Foam Control Technical FAQ

Foam causes significant issues in processes when it gets out of control, be it AD, waste treatment or food preparation. To counter these problems, careful monitoring of foam generation is needed. Getting this right should be an industry priority. Sectors such as AD are increasing in size. The number of incidents will inevitably grow as well. 

We need to understand why it is so challenging to measure foam and why so many current technologies fail. One of the most import reasons is that foam itself generally only contains 1% liquid and 99% gas, making measuring the liquid component with a traditional liquid device near impossible. As such, regular liquid probes are unsuitable and cannot be relied upon to detect foam accurately. Hycontrol provides all of the significant varieties of liquid level technologies but would not recommend any of them to detect foam. You can read more about the problems encountered by different types of probes in our white paper, 'What Makes Foam Detection so Difficult?'. 

Hycontrol foam probes work on aqueous (water-based) foam by utilising our patented IMA Sensing® technology. IMA works by passing a small alternating electric current at a very low voltage through the foam into the liquid or the container wall. By measuring the level of the current flowing, we can determine if any foam is present and then measure the density of it. The probes provide efficient and cost-effective foam control across a wide range of water-based process applications. Each stainless steel sensor can be customised to suit the requirements of your process. Different heads and process fittings are available, with standard insertion lengths of up to 3 metres (for a 20 mm diameter probe). For specific laboratory applications, autoclavable probe heads are also available.

Probes can be supplied with up to three separate alarm points as required, allowing for a degree of level measurement and differing actions at differing points. The sensors are hygienic and steam sterilisable, and by utilising Hycontrol’s patented IMA Sensing® technology, they can discriminate between the residual build-up of foam along the sensor probe and the foam created during the process. Thus, it can continue to efficiently monitor foam levels regardless of how fouled the sensor may be.

The unique IMA (Intelligent Multi-Action) sensing facility is at the core of Hycontrol's foam monitoring products. The patented IMA Sensing® technology discriminates between the residual deposits of coagulated foam and product that build up along the sensor during normal use and the foam generated in the process which the user is seeking to measure.

Effectively, the foam sensor ignores the inevitable fouling that will accrue during normal operation while continuing to monitor the foam level. No matter how heavily coated the sensor is, or how dense and sticky the layer, its unique construction enables it to keep measuring foam throughout the process cycle. Because the leakage is measured separately and not as part of the foam signal, the sensor will function unimpeded.

It is often not possible to prevent material build-up on a probe in a process vessel. Indeed, to attempt to do so may disrupt and compromise the process. Hycontrol's IMA technology enables the sensor to function reliably despite extensive coating or fouling. Please watch the video below for more information:

If you are looking to set up your system for the first time, or if you think you may have made a mistake in the initial wiring, please watch this video demonstrating the initial wiring of the SureSense+ system:

Unfortunately, the conductivity of a liquid on its own does not give us enough information from which to assess if the SureSense+ will work in an application. The following notes are an attempt to provide a “rule of thumb” to help to evaluate an application.

The SureSense+ range is calibrated in resistance from 0 to 100% which is equivalent to a measurement range of 100 ohms to 100K ohms. A measure of the conductivity of the liquid, which is generating the foam gives us an idea of how easy the foam will be to measure. Conductivity is measured in millisiemens per centimetre (mS/cm) or microsiemens/centimetre (uS/cm). Technically it is possible to measure the effective conductivity of foam, but it is a complicated task and best avoided. However, the conductivity of the liquid below the foam, together with the tank geometry, gives us an idea of how easy measuring the foam will be. Conductivity alone is not enough as we need to know the geometry of the measurement system comprising the probe in the tank. In practice, the diameter of the tank (assuming that it is metal) and the conductivity gives us a good approximate guide. The other issue which affects the foam measurement is its density based on the liquid content: this is always difficult to estimate and can vary from less than 0.1% liquid up to 5% for a dense foam. 

A simple estimate should help to determine if the SureSense+ will work or not in an application in a metal tank. This estimate is based on conductivity and the vessel geometry and ideally an idea of the foam density. The following data is needed:

• The conductivity of the liquid - uS/cm
• The diameter of the tank or pipe - cm
• The diameter of the probe - 12 mm or 20 mm
• Ideally an idea of the approximate foam density (if unknown assume 1%)

If the conductivity is below 400 uS/cm, then use Figure 1, otherwise, use Figure 2.
 
Using the conductivity and the tank diameter plot a point on one of the graphs below. If the point falls below the line for the probe size, then foam can probably be measured. If the point falls above, then the foam may not be measured. For example: for a 12 mm probe in a 50 cm diameter tank with a liquid conductivity of 320 uS/cm, the point falls below the blue 12mm line in Figure 1. This indicates that the SureSense+ will work in this application for typical foam. If the conductivity were 300 uS/cm or less, then it would not work. This estimate is approximate, based on the average foam density of 1%, which would be denser than washing up type foam but less dense than Guinness foam. Please consult a Hycontrol representative if you have any queries.

    

The names fermenters and bioreactors apply to a whole range of vessels are used for fermentation. The smallest are shake-flasks, which have no controls and are agitated in a temperature-controlled shaker. The next stage up might be ~500 ml vessels which have limited space available for the installation of sensors. The smallest vessels that have a reasonable amount of 'working space' in which to add controls would be around 2-3 litres. These vessels are often characterised by the total volume and the working volume, so a 3-litre vessel might have 2 litres working volume, as there is always a need to maintain a headspace above the media. 

Therefore, as a general rule, the smallest-sized vessel we would expect to be able to detect and measure foam in functionally would have a working volume of around 2 litres. However, the more significant feature is likely to be the size of the ports. The smallest Hycontrol foam sensor available has a 12 mm diameter. These small vessels often only have 6 mm diameter ports, and therefore probes cannot be fitted to them. Vessels of this size are likely to be below 1 litre in volume so would in all probability lack sufficient headspace for a probe to be mounted anyway. 

Hycontrol offers a wide range of fittings that are suitable for small vessels, including PG13.5, ½" tri-clover, 1" tri-clover, 2" tri-clover, PG13.5 and so on. The top ports are now usually PG13.5 or tri-clover. The commonest fermenter fittings now appear to be 1.5" tri-clover. If you have any queries or the connection you require is not listed here, please do not hesitate to contact a Hycontrol representative.

The development of the new and improved SureSense+ foam controller has also resulted in changes to the sensor probes and the employment of a different cable type. While this product has now completely superseded the original SureSense system, there are many such existing SureSense systems out in the field which still function to their operator's satisfaction many years after their initial installation. Therefore, when replacement parts are needed, the question arises as to whether the new-type SureSense+ sensors (with a product code starting FR--) will work with the old-type SureSense controllers? And, in contraposition, can the new-type controllers be used with existing sensors? 

The answer is yes in some instances, and no in others. The chart presented here will help you to gauge the component compatibility of the foam system you currently own with the SureSense+ equipment that is now manufactured by Hycontrol. The following information is for guidance only, and you should always consult a Hycontrol representative before purchasing.
 

Sensor Type	Controller Type	Cable	Compatible?	Comments
Old SureSense FP1 – FP6	SureSense+ FRC1 – FRC6	STP*	Yes	Configure the controller to suit sensor type “FP”. See note 1 below on CE.
Old SureSense FP1 – FP6	SureSense+ FRC1 – FRC6	Lapp	Yes	Configure the controller to suit sensor type “FP”. Connect guard and test wires to –ve terminal in the sensor.
SureSense+ FR1 –FR4	Old SureSense FPC	STP	Yes	The sensitivity of the controller will increase slightly. But this is not a serious issue. See note 2 below.
SureSense+ FR1 –FR4	Old SureSense FPC	Lapp	Yes	The sensitivity of the controller will increase slightly. But this is not a serious issue.
DualFoam FP1-FP4	SureSense+ FPC2	STP	No
DualFoam FP1-FP4	SureSense+ FRC2	LAPP	No
SureSense+ 2point probe.	DualFoam FPC2CW	STP	Yes	Add a link in sensor head between Guard1 & Guard2.
SureSense+ 2point probe.	SureSense+ FRC2	STP	No

* - STP = Screened Twisted Pair. The old-style of cable which has been superseded by Lapp cables.

Notes

1. The SureSense+ has been EMC tested using the Lapp cable, meaning that the CE marking is dependent to some extent on the use of the Lapp cable. However, it works perfectly well with the previous STP (Screened Twisted Pair) cable and if used will not cause any problems.
2. The SureSense+ sensors (part numbers FR) include a 180 Ohm resistor to detect it is present and connected to the controller. If used with an old-type controller, this resistor will affect the controller sensitivity as it measures in parallel with the foam. This will increase the effective sensitivity setting of an old-type controller by a small amount, so at 10K setting the sensitivity will be increased to 10.4K and at 50K setting the sensitivity will be about 60K - not a significant problem but users should be aware of it. 

The usual antifoam pump that Hycontrol uses with its foam control systems is an AWE peristaltic pump. The pump element terminates in a type of hose tail. Use the hose tail as normal by pushing a flexible hose over the top of it and securing with a jubilee clip. The correct type of pipe for this application is a 10mm ID reinforced PVC tube (e.g. RS 368-0205).