Chapter Summary And Outlook

Hydrogen was considered as a candidate energy carrier for the delivery of energy to the public and industry. As a storage medium for energy, hydrogen fulfils several requirements concurrently, proving to be the most environmentally friendly energy carrier. Moreover, hydrogen's special characteristics render it the ideal storage medium for electricity generated from renewable energy sources, making it the most important link in a sustainable energy value chain, which is completely emission free from beginning to end. Unfortunately, the public's first response to the proliferation hydrogen fuel is not associated with the hydrogen's environmental benefits but instead focuses on the safety issues and hydrogen's dubious association with the Hindenburg disaster. Before regulations and the market drive hydrogen to the fuel of chose, the safety issues must be systematically addressed and interdisciplinary techniques defined for application.

Hydrogen has a long history of safe use in the chemical, manufacturing, and utility industries, which are predominantly operated by highly trained people. However, as a large-scale energy carrier in the hands of the general public, where untrained people will deal with hydrogen, it may create safety issues in the society. To make hydrogen available at a large-scale as an energy carrier, an infrastructure covering the following steps must be built up: production, transportation, storage, filling station, and end-use. The technical installations used could fail, and the possibility of handling incidents may occur in many places. Therefore it is reasonable to determine the safety technological conditions and associated operating procedures for the realization of the hydrogen infrastructure at an early stage. This is the goal of the present work in which system-analytic methods, called "quantitative risk assessment (QRA)", are used to evaluate the risks, to identify possible weak points, and to make suggestions for improvement quantitatively. The QRA mainly consists of probabilistic safety analysis, consequences analysis, and risk estimation. Results of the study are presented in the form of individual risk and societal risk.

The QRA study was carried out for seven hydrogen study objects which may represent the hydrogen energy cycle. Total numbers of installation in a study object where a safety evaluation has to be made can be very large. Since not all installations contribute significantly to the risk, it is not worthwhile to include all installations in the QRA study. The QRA may be carried out if the hydrogen is thought to be present at a location (e.g. stationary establishment and transportation routes) in amount that can endanger the environment. The study was focused on hydrogen storages and transports of the objects where the largest hydrogen inventory is available most of the time. The hydrogen study storages include hydrogen storage at production plant, depot (liquefaction plant), filling station, vehicle, and CHP for households. The hydrogen transports include a road tanker truck and hydrogen pipeline.

Accident scenario of the hydrogen cycle is mainly initiated with release events, called "loss of containments events (LOCs)" It includes continuous and instantaneous release. The results showed that a continuous release mostly dominates the accident which is accounted for about 94% and instantaneous (accounted for 6%). The instantaneous release mainly results from a catastrophic failure of tank storage (e.g. tank rupture), and releases all the inventory. The main contributor to the tank rupture is tank overpressure (which accounted for about 50%), it is followed by external events, and spontaneous events. In case of LH2, an additional incident may contribute to the tank rupture, i.e. tank under-pressure (excessively low pressure) with a contribution of about 30%.

Fires and explosions are the two accident outcomes resulting from a hydrogen release in the present of ignition sources. The results showed that the fires mostly dominate the accidents which account for about 60%, explosion of 5%, and the rest (35%) has no effect (harmless) to the environment.

According to the existing standards (e.g. ALARP criteria) the individual risk for both hydrogen storages and transportations run almost entirely in the unacceptability zone. The societal risk level, however, appears globally lower than the individual one. In fact, also the curves relevant to hydrogen transportations and GH2 storage fall well in the acceptable of the UK ALARP zone. However, assuming the limits proposed by Dutch regulations, different in slope and more severe than the U.K. ones, the curves fall within the ALARA zone. Meanwhile, the F-N curves for the LH2 storages fall well within UK ALARP zone and upper the risk acceptance curve of the Dutch ALARA. According to the ALARP principles, for scenarios with risk levels below the acceptable curve no measures to reduce the risk are required. For scenarios with risk level (that lie) between these lines the risk should be reduced if practical. Should the plants be implemented for the public, the risk must be reduced as far as reasonable and practicable, typically subject to cost benefit analysis. For scenarios with risk levels above the upper curve, measures to reduce the risk must be implemented.

Aside from which risk criteria selected the hydrogen objects are comparable to those of LPG objects. Although, the individual risks of hydrogen storage objects seems to be higher than those of LPG, but the maximum effect distances of the hydrogen objects are smaller. In fact, hydrogen poses less consequence than LPG. The large effect distance for hydrogen, especially flash fires are caused by the large energy density and wider ranges of the flammability limit of hydrogen. The societal risks (F-N curves) of all hydrogen objects are lower than that those of LPG. The fire and explosion risks for hydrogen objects are at short distances comparable with those for LPG, but the effect distances for the worst events are smaller. One should remember that equally sized hydrogen and LPG tanks are considered: the latter has much higher energy content per volume.

In order to avoid the greatest potential impacts to the nearby population some failure modes leading to the tank rupture should be avoided. These include tank overpressure, underpressure (for LH2 case only), and spontaneous events (e.g. hydrogen embrittlement, fatigue, ect). Tank overfilling involving human error may greatly contribution to the tank overpressure. An adequate operating procedure and operator training shall be established for the hydrogen public facilities. In case of LH2, loss of vacuum may also contribute to the tank overpressure. Additional safeguards against this event (i.e. vacuum breaker connected to Nitrogen supply) may be considered. Some events like a significant volume of sub-cooled LH2 added and excess withdrawal rates may be considered as initiating event of tank underpressure. Safeguards against these events (such as withdrawal protection, pressure building circuits) shall be high reliability. The best material selection and adequate design of the hydrogen tank should be considered in development of the hydrogen infrastructure, to avoid any spontaneous events such as hydrogen embrittlement, cold embrittlement (LH2 case only), fatigue, etc, that may lead to tank rupture.

Tank leak or piping rupture may result in a continuous release or spillage of the hydrogen content. Protective measures against this scenario should be considered. In case of piping rupture, an emergency shutoff device (ESD) may be remotely or automatically operated should be considered to stop flow of the release. Hand operated valves may not possible to protect this event.

The hydrogen economy has enormous societal and technical appeal as a potential solution to the fundamental energy concerns of abundant supply and minimal environmental impact. The ultimate success of a hydrogen economy depends on how the market reacts. Although the market will ultimately drive the hydrogen economy, government plays a key role in the move from fossil fuel to hydrogen technology. The investments in R&D are large, the outcome for specific, promising approaches is uncertain, and the payoff is often beyond the market's time horizon. Thus, early government investments in establishing goals, providing research support, and sharing risk are necessary to prime the emergence of a vibrant, market driven hydrogen economy.

The public acceptance of hydrogen depends not only on its practical and commercial appeal, but also on its record of safety in widespread use. The special flammability, buoyancy, and permeability of hydrogen present challenges to its safe use that is different from, those of other energy carriers. Another key to public acceptance of hydrogen is the development of safety standards and practices that are widely known and routinely used like those for self service gasoline stations or plug-in electrical appliances. The technical and educational components of this aspect of the hydrogen economy need careful attention.

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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