Vemmelund_edit.qxp 28/10/08 2:41 pm Page 146
Psychrometric Principles
Figure 1: Rotary Honeycomb Unit
To achieve efficient drying, the following conditions are required:
Dry air
• high velocity of the air, to allow rapid evaporation;
Process air
• low dewpoint at inlet;
• high ground temperature; and
• a large surface area for the water film, which is achieved by using
foam pigs to spread the water in the pipelines.
Air heater
Dry air provides effective corrosion protection in the pipeline, as a
relative humidity of below 50% halts corrosion; however, this does not
Wet air Reactivation air
apply to polluted air. This drying system has many advantages
compared with the conventional compressor systems.
The rotary wheel is the heart of the drying unit. The dehumidifier is designed around the drying wheel,
For example, let us take a customer who needs to dry a pipeline to a
which is divided into a segment where moisture is absorbed from the process air, and a reactivation segment
where heated reactivation air absorbs moisture from the rotor wheel. The rotor wheel revolves slowly, at dewpoint of -25ºC. The air capacity for the job is 6,000m
3
/h.
about 10 revolutions per hour. Dehumidification and reactivation are continuous. The dehumidifier operates
unaffected even at temperatures below 0°C.
With the Pipeline Services & Engineering (PSE) dry-air system:
Figure 2: Dry-air Method
• multidwelling unit (MDU) 6,000 international patent pending;
• safer (maximum 1 bar);
PSE Int.
• small footprint;
• low fuel costs; and
Dry air inlet Absorption of humid Wet air inlet
• 100% oil-free air.
air in pipeline
(special pipelines with a large diameter). Upon entering the pipeline, In contrast, a conventional compressor system requires:
the air has a dewpoint of approximately -40°C. The dry air absorbs
the water in the pipeline due to the difference in partial pressure • five to six 1,500m
3
/h compressors;
between the air and the vapour. The temperature of the air in the • two 3,000m
3
/h desiccant air containers; and
pipeline determines the amount of water that can be absorbed. • after-coolers and manifolds. ■
Developing the First CO
2
Pipeline Standard
Together with major industry partners, Det Norske Veritas (DNV) is now developing a new standard for the transportation of CO
2
in pipelines.
Specific issues related to CO
2
in the dense, high-pressure phase are not covered in existing pipeline standards or regulations. “As carbon
capture and storage (CCS) projects could become an important mitigation option related to climate change, this broad co-operation is an
important step forward,” says project manager Freydis Eldevik at DNV. As for CO
2
pipeline transmission, today stakeholders demand a
robust, traceable and transparent approach that gives credibility to the proper management of risks and uncertainties. Unfortunately, the
current pipeline standards do not take into account considerations related to the pipeline transmission of CO
2
from large-scale capture plants
to suitable storage sites. This serves as a barrier to the effective large-scale deployment of CCS.
Broad Joint Industry Project
Therefore, DNV has initiated a specific industrial collaboration to develop a standard reference guideline for the onshore and submarine
pipeline transmission of dense, high-pressure CO
2
. Freydis Eldevik informs us that the project’s partners are StatoilHydro, BP, Shell, Petrobras,
Vattenfall, Dong Energy, ArcelorMittal, Gassnova, Gassco and ILF. The technical reference group consists of government representatives from
the UK, The Netherlands and Norway. The European Commission is also supporting this DNV initiative. “The joint industry project is an
important milestone for CCS and is absolutely timely, since the industry really needs this recommended practice. It will be an important
contribution to the development of large-scale CCS projects,” emphasises Eldevik. The novel issues related to the onshore and submarine
pipeline transmission of dense, high-pressure CO
2
will be covered. The point of departure will be existing pipeline standards for the
transmission of hydrocarbons such as International Standard for Organization (ISO) 13623 and DNV OS-F101.
Minimising Risk Throughout the Life-cycle
The CO
2
transportation guideline is intended to help designers and operators limit and manage uncertainties and risks related to the pipeline
transmission of CO
2
by incorporating knowledge about offshore and onshore operations. It will state rules for managing risks and
uncertainties concerning the design, testing, inspection, operation, maintenance and de-commissioning phases of a pipeline. It will also
incorporate the lessons learned from existing and previous projects. Freydis Eldevik states: “Due to the features lacking in the current industry
standards, the scope of work of this project is related to issues such as safety, fast propagating ductile fractures, fatigue crack growth,
pipeline operation conditions, flow assurance, corrosion and material compatibility.” ■
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EXPLORATION & PRODUCTION – OIL & GAS REVIEW 2008 – VOLUME 6 ISSUE II
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