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From: The eUpdate, 12.3.2013
Electronic Water Treatment: A Clean Line for Food Production
Scale deposits can lead to off-flavors or off-colors, reducing shelf life and even making products unfit to sell
by Jan De Baat Doelman
The formation of unwanted layers of limescale deposits on the surface of process equipment is of critical importance in the food industry. Limescale is particularly prevalent in heat transfer devices, membrane separations and distribution lines. Scale deposits, known as fouling, can cause a number of operational problems such as plugging of equipment, inefficient usage of chemicals, increased utility costs, lost production, and downgraded products from increased dirt counts. In addition, the incorporation of even undesirable trace particulates can lead to off-flavors or off-colors, reducing shelf life, or even making the product un-saleable.
Scaling deposits are common in flowlines subject to changes of pressure or temperature. Regardless of how hard water effects are achieved, the outcome is the same. Scale formation results in reduced diameter or blocked pipes, reduced heat transfer efficiency, seized pumps, inoperarable valves, misleading meter readings and defective heating elements.
In addition to affecting products, limescale is also an insulating layer on heat transfer surfaces. It is estimated that 40 percent more energy is needed to heat water in a system fouled with ¼ inch of limescale. This leads to more power being consumed or to the installation of heavier duty, more expensive heat exchangers to compensate. Scaled boiler tubes mechanically fail as a result of overheating. Cooling tower plates can also collapse due to the weight of scale deposits. Erosion damage can occur as a result of scale particles breaking loose and subsequently impinging upon other surfaces.
Pipework scale reduces the available cross-section area, and fluids are affected by increased pipewall friction. A larger, more power-consuming pump will be required to maintain throughput volumes but this may allow only a temporary solution to the problem. A plant that needs to be shut down for cleaning costs money.
Not only are plant and product integrity at risk but also personnel health and safety may be compromised. Safety valves or emergency process sensors that are fouled may not operate in an emergency. Overheated boilers have been known to explode.
Electronic Water Treatment (EWT) is a non-invasive system utilizing a solenoid coil or coils wrapped around the pipework to be treated. A continuously frequency changing signal generator, within a specified range, supplies current to the coils. The pulse shaped current creates an induced electric field, concentric around the axis inside the pipe. As a consequence to this arrangement, any charged particle or ion moving within the field experiences a so-called Lorentz force generated by the interaction between charged particles and magnetic and electric fields.
The treatment influences the initial nucleation, resulting in crystals that do not "stick" together. Untreated water builds up matted structures that continuously grow. This treatment creates idiomorphic, scattered crystals, which do not form matted structures. They have a rotundas shape, which means that they have a larger volume in relation to a smaller surface. This feature makes them sensitive to water currents and they are easily flushed out of the pipeline. As no new scale layers are formed, the sheer force of the water flow will gradually remove existing layers of scale. The ability to adjust power, frequency, and coil configurations of products like the Scalewatcher on site enables performance to be optimized with no downtime and no pipe replacement.
Some of the processes that are particularly affected by scale formation include the following.
Retort Cookers. Are used extensively within the food manufacturing process. With recycled water reaching temperatures of 284 degrees in the return lines manufacturers experience ongoing problems with calcium build-up.
Steam and Combination Ovens. Are used extensively in bakeries and regularly scale-up requiring frequent downtime to acid clean. In bakeries, water softens cannot be used as the sodium entering the water supply from the softeners is absorbed by the dough.
Reverse Osmosis Units. Often have to be chemically cleaned every 80-90 hours of operation. The cleaning is determined by the permeate flow rates and pressure differentials across the membranes. The drop in flow rates and increased pressure primarily results from the increasing calcium carbonate fouling on the membrane surface.
Milkstone. When milk is treated in an evaporator for the removal of water, scale in the form of "milkstone" builds up on the inside of the tubes, associated equipment, pumps, and pipework. The removal of milkstone is necessary to maintain operating efficiency, with the costs of removal being measured in labor, chemicals, production losses, and increased energy costs due to reduced thermal efficiency.
Brinery. Is used to top up the cans with water. Heated by a steam heat exchanger, water on a continuous feed fills each can in turn on a production line. The can is then sealed and taken to a retort for the final cooking process. In hard water areas brineries and pipework regularly block with scale necessitating plant shutdown to descale.
Heat Exchangers. Fouling increases the overall thermal resistance and lowers the overall heat transfer coefficient of heat exchangers as well as impeding fluid flow, accelerating corrosion and increasing pressure drop across the heat exchanger.
Fouling of equipment is a serious problem in the food industry. It disrupts production, causes equipment failure and increases the cost of production through increased utilization of energy, time, cleaning chemicals, and water. Formation of foulants on the food equipment surface causes reduction in the heat transfer as well as increase in the pressure drop across the plate heat exchanger. Minimizing fouling is hence imperative to achieve better return on investment as well as to improve food quality.
De Baat Doelman is president of Scalewatcher North America Inc. Reach him at 610-932-6888.