Ice pigging

Ice Pigging is the process in which an ice slurry is pumped into a pipe and forced along inside in order to remove sediment and other unwanted deposits to leave the pipe clean. It has many applications in the water, sewage and food industries.^[1] The University of Bristol has held many laboratory trials to investigate various key factors and refine the process. Ice Pigging was invented and patented by Professor Joe Quarini of the University of Bristol.

Effectiveness

The Ice Pigging method occupies a ‘middle ground’ between two of the traditional methods of cleaning pipes;^[2] that of ‘flushing’, which involves pumping high velocity water through pipes in order to carry away residue, and pigging, forcing a solid object through the pipe to push away any loose material. Ice Pigging utilises the main principles behind these two methods.^[3] An ice-water slurry, typically between 50 and 90% ice fraction is introduced to and removed from pipes with little complication, provided the presence of suitable hydrants and valves. The high ice fraction, lends several attributes which are particularly appealing for application in pigging; It is able to hold itself together under continuous shear. If the ice becomes stuck then given enough time it will just melt and be carried away. It is fairly inexpensive to make. It leaves the pipe walls themselves undamaged, and only removes waste residue. Because Ice Pigging is a relatively quick process (when compared to alternative methods), it can be use for a number of applications including: underground pipes for fresh water and sewage, food manufacturing pipe work and many others.^[4]

Environmental Impacts

Ice Pigging uses less water and requires less cleanup than traditional flushing or underground pipe pigging techniques.^[5] However, the process requires more energy since the ice slurries must be chilled and constantly agitated up until the point they are inserted into the pipes.

Research and Development

The University of Bristol have produced a paper entitled "Investigation and development of an innovative pigging technique for the water supply industry." in which they have detailed the research that they have carried out. It looks particularly at how the properties of the ice pig behave with different ice fractions and varied levels of particulate loading as well as looking into the effects of shear strength, viscosity and heat transfer characteristics.^[6]

Process

• The Ice Pig is inserted into the pipe in a semi liquid form and can adapt to the topography of the pipes as well as large changes in diameter.
• Ice Pigging doesn't require expensive excavation or preliminary treatment because it can be inserted into a pipe through existing access points whatever their diameter and then expand to the size required. Likewise the ice will exit the pipe with ease through any fire hydrant.
• Ice Pigging uses less water than traditional pipe cleaning methods. The Pig is pushed through the pipe using just one pipe volume of water and then the pipe is flushed for a short period returning the water quality to its usual limits typically using 1/4 to 1/2 of the pipe volume,^[7] Total water usage is therefore typically 1.5 times the volume of the pipe to be cleaned.
• The Ice Pigging process can be used in pipes of any material and will not damage the internal structure of the pipe.
• The Ice Pigging process takes less time than traditional pigging methods for underground pipes and can be operated by fewer people reducing labour costs.^[8]
• Ice Pigging is a low risk technique and minimal enabling works are required to insert the ice and remove it.^[9]
• Ice Pigging in manufacturing can reduce effluent costs and provide product recovery benefits, when compared to water flushing.^[10]

References

www.ice-pigging.com

Further reading

• G.S.F. Shire, G.L. Quarini, T.D.L.Rhys, T.S. Evans (2008). "The anomalous pressure drop behaviour of ice slurries flowing through constrictions".
• G.L. Quarini (2011). "Thermal Hydraulic performance of ice pigging in narrow tubes".
• G.L. Quarini, E. Ainslie, M. Herbert, T. Deans, Dom Ash, T.D.L. Rhys, N. Haskins, G. Norton, S. Andrews, M. Smith. "Investigation and development of an innovative pigging technique for the water supply industry".
• J.W.Meewisse and C.A.Infante Ferreira. "Freezing point depression of various ice slurries".
• J. Bellas, I. Chaer, S.A. Tassou (2002). "Heat transfer and pressure drop of ice slurries in plate heat exchangers".