Monitoring compressed air in food processing

One of their most important process media is compressed air. While it is mainly used as control air for their production plants, it comes into direct contact with their products at a few points along the production chain. This means that the compressed air must be free of oil in all its forms – liquid, aerosol and vapor. This standard must be maintained across the entire system and at all times. Nölke needs to monitor and document the quality of compressed air in real time.

These requirements pose a huge challenge for most businesses, as the monitoring of the residual oil concentration in compressed air systems is a very difficult task. Most conventional solutions are only able to determine the oil content after it is produced, rather than offering a measuring strategy that detects problems before the damage is done.

Most companies that use oil-free compressed air are well able to determine the residual oil content in lab tests. The results of these tests are however only available days or even weeks after the samples have been taken. Due to this delay, they are not able to respond quickly and effectively to problems caused by contaminated compressed air. In a worst-case scenario – which is also the most common case – problems with the product or the production process have already become obvious before the lab results are back. The consequences are product stops, high reject rates or even claims for damages, which are all extremely costly.

Worldwide, the damage caused by contaminated compressed air in production and processing plants amounts to millions of Euro. Most of these incidents are due to undetected ingress of oil into the compressed air system and its subsequent distribution across the system to the points of consumption.

Such problems are mainly caused by oil aerosols and vapors. The oil contained in the compressed air sometimes escapes at tools and machines where it might form a film on surfaces and come into contact with the product, contaminating it.

The quality of compressed air is commonly classified according to ISO 8573-1. There are however many applications where compressed air of class 1, which is deemed to be technically oil-free, is not clean enough.

According to the above standard, compressed air of class 1 must not contain more than 0.01 mg/m³ of oil (liquid, aerosol or vapor), which is only about 4% of the concentration found in normal ambient air. These concentrations are already so small that they are virtually undetectable.

However, many compressed air applications – for instance in the field of medical technology, pharmaceutical production, measuring technology and food processing – require even lower oil concentrations to ensure process safety. Nölke is among the processors who need compressed air with a residual oil content of less than 0.003 mg/m³.

At such low concentrations, it is more difficult to monitor the quality of the compressed air than to produce it. Continuous, real-time residual oil concentration monitoring of the compressed air with proper documentation is something most operators have not achieved yet.

Instead, they opt for frequent lab tests, which is very time-consuming. As the test results are only available days or even weeks later, corrective action can only be taken after the damage has been done. Far too often, companies need to stop production and remove potentially contaminated products from their shelves, which is very costly.

Even less satisfactory than the lab testing method is keeping one's fingers crossed, trusting that, as long as there are no obvious problems in the production process, everything will be OK. While everybody would agree that simply hoping for the best is not really an adequate strategy, it is still widely practiced.

Nölke in Versmold has chosen a different approach: a strategy of continuous improvement. They use advanced technology to assess and ensure the quality of their processes as close to real time as possible. For compressed air, they have invested in an innovative measuring system that allows them to continuously monitor the residual oil content. A real milestone in process safety.

We are talking about the METPOINT OCV, a hydrocarbon monitoring system that measures the concentration of hydrocarbon vapors. It has been designed for the stationary inline measurement and monitoring of residual oil vapors in compressed air based on the ISO 8753-5 standard.