Bosma.qxp 1/7/09 4:12 pm Page 82
Global Environmental Challenges to Liquefied Natural Gas Projects
Figure 4: Generic Abatement Curve
offers a fuel saving. Since 2003, Shell-advised LNG sites in Oman,
Malaysia, Brunei and Australia have carried out trials with alternative
Positive
solvents, mostly successfully.
CO
III
2
price screening value
Shell has introduced advanced process control (APC) to a number of
its LNG plants, including Nigeria trains 1–3 and Oman.
8,9
APC can
optimise plant performance, for example by optimising the mixed
II
refrigerant composition and flow rates such that compressor shaft
Net cost (US$/ton)
Accumulated tonnes of CO
2
abated
power is minimised. APC also offers constraint control: it allows the
I
plant to operate closer to its optimum set-points while avoiding trips.
I Cost-effective energy efficiency (EE) improvements
II EE and carbon capture and storage (CCS) that fall within
expected carbon trading costs
Negative III EE and CCS that fall outside expected carbon trading costs
Carbon Capture and Storage
Carbon capture and storage (CCS) is the process of separating out CO
2
Table 2: CO
from vented gases and transporting it to a permanent storage location,
2
Emissions Across the Value Chain
7
typically an underground aquifer or abandoned oil/gas well.
10
CCS
Typical Emission Typical Range
offers a solution for reducing greenhouse gas emissions, but at present
Operation (kg CO
2
/ton LNG) Parameters (kg CO
2
/ton LNG)
Gas production 40 Gas well pressure 20–100
the costs involved do not make it economically viable. Economic
LNG plant 30 Ambient temperature, 200–450 incentives are needed, in addition to carbon trading schemes, to fund
feed gas composition,
large-scale demonstration projects.
liquefaction process,
cooling medium,
turbine efficiency The learning and operating experience gained from these projects
Shipping 150 Ship size, 90–450
should lead to technology improvements and reductions in costs.
travel distance,
propulsion type
Statoil’s LNG facility in Snohvit, Norway is designed to capture
Re-gasification 15 or 45 Open rack vaporiser 1–50 700,000kg of CO
2
annually from a 4.1MTPA-capacity plant and store
or submerged
it 2,600m beneath the seabed in an aquifer.
11
It started operations in
combustion vaporiser
2007. The CO
2
captured in these schemes is routed to an underground
location for permanent storage. Research is under way to also find
LNG plants traditionally used steam boilers and fired heaters to raise feasible applications for the captured gas in the spheres of agriculture
process heat and did not include any waste heat recovery. Heat- and biofuels. If CO
2
gains value as a by-product from the LNG plant,
recovery steam generators (HRSGs) installed in gas turbine exhaust this would have a positive impact on project economics.
stacks can be used to raise high-pressure steam for process heating.
Heat recovery is possible at the gas turbine drivers for the refrigerant Concluding Remarks
compressors in the LNG trains as well as the gas turbine generators As the world’s governments and international organisations
(GTGs) in the power plant. The ‘combined-cycle’ heat and power implement programmes to transform the energy sector, there are new
generation design can be optimised, weighing fuel-efficiency benefits challenges for capital projects. Recognising that fossil fuels will
with increased complexity and inter-dependence, sparing requirements continue to make up a large proportion of the world’s energy mix,
and preferences for standard equipment sizes. natural gas has a lower carbon footprint than oil and coal. This makes
it an attractive choice for energy projects.
Existing Operations
The scope for CO
2
abatement at an operating site is obviously much Even so, a gas or LNG project is not without its challenges. In order to
more restricted than with a new greenfield design. Abatement obtain permits to construct and operate facilities, energy companies
usually takes the form of energy and efficiency improvements that must demonstrate that they have adhered to the principle of ALARP
can be achieved by minor modifications and operational means. and that they have actively minimised environmental impact in a local,
regional and global context. Technical solutions for these global
A review of the solvents utilised in the gas treating units compared environmental challenges continue to be developed, with the ultimate
with newer alternatives and current feed gas composition may aim of an LNG value chain with high efficiency, minimised losses and
highlight potential for ‘solvent swap’. A more selective solvent that attention to greenhouse gas emissions as well as the local/regional
co-absorbs less hydrocarbon from the feed gas will reduce CO
2
impact. With a systematic approach and control framework, good
emissions. Improved solvent selection reduces reboiler duty and thus project execution can deliver the required result. ■
1. King RF, Energy Information Administration (EIA), Natural Gas 5. Shell Global Solutions, High-performance gas treating and Efficiency and Performance at Baseload Plant, LNG Journal,
& the Environment, Natural Gas 1998 Issues & Trends, sulphur recovery technology, Claus and Shell Claus Off-gas Oct 2008;17–21.
Chapter 2, DOE/EIA-0560(98). Treating (SCOT) processes. 9. Den Bakker K, A Step Change in LNG Operations through
2. European Environment Agency, Energy and Environment 6. Rabeau P, et al., How to Reduce CO
2
Emissions in the LNG Advanced Process Control, 23rd World Gas Conference,
Report 2008, June 2008. Chain, Technip, Paper PS2-7, 15th International Conference Amsterdam, 2006.
3. Intergovernmental Panel on Climate Change, Climate Change and Exhibition on Liquefied Natural Gas, 2007. 10. Gibbins J, Chalmers H, Carbon Capture and Storage, Energy
2007. 7. Tanaeva I, et al., Shell Global Solutions,Big and Clean – A Policy, 2008;36:4317–22.
4. Fabricius N, Shell Global Solutions, Water Management in the Novel Design for LNG Plants, International Petroleum 11. Steeneveldt R, Berger B, Torp TA, Statoil ASA, CO
2
Capture
Pearl GTL Project, 6th Doha Conference on Natural Gas, Technology Conference, Dubai, 2007. and Storage. Closing the Knowing–Doing Gap, Chemical
2007. 8. Wilson J, van der Wal G, Oman LNG, Oman LNG Boosts Engineering Research and Design, 2006;84(A9):739–63.
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HYDROCARBON WORLD VOLUME 4 ISSUE 1
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