Design and implementation of automated control systems in explosive areas: correct selection of components

Greetings, friends! Automation Spirit Alliance has extensive experience in creating automated control systems for process lines in explosive areas. These include oil production, oil refining, gas production, petrochemical, chemical, pharmaceutical, and even food enterprises. Today we would like to talk about the means and solutions we use to ensure the efficiency and complete safety of such systems.

Strict following the rules and restrictions

In Europe, the selection of equipment and work processes in explosive areas are regulated by ATEX directives, as well as the generally accepted IECEx certification system. The set of measures and design solutions to ensure safety depends on possible sources of risk. These can be objects whose temperature at various stages of the technological process is equal to or higher than the ignition temperature of surrounding substances. Or side emissions of energy (sparks), which upon contact with surrounding substances cause ignition.

We quite often face situations when the customer at the planning stage takes into account only one of the risk factors, while ignoring the rest. For example, to select equipment, only the class of the уxplosive area is indicated. ASA analyzes the technological process comprehensively, identifying all possible sources of danger, starting from the temperature to which the equipment is heated and the electrical parameters of the signals, ending with the composition of the air-gas mixture in the environment.

Technological schemes are created by our designers taking into account the polling of signals in dangerous areas, incoming and outgoing commands. To obtain intrinsically safe electrical circuits, we use converters and intrinsically safe barriers with the necessary parameters. After implementation and commissioning of the production line, the customer is issued a full list of certificates confirming the compliance of the selected equipment with current requirements and standards.

Source of danger - high temperature

Group II explosion-proof equipment, most popular in industrial automation, is used in work environments where flammable gas or vapor may be present during malfunctions or emergency situations. When choosing it for technological lines, Automation Spirit Alliance is guided by the classifier (T1-T6). For example, when working with gasoline or hydrogen sulfide, you can only use equipment of class T3, the maximum surface temperature of which does not exceed 200°C. This must be taken into account when designing the production line.

Source of danger - sparks

When selecting Group II (gas/steam) and Group III (dust) equipment for working environments where sparks may cause ignition, we take into account the categories of explosive mixtures present in these environments. Thus, if there is methane, ethyl ether or hydrogen sulfide in the environment, an equipment marked IIB should be used.

Classification of explosive areas

Before including equipment of a particular protection class into a project, we analyze the technology and the area in which it will be implemented. For environment containing gas or steam, the following classification is used:

• Zone 0 - an explosive atmosphere (air mixed with flammable gasses or vapors) is present at the facility constantly or regularly.
• Zone 1 - under standard operating conditions, an explosive atmosphere periodically appears at the site from a mixture of air and flammable materials.
• Zone 2 - under normal operating conditions, an explosive atmosphere does not arise at all or occurs for a very short period.

In the case where the source of danger is flammable dust, facilities are divided into zones 20, 21 and 22, where zone 20 is the most demanding in terms of explosion protection of equipment, and zone 22 is the least demanding.

ATEX Directive 2014/34/EU and EN 60079-0 standard

Creating a project or implementing a technological line, ASA engineers pay special attention to the selection of units and components of automated control systems that meet the operating conditions.

According to European regulations, equipment, protections and components used in explosive atmospheres must be marked in accordance with the ATEX directive 2014/34/EU, which defines the categories of such products, as well as EN 60079-0, which indicates the level of protection of a particular device or component.

The ATEX Directive takes into account:

• A group of devices, where group I is equipment and components for the mining industry. Group II - other industries, including chemical, petrochemical and others.
• Device categories from 1 to 3, where the first is suitable for zones 0 and 20, the second - for zones 1 and 21, the third - for zones 2 and 22.
• The operating environment, where G is gas and D is dust.

The marking of the most explosion-proof device that can be used in any industry except mining will look like this: Ex II 1 G.

The EN 60079-0 marking contains more information:

• Intrinsically safe class and protection level (ia), where a is suitable for zones 0 and 20.
• Group and subgroup of the environment (II C), where II is a gaseous environment, and C is a subgroup including hydrogen, acetylene and carbon disulfide.
• Temperature class T1-T6
• Equipment protection level (Ga), where G is gas and zones 0 and 20.

Thus, the marking of the most explosion-proof device according to EN 60079-0 will look like this: Ex ia IIC T6 Ga.

One of the latest projects in this area was the creation of an automated control system for a transfer pump with cooling for an oil refinery. After a detailed study of the technical specifications, the requirements were agreed upon with the customer and the parameters for the selection of equipment were established: zone 1, category IIB T3. Accordingly, it is determined that:

- the motor housing must comply with explosion protection class d (explosion-proof shell).

- distribution boxes must be explosion-proof

- temperature, pressure and vibration sensors are selected taking into account operation in an explosive environment.

- in the control cabinet (located outside the dangerous area), converters must be installed on the control signals to protect the interrogation of signals in the dangerous area.

To connect equipment in an explosive environment, the customer proposed using a 12-core intrinsically safe cable in a protective metal conduit made of galvanized steel. However, according to Directive 2014/34/EU, to ensure explosion protection for such operating parameters and device configurations, only armored cables of the appropriate cross-section are permitted. The choice was made in favor of the second option.

The entire range of measures to create an effective control system and ensure the explosion safety of the facility has been completed, the equipment has been put into operation by ASA specialists and is functioning successfully.

We offer only safe and effective solutions

Automation Spirit Alliance has many years of experience in the development and implementation of automated control systems, as well as the launch of turnkey process lines. We have modernized infrastructure enterprises from the chemical, petrochemical, oil refining, energy, metallurgical and other industries. And each time we focused on the maximum safety of these facilities. We know how to create optimal production conditions in compliance with all requirements and are ready to implement the most complex projects.

To discuss your task, please contact us in any convenient way.