Problem:
- existence of explosion hazard zones at the site producing alkyd resins
- risk of electrostatic discharges during the process of unloading/loading road tankers and during the production process on the technological installation
- no ability to monitor the current earthing condition (only simple ground clamps and wires are used)
- the need to meet the insurer’s requirements for effective grounding of installations and process equipment by certifying the solution
Solution:
- ensuring safe unloading and loading of road tankers by means of a system allowing to monitor the state of the grounding during the process
- application of a grounding monitoring system that allows up to eight elements of the process installation to be monitored simultaneously
- protection of pouring / mixing processes against electrostatic discharges through the use of grounding monitoring systems for metal drums and tanks
Check the details of the implemented devices and services:
- grounding of road tankers
- grounding of the process installation
- grounding of metal drums and tanks – mains supply
- grounding of metal drums and tanks – battery power supply
In the alkyd resin production plant where explosion hazard zones are defined, the conducted technological processes are subject to the risk of electrostatic discharges. These, in turn, are a potential ignition source that could result in serious consequences from an explosion or fire.
The manufacturer, wishing to increase the level of safety in its plant and at the same time meet the insurer’s requirements for effective grounding of installations and process equipment, asked our company to select the appropriate technical solutions. The task included the selection and delivery of several types of earthing systems for various purposes for a total of 22 workstations.
Unloading and Loading of Road Tankers and Electrostatic Discharges
During the processes related to unloading or loading of road tankers, which are carried out on a daily basis at the plant, there was a high risk of ignition due to electrostatic discharge. The main risk in this case was posed by road tankers (this type of vehicle with a capacity of 5000 pF can cause electrostatic discharge even up to 2250 mJ).
Discharging electrostatic electricity from vehicles would certainly be possible through the use of ordinary ground clamps used so far, but they did not provide the possibility to obtain information on the current state of grounding and tolerated mistakes made by drivers (e.g. disregarding the requirement to connect the tanker to a clamp or placing a clamp on a fender or other vehicle components that would not ensure proper discharge of static electricity). For these reasons, it is becoming increasingly common practice to use dedicated systems that, in addition to grounding itself, also monitor its status in real time. As a result, 4 road tanker grounding monitoring systems (RTR) have been supplied which minimize the risk of vehicles being mis-grounded during unloading and loading to practically zero.
The operation of the system is based on the calculation of the electrical capacity, which allows the identification of the road tanker. This ensures that the system is connected to the road tanker and not to any other structure or metal object, and that the vehicle component to which the clamp is connected will allow for the proper discharge of static electricity from the tanker. This will be confirmed by the lighting of the green LED on the monitoring unit.
Undoubtedly, the advantage of the RTR system is that it monitors the tanker’s connection to the ground in real time. If the connection is lost due to e.g. loosening of the clamp or damage to the cable, which can easily happen at the plant, the filling/unloading of the tanker will be blocked.
Simultaneous Grounding of Several Process Installation Components with a Single System
In the case of process installations, static electricity generated on the surface of the equipment can lead to serious process disturbances, but above all they pose a risk of explosion of the mixture of flammable liquid vapours with air. The customer’s plant has an installation where eight components (stations) required grounding. As in the case of road tankers, ground clamps alone did not provide effective protection. In such situations, separate grounding monitoring systems of individual components of the installation are usually used. From an economic point of view, however, this was not a good solution.
A way out of the situation was the use of the MULTIPOINT II system which was designed to ground and monitor up to eight individual components of the process plant at the same time. The solution allowed the customer to ensure continuous discharge of static electricity from all stations at the same time. It also helped to reduce cabling costs (the use of 8 separate systems would require separate electrical wires, cable trays) and decrease energy consumption.
The system itself consists of a monitoring unit with eight pairs of red and green LED indicators. It is connected to the distribution box and then to the intermediate boxes from which the wires with ground clamps come out. Each of these boxes has a special bolt for hanging up the clamp.
The monitoring unit continuously checks the correctness of grounding of individual components of the installation. Importantly, the correctness is confirmed by the system only if the loop resistance on each channel is less than 10 Ω.
It is worth noting that MULTIPOINT II has Ex certificates for the whole device (separate monitoring unit, power supply unit and ground clamp).
MULTIPOINT II – example diagram
In the example above, MULTIPOINT II is configured to ground four mixing stations (1-4) and two filling stations (5 and 6). If any of the mixers is not properly grounded, the system will block its operation and the LED will turn red. This will prevent the build-up of static electricity on the equipment. The same applies to drums – if there is no grounding, the pump feeding the filling station will be switched off immediately.
Effective Grounding of Metal Drums and Tanks
There was also a risk of electrostatic discharge in the area where metal drums and tanks with flammable liquids are stored. In such cases, static electricity can be generated during filling and emptying drums/tanks (pouring processes), mixing liquids or cleaning containers. Electrified personnel in the danger zone are also a source of danger.
In this case, a total of 10 Bond-Rite systems have been applied. Some of them are mains-powered and will be used to monitor the grounding of containers from which the product is regularly taken, others are battery-powered. In the Bond-Rite systems used, the warning diode is located on the housing of the monitoring unit, so that the operator can easily verify the correctness of the container’s grounding. Importantly, the stainless steel ground clamps that all the supplied systems are equipped with have sharp tungsten carbide teeth that ensure penetration through rust, paint, glue, etc.
It should be remembered that the solutions for the grounding of tanks / drums should always be adapted to the conditions prevailing in the plant. For example, a portable set of self-testing clamps is sometimes applied, but this solution can be used for up to 6 hours a day. Moreover, in this case, the monitoring system diode is mounted on the clamp, which will make it difficult to read the current grounding status if the diode becomes obscured by dirt.
High Quality as a Guarantee of Safety
Replacing simple grounding terminals with high quality certified grounding monitoring systems for a total of 22 different production sites has significantly contributed to increasing the level of safety in the plant and at the same time allowed to meet the requirements set by the insurer.
Obligation to Provide Protection Against Static Electricity
It is worth remembering that in the production of various types of raw materials, substances are used whose minimum ignition energy is really very low, and thus their ignition capacity is higher (e.g. methanol 0.14 mJ, ethyl acetate 0.46 mJ, epoxy resin 9 mJ). Therefore, it is necessary to ensure that technical and technological installations and equipment (pipes, containers) are equipped with appropriate protective measures in accordance with the Polish Standards for protection against static electricity.
The employer is obliged to undertake such actions by relevant regulations (Regulation of the Minister of Internal Affairs and Administration of 7 June 2010 on fire protection of buildings, other construction objects and areas (Journal of Laws of 2010 No. 109, item 719) chapter 7 par. 35 (8) and the Regulation of the Minister of Economy of 8 July 2010 on minimum requirements for health and safety at work related to the possibility of explosive atmosphere at workplace (Journal of Laws of 2010 No. 138, item 931).
