A .PDF brochure about Persimmon™ is available for download.

• A Network Rating Program for evaluating the performance of an existing heat exchanger network.
  
  
• An Automatic Data Reconciliation module, where raw data is automatically reconciled to generate accurate and representative heat balances from raw plant information. This feature significantly reduces the time and effort required to complete a Persimmon evaluation of the heat exchange network.
  
  
• A Network Simulator for performing cleaning cycle optimizations, operating scenario case studies, and fouling analyses of the existing network, and for exploring the impact of structural changes in the existing exchanger arrangement, including new exchanger services, exchanger reconfigurations, and new stream splits.
  

In addition, Persimmon contains Performance Trending capability with direct links to an external database for the trending and analysis of key performance parameters.

Persimmon Benefits

Overall Persimmon users can expect lower energy costs and greater throughput. The software provides users with a better understanding of their unit and an improved analytical capability to facilitate decisions about how to improve performance. Other benefits include:

• Time savings. Persimmon allows operations and technical services engineers to rationalize preheat train performance much more rapidly than by other methods.
  
  
• Ease of use. Persimmon is spreadsheet based and driven by automated procedures. The result is an extremely easy-to-use program that requires no special computing skills to operate effectively.
  
  
• Better exchanger cleaning decisions. Persimmon's exchanger cleaning analysis module allows easy analysis of the economics of exchanger cleaning, leading to better decisions on which exchangers to clean for maximum throughput and maximum energy savings.
  
  
• Exchanger performance diagnosis. Persimmon can identify operating problems in individual exchangers.
  
  
• Flexibility. Persimmon's simulation capability allows users to very easily answer 'what if?' questions about operating changes.
  
  
• Consistency. Persimmon's rigorous, systematic approach assures that the results generated are consistent, thus facilitating accurate, long-term data trending.

Also, various staff can use Persimmon and generate information on the same basis, facilitating better communication and decision-making.

Technical Features

The program utilizes the advanced mathematical, graphical, and programming capabilities of the Microsoft Excel® spreadsheet program to perform complex analytical and data organizational functions with a user-friendly Windows™ interface. As a result, users gain great flexibility in tailor-making the look and functionality of the program to suit their needs. Furthermore, users can make changes without the need for computing expertise—only a working knowledge of spreadsheets is required.

The program functions combine to give the user a wide range of capabilities for analyzing the performance of complex crude preheat trains and for optimizing their performance. Case studies are simple to perform and results are generated in a matter of seconds.

Interfacing to plant historian data is possible in a streamlined manner based on our experience with a broad range of plant data historians, thus providing online exchanger monitoring capability.

Network Rating Program

The Network Rating Program evaluates the performance of an existing heat exchanger network based on actual operating data. Flow, temperature, and fluid property inputs are dialog driven, or can be entered via automated access to data in plant information systems. By establishing flow connectivity within the spreadsheet, data input is simplified and minimized. For an existing unit, exchanger characteristics and connectivities need only be specified once during setup.

• Exchanger characteristics are entered into familiar, TEMA-type data sheets for each exchanger.
  
• Fluid property characteristics are handled by specifying the property at two temperatures. A dialog interface facilitates operating condition and fluid property updates.
  
• Operating data and fluid property data inputs can be automatically saved and retrieved for different production runs, crude slates, and operating modes.
  The program exploits the sophisticated task automation capabilities of the underlying spreadsheet program. Data editing, result reporting and viewing, generating and viewing trend analyses, and network simulation functions are all executed via automated built-in procedures, which are similar to the icon buttons in Windows™ applications.
  

Data organization is important. Results are presented in both graphical and tabular formats (Figure P-1 and Figure P-2). Information on fouling, pressure drop, heat transfer coefficients, heat balances (Figure P-3), and exchanger operating characteristics (e.g., velocity, Reynolds No., film coefficient, tubewall temperature) are conveniently organized for efficient analysis (Figure P-4).

An economic summary reflects the hourly operating cost of the unit including credits for steam generation (Figure P-5). Potential operating problems are flagged (low tube velocities, high tubewall temperatures, low bundle cross flow, heat and material balance inconsistencies, etc.).

The Network Rating Program contains a Process Flow Schematic that includes summaries of heat exchanger operating temperatures, duties and percent error in the heat balance for each exchanger (Figure P-6).

Network Simulator

Persimmon has been devised to be quick and as user friendly as possible, while still maintaining acceptable levels of analytical rigor. The familiar spreadsheet format encourages use by non-expert users to improve unit performance monitoring and management reporting. The integrated Network Simulator is exceptionally quick and provides significant case study capabilities. Overall, the program offers a wide range of monitoring and optimization capabilities, both within the constraints of the existing structure, and for proposed design modifications.

The Network Simulator uses the Effectiveness Approach to enable simulation of complex networks within a spreadsheet format. The solution method is iterative, quick, and stable—even for systems as complex and interactive as large Crude/Vacuum unit heat exchanger networks.

The simulator takes its base case exchanger characteristics and structure from the Network Rating Program. Case studies can then be performed on the existing structure very simply and very quickly. The Network Simulator contains a Process Flow Schematic that includes summaries of heat exchanger operating temperatures and duties.

• The input format and ergonomic characteristics for performing case studies is the same as for the Network Rating Program. Network sensitivities to changes in exchanger fouling factor, product draw temperatures, feed and product flow rates, split flow rates and pump-around flow rates can be easily and quickly determined.
• Exchangers can be specified as area or duty based simulating the effect of exchanger bypassing or additional shells for studies on temperature control or to maintain fixed pump-around duties. Adjustments are made to both tubeside and shellside heat transfer coefficients to account for changes in flow conditions and the temperature dependence of fluid properties.
• The Effectiveness Approach reduces the exchanger performance equations to a set of linear relationships, hence the stability, speed and robustness of the iterative solution approach
  

New structures. As an additional feature, a module is supplied which enables the engineer to explore different network structures. This includes re-arrangements of the existing heat exchanger units, new product and crude feed splits, and new exchanger units. Allowance has been made to add up to 10 new exchanger services. For each new structure, connectivities must be specified for flow, temperature, and fluid property. The spreadsheet has been set up to make these connectivity changes quickly and simply. Existing exchangers are re-rated in their revised configurations, taking into account changes in Reynolds No. and fluid properties For the new services, UA requirements are calculated and fluid properties reported in an exchanger specification data sheet for input to external exchanger design programs.

Exchanger cleaning. The program has also been equipped with two exchanger cleaning analysis modules. The impact of cleaning exchangers individually or evaluating a combination of exchangers (Figure P-7 and Figure P-8) over time is determined in the overall network context (Figure P-9). Time dependent fouling is accounted for, and both furnace fuel and steam generation impacts are fully evaluated. The costs of performance loss due to exchanger downtime and user-specified cleaning costs are also accounted for in the analysis.

The fouling model for the cleaned exchanger can be user specified according to analytical models or from plant operating records and experience. These models are used for projecting heat transfer coefficients over a period of time. This feature is essential in identifying key exchangers affecting network economic performance. This information is invaluable in developing optimum exchanger cleaning schedules (Figure P-10). It can also be used by process designers to optimize existing structures and to design new structures (for example, in conjunction with Pinch Technology retrofit methodologies) for unit de-bottlenecking or expansion requirements.

Performance Trending

Persimmon provides capabilities for the storage and trending of key performance parameters. Key parameters calculated from the performance analysis are stored to maintain historical records of unit performance. Additional, user-defined parameters can be specified at the time of setup. The variables are retrieved into Persimmon for user viewing and analysis.

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