Application One
A grain handling and storage company in Western Australia have had a problem with several of their existing vertical storage bins. The bottom of the grain silo foundation is some 11m below ground, with grain being stored to 6m below and is part of a multi million-dollar facility. After 30 years of use, 4 silos were found to be prone to water entering the silos through breakdown in the layers of pitch used to waterproof the concrete during construction, and water was a problem generally all the way up until Christmas. During the rest of summer and autumn about a week after a heavy storm, the water would again find its way into the silos, and during the winter the silos are obviously very wet.
The challenge here is not just lowering the water table to below the silos foundations, allowing the grain to stay dry, but the fact that the water seepage is slow due to the tight clay soil surrounding the area. A conventional electric pump would not find enough flow to work effectively even during the winter at about 80L in 24 hours, and the tapering off and the sporadic nature of the flow during the warmer months would make the task even more complicated for a conventional de-watering pump.
However, by breaking through the silo foundations, and positioning an Airwell Pump below the desired reduction in the surrounding water table was achieved and maintained throughout the year, allowing the facility to be used to store grain without water damage. It is the automatic nature of the Airwell system that enables this. The internal conductivity probes provide a signal to the controller at the surface with indication when the pump vessel is both full and empty. When full, the control circuit opens the solenoid valve to allow air into the pump to displace the water, and upon getting an empty signal closes the valve, stopping the flow of compressed air, thus allowing the pump to refill. It doesn't care how quickly or slowly this sequence takes, and uses no energy whilst waiting for the pump to fill. In winter the pump may cycle hundreds of times an hour, whilst in the height of summer this may be down to perhaps 20 cycles a week and its all self regulated. If the water table rises due to a summer storm, the pump automatically increases its cycle rate to maintain the water table level. This installation has been working for six years with no maintenance to date.
This type of application for the de-watering of foundations and damp spots in mines is very successful and is becoming more common.
Application Two
We know that wherever oil and fuel have been stored in the past there has inevitably been a certain amount dropped or leaked into the surrounding soil causing contamination of the earth, and inevitably the groundwater. Being lighter than water, the oil floats on the water surface, and although the point of the spill is very local, in a similar way to dropping ink onto blotting paper, the oily plume disperses outward when it reaches the water table. The speed with which it spreads is dependent upon the soil type, but always, what starts as a small area of contamination gradually increases in size. It is also widely documented that what ever pollutants get into the groundwater will affect many aspects of our lives in the future, a concept not understood or possibly even ignored in our not so distant past.
At an oil storage facility locally, spilt oil was found to be leaching into the harbour. After testing the site, the extent of the contamination was established and a procedure developed to stem the flow of oil into the ocean whilst recovering the spilt contaminant from the ground. The problem at this facility was further exacerbated by the tidal influence on the groundwater level. As the tide comes in the level rises, as does the interface of oil and water, and as the tide goes out, the interface drops. To tackle this problem we needed to vary the flow rate of the pump in relation to the movement of the tide in order to maintain a stable interface level to maximise product (oil) recovery whilst minimizing further contamination of the surrounding soil.
To achieve this we incorporated the use of an Airwell top filling total fluids pump to pump large volumes of groundwater with limited contamination, a skimmer pump at the interface that selectively pumps oil, and all controlled by a PLC (programmable Logic Controller).
Also suspended down the bore are pressure transducers, in turn attached to the PLC. The controller monitors the signal from the pressure transducers that are calibrated internally to provide the controller with detail of the movement of the tide. As the tide rises, the PLC automatically increases the speed at which the Airwell pump cycles, increasing the flow rate, and as the tide falls, so does the cycle speed of the pump, as does the flow rate, maintaining a constant interface level and optimising product recovery.
The energy used for pumping is compressed air - making it safe in a potentially explosive atmosphere, and is a preferred option for remediation pumps in bores at tank farms, oil refineries and of course service stations. Airwell Pumps have been used in many fuel storage spills, often replacing the North American equipment, and new environmental legislation is likely to require service station and other oil storage owners to clean up their sites sooner rather than later.
Application Three
This site in a past life has been used to produce CFC's, Hydrofluoric Acid, and a Chromium plant amongst other things, and its proximity to the Parramatta River makes it even more sensitive these days.
The chief contaminants to extract here were Carbon Tetrachloride, Chloroform and Chromium. The HF Acid was discovered after installation of the system. The three C's mentioned are all DNAPLS, or sinking contaminants, and sit under the water, on the bedrock. This project was initially two separate parts - the pumping system, supplied by Airwell, and the process equipment for removing the pollutants, supplied by others, about 300m away from the bulk of the pumps.
For this project, we use bottom-filling pumps, whereby the screened inlet is suspended in the contaminated solution on the bedrock, and the pumps fill from the bottom, thus picking up the sinking contaminant. There were 20 pumps initially, driven from a central PLC system and compressor. Each pump has its own control sequence in the PLC program, allowing the flow of each pump to be varied according to the degree of contamination in that particular area. The addition of a telephone line and modem also allowed access to the system from anywhere in the world on a standard PC, whereby the system could be monitored and pumping characteristics of each pump changed without a visit to site.
As said earlier, we had no influence on the process plant initially, apart from influencing the type of PLC control system used. The process system was manual only, with the PLC just locally monitoring what was going on and raising local alarms if things went awry.
A decision was made to automate the plant, and due to the confidence the consultants had in us as a company, requested us to automate the system and integrate it with the pumping system we had already installed. We have successfully completed this project, and not only is the remediation process now fully automatic, all performance and status criteria is available from a remote PC, and plant status, pump status, fault status information is all readily available from the office or home. The additional innovative use of home burglar alarm allows the 24-hour monitoring of alarm conditions within the plant, without the expense of having someone on site.
We are expecting further expansion of work on this site in the near future.
As you can glean from these three very different examples, the variety of applications that are open to using Airwell products and expertise is vast. With the environmental legislation still being developed here in Australia we can only expect to see the remediation business increase as laws relating to the clean up of polluted sites are strengthened and enforced.