Data processing: structural design – modeling – simulation – and em – Simulating nonelectrical device or system – Fluid
Reexamination Certificate
1998-04-20
2001-01-23
Teska, Kevin J. (Department: 2763)
Data processing: structural design, modeling, simulation, and em
Simulating nonelectrical device or system
Fluid
C703S009000, C700S029000, C700S036000, C700S282000
Reexamination Certificate
active
06178393
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the pumping of liquids, and, more particularly, to control systems and methods for pumping wastewater.
DESCRIPTION OF RELATED ART
In a typical fluid-pumping application the goal is to maintain the quantity of fluid in a vessel. One or more pumps are used to compensate for inflows or outflows caused by events external to the system, and these pumps are selectively activated and controlled to maintain the state of the system within a predetermined range.
In the example of a wastewater lift station, wastewater flows into a wet well from sources such as residences, roadway drains, or other lift stations. One or more pumps remove water from the wet well as necessary to maintain the level within predetermined limits. Transducers can measure wet-well level, wet-well outflow from or inflow to each pump, flow through inlet or outlet pipes shared by multiple pumps, power input to the system or to individual pump motors, and other operating parameters. There may be one or more check valves in parallel or in series with each pump. When the station includes multiple pumps, they are usually in a parallel orientation.
The transducers and pump motors are connected to a pump station control system, which includes motor starters for starting and stopping the motors in response to operating conditions. The control system also includes alarms, displays, logic circuitry ranging from relays to microprocessors, and disk drives and/or semiconductor memory for storing data and programs. The control system can also include means for communicating, such as by radio or land-line telemetry, with a remote monitoring system. The information to be communicated can include data or calculated parameters that characterize the operating conditions of the lift station, desired control parameters, alarms, and desired changes in the program to control the system.
The control apparatus and methods used in pumping stations are generally focused on maintaining desired operating conditions reliably, but without specifically addressing or even calculating operating efficiencies and/or costs. For example, in a typical wastewater lift station one pump is turned on when the water in the wet well reaches a preset “pump start” level and is turned off at a preset (lower) “pump stop” level. If the pump has a variable-speed drive, the pump is initially activated at a preset “start speed” that is less than 100% of the pump's rated speed. The pumps, control levels, and control speeds are usually chosen such that the starting pump outflow exceeds the average inflow, and therefore the wet-well level begins to fall as soon as the pump is activated. The typical operating pattern thus includes intermittent pump operation, with the wet-well level cycling between the “pump start” and the “pump stop” levels. In this operating mode the pump duty cycle increases or decreases with flow, but the number of pumps and pump speed are constant during each “on” portion of the cycle. At times of higher inflow, however, it may be desirable to increase outflow by increasing pump speed or activating additional pumps in parallel with the lead pump. For example, the lead pump outflow may simply be insufficient to keep up with the inflow. The system typically detects this condition because the wet-well level continues to rise even after lead pump activation.
There are numerous methods for selecting the pump speed or pumps to be activated, which can dramatically affect pump station energy consumption, generally a major operating cost. In most lift stations, however, the control system does not even calculate an efficiency parameter. For example, in multipump systems the control system usually alternates between pumps for each on-off cycle.
In variable-speed systems pump speed is generally a linear function of level above the “pump start” level. While previously known systems calculate efficiency parameters, the methods do not effectively optimize efficiency.
In other art areas, computer-driven control systems and methods are known that monitor a plurality of operating parameters for the purpose of controlling some or all of these operating parameters to optimize a particular parameter, such as efficiency. Additionally, it is known to provide time histories of such parameters for maintenance and diagnostic purposes.
Such systems include those disclosed by Juhasz et al. (U.S. Pat. No. 4,258,421), directed to a vehicle monitoring and recording system; Teass et al. (U.S. Pat. No. 4,459,671), directed to a fuel management control system; Kugler (U.S. Pat. No. 4,916,628), directed to a control and status monitoring system for power generating stations; Crane (U.S. Pat. Nos. 4,843,575 and 4,334,425), directed to an interactive dynamic real-time management system for improving the operating efficiency of powered systems; Julovich (U.S. Pat. No. 4,642,992), directed to a method for maximizing the efficiency of cooling pumps in a power generating plant; Colovas et al. (U.S. Pat. No. 4,475,380), directed to a fuel efficiency monitor.
Systems specifically directed to fluid-flow control include those disclosed by Battah (U.S. Pat. Nos. 4,486,148 and 4,330,237), directed to a method of controlling a motive power and fluid driving system; and Bartley et al. (U.S. Pat. No. 4,108,574), Crane (U.S. Pat. No. 4,584,654), and Martin (U.S. Pat. No. 4,835,687), directed to monitoring and control of piping systems. Pump systems in particular are addressed by McClain et al. (U.S. Pat. No. 4,370,098), Shiraishi et al. (U.S. Pat. No. 4,178,132), Rishel (U.S. Pat. No. 4,805,118), Palmu et al. (U.S. Pat. No. 4,999,117), Mabe (U.S. Pat. No. 5,240,380), Gill (U.S. Pat. No. 5,092,739), Prevett (U.S. Pat. No. 3,744,932), and Corso et al. (U.S. Pat. No. 4,120,033).
Plant monitoring and control systems have been disclosed by Impink, Jr., et al. (U.S. Pat. No. 4,803,039); Lipner et al. (U.S. Pat. No. 5,121,318); and Wilson et al. (U.S. Pat. No. 5,386,360).
Two types of efficiency parameters have been known in the art: the power ratio and the material throughput per unit energy. All of the types of power ratio used thus far measure the rate of work output by the powered system and the power consumed by the system and taking the ratio thereof.
A longstanding practice in the wastewater pumping industry is to use the “wire-to-water efficiency” as a measure of the efficiency of a pumping system (Rishel '118, Corso '033). This term is defined as the (hydraulic horsepower output of the pump divided by the electric horsepower input to the pump motor) times 100. Since electric horsepower decreases with a decrease in pump speed, it has been assumed that energy costs would also decrease. Therefore, the wire-to-water efficiency has been deemed to be the best measure of energy efficiency and effective pump speed.
The fluid volume pumped per unit energy, the second type of efficiency parameter, comprises a measure of the throughput efficiency. Efficiency values are taught to be calculated and displayed in a pipeline system by Crane (U.S. Pat. No. 4,584,654).
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a monitoring and control system and a method for interfacing between an operator and a pump station controller.
It is a further object to provide such a monitoring and control system and a method that include means for tracking a plurality of system parameters over a predetermined time period.
It is an additional object to provide such a monitoring and control system that includes a plurality of real-time information screens accessible by the operator.
It is another object to provide such a monitoring and control system and method that sense a plurality of system parameters, performs diagnostic checks, and issues alarms when determined to be necessary.
It is yet a further object to provide such a control system and method that include menu-driven programmable logic control that permits an operator to alter the system configuration.
It is also an object to provide a control system and method that enable t
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Sergent Douglas W.
Teska Kevin J.
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