Hydrogen Tech World October 2023 | Page 26

[ ammonia ]

energy sources ( RES ), has gained even more relevance .

Therefore , the interest in ‘ green ammonia ’, produced using green hydrogen ( instead of being derived from natural gas via SMR ), is driven both by the need to decarbonize the current ammonia production for its existing uses and by the potential of ammonia to serve as an economically viable carrier for long-distance transportation of green hydrogen .

Transitioning from conventional ammonia to green ammonia presents several challenges . To begin with , it is not as straightforward as merely substituting the hydrogen production process with green hydrogen instead of grey hydrogen to supply the Haber-Bosch ( HB ) plant . The HB process has been optimized for over a century to operate in conjunction with SMR plants , relying heavily on the residual heat generated during the SMR process . Consequently , producing green ammonia requires the electrification of the HB process , which conventionally depends on the residual heat of the SMR process .

Furthermore , the HB process is known to have low flexibility , meaning that it is challenging and timeconsuming to adjust the operational parameters of the process . For example , controlling the mass

flow into the reactor cannot be as rapidly executed as changes in hydrogen production when derived from an electrolyzer connected to RES with an inherently variable production profile . This implies the necessity of incorporating storage and buffer stages between the green hydrogen production phases and the HB inlet itself .

While these technical and economic challenges represent obstacles to overcome , the pressing need to decarbonize ammonia production cannot be ignored . Nonetheless , there is room for optimism regarding future strategies to address these challenges .

Electrified Haber-Bosch process

One key factor driving the development of green ammonia projects is flexibility in both the production process and the energy sources used . Transitioning from the conventional natural-gas fed HB process to green ammonia production through an electrified HB introduces several new challenges as well as opportunities for increased energy efficiency .

The energy consumption of green ammonia production is dominated by hydrogen production . In the HB plant , the compression of inlet gases ( hydrogen and nitrogen ) accounts for the majority of energy consumption , and it is dependent on the pressure of the incoming hydrogen stream . 9 , 11

Electrified Haber-Bosch

Fig . 2 . Typical electrified Haber-Bosch plant configuration

26 Hydrogen Tech World | Issue 12 | October 2023