What is Magnetic Water Treatment?
The subject of Antiscale Magnetic Treatment (AMT) and other physical
methods of scale suppression remain controversial and are still
labelled as gadgetry in some scientific circles. The debate is understandable;
for many years the positive effects well documented in trade literature
resulting from industrial applications have been undermined by the
apparent lack of good results from laboratory tests. In addition,
some manufacturers continue to promote ineffective devices (with
dubious literature) for applications where no real evidence exists,
anecdotal or otherwise to show that they could ever, or have ever
worked. However, many devices on the market have reasonably good
track records, but even these have occasionally proven ineffective
in certain situations. Many designs of commercial magnetic treatment
devices (MTD's) are available; some use electromagnets whilst others
use single or arrays of permanent magnets. Other MTD's are clamped
on to the pipe, but these typically display lower field strengths
than the 'plumbed in' variety. Other physical conditioners generate
electric fields or alternating radiofrequency and often claim to
be more effective that MTD's but on the basis of our literature
work, we could find no hard evidence to substantiate this. Other
conditioners subject the flowing water to an electrostatic charge
(produced by a chemical potential difference) between two or more
electrodes.
Upon reviewing the literature, we arrived at the conclusion that
most reported successful applications of magnetic treatment devices
(MTD's) have occured in continuously recirculating systems enabling
repeated treatment of the process water. The viability of AMT in
certain applications can be emphasised by looking at the sales of
CEPI-Co, Belgium, one of Europe's longest established manufacturers
who have sold in excess of 700,000 units worldwide; current estimates
are that 70% of sales are for industrial cooling circuits. In these
instances operators often describe an accumulation of sedimented
scale in low flow areas of the system and formation of a softer,
less tenacious scale. Encrusted scale has also been removed over
periods of three to six months. It is fairly well agreed that the
antiscale effect results from changes in crystallisation behaviour
promoting bulk solution precipitation rather than formation of adherent
scale. The magnetic effect also appears to be enhanced under conditions
of supersaturation and a high ionic load of the process water. Credible
laboratory studies have detailed increased solution precipitation
rates, crystal size and morphology changes, enhanced and retarded
coagulation and a retention of the antiscaling properties of the
water for hours or days following treatment. In many of these studies,
the results have only been apparent under dynamic magnetic treatment
i.e. the solution moving sufficiently rapidly through the (predominantly
orthogonal) field.
Many mechanisms for the antiscaling effect have been proposed, some
clearly ill informed such as magnetically induced changes in electron
configuration (this would require a huge field). None however are
fully comprehensive and can account for all of the observed effects.
Early Russian work which claimed changes in the structure of water
resulting from magnetic exposure has now been largely disproven
by subsequent work. Other Russian workers have more recently proposed
models to support the theory of enhanced nucleation in the bulk
solution. However, on the basis of current crystallisation theory
European experts have concluded that any effects on heterogeneous
nucleation would have a relaxation time of nanoseconds and any effects
on homogeneous nucleation would be unlikely, even after exposure
to a reasonably strong (5000 gauss) magnetic field. Others believe
that the reason for the ‘soft scale’ so often described
results solely from magnetically induced changes in crystal habit
i.e. calcite to aragonite, however, this is also unlikely since
many other factors (specifically the presence of contaminants, heat
or pressure) influence the preferred crystallising form of calcium
carbonate, in addition aragonite may prove to be a troublesome deposit
because it will recrystallise as calcite at low temperatures and
pressures. Another school of thought involves the influence of contaminants
(specifically Fe2+ or Zn2+) introduced by magnetically induced corrosion
or by slow release from the MTD. One thing is for sure - there is
an interaction between a magnetic field and crystallising matter
which can, on occasions affect its scaling behaviour. As engineers
we are primarily interested in deducing a satisfactory design basis
and the conditions under which the process will repeatedly work,
as scientists we want to know how it works.
The lack of a comprehensive mechanism was demonstrated by a recent
seminar at Cranfield University which invited leading researchers
from Europe, South Africa, Japan and the USA to present current
scientific progress on the understanding of AMT. Various views were
represented. Prof. Donaldson of Brunel University and Prof. Higashitani
from Kyoto University wre both in agreement that the main effect
could be on surfaces present in the system, however Prof. Donaldson
favours a charge redistribution scenario whereas Prof. Higashitani
purports that the field causes semipermanent changes in the nature
of the adsorbed water. Prof. Coetzee of Johannesburg University
has investigated links between zinc release (at the ppb level) from
MTD’s and has found a positive correlation between the rate
of zinc release and the effectiveness of the device. Other research
conducted at Baylor University, Texas indicated a credible mechanism
based upon the solid scientific principles of electromagnetic induction
and magnetohydrodynamics, promoting either corrosion and/or precipitation
or even orthokinetic flocculation when a conducting solution is
made to flow through a magnetic field, Professor Busch of Baylor
summed up - 'there may be a whole bunch of effects going on'.
What is needed is a complete analysis of all instances where AMT
has worked effectively and more importantly - where it has not.
In this way it may be possible to deduce which factors are crucial
in terms of a successful application. In addition it can be seen
that real results are realised after periods of months whereas most
laboratory studies have tried to achieve results after hours or
days using accelerated scaling techniques. A recent article in Water
(Australia) compares AMT to biological enhanced phosphorous removal
from sewage in that it was developed and used by engineers long
before a microbiological rationale was suggested. Whatever the outcome
of the debate, the benefits of non chemical water treatment are
obvious, from both an econonmic and an environmental point of view.
The results of current research into antiscale magnetic treatment
at The School of Water Sciences, Cranfield University investigating
magnetic effects on the crystallisation behaviour of Calcium Carbonate
in once through systems.
Magnetic Water Treatment -General
The build up of scale deposits is a common and costly problem in
many industrial processes using natural water supplies. In Britain
alone the formation of scales in industrial process plant where
water is heated or used as a coolant is estimated to cost £1
billion per year. Such costs can be attributed to cleaning (i.e.
descaling) or the poor thermal conductivity of scaled surfaces;
heat transfer is decreased by 95% by a CaCO3 scale layer 25 mm thick
whereas an SiO2 scale layer 0.5 mm thick results in a 90 % decrease
in heat transfer.
Scale formation is the precipitation of sparingly soluble salts,
most commonly calcium carbonate, which form an encrustation on susceptible
surfaces. Most commonly this occurs as a result of temperature or
pH changes, influencing the solubility of the scale former. Other
common scale-forming compounds include calcium sulphate, barium
sulphate, calcium phosphate, magnesium hydroxide, zinc phosphate,
iron hydroxides and silica, all of which occur naturally in raw
water supplies.
Traditional chemical methods of scale control or water softening
involve either the pre-precipitation of the scale former with lime
or soda ash, the addition of scale inhibiting reagents or the replacement
of the scale former with soluble ions by ion exchange. All of these
methods, though effective in scale control, substantially change
the solution chemistry and can be prohibitively expensive.
Antiscale magnetic treatment (AMT) has a long and controversial
history and has been reported as being effective in numerous instances
(Baker and Judd, 1996). Its effect is to either reduce scale deposition,
remove existing scale or produce a softer and less tenacious scale.
Many reports claim large savings in energy, cleaning (i.e. descaling)
and process downtime costs from the installation of magnetic water
conditioners in real systems. However, installed MTD's have also
often proved ineffective in real installations though the precise
reasons for their inefficacy are rarely examined in such cases.
Reported effects of magnetic conditioning of water have appeared
in the literature since the late 1930's. These have usually related
to AMT, though there is some evidence that magnetism interacts directly
with microorganisms. Reported effects appear to vary widely, possibly
reflecting variations in water quality, and the apparent lack of
their reproducibility has tended to undermine the credibility of
the process. The paucity of systematic studies of the phenomenon,
independent of AMT device manufacturers, and the lack of recorded
design criteria have prevented acceptance of the method by process
designers and plant engineers. The scientific literature is still
unable to explain confidently why AMT works in some applications
and not in others. Recent research at Cranfield has identified conditions
under which magnetic treatment can lead to a maximum of 70% reduction
in calcium carbonate scale formation. The degree to which scale
formation is inhibited has been identified to be dependent on a
number of physicochemical conditions such as temperature, pH, hardness
and alkalinity. This work has also identified effects on pH, particle
size, nucleation rate and crystal form.
Recent publications
1. Baker, J S. and Parsons, S A. (1996). Anti-scale Magnetic Treatment,
Water and Waste Treatment, 39, 36-38.
2. Ifill, A S, Baker, J S. and Judd, S. J. (1996). Magnetic treatment
of simulated swimming pool waters. Trans. IChemE, (Part B), 74,
120 - 123.
3. J S Baker and S A Parsons, (1996). Antiscale Magnetic Treatment,
Water and Waste Treatment, 39, 36-38.
4. Parsons S A, Wang B L, Judd S J and Stephenson T, (1997). Magnetic
treatment of calcium carbonate scale- effect of pH control. Wat.
Res., 31 339-342.
5. Baker J S, Judd S J and Parsons S A, (1997). Antiscale magnetic
pretreatment of RO feedwater. Desalination, 10 (1).
6. Parsons S A, Wang B L, Udol S, Judd S J and Stephenson T, (1997).
Magnetically augmented water treatment. Trans. IChemE (Part B),
74,98-106.
7. A-Barrett R and Parsons S A, (1998). The influence of magnetic
fields on calcium carbonate precipitation. Wat. Res.,32, 609-612
.
8. Wilson D I and Parsons S A. (1997) Mitigation of Heat Exchanger
Scaling by Magnetic Treatment Devices. 5th UK National Heat Transfer
Conference.
9. A-Barrett R, Parsons S A, Hillis P and Coetzee P P. The Effect
of Magnetic Fields on the Precipitation of Calcium Carbonate, WISA
‘98, Cape Town, May, 1998.
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