Features and technologies of pumps for water treatment

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This post was last edited by yinkuilin6868 on 2016-6-17 09:33. I. Introduction Water is a fundamental condition for the survival of all living things, and it is essential for human life and production. Our country suffers from a shortage of water resources, which are unevenly distributed in terms of time and space. With the growth of the population and the national economy, the scope and severity of water pollution are increasing. Water pollution in China’s major rivers and coastal areas is extremely severe, and the resulting water crisis has severely hindered the rapid development of various industries as well as the improvement of people’s living standards; therefore, water treatment has become an absolute necessity. Pumps are important devices in water treatment for transporting fluids, providing energy to them so that they can overcome the resistance encountered during flow and maintain a certain flow rate within the equipment or pipes. Additionally, during water treatment, it is also necessary to transfer chemical reagents from Tank A to Tank B, from a lower level to a higher level. All of this is accomplished through the work done by water pumps. It is evident that choosing pump products appropriately and understanding the technological development trends of pumps used in water treatment have become important aspects of water treatment work. This article provides a brief introduction to the structural features and application scenarios of pumps used in water treatment, for reference by relevant professionals. II. Classification of pumps for water treatment. In the field of water treatment, there are a wide variety of pump devices in use, and it is difficult to provide a comprehensive classification using just one method; instead, classification is often carried out in different ways depending on actual needs. A brief introduction is provided below. 1. Classified by working principle: Vane pumps: These use the interaction between vanes and the liquid to transport it, such as centrifugal pumps, mixed-flow pumps, axial flow pumps, and vortex pumps. Positive displacement pumps: These pumps use the periodic variation in the volume of the working chamber to transfer liquids, such as piston pumps, plunger pumps, diaphragm pumps, gear pumps, vane pumps, and screw pumps. Other types of pumps: Pumps that only change the potential energy of the liquid, such as water wheels, etc ； Pumps that use liquid energy to transport liquids, such as jet pumps, water hammer pumps, and acid egg pumps. 2. Classified by the medium they transport, there are three types: single-phase medium transfer pumps, two-phase medium transfer pumps, and multi-phase medium transfer pumps. 3. Classification of centrifugal pumps for water treatment
Among pumps used in water treatment, centrifugal pumps are the most widely applied. The common types include: single-stage pumps, multi-stage pumps, double-suction pumps, mixed-flow pumps, axial-flow pumps, submersible pumps, sewage submersible pumps, screw pumps, metering pumps, plunger pumps, screw compressors, and jet pumps, etc. III. Introduction to Main Products 1. Centrifugal Corrosion-Resistant Pumps These pumps are primarily single-stage, single-suction, cantilever-type corrosion-resistant pumps, used for transporting corrosive fluids free of solid particles, with operating temperatures ranging from 0 to 100°C. In water treatment, it is commonly used for transporting H-water in ion exchange processes. The materials of the flow-through components in contact with the conveying medium are stainless steel and plastic. The difference between the two lies in the way the pump body, pump cover, and bracket are connected. In the former case, the pump body is fixed to the trailer, and then the pump cover is fixed to the pump body ； In the latter case, the pump body is fixed to the bracket by means of the flange on the pump cover, which also fixes the pump cover. 2. Sewage pump: A sewage pump mainly consists of components such as the pump body, pump cover, bearing housing, impeller, and shaft. It is mainly used to transport fluids with fibers or other suspended particles at temperatures below 80°C, as well as wastewater that is acidic, alkaline, or otherwise corrosive. There are two main types of sewage pumps in common use: one is the sewage pump driven by a regular electric motor, and the other is the submersible sewage pump. 3. Split-case pump: Split-case pumps are used in water treatment processes for transporting fluids such as clean water, with a maximum temperature of 80°C. Commonly used center-opening pumps include S-type centrifugal pumps and flSh-type centrifugal pumps. The S-type centrifugal pump features high efficiency and low production costs, making it energy-efficient. Sh-type centrifugal pumps have high operational reliability and a long service life. A split-case pump, as the name suggests, has a pump body of split design, divided into upper and lower parts. Its joint seam and the axis center are on the same plane, separated by a paper pad in between. The upper and lower bodies are positioned with pins and secured with bolts. Both the suction port and discharge port are on the lower body, oriented horizontally and perpendicular to the pump shaft. After the upper and lower parts are brought together, two symmetrical suction chambers are formed on either side of the impeller; these two chambers share a single suction inlet. The area in between is the high-pressure chamber, whose bottom is connected to the discharge pipe at a 1:1 ratio. When the impeller of a centrifugal pump is in operation, the presence of a low-pressure side (the inlet) and a high-pressure side (the outlet) within the pump results in uneven forces acting on both sides of the impeller. To avoid this problem, several balance holes are made in the middle of the right side of the impeller, allowing a small amount of high-pressure water on the right side to flow back into the low-pressure area, thereby balancing the axial thrust. 4. Reciprocating pump: A reciprocating pump relies on a piston (or plunger) that moves back and forth within the pump cylinder to change the volume of this cylinder; together with the action of two check valves, it achieves the purpose of sucking in or discharging liquid. Based on the structure of the piston, reciprocating pumps can be classified into three types: piston-type reciprocating pumps, plunger-type reciprocating pumps, and diaphragm-type reciprocating pumps. The main component of a piston reciprocating pump is the piston, which relies on its movement within the pump cylinder to draw in or discharge liquid. The main component of a plunger-type reciprocating pump is the plunger (which is columnar in shape); it has a larger contact area with the surface and is more wear-resistant. Its mechanism of action is exactly the same as that of a piston. The main component of a diaphragm reciprocating pump is also the plunger. Unlike piston reciprocating pumps, a rubber (or steel) diaphragm separates the pump’s working chamber from the cylinder body; as the plunger moves back and forth, the diaphragm expands and contracts accordingly, thereby facilitating the suction or discharge of liquid. 5. Metering pumps and screw pumps are widely used in water treatment processes; metering pumps and screw pumps are particularly common in such applications. (1) Metering pumps: There are two types of metering pumps, piston-type and diaphragm-type. They are mainly composed of a worm gear, an eccentric wheel, a bow-shaped frame, a crosshead, a piston, an eccentric shaft, an adjustment screw, and a motor. A metering pump is a reciprocating pump that enables dynamic or static adjustment of flow rate: the flow rate is controlled by adjusting the distance between the screw and the eccentric shaft. The smaller the distance between the screw and the eccentric shaft, the greater the pump’s stroke, and thus its flow rate as well ； Conversely, the pump flow rate also becomes smaller. J-type metering pumps are widely used in applications where accurate metering, adjustable dosing, and continuous delivery of a medium are required. In water treatment processes, it is used to transport and add corrosive and non-corrosive chemicals that contain no solid particles. Depending on the chemical properties of the medium being transported, the flow-through part of the hydraulic cylinder can be made from appropriate corrosion-resistant materials. (2) Screw pumps include single-screw pumps, twin-screw pumps, and triple-screw pumps. It can be used to transport fluids containing a single medium or multiple media, including those that are neutral or corrosive, clean or abrasive, gas-containing or prone to bubbling, high-viscosity or low-viscosity, as well as liquids containing fibers or solid particles; it is widely applicable in various industrial sectors. The operating principle of a screw pump is as follows: when the screw pump is in operation, the liquid is drawn in and enters the sealed space formed between the threads and the pump casing. As the driving screw rotates, the sealed volume within the screw pump increases under the compression exerted by the threads, thereby raising the pressure and causing the volume to move axially. Since the screw rotates at a constant speed, the flow rate of the liquid output is also uniform. Therefore, screw pumps have the advantages of good economic performance, high pressure, uniform flow rate, and high rotational speed. IV. Technological Development Trends To better meet the requirements for pumps in the water treatment industry, the main technological development trends for water treatment pumps are as follows. 1. Technical research on the safety of pump operation. In the water treatment industry, water pumps are extremely important equipment. The safe operation of water pumps has a direct impact on the proper functioning of water treatment processes. In the event of serious failures, the entire water treatment process will come to a halt, causing significant inconvenience to people’s daily lives and industrial activities. Based on the current analysis of the operation of pumps used in water treatment, common faults include surface corrosion of the impeller due to prolonged exposure to sewage, premature fatigue fracture of the blades, wear of the flow-through components of the pump, bending of the pump shaft, and damage to the motor and bearings. Research on operational safety is very important; through such research, not only is the safety of pumps improved, but their service life is also extended. 2. Technical research on automatic pump control: During water treatment processes, the water consumption and pressure in the system change frequently. If these requirements cannot be met, it will affect the normal operation of production and lead to significant waste. To manage effectively, it is necessary to conduct remote monitoring and on-site control of the production system ； To improve production efficiency and safety, it is also necessary to inspect the key parts of water treatment pumps. It is evident that conducting research on automatic control technology is an important technological development trend. Currently, there is substantial research being conducted on automatic frequency conversion technology, and initial satisfactory results have been achieved, bringing significant economic and social benefits. The method of adjusting the rotation speed achieves good energy-saving effects, as has been proven by numerous practices in China. In many applications for pumps, it is sometimes necessary to keep the performance parameters of the pump constant, while at other times those parameters need to vary depending on the operating conditions. Adjusting the speed can achieve this goal; it also improves the efficiency of the piping system, thereby significantly enhancing the overall efficiency of the device. 3. Technical research on pump selection and system energy conservation: For various reasons, there are many unreasonable practices in the selection and design of pumps, which leads to energy waste and has a significant impact on energy-saving efforts. (1) Principles to be followed in the selection of water pumps: 1) The user should determine reasonably the performance parameters and necessary operating conditions of the pump. 2) The design department should reasonably determine the type and parameters of the pump to adequately meet the on-site operating conditions. 3) Comprehensively consider the pump’s maximum efficiency, high-efficiency range, and actual operating efficiency indicators. 4) Conduct a techno-economic comparison to select a technically advanced and economically reasonable scheme. (2) Improving the efficiency indicators of centrifugal pump systems. Energy-saving efforts for centrifugal pumps should not be limited to examining the efficiency of the pumps themselves; rather, it is necessary to assess the efficiency indicators of all aspects of the entire system, in order to achieve efficient energy use across the whole system. There is considerable potential in this regard. Detailed analytical research should be conducted in the following areas. 1) Whether the configuration of the pump unit and the entire production system is reasonable, ensuring both that the operational requirements are met and that energy-saving objectives are achieved. 2) Whether the configuration of the centrifugal pump and the motor is reasonable, and what the energy-saving efficiency of the motor is. 3) Is the piping layout reasonable? Reduce the number of pipes to improve piping efficiency. 4) Whether the configuration of the transmission mechanism is reasonable; the selection and use of the transmission mechanism not only affect transmission efficiency but also have an impact on the efficiency of the power engine, water pump, and pipelines. 5) Whether the efficiency and steam usage are reasonable. 6) Whether aspects such as piping and maintenance for the operation of the centrifugal pump system are reasonable. 4. Research on special properties: Due to differences in operating conditions, in addition to the technical research outlined above, it is also necessary to conduct further research on certain special properties, mainly in the following areas. 1) Research on special conveying media, such as solid-liquid mixed conveying media. 2) Research on special materials; such materials should possess strong corrosion resistance and wear resistance. 3) Research on special structures, such as unobstructed flow channels and double-layer special structures. V. Conclusion Pumps are important equipment in water treatment processes. A brief analysis of several major types of water treatment pumps is provided, summarizing their structural features and operating conditions to offer a reference for the rational selection of pumps for water treatment. At the same time, it points out the technological development trends in pumps for water treatment. To achieve higher efficiency as well as energy savings and reduced consumption, further exploration and research are needed in four areas: pump operation safety, automation, energy efficiency, and special performance features.