Explosion protection of a spray dryer

Donat Czapski

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Under an order placed by IEP Technologies GmbH, the WOLFF GROUP installed and commissioned an explosion protection system for a powdered milk production unit. The end client was an international corporation and globally one of the largest cheese producers and distributors.

The explosion protection system was based on the principle of explosion suppression, and it featured relief panels and explosion isolation systems. Owing to such a combination, a high safety level was attained while costs could be minimised at the same time.

The explosion protection system installed covered the following technological units of the process line:

  • spray dryer (secured by a relief panel along with a duct to release the explosion effects outside the hall),
  • fluidised bed (secured by an explosion suppression system),
  • two cyclones (secured by an explosion suppression system),
  • air filter (secured by a relief panel along with a duct to release the explosion effects outside the hall).

What was also important was that ducts connecting individual devices were furnished with explosion isolation systems featuring HRD cylinders.

Under the contract, the WOLFF GROUP conducted the following works:

      • mechanical and electrical installation of system components,
      • commissioning of the explosion isolation and suppression system based on HRD cylinders,
      • programming of four FAB signal transducers,
      • tests of the explosion protection system control centre as well as tests of alarm and failure message transfer,
      • personnel training in the scope of the explosion protection system operating principles and other safety principles with reference to the system components installed as well as operation and inspection of the explosion protection system and procedures in cases of system defects or failures.

Explosion protection of spray dryers

The very heart of a powdered milk production unit is a spray dryer. Its function is to dewater liquid products in order to obtain powder. This goal is attained by spraying the fluid inside the dryer chamber while simultaneously blowing hot drying agent in (air or inert gas at temperatures of 130÷250°C, depending on the product treated). The fluid is sprayed in the upper section of the dryer, whereas hot air (or other gas) is fed from the bottom. Moisture is rapidly removed in a process of counter-current drying, and thus granulate is received. The powder gravitationally falls to the dryer bottom from where it is collected and transported to subsequent process stages. Spray dryers are commonly used in the food processing industry, including in powdered milk production facilities.

In the unit in question, air from the drying process is transported to two cyclones and then to a filter where it is purified to remove fine product particles. The product itself, on the other hand, once it has been collected form the spray dryer bottom section, is delivered to the fluidised bed where it is cooled down.

Due to the operating conditions of the entire unit (ongoing presence of explosive dust atmosphere, increased temperature in the dryer), one must take serious explosion hazard into account. In accordance with both Polish and European legal regulations, in such cases, it is necessary to deploy means of prevention (reducing the explosion risk) as well as explosion protection minimising negative effects of potential incidents to a safe level. As regards the latter (comprising the subject of the task performed by the WOLFF GROUP), there are three basic techniques of protection available:

    1. explosion relief, which, once an explosion occurs, allows for the overpressure which may cause rupture of the given piece of equipment to be released into the environment,
    2. explosion suppression, which ensures that the explosion is extinguished at a very early stage of development by injecting special powder into the given device, thus preventing the explosion from escalating,
    3. explosion isolation, which prevents the explosion effects (pressure and flame) from spreading to adjacent pieces of equipment.

SCOPE OF WORKS: commissioning and securing of the explosion protection system.

LOCATION: Poland, Warmińsko-Mazurskie Province.

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