CONTROL FOAM TO CONTROL COSTS
Control of foaming in industrial processes presents many challenges in almost every market sector: pharma, brewing, paint manufacture, waste water treatment, oil & gas, food processing and more. To complicate matters, foam can be an integral [and important] part of a process and needs to be carefully controlled, or it can be an unwanted side effect.
In general, foam is an unstable, two-phase medium of gas and liquid: gas pockets trapped in a network of thin liquid films. There are a wide range of chemicals available that can be used to prevent foam forming, to disperse it once formed, or both. After addition to a process, these chemicals operate by being absorbed into bubble surfaces where they are effective in causing surface tension to change, collapsing the bubble; an effective de-foamer can disperse foam in a few seconds. Some process foams are highly stable and long lasting, others constantly collapsing and resurging and the addition of anti-foam chemicals to control foam layers is a manual procedure. Often, the decision to add such chemicals is based upon the visual observation and experience level of an individual observer/operator, a perfectly reasonable method except that different individuals can have different opinions as to the severity of the foam layer and therefore the right amount of chemical to add. This leads to inconsistency in chemical addition and can impact operating cost and process performance/yield. It is clear that in most instances, it is highly desirable to have effective monitoring, measurement and control of foam in a process environment.
Why You Need to Control Foam
Foam generation can cause expensive and time-consuming problems such as environmental release, poor product quality, even plant downtime and cleanup costs if excessive foam is allowed to spill over from the process. Furthermore, excess foam can limit process throughput and can contribute to damage of plant equipment like pumps, filters and valves. Add the ongoing cost of over-dosing of de-foamer chemicals and it is clear to see the benefits of implementing effective foam control.
The key issues are being able to understand foam characteristics and its depth or thickness. In some applications, it is also beneficial to measure both liquid level and foam layer depth; i.e. to understand where the foam-liquid interface is located in a vessel. The effective and reliable measurement of foam layer thickness and the location of the foam-liquid interface has been challenging in the past as results can be adversely affected by a number of factors including varying foam density and the coating or fouling of measurement elements with residual product. A variety of techniques have been tried. 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 is they become coated with process material, giving continuous false positive indication. In any case, once foam is detected by a point level system 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/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!
Where Foam Control is Headed
Many of the techniques tried up to now as attempts at improvement over visual/manual monitoring of foam level have fallen short of providing adequate and sustainable solutions to foam control. The main issues have been 1) process fouling of single point systems rendering the detection method non-operable until cleaning can be implemented, and 2) the inability of continuous level systems to distinguish between liquid level and foam layer.
The introduction of IMA (Intelligent Multi-Action) Sensing 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 de-foaming agent. Single point systems are available from Hycontrol under the SureSense brand. Following the implementation of the IMA technique in single point foam detection systems, Hycontrol expanded the technology to continuous level with a multi-segment sensing system. Here, a continuous level probe made up of a stacked array of individual sensors is inserted into the process. Marketed as the MultiSense System, each sensor works independently but all are used collectively to build up a profile of the total level in the vessel, simultaneously providing both accurate liquid level indication and a measurement of the thickness of any foam layer above.
How SureSense and MultiSense Systems Control Foam
Both the SureSense and MultiSense systems are specifically designed for measuring foam presence/depth/thickness, detecting foam-liquid interface and accurately measuring liquid level while ignoring any foam present in real time. Neither are modified or repurposed level sensor designs and both can be used for foam control strategies in a wide variety of applications across many industries. They provide the benefit of reliability of measurement leading to real reduction of cost and in many cases, increased yield/production efficiency. Some users claim to have reduced anti-foam agent addition by 75% or more after implementation of reliable foam measurement in their control strategy.
It should be recognized that most foam reduction systems are reactive rather than proactive. Although IMA Sensing and Multi-Segment Technology can and do contribute to dramatically improved foam control in many applications, there are still certain applications where installing sensors is just not practical. To overcome this, Hycontrol has further innovated and utilized its foam sensing technology in a predictive Foam Tendency Analyzer (FTA Analyzer). Instead of measuring foam created in a process, the FTA is used to predict, in advance, when foam will occur thereby allowing appropriate action to be taken before any significant foam event occurs. Samples are automatically taken serially from the process and the analyzer tests them at line for any tendency to foam. Results from each test can be used to preempt any foam out situation: add anti-foam agent, reduce agitation or gas feed rate, or others. The FTA can be used stand alone or as part of an overall control system.
Uncontrolled foam generation can affect productivity in a wide range of industries. The introduction of reliable foam measurement instrumentation the pharmaceutical, wastewater, O&G and food and beverage industries has been effective in bringing down costs and providing productivity improvements. Reliable real time monitoring and measurement of foam production ensures controlled quantities of de-foamer chemicals are only added when required, provides for repeatable production process and stops unexpected and expensive foam out events from happening. To see more about foam control applications, visit our page here.