Air Liquide and Aurubis launch air separation unit project

The French company Air Liquide, which has been operating in the Bulgarian market for years, has launched a project to expand its air separation unit (ASU). The innovative facility will be located on the territory of the copper mine in Pirdop, currently operated by the German company Aurubis. A notification for an investment proposal has already been submitted to the Regional Inspectorate for Environmental Protection in Sofia.

The installation is due to come into operation in 2027.

The investment worth 100 million euros was announced by Air Liquide last year. In addition to the installation's expansion in Pirdop, the project envisages the renovation of four air separation units in Germany.

The Pirdop project will extract oxygen, nitrogen and argon from the surrounding atmospheric air. It is an important project for the German mining giant as it will not only increase the quantities of oxygen and nitrogen but will also allow Aurubis to produce argon for industrial and commercial markets across Europe.

The new installation will consume less electricity and save carbon dioxide emissions - a priority for Aurubis.

What's next?

After the completion of the project, the future configuration will be composed of the following units, which will remain in operation after March 2027: Unit 3 (existing, Sigma 145), Unit 4 (existing, Sigma 190) and Unit 5 – a new installation, subject to the notification.

The older air separation units, commissioned in 1986 (Unit 1 and Unit 2), will be maintained in deep reserve mode and will only be relaunched in emergency situations.

Ambient air is filtered and then compressed by air compressors. The compressed air is then fed into the adsorption unit for the extraction of moisture and carbon dioxide.

The installation will produce: 

• a stream of oxygen that is sent to the piping system of the client;
• a stream of nitrogen that is sent to the piping system of the client;
• liquid oxygen flow;
• liquid nitrogen flow;
• liquid argon flow.

How will the ASU work?

The ASU will operate according to the principles of air separation, through adsorption-desorption of compressed air. The process is based on an internal compression cycle, thus producing gaseous oxygen at the required pressure.

The air that is separated enters the compressor, previously dedusted through a filtering device. A multi-stage centrifugal compressor compresses the air, which passes through a cooler and undergoes adsorption (removal of water and carbon dioxide).

The adsorber consists of two layers, each filled with aluminium oxide and a molecular sieve. One of the two adsorber vessels is in operation, and the other is in regeneration to the cold part of the installation. An electric heater heats the regeneration gas.

The compressed air goes into a booster compressor, combined with a turbine, which accelerates the speed of the airflow. After passing through the heat exchanger, part of the air expands in the turbine to generate "cold energy", which is necessary to start the compensation of heat loss. After being cooled through a heat exchanger, the air has reached its dew point and is sent to a double distillation column.

Distillation columns produce the following products - pure nitrogen gas, gaseous oxygen, as well as liquid oxygen, nitrogen and argon.

The operation will have a water consumption of about 28 cubic meters per hour, or about 244 thousand cubic meters per year. The water will be supplied by Aurubis Bulgaria AD, which has a permit for water abstraction from the Dushantsi Reservoir. If necessary, Aurubis Bulgaria AD is ready to submit the necessary documents for registration of the French company as a water user under this permit.

There will be no water extraction from other water bodies and thus no water extraction facilities will be constructed.

There is a need to issue a building permit according to the Spatial Planning Act.

Translated by Tzvetozar Vincent Iolov