Patent Publication Number: US-2015086385-A1

Title: Method for controlling pumping of pump units in a wet well

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to pumping control methods, and more particularly, to an energy-saving pumping control method applied in a wet well. 
     2. Description of Related Art 
     Conventional wastewater pumping stations are divided into wet well and dry well types according to the installation of pump units. The pump units in a dry well typed pumping station are installed in a pipe gallery to facilitate visits by staff for maintenance and repairs, while the submersible pump units in a wet well typed pumping station are installed in a sewer tank that is used for temporarily storing wastewater. The wet well typed pumping station can have a reduced volume and save cost for deep excavation of the pumping station. 
     Since wastewater can be temporarily stored in the wet well, the pump units are generally started to pump wastewater out of the wet well when the wastewater level rises to a high level. During the wastewater pumping process, the total pumping capacity of the pump units is greater than the inflow of the wet well and therefore the wastewater level in the wet well begins to drop. When the wastewater level reaches a low level, the pump units are stopped. Meanwhile, wastewater continuously flows into the wet well and the wastewater level begins to rise again. When the wastewater level reaches the high level, the pump units are started again for another pumping cycle. 
     In such a pumping method, the pump units are started over and over again. If the pump units are often started before heat generated is completely dissipated out of the pump units, the pump units are easily damaged. Further, multiple pump units that are connected in parallel in the wet well may come from different manufacturers and have different characteristic curves and different horsepower. As such, even if the pump its are set at the same rated flow, it is difficult to achieve optimum efficiency and energy saving through manual operations. Furthermore, a high operating safety factor is required in manual operations and it is difficult to perform a customized adjustment of operating frequencies of the pump units through manual operations. Therefore, the above-described method easily causes energy waste and the device lifetime is adversely affected by frequent switching of the pump units. 
     Therefore, there is a need to provide a method of pumping control in a wet well that is applicable to a plurality of pump units so as to overcome the above-described drawbacks. 
     SUMMARY 
     In view of the above-described drawbacks, the present disclosure provides a method of pumping control in a wet well. The method includes calculating the number and operating frequencies of pump units to be started according to inflow of the wet well so as to cause the total pumping capacity of the pump units to be equal to the inflow of the wet well, thereby reducing the incidence of a low liquid level, reducing the switching frequency of the pump units and achieving optimum efficiency and energy saving. 
     The present disclosure provides a pumping control method for controlling pumping of a plurality of pump units in a wet well, which comprises the steps of: (1) monitoring inflow of the wet well; (2) when the liquid level in the wet well reaches a first predetermined level for pumping, calculating an objective through an algorithm according to pumping performances of the pump units and the inflow so as to determine one of the pump units to be started and its initial operating frequencies and to generate an initial control signal; (3) sending the initial control signal to the one of the pump units to be started to set its initial operating frequencies for pumping; (4) monitoring the liquid level in the wet well in real time to obtain real-time state information; (5) determining whether a fine adjustment condition is met according to the real-time state information, wherein if yes, the initial operating frequency of the one of the pump units to be started is fine-adjusted and the process goes back to the step (4), and if not, the process goes to the step (6); and (6) determining whether the liquid level in the wet well reaches a second predetermined level for stopping pumping, wherein if yes, the pump units are stopped, and if not, the process goes back to step (4). 
     According to the present disclosure, the minimum total energy consumption is calculated by using a genetic algorithm according to the pumping performances of the pump units and the inflow of the wet well so as to determine which of the pump units are to be started and their initial operating frequencies for pumping. During the pumping process, the liquid level of the wet well is continuously monitored and it is determined whether a fine adjustment condition is met such that the initial operating frequencies of the pump units to be started are fine-adjusted so as to cause the total pumping capacity to be equal to the inflow of the wet well, thereby reducing the incidence of a low liquid level, saving energy consumption, reducing the switching frequency of the pump units and increasing the device lifetime. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a flow chart showing a method of pumping control in a wet well according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following illustrative embodiments are provided to illustrate the disclosure, these and other advantages and effects can be apparent to those in the art after reading this specification. 
     It should be noted that all the drawings are not intended to limit the present disclosure, Various modifications and variations can be made without departing from the spirit of the present disclosure. Further, terms such as “on”, “a” etc. are merely for illustrative purposes and should not be construed to limit the scope of the present disclosure. 
       FIG. 1  is a flow diagram showing a method of pumping control in a wet well according to the present disclosure. The method of the present disclosure is applicable to a plurality of pump units that are connected in parallel in the wet well or in other combinations. 
     Referring to  FIG. 1 , at step S 01 , inflow of the wet well is monitored. In particular, the liquid level in the wet well is sensed through a plurality of liquid level sensors in the wet well such that the inflow of the wet well is calculated according to the change of the liquid level with time. At step S 02 , when the liquid level in the wet well reaches a predetermined level for pumping, as sensed by a high liquid level sensor, the process goes to step S 03 . At step S 03 , an objective is calculated by a computer through an algorithm according to pumping performances of the pump units and the inflow of the wet Well so as to determine which of the pump units are to be started and their initial operating frequencies and generate an initial control signal. In particular, the objective is a minimum total energy consumption of the pump units. 
     The pump units may be manufactured by different manufacturers and therefore have different performances. Further, the pump units may have different pumping capacities according to their positions and connections to the pipeline of the pumping station. Therefore, the pumping performances of the pump units include pumping capacities and energy consumptions that are assessed through performance curves of the pump units and pipeline system curves of the pumping station. The pumping capacity can be a maximum pumping capacity and a minimum pumping capacity, for example. The energy consumption can be energy consumption at the maximum pumping capacity, energy consumption at the minimum pumping capacity, or energy consumption at a pumping capacity between the maximum pumping capacity and the minimum pumping capacity. 
     The algorithm performed by the computer is a genetic algorithm. The genetic algorithm determines which of the pump units are to be started and their initial operating frequencies according to the pumping performances of the pump units and the inflow of the wet well so as to achieve an optimum total pumping capacity that is equal to the inflow of the wet well and a minimum total energy consumption. Further, the algorithm can be operated based on a condition that the total pumping capacity is equal to the inflow of the wet well. 
     The genetic algorithm is an optimum search algorithm, which originates from Darwin&#39;s theory of natural selection and survival of the fittest. The genetic algorithm generates chromosomes by coding variables, calculates fitness values of the chromosomes and then performs selection, crossover and mutation to generate offspring chromosomes, thereby gradually approaching an optimum solution. In particular, the genetic algorithm includes the steps of:
         (1) setting chromosomes according to the pumping capacities and energy consumptions of the pump units;   (2) setting a margin of error for the pumping capacities;   (3) setting an error weight Wq for the pumping capacities and an energy consumption weight Wp, wherein Wq and Wp are values between 0 and 1, and the sum of Wq and Wp is 1;   (4) inputting chromosomes, wherein N randomly selected chromosomes are provided, N is a constant and each of the chromosomes represents the pumping capacity and energy consumption of one of the pump units;   (5) fitness sorting, wherein if the pumping capacities of the chromosomes are within the margin of error, the chromosomes are sorted in an ascending order of energy consumptions, otherwise, if the pumping capacities of the chromosomes are out of the margin of error, a fitness function based on Wq and Wp is calculated for the chromosomes such that the chromosomes are sorted in an ascending order of the fitness function values;   (6) keeping a number of excellent chromosomes in the order of the fitness function values and replicating the chromosomes to cause the number of the chromosomes to reach N;   (7) keeping the first X % of the chromosomes in the order of the fitness function values and crossing the first X % of the chromosomes with the remaining (1-X %) of the chromosomes, wherein X is a constant;   (8) mutating the crossed chromosomes to keep the diversity advantage of the chromosomes, thereby preventing omission of important information in the search process;   (9) calculating the number of pump units that have a minimum total energy consumption according to the mutated chromosomes;   (10) determining whether the desired number of convergence times for calculating the minimum total energy consumption is reached, if yes, the process goes to the next step, otherwise, the process goes back to step (5) for fitness sorting; and   (11) outputting the pump units to be started and their initial operating frequencies and generating an initial control signal, wherein the pump units to be started have a minimum total energy consumption.       

     Through the above-described genetic algorithm, which of the pump units are to be started and their suitable pumping capacities as well as their operating frequencies are determined based on a condition that the total pumping capacity is equal to the inflow of the wet well so as to achieve the objective of a minimum total energy consumption. For example, five pump units 1, 2, 3, 4, 5 can be provided. The pump units 2, 4, 5 are determined to be started. The total pumping capacity is the sum of the pumping capacities of the pump units 2, 4, 5, and the minimum total energy consumption is the sum of the energy consumptions of the pump units 2, 4, 5. The pump units 2, 4, 5 have their respective operating frequencies. Therefore, an initial control signal is generated by the computer. Then, at step S 04 , the initial control signal is sent to the pump units to be started so as to set their initial operating frequencies for pumping. Before setting the initial operating frequencies of the pump units to be started, a step of determining whether the pump units to be started are already started is performed. If the pump units to be started are already started, the initial operating frequencies of the pump units are set. If the pump units to be started are not started, the pump units are started first and then their initial operating frequencies are set. 
     During the pumping process, at step S 05 , the liquid level in the wet well is continuously monitored in real time by the computer through the liquid level sensors so as to generate real-time state information. The real-time state information is a liquid level difference in a unit time. In an embodiment, the real-time state information is a liquid level difference per second. In the present disclosure, the liquid level difference in a unit time is the change of the liquid level in each time interval. For example, Δh(t)=h(t)−h(t−1). Therein, t represents time, h represents the liquid level, and Δh(t) represents the liquid level difference in a unit time. Since the inflow of the wet well is not fixed, the change of the liquid level in the wet well needs to be monitored in real time so as to generate real-time state information of Δh(t), thereby determining whether the liquid level is rising, dropping or steady. According to the real-time state information, the operating frequencies of the started pump units can be fine-adjusted through the computer so as to cause the total pumping capacity to be equal to the inflow of the wet well, thus reducing the incidence of a low liquid level. To perform the fine adjustment process, the computer determines whether the real-time state information meets a fine adjustment condition at step S 06 . 
     1. The Fine Adjustment Condition Not Being Met: 
     If Δh(t) is less than a minimum allowable value but greater than zero, the fine adjustment condition is not met. In such a circumstance, the liquid level is substantially steady and the inflow of the wet well is slightly greater than the total pumping capacity. The minimum allowable value is the minimum margin of error set by a user. Since the inflow of the wet well is not fixed, the total pumping capacity may not be always equal to the inflow of the wet well. Such a margin of error prevents an adjustment of the operating frequencies of the pump units when a slight change of the liquid level occurs so as to save energy consumption. Therefore, if it is determined that the fine adjustment condition is not met at step S 06 , the process goes to step S 08 . 
       2 . The Fine Adjustment Condition Being Met: 
     On the other hand, if it is determined that the fine adjustment condition is met at step S 06 , the operating frequencies of the started pump units are fine adjusted at step S 07 . The fine adjustment condition is determined to be net when the liquid level rises or drops significantly. 
     If the liquid level rises significantly, i.e., Δh(t) is greater than a limit value set by a user, it means that the inflow of the wet well increases and the total pumping capacity is less than the inflow. As such, the operating frequencies of the pump units need to be fine-adjusted so as to increase the total pumping capacity. Otherwise, the liquid level may rise fast to a warning liquid level and become dangerous. Therefore, when Δh(t) is greater than the limit value, the initial operating frequencies of the pump units to be started are fine-adjusted upward so as to cause the total pumping capacity of the pump units to be equal to or greater than the inflow of the wet well. 
     If the liquid level drops significantly, i.e., Δh(t) is less than zero, it means that the total pumping capacity is greater than the inflow of the wet well. As such, the operating frequencies of the pump units need to be fine-adjusted so as to reduce the total pumping capacity. Therefore, the initial operating frequencies of the pump units to be started are fine-adjusted downward. But the initial operating frequencies must be greater than a minimum safety frequency so as to prevent the pump units from coming into an unsafe area where an erosion of the pump units may occur. 
     After the fine adjustment of the operating frequencies of the pump units at step S 07 , the process goes back to step S 05  to continuously monitor the liquid level in the wet well so as to determine whether there is a need to fine-adjust the operating frequencies of the pump units. If it is determined that the liquid level difference per second does not meet the fine adjustment condition, the process goes to step S 08 . At step S 08 , it is determined whether the liquid level in the wet well reaches a predetermined level for stopping pumping, as sensed by a low liquid level sensor. If it is determined that the liquid level in the wet well reaches the predetermined level for stopping pumping, the process goes to step S 09  to stop the pump units. Otherwise, if it is determined that the liquid level in the wet well does not reach the predetermined level for stopping pumping, the process goes back to step S 05  to continuously monitor the liquid level in the wet well so as to continuously determine whether there is a need to fine-adjust the operating frequencies of the pump units until the liquid level in the wet well reaches the predetermined level for stopping pumping. 
     According to the present disclosure, a genetic algorithm is used to determine which of the pump units are to be started and their initial operating frequencies for pumping according to the pumping performances of the pump units and the inflow of the wet well, thereby achieving a minimum total energy consumption. Further, during the pumping process, the operating frequencies of the pump units can be fine-adjusted according to the real-time change of the liquid level in the wet well so as to cause the total pumping capacity to be equal to the inflow of the wet well, thereby reducing the incidence of a low liquid level, saving energy consumption, reducing the switching frequency of the pump units and increasing the device lifetime. Therefore, the present disclosure achieves optimum efficiency and energy saving. 
     The above-described descriptions of the detailed embodiments are only to illustrate the preferred implementation according to the present disclosure, and it is not to limit the scope of the present disclosure. Accordingly, all modifications and variations completed by those with ordinary skill in the art should fall within the scope of present disclosure defined by the appended claims.