Decarbonisation Technology - February 2022 Issue

If hydrogen is intended for injection into gas transmission pipelines, producing it at high pressure is a tremendous benefit because a hydrogen compressor after the reformer can be avoided. This reduces both Capex and electrical power demand. This is one of the drivers for the selection of ATRs in proposed Giga-scale projects if an application of the hydrogen is to substitute natural gas to decarbonise domestic cooking and heating applications. Hydrogen from coal gasification also pulls for Giga-scale oxygen supply Beyond natural gas reforming and partial oxidation, coal and petcoke gasification is another Giga-scale pathway to make hydrogen-rich syngas. Gasification, like ATR and POX, requires oxygen. The use of pure oxygen, instead of air, is beneficial for precise control of the oxidation chemistry and avoids costly flue gas de-NOx systems. It also makes the integration of CCS more cost-effective because the system can be much smaller due to the avoidance of processing thousands of tonnes of nitrogen from the air. One of the world’s largest gasification projects will come into operation at Saudi Aramco’s Jazan refinery where more than a dozen gasifiers built by Técnicas Reunidas will produce syngas from heavy refinery residues and petcoke. In total, the gasifiers at Jazan will be capable of producing 2 million normal cubic metres per hour of syngas. At Jazan, the gasifiers will produce enough syngas to generate a total of 4 GW of power and steam. The syngas will be fired directly in gas

energy-dense export products. Oryx has two large ATRs. Each is fed by a large ASU, rated at 3,500 tonnes per day of oxygen. The two ASU cold boxes for Oryx were built by Air Products at Acrefair in Wales. In a similar project, the Escravos GTL facility in Nigeria started up in 2014. It is of a similar configuration to Oryx, and it also uses two Air Products ASUs rated at 3,500 tonnes per day of oxygen. Shell’s Pearl GTL facility was constructed at Ras Laffan in Qatar, close to the Oryx plant, and started up in 2011. It is fed by eight Linde ASUs, each one rated at around 3,500 tonnes per day of oxygen to produce almost 30,000 tonnes per day. In contrast to Oryx, Pearl uses partial oxidation (POX) to convert natural gas to syngas. The use of POX natural gas gasification technology for GTL production was pioneered by Shell in 1993 at Bintulu on the island of Sarawak. At Bintulu, oxygen for the POX gasification reactor is supplied by a 3,200 tonne per day ASU supplied by Air Liquide. Partial oxidation is like autothermal reforming because the reaction takes place in one unit, to which oxygen and natural gas are supplied. But it differs from both the SMR and ATR processes because neither catalyst nor steam are used. When wood, coal, or petcoke are used as feedstock, this process is called ‘gasification’. A subtle difference between the SMR, ATR, and POX processes is the pressure at which they operate. Whilst SMRs typically operate in the range of 15 to 40 bar, ATRs are more comfortable in the 30 to 50 bar range and POX reactors can operate up to 80 bar.

Air Fuel

Oxygen

Feedstock & steam

Feedstock

Flue gas

Syngas

SMR, ATR and POX technologies for hydrogen production from natural gas