FOAM DETECTION & CONTROL

1. A foam sensor is fitted through the top (or the side) of a process vessel. The sensor is connected to a foam controller, which in turn is connected to a pump controlling the flow of antifoam into the vessel.
2. As the process begins, foam starts to form on top of the liquid.
3. As the foam level increases, the sensor signals back to the controller that foam has been detected. The ‘sense’ light illuminates on the controller to indicate the increasing level of the foam.
4. When the foam reaches a pre-set level, the sensor signals the controller to start adding antifoam. The ‘activate’ light on the controller illuminates to indicate that action is being taken to reduce the foam.
5. Because the sensor and controller are very sensitive to foam levels, the antifoam is only added as required, the amount of antifoam used is strictly regulated, producing significant cost savings.
6. With the level of foam now returned to normal, the antifoam pump stops, leaving the sensor and controller on standby until the cycle starts again.

A variety of techniques have been applied to the challenge of accurate measurement and reliable control of foam levels:

• Radar type level systems mounted in the top of a vessel can be tuned to see the topmost layer of a process, but can be fooled if any foam layer becomes lighter or if the process liquid becomes denser or more reflective.
• Microwave level sensors will more likely than not acquire the level of the liquid below any foam layer.
• Admittance or capacitance technology probes can be quite successful in detecting the presence of foam as point level devices, but cannot distinguish between foam and liquid and most will be disabled if they become coated with process material, giving continuous false positive indication. In any case, once foam is detected by such systems, and depending upon the height it is set above the process, it can be too late to prevent a “foam-out” situation where vessel overheads are filled with process material, causing blockage of filters and build-up and contamination in vent lines. This is particularly an issue for bioreactor operations where liquid levels can vary through a batch, and foam generation can be rapid and sometimes unexpected.
• The over-riding problem with these methods is that the instrumentation used is designed to measure liquid level, not foam level. Foam is about 1% liquid, so it’s not surprising that liquid level instruments struggle to reliably measure foam level.

Product fouling and deposits on a measuring probe are common in many foaming applications, and have a serious impact on foam measurement.

Hycontrol’s IMA technology out-performs other detecting techniques, as it operates efficiently and repeatably even when the probe becomes heavily fouled with residual product.

The SureSense+ foam control system uses a special guard electrode which nullifies the desensitizing effect of accumulated fouling on the probe. With the effects of fouling removed, the main foam sensor is able to ignore the product buildup, and only monitor the foam within the process. Regardless of how dense or sticky the fouling on the sensor becomes, the Hycontrol foam sensor continues to function, providing accurate, repeatable, and reliable foam control.

The IMA-equipped Hycontrol SureSense+ sensor shown in the photo below continued to operate as designed, providing accurate foam measurement, despite the severe buildup evident in the photo.

Many of the techniques tried up to now to improve visual and manual monitoring of foam level have fallen short. The main issues have been process fouling of single-point systems rendering the detection method non-operable until cleaning can be implemented, and the inability of continuous level systems to distinguish between liquid level and foam layer.

The introduction of intelligent multi-action (IMA) technology by Hycontrol is a major turning point in the ability of foam sensing systems to provide reliable measurement for foam control strategies. Foam detection probes with IMA sensing capability have a separate guard sensor that detects when the probe is coated with process material, essentially nullifying its effect and maintaining the measurement on line. The IMA technique prevents false positives and therefore overdosing of the process with defoaming agent.

In food processing, raw materials are processed and prepared for consumers around the world. These photos show how foam can be a real problem in a pea processing plant. The peas are washed and then cooked prior to flash freezing or canning. As peas are cooked, a great deal of foam can be generated, and this gets into the cooker vent pipes and overheads, impeding process efficiency.

Antifoam additives are often used to control “foam-outs”, but without reliable foam measurement, are often ineffective due to overdosing or foam detection errors which arise when foam sensors have been coated. Using a Hycontrol foam sensor with IMA technology allows the addition of just the right amount of antifoam agent to knock down the foam layer and prevent foam from spreading through the plant, cutting costs, cleanup, and downtime.

Before installing IMA-equipped Hycontrol foam control systems:

After installing Hycontrol systems:

See the difference for yourself!