Ejectors for the introduction of gaseous oxygen
Ejectors for the introduction of gaseous oxygen are similar in construction form and mode of operation to apparatus supplied with compressed air. They are installed principally within the aeration tank and are operated by dryor wet-installed centrifugal pumps. The difference to the ejectors supplied with compressed air is that the gaseous oxygen is injected between the pressure side of the pump and the entrance to the ejector by a nozzle system in the connecting pipeline. So intermixing takes place at the highest pressure level, even before entry into the ejector.
The intermixing is intensified during perfusion of the ejector – whereby a considerable portion of the gas is dissolved already in the waste water. In the ejector, static pressure energy is converted into kinetic energy so that the two-phase mixture enters the aeration tank with high turbulence.
Fields of application
Apart for oxygen introduction, ejectors can also be designed for the complete intermixing of an aeration tank – without gas supply – so that their utilisation facilitates an intermittent nitrification/de-nitrification – without additional agitators. The action of flow over the tank floor by the ejectors prevents deposits. The oxygen transfer system is optimised by means of individual adaption of the maintenance-free ejectors to the respective operating conditions, power consumption and numbers of necessary pumps are reduced..
Ejectors are applied
- for peak load coverage
- for basic load coverage
- for introduction of gaseous oxygen occurring as off-gas in ozone plants
Apart from multi-path ejectors, single-path jet ejectors find application as well. Installation can take place on the aeration tank floor as well as through the tank wall. All ejectors are manufactured in chrome-nickel steel whereby the material quality depends on the respective waste water composition.Furthermore, their compact construction form permits a later installation on a base frame as a mobile oxygen transfer system.
Oxygen transfer system in one of the two 3400 m³ sized aeration tanks belonging to the Lang paper mill in Ettringen. Eight six-path ejectors each are supplied with oxygen generated as off-gas in a downstream ozone plant.
The installation of 12 six-path ejectors was completed during the course of converting the waste water treatment plant of the Rheinland Raffinerie Godorf Works belonging to Shell Deutschland Oil GmbH to an intermittent gassing with pure oxygen. Respectively 3 ejectors each are connected with a pipeline and fed mutually from a submersible motor-driven pump. The pump is mounted on the pipeline by means of an underwater coupling and can be retrieved any time via guide tubes.
Towards the end of 2009 Körting Hannover AG received an order from the Westfalen AG covering the supply of an oxygen introduction system for application in the waste water treatment plant of a German food maker. As the system had to be installed during active plant operation, a so-called "skid-mounted unit" was chosen which consisted of two single-path ejectors and a submersible motor-driven pump mounted on a common base frame. The 22 kW unit delivers an hourly amount of 400 m3 waste water into which 80 kg of gaseous oxygen is introduced. With this, the microorganisms in the 2600 m3 large activation tank are kept alive and moving.
Apart from the oxygen introduction system, a square section with lifting eyes for lowering the completely assembled unit made up of ejectors and submersible motor-driven pump as well as a small switchboard cabinet belonged to our scope of supply. The system was installed and put into operation without any problems occurring.
At the same location the final customer also operated a further identically constructed aeration tank which, one year later, we were able to equip with an identical oxygen introduction system. Here too, our customer was the Westfalen AG.
With this project, the Westfalen AG, as a national and international supplier of technical gases, and Körting Hannover AG, as an independent manufacturer for oxygen introduction technology, have laid the foundation stone for a successful collaboration.
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