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Magnetic or electrostatic scale control technologies can be used as a replacement for most water-softening equipment. Specifically, chemical softening (lime or lime-soda softening), ion exchange, and reverse osmosis, when used for the control of hardness, could potentially be replaced by non-chemical water conditioning technology. This would include applications both to cooling water treatment and boiler water treatment in once-through and recirculating systems.

About the Technology

The technology addressed in this FTA uses a magnetic or electrostatic field to alter the reaction between scale-forming ions in hard water. Hard water contains high levels of calcium, magnesium, and other divalent cations. When subjected to heating, the divalent ions form insoluble compounds with anions such as carbonate. These insoluble compounds have a much lower heat transfer capability than heat transfer surfaces such as metal. They are insulators. Thus additional fuel consumption would be required to transfer an equivalent amount of energy.

The general operating principle for the magnetic technology is a result of the physics of interaction between a magnetic field and a moving electric charge, in this case in the form of an ion. When ions pass through the magnetic field, a force is exerted on each ion. The forces on ions of opposite charges are in opposite directions. The redirection of the particles tends to increase the frequency with which ions of opposite charge collide and combine to form a mineral precipitate, or insoluble compound. Since this reaction takes place in a low-temperature region of a heat exchange system, the scale formed is non-adherent. At the prevailing temperature conditions, this form is preferred over the adherent form, which attaches to heat exchange surfaces.

The operating principles for the electrostatic units are much different. Instead of causing the dissolved ions to come together and form non-adherent scale, a surface charge is imposed on the ions so that they repel instead of attract each other. Thus the two ions (positive and negative, or cations and anions, respectively) of a kind needed to form scale are never able to come close enough together to initiate the scale-forming reaction. The end result for a user is the same with either technology; scale formation on heat exchange surfaces is greatly reduced or eliminated.

These technologies can be used as a replacement for most water-softening equipment. Specifically, chemical softening (lime or lime-soda softening), ion exchange, and reverse osmosis (RO), when used for the control of hardness, can be replaced by the non-chemical water conditioning technology. This would include applications both to cooling water treatment and boiler water treatment, in once-through and recirculating systems.

Energy-Savings Mechanism

The primary energy savings result from a decrease in energy consumption in heating or cooling applications. This savings is associated with the prevention or removal of scale build-up on a heat exchange surface where even a thin film (1/32" or 0.8 mm) can increase energy consumption by nearly 10%. Example savings resulting from the removal of calcium-magnesium scales are shown in Table 1. A secondary energy savings can be attributed to reducing the pump load, or system pressure, required to move the water through a scale-free, unrestricted piping system.

Table 1. Example Increases in Energy Consumption

as a Function of Scale Thickness

Scale Thickness(inches) Increased EnergyConsumption (%)

1/32 8.5

1/16 12.4

1/8 25.0

1/4 40.0

When the scale-forming reaction takes place within a heat exchanger, the mineral form of the most common scale is called calcite. Calcite is an adherent mineral that causes the build-up of scale on the heat exchange surface. When the reaction between positively charged and negatively charged ions occurs at low temperature, relative to a heat exchange surface, the mineral form is usually aragonite. Aragonite is much less adherent to heat exchange surfaces, and tends to form smaller-grained or softer-scale deposits, as opposed to the monolithic sheets of scale common on heat exchange surfaces.

These smaller-grained or softer-scale deposits are stable upon heating and can be carried throughout a heating or cooling system while causing little or no apparent damage. This transport property allows the mineral to be moved through a system to a place where it is convenient to collect and remove the solid precipitate. This may include removal with the wastewater in a once-through system, with the blowdown in a recirculating system, or from a device such as a filter, water/solids separator, sump or other device specifically introduced into the system to capture the precipitate.

Water savings are also possible in recirculating systems through the reduction in blowdown necessary. Blowdown is used to reduce or balance out the minerals and chemical concentrations within the system. If the chemical consumption for scale control is reduced, it may be possible to reduce blowdown also. However, the management of corrosion inhibitor and/or biocide build-up, and/or residual products or degradation by-products, may become the controlling factor in determining blowdown frequency and volume.

Aside from the energy savings, other potential areas for savings exist. The first is elimination or significant reduction in the need for scale and hardness control chemicals. Second, periodic descaling of the heat exchange equipment is virtually eliminated. Thus process downtime, chemical usage, and labor requirements are eliminated. A third potential savings is from reductions in heat exchanger tube replacement due to failure. Failure of tubes due to scale build-up, and the resultant temperature rise across the heat exchange surface, will be eliminated or greatly reduced in proportion to the reduction in scale formation.

Where to Apply

Non-chemical scale control technologies can be used for either boiler scale control or cooling tower scale control. Boiler scale control applications are the majority of the installations, but the control of silica scale in cooling water applications is also possible. Non-chemical scale control technologies are best applied:

· When the use of chemicals for water treatment is to be minimized or eliminated. Lime, salt and acid for cleaning can be reduced or eliminated.

· When space requirements do not allow installation of lime softening equipment or ion exchange equipment. The non-chemical technologies are generally very space efficient.

· When particulate matter in the water can be tolerated by the process; solids separation is required.

· When frequent system shutdowns are required for descaling even with a diligent chemical scale control program.

· In remote locations where delivery of chemicals and labor cost makes conventional water softening or scale control methods cost prohibitive.

Maintenance Impact

There is a significant, positive impact on maintenance. Field applications have shown the technology to be capable of controlling scale for extended periods of time, months or years, eliminating the periodic cleaning or descaling of process equipment that is typical of conventional, chemical-based scale control technologies.

Additional Considerations

There are additional considerations to be taken into account. Primary among these is the reduction in chemical use at the facility for water softening. The chemical use reduction may lead to reduced safety, training and reporting requirements.

Electricity consumption will also be reduced. The actual reduction is highly dependent upon the technology employed. Permanent magnets use no electricity, so both the on-site electricity used for chemical treatment as well as the off-site energy required to produce and transport the chemicals will be eliminated. For the electronic units, on-site energy requirements may vary from as little as 10% of the chemical-based treatment system energy consumption--typical, to 10 times the energy consumed by the chemical-based treatment system.

Energy consumption reductions will lead directly to reductions in air combustion emissions. There will also be additional indirect reductions due to decreased transportation of fuels and decreased fuel processing. The latter will also lead to reductions in water use, water pollution, and solid wastes from mining and processing operations.

Technology Performance

User experience has been positive. Two experiences have been common. First, users have noted a dramatic reduction in scale formation to the point where the need for chemical scale control is eliminated. Second, the prior build-up of scale on heat exchange surfaces has been removed over time. This last process has been noted as taking from 30 days to over a year, depending upon the thickness and composition of the scale.

Environmental Impacts

There are areas where the technology mitigates environmental impacts. The first is air quality due to emissions reduction associated with decreases in fuel consumption. The second is a corresponding decrease in solid wastes, ash and other fuel combustion residues to be disposed. Of course, this will only be applicable in the situation in which an end user combusts fuels on-site for the production of power. A third area is the reduction in release, or potential for release, of water treatment chemicals stored at a facility. Since chemical consumption will decrease, emissions from storage will also decrease. The wastes associated with disposal and management of used chemical containers will also be reduced.

Savings Potential

Energy savings can result from two areas. First is the reduction in fuel used in generating heat. The fuel consumption savings is equal to 10% of the baseline fuel consumption. Second is the energy savings resulting from decreased pressure drop within the heat exchanger. This is not quantified here, but could be quantified if the pressure drop through the current system was known, along with the energy characteristics of the pump so that reductions in pressure could be related to energy consumption.

Cost savings also result from reductions in chemical use. Chemical softening will be reduced, and likely eliminated, by the use of non-chemical treatment technologies. There will also be a corresponding energy decrease from the shutdown of chemical mixing equipment and water treatment equipment used in the softening process.