Investigation of the gas losses in transmission networks

As air pollution has become a major issue in nowadays world, reducing methane emissions from the natural gas transmission systems is an issue that definitely has to be addressed. In order to do that, there are a few solutions available, such as the replacement of steel pipes with high-density polyethylene (HDPE) pipes. The main causes of these leaks are the corrosion defects and third-party interventions. The paper presents a new methodology for technological gas loss calculation from the natural gas transmission system. In order to obtain the most accurate calculation formulas, the flow coefficients for different cases were determined by experimental measurements. The paper presents the details regarding the construction and equipment of the experimental stand, as well as a new method for calculating the volumes of gas lost due to defects of this type. Thus, the aerial and buried defects were studied and the results obtained on statistical data were verified. Using the results of the study, the average emission of CH4 per year in Romania was calculated, and it was proven to be about 30% bigger than the European average. The findings of this study can help for a better understanding of the level of the losses and the effect on the final costs for the population, as well as the negative impact on the environment, in case the transporter does not take any measures.

Efficiency Enhancement of Gas Turbine Systems with Air Injection Driven by Natural Gas Turboexpanders

The fuel source of many simple and combined-cycle power plants usually comes from a nearby natural gas transmission pipeline at a pressure from 50 to over 70 bar. The use of a turboexpander instead of throttling equipment offers a promising alternative to regulate the pressure of natural gas introduced to the power plant. Specifically, it helps recover part of the available energy of the compressed gas in the transmission pipeline, increase the power output and efficiency of the gas turbine system, and decrease the fuel use and harmful emissions. In this paper, the addition of such a turboexpander in a gas pressure-reduction station is studied. The recovered power is then used to drive the compression of extra air added to the combustion chamber of a heavy-duty gas turbine. The performance of this configuration is analyzed for a wide range of ambient temperatures using energy and exergy analyses. Fuel energy recovered in this way increases the output power and the efficiency of the gas turbine system by a minimum of 2.5 MW and 0.25%, respectively. The exergy efficiency of the gas turbine system increases by approximately 0.36% and the annual CO2 emissions decrease by 1.3% per MW.

Pressure-Based Energy Storage in Natural Gas Transmission Networks: Proof-of-Concept Analysis

This paper presents the possibility of energy storage in natural gas transmission networks using two strategies. Proof-of-concept calculations were performed under a steady-state assumption, and the more promising option was additionally modeled in a transient approach. The first strategy is based on a dedicated compressor–expander system installed at two ends of a pipeline. An electric-driven compressor increases the gas pressure in periods of peak electricity generation, while a gas expander allows energy recovery at a later stage. The compressor–expander distance determined by the inlet flow velocity of 5 m/s and a 4–5 h time shift ranges from approx. 75 to 120 km. The system provides a synergy effect, which allows to exceed 100% storage efficiency by reducing transmission losses. Storage efficiency obtained from the simplified model ranges from 70% to 128% for the performed case study. The second option uses existing compressors and pressure letdown stations expanding the gas to the distribution pressure. Here, gas pre-heating required prior to the expansion reduces the storage efficiency to about 30–40%. The dedicated machinery option was also evaluated using a transient model, which reports a lower efficiency if applied to the same assumptions. The system redesigned with the transient model is characterized by a longer storage duration (about 12 h) and a promising efficiency of 103.5%. Further research is needed to find the optimum design system parameters and to solve the detected problem of simultaneous compressor–expander operation which introduces idle work to the designed system.

Evaluation of the Structural Integrity of Bell-Spigot Joints in Steel Gas Pipelines

The most common joining method in steel gas pipelines is welding; however, this method involves time-consuming, expensive manufacturing and assembly processes to ensure quality in operation. Bell-Spigot joints, which work by mechanical interference, have started to be used as an alternative joining method in steel pipes. Its use has increased due to its reduced assembly time and less post-assembly inspection requirements. In this paper, the structural performance of Bell-Spigot joints in 16-inch steel pipe API 5L X70 with Fusion Bonded Epoxy (FBE) coating for Natural Gas transmission pipeline are evaluated experimentally and by modeling. Test pieces were taken from the gas pipeline after 3 years of operation. Then, tensile pull-out and bending with hydrostatic pressure tests were performed to replicate operating conditions. Deformations, displacements, and the potential presence of leaks were monitored. Experimental results were compared with a Finite Element Method model. Finally, an analytical model for the calculation of stresses and strains in the joint system's components was developed. It was determined that the tightness of the joint depends mainly on the radial interference and the interference length. A higher safety factor can be obtained at the bell-spigot joint than the base pipeline by optimizing selection of joint design variables and the service loading conditions. If the interference pressure is lower than half of the operation pressure, the joint's mechanical strength will be higher or equal that the base pipe.

Nigerian Gas Transportation Network Code NGTNC; Emerging Opportunities for Local Gas Transmission Operations

Historically, both regulatory and contractual constraints have inhibited the overall optimization of natural gas transmission systems. The Nigerian National Petroleum Corporation (NNPC) currently supplies gas either as source of fuel or as feedstock to different industries. More local industries are now aware of the advantages and benefits of using gas; hence creating an increase in demand. Recent changes in the regulatory framework and the introduction of the Nigeria Gas Transportation Network Code (NGTNC) to deepen the growth of gas market in the country are however, fostering the pipeline companies into a new competitive position, creating strong incentives as well as opportunities. This work provides a section-by-section summary of the Code for the benefit of those who are passionate about understanding the nuances of the Code and of course makes cogent survey and recommendations, to expedite the success of the Code. In the course of this research, questionnaires were administered and 130 respondents were chosen based on their level of knowledge and experience in the industry ranging from operations, management, regulatory and Gas Associations. Responses were collated and analysed using simple statistical tools, tables, and graphs to identify opportunities. The result of the study illustrates the stakeholder's presumption and commitments in using NGTNC for optimized Gas transmission operations.