Problem
The customer's aspiration system filter did not comply with ATEX standards. It was not protected against the spreading of air-dust mixtures to adjacent units.
Combustible dust is invariably present in food processing plants where there are loose products. Combined with air it forms an explosive mixture, which is a frequent cause of accidents in grain elevators, bakeries and bakeries.
Combustible dusts are always present in the "dirty area" of the suction filters, so the risk of explosion cannot be completely ruled out. EN 1127-1 stipulates that explosion protection devices suitable for the conditions of use must be installed in such areas.
Combustible dusts are always present in the "dirty area" of the suction filters, so the risk of explosion cannot be completely ruled out. EN 1127-1 stipulates that explosion protection devices suitable for the conditions of use must be installed in such areas.
Task
The choice of equipment was restricted by the complex duct geometry. The customer wanted to avoid alterations to the duct design and still meet the requirements for safe installation distances and angles of inclination.
Solution
In this project, we rejected the use of passive explosion protection by using explosion containment devices such as B-FLAP check valves. They are economical, easy to maintain, but it was not possible to install them in existing ducts without changing the design of the pipes. Otherwise, the manufacturer's requirements for the installation distance and the angle of the damper were not met.
We have offered the option of active containment devices - HRD barriers. When installing them, there is no need to modify the ducting. It is sufficient to maintain a minimum installation distance from the equipment to be protected.
We carried out the following work:
- Determination of the explosion hazard characteristics of the organic dust present on site;
- Analysis of the customer's existing duct configuration;
- Selection of the required explosion protection equipment and its delivery from the manufacturer;
- Commissioning of the explosion protection system.
The customer used an external contractor for the installation. During commissioning, our technicians discovered that they had made some serious mistakes. Firstly, the HRD nozzles of the cylinders had not been installed correctly. Secondly, poor quality cable had been used for the activation and detection lines.
For reference. An HRD barrier consists of detection detectors, a control controller and extinguishing agent cylinders. At the nucleation stage of an explosion, the detectors respond to an increase in pressure and temperature. They send a signal to the controller, which issues a command to activate the suppressant bottles. This localises the explosion and prevents it from penetrating adjacent pieces of equipment.
Incorrect installation of the nozzles results in incorrect atomisation of the extinguishing agent. It does not cover the entire area of a possible accident and the system does not actually fulfil its basic function, i.e. containment of an explosion. The use of only good quality shielded cable during installation is necessary to protect the devices from false alarms.
Our specialists promptly rectified the installation faults and put the system into operation. In addition, we trained the customer's technicians in operating the explosion protection system and the CONEX controller.
The result
We completed this project within the time frame specified in the contract. However, it once again convinced us that all phases of the explosion protection work must be carried out by qualified, proven subcontractors.