PI – Luc Véchot
Ethylene pipeline rupture modelling and medium scale experimental validation
Olefins, principally ethylene and propylene, represent very large volume feedstocks to the petrochemical industry. High amounts of Ethylene are used in the production of styrene, polyethylene and other plastics. In order to get the magnificence of the ethylene, Europe can be taken as an example, where approximately 90% of its olefins pipeline network is ethylene service. Qatar is playing an increasing role in the petrochemical industry via the development of its capacities to produce of polymers (Polyolefins) to respond to the growing global demand in the world. The Qatari petrochemical industry has been rapidly growing in the latest years. As part of its expansive economic strategy set in the National Vision 2030 and the national development strategic 2011-2016, the State of Qatar is investing around USD 25 billion in its petrochemical sector (from 2012 up to 2020) in order to increase its petrochemical production from about 10 million tonnes to about 23 million tonnes.
Ethylene is a chemical intermediate needed in the production of many plastic materials (polyethylene, polystyrene, PVC, …) used in agriculture, auto industry, chemical industry (oil additives, paints, solvents,…) and everyday life; for economic, safety and environmental reasons it is transported only in pipelines. Ethylene is transported thorough pipelines at high pressures and temperatures (above its critical point), and therefore it behaves as a super critical fluid (gas and liquid phases are indistinguishable). When the depressurization occurs, very low temperatures (below -100 °C) are achieved. Due to these low temperatures, pipelines used to transport ethylene pose high risk of rupture because the carbon steel can lose its ductile strength leading to the formation of a hole, further propagation and final rupture. The lack of fundamental understanding and improper hazard assessment for pipeline transporting ethylene and other hydrocarbons are frequently the cause of serious incidents in the petrochemical process industry which have led to significant fatalities, environmental and economic losses. Due to the magnitude of the potential causes of these incidents, fines exceeding hundreds of millions of dollars are being imposed to operating industries involved in incidents causing environmental damages. The current operating Qatar’s ethylene pipeline goes from Ras Laffan to Messaid. In order to avoid potential incidents related with the transport of ethylene through pipeline, it is of paramount importance understand the hazards involved and to perform a complete Risk Assessment program along the existent and future pipeline path. Depth experimental and theoretical studies are needed in order to investigate the hazards associated with the transport operation of ethylene, the properties of ethylene when encountered as a super critical fluid, the potential and characteristics of ethylene releases and most important the methods to prevent and mitigate the consequences of these releases.
In order to fully and properly asses the hazards associated with the depressurization of a pipeline containing ethylene, it is imperative to accurately predict the outflow following rupture or puncture of a pipeline containing pressurized ethylene, the fluid and wall temperatures, efflux rate, composition, phase and fluid pressure in the pipeline. The Health and Safety Executive (HSE) recently analyzed the performance of different computer codes used to calculate hydrocarbons pipeline blowdown, based on the comparison of the modeled results with experimental data (regarding LPG releases) and concluded that current computer codes are able to model full bore pipe ruptures, but the predictions show poor or non-fit to experimental data on puncture. This clearly demonstrates that the phenomena of how pipeline releases of hydrocarbons, and in this, ethylene occurs in small breaches is not well understood.
Therefore, it is of paramount importance to make further efforts in the modeling of ethylene pipeline releases in small breaches. It is important to notice that this cannot be possible unless enough and reliable set of experimental data is available to validate the simulation results. Currently no experimental data on ethylene releases are available in literature.
The objective of this work is to construct a pilot plant station capable to acquire reliable and trustable data on pipeline outflow releases transporting ethylene in order to be able to evaluate current models used to predict ethylene pipeline releases properties and make further improvements on these models when it is needed. In particular there is a need for a better understanding of:
- modelling accurately the flow deriving from small breaches in the pipeline;
- validating existing model describing the releases of supercritical fluids for the case of ethylene;
- study the effect of corrosion of the pipeline due to aging ;
- analyse the problem of the formation of hydrates;
- study a model for the dispersion of ethylene;
- study the consequences of the thermal radiation from an ignited ethylene release;
- NaTech (Natural hazard triggered Technological accidents) influence on ethylene pipeline.