Boresaver - A Crystal Clear Solution
Iron oxide residues in groundwater are becoming an increasing problem, estimated to affect about 40% of the world’s water bores, and anecdotal evidence indicates that this number is steadily increasing. Whether caused by naturally occurring bacteria or straight chemical means, these residues will eventually affect nearly everyone who sources water from groundwater aquifers.
These residues result in an oxide and bio-film that builds up in pumps and headworks and this is particularly significant for a geothermal heating plant. Any blockages or restrictions within the pipe work and distribution system will severely reduce the flow section of the system and increase the friction losses, causing inefficiency, wasted energy, increased operating costs and compromising the original reason for opting for geothermal energy.
This case study considers an air conditioning system servicing a 150,000m2 retail/industrial complex in Milan consisting of numerous offices, multiple car showrooms, mechanical workshops, training facilities and warehouses. The system, producing 6MW (COP=4), comprises nine geothermal plants (with the largest system 50,000 litre capacity), 3 wells (each approximately 40 metres deep) and 10km of pipework between 250mm & 10mm diameter. Groundwater is pumped for 4 months during the summer (from mid May to mid September) and for 6 months in winter (mid October until mid April). There is a one-month interruption between these two periods when, conveniently, maintenance can be carried out.
Within the secondary closed circuit - that carries the conditioned waters coming from the heat exchange plant to the various buildings – there had been cases of blockages due to bio-film containing iron hydroxide. Tests and analysis carried out showed an increase of iron and iron-related bacteria (IRB) levels both in groundwater (at the beginning of the water circuit) and in the water flowing in the secondary circuit (at the end of the water circuit).
Iron-bacteria can be dangerous for two main reasons: first it can damage metallic pipes by corroding the non-plated parts of the pipes, increasing any electrochemical corrosion that may already be present. Secondly, it causes biofilm (biofouling) which can build-up within the pipes, reducing the system flow rate.
This particular system was severely contaminated with iron related bacteria (IRB) including the extraction wells, primary and secondary heating loops and even the convector heating systems in the offices where the pipes are as small as 10mm. Typical symptoms included poor flow, orange brown residues inside the pipes and filters and high working pressures in the secondary system. The system was clogged and in some cases completely blocked by the bio film and oxide residues produced as a direct consequence of the IRB.
The consultant decided to use BoresaverTM to solve the problem because of its ability to dissolve the oxide residues as well as combat the IRB contamination. The product could be used without dismantling the equipment and would not attack or deteriorate any of the materials inside the system.
Boresaver dissolves and/or loosens oxide deposits by processes of reduction and complex formation in mildly acidic conditions. In the process, components of Boresaver are converted to carbon dioxide and water. Boresaver is readily and rapidly biodegraded under aerobic and anaerobic conditions after it has done its work and has been diluted in the flushing process. One of Boresaver’s key compenents is Ethanedioc acid (oxalic acid), a substance that occurs naturally in plants and vegetables, making the product both biodegradable and environmentally friendly.
Boresaver is approved by the Drinking Water Inspectorate (DWI), part of DEFRA for use in potable water applications, useful if water from the wells is used for both geothermal applications and for a potable water supply.
The first part of the system to be treated was the extraction well. Then the treated water was used to fill the whole system, including the secondary loop which had ultimately compromised every part of the system. The pumps and system remained intact whilst the treatment was carried out. This reduced the down time for the plant and minimised costs of the rehabilitation. Following treatment of the wells, the pumps were then used to manage the movement of further Boresaver Ultra C treatment throughout the rest of the distribution pipe work, evaporators and condensers of the heat exchanger. The complete treatment of the each well and distribution system was completed within 4 days.
The secondary systems were cleaned using the Boresaver Ultra C by pre-dissolving the chemical in IBCs and then pumping this solution using small circulating pumps around the various systems. Once inside, the main circulating pumps were used to recirculate the treatment water for a period of 24 to 48hrs. Following which, the system was purged with fresh water from the wells and then finally refilled.
Once the systems were cleaned it was essential to control the iron related bacteria so that future treatments could be carried out on the basis of a maintenance dose rather than at the full dose. Since the bacteria populate exponentially it is better to maintain a suitable proactive maintenance regime than to react when the system becomes a catastrophic failure. Over time this has proved to be more cost effective. This regime also included use of the Boresaver Liquid maintenance product which was dosed into the closed secondary loops as well as into the wells, the ultimate source of the original contamination.
Since the treatments can be carried out without removing the pumping plant and dismantling the system great savings can be enjoyed whilst still enabling the system to be successfully cleaned. In all cases good monitoring is essential to manage the most effective time for the on going treatments. Regular proactive maintenance always proves to be most cost effective in the long run
The result of this treatment was that the iron mass was removed from the circuit itself and that other material trapped within the residues(sand, slime, clay etc) were released. All the above material - easily removed after the treatment - would otherwise have blocked the pipes, preventing the plant from working properly.
The same treatment was repeated in the other two wells and in the related water circuits. It was suggested to repeat the treatment every two years for maintenance and prevention.
The M&E contractor later reported a doubling of performance on the three worst affected plants with an increased performance across all plants.
Geodrilling International - March 2009 Edition.