In 2000, the Norwegian Pollution Control Authority (SFT) issued emission permits for NMVOC (Non Methane Volatile Organic Compounds) emissions from offshore shuttle tanker loading operations to the operators of 11 oil fields in the Norwegian sector. The emission permits require that by 2006, 95 percent of all offshore loading of tankers must be performed using emission-reduction technology.
The emission permits issued by SFT have in-creased the amount of attention being paid to VOC emissions from offshore shuttle tanker loading. Work is currently being done on guidelines for the quantification of emissions, the development of reduction techno-logy and measurements onboard shuttle tankers to verify emissions. MARINTEK is involved in field measurements and simu-lations for the implementation of the new emission permits. With more than 15 years of experience in this field, MARINTEK and the SINTEF Group have been involved in:
- VOC emission measurements
- Without and with emission-reduction technology
- Simulations of VOC emissions
- Simulations and assessments of the effects of alternative new measures and system configurations for VOC emission reduction
- Establishing operational parameters for VOC recovery plants.
Example of simulation results with VOCSim - gas composition of gas out of tank during loading.
VOC emissions during loading and on the transport voyage can be simulated with the computer program VOCSim, which has been developed by SINTEF. The program provides, as functions of time:
- flow rate of emitted gas
- temperature of emitted gas
- composition of emitted gas. Typical gas components are: C1, C2, C3, iC4, nC4, iC5, nC5, C6, C7, C8, C9, C10+, N2, CO2 and O2.
- Accumulated emissions of VOC, methane and inert gas.
MARINTEK has performed simulations that will assist oil companies and vessel operators in the design of reduction measures and the assessment of the present situation with respect to the quantities and composition of VOC emissions. Examples of typical simulations are:
- Mean emissions on a particular field
- Emissions in the future due to changes in oil composition
- The effects of changing the temperature of the loaded crude
- The effects of changing the loading rate for each tank, e.g. by loading fewer tanks simultaneously
- The effects of sequential transfers of tank atmospheres during discharge and loading
- The effect of gas return to an FPSO/ FSO
This is the challenge
During the storage, loading and transportation of crude oil, Volatile Organic Compounds (VOC) is emitted to the atmosphere. The emissions vary between different oil fields because of type of loading operation involved, the composition and temperature of the crude, loading rate, weather and ship motions and ship design. It is clear that emissions involve serious financial losses as well as having negative effects on the environment.
VOC consist of methane, which is a greenhouse gas, and NMVOC. NMVOC (Non Methane Organic Compounds) is a common denominator for volatile organic compounds which, in combination with NOx, generate ground-near ozone. Ozone is a toxic gas that can damage vegetation, materials and human health.
Emissions of VOC from offshore loading represent approximately 45-50 percent of the total Norwegian VOC emissions. Norway is committed by international agreements to reducing VOC emissions by 30 percent below the 1989 level by 1999. Norway has not managed to comply with these obligations, and in fact, NMVOC emissions have risen by approximately 25 percent during this period. Norway’s obligation to reduce NMVOC emissions according to the Gothenburg Protocol of December 1999, follows from a previous commitment in the Geneva Protocol of 1991, concerning the Control of Emissions of Volatile Organic Compounds or their Transboundary Fluxes.
Installation for direct measent of VOC emissions on a shuttle tanker.
Three alternative methods has so far been developed and tested to reduce NMVOC emissions during loading operations:
- Absorption of NMVOC into the crude during loading
- Liquefication and storage of NMVOC and use as fuel
- Sequential transfers of tank atmospheres during loading and discharge
Full-scale prototype absorption and liquefication plant concepts have been installed onboard M/T "Anna Knutsen" and M/T "Navion Viking". Both plants are expected to have NMVOC recovery rates of at least 70 percent
(Article in MARINTEK Review No 1 - 2001)