Special Report: Converting sour gas challenges into opportunities
Angie Slavens, MD of UniverSUL Consulting, studies the benefits of sulphur
Many of the non-associated gas fields in the Middle East are extremely sour, with H2S concentrations in the range of 15%-30% and total acid gas (H2S + CO2) content reaching nearly 50% in some extreme cases. Such high levels of contamination present obvious economic challenges for GCC nations, most of which currently utilise natural gas for more than 90% of their power generation.
The processing facilities which treat these sour gas streams require large facilities for the removal of acid gas and recovery of elemental sulphur. These units alone can comprise up to 40%-50% of the total capital cost of the central processing facility. In addition, utility costs associated with amine circulation and regeneration in the acid gas removal unit and in the tail gas treating unit (TGTU) make up a significant portion of the total operating cost of the facility, especially when solvent chilling is required to achieve temperatures below that which can be achieved with air cooling alone.
On the surface, it would appear that sour gas developments in the Middle East would have difficulty competing with sweet gas, which is available in large quantities in other parts of the world. However, in their quest to achieve energy independence, GCC countries are turning sour gas challenges into opportunities, which was one of the key themes at the Middle East Sulphur Conference, which took place last month in Abu Dhabi.
Sulphur value chain
Elemental sulphur is primarily produced as a by-product of fossil fuel production. Sulphur components must be removed from raw oil and gas streams to minimise sulphur dioxide (SO2) emissions to the atmosphere which contribute to acid rain. Most oil and gas producers view sulphur as a waste product and strictly a cost of production.
However, this essential element actually has a very robust value chain of its own. Sulphuric acid is a critical intermediate in the production of phosphate fertilisers and is a necessary feedstock to thousands of other industrial processes. As the world’s most widely produced chemical, the consumption of sulphuric acid provides a good indicator of a nation’s industrial strength. The Middle East became the world’s largest sulphur producing region in 2015 and will dominate supply in the foreseeable future, with Saudi Arabia and the UAE leading the way; each currently produces around 10% of global sulphur supply (approximately 6 million tonnes per annum each).
Because elemental sulphur is derived primarily as a by-product, its price has been somewhat volatile over the past several decades. When in significant oversupply, price remains relatively low; however, when the market is undersupplied, price can become quite volatile. Neither situation is ideal. At very low prices, sour gas plant operators suffer, ultimately leading to higher energy prices.
When the sulphur price is high, fertiliser producers suffer, ultimately leading to higher food prices. Access to affordable energy and food supplies are two of the key facets affecting the wellbeing of a society. As such, several GCC nations are considering socially responsible endeavours that could more effectively link sulphur supply with fertiliser production, thereby minimising economic volatility in areas related to meeting the vital needs of their citizens.
Sulphur recovery energy benefits
Waste heat from the exothermic Claus reaction is recovered as HP and LP steam, which makes the sulphur plant a net energy exporter, supplying needed steam and/or power to the processing complex. It is common for extremely sour gas plants to employ steam turbine power generation facilities that convert HP steam from the sulphur recovery unit (SRU) into power, which may supply up to 50% of the total sour gas plant power requirements.
While the SRU is normally an energy exporter, amine-based tail gas treating can consume between 40%-100% of the energy produced by the SRU. In desert climates, a significant portion of this energy consumption is associated with solvent chilling in the TGTU.
As a result, many technology suppliers are exploring various energy-optimising features, including solvent innovations which would eliminate the need for propane refrigeration. Additionally, alternative tail gas treating technologies, which yield products such as sulphuric acid or ammonium sulphate, have recently gained significant interest due to the fact that they reduce energy consumption in the TGTU and/or convert the unit from an energy importer into an energy exporter, further enhancing power benefits in the steam turbine generators.
Sulphur for solar energy storage
In 2012 the UAE announced plans to diversify its energy mix in order to sustain growth while also minimising environmental impacts associated with burning natural gas. Specific targets include producing 7% of the country’s total energy from renewable sources by 2020, and generating 30% of the country’s energy from clean sources (solar and nuclear) by 2030. Ironically, sulphur from sour gas processing may play a role in helping the country achieve its solar energy aspirations.
A solar sulphur cycle (SSC) concept presented by DLR, General Atomics and Masdar Institute, aims to utilise sulphur as an alternative for energy storage from concentrated solar power plants, due to its superior energy density versus conventional molten salts. During the day, solar thermal energy from concentrating mirrors is thermochemically stored by decomposing sulphuric acid into sulphur, water and oxygen.
Sulphur, the energy carrier, can then be combusted during non-daylight hours to produce power, and the resulting SO2 converted back into sulphuric acid. Sulphur can be stored easily and holds the potential to significantly reduce storage size and associated costs compared to state of the art molten salt thermal energy storage technologies.
A SSC demonstration project is currently underway in Europe. Masdar Institute, DLR, General Atomics and UniverSUL are currently seeking opportunities to initiate a similar pilot or demonstration facility in the UAE.
While sour gas reservoirs present many technical and economic challenges for developers, they can also present unique opportunities for those who are willing to be creative and think beyond the confines of the processing facility. Sulphur recovered from sour oil and gas has the potential to generate and store energy, while also contributing to the vital food supply chain. Both of these topics are of critical importance to GCC countries, which is why Middle Eastern nations are taking a more proactive approach toward harnessing all of the value that sulphur has to offer.