- Published on 14 February 2017
- Hits: 140
By Charles Nicolson
We check back on the local Enigma non-chemical scale inhibiting system’s trial run to see what the results are saying.
In the January 2017 issue of RACA Journal, ‘Getting Technical’ presented a detailed case study of a trial run using the Enigma non-chemical scale inhibiting system to reduce scale fouling and increase the efficiency of a gold elution circuit at Mogale Gold near Krugersdorp in Gauteng. The trial was run for three months during 2016, producing several positive results. Further applications in leaching circuits are presently being planned. One particularly interesting outcome of the trial was the demonstration that the Enigma system was capable of inhibiting formation of scaling at pH levels running from 143.5 right up to the maximum pH of 14.0, showing that non-chemical treatment can work where it is not possible to use chemical dosing.
Rapid scaling problems in elution closed circuits are caused by the combination of ultra-high pH with high circulating water temperatures. The anti-scaling success of the Enigma unit under these conditions does not, however, imply that similar results will occur in the types of closed heated and hot water circuits used in HVAC plants. In fact, relatively minor scaling does often happen in many closed heating and cooling HVAC water circuits, but only small volumes of top-up water additions limit scale build-up to the extent that scaling in these circuits is normally disregarded. Problems arising from rapid scaling in HVAC installations occur mostly in evaporative cooling water circuits flowing through condensers, either shell and tube type condensers cooled by open cooling towers, or evaporative condensers in which scaling can accumulate rapidly due to small sump volumes relative to the much larger amounts of water these units evaporate.
Circulating water in evaporative condensers is deliberately concentrated up to reduce supply water usage as much as possible and usually contains between five and 10 times the total dissolved solids (TDS) content of the supply water. This high TDS water sprays directly onto galvanised pipes containing compressed refrigerant at temperatures which can go up to well over 100°C, creating situations that are not as severely scale-forming as those inside elution circuits, but still capable of generating scale quickly enough to effect condensing efficiency within a few weeks, or sometimes even a few days. Continued scaling will ultimately cause refrigerant compressors to trip-out on high discharge pressures.
Over the past 50–60 years — more than half a century since factory-built evaporative condensers became generally available — there have been many recorded applications of non-chemical treatment for inhibiting scaling. Some have claimed not only complete prevention of scale build-up, but also on-line removal of existing scale deposits. Others have reported no measurable benefits. In general, field trials that have been properly run and monitored have produced positive anti-scaling effects similar to those obtained in controlled laboratory scale test runs, demonstrating how non-chemical units, which induce alternating electromagnetic pulses into full water flows in circuits, can provide low intensity but continuous inhibition of scaling. During the three-year period from around 2007–2010, regular publications were posted on the internet, detailing positive scale control trial results along with greatly reduced cost and environmental benefits from not needing chemical dosing.
Circulating water in evaporative condensers is deliberately concentrated up to reduce supply water usage as much as possible and usually contains between five and 10 times the TDS of the supply water.
Since 2010, the number of new trial results posted has decreased to the extent that further information has dried up almost completely. One of the main reasons for this is that prices of non-chemical water treatment units and systems have risen substantially due to increasingly complex electronics necessary for producing pulse output signals, which modulate extremely rapidly in both frequency and amplitude. There are probably other reasons in the current rapidly globalising post-truth era for withholding the publication of trials as well as operational information concerning progress in non-chemical scale control. The upshot is that we do not know whether successful trials have led to non-chemical units being included in standard operating treatment programmes for evaporative cooling water circuits.
However, there has been one site where two BAC evaporative condensers on a cold storage plant were switched over from automatic chemical dosing for scale control to automatic non-chemical control by an Enigma system at 14:00 on 16 July 2013. The site is Supreme Cold Storage in Bloemfontein.
The evaporative condensers are two BAC VXC 135 units in an ammonia refrigeration plant. The writer personally switched off the scale control chemical metering pump in the presence of the managing director of AWA Water Management, Emil Weber, and the CEO of Enigma Electronic Descaler, Harry Lipschitz. A few technical ‘glitches’ have occurred, but after three and a half years, these condensers continue to operate under successful scale control by the Enigma component of the water treatment programme.
Many RACA Journal readers and people involved in HVAC&R will remember Emil Weber who sadly succumbed to cancer in December 2015. Weber came from his native Switzerland to South Africa in 1982 and started AWA Associates with a partner, Dieter Ahrend, promoting the German Aquasal electromagnetic scale inhibiting unit. One of Weber’s earliest successful applications was a multiple Aquasal installation treating the total amount of fresh water supply to a branch of Nels Dairy, located at that time in the Johannesburg suburb of Victory Park. Included in the dairy machinery were two BAC VXC evaporative condensers, which, after running for approximately six months on the Aquasal, treated supply water and remained essentially free from any build-up of scale. Encouraged by this success, Weber then called on the local BAC Agency, Baltico Associates in Johannesburg where he was referred to the writer who, at that stage, was the water treatment consultant for Baltico. The meeting with Weber initiated a co-operation that resulted in hundreds of Aquasal units being installed on BAC and other types of evaporative condensers, as well as evaporative closed circuit coolers and open cooling towers, initially in the Witwatersrand area, but subsequently spreading throughout South Africa via appointed agents.
Continued scaling will ultimately cause refrigerant compressors to trip-out on high discharge pressures.
Without any previous experience in water technology or having chemical qualifications, Weber mastered the basics and then the main requirements of cooling water treatment amazingly quickly. AWA Associates became AWA Water Management. Weber took the view that although Aquasal units had their particular applications in cooling water systems, traditional chemical dosing would, for both technical and commercial reasons, probably continue as standard water treatment on the majority of cooling water circuits for the foreseeable future. He expanded AWA Water Management to supply and service either chemical or non-chemical treatment installations. During the 1990s, German-made Aquasal units became unavailable so Weber simply replaced them with similar locally manufactured components, assembled and tested by AWA and supplied as Aqualec units. However, a factor in the Aquasal/Aqualec designs limited water flow rates to maximums according to electrode chamber diameters. This limitation meant that Aqualec units large enough to treat full flow water lines in cooling water systems or full flows in evaporative condenser spray nozzle supply lines would be prohibitively expensive. Consequently, Weber decided that Aqualec units and systems would only be recommended on relatively small refrigeration and chiller condensers in which circulating water quality remained within specific parameters.
Enigma electromagnetic treatment units are not subject to water flow maximums. Their induction coils are simply wound around whatever the pipe size is at treatment points selected. Larger pipe diameters need larger electrical pulse inputs, but only on the scale of a few watts more than smaller pipes require. Enigma units, therefore, can achieve optimum effectiveness by treating both supply water lines and full flows through evaporative condenser riser pipes carrying water being pumped from sumps to spray nozzle distribution systems. Recognising the flow rate limits of Aqualec units, Weber proposed to Lipschitz that he provide and install an Enigma system sized to provide continuous scale control through induction coils on the common make-up supply line to the two BAC VXC 135 condensers at Supreme Cold Storage, as well as larger diameter coils treating the full flow of circulating water in each condenser riser pipe.
Weber further proposed that when the Enigma system had been installed and tested, that the existing automatic chemical dosing pump feeding anti-scaling chemical into the common make-up line in proportion to supply water demand be turned off, which, as previously mentioned, took place in July 2013. The water treatment programme then became TDS control in each condenser by existing AWA automatic bleed-off units and Enigma non-chemical scale control. AWA would continue regular service visits, including checking indicator LED lights on the Enigma control panels, and ensure that Supreme Cold Storage management and all other responsible people were kept fully informed.
Previously, standard automatic chemical dosing and bleed-off had been installed and commissioned on the first VXC 135 condenser, which started operating during 2007, and an additional bleed-off was commissioned on the second VXC 135 condenser two years later in 2009. Normal Bloemfontein municipal water was initially used to supply the condensers but subsequently replaced with borehole water, which required higher chemical dosing for scale control but still provided a cost saving compared to using municipal water.
Average loading on the refrigeration plant varies in accordance with seasonal conditions in Bloemfontein, resulting in supply water demand by the condensers at around 700m3 per month during summer months, dropping by almost 50% to about 370m3 per month in the much colder autumn and winter months. The quality of the borehole water as tested by an independent laboratory, Buckman Laboratories, in 2008 has varied very little from the original measurements, which were:
|TDS||480ppm (or mg/litre)|
|Calcium hardness||257ppm (as CaCO3)|
|M-Alkalinity||255ppm (as CaCO3)|
|pH @ 21°C||7.75|
This water has a Ryznar Stability Index (RSI) of 6.12, which indicates a relatively low but positive potential for scale formation. However, to reduce supply water usage to a reasonable practical minimum, the bleed-off units maintained an average of between 4.0 and 5.0 cycles of concentration in the evaporative condensers, reducing circulating water RSI values to between 5.2 and 5.4, which means a substantial increase in scaling potential.
After operating for 90 days on the combination of automatic bleed-off and Enigma anti-scaling, there was no visible evidence of any new scale formation, therefore, no changes were made. The original plan had been to run for 12 months to cover both winter and summer conditions. However, after 10 months, visual inspection of the condenser coils showed definite signs of gradual re-dissolving of the original thin layer of scale, so it was decided that further inspections would continue to be done at three-month intervals to confirm whether this gradual but definite reduction of scaling continued.
Nearly three years after starting this scale control programme, the maintenance manager at Supreme noticed that new scaling on the coil of one of the condensers was evident, which was confirmed during a site visit by Lipschitz of Enigma. The cause was found to be a burnt-out solenoid bleed-off valve, resulting in very high circulating water TDS with resulting scaling. After replacing both bleed-off valves with newer non-block ball-type valves, the plant has now been operating for six months during which the scaling, which had not yet become settled into a hard compacted state, has re-dissolved into circulating water and purged to drain through the refurbished automatic bleed-off system.
16 July 2013: appearance of top coil tubes. Thin, even coating of porous scale is having no measurable effect on condensing efficiency.
December 2016. Most of the scaling from recent high TDS has re-dissolved in circulating water. It is evident that over approximately 42 months, the original thin scale covering has reduced to the extent that areas of galvanised coil tubes are visible.
Figures 1 and 2 represent a graphic summary of a field trial, which has now become a continuing operating run. However, it must be emphasised that water treatment programmes for evaporative cooling water circuits, particularly those circuits where evaporation rates are relatively high on low water volumes, must be designed by qualified and experienced water treatment people, taking into account the quality of available supply water. The outbreak of scaling due to bleed-off failure described in this account is just one of many types of technical ‘glitches’ which can arise, which also highlights the importance of regular on-site servicing by qualified technicians to identify and rectify problems before they escalate into high-cost failures.
As stated earlier, due to declining publications of trial results we do not know whether successful trials have led to non-chemical units being included in standard operating treatment programmes for evaporative cooling water circuits. Three and a half years of initial trial, turning into operational running with professional servicing and monitoring, has shown what is possible and practical. Unless other similar case have not been widely published, this must be a South African ‘first’ — and quite possibly a ‘world first’.
Due to space limitations, technical and operating specifications of Enigma scale control systems will be included in a forthcoming article. In this regard, Harry Lipschitz will be happy to provide further information and can be contacted on +27 (0) 82 219 5151.