Evaluating Heat Exchanger Constructability
Designing heat transfer systems is a complex process. Identifying the optimal solution through intuition alone is difficult because each problem can have many alternative solutions with their own complex economic and performance interactions. And the installation cost is often much higher than the purchase price for the heat exchanger.
Finding the best solution requires evaluation of the economics of the entire system, including design, manufacture, installation, operation, and maintenance.
Case Study: Distillation Column Overhead Condenser
Two possible solutions for an overhead condenser are an AHU or an AGU design. The G shell solution requires a larger tube pitch and shell diameter in order to meet the required shellside pressure drop. The results of an Xchanger Suite rating for both possible designs are summarized in Table 1.
Table I. Xchanger Suite ratings for AHU and AGU designs
|Shell diameter, mm||1050||1250|
|Tube length, mm||6400||5000|
|Surface area, m2||415||410|
|Empty weight, kg||124000||131000|
Figuring out the ideal solution requires evaluation of the economics. Exchanger Optimizer from HTRI can estimate the purchase and installation costs, and the software handles multiple currencies and places of manufacture. The results for the two options are summarized in Table 2, using Euros as currency.
Table II. Exchanger Optimizer cost comparisons for AHU and AGU designs
|Purchase price, Euro||144000||151000|
|Installation cost, Euro||486000||379000|
|Total installed cost, Euro||630000||530000|
The H shell has the lowest purchase price, but the G shell has a much lower installation cost. The costs to fabricate, install, and insulate the piping manifolds for the H shell are significant at approximately €110,000. The piping manifolds require additional pipe fittings, and increase the weld count of the piping network. Paying slightly more for the heat exchanger saves €100,000 in the installed cost. A breakdown of the installation cost for the H shell is shown in Figure 1. As is often the case with shell-and-tube heat exchangers, piping costs dominate the installation cost of the heat exchanger.
Using Exchanger Optimizer to find the solution with the lowest total installed cost can result in significant cost savings. This is especially true when installing heat exchangers in plant locations where the local labor rate is high or when the piping cost is high.
Download a trial of Exchanger Optimizer at www.exchangeroptimizer.com and start evaluating the constructability of your heat exchangers.