Clean coal: the view from Sardinia

The IEA Clean Coal Centre’s biennial conference on clean coal technologies returned to the island of Sardinia, perhaps more known for its beaches than its key historic role as Italy’s only domestic source of coal.

Despite the numerous challenges currently facing the coal industry, this edition welcomed an unusually large number of delegates from over 30 different countries – testament to the ongoing relevance of coal power in many regions and the growing need for technological innovation by researchers and manufacturers. Hosted by local energy research institute Sotacarbo in the city of Cagliari, the three-day meeting covered all aspects of cleaner coal utilisation, with principal themes of high-efficiency power plant, pollutant controls, carbon capture, and gasification and conversion technologies.

Bringing coal into the digital age

Since acquiring Alstom Power two years ago, GE accounts for a huge share of the global coal generation market and has become a champion of the role high-efficiency coal can play in bringing power to developing economies. A keynote address from general manager of steam plant Ashok Ganesan highlighted how the company is focussing on bringing power plants into the digital age, claiming that plant efficiencies could be pushed towards 50% simply through better use of plant data and intelligent control systems, which allow a more integrated approach to plant operation. To support these developments the company opened a dedicated research centre for excellence in steam power plant efficiency earlier this year, which will focus on the coal fleets in China and India.

This kind of incremental approach to gaining a significant boost to plant efficiency echoes the approach of Professor Weizhong Feng at the now-famous Waigaoqiao No 3 plant in Shanghai (see for example MPS, March 2013, pp 12-14), where more tangible measures such as eliminating solid particle erosion and improved air preheater sealing have gained the plant several percentage points efficiency. The team’s latest modification is to raise the high and intermediate pressure turbines to the level of the furnace superheaters, massively reducing the length of expensive steam pipe required and reducing efficiency losses associated with pressure drops and the low pressure exhaust (Figure 1). As presented at CCT2017, this idea will be implemented for the first time for a double reheat steam cycle at the recently approved Pingshan Phase II power plant – a single 1350 MW unit which aims to exploit the other techniques used at Waigaoqiao to become the most efficient coal plant in the world at 49.8% (net, lower heating value (LHV), site conditions). Construction on the project should start this year.

Japanese IGCC renaissance

Meanwhile, Japan is leading a renaissance of integrated gasification combined cycle, with the air-blown gasifier concept successfully tested at the Nakoso demonstration plant since 2013 now being scaled up for two 540 MW units as part of a revitalisation initiative for the Fukushima region. Manufacturers Mitsubishi Hitachi Power Systems described how these units should achieve up to 48% efficiency (net, LHV, ISO) and SOx and NOx levels of a few ppm, while offering greater fuel flexibility than a conventional pulverised coal plant due to their tolerance of slagging coals. With government support, the company is also pursuing an oxygen-blown gasifier technology for the 166 MW Osaki Coolgen demonstration, which was commissioned in March and expects to operate commercially in 2019. Later phases of this project will include carbon capture tests and the addition of a hydrogen-powered fuel cell cycle to further raise efficiency.

Flexibility vs efficiency

For coal plants in many parts of the world, flexibility is taking centre stage from efficiency, as they are obliged to act primarily as back up to intermittent wind and solar power. Quite apart from the financial demands of these low load regimes, frequent start-up and ramping operations are putting strain on plant components that they were not designed to cope with. New analysis by German energy industry association VGB Powertech has shown that the rate of unplanned unavailability incidents has increased with greater load cycling of the country’s hard coal plants, although it remains unclear whether this is simply due to other factors such as ageing plant and reduced maintenance budgets (Figure 2).

Wind and solar are also seeing rapid deployment in India, where the government has targeted an additional 160 GW of capacity over the next decade to accompany around 60 GW of planned coal plant. Reliance Power discussed how coal plants are already feeling the economic effects of reduced operating hours and load cycling, and presented modelling analysis that echoed VGB’s concerns over the effects of thermal fatigue on key components such as the turbine pressure valve.

Mixed fortunes for CCS

Carbon capture and storage has experienced mixed fortunes in the last few years, but this year sees the opening of three major demonstration projects in the USA – two of which are on coal power plants. Speakers from the US Department of Energy lauded the achievements of the Petra Nova project in Texas, which became the world’s largest coal power CCS project when commissioned on schedule and on budget early this year, but contrasts with the well-documented problems at the even larger Kemper County facility.

Following the cancellation of the UK’s CCS programme nearly two years ago, the ROAD project in Rotterdam remains the only near-term prospect for demonstrating the technology in Europe. The proposal from Engie and Uniper to capture carbon dioxide from roughly a quarter of the emissions of the new 1000 MW Maasvlakte coal power plant was put on ice in 2012 due to the collapse of the EU ETS CO2 price, but was reactivated in 2015 based on a new business model and selection of a more economic CO2 storage site in an old gas field just offshore. As outlined by ROAD’s Andy Read at CCT2017, the new project structure is based on compensation for three years of operating costs from the EU’s ERA-NET programme, and capital grants from various sources including the Dutch government (Figure 3). However, with a ruling coalition still to be formed in the wake of March’s election and some parties calling for an end to all forms of coal power, the future of the project is still hanging in the balance.

SOx, NOx, PM and mercury

Tightening regulation of the non-greenhouse pollutants, SOx, NOx, and particulate matter, present another major challenge for coal plants, together with the widespread adoption of some form of mercury emission limits, which are already in force in the USA (see pp 32-33). In Europe, the new BAT/BREF standards impose demanding reductions for all of these species, and have left many plants facing difficult investment decisions over whether to upgrade or close. India has also recently introduced SOx, NOx and mercury standards for the first time, which require new plants to go even further than the EU limits, and are a daunting prospect for a coal fleet effectively starting from zero. A presentation from NGO CSE India judged that progress in meeting the limits has been slow, with many plants waiting for further guidance and even plants currently under construction largely continuing without modification. The total cost to the sector of meeting the new limits is likely to reach at least $10 billion and, as in Europe, investment in new equipment is unappealing when plants are simultaneously facing the financial squeeze of reduced running hours. CSE maintains that the upgrades are feasible and affordable, but power producers such as Reliance warned that tariff increases will be required to fund them and that the associated downtime could lead to a supply shortage.

While existing Indian plants will be able to adopt standard low NOx burners to meet the new NOx standards, many European plants are turning to advanced forms of combustion optimisation and targeted ammonia or urea injection as lower capital cost alternatives to selective catalytic reduction units, and several such technologies were presented at CCT2017. Once considered the preserve of smaller units, selective non-catalytic reduction is now being deployed by manufacturers such as ERC and FuelTech at 400 MW and above. Providers of the diverse mercury removal technologies developed in the USA have also scented a business opportunity in Europe, with suppliers such as Gore and Nalco presenting their systems, which are integrated with flue gas desulphurisation units, as a more effective alternative to simple carbon injection.

Committed to coal

Despite this difficult environment for coal power, many countries remain committed to the fuel as a low cost and secure supply of power, even outside the developing economies of South Asia. A striking example is Dubai, where low-cost solar power installations have grabbed headlines, but much less is said about the emirate’s parallel commitment to high efficiency coal in its effort to reduce reliance on Qatari gas imports. Presented by the Dubai Electricity and Water Authority, the planned 3600 MW Hassyan plant will begin with a first phase of four ultrasupercritical 600 MW units, to be commissioned from 2020, offering a levelised power tariff of 5 cents/kWh.

Elsewhere, a talk from Turkey’s state coal enterprise emphasised the country’s intention to further exploit domestic coal reserves, with a particular research focus on technologies for converting some of the country’s extensive lignite resource to gaseous and liquid fuels.

Polish energy company Tauron discussed a new generation of large (~1000 MW) ultrasupercritical plants for providing baseload power, while calling for greater exemptions in implementing the costly EU reforms to emissions standards and the ETS.

As coal is increasingly deployed in these regions and others with more limited financial resources, it is crucial that research forums such as the CCT series continue to promote the development and adoption of cleaner coal technologies in the place of polluting and low-efficiency power plant. We anticipate another informative event in South Africa in two years time.