(80d) Evaluation of Helium Extraction Technologies While Considering Optimization and Integration with Nitrogen Rejection

Helium is a widely used component in MRI scanners, aerospace and aircraft manufacturing, industrial-leak detection systems, electronics and fiber optics fabrication, welding, nuclear industry and research facilities. It is the second most abundant element in the universe after hydrogen. However, due to its light weight, it easily escapes gravity and is exceedingly scarce in the Earth. Although the Earth’s atmosphere is the main terrestrial inventory of helium, it has been widely concluded that extracting helium from the air is not viable due to its very low concentration of 5 ppm. Hence, the only economical helium source is natural gas (NG) reserves with 0.3 to 2 mol% in so-called helium-rich NG fields and as high as 8 mol% in some fields. The USA is so far the world’s leading helium supplier with a share of nearly 55% in 2016, followed by Qatar (33%), Algeria (6%), Australia (3%), Russia (2%) and Poland (1%). Helium is marketed in two specifications: crude helium (50-70 mol%) and purified helium (>99.99 mol%).

The extraction of helium from natural gas typically requires four processing steps. The first step is to remove the typical impurities in the gas, namely acid gases, water, and mercury. The second step involves the extraction of heavier hydrocarbons. The third step is nitrogen rejection, which separates a mixture of nitrogen and helium from the product gas. The final step is to recover helium (crude or upgraded [>90 mol%]) from the nitrogen-rich stream, which can be either a cryogenic distillation-based or a membrane-based process. The upgraded helium is then purified to 99.99 mol% helium using pressure swing adsorption (PSA).

Most NG reserves with high helium contents have much nitrogen. This is why both nitrogen rejection and helium extraction are required simultaneously. Thus, there is a strong incentive to integrate them in order to reduce the cost of helium. Several articles (Hamedi et al., 2018; MacKenzie et al., 2002; Rufford et al., 2012) compare the performance of a standalone NRU (Nitrogen Rejection Unit). However, an attempt to examine its integration with a cryogenic distillation-based HeXU (Helium Extraction Unit) is missing in the literature. Alders et al. (2017) compared cryogenic distillation with membrane separation for helium extraction from an NRU. However, they used a hypothetical simulation for NRU to derive the feed to HeXU. In other words, there was no real integration between NRU and HeXU and no optimization.

This study proposes two integrated HeXU and NRU processes, one based on cryogenic distillation and the other based on membrane separation. Then, it optimizes each integrated process using Particle Swarm Optimization (PSO) for minimum power consumption. The optimization is done for various scenarios such as crude helium, upgraded helium, and low versus high pressure nitrogen product. The optimum process solutions are then compared economically to derive a comprehensive map for selecting the right technology for helium extraction. The results show that when the nitrogen is considered effluent and released into the atmosphere, the cryogenic distillation technology outperforms the membrane system due to the significant advantages in both power consumption and capital costs. The cryogenic process can reduce power consumption by 10-40%. In contrast, when the nitrogen product is needed at high pressure and the helium concentration is not very small in the HeXU feed, the MBHeXU consumes less energy compared with the CDBHeXU (maximum 5% reduction). However, it still accounts for higher capital costs compared to cryogenic distillation separation due to a more expensive compression system.

Alders, M., Winterhalder, D., Wessling, M., 2017. Helium recovery using membrane processes. Separation and Purification Technology, 189, 433-440. doi:10.1016/j.seppur.2017.07.084

Hamedi, H., Karimi, I. A., Gundersen, T., 2018. Optimal cryogenic processes for nitrogen rejection from natural gas. Computers and Chemical Engineering, 112, 101-111. doi:10.1016/j.compchemeng.2018.02.006

MacKenzie, D., Cheta, I., Burns, D., 2002. Removing nitrogen. Hydrocarbon Engineering, 7(11), 57-63.

Rufford, T. E., Smart, S., Watson, G. C. Y., Graham, B. F., Boxall, J., Diniz da Costa, J. C., May, E. F., 2012. The removal of CO2 and N2 from natural gas: A review of conventional and emerging process technologies. Journal of Petroleum Science and Engineering, 94-95, 123-154. doi:10.1016/j.petrol.2012.06.016