Grounding of road tankers equipped with pump distribution systems – how to block the product transfer in the case of lack of proper grounding

Grupa WOLFF

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Grounding of road tankers equipped with pump distribution systems

Problem:

  • risk of ignition of explosive atmospheres by electrostatic discharge when unloading flour and sugar tankers equipped with pump distribution systems
  • unloading bays in the facility are not equipped with their own pumps, which prevents the use of the grounding system’s function of blocking product transfer in case of loss of tanker’s grounding
  • the compact construction of transport pipelines and close proximity to the wall make it difficult to install butterfly dampers

Solution:

  • equipping of the unloading bays with grounding control systems for road tankers (delivery and installation of systems)
  • modernization of the pipeline route angle to enable installation of butterfly dampers (disassembly of old elbows / arches of loading pipelines and installation of new ones, including flanges)
  • delivery and connection of the necessary automatics and electrical equipment enabling the development of opening and closing signals for butterfly dampers depending on the proper grounding of the road tanker

Check out the details of the installed equipment and services provided:

Static electricity hazard when unloading road tankers

A road tanker is the largest potentially insulated conductive component that enters the facility and, if not properly grounded, will pose a serious risk of ignition. With a capacity of 5000 pF, it can cause electrostatic discharge up to 2250 mJ.

The risk of electrostatic discharge occurs, for example, during unloading or loading of vehicles. Therefore, the bays for which combustible and explosive substances are supplied should be equipped with grounding control systems. Discharging the accumulated static electricity from the tanker reduces the risk of an electrostatic flash-over that otherwise could lead to ignition of the potentially explosive atmosphere. In addition to the tank grounding itself, systems can easily and safely verify that accumulated electrostatic charges are properly discharged to the ground. If this is not the case, the controllers block the process.

Securing the unloading bays of flour and sugar at the food manufacturer

One of the plants belonging to a food concern has two places for unloading road tanks to silos. The first one is a station for unloading sugar into one silo, the second is for unloading flour into 10 silos.

Since the bays are not equipped with unloading pumps, the vehicles that arrive at the plant have their own distribution systems with pumps by means of which the material is transported through pipelines to tanks.

For the grounding of road tankers, systems have been proposed which, in addition to vehicle grounding, are used for monitoring the proper discharge of electrostatic charges to the ground.

As a general rule, if the connection between the tank and the ground is lost by, for example, loosening the clamp, damage to the cables, etc., the system of emptying the vehicle will be blocked. In the described cases, however, it was not possible to use this function because the unloading bays were not fitted with their own pumps.

Tanker with pump distribution systems – how to block the product transfer in the case of lack of proper grounding

In order to ensure a high level of safety of the processes carried out and to enable the full functionality of the grounding system, it was decided to use butterfly dampers which were permanently installed on transport pipelines.

However, their installation was difficult due to the compactness of the pipelines (installation before and after the arch was not possible due to lack of space, while installation on the arch would result in abrasion of the gate and a high probability of system malfunction).

It was therefore not possible to mount the dampers without changing the pipeline route angle. The modernization was made in such a way that it did not affect the process of transporting the product in any way, but allowed for the installation of the gate valves and their connection to the grounding control system. Connection of the necessary automatics and electrical equipment enabled the development of opening and closing signals for butterfly dampers depending on the proper grounding of the road tanker.

This means that if the system verifies that the tanker is properly grounded and connected to a specific hopper, the damper will be opened and the product will be transported to the silo, while if the pipe is disconnected from the vehicle or there is no grounding, the damper will be closed and the unloading process will be stopped.

As a result of the work carried out, the Client has received a system that will be able to perform its functions fully, so that the unloading processes of the tanks will have a safe, monitored flow.

The general and specific requirements for the organization and implementation of static protection of facilities, installations and technology equipment, with particular regard to explosion hazard zones, are contained in the Polish Standard PN-E-05204:1994 established in October 1994.

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