Explosion protection for tanks

Danger of tanks explosion

Every year, 400-500 explosions occur at plant storage and processing facilities worldwide, including food processing plants. And about half of the explosions involve various containers: silos, bunkers, containers.

The danger is due to the characteristics of the technological process:

• The presence of a combustible dust/air mixture;
• An explosion source in the tank due to self-heating and self-ignition of product mounds;
• Release of flammable gases during fermentation of raw materials due to high humidity.

Prolonged storage of self-heating products in containers leads to self-ignition. In this case, combustible gaseous products of the thermo-oxidative reaction in dangerous concentrations such as hydrogen, methane and carbon monoxide enter the overhead and underfloor spaces as well as the overhead and underfloor spaces.

Also in the process of transporting loose raw materials fine organic dust is generated: grain dust, flour dust, sugar dust, coal dust, etc. It is flammable and in contact with air forms an explosive dust/air mixture. Visually, it may not be noticeable. On contact with an ignition source, however, the dust ignites with detonation.

A primary explosion initiates the flame propagation to the unburned part of the dust/air/dust mixture in an enclosed space and a series of secondary explosions follow. The entire accident process is rapid and, without the use of special explosion protection systems, virtually impossible to contain. Explosive combustion of the gas-dust-air mixture in an enclosed space raises the pressure to 700-900 kPa, which exceeds the values safe for the equipment.

Sources of ignition initiation

EN 1127-1-2014 classifies 13 active ignition sources which, in contact with a combustible dust/air mixture, may lead to an accident.

What hazards may be present in the tanks

• spontaneous combustion (burning, smouldering) of bulk products;
• heated surfaces due to lack of insulation;
• unloading of burning product from silos and hoppers leading to a fire in the underlying floor;
• mechanical and electrical sparks;
• static electricity;

Silo and silo regulations stipulate that accumulations of dust, prolonged storage of plant material and temperature and humidity must be avoided. Preventive measures reduce the risk of explosion, but do not eliminate it completely. If the operating rules are not observed, the risk of explosion multiply.

Safety standards for the owner of a hazardous industrial facility

Silos and hoppers are classified as hazardous objects due to the presence of hazards. The minimum requirements for their explosion protection are specified in Directive 99/92/EC.

When operating hazardous facilities, it is necessary to:

• Assess the risks taking into account the likelihood of explosive atmospheres;
• Classify and mark hazardous areas with combustible dusts;
• Install explosion protection devices for the equipment.

Technical solutions

The safety of the tank is ensured in three ways:

1. Observance of silos and hoppers operation rules, rules for storage of plant material.
2. The use of modern aspiration systems.
3. Installation of systems for containment, cutting off an explosion and (or) safe release of an explosion — explosion dischargers..

Explosion protection systems are selected on the basis of the operating conditions and the nature of the raw materials stored in the tank. We therefore first carry out a risk analysis to determine the hazardous area classification and the level of protection in accordance with IEC 60079-10-2-2011.

For this purpose, we take combustible dusts for laboratory tests under "controlled explosion conditions". As a result, we determine the explosion hazard parameters of the production facility:

• Low Explosion Level / LEL
• Maximum rate of explosion pressure rise / (dp/dt)max
• explosion class / Kst
• Minimum explosion temperature / MIT
• Minimum ignition temperature / GT
• Minimum explosion energy / MIE
• Oxygen concentration limit / LOC

Based on this data, we select specific explosion protection equipment.

In cooperation with RSBP, we offer standard technical solutions for tank protection: explosion suppression, overpressure relief and flameless explosion release. We adapt them individually to the customer's site.

The HRD system is an active protection device. It quickly detects spontaneous combustion of raw materials in a silo or bunker and extinguishes it at the incipient explosion stage. Explosive suppressants are used for this purpose. The HRD system reduces the pressure of an explosion to a safe level so that the container is not destroyed.

Special features:

• Sensors detect an increase in pressure in the equipment to be protected within 1 ms
• A signal via the control centre to the activators provides an almost instantaneous command to activate HRD cylinders with extinguishing agent
• The sensitivity of the system allows for suppressing explosions below 0.2 bar, i.e. at the nucleation stage
• The system is assembled in only two steps using prefabricated drawings - installation of the elements and adjustment of the electrical connections
• No modifications to the equipment design are required
• System maintenance consists of visual cleanliness checks and pressure checks on the cylinders only
• Has a long service interval of 6 months to 10 years

Used HRD cylinders are easy to replace. The inerted explosion suppression system, unlike standard explosion detectors, is safe for use where people are working. It also complies with the strict hygiene requirements for the food and pharmaceutical industries. For example, water can be used as an extinguishing agent.

The HRD system for tank protection is used as a stand-alone technical solution or in combination with VMP explosion dischargers, FLEX flame arresters and HRD barriers at pipe connection points.

Explosion overpressure relief

Devices are used to protect hoppers, silos, separators, containers located outside the building. The release of the explosion must take place in a safe area where the shockwave and flames will not damage the equipment, working people.

Special features:

• Reduces the pressure quickly to safe values;
• Low-cost design and operation;
• Applicable to equipment already in operation;
• The explosion relief zone is up to 30 m, so that the explosion can only be released via VMP panels in areas that are free of people;
• Explosion relief devices are installed outdoors;
• The static opening pressure can be regulated;
• Panels are available in various shapes and sizes;
• The system is effective even when the explosion hazard class of the site is high.

VMP panels are simple to install and easy to maintain during operation. After a failure, they are easy to replace. The panels are also resistant to mechanical damage and unfavourable weather conditions.

fireless explosion release

This method is used for containers located in enclosed spaces. FLEX flame arresters certified in accordance with TP TC 012/2011 and EN 16009 are used in flameproof protection.

They consist of an explosion panel and an outer casing with a scattering surface. The flame arresters prevent the spread of open flames and rapidly reduce the pressure and temperature of the explosion.

The shockwave and combustion products pass through a system of special grids. Due to the dissipation effect, the temperature of the explosion is reduced from 2600 °C to safe levels and open flames are prevented from spreading into the working area. At the same time the overpressure is reduced to values to which the elevator design is resistant. Importantly, the process is automatic - no operator is needed to operate the flame arrestor correctly.

Special features:

• Can be installed indoors;
• The smoke hazard zone is no more than 1.5 m, which allows you to organise areas that are safe for people to work in the vicinity of the elevator;
• Flame arresters are certified for explosive dusts with very low minimum ignition energies (MIE) and minimum ignition temperatures (MIT).

The explosion extinguishing system is easy to install and maintain in operation. It does not require expensive construction work or modifications to existing equipment. Most importantly, the system will reliably protect the elevator from the devastating effects of an explosion and localize the consequences of an accident.

Stages of work

• Step 1. Evaluate the explosion hazard of the process and equipment.
• Step 2. Discuss the technical specifications with the customer.
• Step 3.Selection of an explosion protection solution in accordance with the applicable industrial safety legislation, the customer's wishes and the manufacturer's recommendations.
• Step 4.Preparation of the project and its approval by the supervisory authorities.
• Step 5.We deliver protection systems anywhere in the country.
• Step 6. We assemble equipment or provide quality control of third party installation works.
• Step 7. We carry out commissioning of explosion protection systems.
• Step 8. We provide service and warranty support.

ATEX.CENTER takes care of the effective explosion protection in your plant.

Guarantees

ATEX.CENTER is an official distributor of the leading European distributor of explosion protection RSBP spol. s r.o. Our specialists periodically confirm their qualifications in his commission of expertise.

In cooperation with the RSBP, we have implemented more than 20 large-scale explosion protection projects. Thanks to intelligent solutions we were able to prevent more than 1 260 000 EUR of damage and save the lives of over 600 employees in 5 companies.

We give all our customers the opportunity to visit an RSBP test facility in the Czech Republic to see explosion protection in action.

The RSBP explosion protection symbol on your equipment is a guarantee of safety for your company