Risk Analysis
A risk analysis is a systematic use of available information to identify hazards and to estimate the risk to individuals or populations, property or the environment. In a plant, it can be further separated in at least three levels 71 , depending on how detailed the analysis is to be and the labour resources available, i.e. qualitative methods, semi-quantitative methods, and quantitative methods. During risk analysis, all three levels can be used in sequence. The first methods are used to...
Quantitative Risk Assessment
Risk 107, 2, 242 may be defined as a combination of hazard and probability of hazard occurrence, where hazard is defined as the degree of harm to human beings, property, society or environment. In this sense the risk is defined as a quantitative measured of hazard. In order to estimate the risk a quantitative risk assessments QRA method may be applied. system definition, hazard identification, etc. risk tolerability, analysis of option, etc RISK REDUCTION CONTROL decision making,...
Event Tree Analysis
Having identified a set of top events and estimated their initial frequencies as discussed at the previous section, it is necessary to consider the range of possible consequences that could occur after the original failure, and to estimate the probabilities of alternative outcomes. This can be done with using an event tree analysis ETA . An event tree is a logic diagram in which all of possible outcomes of a single initiating event are described. Immediate Formation Pool ignition of pool...
A Density and Related Measures
Hydrogen has the lowest atomic weight of any substance and therefore has very low density both as a gas and a liquid. Density is measured as the amount of mass contained per unit volume. Density values only have a meaning at a specified temperature and pressure since both of these parameters affect the compactness of the molecular arrangement, especially in a gas. The density of a gas is called its vapour density, and the density of a liquid is called its liquid density. Specific volume is the...
Regulation
TRG 730 Hydrogen filling stations Richtlinie f r das Verfahren der Erlaubnis zum Errichten und zum Betreiben von F llanlagen BImSchG Construction and installations Bundesimmissionsschutzgesetz TRD_Pressure vessel and pipeline Technische Regeln f r Dampfkessel_ Verordnung ber elektrische Anlagen in Kennzeichnung von Rohrleitungen nach dem Verband der Technischen berwachungs- Verband der Elektrotechnik Elektronik Table D-5 The most important legislation for operation of hydrogen vehicles 229...
B Biomass Fermentation
From high moisture content biomass a liquid manure biogas can be produced via methane fermentation. This gas contains high CO and CH4. Although it contains hardly any hydrogen, this gas can be used as a fuel for advanced high temperature fuel cells MCFC , whereby methane reformation takes place directly at the electrode due to the high temperatures 650 C . The fermentation process of biomass is commercially tested and available. The combination of the process for the production of hydrogen has...
Bibliography
1 AIChE CCPS Daw's chemical exposure index guide CEP technical manual, American Institute of Chemical Engineers AIChE , New York, 1994. 2 AIChE CCPS Guidelines for chemical process quantitative risk analysis, Second Edition, American Institute of Chemical Engineers AIChE , New York, 2000 3 AIChE CCPS Guidelines for chemical transportation risk analysis American Institute of Chemical Engineers AIChE , New York, 1995. 4 AIChE CCPS Guidelines for Evaluating the Characteristics of Vapor Cloud...
E TNT Model
The program has three methods for calculating the effects of explosions, i.e. TNT, Multi-Energy, and Baker Strehlow. The study uses TNT method as the program default to calculate explosion impacts from the hydrogen system. Therefore, the appendix discuses this model only. The program calculates the mass of TNT that is equivalent to the effective flammable mass in the cloud 49 where HTNT 4.7 x 106 J kg-1 is the heat of combustion of TNT using up its own oxygen, i.e. without additional oxygen...
Dispersion
Accidental release of gaseous hydrogen or spillage of liquid hydrogen lead to evolution and dispersion of a gas could whose shape is influenced by the type and rate of release and by atmospheric conditions as well as by topography. There are several concentration graphs generated by PHAST, each of which shows a different aspect of the concentration profile for the cloud. These graphs are generated from the source models, and the dispersion report shows the details of the values plotted in the...
Consequences Modelling Results
The consequence analyses that are passed to the impact calculations give the shapes and sizes of the different effect zones. For some impacts the results may be independent of weather conditions. For other impact there is a separate result for each weather condition. For example, the effect zone shape of BLEVE fireball is a circle and is weather independent. Therefore, the effect zone is centred at the release point. This section presents the consequence modelling results for the hydrogen study...
C Causes Of The Accidents
Seven generic cause categories of hydrogen accidents have been defined by Balthasar and Schodel 21 prepared for the hydrogen safety manual for the Commission of the European Communities, as shown in Table C-3. The accident categories were defined based on the hydrogen accident report for the US DOE. Additionally, the causes of the 96 NASA incidents as described in section C. 1.9 are presented in Table C-4. Table C-3 Cause of hydrogen accidents 21 Table C-3 Cause of hydrogen accidents 21 Table...
G Fault Trees
The analytical method for constructions and evaluations of the fault trees is given in Appendix F. The fault trees include two or three sub-fault trees representing the instantaneous and continuous both in liquid and vapour phases release of hydrogen from the containment systems. The sub-fault trees are as follows 1. Instantaneous release of hydrogen from GH2 tank in the production plant G1. 1 2. Continuous release of hydrogen from GH2 tank in the production plant G1.2 3. Instantaneous release...
The Hydrogen Scenarios Considered
Germany, the world fifth largest consumer of energy, depends heavily on energy import to meet energy demand. Nearly all petroleum and about 80 of natural gas used are imported 176 . About one fourth of final energy consumption of the country 1990-1999 is demanded by industry. The traffic sector has nearly 30 followed by households with 28.5 . Small businesses hold a share of 16 of the final energy consumption. The military is below one percent. It is also shown that the energy consumption of...
A Hydrogen Embrittlement
Constant exposure to hydrogen causes a phenomenon known as hydrogen embrittlement HE in many materials. The HE can lead to leakage or catastrophic failures in metal and non- metallic components. The mechanisms that cause HE effects are not well defined 36 . Factors known to influence the rate and severity of HE include hydrogen concentration, hydrogen pressure, temperature, hydrogen purity, type of impurity, stress level, stress rate, metal composition, metal tensile strength, grain size,...
C Redstone Complex Alabama
On October 31, 1980, a hydrogen explosion occurred in an auxiliary building at a test stand complex at the NASA Redstone complex in Alabama. The explosion destroyed two support buildings and severely damaged a large amount of equipment. Fortunately, no one was injured. Gaseous hydrogen leaked into one of the auxiliary buildings from a high pressure hydrogen gas system. The system piping was 88.9 mm 3.5 inch outer diameter, carbon steel of 15.2 mm 0.6 inch wall thickness meant to handle high...
Risk Presentation
Two risk measures were considered to present the risk associated with the hydrogen study objects, i.e. individual and societal risk F-N curve , as described in section 4.6.1. The IR of the hydrogen study objects are presented as risk profiles. To create a risk profile, the triplets of the overall risk in Table 5-32 must be transformed into risk profiles and plotted by means of the CCDF, as described in section 4.6.2.2. The risk is expressed as individual risk depending on distance from the...
The Accident Scenarios
This section describes the possible accident scenarios of the hydrogen objects included in the study. The FMEA method was mainly used to define a list of undesired events that consider all possible breaks or ruptures of items of equipment which would lead to a loss of containment from the hydrogen study objects. The QRA study on hydrogen systems are concerned with flammable properties of liquid, of gas, and the systems have therefore been examined to identify the events which could lead to the...
C LH Accidents in Three Hydrogen Plants
Edeskuty 56 summarizes three hydrogen accidents related to liquid hydrogen LH2 , i.e. 1 minor explosions in a hydrogen vent system, 2 combustion of hydrogen in the open atmosphere, 3 liquid hydrogen dewar storage explosion. In the first accident, several explosions occurred in a liquid hydrogen facility consisting of 15,000 kg of LH2. All of the hydrogen vents were manifolded into a common vent system terminating in a flare stack. During no operation of the system the liquid hydrogen was...
B High Pressure Water Electrolysis
Through a special material choice and optimization, high pressure water electrolysis allows the generation of hydrogen at pressures of up to 5 MPa. The processes under development attempt to find an appropriate capacity optimization that will also allow a problem free connection of the electrolyser with a fluctuating current supply e.g. Wind or PV connection for isolated plants . A development work to mention is that being carried out by GHW Gesellschaft f r Hochleistungswasserelektrolyse for...
Consequence Modelling
Once the initiating event is defined, source models are selected to describe how materials are discharged from the process. The source model provides a description of the rate of discharge, the total quantity discharged or total time of discharge , and the state of the discharge, that is, liquid, vapour or a combination. A dispersion model is subsequently used to describe how the material is transported downwind and dispersed to some concentration levels. If there is an immediate fire or...
Hydrogen Energy Cycle
Conceptually, the purpose of a hydrogen energy economy can be categorized as the 1 production, 2 storage and transport, and 3 use of hydrogen. Some applications may involve all three categories. Figure 2.3 illustrates a structure of an energy supply system for an industrialized country e.g. Germany with import clean hydrogen i.e. hydrogen energy economy , proposed by Winter and Nitsch 200 . In the system, hydrogen is fed into the supply system in a similar way as today natural gas. In the case...
B Coal Gasification
Coal gasification is defined as a process, in which coal is converted to gaseous products. When coal is fed into a gasification reactor and heated up, it mainly undergoes pyrolysis reactions in which gases, volatile tar components and char are formed see Fig. B.3 . Coal gasification is generally done with oxygen of 95 purity, at high temperatures and elevated pressures. It is used for the production of hydrogen or hydrogen-rich gas products. Gasification reactions are Basically, all types of...
B PRODUCTION FROM FOSSIL FUELS B Steam Reforming of Natural Gas
Steam reforming refers to the endothermic, catalytic conversion of light hydrocarbons Methane to Gasoline with water vapour. A simplified basic flow diagram of the conventional steam reforming process is shown in Figure B.1. Industrial scale processes of this kind are normally carried out at temperatures of 850 C and pressures in the order of 25 bar, according to CnHm n H20 - gt n CO n m 2 H2. Exothermic catalytic conversion shift reaction of the resulting carbon monoxide produces pure hydrogen...
Fire and Explosions
PHAST automatically generates the existing fires and explosions models as long as the material is flammable. This section presents a summary of the consequence calculation results for the study objects presented both in the form of tables and graphs. Each of the models is presented by two graphs and a table, each of which shows thermal or overpressure impacts from different study objects. The first graph shows thermal radiation or peak overpressure levels vs downwind distances, and the second...
A Cold Embrittlement
Hydrogen in liquid phase LH2 is classified as a cryogenic liquid. The cryogenic temperature can affect structural materials. With decreasing temperature, ultimate stress and yield stress increase for most metals, generally connected with a corresponding drop in fracture toughness which is a measure of the material's ability to resist crack propagation. The lower the toughness, the smaller is the tolerable crack length. A material can change from ductile to brittle behaviour as soon as the...
F Determination of Minimal Cut Sets by Analytical Methods
The analytical method uses Boolean algebra operations in order to transform a fault tree into minimal cut sets. In contrast to the simulation methods, it does not require information on component failure behaviour 242 . This is only needed for calculating the failure probability of the system. It finds all minimal cut sets of a system. In order to avoid difficulties with computer capacity, a cut-off criterion must be applied 242 . Basically two approaches may be used in the method, i.e. the...
Hydrogen Standards Codes and Regulations
Development of hydrogen codes, standards, and regulations are essential when hydrogen becomes a significant energy carrier because they are required to establish a market-receptive environment for commercializing hydrogen-based products and systems. Several studies on hydrogen safety as well as expert opinions stated that hydrogen's safety has been shown to be on a par with the current fuels when proper regulations, codes and standards, and best practices are followed. Tables of codes,...
Households Scenarios
The Federal Republic of Germany is a densely populated country with approximately 83 million inhabitants 2003 , which corresponds to a population density of 230 persons per square kilometres. The Federal Republic of Germany is characterized already today as an industrialized country with having a low number of young people. The population development shows that in a few years there will be more people aged 65 years than aged 15 years or less. Low numbers of births and a declining propensity to...
B Partial Oxidation of Heavy Oil
As steam reforming is not applicable to convert hydrocarbons heavier than naphtha to hydrogen, partial oxidation of heavier feedstock is used to produce hydrogen. A simplified flow diagram of the process is shown in Figure B.2. The process basically proceeds at moderately high pressure with or without a catalyst, depending on the raw material and process selected. The catalytic partial oxidation which occurs at 600oC, uses feedstock ranging from methane to naphtha. The non-catalytic partial...
Fig Steam reforming process [ Hydrogen Storage and Transportation
2.3.2.1 Compression and Liquefaction Packaging Hydrogen still requires further preparation according to the demands of the intended end use. Firstly, cleaning of the hydrogen is required in order to ensure that the required quality is met. Following this it must be compressed, whereby the pressure level is dependent on either the end application or the intermediate storage method. Alternatively, liquefaction may be the reasonable option if transport over long distances is required or if the end...
Hydrogen Pipeline GH
The expected frequency of the GH2 pipeline is estimated from the base failure rate for the pipelines given in Table 4-5. It allows one to focus on the likelihood of holes and ruptures. These rates now need to be adjusted to the increased wall thickness used for this pipeline as compared to the typical wall thickness for this diameter. Table 5-22 shows reduction factors of the failure rates for pipe rupture and holes recommended by 3 . The factors were judged based on the benefits of increased...
D The Eu Regulations
Table D-2 EU Directives for hydrogen filling station and other infrastructures 225, 226 _ Directive Regulated Aspects descriptions 97 23 EC PED Pressure Equipment Directive 94 9 EC ATEX directive - Concerning equipment and protective systems intended for ATEX use in potentially explosive atmospheres relevant for manufacturers of hydrogen equipment and applications 1999 92 EC ATEX directive - Minimum requirements for improving EU Protection of ATEX Workers in Explosive Atmospheres relevant for...
System Description
The station is designed to provide hydrogen as fuel for transportation purposes both in liquid LH2 and compressed gaseous CGH2 form. The CGH2 is required for a BVG city bus operated on a regular route in Berlin. On the study visit the station was not used to deliver LH2 to any vehicle, and all the hydrogen was converted into CGH2. The station stores hydrogen in liquid LH2 form -253 C, 0.8 MPa , and delivers it in the form of CGH2 to a hydrogen storage at vehicles at 25 MPa and 15 C 228 . Figure...
Outline Of The Study Objects
A key of precondition for the realisation of a hydrogen economy is the development of a hydrogen infrastructure which, by definition, includes the systems needed to produce hydrogen, to store it, and to deliver it to users. As discussed in Section 2.3, in order to realize the hydrogen energy economy in Germany, the required clean hydrogen may be imported from other countries 200, 201,168 . For example, the Euro-Quebec Hydro-Hydrogen Pilot Project, 1989-2001 EQHHPP considered to import hydrogen...
F FAULT TREE ANALYSIS F Fault Tree Basics [
Any accident starts with an initiating event, often the failure of an operational component. In order to counter-act this, a technical system usually disposes of a protective amp safety systems made up of stand-by components. These are normally capable of coping with the major part of initiating events and may be considered as barriers between those and the undesired events. The undesired events only occur if these barriers fail. If components from several barriers have to fail for the...
Fault Tree Analysis
Fault tree analysis FTA 86, 42, 107 is an analytical tool that uses deductive reasoning to determine the occurrence of an undesired event called Top Event . The FTA, along with component failure data and human reliability data, can enable determination of the frequency of occurrence of an accidental event. It yields both qualitative as well as quantitative information. A logical relationship between Top events and the corresponding contributory events are conveniently represented as a 'fault...
Hydrogen Energetic Applications
Hydrogen has many potential energy uses, including powering non-polluting vehicles, heating homes, and fueling aircraft. Energetic applications of hydrogen can be classified into two main categories, i.e. direct combustion e.g. internal combustion engine and fuel cells. An internal combustion engine ICE transforms chemical energy contained in a fuel into mechanical energy through combustion in a piston or rotary engine. Modified ICE can utilize hydrogen in place of gasoline. Optimized hydrogen...
The LH Storage 1
The liquid hydrogen LH2 storage system is a cryogenic, double wall type, and vacuum super-insulated tank. It consists of an inner vessel of cryogenic chromium-nickel steel to hold liquid hydrogen at a temperature of -253 C and pressure of 0.8 MPa, and a supporting outer vessel of carbon steel. The space between the inner and the outer vessels is under vacuum and super-insulated with perlite. Fig. 3.11 shows a simplified piping and instrumentation diagram P amp ID of the LH2 tank installed at...
Storage at Depot LH
Similar to the previous object 5.3.1 the expected frequency of the accident scenarios considered for the LH2 storage at the hydrogen filling station was synthesised from the component failure data associated with each of the identified failure modes, using the FTA approach. The accident scenarios considered for the study objects can be classified into two TOP events, i.e. instantaneous and continuous. Additionally, the continuous release scenario includes hydrogen release both in the liquid and...
Impact Models
The source models generate a variety of outcomes that are caused by release of hazardous material or energy. The dispersion models estimate concentrations and or doses of dispersed vapour. The explosion models estimate shock wave overpressures and fragment velocities, and fire models predict radiant flux generated from the outcomes. These models rely on the general principle that the severity of the outcome is a function of distance from the source of release. The next step in the QRA is to...
Risk Acceptance Criteria
There is no zero risk situations. All actions, decisions or situations involve some level of risk, though in most cases the risk is very low. Very low or reasonable risk is considered to be acceptable. Many regulatory frameworks require the management of risk to a level that is reasonable but fall short of defining the specific criteria for major unwanted events. In many risk assessments it may be necessary to determine the level of acceptable risk during the Scoping process. The criteria must...
Hydrogen Private Car
Size of little fuel cells technologies and internal combustion engines are today implemented. They showed excellent performance and safety in hydrogen city buses as well as in private cars. For example, BMW has successfully demonstrated hydrogen private cars e.g. BMW 753i for the past five or more years, since 1990 51 . Hydrogen fuel in the vehicle can be stored in gaseous form compressed gas , as a liquid -253 C , or in solid media. A cryogenic hydrogen LH2 storage for vehicles offers great...
The GH storage
The high-pressure hydrogen tank of the plant stores the largest hydrogen inventory of 5000 Nm3 compared to other components. It may be the largest contributor to societal risk as assessed in this study. Therefore, the study is focused on the two horizontal cylindrical high-pressure hydrogen storages Fig. 3.4 with an operating pressure of 3 MPa at ambient temperature. The tank is filled directly from the water electrolysis in the plant generated from the two low-pressure electrolyzers requiring...
E Pool Spreading and Vaporization Models
Immediately after release, the liquid hydrogen spreads out on the ground. It will spread until it meets an artificial boundary such as a dyke, until it reaches a minimum depth at which no longer spreads, or until the evaporation rate is equal to the release rate so that the amount of liquid in the pool is no longer increasing. Also immediately after release, the liquid hydrogen starts to boil off as it absorbs heat from the atmosphere, the ground and possibly from the sun. Mass is also lost...
Road Tanker Truck LH
Similar to the onboard storage in the passenger car, the overall failure frequencies of the LH2 tanker truck was derived from the traffic accident data. Table 5-16 shows that the accident rate of a road transport by truck in Germany is about 1.6 x 10-7 veh.km. As for comparison the truck accident rates average values for California, Illinois, and Michigan are 1.5 x 10-6 veh.km for rural area and 5.8 x 10-6 veh.km for urban area see Table 4-2 . As described in the section 3.4.2, the study...
E Jet fire
There are two jet fire models available in the PHAST, i.e. API and Shell models. The Shell method treats the flame as a tilted cone frustum, whereas the API model treats it as a banana-shaped plume i.e. tapered at the ends, and bent by the wind. The study uses API model to calculate thermal impacts resulted from jet fires. Therefore, only the API model to be discussed in the appendix. Fig. E.5 Shape of API RP521 Jet fire 49 Fig. E.5 Shape of API RP521 Jet fire 49 The flame is a jet that may be...
Acknowledgments
This dissertation was completed during my work as a research assistant at Department of Process Design and Safety, the Institute of Process Equipment and Environmental Engineering, the Faculty of Process and Systems Engineering, the Otto-von-Guericke-University Magdeburg, Germany, in the period of February 2002 to March 2006. Foremost I would like to express my deep gratitude to the head of the department, Prof. Dr.-Ing. Ulrich Hauptmanns. He gave me suggestions to this work and opportunity to...
y x ZZk Z Z Z KJ Lk kL
An upper bound of the occurrence probability of the system is equal to the expectation of the first term on the right side of the Eq.3, a lower to that of the first two terms, a close upper if the three terms are evaluated, etc. Since the used probabilities are usually small numbers, in most cases the evaluation of the upper bound is a satisfactory approximation to the true result. If initiating events are taken into account, the Eq. 3 is evaluated for each of them separately using...
Hydrogen Storage at Depot
The study considered the large-scale liquid hydrogen storage as depot , having a capacity of 270 m3 270,000 litres , and situated in Ingolstadt. It is used to store hydrogen in the liquid phase 16,000 kg of LH2 at temperature of -253 C and pressure of 1.3 bar Section 3.4 . The hydrogen plant is subjected to the accident regulation of German Storfallverordnung 78 . The hydrogen storage has a maximum liquid inventory of 16 tons, which is more than the quantity thresholds Section 5.1 . Therefore...
C Hanau Accidents
In October 1991, the Heraeus Quarzglas company, an optical fiber production firm in Hanau, Germany, suffered a hydrogen vapor cloud explosion. A 100 m3 storage tank containing 370 kg of hydrogen gas burst about 35 minutes after being refilled. The following vapor cloud explosion caused property damage and fortunately only a few personnel injuries. The tank had suffered a structural failure. Investigation revealed that the tank had been modified to position it vertically. Tank welds experienced...