Analysis of Models to Calculate Greenhouse Gas Emissions

A group of researchers from Scotland, UK, reviewed several models such as the Institute of Petroleum’s guidelines for quantifying greenhouse gas emissions from decommissioned oil and steel structures and analyzed current guidelines for achieving net zero greenhouse gas targets. This research was published in the journal Energy Policy.

To learn: Quantifying Greenhouse Gas Emissions from Decommissioned Oil and Gas Steel Structures: Can Current Policies Achieve NetZero Goals? Image source: DesignRange

A significant amount of steel is used in the oil and gas (OGI) industry to explore, extract, transport, and refine hydrocarbons, as well as recycling the same steel after it has been decommissioned. Some common steel structures used in OGI are steel jackets, drilling rigs, topsides, and pipelines.

According to OGUK (2019), decommissioning accounts for 10% of OGI’s total spending, with around £ 1.5 billion a year currently being spent on decommissioning activities in the UK alone. Currently, the 20-year-old guidelines of the Institute of Petroleum (IOP) “Calculation of energy consumption and gaseous emissions” are the current best practice for calculating the GHG emissions that arise during decommissioning work in the north-east Atlantic region.

What are the problems with IOP guidelines?

First, the IOP guidelines have not been regularly updated for 20 years. It tries to take a life cycle assessment (LCA) approach but does so in a very limited way that contains some important assumptions which overlooks large amounts of greenhouse gas emissions. It shows inconsistencies, biases, and assumptions like the following.

The directives apply the same values ​​for GHG emissions for steel for both recycling and reuse, regardless of whether it is reprocessed after smelting or reused unchanged, and these two are completely different in terms of energy demand and energy generated Emissions.

The guidelines assume that materials that are left on site can be effectively removed from the material cycle and that newly manufactured materials can replace the lost materials in the event of greenhouse gas emissions. However, this only applies to materials that can be recycled and GHG emissions associated with non-recyclable materials such as plastics and cement are ignored.

The IOP guidelines also do not take into account the location of recycling and waste treatment, and do not take into account GHG emissions from the transport of materials to these recycling points.

It is assumed that all primary steel (steel from virgin material) is produced in a blast furnace (BF) or basic oxygen furnace (BOF) and all recycled (secondary) steel is processed in an electric arc furnace (EAF). It is also believed that EAF will always use electricity from renewable sources, while in reality EAFs are often powered by coal. Both BOF and BF use a significant proportion of secondary steel in primary steel manufacture.

What is the current scenario of global steel recycling and the corresponding greenhouse gas emissions?

China is by far the largest steel producer with 996 million tons of production in 2019 and 920 million tons in 2018, followed by India with around 10% of that number. The amount of scrap steel recovered for recycling was 105 million tons in 2018, while primary steel production was 1808 million tons.

The IOP figures for the GHG emissions associated with the production and recycling of steel are 1889 kg CO2 (eq) per ton of primary steel produced and 960 kg CO2 (eq) per ton of secondary steel. According to the World Steel Association (2020), every ton of steel produced releases 1.85 tons of CO2 (eq),

What are the different levels of GHG emissions in secondary steel production?

According to previous reports, the GHG emissions from steel production in an EAF are 734 kg CO2 (eq) per ton of steel. It depends on the amount of hydrocarbons in the charge, the burner, the efficiency of the processes and the carbon content of the steel scrap, graphite or other additives used.

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GHG emissions from electricity generation consumed by the EAF are considered by Chesnokov as “indirect emissions”. The EAF’s indirect greenhouse gas emissions can be higher than those of the direct emissions. The generation of electricity used in the EAF is the primary indirect source of greenhouse gas emissions.

The GHG emissions from generating electricity for use in an EAF depend on the type of fuel used and the thermal and generation efficiency of the power plant. Electricity from renewable sources such as sun, wind or hydropower significantly reduces the carbon footprint. On the other hand, fossil fuels that are used to generate electricity have a significantly larger carbon footprint that has to be calculated.

Coal power plants produce 583 kg CO2 (eq) per ton of steel and renewable energies such as wind produce only 3 kg CO2 (eq) per ton of steel.

GHG emissions from transporting steel scrap to recycling centers are another important factor. GHG emissions from shipping are responsible for 3% of all global GHG emissions with around 1 Gt CO2 (eq) y-1, which makes shipping the sixth largest producer of global GHG emissions.

The European Environment Agency (EEA) (2017) reports GHG emission values ​​for maritime transport of up to around 135 g CO2 (eq) km / l. The greenhouse gas emissions caused by shipping should include the effects of the size of the ship, the age of the ship, the efficiency of the engine, the fuel consumption, the speed, the route, the number of stops, the weather and the ocean currents and winds, the cargo volume and number and type of ship maneuvers so that the GHG emissions from shipping can be calculated precisely.

reference

A. Davies, A. Hastings, Quantifying Greenhouse Gas Emissions from Decommissioned Oil and Gas Steel Structures: Can Current Policies Achieve NetZero Goals? Energy Policy, 160, 2022, 112717, ISSN 0301-4215. https://www.sciencedirect.com/science/article/pii/S0301421521005826?via%3Dihub

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