Greenhouse gas emmisions by sector

The iron and steel industry produces by far, the highest greenhouse gas emissions. The cement industry and the chemical industry are the other major emitters. Process-related greenhouse gas emissions play a pivotal role in these three sectors.

The cement industry

Cement production releases large quantities of greenhouse gases into the environment. These greenhouse gas emissions are caused in particular by two processes: First, very high temperatures are required for the combustion process during which the initial material limestone is converted into clinker. This leads to high energy consumption and consequently to high energy-related emissions. Second, the chemical reaction during combustion leads to the release of greenhouse gases because the limestone is deacidified during the process. These process-related greenhouse gas emissions account for around 50 per cent of total emissions.

Decarbonising the cement industry is extremely demanding, as to date, no technology has been developed that can extensively reduce greenhouse gas emissions. In this case, a combination of measures and technologies must be found to make the cement industry climate-neutral.

The following greenhouse gas reduction strategies are currently being pursued:

  • Material substitution (replacement of concrete as a building material, reduction of the cement content in concrete, reduction of the clinker content in cement);
  • CO2 capture and utilisation (Carbon Capture and Utilisation – CCU);
  • Energy efficiency and fuel substitution;
  • Minimisation of transport routes;
  • Adaptation of building regulations and standardisation, as well as public procurement. The approaches to material substitution and CCU aim at minimising process-related greenhouse gas emissions.

The steel industry

A large proportion of greenhouse gas emissions in the steel industry are process emissions, produced primarily during the blast furnace process, which is based on the use of fossil carbon carriers (mainly coke) as a reducing agent.

Several practical approaches are already known that could lead to a significant reduction in steel industry emissions. In principle, process-related emissions can be significantly reduced by complete process conversions, and relevant approaches are currently being developed.

The following greenhouse gas reduction strategies are presently being pursued:

  • The restructuring of the production process:
    • use of electrolytic processes;
    • use of gas-based direct reduction processes.
  • Reduction within existing production processes:
    • more efficient use of process gases;
    • increased energy efficiency by shortening process chains (avoidance of heat losses);
    • increased recycling rates (secondary steel production via electric furnace route, in particular with the use of renewable electricity).
  • The use of new steel grades.

The restructuring of the production process targets the reduction of process-related greenhouse gas emissions. Electrolytic processes are still at an early stage of development. Gas-based direct reduction processes are already being operated worldwide on an industrial scale using natural gas. In a first process step, the natural gas is split into CO and H2. The alternative direct use of regeneratively-produced hydrogen is currently being tested in various projects.

The chemical industry

The production of ammonia is the main source of process emissions in the chemical industry and consists of two integrated process steps:

  1. Hydrogen production via steam reforming of natural gas, emitting around ten tons of CO2 per ton of hydrogen produced
  2. Ammonia synthesis from nitrogen and hydrogen via Haber-Bosch process

By using water electrolysis to produce hydrogen with renewable energy, the process-related greenhouse gas emissions of ammonia production could be avoided completely. However, in that case further process adaptations become necessary, such as an air seperation unit for providing the required nitrogen.