Process Modeling Simulation & Control

11. What is the purpose of the following calculation modes: Design, Rating, Find Fouling, and Simulation? • Design Mode: Performs an extensive design search to find the best exchanger geometry to achieve the specified duty. Requires a set duty and allowable pressure drops. • Rating/Checking Mode: The geometry and process conditions are specified by the user. The program compares the area required to perform the duty with that specified in the input. The main results are the area ratio (>1 the exchanger is over-surface, <1 the exchanger is over surface). Some engineers use repeated rating calculations to manually find their choice of design. If the area ratio is far removed from 1.0 then Simulation will provide more reliable results. • Simulation: Considers the exchanger geometry to be fully specified and calculates the outlet stream conditions that can be achieved in the exchanger from the specified inlet conditions. • Find Fouling: This calculation mode is similar to rating but adjusts the fouling resistance to determine the maximum values which gives an area ratio of 1. .

10. What steps do you take to reduce vibration and resonance issues in exchanger designs? EDR does a full vibration and resonance analysis on tubes susceptible to vibration. On the Tubesheet Layout diagram in the Mechanical Summary you can view which tubes were identified by the program as possible vibration tubes. The Thermal/Hydraulic Summary shows the report of the Fluid Elastic Instability and Resonance Analysis for each of these tubes. EDR vibration calculations are based on HTFS methods or the TEMA Analysis can also be run. If any vibration indicators are detected, this will be reported in the Warnings section as an Operation Warning. Users can easily compare double-segmental baffles with single segmental; they can explore no- tubes in window segmental baffles and specify additional supports. It may also be effective in some cases to explore alternative shell configurations. .

9. Can I specify heat loss in Aspen EDR? EDR programs do not consider external heat loss in the analysis. We assume there is a highly effective insulation in place. .

8. How accurate are the calculated costs vs. actual costs in EDR? This will depend on the specific cost factors that you use and how closely they match to the actual fabrication cost. We do have fabricators who customize the labor rates, material costs, and other database entries to get accurate cost figures. We have several standardized lists to choose from and you can enter your own cost factors by opening the “Tools” menu and selecting “Costing Database” .

7. Can you compare a spiral exchanger design with EDR? The Alfa Laval spiral type is not currently modeled by EDR. .

6. Does EDR perform special code calculation, such as those required for graphite heat exchangers? ASME has new code calculations for graphite exchangers. If the market requirement is large enough, we may add these to our mechanical products in the future. .

5. What would be the recommended approach to modeling plate and frame heat exchangers if EDR does not have built-in plate designs from vendors such as Alfa Laval? You can use Aspen Plate Exchanger to design, rate, and simulate plate and frame, brazed plate, or welded plate type exchangers. Aspen Plate Exchanger uses our own proprietary plate heat transfer and pressure drop models and correlations. It is used by many customers as an independent evaluation of vendor designs. This can be especially critical in two-phase applications. .

4. Can this design be applied to a solid-liquid heat exchanger? We do not currently model solid-liquid heat exchangers. .

3. Is there an option for hairpin HX in EDR? Yes, under Input > Exchanger Geometry > Shells/Heads/Flanges > Shells/Heads. Here, you can select the shell type as Hairpin multi-tubular (we designate “M-type”). .

2. How effective is Aspen EDR in evaluating/designing vertically oriented exchangers? The program can design, rate, or simulate vertically orientate units with the same ease and accuracy as horizontal units. .

1. Does Aspen EDR carry out twisted tube design? Aspen Shell & Tube has links to the Koch Heat Transfer twisted tube modeling via a special “dii” module, which can be obtained from the Koch Heat transfer. When present, it links into the local shell-side and tube-side calculations of Shell & Tube to fully model a twisted tube unit. .

Exchanger Design & Rating (EDR) Capabilities .

6. Is the complex design, Triple Segmental, supported by TEMA? TEMA recognizes single-segmental, double-segmental, and triple-segmental baffle arrangements. If you have a large shell diameter and a large number of tubes, this can give a practical design that has a feasible baffle overlap (usually 2 or more tube rows overlap). Several of our fabricators who have been using our arrangement of triple-segmental baffles for years have had good results. .

5. How do you anticipate and compensate for fouling pressure drop increases? If the user specifies a fouling layer thickness explicitly under Input > Program Options > Fouling the program will calculate the impact of this on hot-side and cold-side pressure drops. On the shellside, the fouling will be assumed to also block the tube-to-baffle clearance and the shell-to-baffle clearance. If you specify a process fouling, resistance, and thermal conductivity of the fouling material, the layer thickness can also be calculated. .

4. How do you optimize a thermosiphon reboiler in an ethylene oxide process? Our research shows that the program does a very good job of predicting actual circulation rate for both vertical and horizontal thermosyphon reboilers. Two-phase flow patterns are calculated while the program checks for potential instability. .

3. Can EDR handle a thermosyphon reboiler? Is there an example file of it? Aspen Shell & Tube Exchanger can design, rate, and simulate operation of themosyphon reboilers. The program allows you to specify the interconnecting pipework in detail (if you have that information). Simulation mode is important, as the circulation rate and the thermal performance are highly interdependent. The program can also calculate the circulation rate that will be achieved. We provide two example files for thermosiphon reboilers. These examples are installed with Aspen EDR and you can find them and other EDR Shell & Tube sample files at the following location in Windows Explorer: C:\Program Files (x86)\AspenTech\Aspen Exchanger Design and Rating V8.0\Examples\Shell&Tube. .

2. Are there any recommendations for hydraulic aspects, optimum velocity in tubes, etc.? EDR Shell & Tube provides a full Flow Analysis including RhOV2 calculations at the Shell &Tube entrance and exit points and nozzles. Warnings will alert the user when calculated values exceed the TEMA limit. Full documentation of our flow calculations—as well as a design guide for choosing economic velocities for the tubeside and shellside streams—can be accessed with a subscription to the HTFS Research Network. Under Input > Program Options > Design Options >Process Limits the user can constrain the design search by minimum and maximum velocities. .

1. Is there a database or recommendations for the fouling factors? Yes, we provide the recommended values for TEMA Design Fouling Resistances for Industrial Fluids, Chemical Processing, Natural Gas Processing, Oil Refining, and Water. For links to the data, open the Help menu and choose “Search for help on.” Type “TEMA Design Fouling Resistances.” .

General Heat Exchanger Design

Optimize Thermal & Mechanical Design for Shell & Tube Heat Exchangers .