Vacuum
A vacuum is used to send the flue gas to the atmosphere, if it is not hazardous. A vacuum can be created by:
- Drehende Maschine: removing air from a space using a vacuum pump (based on compression by reducing the volume of chamber of pump)
- Strömungsmachine: by reducing the pressure using a fast flow of fluid (based on Bernoulli). Steam would be used, since it can reduce a large volume by condensation.
It should be noted, that the vapor pressure of water should be considered. It can cause a large amount of water in our gas stream, which is not desired for vacuum.
The type of vacuum pump will depend on the degree of vacuum required, the capacity of the system, and the rate of air in-leakage.
Reciprocating and rotary positive displacement pumps are commonly used where moderately low vacuum is required, about 10 mmHg (0.013 bar). A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum.
In the suction side of the pump, the vane chambers are increase in volume. These increasing-volume vane chambers are filled with fluid forced in by the inlet pressure. Inlet pressure is actually the pressure from the system being pumped, often just the atmosphere. On the discharge side of the pump, the vane chambers are decreasing in volume, forcing fluid out of the pump.
Steam-jet ejectors can handle high vapor flow rates and, by using several ejectors in series, can produce low pressures, down to about 0.1 mmHg (0.13 mbar).
The pressure ratio is important and the vapor pressure of steam. After every stage, the steam will be condensed and separated from our gas and used for the second stage. The last stage has a seperator with an ambient pressure, since the gas will be sent to the atmosphere, if it is not hazardous.
