and Absorption Humidification Assignment
Packed Tower Pressure Drop Assignment
Pressure Drop through a Packed Column
Pressure drop is an important consideration in the design and operation of packed tower unit operations. In designing packed tower equipment, the pressure requirement determines equipment selection (i.e. pumps and blowers), energy requirements, and transport efficiency. These factors directly affect capital and operating costs. For packed tower operations involving two phase flows such as absorption or distillation towers, pressure drop is a measure of performance efficiency. For single phase flow, pressure drop through a fixed packed bed is usually correlated using the Ergun equation (Eqn. 3.12-1 in Geankoplis, 3rd ed, also see McCabe, Crowe, class notes, etc.). The Leva correlation (shown in Fig. 6.26 of Treybal- Figure 10.6-5 in Geankoplis and/or Fig. 18.6 and 18.7 in McCabe) is appropriate for countercurrent flow of gas and liquid in a packed tower. The optimum flow conditions for operation of packed bed absorbers and cooling towers is at approximately 50% of the flooding velocity. Conditions of loading and flooding are described well in Chapter 6 of Treybal- also in Geankoplis and McCabe.
The Lab Column
Our laboratory column is comprised of two 3 foot sections of 4 ID glass pipe with a liquid redistributer in between sections. Analog meters give pressure drop across the column. Air is provided by a variable speed blower, and air flow rate is determined by pressure drop across an orifice flow meter (do not confuse this with pressure drop across the column). A calibration sheet for the orifice meter is provided here. Liquid inlet and outlet flow is provided by two variable speed gear pumps. Inlet liquid flow rate is sensed by a turbine flow meter and the results given on an LED panel meter in units of ml/s. There is a level in sensor the bottom of the column for eventual control of the outlet pump. At this point in time there is no controller attached to the level sensor and care should be taken to maintain the liquid level at a height that does not threaten to flood the blower. Make sure you fully discuss with the instructor or TA how to prevent this occurrence before attempting to operate the column.
Assignment
file:///W|/mans486/absorber/Absorption_Humidification_Assignment.htm (1 of 2)9/13/2004 4:49:40 AM
Absorption and Humidification Assignment
1) Design an experiment to measure the pressure drop across the dry column (use at least 3 flow rates- try to choose rates with both laminar and turbulent flow if possible- this will require some calculation prior to lab!). First determine the pressure drop in the dry column as a function of air flow rate. Compare your results to those predicted using the Ergun equation. Use Table 10.6-1 of Geankoplis to estimate packing characteristics- some specific information on our 10mm borosilicate Racshig rings (and other data including orifice calibration for air flow rates) is located h...