Recovery and use of ammonia from coke-making processes

Abstract

The increase in energy demand and continuous rise of greenhouse gas emissions urge for a development of clean technologies to transition energy sector to a carbon-neutral future. Approximately 80 % of the global energy is produced by burning oil, coal and natural gas. Coal is the most consumed energy source globally, mainly used in China (25538 TWh), India (6105 TWh) and the United States (2276 TWh) [1]. Coal has a relatively high heat value and low moisture content and provides 38% of global electricity. Coal power plants have been gradually phasing out in the United Kingdom, there are four coal-fuelled power stations which are on standby. Coal’s contribution to the UK’s energy mix has been declining and currently, only about 1% of annual energy is generated from coal, according to the National Grid data [2]. The UK is one of 194 parties that have adopted the Paris Agreement. It commits to achieving carbon neutrality by 2050 and reducing greenhouse gas emissions, from over 319 million metric tonnes of carbon dioxide in 2022 to zero by 2050 [3].

Even though the use of thermal coal as an energy source is decreasing, the steel industry largely relies on metallurgical coal as it is one of the main raw materials for the production of steel. The steel industry is one of the biggest greenhouse gas emitters in the world, responsible for approximately 7-8% of global carbon dioxide (CO₂) emissions. Metallurgical coal contains low levels of sulfur and agglomerates easily, making it suitable for coke production. The coke-making process is an energy-intensive process which involves heating coal at temperatures of around 1200 ˚C under an oxygen-free atmosphere for approximately 18 hours. During the process, a by-product known as coke oven gas (COG), is produced. COG contains a mixture of valuable components that can be used as fuel on-site, and harmful impurities that are processed in by-product plant.

This project focuses on the use of ammonia from a waste stream generated during coke oven gas cleaning processes at Tata Steel, Port Talbot. The Port Talbot plant produces approximately 44 000 m³ of COG every hour. This is processed in by-product processing plant so that COG can be utilised on site as a fuel gas. The processing of COG generates waste stream which is currently incinerated at the flare stack (the final step of COG processing). Disposal through incineration is a huge waste of energy and waste of valuable resource like ammonia.

The aqueous waste is rich in ammonia and contains a mixture of other components including phenol (PhOH), carbon dioxide (CO₂), hydrogen sulfide (H₂S), and other minor impurities. Recovery of ammonia from COG is very challenging due to the high solubility of hydrogen sulfide in the mixture, the presence of tar impurities and difficulties in efficient separation of the components without creating harmful products.

Solid oxide fuel cells (SOFCs) can convert ammonia gas to electrical power and heat when operating in fuel cell mode [4]. In this work, the conversion of a liquid ammonium hydroxide solution, phenol in solution, aqueous ammonium carbonate and hydrogen sulfide, was investigated using a commercially available anode-supported button cell. These mixtures served as a basic simulation of the waste ammonia streams produced from coke-making processes. Analysing the impact of each component, particularly ammonia, on the performance of the SOFC was crucial in order to establish the cell’s tolerance levels and understanding the reaction pathways that take place during the operation. By simulating mixtures that reflect the composition of the actual waste, it was possible to determine how these compounds interact with the cell without risking irreversible damage from highly toxic and concentrated waste. Due to time constraints, the actual COG waste was not supplied to the SOFC and the primary focus of this study was to evaluate the feasibility of introducing ammonia and other components to the SOFC and form basis for potential further work.

The electrical performance of the cells was characterised using I-V curves and electrochemical impedance spectroscopy, and the output gases of a cell were measured in real-time using quadrupole mass spectrometry (QMS) and at the end of experiments, the cells were analysed with scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS).

Energy demand and the rise in pollution are the main topics in modern society. This thesis explores the possibility of integrating the two problems – reducing pollution from COG cleaning by turning it directly to electricity or hydrogen that could be stored and used to produce electricity.

Date of Award	26 Nov 2025
Original language	English
Sponsors	KESS 2 PhD Student, University of South Wales & Tata Steel
Supervisor	Christian Laycock (Supervisor), Alan Guwy (Supervisor) & Gareth Owen (Supervisor)