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Tetrafluoroethylene (TFE) is an industrial scale starting material e.g. for polymer production (PTFE, FEP). When ignited the chemically unstable TFE is capable of decomposing in an explosive way. Explosion propagation through pipe systems of production plants have led to damage and fatalities within the last seven decades.
Incident analyses identified compression heat a relevant source of ignition. Chemical plants consist of pipes, vessels, separating valves, strainers and other components. Before restarting the process after maintenance work, different parts of the plant components could be filled with TFE, nitrogen or air at different initial pressures ranging from vacuum or atmospheric to TFE at operating pressure. Valve opening procedures may cause a temperature increase in the gas phase. Compression takes place at polytropic conditions. Heat losses cannot be neglected. The temperature development in the gas depends upon the surface to volume ratio of the enclosure, geometrical influences, the state of gas flow, how fast the valve opens, and the heat capacity of the gas being compressed.
Laboratory scale tests (Meyer, 2009) revealed ignition of TFE/air due to compression heat. Tests in pipes of 28 mm inner diameter, i.e. already industrial scale, were performed by (Kluge et. al., 2016). In the present contribution initial test results from a 63 mm pipe will be compared with existing 28 mm pipe data. A description of the experimental setup as well as an explanation of the hazard diagram will be given.
Furthermore, a method allowing for the identification of hazardous conditions will be discussed.
There is a lack of data on the self-ignition behaviour of tetrafluoroethylene (TFE) in industrial sized
equipment. In order to assess the tendency of TFE for
decomposition in large scale vessels, , a facility was
designed and constructed. Tests were
carried out in a cylindrical reactor with a volume of 100 L with initial
pressures of 5 and 10 bar(a). The effect of the reacto
r adjustment (vertical or horizontal) was taken into
account. The current work describes the test set
up and summarizes the experimental results achieved.
Furthermore, this paper reports on a numerical model for
the prediction of the self
-heating of TFE in closed
vessels, which was previously developed for small scale reactors and has been here validated for larger
dimensions with the experiments performed in the new facility.
The Ignition Temperature (IT) of stoichiometric tetrafluoroethylene–air mixtures on hot walls was determined in a 3-dm³-reactor. Tests at elevated pressure conditions were performed, namely at 5, 15 and 25 bar(a), showing a decrease of the IT with the initial pressure. Furthermore, the measured ignition temperatures of stoichiometric tetrafluoroethylene–air mixtures were lower than the ignition temperatures required for the decomposition pure tetrafluoroethylene (Minimum Ignition Temperature of Decomposition, MITD) reported in previous works.
Equations from the Semenov thermal explosion theory on spontaneous ignition were used to identify approximate combustion kinetics of tetrafluoroethylene from the experimental results. The determined kinetics was used for the prediction of the IT of stoichiometric tetrafluoroethylene-air by simplified calculation methods. A very good agreement with the experimental results was observed.
This work investigates the ignition of tetrafluoroethylene induced by the adiabatic compression that can arise by activating a high speed valve separating two portions of a pipeline with a high pressure difference. In the tests performed the high pressure zone contained tetrafluoroethylene at pressures between 15 and 30 bar. For the low pressure zone, experiments with nitrogen, air and tetrafluoroethylene were carried out. The pressure range in the low pressure zone was comprised between 0.05 and 1 bar. The pipe diameters analyzed were 15 and 20 mm. For the analyzed geometries, special conditions were required in order to reach reproducible ignitions, namely air at temperatures of at least 105 °C had to be present in the compression pipe. Furthermore, a minimum length of the compression pipe had to be used. The current work describes the experimental setup employed for the tests and discusses the achieved results. Numerical simulations were performed in order to clarify unexpected findings.
In the industry there is a lack of data on the Minimum Ignition Temperature of decomposition of tetrafluoroethylene in industrial sized equipment. In order to determine the Minimum Ignition Temperature of Decomposition of tetrafluoroethylene in large scale vessels, a facility was designed and constructed. Tests were carried out in a cylindrical reactor with a volume of 100 dm³ with initial pressures of 5 and 10 bar(a). In agreement with previous experiments with small scale cylindrical vessels, the Minimum Ignition Temperature of Decomposition of tetrafluoroethylene was observed to decrease with the initial pressure. The current paper describes the test setup and summarizes the experimental results achieved. The effect of the reactor adjustment (vertical or horizontal) is discussed. Moreover, simplified equations from the Semenov thermal explosion theory are used to attempt extrapolations of previous and current data on the Minimum Ignition Temperature of Decomposition of tetrafluoroethylene to other initial pressures and vessel volumes.
There is a lack of data on the self-ignition behaviour of tetrafluoroethylene in industrial sized equipment. Therefore, a facility was designed and constructed for the determination of the Minimum Ignition Temperature of Decomposition of tetrafluoroethylene in a cylindrical reactor with a volume of 100 dm3. Tests with initial pressures of 5 and 10 bar(a) were performed. The Minimum Ignition Temperature of Decomposition of tetrafluoroethylene was observed to decrease with the initial pressure, in agreement with previous experiments with small scale cylindrical vessels. This paper describes the test set-up und gives an overview of the achieved experimental results. In particular the effect of the reactor orientation (vertical or horizontal) is discussed. Furthermore, simplified equations from the Semenov thermal explosion theory are used to attempt extrapolations of previous and current data on the Minimum Ignition Temperature of Decomposition of tetrafluoroethylene to other vessel volumes or initial pressures. Moreover, the experimental data are plotted together against the heated volume to heated surface ratio, which should provide a better extrapolation to other vessel dimensions by taking into account that the efficiency of the dispersion of the heat generated by the reaction is different for two reactors with the same volume but different diameter. Finally, simplified methods for predicting the Minimum Ignition Temperature of Decomposition of tetrafluoroethylene presented previously by the authors are validated for large scale reactors with the experimental data collected within the current work.
The Minimum Ignition Temperature of Decomposition (MITD) of tetrafluoroethylene in a partially heated pipe was analyzed for different initial pressures (5, 10 and 15 bara). The pipe used had an internal length of 1 m, an internal diameter of 30 mm with a volume of about 0.7 dm³ and was vertically oriented. Pressure at the pipe top and temperature at four different locations along the pipe axis were measured. Tetrafluoroethylene was found to decompose at lower temperatures for increasing initial pressures, in agreement with previous tests with reactors with fully heated walls. A complete passive quenching in the non-heated part of the pipe was observed only for an initial pressure of 5 bara, while for higher initial pressures, the decomposition propagated completely along the test pipe. Moreover, the test results on the MITD were compared with data from previous experiments in fully heated 0.2 and 3 dm³ cylindrical reactors and showed a decrease of the MITD with the heated volume through heated surface ratio of the vessel. Furthermore, the prediction of the MITD of tetrafluoroethylene by simplified calculation methods was attempted, showing a good agreement with the experimental results.