CFD-Based Safety Assessment of a Novel Concept of a CNG Ship

The GASVESSEL project aims to prove the techno-economic feasibility of a new CNG (Compressed Natural Gas) transport concept, enabled by a novel patented Pressure Vessel manufacturing technology and a new conceptual ship design including safe on- and off-loading solution. This article describes the CFD models that have been defined for a preliminary safety assessment on the ship. Analytical models and numerical simulations were used in order to have a better understanding of the problem and give to the partners of the project the indications necessary to identify the proper solutions to improve safety on the ship. First, a possible gas leakage in the hold is analyzed, considering all side effects caused by the low temperature exposure, and a CFD study on the flow through a small crack with a high pressure differential is studied. Then the focus is moved to the compressor room, where different ventilation solutions are analyzed to reduce explosion risks in case of gas dispersion and to allow partners to understand which one best suits the requirements. Finally, an emergency vent mast system, that is activated in case of critical gas dispersion to evacuate the gas from the hold, is analyzed. In particular, the aim is to determine if the gas cloud will impact the exhaust chimneys at the ship's stern or the accommodations at the ship's bow.

Initial Design and Analysis of a Compressed Natural Gas Transport System

Offloading hoses/flexible pipes are used to transfer compressed natural gas (CNG) from an intermediate floating storage and offloading unit (FSO) to CNG vessel (GASVESSEL). The floating hoses are subjected to environmental loads that are mainly waves, current, and vessel motions from both the FSO and the CNG vessel. Preliminary design of loading/unloading system and dynamic positioning system has been performed. Dynamic analysis of the loading/offloading hose and positioning analysis of the FSO and CNG vessel have been carried out numerically in this study. It is verified that the designed loading/unloading system and positioning system of the two vessels (FSO and CNG vessel) are able to operate safely under the sea-state Hs = 6 m within the defined ESD1 zone.

Planning natural gas networks and storage in emerging countries – an application to Brazil

Some emerging countries, such as Brazil, have large remaining natural gas resources but relatively poor infrastructure to monetize it. When most of the natural gas extraction derives from associated gas, this results in high reinjection rates in production fields combined with fuel imports also to deal with an increasingly variable demand. This study test the hypothesis that modeling the natural gas transportation network expansion with Underground gas Storage (UGS) is crucial, as UGS can reduce transportation costs by better fitting natural gas supply and demand. Without UGS chances are that network expansion will be based in oversized pipelines, or pipelines often challenged by peaking demands. Therefore, this study emulated a real natural gas transport network in a thermo-hydraulic model, aiming at diagnosing its bottlenecks mainly caused by demand intermittency, and pointing out infrastructure solutions. Findings indicated the design of UGS associated with new pipelines as a problem-solver for network bottlenecks, under a least-cost approach. This option reduced idleness and lowered gas transmission costs by 60%. In addition, it increased the network operation reliability and created a virtuous cycle, where a better planning reduces the gas tariffs and spur infrastructure expansion by raising the fuel competitiveness.

Energy-Saving Control Algorithms of Electrically Driven Aggregates of Gas Transportation Technological Installations

Optimal principles of energy efficient management of natural gas transport using electric drive units along gas pipelines based on the existing regulatory and technical documentation are considered. The methodologi-cal basis of the control principles is the apparatus of the theory of experiment planning and invariant systems using strategies of low-population technologies and intelligent electric drive systems. The scheme and modern technical means of frequency-controlled electric drives and algorithms for optimal control of the main techno-logical units of compressor stations of the main gas transportation are presented, which ensure the stabiliza-tion of the parameters of the pumped gas at the optimal level.

Automated Error Identification During Nondestructive Testing of Pipelines for Strength

The United States Pipeline and Hazardous Materials Safety Administration (PHMSA) recently revised the federal rules governing natural gas transport. PHMSA added a new section on the verification of pipeline material properties for pipeline assets with insufficient or incomplete records. This section permits the use of nondestructive examination (NDE) technologies to estimate material properties, which include yield strength (YS) and ultimate tensile strength (UTS), if several conditions are satisfied. These include that NDE measurement accuracy and uncertainty be conservatively accounted for, that the NDE technology be validated by experts, and that proper calibration procedures be implemented. One such NDE technology is Instrumented Indentation Testing (IIT), which can be used to estimate YS and UTS. Precise quantification of any NDE technology’s precision and accuracy requires consistent identification of test errors: if an error occurs during a measurement such that the data should be excluded from subsequent analyses, analysts need to be alerted to the data characteristics prior to including these results. These testing errors are distinct from the inherent measurement uncertainty due to both random error and systematic error. Any NDE measurement will contain some degree of uncertainty; however, faulty measurements exhibiting clearly identifiable errors must be excluded from subsequent analyses to maintain the integrity of the data set. Accordingly, this paper extends Pacific Gas and Electric’s (PG&E’s) previously reported efforts on IIT uncertainty quantification by presenting observations of a specific type of IIT error related to tool fixturing that has occurred during in-situ testing and describing the characteristics of how this error was exhibited in the test data. Once this test error was clearly identified, isolated, and was found repeatable; pre-processing algorithms were adapted to detect and alert NDE technicians to this error during testing, ultimately evolving NDE work procedures. This paper discusses this process from the initial recognition of a test error, to the adaptation of appropriate detection algorithms, and then finally to resulting revisions in operator procedures. Ultimately, these modifications have improved validation data quality and reduced the error rate of IIT measurements collected in the field.

H2 in an Existing Natural Gas Pipeline

N.V. Nederlandse Gasunie (Gasunie) has converted an existing gas transmission line from transporting natural gas to transporting a mixture of gaseous hydrogen and 30% to 0% methane. To enable this, an assessment was carried out on technical safety, process safety, work safety and external safety. The pipeline, with two valve stations, was constructed in 1996 according to applicable Dutch regulations and actively managed in accordance with Gasunie company standards. The pipeline was evaluated for hydrogen transportation and, based on the following measures, this was seen as being feasible: - The water dew point of the feed must not exceed −8° C; - The pipeline must be separated from the natural gas transport system; - Blowdown must be performed either at the site of the supplier or the user of the hydrogen; - Gas measurement equipment, personal safety and leak detection must be suitable for hydrogen; - Due to the assignment of hydrogen as a chemical agent, the safety contour was reduced by performing extra measures, such as additional communication to landowners, additional requirements for the pressure-regulating system and verification of additional settlement and stresses. The operational changes consist of a number of maintenance and management issues: • In-service welding and hot tapping are not allowed; • Equipment suitable for use in gas group IIC (ATEX) must be used; • Emergency and maintenance procedures must be updated to those applicable for pipeline and valve stations containing hydrogen.