Optimize Spray Dryers and Fluidized Bed Reactors with ® Aspen Plus Webinar Q&A This document summarizes the responses to questions posed before and during the webinar. Additional questions should be directed to AspenTech to AspenTech Support .
General Questions Q: Is there a leaching operation included? A: We A: We don’t have a special a special leaching unit operation. You could try using one of the reactors models (CSTR etc.) and ELECNRTL as a property method to model leaching. _____________ ____________________ _______________ ________________ _______________ ______________ _______________ ___________________ _________________ ______________ _______________ ______________ _______________ __________ __ Q: Could we have today’s presentation example file? A: There A: There are dozens of self-guided demos available on Aspen on Aspen Tech’s Tech’s Solids Solids Modeling Webpage, the Support Center , and through ® aspenONE Exchange. Included in this set of examples are the spray dryer model and a simple version of the fluidized bed reactor model. _____________ ____________________ _______________ ________________ _______________ ______________ _______________ ___________________ _________________ ______________ _______________ ______________ _______________ __________ __ Q: Does AspenTech anticipate modeling any auger-type reactors for pyrolysis? A: The A: The Aspen Plus model library contains different reactor models (e.g. CSTR and plug flow reactor). To model an auger-type reactor, you could try a plug flow reactor or a series of CSTRs. _____________ ____________________ _______________ ________________ _______________ ______________ _______________ ___________________ _________________ ______________ _______________ ______________ _______________ __________ __ Q: In V8.2, I couldn't see a way to enter a sorption isotherm. Is this now possible in V8.4? A: In A: In the current version 8.4 of the dryer, the user specifies the equilibrium moisture content content as a single value, meaning there is no option available to specify a sorption isotherm. You can try to use a calculator block to determine the equilibrium moisture content based on a sorption isotherm and the dryer’s outlet conditions. You can then set the calculated value for the equilibrium moi sture content in the dryer. _____________ ____________________ _______________ ________________ _______________ ______________ _______________ ___________________ _________________ ______________ ________________ _______________ ______________ _________ __ Q: Are there any example models for crystallization? A: Yes, A: Yes, we have an example of crystallization in the potassium chloride self-guided demo. This example, along with other solids modeling self-guided demos, is available on the AspenTech Solids Solids Modeling Modeling Webpage Webpage , the Support Center , and through aspenONE Exchange. _____________ ____________________ _______________ ________________ _______________ ______________ _______________ ___________________ _________________ ______________ _______________ ______________ _______________ __________ __ Q: Are there any example models for extrusion? A: Currently, A: Currently, we don’t have any examples any examples for extrusion. To describe an extruder, you could use a granulator block and then select the “specify outlet PSD” option. _____________ ____________________ _______________ ________________ _______________ ______________ _______________ ___________________ _________________ ______________ _______________ ______________ _________________ __________ Q: When the optimization has completed, how much margin do you leave on your results to ensure that you are safe in operation? A: We can’t answer this on this on a general basis. It depends on the process, the model, etc. It might be a good idea to run a sensitivity analysis around the optimal parameter values to better understand how sensitive the process is against the changes of these parameters.
Q: Can we simulate an airlift reactor w ith Aspen Plus? A: If we were to assume that solids and gas be put in plug flow, you can try to use a plug flow reactor (RPLUG) to model an air lift reactor. If you also want to account for the pressure drop, you might try to use a sequence of RPLUG and pipe models. The pipe model can then describe the pressure drop due to t he pneumatic transport of the solids. ___________________________________________________________________________________________________________
Spray Dryer Questions Q: Can you model a closed-loop, as well as optimize a condenser? A: If you are talking about the spray dryer example, then yes, you could model that. ___________________________________________________________________________________________________________ Q: Can the spray dryer model hollow spheres? A: This capability is not available in the current version of Aspen Plus. ___________________________________________________________________________________________________________ Q: Can you use drying gas other than air? A: Yes, you can specify a drying agent other than air as long as it’s in the Aspen Properties database or you have information about its viscosity, heat capacity values, etc. that you can enter into the database. ___________________________________________________________________________________________________________ Q: For the spray dryer, I want to look at RH% in the cyclone for closed-loop and test the sensitivity a ccording to other parameters, such as condenser or mass flow rate of drying air or solution feed. Can we use Aspen Plus to do this? A: Yes, you can define any conventional components as “moisture components” i n Aspen Plus. The liquid is then considered a part of the solid phase and cannot be evaporated by a flash. This enables you to track the moisture of the solids for each stream in the process. In your particular case, you can analyze the influence of the different process parameters (e.g. drying agent flow rate, temperature, spray rate, etc.) on the residual moisture of the particles. ___________________________________________________________________________________________________________ Q: For spray drying, how much design information does Aspen Plus supply for a given feed, dissolved solids density, and concentration? A: The spray dryer model itself doesn’t have a design mode— it predicts the outlet stream conditions based on given geometry and operating conditions. Aspen Plus offers different tools (e.g. optimization, design) that allow you to specify the outlet conditions you want to achieve to then change certain parameters in the flowsheet (e.g. geometry parameter, flow rates, temperatures, etc.). You can use this workflow to determine the design information you are looking for. ___________________________________________________________________________________________________________ Q: What data is needed to predict the dryer performance and the diffusion-limited part of the drying curve? A: The spray dryer and the convective dryer model considers the constant drying r ate period (first drying period) and the diffusionlimited falling rate drying period (second drying period). To describe the second drying period, we use a normalized drying curve. To specify the normalized drying curve, you need the criti cal and the equilibrium moisture content, as well as the normalized drying curve data itself. You can determine this data fr om a drying experiment. During the webinar on granulation and convective drying , we explained how to determine the normalized drying curve based on measured data. In addition to viewing this webinar, you can find an explanation on how to determine the normalized drying curve based on measured data in the belt dryer example in the knowledge base. ___________________________________________________________________________________________________________ Q: Is there a model where you can consider agglomeration on the spray dryer process? A: The current implementation of the spray dr yer model does not consider agglomeration. You can try to add a granulator block downstream of the spray dryer and consider the agglomeration of the particles.
Fluidized Bed Reactor Questions Q: Can a spouted bed reactor be simulated with the fluidized bed reactor? A: The current implementation of the fluidized bed is developed with bubbling and circulating fluidized beds in m ind. For the fluid-mechanics of the bottom zone, we use a model according to Werther and Wein. For the freeboard, we use a model according to Kunii and Levenspiel. All the sources are fully documented in the help system and the PDF documentation files. Please review the equations and decide on your own if this model is applicable to your specific application. ___________________________________________________________________________________________________________ Q: Can a specific kinetic be introduced in the block of the fluidized bed reactor? A: To consider chemical reactions in the fluidized bed, you can assign a chemistry object to the block (similar to RCSTR and other reactors). The chemistry object then allows you to specify different types of reaction kinetics. We have published an example that explains step-by-step how this works. This and other examples can be found in aspenONE Exchange and on the AspenTech Support Site. If for some reason the available reactions kinetics do not fit your special case, you also have the option to introduce a user kinetic. ___________________________________________________________________________________________________________ Q: How do we get a bubble diameter in a f ludized reactor? A: For the fluid-mechanics of the bottom zone, we use a model according to Werther and Wein. This model considers the growth and splitting of bubbles. Based on the gas distributor geometry and the f luidization gas flow rate and properties, we estimate the initial bubble size and then use the model according to Werther and Wein to calculate the bubble diameter, bubble volume fraction, bubble rise velocity, etc. The m odel is fully documented in the help system and the PDF documentation files. Please review the equations for more details. ___________________________________________________________________________________________________________ Q: Where do you get information on the models selected for inputs for fluidized bed reactors? A: All the sources for our models are fully documented in the help system and the PDF documentation files. Please review documentation to get more details on the different models available. ___________________________________________________________________________________________________________ Q: Could the particle density decrease as it increases in size, for example due to coke build-up? A: Aspen Plus allows you to define each particle type as a separate sub-stream. The particle type (sub stream) is then described by its composition, particle size, and eventually moisture content. Please see the multiple particle type examples in aspenOne Exchange or the knowledge base for more details. If you change the composition of the particles by a chemical reaction, it will also change the particles density. ___________________________________________________________________________________________________________ Q: Can Aspen Plus compare the difference in reactions between a fluidized bed reactor and an auger-type reactor? A: The fluidized bed reactor model assumes the solids are ideally mixed, while the gas is in plug f low. For an auger-type reactor, both the gas and the solids are in plug flow. To compare these different reactors,define a flowsheet containing both a fluidized bed reactor and a plug flow reactor (RPLUG block) and then you can compare the r esults from both blocks. ___________________________________________________________________________________________________________ Q: Can you specify a solid feed to the fluidized bed and if it would be able to account for char and ash ? A: The fluidized bed has at least two inlet streams, the fluidization gas and the solid feed. In addition to this, the f luidized bed can have several additional gas inlets. The composition, PSD, mass flow, temperature, etc. of the solid feed stream is set by the upstream block. In the simplest case, this is a feed unit where you can fully specify the solid feed stream for the fluidized bed. You can also consider char and ash in your model. Please notice that coal is considered as a non-conventional component in Aspen Plus, meaning we have special thermodynamic models that use atomic analysis (e.g., %C, H, O...). The analysis is defined through component attributes such as ULTANAL, PROXANAL, etc. The computer-based training module for solids contains m ore detailed information on this and are available on the AspenTech Support Site.
Q: Can you simulate the fluidized bed combustion of a solid coal/biomass feedstock and specify the amount of fly ash and bottom ash produced in the combustion process? A: The reactions in the fluidized bed are described by reactions kinetics. Therefore, you cannot directly define the amount of ash and bottom ash produced, but it will calculate based on the defined kinetics. ___________________________________________________________________________________________________________ Q: Is it possible to simulate a CFB furnace with wood dust (biomass), coal combustion (Gibbs reactor), or primary and secondary air? A: The fluidized bed model allows you t o consider several additional air streams. You can also consider c hemical reactions by assigning chemistry objects to the block.
