Did you know that a rupture of a vessel containing CO2 could escalate to create a "Boiling Liquid Expanding Vapour Explosion (BLEVE)?"
DNV says, "The probability of this occurring is believed to be extremely low but CO2 system designers should be aware of the potential.”
Do you know the hazardous limit of CO2 in air? (7 per cent, in case you were wondering – compared to 0.07 per cent for hydrogen sulphide).
Did you know that liquid CO2 is an excellent solvent which can break down lubricants and damage seals?
These are some of the points covered in CO2RISKMAN, a guidance for how to handle CO2 in a carbon capture and storage system (between the capture plant and subsurface injection facility), which has been put together by energy consultancy DNV KEMA and is available for download free of charge from www.dnvkema.com/ccs.
The guidance has been written at 4 different levels, ranging from level 1, a concise executive summary, to level 4, a 300 page in-depth knowledge source with separate sections for each link in the chain. The level 4 guidance has chapters for capture facilities, online pipelines, submarine pipelines, wells, offshore injection facilities, intermediate storage, ships used to carry CO2.
The guidance describes possible causes of hazards, escalation routes and possible consequences. It also provides guidance on hazard identification, risk assessment and how to bring risks down to an acceptable level.
The guidance follows a 15 months joint industry research project which began in August 2011, with support from 16 industry and regulator organisations. The plan is to update the guidance after a few years, when more knowledge is available.
Organisations involved in the research include gases company Air Liquide, Norwegian pipeline operator Gassco, engineering contractor AMEC, oil companies Chevron, Shell and Maersk Oil, power company E.ON, UK power transmission organisation National Grid, Norwegian CCS research centre Gassnova, the Norwegian Petroleum Safety Authority, the UK government’s Environment Agency and Health and Safety Executive, the Scottish Environment Protection Agency, the International Energy Authority Greenhouse Gas Research program (IEAGHG), the Global CCS Institute, and the Institute for Studies and Power Engineering (ISPE - Romania).
The companies in the research group had complementary expertise. For example, Air Liquide has strength in handling liquid CO2, and AMEC has strength in pipelines.
Some of these organisations are in competition with each other, but they also recognise that all of the industry gains from a better understanding of the risks of CO2 handling.
It follows other joint industry projects organised by DNV, covering the capture process (CO2CAPTURE), pipeline transportation (CO2PIPETRANS), wells (CO2WELLS) and storage (CO2QUALSTORE).
The risks of CO2 handling are very different to the risks of CO2 storage, which are mainly about making a good assessment of a storage site, says Kaare Helle, head of CCS business development DNV KEMA.
The guidance could also be used as a basis for certification – a safety organisation, regulator or consultancy could certify a CO2 project as having thoroughly examined a CO2 system for hazards, based on information in the guidance, and taken adequate steps to address the associated risks.
The right balance
DNV aims to find the right balance between making sure people are aware of the risks so that they can be effectively managed and also making sure people are not too worried about the risks that nothing gets done.
“Raising awareness and providing information on potential hazards helps CCS projects manage their risks but it can also create concern amongst other stakeholders, stakeholders who may not have been aware of the potential hazards in the first place” says Hamish Holt, CO2RISKMAN project manager and principal consultant at DNV. “The CO2RISKMAN guidance tries to strike an appropriate balance by providing detailed information on potential CO2 hazards in a factual, non-alarmist way, along with risk reduction measures which CCS projects can consider.”
A key statement in the guidance is that there is no reason why major accident risks from a CO2 handling system within a CCS operation cannot be “low and well within acceptable limits,” but to achieve this will require the application of existing rigorous hazard management processes combined with an adequate understanding of the properties and behaviours of CO2.
“A significant leak from a large inventory CO2 handling system has the potential to be life threatening to people caught within the ensuing dispersing cloud or could pose local environmental harm,” it says.
Competence
Industry can get better at reducing risks as it gains experience with CO2 – but to put that another way, one of the biggest risks from CO2 handling today stems from the industry’s lack of experience with it.
There is much considerable experience in the US in handling large quantities of naturally occurring CO2, where it has been used for enhanced oil recovery for a long time, but “there is much less experience handling very large quantities of CO2 outside the US,” says Hamish Holt.
“With the introduction of CCS this will change. CCS engineers, project management, system operators, hazard management specialists, and others who have a key role in delivering a safe operation need to have adequate understanding of the potential CO2 hazards so that they can effectively manage the associated risks.”
The CCS industry needs to take the existing technologies, experience and practises, ensure they are suitable for CCS, and then integrate the various links in the chain together.
Risks of CO2
Here are some of the risks of CO2 presented at an overview level.
If any water enters a CO2 system, it can form carbonic acid, which can corrode carbon steel (for example in the pipeline).
If as part of the CO2 capture process significant levels of hydrogen, nitrogen or other substances are mixed with the CO2, it can have an effect on the phase calculations (the temperatures and pressures at which CO2 becomes liquid or solid).
If a CO2 system is depressurised, there can be very cold temperatures.
It can be toxic if people breathe air with CO2 concentrations at above 5-7 per cent. This compares with dangerous limits of hydrogen sulphide at 0.07 per cent and nitrogen at 35 per cent.
For risk assessment, it is important to bear in mind that there is not much historical data about leaks, and not much release modelling work has been done.
CO2 is heavier than air (and so won’t rise up and out of the way as hydrogen and natural gas release would).
If there is a failure upstream, which allows an impurity into the CO2 stream, it can cause problems downstream.
Liquid CO2 is an excellent solvent, which is capable of breaking down some lubricants and damage seals, so you have to ensure the materials you choose are suitable.
If CO2 is depressurised, it can cool down to -78°C -78 degrees and freeze - and frozen CO2 could also block CO2 pipelines.
CO2 density is also sensitive to temperature changes especially close to critical point conditions (i.e. 31°C and 74 bars). This can lead to system over pressurisation with a relatively small change in CO2 temperature.
There is "considerable knowledge" on managing risks associated with cracks in natural gas pipelines, and this knowledge is being used for CO2 pipeline design.