How is natural gas treated?



In 1969, the Ekofisk field, in the middle of the North Sea, the first oil and gas deposits were discovered. Since then, around 50 million m³ of natural gas have been transported daily through 5 pipelines. This natural gas is transported to mainland Europe and sold there to millions of consumers. A large part of the natural gas is transported through pipelines that run under the seabed to a gas processing plant in Emden. After this cleaning process in Emden, gas of the highest purity and quality flows into four European countries through the natural gas network.
The plant is controlled by the Phillips Petroleum Norsk A / S operated for the Phillips Petroleum Norway Group and can process up to 96 million m³ of gas per day. Apart from its use as a clean fuel for domestic and industrial firing, natural gas is also used as a basic chemical material. For example, in Delfzijl, on the Dutch side of the Ems estuary, more than two million m³ of gas are processed to produce methanol.

The Emden plant

The Emden plant is located at the end of the sub-seabed pipeline (91 cm diameter and 443 km length) that comes from the Ekofisk fields in the North Sea and is owned by Norpipe A / S. Laying the pipeline on the seabed from Ekofisk to the coast was a technical challenge for the planners and designers. The greatest problems were the distance to the coast, the course of the seabed and the weather. 35,000 steel pipes, which together weigh 209,000 tons, and an additional 275,000 tons of corrosion-resistant material and concrete jackets were used to build the natural gas pipeline to the Federal Republic of Germany.

The center of all natural gas and crude oil production is the Ekofisk complex. The natural gas, which consists of around 85% methane, is separated from crude oil and liquefied gas at sea. It starts its journey to Emden from the riser platform "R". Gas turbines drive four centrifugal compressors that transport the gas to Emden. Before the gas is introduced into the pipeline, it is treated in processing plants in the Ekofisk center, i.e. the natural gas liquids are removed and the gas is "dried" in order to rule out condensation and thus possible corrosion problems in the pipeline.

Two compressor stations regulate the temperature in the pipelines via the pressure: the temperature must not fall below 0 ° C in the sections of the route where it runs unprotected on the seabed because of the risk of dew point. To raise the temperature by 0.45 ° C, 1 bar pressure is required. The compressor stations, which are stationed at regular intervals along the pipeline, also serve to seal off sections of the pipeline in emergency situations.

Inside the plant, there is a high flare 74 m high, with the help of which excess gas, which arises in the event of operational changes or process disruptions, is burned. In addition to the high flare, there is also a ground flare. Both flares, which work smokeless by feeding in steam, can safely burn large volumes of gas in emergencies.

Preparation of the gas

The gas from the Ekofisk area reaches the Emden plant after 443 km.
The Emden plant has the task of carrying out this cleaning continuously.

At the beginning, two gas scrubbers remove liquid hydrocarbons that were transported with the gas or that were precipitated during the long pipeline transport. Small amounts of sulfur compounds, mainly derived from hydrogen sulfide, are removed from the gas by an adsorption process. This causes the impurities to collect on the surface of very small molecular sieves, which act like a filter. Since large quantities of gas are cleaned in Emden, billions of molecular sieves are required, which are housed in nine parallel cleaning lines.

Each of the nine "cleaning lines" consists of four cleaning tanks and a gas heater. The cleaning containers have a characteristic pink color, which is not used for embellishment. The outer color layer consists of a heat-sensitive special lacquer that turns deep blue when overheated. Such a discoloration supplements the warning signals in the control room and supports the operators in troubleshooting.

When the purification vessels are saturated with sulfur compounds, a small portion of the treated gas is heated to purify or "regenerate" the molecular sieves. The polluted regeneration gas that leaves the adsorption container is cleaned in a separate area of ​​the system.

The regeneration gas flows through amine and glycol systems to precipitate sulfur compounds that come from the cleaning tanks. The gas is then dried in order to comply with the sales conditions. The sulfur compounds are removed by controlled combustion in a special burner.

After cleaning, the regeneration gas has lost a significant amount of pressure. It is therefore compressed before it is returned to the retail outlet.

The cleaned gas flows via measuring stations through three pipelines into the buyer's natural gas network.