# Petroleum Sector-Driven Roadmap for Future Hydrogen Economy
## 2 Hydrogen Technology: How to Produce, Transport, and Store  
The production, storage, and transport of blue hydrogen is presented in this section. The main five steps in the process include production via steam reforming, carbon capture and storage, transportation in pipelines, daily/seasonal storage, and industrial applications [14]. Researchers have discussed major hydrogen production methods including both the conventional and renewable approaches, along with the technical and economic aspects [18; 19; 20; 21; 22]. These official classifications are based on the production process of hydrogen [23]. [PERSON] and [PERSON] provide an overview of the methods that produce hydrogen from fossil fuels as well as renewable energy sources [18]. [PERSON] and [PERSON] have assessed them for environmental impact perspectives, including the social cost of carbon concept, economic factors, and energy and exergy efficiency [19]. [PERSON] and [PERSON] [20] and [PERSON] [22] have specifically given an overview of the state-of-the-art hydrogen production technologies using renewable and sustainable energy resources, such as supercritical water gasification (SCWG) of biomass and nuclear energy and from energy recovery processes, respectively. The main portion of hydrogen today is produced via methane (CH\({}_{4}\)) reforming, so-called 'grey hydrogen' because of its natural gas origin and the release of CO\({}_{2}\) in the atmosphere. The cost range of this type of hydrogen is \(\xi\)1.5/kg which depends on the price of gas and carbon emissions [23]. According to the literature, steam conversion of one ton of CH\({}_{4}\) releases about four tons of carbon dioxide into the atmosphere. In case the CO\({}_{2}\) is captured and stored using CCS technology [21], the produced hydrogen is then labeled 'blue hydrogen'. Both steam methane reforming (SMR) and auto thermal reforming (ATR) have acceptable technology readiness levels (TRL) and have considerable market share potential for the production of blue hydrogen and have almost the same route in which natural gas reacts with hot steam leading to the production of syngas. The process consists of natural gas pre-treatment, pre-reforming, reforming, water-gas-shift reaction, and hydrogen separation [24; 25]. The sizes of SMR and ATR plants vary in a range of 15,000-300,000 nm\({}^{3}\)/h [14]. The process flow of blue hydrogen at the system level is briefly shown in Figure 1[21]. Syngas production, separation technologies, advanced hydrogen production with CO\({}_{2}\) capture, and outlook on production and use of hydrogen in a CCS context have been particularly discussed by [PERSON] et al. [21]. 'Green hydrogen', however, is produced via an electrolysis process by converting electricity generated from renewable energy (e.g., wind and solar) into hydrogen, which can be stored in large tanks and released when/if needed. The cost range of this type of hydrogen is \(\copy 2.5\)-\(5.5\)/kg. No GHG is emitted during the process of green hydrogen [23]. As a matter of fact, it will contribute to coping with intermittent electrical power from wind, solar, and other renewable sources. The green hydrogen concept (i.e., Power to Gas, P2G) is shown in Figure 2[26]. For a smooth transition to a hydrogen economy, an interconnection between hydrogen production units and industrial applications is needed. This downstream conversion enables hydrogen implementation, however parallel policy is also required to guarantee the integration of green hydrogen and the phasing out of blue hydrogen in the upcoming decades [14]. In addition, social acceptance for fossil fuel usage along with CCS and hydrogen transport is crucial for successful implementation of blue hydrogen projects. As shown in Figure 1, CO\({}_{2}\) as a by-product of natural gas reforming can be captured and stored, and then the blue hydrogen chain can be climate-neutral despite relying on hydrocarbon.