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Hotspot prevention and emission monitoring – our filtration services take our customers' safety into account

DESOTEC is committed to finding solutions to our clients’ filtration requirements. To supplement our core provision of mobile activated carbon filters, our technical team develops products that address particular issues raised by clients. In the past few years, we have mainly focused on two areas: safety, and emission monitoring. Three products are now in widespread use in our projects: the INERTI-BOX, the HC-BOX, and the VOC-BOX.

Safety: the INERTI-BOX and the HC-BOX

DESOTEC filters are very safe, particularly as we handle all spent carbon away from clients’ sites. However, for some applications there is an increased risk that hotspots could develop.

These are formed when high concentrations of certain molecules, such as aldehydes and ketones, are adsorbed onto activated carbon, generate heat, and cause parts of the carbon bed to smoulder.

Hotspots could damage the filter unit and other equipment, and cause an unsafe production environment. Once they develop, customers need to exchange the filter as soon as possible, potentially wasting unused carbon.

Preventing hotspots: the INERTI-BOX

The INERTI-BOX was developed in response to client concerns about hotspots.

It comprises a nitrogen dosing system to be connected with electrical control system and carbon monoxide (CO) sensor from the client. If the sensor detects a hotspot forming, the system closes the filter valves, cutting off the air supply. It then douses the filter with nitrogen, reducing the oxygen levels and eliminating the risk of a hotspot developing further. This procedure takes place automatically, with no need for an operator.

DESOTEC has created a new type of INERTI-BOX that can operate up to three filters in parallel or in series. Because of this adaptation it is no longer necessary to flush all filters with nitrogen in case of a hotspot. This reduces the nitrogen consumption and makes sure that the filter(s) without hotspots can still be used to treat emissions.

Connecting toolkit: the HC-BOX

The HC-BOX is combined with the INERTI-BOX to create a turnkey solution for smaller filters and the AIRCON HC and HC-XL model. It comprises a simple skid containing inlet/outlet/bypass valve, with the INERTI-BOX on top. This is connected to a rack with nitrogen bottles.


One customer in Belgium left a filter unventilated over the weekend after using it all week. When oxygen was added to the filter on the Monday morning, it effectively fanned the hotspot, causing it to smoulder.

The customer ordered a new filter and an INERTI-BOX.

INERTI-BOXES are also widespread in our pharma projects due to the hazardous chemicals used and the potential cost of any downtime.

Two HC-BOXES and one INERTI-BOX are in use at a petrochemical site at the Port of Antwerp, Belgium.

Emissions monitoring: the VOC-BOX

To determine when to order a filter exchange, customers need to measure the filter outlet to detect any breakthrough of emissions.

They can contract an external company to carry out monitoring at regular intervals, but run the risk of exceeding limits without realising between visits. Handheld devices are also available for certain molecules, but are not always reliable.

As companies seek to improve their environmental performance and meet increasingly strict regulations, accurate and timely emissions monitoring is becoming ever more important.

DESOTEC developed the VOC-BOX in response to customer requests for a continuous emissions monitoring device.

The VOC-BOX is fixed to the outlet of the filter on a permanent basis. Its technology is based on Flame Ionisation Detection (FID), which is widely recognised as one of the most reliable measurement methods.

Servicing, calibration and upgrading is carried out by an external company, ensuring the VOC-BOX is always accurate and up-to-date.

The biggest advantage of the VOC-BOX is its software platform, which enables customers to view real-time emissions from any device at any time.

The VOC-BOX in action

VOC-BOXES are best suited to larger companies with strict CSR commitments. At DESOTEC’s headquarters in Belgium, we have fitted them to our own filters, which treat emissions from the coatings and paints that we use.