COVER STORY | CONTAINING CARBON
emissions by 82% by 2035 and produce net zero steel by 2050. Its low carbon roadmap was launched in October 2021. Some emissions reductions are achievable with management actions such as recycling, and in its most recent decarbonisation action plan British Steel says it has increased its recycled content from a historic average of 13.8% to an average of 24.7%. The roadmap also includes feasibility studies into integrating electric arc furnace steelmaking and replacing methane gas with hydrogen in operations that require direct heat. Other steel companies are also reducing their carbon
load. In a recent blog Dr Debashish Bhattacharjee, VP, Technology and R&D, Tata Steel, said the company had recently conducted a successful trial injection of hydrogen gas in one of the blast furnaces at its Jamshedpur Works. This is the first time in the world that such a large quantity of hydrogen gas was continuously injected in a blast furnace. The trial demonstrated the potential for a 7-10% reduction in carbon emissions per tonne of crude steel produced. He said: “By studying the data, we now know what happens when we inject massive amounts of pure hydrogen into the furnace in terms of gas volume, reaction rates and temperatures”. Global Energy Monitor (GEM) believes that the steel industry has begun a ‘pivotal’ shift: its recently released report says 43% of planned steelmaking capacity is now based on electric arc furnaces, with 57% using coal-based blast furnace-basic oxygen furnaces (BF-BOF). Although electric arc technology represents less than half planned capacity the ‘pivot’ from last year’s report is significant: at that time just 33% of planned capacity was set to use electricity, against 67% based on fossil-fuelled blast furnaces. As with the cement and concrete sector, CCS is a key technology in reducing emissions.
Below: Sizewell C is a near copy of Hinkley Point C but is expected to have a much smaller embedded carbon footprint
The impact of delivering power The embodied carbon across the electricity sector can be reduced by low-carbon variants of the major materials. High on the list for decarbonising the system as a whole is cutting emissions in the electricity transmission system, from the power plant switchyard through to the end user. Again, these types of losses affect all forms of power generation that are connected to the electricity network. The Ricardo report on Hinkley Point C showed that power
as generated at Hinkley Point C will carry less of a carbon burden than the electricity as delivered to the user.
It said: “Almost half of the total GWP value associated with a delivered kWh of electricity from HPC, comes from downstream impacts… this encompasses the infrastructure and operational requirements of the grid itself and includes the impacts of materials needed such as metals for pylons and emission leakages of SF6 insulation (a powerful greenhouse gas)”. That is compounded by losses on the transmission and distribution network, which add 6% to the total emissions because that loss has to be ‘topped up’. A major problem with decarbonising the delivery phase is sulphur hexafluoride. This gas – generally abbreviated to its chemical formula, SF6, as referred to in the Ricardo comment above – has been routinely used in substations and switchgear over recent decades, as well as in smaller sealed items of electrical equipment. It provides an electrically insulated environment for substation equipment, which would previously have relied on an ‘air gap’, to avoid short circuits and subsequent local blackouts. Because its insulating properties are so much better
than air, electrical arcing is about 100 times less likely in SF6 than in air. As a result, sealing the switchgear in an SF6 atmosphere means the various components can be placed much closer together, so the volume required by the substation is smaller. The footprint of a substation with gas-insulted switchgear is 30-40% smaller than that an air- insulated version. This gives network and building designers more options on where to place electrical equipment and it is important in areas – such as cities – where space is expensive. After all, eventually, the space cost of substations feeds back to user bills. In addition, air insulated switchgear is generally exposed to environmental conditions – dust, rain, or even animals – which makes it vulnerable to failure. But SF6 carries a sting: it is the single most damaging
greenhouse gas. Each tonne is equivalent to 23,900 tonnes of carbon dioxide. It is (with similar gases) the biggest contributor to transmission companies’ business carbon footprint (BCF) because on occasion the gas leaks. The electricity supply industry is almost the only use of
SF6 and emissions to air had increased noticeably since it entered common use. Legislators are cracking down. The European Union, for example, had previously excluded the electricity industry from restrictions on so-called F-gases imposed in regulations in 2014. But revised regulations will affect the electricity sector. Meanwhile, as the cost of carbon increases the electricity industry has greater incentive to halt leaks. Over time, new options will replace SF6 in network equipment but the use of alternatives has been slowed as technology is developed. One technical route to replace SF6 is largely based on air but has a proportion of so-called per-and polyfluoroalkyl substances. Abbreviated to PFAS, these have caused concern over a potential threat to health – dubbed ‘forever chemicals’ in the press – and their use is set to be strictly limited, at least in the USA and the EU, where new regulations are progressing through the respective legislatures. A second alternative is not yet commercially available at high voltages. However, by the time a new plant at Sizewell is installing its switchgear and exporting power, it should be able to guarantee lower- carbon delivery of electrons across the network. Between two reactor timelines, for Hinkley Point C and
Sizewell C, initiatives to decarbonise are taking effect across the electricity industry and across the economy. They are not unique to the nuclear industry – but nuclear can benefit from the changes in telling its low-carbon story. ■
16 | September 2023 |
www.neimagazine.com
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