Pressure release and CO2 recovery

In reality, there is a distribution of temperature over the vessel and within the walls and the pressure and temperature transients do not show linear behaviour. In German codes for the design of pressure vessels [9] it is of great importance, whether or not the wall temperature falls below - 10 C. Bearing this in mind, tests were carried out using a 50 1 vessel, initially containing 

Due to the radial distribution of temperature, thermal stresses in the cylinder wall are caused, which add to those produced by the pressure inside the vessel. From an examination of the thermal data and the stresses produced in tests such as the above, the author concludes [22] The following implication for natural substance extraction may be stated if the pressure release times are sufficiently long and if the temperatures of pressure vessel and charge are adjusted beforehand, the lower part of the pressure vessel need not be constructed of low-temperature steel.  

In the case of large batch-operated production plants, it is necessary for economic reasons to recover most of the CO2 which leaves the extractor during pressure release. This operation then takes place in three steps  

Reduction of pressure in the extractor by blow-off via a reducing value and 

Further reduction of pressure by pumping gaseous CO2 from the extractor into the storage vessel via a condenser. The pump suction pressure progressively falls during this operation, finally coming to a value between 2 and 8 bar which is set by the capabilities of the pump. The pump requirements are discussed further in sections 9.4 and 5.7.1 

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