Condensers costs

Calculate the reboiler and condenser cost using Equation 7.13... 

The next step is to obtain equations for the solution of the shadow and marginal prices. This requires the evaluation of various derivatives of the constraint equation matrix. However, because not all the constraints are in algebraic form (those constraints that are functions of steam table properties) numerical derivatives must be evaluated. One other note, there are two condenser costing equations. This means that two separate derivatives must be taken and the derivative corresponding to whichever costing equation is valid for that value of condenser area, is the one that should be used. 

This however complicates the optimization procedure. The problem can be alleviated by using an entropy penalty function P8, which serves to properly apportion the total condenser costs to the reboiler and column. The entropy penalty function, which Evans describes as "negentropy" (12-13), can also be viewed as the commodity or product which the condenser sells to the tower and reboller. The entropy penalty function leaving the condenser Is given by (9, 13-14)... 

Thus by requiring the reboller and column to purchase P8 r r and p8 coi from the condenser, the condenser costs are properly included In the optimization procedure. However, the money balances will need to include the money flows associated with the entropy penalty function transactions. 

Solution. The variable costs involved are cost of column, cost of reboiler, cost of condenser, cost of steam, and cost of cooling water. Each of these costs is a function of the reflux ratio, and the optimum reflux ratio occurs at the point where the sum of the annual variable costs is a minimum. The total variable cost will be determined at various reflux ratios, and the optimum reflux ratio will be found by the graphical method. 

Because the performance of a power station is very dependent upon the steam pressure within the condenser, cost analysis is often based on the achievable condenser pressure. In general terms the lower the condenser pressure the lower the unit production cost of electricity. 

Vertical ln tube condensers—downflow. This configuration is popular in the chemical industry (68). It can lead to heat transfer coefficients even higher than shell-side condensation (319), and has distinct advantages for multicomponent mixtures if significant pressure drop can be tolerated. It also minimizes condenser costs when highly corrosive materials are handled (68). An application of this condenser t3 pe as an internal condenser is illustrated in Fig. 15.14d. 

Lowest permeate condensation costs (ability to operate at higher coolant temperatures)... 

Vertical shell-and-tube condenser with liquid coolant on the shell side and vapor entering the tubes at the top (Figure 3.2). This type is popular in the chemical industry because it minimizes condenser cost when highly corrosive process materials must be handled. 

Another variable that needs to be set for distillation is refiux ratio. For a stand-alone distillation column, there is a capital-energy tradeoff, as illustrated in Fig. 3.7. As the refiux ratio is increased from its minimum, the capital cost decreases initially as the number of plates reduces from infinity, but the utility costs increase as more reboiling and condensation are required (see Fig. 3.7). If the capital... 

Z. Evaporation. If the wastewater is in low volume and the waste material involatile, then evaporation can be used to concentrate the waste. The relatively pure evaporated water might still require biological treatment after condensation. The concentrated waste can then be recycled or sent for further treatment or disposal. The cost of such operations can be prohibitively expensive unless the heat available in the evaporated water can be recovered. 

Example A.4.1 The purchased cost of a distillation column is 1 million, and the reboiler and condenser are 100,000. Calculate the annual cost of installed capital if the capital is to be annualized over a 5-year period at a fixed rate of interest of 5 percent. 

If regulations governing specific emission limit VOC concentrations to the low ppm range then, of course, vapor fractions such as those illustrated by the above tabulation will not be acceptable. It may, however, still be justified to consider VOC condensation as a precursor to a final abatement device such as an adsorption bed. Removing most of the solvent from a vent stream by condensation, can drastically reduce the size and cost of a downstream cleanup system. 

In 1994 Stamicarbon introduced a pool condenser in the synthesis section (see Figs. 4 and 5). This allowed a 34% decrease in reactor volume and a 45% decrease in carbamate heat-exchange area, thus reducing costs considerably for equipment, stmctural steel, and constmction. 

Although the rapid cost increases and shortages of petroleum-based feedstocks forecast a decade ago have yet to materialize, shift to natural gas or coal may become necessary in the new century. Under such conditions, it is possible that acrylate manufacture via acetylene, as described above, could again become attractive. It appears that condensation of formaldehyde with acetic acid might be preferred. A coal gasification complex readily provides all of the necessary intermediates for manufacture of acrylates (92). 

A.nnual energy and fuel costs electric energy costs chiller or compressor pumps chilled water heating water condenser or tower water weE water... 

Gaseous Effluents. Twenty percent of the carbon disulfide used in xanthation is converted into hydrogen sulfide (or equivalents) by the regeneration reactions. Ninety to 95% of this hydrogen sulfide is recoverable by scmbbers that yield sodium hydrogen sulfide for the tanning or pulp industries, or for conversion back to sulfur. Up to 60% of the carbon disulfide is recyclable by condensation from rich streams, but costly carbon-bed... 

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