wtil-NO--768 C OtiF- 9603 - 7 NO9705199 Norske Sivilingeniorers Forening OIL FIELD CHEMICALS 7th international symposium 17-20 MARCH 1996 Dr Holms Hotel Geilo, Norway Electrical Scale Elimination Technology 9 LECTURER: A G Hunton, Humber Technical Services, UK Reproduction is prohibited unless permission from NIF or the Author DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document ELECTRONIC SCALE ELIMINATION TECHNOLOGY by Alan G Hunton, B.Sc., M.LW.Soc. Humber Technical Services and technical adviser to Scalewatcher UK Ltd. SUMMARY The useof magnetic and electric fields for the purpose of preventing deposition of mineral salts and reducing corrosion in flowlines has been reported in the literature for about one hundred years (1,18). The technology has developed only slowly on account of unreliableperformance and no credible proven mechanism to explain the claimed effects. However, potential cost benefits to the end-user and the need for better environmental protection has renewed interest in the subject. During the last fifteen years a technology has been developed which uses the fieldsgenerated by electronic circuitry in order to achieve positive results. Working in the audio frequency range these devices appear to affect the nucleation processes although there is still no basic understanding of the fundamental mechanisms. Case histories and results from independent laboratory studies do seem to confirm that electronic and magnetic devices can influence the deposition of calcium carbonate and other scaling minerals. A review of scientific literature is presented relating to the use of magnets and electronic devices for scale prevention. Operational features of the electronic devices are presented as well as information on the scope of application. Potential advantages of electronic devices are described and a number of case histories are given from differing industrial sectors. 1 wfwwm of im document s awiED On LITERATURE REVIEW: ELECTRONIC AND MAGNETIC DEVICES. Water conditioning devices have had a controversial history. Welder (1) reviewed the early devices offered to the consumer during the period 1865 to 1954, claimed for scale and corrosion control. The earliest products were based on electric or electrolytic fieldbehaviour and were sold on the basis of corrosion control. The use of magnets became more prevalent after about 1925. At this time reports of scale prevention and scale removal were also more common. With no basis for understanding how their devices worked, marketing strategies used by some vendors became exaggerated and included claims such as "water being rendered electrochemically neutral' and that devices 'probably scared the ions so that they never dared unite to form scale': such statements ensured the technology was not taken too seriously by industrialists or academics. Indeed, even today there has still been no consistent, long-term and widespread use of a single device reported in the reputable literature. Early academic studies on the effects of applied fields gave mixed results; Eliassen and Uhlig (2,3) reported in 1958 that a series of experiments on calcium carbonate failed to show any improvement in scale control in the presence of magnetic or electrolytic devices. Despite some negative results there continues to be a significant number of positive claims from other academic workers. Donaldson(4) describes benefits of magnetic treatment of hard water and reports the descaling effects also noted by many industrial users. Gehr(6) notes significant changes in water properties for calcium sulphate solutions in the presence of a strong magnetic field. It is claimed that statistically significant changes in surface tension and solution viscosity were observed. It is interesting to note that laboratory experiments utilising once-through systems generally failed to give significant results, e g. Hasson and Bramson(5) whereas those utilising recirculating rigs showed greater effects(6). Baker and Judd(10) also note the importance of recirculating or flowing systems to obtain enhanced results. A further experimental difficulty stems from the fact that early devices and some that are still available today are based on an intrusive design. The disturbance in flow pattern caused by the device itself and the potential for increased internal corrosion are factors that could have influenced accurate monitoring of that system. Donaldson has shown that magnetic fields can result in changes in mineral growth characteristics such as particle size, crystal morphology, solubility and he also notes changes to zeta potential(7). Calcium carbonate crystals were generally larger in an applied field but, curiously, those of calcium sulphate were reported smaller. In a separate study Donaldson(13) reports evidence that barium sulphate particles were apparently smaller after exposure to applied fields but suggests this is due to reduced aggregation of fundamental particles. Chibowski(8) also found differences in zeta potential and surface free energy using radiofrequency derived electric fields. Higashitani(9) found reduced nucleation frequency of CaCOs particles by magnetic fields although growth rate was accelerated. Pandolfo(l 1) reports that in the presence of magnetic fields, CaCOs crystallises in the form of aragonite (an unstable form at normal temperatures) at high flow rates and that the ratio of aragonite to calcite is affected by ferrous or ferric ions. A possible mechanistic role of iron was also explored by Herzog and Katz(12) who showed that trace concentrations of ferrous ions would inhibit the growth of calcite but not aragonite. No relationship between scale prevention, applied field and ferrous ion concentration has yet been reported . There is considerable evidence that particle size and growth characteristics are affected by applied fields underspecific conditions but the results reported do not always show a consistent pattern. Curiously, Higashitani(9) found that in the two brine system Na2S04 + CaCh, it is only the NazSCk component water which needs to be 'magnetised' in order to achieve a change in absorbance due to CaS04 precipitation. He also reports on the 'memory effect'; the apparent ability of the conditioned water to retain the properties of scale prevention for many hours or even days after passing through the device. Further he reports that incompatible brines such as NaiSCM and CaCb brine solutions, can be separately 'magnetised', then stored and still inhibit scale when mixed to induce supersaturation, 120 hours later. Other workers also report similar effects. Scale deposition experiments by Ellingsen(15) indicate that rate of scaling varies with field strength, levelof supersaturation, TDS and pH. Ellingsen did not find significantflow rate dependency but most workers note that flow rate is critical for magnetic devices and in addition a minimum magnetic field strength is needed before beneficial effects are observed. These latter two observations are of considerable consequence when we compare claims for the performance of magnetic and electronic devices. Recent work at Cranfield University and also Portsmouth University has demonstrated the reduced deposition of carbonates in the presence of an electronic device. Contradictory claims are commonplace. For example a scan of the scientific literature shows that there are about equal number of claims that devices cause increased corrosion as there are that they reduce corrosion. By comparison, vendors literature either gives no information or claims 3 ScalevR7/c7/cr Scalen-.jfcfer Early products claims and potential benefits 1870- el ectroiytic / electromagnet devices used to prevent • prevent hardness scale * environmentally friendly. formation. corrosion. * complete/partial chemicals replacement. • remove or soften existing 1925- deposits. * performance synergism permanent magnets used for scale prevention. • reduce bacterial Induced with chemicals. corrosion. * almost maintenance free. • ............. and other * very lowrunning cost. no single device has evolved that has achieved miscellaneous benefits long-term, widespread use with consistent performance proven throughcontrolled monitoring. Scalevp.jteAcr Scalew-i7fcter Historical problems Donaldson and Grimes (Brunei u> have shown applied fields.... x results often Inconsistent x poor reproducibility between'similar'installations. result in x no fundamental mechanism proposed to explain the V changes In particle size observations /claims. V changes in crystallinity x technology not highly regarded by scientific community, V changes In crystal morphology x technology underfunded, V changes in solubility x no predictive tool developed, •/ changes In rate of precipitation x end-user not confident V changes in surface charges ScalOHWc/tfr SC&ld»'<7tcher Other workers (s.fl. sennas) Scale deposition tests with magnets have shown that applied fields.... cublished laboratory work shows scaling rate varies: result in v changes In aragonite proportion ■* magnet field strength V changes In zeta potential •* supersaturation v changes in surface free energy ■» IDS v 'memory effects •* pH ■* flowrate and report ■* flow configuration (once through/recirculating effect ■f role of Fe2+ ions (e.g. Herzog) for laboratory rigs) but....data is not always reproduced in different laboratories. N.B. variance, laboratory results and field clavned resute 4 i 3C8&8*\ifcbcr Sca!e-.:Y/K(;;.'T Permanent Magnets types