Tower optimization temperature

The proportion of Ml increases in warm weather regions. M2 and M4 increase when water transport lines are long and the proportion of M3 is lowered as the maximum allowable chilled water temperature rises. However, regardless of these proportions in a particular installation, the goal of optimization is to find the minimum chilled water and cooling tower water temperatures that will minimize the total cost of operation. 

Crude oil fractionators are an example of a more elaborate system. They make several products as side streams and usually have some pumparound reflux in addition to top reflux which serve to optimize the diameter of the tower. Figure 3.13 is of such a tower operating under vacuum in order to keep the temperature below cracking conditions. The side streams, particularly those drawn off atmospheric towers, often are steam stripped in external towers hooked up to the main tower in order to remove lighter components. These strippers each have four or five trays, operate... 

Extraction of potable water from saline waters by means of immiscible solvents has been shown to be theoretically possible, experimentally feasible, and economically attractive. Data presented show the process to be especially adaptable to the conversion of feed water in the range of 5000 to 10,000 p.p.m. It is adaptable to use of low-quality heat such as hot water from cooling towers or low pressure waste steam. By use of mixed solvent systems, the process can be optimized to take advantage of seasonal changes in temperature and sources of cold feed water and low-level heat sources. The process, in general, is somewhat more economical when a cold source of feed water is available. 

Example 7 Multicomponent Absorption Dilute Case Air entering a tower contains 1 percent acetaldehyde and 2 percent acetone. The liquid-to-gas ratio for optimum acetone recovery is L /Gm = 3.1 mol/mol when the fresh-solvent temperature is 31.5°C. The value of y°/x for acetaldehyde has been measured as 50 at the boiling point of a dilute solution, 93.5°C. What will the percentage recovery of acetaldehyde be under conditions of optimal acetone recovery ... 

Three main options from different possible combinations of process units have been previously studied (Khan and Amyotte, 2005, Palaniappan et al., 2002b). The first option is the base case with no additional inherent safety features. The second and third options are revised versions of the first one. Modifications can include some or all of the following a quench tower to reduce the temperature, change of solvent to lower the severity of the operating conditions, an extraction column, a solvent mixer to optimize the use of solvent and efficiency of acid extraction and the use of solvent recycle. 

Feed Temperature A hotter feed can increase feed vaporization and thus reduce reboiling duty. However, higher temperature feed could cause too much vapor resulting in rectification section flooding. For an existing tower, the optimal feed temperature corresponds to the lowest reboiling duty, while the tower can meet product specifications. 

Pump-Around Many fractionation towers have pump-arounds to remove excess heat in the key sections of the tower. The effect of increasing pump-around rate is reduced internal reflux rate in the trays above the pump-around, but increased internal reflux rate below the pump-around. Thus, change in pumparound duty affects fractionation. On the other hand, pump-around rates and return temperature have effects on heat recovery via the heat exchanger network. It is not straightforward in optimizing pump-around duties and temperamres since the effects on both fractionation and heat recovery can only be assessed in a simulation model. An APC application incorporated with process simulation should be able to handle this optimization. 

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