Breathing valves with end flame arresters – how to reduce investment costs

WOLFF GROUP

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Krzysztof Tetla
Breathing valves with end flame arresters - how to reduce investment costs

Problem:

  • need to protect three tanks for storing petroleum-derivative substances against pressure drop/increase during filling and emptying
  • risk of fire penetration into the tank due to the presence of flammable vapours of the stored liquids
  • need to ensure low flow resistance in the protection system
  • need to guarantee the best price

Solution:

  • supply of positive and negative pressure breathing valves with integrated flame arresters
  • use of a new design of flame arresters to guarantee lower flow resistance, which in turn reduced the investment cost (the possibility of using smaller equipment in comparison to traditional flame arresters)

Check the details of the implemented equipment and services:

We have just completed a project supplying four breathing valves integrated with flame arresters. The systems will be used to protect three petroleum-derivative substances storage tanks (one of the valves will serve as backup).

Customer requirements

In the request for quotation, the customer provided a number of details, including the volume of each tank (100, 100 and 63 m3) and the size of the ports on which the breathing valve / flame arrester assemblies were to be mounted. For each tank, the diameter was 250 mm.

Typical supplier approach

With this type of information, many companies, wanting to shorten the time necessary to prepare a quotation, do not carry out calculations allowing to choose the optimal solution. In return, these quotes are practically based solely on the port diameter. This approach can have a number of consequences, including, for example, bursting or drawing in of the tank walls as a result of excessive positive or negative pressure. There is also a possibility of the opposite situation, i.e. selection of an oversized system, which results in an unjustified increase in the investment cost.

How we reduced investment costs despite offering a higher class solution

Being aware of the potential negative repercussions of the improper selection of protection systems, our specialists made the necessary calculations. The analysis showed that the most optimal solution would be the use of breathing valves integrated with a new generation of flame arresters. That way, it was possible to reduce the connection diameter of the system – from DN250 to DN150. This allowed us not only to reduce its size and weight but, above all, its price.

What is the difference between a Tornado arrester and a classic solution

The most important element of each flame arrester is the so-called flame filter unit. It is this element that constitutes an impassable barrier to the flames, preventing them from passing to the other side of the arrester. In the past, cartridges filled with steel or basalt balls, sand or compressed wire were used as the filter. Currently, the most popular solution is made of a coiled steel band with a special shape. This solution, unlike the previously described, has slots of specific sizes, which allows selecting their size to match a given flammable substance.

In the Tornado solution, the flame filter unit is made up of flat metal rings, with gaps created by using appropriate spacers. Thanks to its simplicity, this solution is very universal, and its most important advantages include:

  • reduction of flow resistance or pressure drops for all explosion groups each pair of rings creates one continuous gap with dimensions corresponding to the diameter of the rings and the heat receiving surface corresponds to the difference between the outer and inner diameters of the rings, providing – together with the distance between one ring and the other – the MESG required for specific explosiveness groups;
  • possibility of precise removal of impurities without damaging the ring unit gap; After peaceful disassembly in the workshop, we have the possibility to reach each of the rings forming our TORNADO flame filter unit;
  • much easier control of the dirt level inside the unit, without the need for dismantling at the installation site and using a light sources adapted to the potentially explosive atmosphere, directed along the gap – which makes it very easy to assess the presence of dirt, thus saving time and financial resources related to inspections of the protection device;
  • better resistance to harsh conditions, confirmed by many years of operation in conditions of high pollution with various substances (dusts, fumes);
  • elimination of the possibility of confusion when reassembling a multi-disc flame filter unit in accordance with the manufacturer’s guidelines in case of several discs with different gap gradients (right- or left-leaning, straight), the order in which the discs are put back together after maintenance is crucial – it is easy to make a mistake due to a lack of focus, which may result in the risk of the device not working properly when reassembled in the wrong way;
  • simplicity of assembly/disassembly, lower manufacturing costs, lower weight which are further advantages of the TORNADO ring units.

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