Sample Process Simulation Projects

PROCESS' licensed commercial process simulation softwares, Chemstations' ChemCAD and CCTherm, have been used increasingly with great effectiveness in the course of process engineering and process design projects. Several of our engineers are also familiar and proficient with other popular simulation packages such as Aspen, Hysis, Pro/II, Simsci, etc. With engineers proficient in the use of these softwares, PROCESS has been able to utilize these tools to save engineering time on projects (resulting in corresponding savings to our clients).  Recent examples of the application of these softwares to projects include:

Optimization of a Crude Distillation Unit

Capacity Evaluation of a Batch Plant Vent System

Simulation and Evaluation of Organic Chemical Production Distillation Towers

Simulation and Preliminary Process Design of a Crude Vacuum Distillation System

Evaluation/Optimization of a Light Ends Fractionation System

Design of a Sodium Hydrosulfide Production System

Evaluation/Design of an HCl Regeneration System

Elimination of Condensing Solvent Recovery System Downtime

Simulation of Solvent Recovery Distillation System

Evaluation of a Refinery Flare System Capacity

Optimization of a Multi-Tower HCl Absorption System

Design of a Fume Incinerator Heat Recovery System

Design of Nuclear Facility Cooling Water Loops

Design of a Refinery Fuel Gas Conditioning System

Optimization of a Crude Distillation Unit. PROCESS constructed a simulation model of an existing crude distillation unit and tuned the model to actual plant data to allow PROCESS to evaluate existing unit performance, conduct a parametric study of the heat exchanger network simultaneously with distillation optimization, and determine the ultimate capacity of the major unit equipment. The crude unit consisted of the preheat train (11 exchangers and a crude desalter), a pre-fractionation tower, two fired heaters, an atmospheric crude distillation tower, and a vacuum distillation tower. The heat exchanger network was modeled using CCTherm, and a pinch analysis was performed using composite curves generated by ChemCAD. The composite curves were evaluated simultaneously with the optimization of the distillation objectives in order to maximize modeled unit capacity and energy recovery at minimum unit revamp cost. Information from the simulation effort included: overall unit mass and energy balances; tower operating profiles; tower tray, packing, and grid loadings; tower ultimate distillation capacity per section; heat exchanger pinch analysis and composite curves; hydraulic piping losses and heat exchanger pressure drops; and product distillation curves and properties. Simulation Diagram

Capacity Evaluation of a Batch Plant Vent System. PROCESS constructed a detailed process simulation of an existing plant-wide vent system (view Simulation Diagram ) that included individual unit operation vent lines, vent sub-headers, vent headers, a vent blower, and a thermal oxidizer. The purpose of the simulation was to evaluate the effects of the addition of a new batch specialty organic chemical production process to the existing system. PROCESS used existing vent system drawings as well as new field sketches developed by PROCESS to build all vent system details into the simulation. New vent stream physical and chemical characterizations developed by PROCESS were used as inputs to the simulation. Using the fluid dynamics package of the process simulation software, PROCESS was able to predict vent system flow rates, velocities, and pressures at all points in the system and was thus able to pinpoint pressure bottlenecks and to formulate and demonstrate the appropriate design remedies. PROCESS was also able to evaluate the capability of the existing vent system blower to handle the new flow rates and was able to develop design and control modifications required for the blower system. In addition, the Gibbs Free Energy Reactor module was utilized to accurately model and evaluate the capacity of, and required operating conditions for the existing thermal oxidizer, and the results were used as the basis for design and control system changes for the thermal oxidizer as well. Finally, the simulation allowed PROCESS to pinpoint potential explosive limit mixtures at various points in the vent system. Simulation Diagram

Simulation and Evaluation of Organic Chemical Production Distillation Towers. PROCESS constructed multiple simulation models for the multi-tower purification of intermediate and final specialty organic chemical products. The intermediate product purification involved two towers: Tower 1 for separating the intermediate product and residues (bottoms) from the excess organic raw material and water (distillate) and Tower 2 for separating the residues (bottoms) from the intermediate product (distillate). The final product purification also involved two towers: Tower 3 for separating final product (bottoms) from all impurities (distillate), and Tower 4 for separating heavy impurities and trace product (bottoms, recycled to Tower 3) from light impurities (distillate). Tower 1 included an overhead decanter to separate water (product) and raw material (reflux) and a side draw for high-purity raw material for recycle, and had to be evaluated considering the water / raw material minimum boiling azeotrope. Multiple runs were required for all towers for the purpose of selecting the best tower for each application from several packed and trayed towers that were available at the plant as well as for selecting and/or designing distillation system ancillary equipment (overhead condensers and receivers, reboilers, and product pumps). Due to the specialty nature of the organic chemicals involved, laboratory vapor-liquid equilibrium data had to be developed by the client and regressed by PROCESS in the simulation software thermodynamics package. Simulation Diagram

Simulation and Preliminary Process Design of a Crude Vacuum Distillation System. PROCESS constructed a detailed simulation model of a grass-roots crude oil vacuum distillation system to be designed to produce light vacuum gas oil (LVGO) and heavy vacuum gas oil (HVGO) from atmospheric crude distillation tower bottoms products. Using requested boiling point curve analytical data, PROCESS utilized the simulation software thermodynamics package to develop normal boiling point (NBP) pseudo-component characterizations of the feed, LVGO, HVGO, and vacuum residuum. The resulting vacuum system simulation model produced the following information relative to the system: overall system mass and energy balances; tower operating pressure and temperature profiles; required heights for the vacuum tower mass transfer / equilibrium packed sections; number of trays for a tower stripping boot; stripping steam rate; LVGO and HVGO pumparound rates, pumparound cooler duties (crude pre-heat train heat recovery potentials), and pumparound return temperatures; fired pre-heater required duty; overhead vapor vacuum system and condenser duties; quench residuum stream flow rates and temperatures; and overall tower height and diameter. Simulation Diagram

Evaluation/Optimization of a Light Ends Fractionation System. PROCESS constructed detailed simulation models of a two-tower valve tray fractionation system for four different light ends separation applications. The client had purchased the system, originally designed for depropanizing and debutanizing gasoline fractions, for deethanizing pipeline propane and for producing high-purity propane, iso-butane, and n-butane from separate commercial feedstocks. The simulation models were first developed to determine the feasibility of producing the high-purity products for the four applications then later refined to determine optimum operating conditions for maximizing system processing capacity and minimizing operating costs. Sensitivity analyses were also executed for the major operating parameters (feed temperature, overhead temperature and pressure, reflux rate, product flow rates, and bottoms temperature) for the purpose of determining critical control parameters and developing a process control strategy for each application. Additional simulation runs were executed to determine system design modifications that could be implemented (e.g., feed tray location, additional trays, additional heating and cooling) to further improve system performance. Simulation Diagram

Design of a Sodium Hydrosulfide Production System.  PROCESS simulated a continuous reaction system designed to produce sodium hydrosulfide (NaHS) from H2S gas and NaOH solution.  Multiple cases were run quickly to optimize the reaction system (maximizing NaHS product concentration, minimizing Na2S formation in the product, and maximizing yield) by manipulating reactor volume, NaOH concentration, and reactor recycle rate and recycle stream temperature.  In addition, designs were completed for system ancillary towers (vent gas scrubber, inlet gas stream HCl absorber, and reactor offgas H2S scrubber).  For each tower, the software was used to determine the number of required theoretical stages, the HETP, and the optimum tower diameter.  A process flow diagram of the entire reaction system was generated by the software once the process design was completed. Simulation Diagram

Simulation of Solvent Recovery Distillation System. PROCESS constructed a detailed simulation model of a solvent recovery distillation system in preparation for significant process upgrades for several client solvent recovery facilities. This existing distillation system included several complications: the combination of a packed stripping section and a trayed rectifying section; a two-phase liquid overhead byproduct; and a side draw product. Using requested boiling point curve analytical data, PROCESS utilized the simulation software thermodynamics package to develop normal boiling point (NBP) pseudo-component characterizations of the feed, side draw solvent product, bottoms solvent product, and the light overhead and heavy organics byproducts. Using requested process and engineering information, PROCESS was then able to develop an accurate, detailed process simulation of the distillation system. Simulation Diagram

Evaluation/Design of an HCl Regeneration System.  PROCESS simulated both a double-effect evaporator and packed distillation tower for regenerating (concentrating) a hydrochloric acid stream.  The software thermodynamics package was used to predict the shift in the HCl/water azeotrope caused by the presence of antimony trichloride.  PROCESS was able to show that the operating envelope for the preferred (from an energy consumption standpoint) evaporation system was far too small for practical process control.  The selected distillation system process design was then completed (required number of theoretical stages, HETP, optimum column diameter, and reboiler size) using the software.  Additional simulation cases were quickly run to determine designed distillation column performance under various postulated operating conditions. Simulation Diagram

Elimination of Condensing Solvent Recovery System Downtime.  PROCESS used the simulation software to characterize a multi-condenser solvent recovery system and to develop new design and operating conditions for the system that will reduce the pharmaceutical production system's downtime due to condenser freezing to essentially zero. Simulation Diagram

Evaluation of a Refinery Flare System Capacity.  PROCESS constructed a detailed hydraulic model of a complex refinery flare system using the simulation software and tested the system's carrying capacity under various multiple pressure relief scenarios.  The use of the software's thermodynamics capabilities for the flare capacity evaluation gave much less conservative (more realistic) results than more traditional approaches due to its ability to accurately predict two-phase behavior.  This prevented the client from making costly (and unnecessary) system modifications. Simulation Diagram

Optimization of a Multi-Tower HCl Absorption System.  PROCESS used the simulation software to quickly execute multiple cases for a three-tower HCl absorption system designed to produce concentrated hydrochloric acid from two production offgas streams with widely differing flow rates and HCl concentrations.  The following variables were adjusted in a systematic fashion using simulation to maximize acid concentration, minimize offgas HCl emissions, and minimize operating costs: tower packed heights, recycle flow rates and temperatures, quench/absorption water flow rates, and feed gas and intermediate stream routings.  After design was complete, sensitivity analyses were run on the key process variables to determine the "controllability" of the system during changes in operating conditions. Simulation Diagram

Design of a Fume Incinerator Heat Recovery System.  PROCESS demonstrated, using the simulation software, how the addition of a recuperative heat exchanger to a fume incineration system could save 65% of current fuel costs.  The software was also used to produce the basic design information for the exchanger. Simulation Diagram

Design of Nuclear Facility Cooling Water Loops.  PROCESS used the fluid dynamics package of the simulation software to perform detailed process designs of complex cooling water loops for a nuclear research facility.  Loop pressure profiles were precisely calculated to prevent overpressure of specialty technical components in the loops.  Line sizes, and flow control valve sizes and normal operating positions were also determined using the software. Simulation Diagram

Design of a Refinery Fuel Gas Conditioning System.  PROCESS used the simulation software to construct a mass and energy balance for a petroleum refinery central fuel gas conditioning system, with the end goal being the redesign of the system to provide fuel gas with a more consistent heating value, a higher purity, and a more consistent supply pressure.  PROCESS simulated both the existing system and the redesigned system. Simulation Diagram

 

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