This detailed case study from Europe shows the optimisation of air distribution and aeration control in a plug-flow tank, highlighting the next frontier in aeration efficiency for Australian water treatment plants.
The need to increase energy efficiency while stabilising process and meeting the new environmental goals of the city of Kiel in the EU required a comprehensive modernisation of the existing aeration system. The long rectangular tanks were splitted into 2 control zones, equipped with new control valves and a dynamic real-time controller, significant savings were achieved and process stability was sustainably improved.
Customer Benefits
→ Annual energy savings: approx. 300,000 €
→ Demand-based air supply and distribution of air flow into long, narrow tanks
→ Reduction in oxygen carryover improves biological nitrogen removal
→ Stable treatment performance even during sudden load fluctuations (e.g. heavy rainfall)
→ Flexible, future-proof operation with expandable control functions due to a fully modular design
The challenge
The wastewater treatment plant is the largest municipal energy consumer in the climate-conscious city of Kiel.
Each long rectangular aeration tank with a plug flow was equipped with a common control valve. That led under normal conditions to an insufficient air supply in the first half and over-aeration in the second half (up to 5 mg/l). Especially in the night dissolved oxygen was carried over into the denitrification tanks, disturbing biological nutrient removal every day for several hours.
During high load conditions, the oxygen supply and so the treatment performance was insufficient, ammonia broke though during every heavy rainfall, which happens often in the Baltic Sea area.
The high pressure loss of the common valves required an increased power consumption of the blowers. Non-linear control characteristics led to a limitation in the usable control range of the valve to a range with especially high head loss (20 to 80%). Test measurements were done and confirmed expected numbers of 40 to 70 mbar.
Only a complete modernisation could unlock the full optimisation potential.
The solution
Process & Control improvement:
The four rectangular tanks were divided into two indepen-dent controllable zones, each one equipped with one air flow meter and control valve.
The AI-supported algorithm of the installed aeration controller calculates dynamically in real-time the air flow requirements along the flow path and the related required stroke of the valves. The system was integrated into the existing SCADA infra-structure with minimal effort and in a short time.
Reduction of power consumption:
The VACOMASS® jet control valves have an extra-ordinary venturi design and so related pressure drop of the valves is significantly lower compared to the common valve.
The intelligent control algorithm adjusts the DO-SET concentration based on actual needs. In low load times the DO-concentration can be reduced – this saves another portion of blower´s energy consumption.
“With flexcontrol, we were able to largely automate our biological stage—this gives us greater process stability, less manual operation, and a noticeable efficiency boost.” said Michael Wuttke, Head of Process Engineering, Bülk Treatment Plant.
Typical system response to a heavy rainfall event
– automatic adjustment of DO-SET concentration, valve opening, and system pressure to stabilize treatment performance.
The old compressors with manual regulation limited the required pressure increase over time.
The control valves open fully, significantly reducing the ammonium breakthrough compared to the previous situation.
OPEX Savings
Plant data
Average air flow rate 4 tanks:
20,000 Nm³/hr
Specific costs electricity:
0.30 EUR/kWhr
Average efficiency of the blowers:
0.7
CO2-Emissionfactor:
0.363 kg CO2/kWhr
Pressure drop of the valve:
40 mbar → 80,000 EUR per year
Dynamic header pressure control:
570 mbar → 520 – 542 mbar
9% →100,000 EUR per year
Ammonia based DO-control (ABAC) plus switch to intermittend aeration in the night hours:
11% → 120,000 EUR per year
Improvement CO2-footprint:
115 kW → – 346 t CO2/year
Further positive side effects:
→Less man power because of automatic operation
→More stable cleaning performance
→One step ahead with digitalization and automatic operation
CAPEX
450,000 EUR including installation & costs for pipe adaptations & implementation in the SCADA
|
OPEX Savings 2019 |
2020 |
2021 |
2022 |
|
|
Digester gas production [Nm³/a] |
4,273,263 |
4,136,965 |
4,927,312 |
4,662,585 |
|
Power generation [kWh/a] |
9,212,294 |
10,601,728 |
10,805,222 |
10,101,296 |
|
Energy consumption [kWh/a] |
10,604,294 |
10,760,472 |
10,512,752 |
9,985,902 |
|
In-house power Generation [%] |
87 |
99 |
104 |
102 |
|
Spec. power consumption of the plant [kWh/PE*a] |
31 |
31 |
31 |
28 |
For more information, visit bindergroup.info and pumpandvalve.com.
For more information or enquiries contact Tony Girach of Aeration Control Systems at tony.g@pumpandvalve.com or in New Zealand contact Justin Engels of Pump & Valve at justin.e@pumpandvalve.com
