Biological fouling of geothermal wells and heat exchangers:

Observational studyof the I2/APF method forthe elimination offouling.

I2 Air Fluid Innovation, Inc.

Oceanside, NY, USA

Abstract

This paper reports on an observational study to determine the efficacy of the I2/APFprotocol foreliminating foulants fromthe interior of plate heat exchangers and diffusion well screens as well as means to prevent futurefouling. The study was requested by the facility management staff at Standard Microsystems (SMSC), Hauppauge, NYas a response to rapid fouling caused by iron reducing bacteria (IRB) within the heat exchanger and diffusion wells which reduced system function.

SMSC is a design and testing center which utilizes an open loop geothermal system for floor and mechanical cooling. Shortly after the 300 gpm geothermal system was put online,fouling issues occurred at both the heat exchanger and diffusion wells. Diffusion well fouling increased back pressure and reducedwater flow. Heat exchanger fouling reduced heat transfer effecting efficiency and increases energy demand. Pressures in and out of the exchanger were elevated indicating exchanger and diffusion well fouling.

Maintenance of the system required exchanger disassembly and mechanical cleaning with caustic chemicals. This did not rectify the diffusion well issue and rapid fouling would occur. Intra well video indicated advanced bio-fouling on the slot screen. SMSC sought to replace its system with an air to air unit if an effective maintenance program could be utilized.

The program requirements were;

  • Effectively remove existing surface bacteriological and mineral foulant.
  • No disassembly of exchanger.
  • No environmental impact or use of caustic chemicals.
  • No mechanical impact to exchanger or geothermal system.
  • Minimal down time and labor needs.
  • No staff interaction necessary.
  • Improve and preserve diffusion well function.
  • Relatively low cost.

Keywords

Iron, bio-fouling, geothermal, plate heat exchanger, diffusion well

Introduction and background

A geothermal heat pump is aneco-friendly cooling/heating system that pumps heat to or from the ground. It uses the earth as a source of heating or cooling. It is designed to take advantage of the moderate temperatures in the ground to boost efficiency and reduce the operational costs of heating and cooling systems. Geothermal systems are cost effective, generally returning cost of setup in reduced energy needs over 3-10 years. Open loop systems rely on a supply well as a water source, and diffusion or injection wells as a return site. As a means to utilizethe temperature variant for facility use, a heat exchanger is used. Supply well water chemistry and bacteriological makeup are a concern since fouling on the plates within the exchanger reduces heat transfer. This increases the need for auxiliary heating or cooling resulting in higher energy needs. Bio-film formation on plate surfaces as little as .01 can increase energy costs by $19,700.00 yearly through ineffective heat transfer. Additionally, as bio-fouling occurs within the exchanger, pieces break off and cause downstream occlusion of screens within the diffusion or injection well. This has the effect of adding increased back pressure which slows water flow through the exchanger reducing heat draw. This condition adds additional load on supply well pumps increasing energy demand and reducing pump life.

There are three identified mechanical methods that may initiate and promote exchanger fouling;

  • Heat induced precipitation of metals on the plate surface.
  • Foulant settling on the plate surfaces due to fluid motion and gravitational influence within the exchanger.
  • Low velocity zones near surfaces and around gasketsthat may impede water flow allowing for attachment.

The I2 method is a patented protocol for the reduction of microbes through the intermittent infusion of iodinated air bubbles into a fluid. Used in the health industry,

the I2 method eliminates the needs for high levels of biocides through a novel air/iodine vapor/microbe interaction. Additionally, the bubble stream acts as an air sparging device which helps to prevent bacterial and mineral attachment.Used periodically, the APF protocol removes bio-film and minerals from internal surfaces through pressurization, purging, agitation cleaning and flush, using a proprietary cleaner prior to bubble stream introduction. It cleans interior components anddoes not expose staff and environment to caustic chemicals.

SMSC had a geothermal system evaluation done by P.W. Grosser, Bohemia, NY, a hydrology, geo-environmental and engineering firm. Their appraisal indicated that bacteria, iron and dissolved oxygen were entering the water flow. Microbial studies showed high IRB counts at the exchanger. Their recommendation was complete system disinfection of the supply and diffusion wells along breakdown and disinfection of the exchanger. SMSC was considering replacement of the geothermal system with an air cooled system. Mr. Bruce Birdwell, a water quality consultant, introduced the facilities staff at SMSC to I2 Air Fluid Innovation, Inc. for the purpose of possibly performing a study prior system disinfection or replacement. The study was to determine whether I2 AFI’s method for dental waterline maintenance protocol would be applicable for geothermal/exchanger systems of 300 gpm. After receiving well discharge approvals by the DEC, the study was started.

Objective

1. To determine the effectiveness of a protocol that uses an in-situ method for the disruption and removal of formed bio-film/mineral coatings on heat exchanger plates.

2. Todetermine the reduction in fouling rate through the intermittent introduction of iodinated air bubbles into the heat exchanger by the;

  • Elimination of low velocity zones.
  • Removal of recently attached foulants.
  • Prevention of Brownian motion and gravitational effects.
  • Prevention of attachment of biological and inorganic foulants.
  • Mitigation of higher temperature zones near the plate surface.
  • Inactivation of bacteria within the exchanger.

3. Through the elimination of downstream bio-mass movement and low dose iodination the reversal and resolve of diffusion screen occlusion.

Materials and methods

A Taco plate heat exchanger is supplied from a single 300 gpm supply well and deposits intothree 300 gpm diffusion wells. The exchanger cleaning method,the APF protocol,requires an air source, drain and water soluble APF cleaner. The iodinated bubble infusion is formed by the patented I2 Air Infuser. All infusion and drainage is done through the APF assembly attached to the exchanger drain. No modification is done to the exchanger.

The study to include the following;

  • Confirmation of both IRB and dissolved iron at exchanger.
  • Monthly testing to determine iodine sublimation.
  • Pressure comparison on inlet and outlet pre and post APF protocol.
  • Intermittent exchanger breakdown for visual observation of plate integrity and fouling.
  • After cleaning, the exchanger would be allowed to foul to determine rate of foul layer formation without I2 infusion.
  • After cleaning, a comparison of the fouling rate withI2infusion.
  • Diffusion well resolve based on outlet pressure.

The APF protocol consists of exchanger isolation, pressurization, purging, cleaner introduction, cleaner agitation and flush. The time allotted is 10 minute preparation, 60 minute agitation andflush. The I2 bubble infusion is produced by injecting iodinated air from the I2 Air Infuser Cartridge through diffuser tipsinto the exchanger via the APF assembly. It isto be injected both constantly and intermittently throughout the trial period and the results compared.

All services were performed by a member of I2 Air Fluid Innovation’s staff and overseen by members of SMSC facilities staff who observed and confirmed all readings.

Water composition as determined by IME test ampoules were as follows;

Iron: 5 ppm

Iron bacteria, slime producingPositive 24 hours/high

Once a month, a member of I2 Air Fluid would perform the APF protocol which purges the exchanger and injects the cleaner. Active bubble agitation takes place for 60 minutes after which a flush is performed and the system put back on line. Iodinated air bubbles are infused constantly for periods of time to shock treat the system. Once performance improves the infusion is reduced to 2 hours per day.

Observations

Prior the study,elevated pressures in and out of the heat exchangers indicated advanced fouling within both the exchanger and diffusion wells. Visual observation of the exchanger platesconfirmed microbial and mineral fouling. The foulant appeared to be a hardened, red/brown film not easily removed by mechanical means. Water composition testing presented high iron and the presence of slime forming IRB.

Water drawn from the initial flushing prior the APF protocol indicated slight residue. After agitation with the cleaner, the flushed water appeared very cloudy and contained high amount of particles. The color was slight purple indicating breakdown of bacterial foulants. The APF protocol prevents the cleaner from entering the system and contains all activity within the exchanger. The cleaner is approved for discharge into waste drains and is not caustic to staff or equipment. The air infusion causes an active bubbling which can be heard within the exchanger. This prohibits bacteria and minerals from adhering to the plate surface. This prevents bio-slime formation which can break off for down stream contamination.

After the first application, there was no significant drop in either inlet or outlet pressure but they did not continue to rise. After a period of three months during which time the air infusion was constant and the APF protocol performed monthly, pressure in and out fluctuated by constantly decreased until holding steady at 11 psi in and 4 psi out. Minor fluctuations are attributed to air pressure. There was no need for exchanger breakdown or diffusion well shock. Total time expenditure was approximately 65 minutes per month.

The procedure has been performed for twenty two months without disruption to the exchanger, wells or piping system. The exchangers were only broken down for observation and photo. During the breakdown both the plates and gate valve appeared clean, free of contaminants and undamaged by the protocol. Both appeared cleaner than prior the study.

Prior to one exchanger breakdown, the exchanger was allowed to foul through the disruption in air infusion. Bacterial slime was present after only a seven day period.

The plate condition though was considered “like new”.

Two days prior the monthly APF cleaning in June, 2009, all air infusion was stopped to vent the wells for the purpose of taking comparative video. Although video could not be taken due to well cap issues, the pressures in and out of the exchanger indicated vacuum. This was with one 300 gpm supply well feeding a single 300 gpm diffusion well. Readings at a separate heat exchanger indicated 10 inches of water vacuum.

Conclusion

The APF protocol easily cleaned the interior components of the heat exchanger. Disruption in bio-film formation within the exchanger eliminated transient bio-mass which prevented occlusion within the diffusion well. The active bubbling appears to have improved gate valve condition and maintained plate condition during the 23 month period.

The need for exchanger breakdown was completely eliminated as was the need for system disinfection. Improvement in heat transfer has made the system more effective and the elimination of back pressure has reduced the strain and power draw on the well pump.

The I2 infusion reduced fouling rate through a change in water flow pattern within the exchanger. This appeared to eliminate low velocity zonesand prevent sedimentation. The active bubbles appeared to act as a sparger,lifting existing bio-films and preventing attachment by planktonic bacteria and insoluble minerals. The infusion maintained the plate surfaces long enough to allow for a monthly one hour APF protocol application.

The protocol used approximately six grams of iodine in one month’s time. It appeared to have no physical effect on the exchangers, piping or diffusion well. The bubbling appears to reduce the APF protocol time by presenting a reduced bio-film for removal. Intermittent infusion appeared as beneficial as constant.

The protocol appears to have met all of SMSC requirements. They have since decided not to replace the system and contract I2 Air Fluid to do a monthly service.

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This study contains proprietary content or intellectual property and is intended for the sole educational use of the individual(s) or entity being presented to. Be aware that any disclosure, copying, distribution or use of the contents of this information is strictly prohibited without the authors’ written consent.

Protocol and application is based upon the art and science of U.S. Patent No. 7,329,385 and is the intellectual property of the inventor(s)

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