
Specific illustration of pump model selection for evaporators:
A) Selection of forced circulation pumps in multi-effect or MVR evaporators
l Flow rate and head: For large flow rate but low head, chemical axial flow pumps or mixed flow pumps must be selected.
l Corrosion resistance and material: Titanium or duplex stainless steel must be adopted for brine with a lot of free chloride ion; And select stainless steel or other corrosion-resistant materials for other salts.
l Sealing form: Since it involves the transmission of solid-liquid two-phase crystalline slurry medium, utilize cartridge double mechanical seal with external flush water.
l Drive and transmission mode: Generally powered by motors with coupling connection; belt drive (including fully pipe hung or semi-pipe hung arrangements) can be used.
B) Selection of mother liquor pump, feed pump, raw liquor pump in multi-effect or MVR evaporator
l Flow rate and head: Depending on the project's actual situation, use chemical centrifugal pumps (including chemical process pumps or chemical passage pumps) for medium flow rate and medium head.
l Impeller form: For solid-liquid two-phase slurry medium transmission, employ open or semi-open impellers; closed impellers can be used when dealing with simple liquid phase transmission to achieve higher work efficiency.
l Sealing form: cartridge double mechanical seal with external flush water are often used for solid liquid two-phase slurry medium transportation; single mechanical seals can be utilized for normal temperature clean water mediums.
l Drive and transmission mode: Coupling is commonly employed for connection purposes.
C) Multi-effect or MVR evaporator condensate pump selection
l Flow rate and head: The selection of the chemical centrifugal pump depends on the medium flow and lift, which should be determined based on the actual project conditions.
l Impeller form: For simple liquid phase transport, a closed impeller can be used.
l Sealing form: A high temperature resistant single mechanical seal can be utilized.
l Drive and transmission mode: Generally, coupling connection or direct motor drive is employed.
l Self-priming ability and anti-cavitation ability: An anti-cavitation margin pump or pneumatic diaphragm pump with larger suction capacity should be used.
D) Multi-effect or MVR evaporator vacuum pump selection
l When high vacuum levels are required, dry screw vacuum pumps or jet vacuum pumps can be chosen.
l For large vacuum pumping capacities, Roots vacuum pumps in combination with other types of vacuum pumps are suitable options.
l Water ring vacuum pumps are appropriate for steam-containing environments but require water replenishment through a water seal system. To reduce water usage, liquid ring vacuum pumps equipped with indirect cooling devices can be considered as alternatives.
Sichuan Zigong Pump & Valve Co., Ltd is the TOP manufacturer of chemical axial flow pumps and chemical centrifugal pumps in China, our pumps are working in various countries and regions, providing our clients with satisfying services. Our chemical pump diameter covers from DN250 to DN1800, and are widely used in multi-effect evaporators of chlor alkali, lithium material, MVR waste water treatment and other chemical industries.
Contact us by sales@zgpumpvalve.com or wa.me(Whatsapp: +8613738006567)
