Ejector unit is a relatively simple device which utilizes the pressure energy of the primary fluid to entrain the secondary fluid. It is widely used in the chemical industry, where it usually serves as a reliable pump/compressor/vacuum pump, fluid-fluid(-solid) contactor or gas scrubber. It usually consists of four, simple, non-moving parts:
- a nozzle in which the pressure energy of the primary/motive fluid is transformed in the kinetic energy of high-velocity fluid jet,
- a suction chamber where the jet of the primary fluid and the secondary, entrained fluid are contacted and flow through the converging section to
- a mixing tube where the primary fluid jet disintegrates and mixes intensively with the secondary fluid producing a highly homogeneous mixture, it is connected to
- a diffuser in which the kinetic energy of the mixture is efficiently transformed back to the pressure energy.
In our laboratory, the ejector unit is of liquid-gas type with water being the primary, motive fluid and air the secondary, entrained fluid. The research of the ejector characteristics on this unit started in 1990s with the ejector being a gas distributor for a bubble column. The mass-transfer characteristics of the ejector have been studied by physical absorption of oxygen from the air into the water utilizing
- either desorption column for the production of the deaerated water
- or the sulfite method which removes the oxygen dissolved in water via rapid reaction with sodium sulfite.
The hydraulic and mass-transfer characteristics of the ejector with a bubble column have been published in impacted journals. Unfortunately, further research on the topic has been postponed due to the personnel changes in the team.
Havelka, P.; Linek, V.; Sinkule, J.; Zahradník, J.; Fialova, M. Effect of the ejector configuration on the gas suction rate and gas hold-up in ejector loop reactors. Chem. Eng. Sci. 1997, 52 (11), p. 1701-1713.
Nowadays, we continue on the research with the aim of energy optimization of the ejector unit as a chemical reactor and gas-treating device. The present ejector unit is attached to the bottom of the approx. 1.2 m high bubble column which generates the back-pressure required for a proper function of the ejector. The experimental setup enables to perform the hydraulic and the mass-transfer measurements with the water flow rate up to 3 l/s with the pressure up to 600 kPa. The air pressure in the suction chamber can be adjusted via the throttling valve in the range of 2.5 to 98 kPa. The back pressure generated by the bubble column can be varied in the range of 103 – 212 kPa (the pressure up to 110 kPa can be adjusted via the liquid level in the column, to achieve a higher back pressure an additional throttling valve have to be installed on the bubble column outlet). The ejector unit is of modular design; the body consists of a stainless steel suction chamber to which various nozzles, mixing tubes and diffusers can be attached.
The nozzles used in the ejector vary in their inner diameter (up to 14 mm) and converging angle (from 40 ° to 180 °). It is also possible to introduce parts which change the behaviour of the liquid jet, e.g. swirl bodies, in order to study their impact on the ejector performance. The mixing tube of 18 mm i.d. consists of four parts made of PMMA which enable to vary the length of the mixing tube from 0 to 360 mm. The individual parts are equipped with pressure taps which enable to measure the pressure profile along the mixing tube. The inner diameter of the mixing tube can be further modified via additional reductions.
Recently, we published the article which summarizes the hydraulic and mass-transfer characteristics of the ejector with air/water system utilizing coalescent and not-coalescent batches.
Opletal, M.; Novotný, P., Linek, V., Moucha, T., Kordač, M. Gas suction and mass transfer in gas-liquid up-flow ejector loop reactors. Effect of nozzle and ejector geometry. Chem. Eng. J. 2018, 353, p. 436-452.
Nowadays, we continue with our work on the ejector unit with the intention to provide reliable way how to design these devices for various industrial applications and conditions. The pilot plant unit was rebuilt to enable the measurement in both, upward- and downward-pumping conditions and new, lab-scale unit enabling the measurements with small batches of non-air and non-aqueous systems and over-ambient pressures.