Explosion protection for pneumatic conveying systems

Explosion hazards in pneumatic conveying systems

Special units are often used to transport loose and granular materials, in which raw materials or waste products are moved through pipelines under the influence of air flow. These are pneumatic conveying systems. They are found in the storage and processing of raw materials, in the wood and metal industry, in the pharmaceutical industry and in waste recycling.

Pneumatic conveying systems that transport bulk solids are hazardous. This is due to the presence of an explosive medium, a dust/air mixture that ignites at the source of initiation and leads to an explosion involving an unburned mixture.

A primary explosion in a pneumatic conveying system usually results in a series of secondary destructive explosions. In branched pipelines and storage tanks, there is an almost ideal environment for an accident: a confined space, airflow for the rapid spread of combustion and enough explosive dust/air mixtures.

The problem is not even that pneumatic conveying systems burn and explode. An accident in them quickly spreads to adjacent pieces of process equipment, leading to their destruction as well as to possible loss of life.

Sources of explosion initiation

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

In pneumatic conveying systems, ignition may be caused by:

• mechanical sparks from friction of particles of the transported material, including metal objects;
• heating of certain sections of the pipeline;
• hot particles in the transported material;
• self-heating in dust deposits;
• discharge of static electricity;
• sparks when the electric motor is switched on, etc.

The list of hazards in pneumatic conveying systems is long. The list of hazards in pneumatic conveying systems is long, and explosion risks cannot be completely ruled out - the risk is linked to the very process of moving bulk solids within the confined space of the material pipelines.

Safety standards for the owner of a hazardous industrial facility

Pneumatic conveying systems with an explosive dust/air environment are classified as Hazardous Industrial Facilities (HIFs). According to European Directive 99/92/EC, their operation must:

• Assess the risks taking into account the likelihood of explosive atmospheres;
• Classify and mark hazardous areas;
• Installation of explosion protection devices on the equipment.

The general requirements of Directive 99/92/EC are specified in national legislation.

The specific requirements for the classification and protection of hazardous areas and the technical equipment used in them are laid down in the ATEX standards. These are EN 1127-1, IEC 60079-10-2-2011 with general requirements and the special EN 15089, EN 16447, EN 14373, EN 16009.

Technical solutions

Explosion protection systems are selected on the basis of the operating conditions and the nature of the material to be conveyed. We therefore first determine the Ex zone class and the required protection level according to 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.

For pneumatic conveying systems, the best solution is to contain and isolate the explosion to prevent it spreading to adjacent pipeline sections and neighbouring equipment.

HRD barrier

This technical device detects a primary explosion at the nucleation stage and quickly localises it by applying an explosive suppressant. As a result, it prevents the accident from spreading to neighbouring areas and destroying them.

The device components:

• DetEx pressure and LumEx temperature sensors;
• Controller CONEX;
• HRD cylinders with explosive suppressant.

Highly sensitive sensors react to an increase in pressure and/or temperature in the equipment to be protected within 1 ms. They send a signal to the CONEX controller. This in turn triggers the high-speed actuation of the extinguishing agent cylinders. A special feature of the HRD barrier are the compound geometry spray nozzles. They spray the extinguishing agent in a fan in order to cover the surface to be protected as much as possible and to prevent the flames from spreading to adjacent areas. The entire blast containment process takes no more than 60 ms.

Advantages:

• The HRD barrier is used on indoor and outdoor pipework;
• It is suitable for existing equipment without costly retrofitting;
• A signal via the control centre to the activators provides an almost instantaneous command to activate HRD cylinders containing extinguishing agents;
• The sensitivity of the system allows for suppressing explosions below 0.2 bar, i.e. at the nucleation stage;
• HRD barriers can be easily installed according to a detailed manual which we will pass on to the customer;
• Cylinders are easy to replace after activation;
• The unit is easy to operate;
• The HRD barrier is suitable for use in foodstuffs;
• Suitable for use in the food and pharmaceutical industries.

The HRD barrier is installed as a stand-alone explosion containment device or in combination with explosion detection panels, HRD systems and FLEX flame arresters.

GATEX gate valve

The device is used to shut off a pipeline where an HRD barrier cannot be installed or its use is not economically justified. GATEX is a high-speed pneumatically actuated flap that activates when a primary explosion is detected.

The device components:

• DetEx pressure and LumEx temperature sensors;
• Control controller CONEX;
• Pneumatically actuated gate valve.

Pressure sensors detect an explosion at the nucleation stage and send a signal to the control controller. The controller then triggers a pneumatic actuator, which closes the valve, cutting off the emergency section of the pipeline from neighbouring equipment. The entire process takes a few milliseconds, so the GATEX gate valve can be installed in the immediate vicinity of hazardous areas.

Advantages:

• cuts off the emergency section quickly;
• can be installed in a limited space and does not require a large protection zone;
• can be installed in the open air under unfavourable weather conditions;
• installation in pipelines with a pipe diameter of 50 mm and a maximum pressure of 21 bar;
• actuates even when the power supply is disconnected by means of Fail-safe;
• The GATEX gate valve is easy to operate.

The technical device is used as a standalone technical solution or in combination with the HRD system, VMP explosion detection panels and FLEX flame arresters.

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.