Large Scale ASU Developments for Oxy-Combustion and Pre-Combustion CO2 Capture Applications

The development of large scale ASU (Air Separation Unit) for oxy-combustion application during the period 2007-2011 was driven by extremely high expectations on the emerging carbon capture, utilization and storage market. All world-class industrial gas companies invested a lot of efforts into development of new ASU concepts for oxyfuel applications. Main target was a considerable reduction in power consumption and capital cost. As a result, a new class of cryogenic processes for production of large amount of gaseous low pressure oxygen with purity of 95-97% was developed.  Some features developed include multi-column and multi-condenser processes for reducing the energy consumption, integration of the compressor heat into the steam cycle, greater operational flexibility of the ASU’s, multi-train compression and air purification systems, and, new concepts for rotating equipment incorporating an axial compression stage to enable better heat integration.

As a result of the above efforts, the ASU-efficiency was considerably increased: the specific power for production of low pressure oxygen was reduced from 0.35-0.4 kWh/nm3 to 0.25-0.3 kWh/nm3. Somewhat unexpected was the minor reduction in ASU cost. It is because these new process concepts were still based on more or less conventional equipment for almost all process subunits like purification, heat exchange, rectification etc. Generally, the ASU cost and the impact of the ASU cost on power plant economics was underestimated during this time.

This rapid development has changed abruptly after in 2011 mainly because of dramatically reduced expectation on oxyfuel CCS market. Cancellation of large scale oxyfuel power plant projects in Jänschwalde in Germany and more recently Futuregen in the US were key contributing factors. Other contributing reasons were the lessons learned from other large oxyfuel projects: namely that the real installed cost of an oxyfuel power plant (not ASU only) are considerably higher than expected. This fact has direct impact on the economics of this application and makes the oxyfuel based CCS opportunity not as attractive as expected. Consequently, all development efforts were reduced to a minimum and no mentionable achievements in terms of power consumption, or any disruptive technical developments were presented during the time between 2012 and 2015. However, during this time a considerable improvement has occurred on the combustion side as well as on flue gas side of the oxyfuel power plant process: the elevated pressure boiler instead of conventional ambient pressure boiler becomes an attractive option because of higher efficiency (+2…3%) and reduced cost. These boiler options are still under development, but may become a competitive solution in the coming years.  These new boiler design developments set the new requirements on ASU process design, which has to be developed in the next years. This development will be probably driven by combination of work done in academic and government institutions, as well as start-ups in addition to the industrial gases industry.

The contribution of industry in next years will be of two kinds: 1) improvements in load range and ramping rate of ASU, because of a lot of background activities in this field, 2) further increase in capacity of single ASU, which helps to reduce the number of required ASU units and improve the economics by economies of scale. For example, the Linde Group was able to realize 5 worldwide largest air separation units in Jamnagar, India, each with oxygen capacity of 5250 tpd, which is now the new benchmark.

This presentation will review the details on the past low pressure oxygen production developments and the expectations for the future high pressure oxygen plant developments.