Application in Pump equipment
Application of Frequency Conversion Speed Regulation Technology in Pump Equipment
Description
With the continuous deepening of economic reform and intensifying market competition, energy conservation and emission reduction have become crucial measures to reduce production costs and enhance product quality. Fans and pump equipment are widely utilized in production enterprises, with their electricity consumption, losses associated with valves and dampers, as well as maintenance and repair expenses accounting for a significant portion (7% to 25%) of production costs.
Currently, variable-frequency speed regulation technology has emerged as one of the primary development directions in modern power transmission technology. Its exceptional speed regulation performance, substantial energy-saving effects, enhancement of existing equipment's operational conditions, reinforcement of system safety and reliability, and extension of equipment service life have been comprehensively demonstrated through its expanding application fields.
The use of fans in industrial production and product processing manufacturing industries is primarily seen in boiler combustion systems, drying systems, cooling systems, ventilation systems, etc. The pressure within the furnace, wind speed, wind volume, and temperature indicators are controlled and adjusted to meet process requirements and operating conditions. The most commonly employed control method involves adjusting the damper or flap opening size to regulate the controlled object. Consequently, regardless of production needs' magnitude, the fan must operate at maximum speed; however, changes in operating conditions result in energy loss due to throttling losses incurred by the damper or flap.
In the production process, not only is the control accuracy limited, but it also leads to significant energy wastage and equipment wear and tear. Consequently, this results in increased production costs, reduced equipment lifespan, and higher maintenance and repair expenses. Pumping equipment finds extensive application in various production fields such as water pumping stations, water storage and discharge systems for tanks, industrial water (oil) circulation systems, and heat exchange systems. These applications utilize centrifugal pumps, axial flow pumps, gear pumps, plunger pumps, etc.
In recent years, driven by the urgent need for energy conservation and the increasing demand for product quality improvement, coupled with the inherent advantages of easy operation, maintenance-free operation, high control accuracy, and advanced functionality offered by variable-frequency speed controllers, the utilization of variable-frequency converters as a driving solution has started to replace traditional control methods involving dampers, shutters, and valves. The fundamental principle behind variable-frequency speed control technology lies in the direct proportionality between motor speed and input frequency of the power supply: n = 60f(1-s)/p (where n represents rotational speed, f denotes input frequency, s signifies motor slip rate, and p indicates the number of magnetic poles in the motor). By altering the power supply frequency applied to the motor systemically through a variable-frequency converter unit, it becomes possible to adjust its operating speed accordingly. As an all-encompassing electrical device integrating AC-DC-AC power conversion technology alongside power electronics and microcomputer control technology components.
The fundamental principles of fluid mechanics indicate that wind turbines and pumping equipment impose square torque loads, establishing the following relationships between their rotational speed (n), flow rate (Q), and pressure (H): Q is directly proportional to n, H is directly proportional to n squared, and P is directly proportional to n cubed. In other words, the flow rate varies linearly with rotational speed, while pressure increases quadratically with rotational speed and shaft power increases cubically.
Taking a water pump as an example, its outlet head (H0) is the static pressure difference between the pump inlet and pipeline outlet at rated speed (n0), with fully open valve and pipe resistance characteristic (r0). At rated condition, the corresponding pressure is H1 and outlet flow is Q1. The relationship between flow, speed, and pressure can be observed. In field control, constant speed operation of the water pump is common while adjusting the outlet valve to regulate flow. When reducing flow from Q1 to 50% of Q2, valve opening decreases causing pipe network resistance characteristic to change from r0 to r1; this shifts system operating point along direction I from original A point to B point while reducing throttling action on pressure H1. Actual power output of water pump (kW) can be calculated using formula P = Q · H / (ηc · ηb) × 10-3 where P represents power output, Q represents flow rate, H represents pressure head, ηc represents pump efficiency and ηb represents transmission efficiency with direct transmission being 1. Assuming overall efficiency (ηc · ηb) equals 1 then motor power saved when water pump moves from A point to B point equals area difference between AQ1OH1 and BQ2OH2. The hydraulic resistance characteristic of the pipeline will remain unchanged as the flow rate is reduced from Q1 to Q2 by 50% through speed regulation of the water pump, resulting in a shift of the system working point from A to C along direction II. This adjustment not only ensures more reasonable operation of the pump but also leads to reduced energy consumption when the valve is fully open and only hydraulic resistance exists. The motor power savings can be calculated as the area difference between AQ1OH1 and CQ2OH3. Comparing valve throttling regulation with pump speed control, it becomes evident that utilizing pump speed control is more effective and rational, yielding significant energy-saving benefits. Furthermore, valve regulation may cause an increase in system pressure H, posing a threat to both pipeline integrity and valve sealing performance. However, adjusting the pump speed results in a decrease in system pressure H as the pump speed n decreases, thereby avoiding any negative impact on the system.
