Improving control in wastewater aeration lines with the Bürkert Type 8750
Aeration lanes used in wastewater processing are designed to take in wastewater and introduce compressed air to break down sludge bacteria. This is a critical process in the cleaning process before treated water can be discharged into a river or similar watercourse. A major challenge in the day-to-day running of aeration lanes is energy consumption. Something that all industry exponents are busily trying to decrease, which is where the Bürkert 8750 Flow Rate Controller comes in.
The problem with butterfly valves
A typical wastewater aeration lane will comprise of a series of sensors inside. These can each be set to record different parameters, such as temperature or dissolved oxygen levels. They may also employ various ion selective probes for the measurement of pH and ammonia, for example. Those measurements are then fed to a PLC that controls how much air should be injected into the various different zones within an aeration lane.
A wastewater plant will have very long aeration lanes that are split into zones. Each zone will require very different levels of compressed air rates, depending on the feedback they receive from each of the sensors. Generally, one main blower produces the compressed air and control valves are employed to control the flow of air into each of the different zones.
A series of sensors and control valves feed into and are controlled by the PLC. This entails a considerable amount of load on a PLC, a great deal of wiring and a substantial outlay of capital expenditure on hardware. The control valves employed in wastewater applications are often low-cost butterfly valves, which are well-known for providing an inefficient control philosophy.
Bürkert 8750 Flow Rate Controller
The Type 8750 Flow Rate Controller from Bürkert can replace inefficient butterfly valves with a globe valve designed to provide far more accuracy. “With a butterfly valve, when you get to 60-65% open you may as well have the valve completely open,” says Greg Wainhouse, .water Field Segment Manager at Bürkert. “Whereas, with a globe valve you get a much better control philosophy throughout the valve control curve.”
From the compressor or blower to the aeration lane, a series of flow sensors will typically be deployed. These tend to be mass flow sensors and/or thermal mass sensors. With these devices, thermal mass flow sensors have to be located in the pipework at a very specific depth. These types of sensor arrangements can be very difficult to set up and commission, and can be relatively inaccurate if installed incorrectly.
“The Bürkert 8750 actually has a pair of pressure transducers – one either side of the valve,” Greg continues. “When you have two pressure sensors either side of a valve you can see the pressure drop from the first sensor to the second sensor. The pressure drops as the valve opens and closes, and the air flow rate changes. The differential pressure drop between the two devices (P1 and P2) also changes proportionally. The greater the pressure drop, the lower the flow rate and vice versa, in accordance with Bernoulli’s Principle.”
Flowmeter and control valve in one
With the Type 8750 Flow Rate Controller, Bürkert has successfully developed a product that combines a flowmeter and a control valve all in one package, passing on clear advantages to the customer. “This all-in-one package means we can help to reduce capital expenditure by reducing the number of devices required,” says Greg. “We’re also improving the control philosophy, as well as reducing the load on the PLC because the Type 8750 has its own PID system.
“This only needs to feed a setpoint or flow rate straight to the control valve and the valve will control things from there. The Bürkert 8750 also improves commissioning times and installation times because you are only installing one device as opposed to two, as well as cutting down on the amount of wiring needed,” Greg concludes.
The Bürkert Type 8750 Flow Rate Controller is available to purchase directly from the Bürkert eShop. For more information about the Bürkert 8750, or to discuss you application requirements in more detail, please contact our sales team on +44 (0) 1285 648 720 or email sales.uk@burkert.com.
Flow rate controller for gases
- Reliable and automated flow control on site
- Stable control of the set point, independent on pressure fluctuations
- Programmable alarm functions (pressure monitoring)
- Simple start-up by manual setpoint setting and display
- Leckage air compensation programmable for dense phase conveying systems