by DavidDebunking the Ice Pigging Myth!
There have been multiple reports in the media of the effectiveness of ice pigging, compared to conventional pigging and to air scouring. These reports, however, are not persuasive, primarily because they do not examine its significant downsides.
Here we will not discuss the effectiveness
of ice pigging, which may equal
that of its alternatives; instead we outline its disproportionate financial and environmental cost.
Ice pigging is the process of pumping semi-solid ice flake slush into water mains, and propelling it through the pipeline to scour the pipes.
Ice pigging is claiming to be a superior methodology to cleaning pipelines mainly because of the problems purportedly associated with the other methods of cleaning pipelines. These problems may be, for example,
• blowing pipes during air scouring programmes due to high pressure, or
• conventional pigs becoming stuck in the pipes.
Although these are indeed possibilities
, there is no supporting data offered regarding the frequency
of these occurrences. These two so-called problems alone expose the inherent weakness of ice pigging.
A blown pipe or a stuck pig is extremely rare, but it does mean there is a problem
: a problem that clearly needs to be addressed. Meeting these problems head-on provides vital information, or may even solve the problems that required the cleaning of the pipeline in the first place.
However, ice pigging by its very nature
cannot deal with; it simply melts away. The problem remains, unresolved
. Further, unlike air scouring or conventional pigging methodologies, there is no way to identify where the problem is in the pipe.More alarming is the financial and environmental cost of ice pigging.
An analysis of the methodologies and techniques used in this concept, with respect to cost, power, waste, and metres-cleaned ratio
, shows that the client (often rate-payers) is picking up the tab for something highly inefficient and expensive compared to conventional pigging and/or air scouring.
It is understood that ice pigging is better suited to trunk or delivery mains.
Let us evaluate an exercise with a pigging operation only, leaving aside air scouring.
A 375mm diameter pipeline, 30klms in length.
Raw water delivery, using existing pumps for propulsion.
• Make & use 10 tonnes of ice
(this appears to be the average amount of ice made per day). The metres cleaned using this amount of ice is governed by the size of the nominated pipes to be cleaned. The larger the pipe, the more ice is required to make the ice plug. This would likely increase in warmer temperatures, where some of the ice would be lost transporting the ice to the pipeline, and which would melt faster in warmer waters.
• To make 10 tonnes of ice a minimum of 120 kilowatts of municipal power is required. That is enough to supply the average home for a week (at 18 kwh per house). Keep in mind that the power plant producing the ice must maintain its daily operating procedures for which it is currently used.
• A huge amount of salt is required, on site, to maintain the ice structure for as long as possible during transport.
• A large vehicle is required to move 10 tonne of ice slurry from the plant to the pipe.
• Pigging commences: the mixture is propelled by the existing upstream source. This would commence dissolving the ice slug during travel, undermining its effectiveness. It is difficult to determine how far the sludge travels, or how effective the slurry is over the last 50 or 100m. Assuming the ice travels 500m, the team needs to reset the launch and truck down the road to the next location. It takes time to set-up, and more ice for the next run.
• With the ice slurry dissolved, wastewater becomes an issue. It is now a heavy salt mixture, which cannot and should not
be dumped into the drainage system, or over ground, because of the negative effect on nearby wildlife and waterways. The mixture cannot
be dumped directly into sewerage treatment plants due to the delicate chemical balances required in these plants. So the waste must be pumped back into a waste truck and disposed of at a chemical waste plant, adding to time and cost.
Cost of operation (conservatively): $10,000 per 500 metres charged.
For the stage scenario: $600,000 to complete.
Total cost to for a single operation does NOT include:
• the cost of power consumption to the municipal electricity grid,
• environmental impact if not handled properly,
• appropriate waste disposal, and
• a huge amount of salt is required on site.
• Fabricate a launcher and pig design capable of the distance. If there are no launch points, excavate to create. Cut and remove a pipe section for launch. Fabricate a permanent fixture for future launch point use (which does not result in any efficiency/structural sacrifice to the pipe).
• Launch the pig. The shape, size and type are tailored to travel the 30km run. The pig has tracking capabilities.
• Use existing pumps for propulsion. Travel time is approximately 16 hours for one run. Progress is determined by the concrete evidence of the pig ‘s movement.
• As there are no extra additives in this methodology (i.e. salt), waste is not an issue. Wastes extracted through pigging are natural component growths of water coagulated together and bound to the pipe wall, which restricts flow. The disposal of this discharge can be directed to bushland or flora to re-use and recycle without any detrimental effect or water waste.
Cost of operation: $300 per 500 metres charged.
For the stage scenario: $18,000 to complete.
Total cost for a single operation inclusive of:
• NO municipal grid consumption,
• NO environment impact,
• NO charges contributed to wastage, and
• NO additional additives.
|Additional Ice Pigging Costs:
- Electricity Grid Consumption
- Environmental Impact
- Waste Disposal
- A huge amount of salt is required on site
|Advantages of Conventional Pigging:
- NO Electricity Grid Consumption
- NO Environmental Impact
- NO Waste Disposal
- NO additional additives
Similar comparisons can be made with respect to reticulation systems of between 100-200mm pipelines, or to shorter runs and smaller pipes. Indeed, the deleterious impact of ice pigging on time-efficiency
increases as logistics become progressively arduous. Further, ice pigging equipment is not mobile and thus unsuited to cleaning in urban areas.
The same cost benefit also applies to air scouring, if not more so, especially in urban reticulation systems.The acceptance of this method by clients without a balanced and critical analysis of its costs compared to rival methods is concerning.
Result comparisons of all methodologies can easily be determined, supported by independent lab results, and all clients are encouraged to do this.In conclusion, it comes down to cost and efficiency: this is not a myth.