Written evidence submitted by Professor Jonathan Gibbins (CGE0045)

 

Professor Jon Gibbins, Director, UK CCS Research Centre
Professor of Power Plant Engineering and Carbon Capture, University of Sheffield

This evidence is submitted in a personal capacity.  I have been working in the energy field since 1974, was first involved in biomass gasification in the early 1980s and have been active on CCS, in the UK and internationally, since 2002.  I was recently in the CCUS Cost Challenge Taskforce.

 

Main points

  1. Evidence from modelling studies by the Committee on Climate Change (CCC) and others (e.g. the ETI) suggests that CCUS on both fossil fuel applications and also for negative emission technologies (NETs) will be critical in delivering current carbon budget targets for 2050.  And the importance of CCUS, and particularly NETs, can be expected to increase very significantly if targets shift to net zero, as would be required to deliver Paris commitments.
  2. In the recent high level assessment of NETs published by the Royal Society and the Royal Academy (reference 1) the general characteristics of a wide range of NET approaches were discussed.  Links with the UK’s CCUS deployment activities were noted but, given that the CCUS Cost Challenge Taskforce was also active over the same period, the commercial and engineering issues involved were not covered in detail.  The CCUS Cost Challenge Taskforce report (reference 2) covers the details of CCUS infrastructure development for fossil fuel use, with the main objective of achieving timely initial deployment.  But CCUS-related NETs for later implementation, both via biomass energy with CCS (BECCS) and direct air carbon capture and storage (DACCS), naturally received relatively less emphasis.
  3. BECCS does, however, need very urgent attention if it is to be satisfactorily deployed in the UK quickly enough and at the scale envisaged as necessary by the CCC, of the order of 10-50 million tonnes of net CO2 removal from the atmosphere per year by 2050. The critical issue is whether this BECCS can realistically be delivered by CCS applied to electricity or to hydrogen production (noting that only production of these carbon-free vectors makes maximum use of limited biomass supplies for BECCS - conversion to liquid fuels, for example, will release much of the biomass carbon, even with CCS applied in in the conversion process).
  4. A number of processes for electricity production using BECCS are technically and commercially feasible for deployment at the necessary scale and within the necessary time period (i.e. starting to build up to scale within a decade or so).  But it is doubtful whether the necessary ‘space’ in the UK’s electricity system will be available for BECCS via electricity generation if current trends for the growth in intermittent renewables generation capacity continue.
  5. Hydrogen production with BECCS is therefore being included in UK emission reduction scenarios as an alternative to cope with a lack of suitable electricity demand. But biomass gasification technologies, especially at scale and producing the very clean gases required for hydrogen production, remain essentially unproven after many decades of effort.  This makes demonstrating suitable biomass gasifiers just as urgent, and even more technically challenging, than demonstrating CCUS on fossil fuels and installing the necessary CO2 infrastructure.
  6. Direct air capture and storage (DACCS) is an absolutely essential back-stop technology for achieving net zero emissions. Its cost will probably set the long term cost of emitting CO2 to atmosphere. Research and deployment of moderate scale units is an urgent necessity to reduce this cost as much and as fast as possible and to determine the cost (whether perceived as ‘high’ or ‘low’) to inform policymakers.  It is a complete dereliction of responsibility by governments on behalf of their citizens that, so far, the development of DACCS has largely been ignored (or even actively rejected) in mainstream research and innovation programmes and so has been left to a few venture capitalists and similar entities to develop.

Negative emissions technologies (NETS), achieving UK carbon budgets and intergenerational equity issues

  1. The CCC’s scenarios for 80% reductions in 2050 use of the order of 50MtCO2/yr removal from the atmosphere using NETS, assumed to be BECCS.  This illustrates a very important aspect of NETS, namely that they are essential (and cost-effective) for capturing CO2 released to atmosphere from distributed and/or mobile and/or intermittent sources of anthropogenic sources (including, for example, agriculture).  A NETS plant can be located in a convenient place and be operated continuously, making likely costs much lower than directly capturing CO2 emissions by other means for such applications.
  2. NETS applications that capture the CO2 at essentially the same time as it is released can be arranged to have ‘the polluter pay’.  It is very important, therefore, that the use of NETS in this situation is not conflated with the use of NETS by future generations in situations where they would have no choice other than attempting to claw back CO2 from the atmosphere in order to prevent dangerous climate change.  The amoral nature of the latter scenario should not be used to justify holding back NETS development, indeed the sooner NETS are readily available, technically and from a regulatory perspective, the less likely is it that our children and grandchildren will be saddled with this unacceptable burden.

Biomass energy with CCS for electricity

  1. Biomass use for electricity production in the UK is well developed, both in converted coal plants, most notably at the Drax power plant, and also in new, built and proposed, dedicated biomass power plants.  It is regrettable that some of the new biomass projects are sized at a nominal 299MW to avoid having to include CCS readiness in their permitting applications, rather than being made a more logical 300MW or above, but nonetheless it is likely that at least some of the developers of such plants have had the common sense to still include the very easy provisions that can be made to facilitate capture retrofit.
  2. Capture technology for converting large-scale biomass power plants to BECCS is relatively well-proven, primarily post-combustion capture using amines (as demonstrated on coal power plants at ~1MtCO2/yr scale in North America), as well as, potentially, using oxyfuel combustion.  There will need to be some testing and development to ensure that process designs match biomass requirements at the least cost, and continuous improvement over time can be expected as more plants are deployed. So BECCS for electricity production can be relied on, provided the necessary CO2 transport and storage infrastructure is developed, to the extent that suitable biomass can be sourced, and provided that:
  3. The last criterion is a concern because of the need to run large investments such as BECCS power plants at high load factors to maximise the use of expensive facilities and also because of the technical difficulties in rapidly changing output when handling solid fuels such as biomass.  But if, before CCS has a chance to be deployed, intermittent renewable deployment is allowed to expand to the point where there is no opportunity to run baseload, or even modulated output, then this sub-optimal situation for BECCS power plants will be inevitable and consumer costs can be expected to increase as a result.  The same considerations also apply to fossil CCS power plants but these, particularly, if run on natural gas are both intrinsically more flexible and also intrinsically have a better economic structure (lower capital cost) to allow for the vagaries in operation imposed on them by intermittent renewable output.  The only solution appears to be a ‘joined up’ approach to UK decarbonisation which looks far enough ahead to recognise and provide options and decision points that can resolve such conflicts. As an order of magnitude, 50MtCO2/yr of BECCS that captures about one tonne of CO2 per MWh of would correspond to approximately 6 GW of baseloaded electricity generation capacity.

Hydrogen production with BECCS – but where are the biomass gasification reference plants?

  1. While a detailed examination is beyond the scope of this submission, it seems reasonable to expect that a well-developed hydrogen infrastructure in the UK could use all of the hydrogen that BECCS could produce, particularly if some interseasonal hydrogen storage was available.  The limit would be the amount of suitable biomass available and the number and size of suitable biomass gasifiers that would need to be operational as full-scale, commercial projects in time (e.g. perhaps from 2035 onwards).
  2. The necessary large-scale biomass gasifier technologies and competent industries and project developers to supply them do not appear currently to have been demonstrated satisfactorily in the UK (or elsewhere).  For a review of biomass gasification experience in the UK, including many setbacks, see reference 3.  For a recent scientific review of biomass gasification see reference 4.  Nor is suitable technology necessarily going to be developed overseas in time.  For example, the GoBiGas biomass gasifier in Sweden was stated to be a technical success at 20MW scale but this pilot plant is now mothballed and development of a 200MW version (approaching a more suitable size for large scale hydrogen with BECCS) has not been pursued for economic reasons (see reference 5).  Given the long project development time and subsequent construction and operational testing period that would be required (order 10 years), it therefore seems that, if hydrogen production with BECCS in the UK is to be an option, it is very urgent to take active steps to progress biomass gasification to the necessary level of commercial readiness.  However, it also has to be recognised that, even if started, such an initiative might not ultimately prove successful.
  3. The problem is the intrinsic nature of biomass.  Biomass looks like an attractive fuel in theoretical models for gasification and subsequent ‘shifting’ of the ‘synthesis gas’ (syngas) product to produce hydrogen. The high moisture content of biomass can even be an advantage, in providing a ‘free’ source for the hydrogen, which can be ‘unzipped’ from H2O if the oxygen is offered a carbon atom to bond to instead.  But there is a problem in the details.  As anyone who has sat by a wood fire will know, the products from biomass conversion include tars, the smoke that flavours food but stings eyes.  In gasifier plants that are designed to produce hydrogen from coals these tars are destroyed by taking the gases to high temperatures before they clog up the delicate catalyst beds for the sift reaction.  But the ash particles also present in biomass gases have a relatively low melting point compared to coal ash and, in commonly-used fluidised or entrained bed biomass gasifier configurations, at temperatures high enough to destroy tars and larger hydrocarbon molecules, may form a layer of what is effectively sticky molten glass on the gasifier internals.
  4. Coal gasifiers for syngas production use a different approach, reacting the fuel with large enough amounts of essentially pure oxygen to raise the temperature to levels where the coal ash becomes fluid and leaves the gasifier as molten slag and the syngas becomes essentially a simple mixture of CO, CO2, H2 and H2O.  The CO and H2 are the ‘valuable’ products, the former can be reacted with additional H2O to make more hydrogen.  But this high temperature approach is not available with normal biomass, since the heating value of the biomass is so low that it largely has to be burnt to CO2 and H2O to reach the necessary temperature, leaving little useful product and consuming a lot of expensive oxygen. It is possible to use biomass in conjunction with coal or other higher-heating value fuels in such ‘entrained-flow, slagging’ gasifiers, where the biomass can replace some of the steam that might be added at the expense of slightly higher oxygen and fuel consumption.  Because CCS would be included the overall CO2 removal benefits would still be achieved and this approach may also help to compensate for any seasonal variations in biomass supply. But adding coal gasification may increase costs, if this is not the cheapest fossil fuel route to hydrogen (i.e. vs. natural gas reforming).  Regulations would also have to enable biomass co-use with fossil fuel in any incentive regime, locations where coal can be made available would have to be retained and generally it should be recognised as a possible need in ongoing planning.
  5. An alternative to using biomass with coal in gasification is to upgrade the biomass into something more like coal itself, typically by processes analogous to traditional charcoal production.  But this adds extra process steps, possibly extra costs (although subsequent transport and handling costs may be reduced) and also is likely to involve the release to atmosphere of some of the valuable biomass carbon.

Direct Air Carbon Capture and Storage deployment for ‘learning by doing’

  1. Technologies that can use ‘machinery’ rather than natural systems to directly remove CO2 from ambient air and deliver it in a pure, compressed form ready for secure geological storage provide an essential ‘backstop’ for achieving net zero emissions.  They have aptly been described as ‘the capture of last resort’. Given the inherent limits on biomass production it seems difficult for any responsible government to make a firm commitment to staying within a realistic, finite future GHG emission budget, and hence requiring net zero or possibly net negative emissions, without that government being certain that DACCS was technically available so that it was not necessary to rely on BECCS as the main engineered NET. It would also be of great benefit to have DACCS be as cheap as possibly by the time it was really needed (i.e. when alternative, lower cost measures for GHG emission reduction had already been applied as much as possible).  And, whatever the cost of DACCS turns out to be, this value probably defines the real cost of emitting CO2 to the atmosphere and it would be very helpful to have good estimates for its magnitude.
  2. Development of DACCS was identified as a priority research area in the RS/RAEng NETs report (reference 1) but it was noted that no pilot-scale units were yet operating in the UK.  The recent world-leading proposals for CCUS cluster development in the UK would, with suitable additional incentives, also support ‘learning by doing’ through the installation of working DACCS equipment, linked to the UK’s advanced research capabilities.  To achieve this, it has to be recognised that differentiated support will be needed for DACCS, at a higher level per tonne of CO2 captured and stored than for conventional CCS.  But DACCS units are typically expected to be relatively small, and would then be replicated in large numbers to achieve meaningful total CO2 removal levels, so overall support requirements would still be low.
  3. As well as differentiated levels of support, with support level related to size of the facility to bring on new technologies, it is also important (as with all CCUS technologies at this early stage of development) that the large input from government funding, directly and via ‘market mechanisms’, is made conditional on knowledge transfer from projects so that the field as a whole progresses.  It is striking how little meaningful information has come out of post-combustion CO2 capture projects in the US as well as studies in the UK, with almost every aspect of interest redacted from reports as ‘proprietary’.
  4. It is also essential that DACCS, where the CO2 is made ready to send to storage, is supported on an equal basis to direct air capture (DAC) for CO2 to convert into products such a fuels.  While DAC (or other routes for using carbon taken from the air) is the only way to make such short-lived CO2 utilisation products carbon neutral, in any serious emission reduction programme large amounts of storage of CO2 from the air as an offset will be required.  This route should not continue to be disadvantaged as it has been so far, with most non-government venture capitalist and similar support for DAC going to products such as synthetic fuels for boutique markets.

 

References

1. Greenhouse gas removal, September 2018, ISBN: 978-1-78252-349-9. https://royalsociety.org/topics-policy/projects/greenhouse-gas-removal/?utm_source=royalsociety.org&utm_medium=redirect&utm_campaign=greenhouse-gas-removal

2. Delivering Clean Growth: CCUS Cost Challenge Taskforce Report, July 2018. https://www.gov.uk/government/groups/ccus-cost-challenge-taskforce

3. A. Ernsting, Biomass gasification & pyrolysis, Biofuel Watch, June 2015. http://biofuelwatch.org.uk/wp-content/uploads/Biomass-gasification-and-pyrolysis-formatted-full-report.pdf

4. V.S. Sikarwar et al, An overview of advances in biomass gasification, Energy Environ. Sci., 2016, 9, 2939. https://pubs.rsc.org/en/content/articlelanding/2016/ee/c6ee00935b#!divAbstract

5. GoBiGas demonstration – a vital step for a large-scale transition from fossil fuels to advanced biofuels and electrofuels. Editor: Henrik Thunman. ISBN: 978-91-88041-15-9 https://www.chalmers.se/SiteCollectionDocuments/SEE/News/Popularreport_GoBiGas_results_highres.pdf

 

 

October 2018