Columns distillation tray costs

Figure B-8 Tray costs for distillation columns. (Use vertical vessel charts for shell.)...

Correlations for Estimating fob Purchased Costs for Internals (e.g., Distillation Trays, Absorber Packings, Solvent Extraction Columns, and Others. Referenced to Mid-1968 Dollars with (M S = 273.1). Correlated Using Information from Guthrie [71]... 

The economic objective function is formulated on the basis of (1) capital costs, (2) return on investment, and (3) operating costs. The objective function is formulated as an expression of the desire to minimize the total costs per mole of the most valuable product. The capital costs consist of the installed costs of the following items the pressure vessel or shell of the distillation column, the trays, the condenser, and the reboiler. 

The feed is delivered to the atmosphoic distillation column between trays 58 and 62 the column has a total of 80-85 valve trays. The operation of this column is governed by the requirement that the overhead product should not contain more than 10 ppm of ethanol and 1-3 ppm of hydrocarbons while the water collected in the bottom should be largely alcohol-firee. This design basis proved to be more cost-effective than the downstream addition of a so-called water purification column for the bottoms product of the atmospheric column as it has some times been practised. In order to meet the purity requirements for the overhead and bottom products, ethanol and hydrocarbons have to be withdrawn through side outlets. This can be achieved best, i.e. with minimum losses of methanol, if the two components are withdrawn at the points where their concentrations are highest. Figure 4.5 shows the concentration profiles of methanol, water, ethanol and n-decane for the theoretical number of trays required by the operating conditions for the example as described here. In this system, the atmo-... 

The economic design objective is to minimize total annual cost, given feed conditions, and desired product specifications. The two product specifications are 99.5 mol% water in the distillate and 12 mol% water in the bottoms. The Aspen Design Spec/Vary feature is used to attain these specifications by varying the distillate flow rate and the reflux ratio. The Aspen Tray Sizing feature is used to determine the diameter of the column. A tray spacing of 2 ft is used to determine column height. 

The second stage, including the selection of the best reflux numbers and the quantity of column section trays, will be the important one. The geometric distillation theory makes it possible to determine the feasible compositions that are to be in trays above and below the feed cross-section, then make the design calculations of the trajectory of sections and determine the best ratio of section tray numbers. The new algorithms allow for an increase in the design quality and apart from that, they make it possible to lower the separation costs and to practically exclude the human participation in the process of calculation. 

The vast majority of industrial distillation columns are equipped with trays or plates (sometimes called decks in the petroleum industry) located every 1-3 feet up the column. These trays promote mass transfer of light components into the vapor flowing up the column and of heavy components into the liquid flowing down the column. Vapor-liquid contacting is achieved by a variety of devices. The most widely used trays in recent years have been sieve trays and valve trays because of their simplicity and low cost. 

Determining the number of theoretical and actual trays in a distillation column is only part of the design necessary to ensure system performance. The interpretation of distillation, absorption, or stripping requirements into a mechanical vessel with internal components (trays or packing, see Chapter 9) to carry out the function requires use of theoretical and empirical data. The costs of this equipment are markedly influenced by the column diameter and the intricacies of the trays, such as caps, risers, weirs, downcomers, perforations, etc. Calcvdated tray efficiencies for determination of actual trays can be lost by any unbalanced and improperly designed tray. 

Prior to 1974, when fuel costs were low, distillation column trains used a strategy involving the substantial consumption of utilities such as steam and cooling water in order to maximize separation (i.e., product purity) for a given tower. However, the operation of any one tower involves certain limitations or constraints on the process, such as the condenser duty, tower tray flooding, or reboiler duty. 

Once a distillation column is in operation, the number of trays is fixed and very few degrees of freedom can be manipulated to minimize operating costs. The reflux ratio frequently is used to control the steady-state operating point. Figure El2.4a shows typical variable cost patterns as a function of the reflux ratio. The optimization of reflux ratio is particularly attractive for columns that operate with... 

For equipment such as distillation columns, the costs of several components (trays, shell) must be calculated. 

This illustrative example is taken from the recent work on interaction of design and control by Luyben and Floudas (1994a) and considers the design of a binary distillation column which separates a saturated liquid feed mixture into distillate and bottoms products of specified purity. The objectives are the determination of the number of trays, reflux ratio, flow rates, and compositions in the distillation column that minimize the total annual cost. Figure (1.1) shows a superstructure for the binary distillation column. 

The prices shown for distillation columns are misleadingly low. Most of the cost of a conventional distillation column is associated with the reboiler, condenser, pumps, reflux drum, and internal trays or packing. Equipment costs can be ratioed by the 0.6 power with size to obtain rough prices for larger or smaller sizes. 

Figure 2.62 gives results over a range of reactor volumes. The reactor volume that minimizes TAC ( 1,117,000 per year) is 20 m3, giving a recycle flowrate D of 0.1241 kmol/s. Figure 2.63 gives the values of variables and parameters for the 10 m3 reactor process. The reactor concentration is Ca = 2.099 kmol/m3 (z = 0.262 mole fraction A). The column has 16 trays. The distillate composition is 0.3304 mole fraction A. Energy cost is 427,400 per year. The capital cost of the column is 123,000. The capital cost of the... 

Operating the column at the minimum pressure minimizes the energy cost of separation. Towering this pressure increases the relative volatility of distillation components and thereby increases the capacity of the reboiler by reducing operating temperature, which also results in reduced fouling. Reducing pressure also affects other parameters, such as tray efficiencies and latent heats of vaporization. 

Because of nonequilibrium boiling conditions in a simple distillation, the vapors may not contain the true azeotrope, and the heat cost may be too high. Therefore a column is still used to rectify the exact azeotrope at the head of the column however, only a few trays are required. 

Distillation towers feed-tray location for, 10 optimum reflux ratio for, 371-376 specifications for, 16 (See also Bubble-cap contactors, Packed towers. Sieve trays, and Valve trays) Distribution costs, 194, 196, 207, 211 Distribution in statistical analyses, 745-746 Dividends, tax exemptions for, 259 Documentation, 137-149,452-476 Double-entry bookkeeping, 143-144 Downcomers in tray columns, 684-686 Drives, cost of 532-533 Dryers, cost of 713-716... 

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