In mid-2010 Air Technology Ltd conducted a site survey on the smaller of the two ASP’s at a large sewerage treatment works with a 326,000 PE. This survey includes DO profiling, ammonia profiling, control assessment, power usage and blower testing, to ensure that the plant was running optimally for both process control and energy use. Many potential opportunities to save energy and improve process were identified amongst which that the site could benefit from additional control based upon the combined measurement of the inlet ammonia and individual ammonia meters in the separate lanes.
Ammonia control is a proprietary system developed by Air Technology Ltd and works by varying the ASP’s first zone DO setpoint based upon the inlet ammonia levels. This is controlled by an ammonia meter placed within the anoxic zone of the ASP that automatically adjusts the DO levels depending upon the incoming load. This is supplemented by ammonia meters towards the end of the lanes of the ASP which provides control to the 2nd Zones & further zones as required. If the ammonia levels reach a pre-set HIGH level on the inlet or 2nd zone meters then the system is reverted to fixed DO control at a higher set point to allow for maximum treatment during exceptionally high loading periods. This allows the plant to operate with exceptional resilience to unexpected and highly variable loads. The benefits are both process resilience and energy savings as the site no longer needs to run in a ‘worst case’ scenario with high DO setpoints ready for an unexpected or high load. It is commonly installed with a variable pressure set point to further reduce unnecessary energy consumption from the blowers, this works by reducing blower system manifold pressure if the average position of the actuators is low (which creates a large pressure drop) and in turn the pressure is increased as actuator position increases to allow for increased treatment when required.
Air Technology’s expectations were that a saving of 332,350kWh would be achievable
Air Technology’s expectations were that a saving of 332,350kWh would be achievable and based on this an order was received from the client to go ahead. A further assessment prior to commencement indicated a saving of 415,404kWh was now a more likely scenario and work commenced the following summer. Air Technology managed the project, installed all required capital equipment and installed their proprietary software on new HMI’s whilst giving full code access to the client for any further work they may need doing in the future. The work was commissioned and signed off as complete early the following year.
Once commissioning was completed Air Technology returned to validate the work. In doing so it was found that a saving of 573,598kWh had been achieved far exceeding the expectation
Once commissioning was completed Air Technology returned to validate the work. In doing so it was found that a saving of 573,598kWh had been achieved far exceeding the expectation, this energy saving was fully validated and crossed checked by the client. This result mean that even with a kWh price of just 3.5p, due to on site CHP, payback has been achieved in just 2.5years. Since then the client has tasked Air Technology to attend site once a month to provide calibration & general optimisation work to ensure that ongoing energy savings are being achieved.
