Cooling waters

Cooling water systems are dosed with corrosion inhibitors, polymers to prevent solid deposition, and biocides to prevent the growth of microorganisms. 

Reducing wastewater associated with cooling water systems. 

Total power for heat rejection to cooling water = 0.38 -I- 0.44 = 0.82 MW 

Utilities (fuel, steam, electricity, cooling water, process water, compressed air, inert gases, etc.) 

In early designs, the reaction heat typically was removed by cooling water. Crude dichloroethane was withdrawn from the reactor as a liquid, acid-washed to remove ferric chloride, then neutralized with dilute caustic, and purified by distillation. The material used for separation of the ferric chloride can be recycled up to a point, but a purge must be done. This creates waste streams contaminated with chlorinated hydrocarbons which must be treated prior to disposal. 

The gaseous reactor product is cooled first by boiler feedwater before entering a cooling water condenser. The cooling duty provided by the boiler 

Figure 6.40 A two-level refrigeration system for Example 6.6 with heat rejection to cooling water.

Example 16.4 The stream data for a process are given in Table 16.5. Steam is available condensing between 180 and 179°C and cooling water between 20 and SO C. All film transfer coefficients are 200Wm C For lO C, the 

An alternative inappropriate use of utilities involves heating of some of the cold streams below the pinch by steam. Below the pinch, cooling water is needed to satisfy the enthalpy imbalance. Figure 

There are two esdsting steam mains. These are high-pressure steam at 41 bar superheated to 270°C and medium-pressure steam at 10 bar saturated at 180°C. Boiler feedwater is available at 80°C and cooling water at 25°C to be returned at 30°C. 

If the vapor stream consists of a mixture of unconverted feed material, products, and byproducts, then some separation of the vapor may be needed. The vapor from the phase split is difficult to condense if the feed has been cooled to cooling water temperature. If separation of the vapor is needed, one of the following methods can be used  

Given a network structure, it is possible to identify loops and paths for it, as discussed in Chap. 7. Within the context of optimization, it is only necessary to consider those paths which connect two different utilities. This could be a path from steam to cooling water or a path from high-pressure steam used as a hot utility to low-pressure steam also used as a hot utility. These paths between two different utilities will be designated utility paths. Loops and utility paths both provide degrees of freedom in the optimization.  

In design, the same rules must be obeyed around a utility pinch as around a process pinch. Heat should not be transferred across it by process-to-process transfer, and there should be no inappropriate use of utilities. In Fig. 6.13a this means that the only utility to be used above the utility pinch is steam generation and only cooling water below. In Fig. 6.136 this means that the only utility to be used above 

Solution First, we must construct the balanced composite curves using the complete set of data from Table 7.1. Figure 7.5 shows the balanced composite curves. Note that the steam has been incorporated within the construction of the hot composite curve to maintain the monotonic nature of composite curves. The same is true of the cooling water in the cold composite curve. Figure 7.5 also shows the curves divided into enthalpy intervals where there is either a 

Analogous effects are caused by the inappropriate use of utilities. Utilities are appropriate if they are necessary to satisfy the enthalpy imbalance in that part of the process. Above the pinch in Fig. 6.7a, steam is needed to satisfy the enthalpy imbalance. Figure 6.86 illustrates what happens if inappropriate use of utilities is made and some cooling water is used to cool hot streams above the pinch, say, XP. To satisfy the enthalpy imbalance above the pinch, an import of (Q mjj,+XP) is needed from steam. Overall, (Qcmin+AP) of cooling water is used.  

Where the cold composite curve extends beyond the start of the hot composite curve in Fig. 6.5a, heat recovery is not possible, and the cold composite curve must be supplied with an external hot utility such as steam. This represents the target for hot utility (Q niin)- For this problem, with ATn,in = 10°C, Qnmin 7.5 MW. Where the hot composite curve extends beyond the start of the cold composite curve in Fig. 6.5a, heat recovery is again not possible, and the hot composite curve must be supplied with an external cold utility such as cooling water. This represents the target for cold utility (Qcmin)- For this problem, with AT in = 10°C, Qcmm = 10-0 MW. 

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