Gas 2024 Issue

Hydrogen recovery from refinery off-gas – Part 1: An overview

Using next-generation hydrogen separation membranes to recover unused hydrogen wherever possible

Zach Foss Divigas

M odern refineries have adapted to exploit heav - ier crude oils and meet ever more stringent envi - ronmental requirements for fuel specifications, increasing demand for hydrogen to meet the most severe hydrotreatment needs. Increased hydrotreatment severity has caused an increase in refinery off-gas (ROG) produc - tion in most refineries, which frequently exceeds the pos - sibility of sending it to other units or burning it entirely as fuel gas. The value of these ROG streams increases dramati - cally when the hydrogen component can be purified and recycled as a feed gas back to the hydrotreaters, reducing hydrogen purchases through merchant suppliers or hydro - gen production from the refinery itself. With an increased focus on carbon footprint and net zero goals by 2050, hydrogen production is a key focus area for reducing greenhouse gas emissions. Greater than 96% of hydrogen manufactured today is through steam methane reforming (SMR), where natural gas is heated in the pres - ence of steam over a catalyst to produce hydrogen and carbon monoxide (CO). The CO can be further processed via a water gas shift (WGS) reaction to produce additional hydrogen as well as carbon dioxide (CO₂).

Once the hydrogen product is separated and purified from the CO₂ and other contaminants, most hydrogen plants currently release the CO₂ directly into the atmosphere. This type of hydrogen production is referred to as ‘grey’ hydro - gen. Grey hydrogen production prices are highly variable depending on the cost of natural gas, but a good rule of thumb is a price of $1.50-2.00/kg. To reduce the carbon impact of hydrogen production, many refiners look to move to blue hydrogen, SMR pro - duction paired with carbon capture, utilisation, and storage (CCUS) or green hydrogen produced via electrolyser driven by renewable electricity. These process changes have a significant impact on the price. Blue hydrogen is estimated to double hydrogen costs to $2.80-3.50/kg, while green hydrogen is a staggering five times price increase up to around $8/kg. This cost increase of a crucial feed gas for refinery processes has several implications, one of which is the increased importance of recovering unused hydrogen wher - ever possible. Most of the hydrogen supply for refiners now comes from three locations: the refinery hydrogen plant, which is typically an SMR unit; the catalytic reformer (CR), which produces hydrogen as a byproduct of its reaction;

and third-party-produced hydrogen via pipeline or other transportations meth - ods. To reduce the need for hydrogen from those sources, refineries look to their ROG streams for economically recoverable hydrogen. Gas separation options Hydrogen separation membranes have been utilised in refinery operations since the 1980s but have remained niche in their application due to the lim - itations of legacy membrane technol - ogy. Divigas has developed the Divi-H membrane, a polymeric hollow-fibre membrane capable of separation and purification of hydrogen even in extreme environments. Unlike legacy technologies, Divi-H excels at separa - tion of hydrogen from CO₂.

Modern refineries have adapted to meet ever more stringent environmental requirements for fuel specifications

Gas 2024