Industrial Safety - Laboratory Industrial Safety

TEST EQUIPMENT Spherical test vessels for the determination of flammability limits Two closed vessels with a spherical cavity are used for the study of the flammability limits at elevated pressures. The first vessel has an internal volume of 4.2 l (internal diameter of 200 mm) and is designed to withstand explosion pressures up to 300 bar at a wall temperature of 250 °C. It is equipped with a thermal oil circuit to perform experiments at elevated initial temperatures. This vessel is used for the determination of flammability limits at initial pressures up to 30 bar and initial temperatures up to 250 °C. This maximum initial pressure at which experiments are performed is chosen to be a factor of 10 lower than the pressure rating of the vessel. In this way, the integrity of the test vessel is guaranteed even if a stoichiometric mixture — giving a pressure increase of about 8 at ambient temperature for the mixtures under consideration — is mistakenly introduced into it. The second vessel has an internal volume of 8 l (internal diameter of 248 mm) and is designed to withstand explosion pressures up to 3500 bar at a wall temperature of 350 °C. It is equipped with several electric heating units to perform experiments at elevated initial temperatures. This vessel can be used for the determination of flammability limits at initial pressures up to 100 bar and initial temperatures up to 350 °C. This pressure limit is determined by the maximum inlet pressure of the mass flow controllers. Spherical test vessels for the determination of auto-ignition limits For the experimental determination of auto-ignition limits at elevated pressures two connected 8 l spherical vessels are used. The first vessel (buffer vessel) is designed to withstand explosion pressures up to 3500 bar at a wall temperature of 350 °C, whereas the second vessel (auto-ignition test vessel) is designed to withstand explosion pressures up to 400 bar at a wall temperature of 400 °C. Both vessels are equipped with several electric heating units. Glass tubes for the determination of flammability limits Two vertically placed cylindrical tubes with different internal diameters (60 mm versus 80 mm) and identical length (300 mm) are used for the study of the flammability limits at atmospheric pressure. The first one complies with the DIN 51 649 standard, while the second one complies with the EN 1839 standard. They are made of glass so that the flame behaviour can be observed visually. They are placed inside an oven, which allows experiments to be performed at temperatures up to 300 °C. These vessels are used for the determination of flammability limits at initial temperatures up to 200 °C and atmospheric pressure. Mixture preparation equipment Components having a vapour pressure at ambient temperature above 30 bar will be introduced into the equipment in gaseous form, while the other components will be introduced in liquid form. The flow rate of the gaseous components is controlled by a mass flow controller (MFC). The installation is equipped with three mass flow controllers with different nominal flow rates. The maximum inlet pressure of these mass flow controllers is 100 bar, whereas the maximum cylinder pressure is 200 bar. Therefore, the cylinders are equipped with a pressure reducing valve. Between this valve and the MFC a filter is placed to avoid fouling of the MFC. A back pressure regulator placed behind the MFC ensures that the outlet pressure of the MFC remains constant. Mixing of the gas flows emanating from different mass flow controllers occurs in a specially designed mixing vessel to ensure homogeneity of the mixture. After passage through this mixing vessel, the mixture can be introduced into the test vessel or it can be fed to the evaporator as described below. The flow rate of the liquid components is controlled by a volumetric pump. A cylinder containing nitrogen is connected to the vapour outlet of the cylinder containing the liquid/vapour mixture to obtain a constant pump inlet pressure. To avoid evaporation of the liquid inside the pump, the liquid is cooled before entering the pump. A back pressure regulator placed behind the pump ensures that the outlet pressure of the pump remains constant at approximately 40 bar. After passage through this back pressure regulator, the liquid flows into the evaporator where it mixes with the gas flow coming from the above mentioned mixing vessel. The evaporator guarantees complete evaporation of the liquid together with the homogenisation of the mixture. After passage through this evaporator, the mixture can be introduced into the test vessel. To avoid condensation of the vapour, the piping between the evaporator and the test vessel is kept at a temperature above the saturation temperature of the mixture by means of an electric heating system. Gas chromatography is used at regular intervals to verify the mixture composition. Moreover, it can be used to analyse the combustion products after completion of a test.