Search

Engineering efforts to handle contemporary energy supply challenges and mitigate pollutant emission lead towards more complicated systems. Power plants are supplementing with additional processing units, alternative production modes and higher level of automation. Wind and solar sources, biomass combustion, gasification, carbon capture and storage (CCS), and cogeneration have appeared as important players in the energy systems. The increasing complexity comprises a risk that the systems become less manageable and less stable than currently. Traditional steady-state engineering methods cannot fully address these challenges that are inherently dynamic in their nature. Dynamic process simulation appears as important tool to the systems design and optimisation tasks. A large variety of dynamic process modelling and simulation approaches has been presented recent years. This paper presents a brief review of methods and simulation packages that are generally applied for studying energy systems' transient behaviour. A CCS capable power plant is presented as an example of utilizing dynamic process simulation for virtual evaluation of a novel electricity production concept. The modelling was performed using two simulators Apros and Aspen Plus Dynamics, which were linked together for dynamic simulating the full chain of cryogenic oxygen distillation, oxy combustion, turbine islands and carbon dioxide purification and liquefaction operations.

A series of copolyanhydrides, consisting of 2,3,4,5-tetra-O-acetylgalactaric acid (AGA) and adipic acid (AA) as monomer units, was polymerized. Synthesis of AGA monomer consisted of two steps. First, O-acetylation of galactaric acid secondary hydroxyl groups was performed using acetic anhydride as a reagent. Acetic anhydride was then further used as a reagent in the synthesis of diacetyl mixed anhydride of AGA. Polymerizations were conducted as bulk condensation polymerization at 150 °C. Thermal properties of the copolymers varied depending on monomer composition. Increase in the AGA content had a clear increasing effect on the Tg. A similar increasing effect was observed in Tm. The degree of crystallinity decreased as AGA content increased. There was a slightly lowering tendency in the molecular weights of the obtained polymers when the AGA content in the polymerization mixtures increased. The described synthesis route shows that bio-based aldaric acid monomers are potential candidates for the adjustment of thermal properties of polyanhydrides.

In large and complex processes use of simulators will take place more and more in the future to avoid and learn about transients and unexpected situations. There are plenty of dynamic simulation tools in the markets but most of them have been developed and used for quite specific and limited application areas. At the moment there are just few simulation tools which are capable to handle dynamically in the same simulation case challenging process areas like combustion, distillation, chemistry and control of very large process areas. For this reason, in this study, there was a need to carry out co–simulation where two dynamic simulation tools Apros and Aspen Plus Dynamics were combined together by using Matlab Simulink as an interface. The co–simulation approach was a way to construct large dynamic process simulation environment, where typical operational transients and failure situations of an oxy fired power plant were possible to test and analyze. Under EU 7th Framework Programme (FP7) the FLEXI BURN CFB project an oxy firing concept based on circulated fluidized bed (CFB) combustion and supercritical once-through (OTU) water steam cycle was developed and successfully demonstrated [1] . This project also generated a dynamic simulation model of the 1st generation oxy firing concept, as we call it. In the EU 7th Framework Program's project O2GEN (Optimization of Oxygen-based CFBC Technology with CO2 capture), the 2nd generation concept of CFB based oxy firing was developed. The target of the project was, at first, to increase O2 content in recirculated flue gas to see what kind of effect it has to the heat exchange and corrosion in the boiler. Secondly, the target was to carry out exergy analysis to increase the whole concept efficiency by decreasing energy consumption in the boiler, Air Separation Unit (ASU) and CO2 -purification unit (CPU). Based on these steady state analysis means the refined concept was then modelled for dynamic simulations which were carried out by using Apros and Aspen Plus Dynamics dynamic modelling tools in a co–simulation mode. This paper deals with dynamic simulation of the 2nd generation 600 MW oxy fired CFB once trough boiler. In this paper we will present the dynamic model which includes oxy fired CFB boiler, turbine island, ASU and CPU with all needed equipment like heat exchangers, pipes, pumps, air and fuel feeding systems, distillation columns and sequestration vessels. Automation like measurements, controllers and actuators are included in the model. The simulation case selected for this paper presents an analysis what happens when one of the oxidant fans trips on boiler full load operation and how to handle this kind of failure by decreasing the boiler load to sufficient level of regarding the available oxidant feeding capacity. There were several items which were taken into account in the boiler, turbine island, ASU and CPU side when this kind of failure takes impact. The main findings in the failure analysis will be presented. Finally, discussion and future aspects of the simulation approach described will be given.

Dynamic process simulation provides a tool to evaluate operational issues of a new process concept before the plant construction. This paper studies a carbon capture and storage (CCS) capable power plant concept with a model including a supercritical once-through CFB boiler with gas and water steam sides, a turbine island, an interface from the air separation unit (ASU) and the control system to manage typical operational transients. Switching between the air and oxy firing modes is one of the key operations in oxy combustion processes. The selected mode switching strategy uses simultaneous linear ramps for the mass flows of the primary and secondary air, oxygen, and recirculated flue gas. The results show that the firing mode can be successfully switched within 25–37 min. The flue gas path difference between the air-firing and oxy-firing modes due to the flue gas recirculation causes significant differences in dynamic behaviour. The simulations emphasize importance of good control and coordination of the gas flows. Feedback control of the flue gas and/or oxidants O 2 content during the mode switching is suggested to improve robustness against disturbances, for example, in oxygen delivery, flow measurements, fuel feeding and combustion.

Complex refractive index of strongly depolarizing starch acetate is investigated as a function of bulk package density, which is compulsory parameter in analysis of light scattering from nanoscale starch acetate pigments and fillers. The measurements were made using a laser-goniometer and spectrophotometer to gain data for refractive index analysis according to the Brewster’s law and Fresnel equations. The real part of refractive index was verified by microscopic immersion method.

As a dispatchable clean energy source, concentrated solar power (CSP) can be one of the key technologies to overcome many problems related to fossil fuel consumption and electricity balancing problems. Solar is a variable location, time and weather dependent source of energy, which sets challenges to solar field operations. With proper dynamic simulation tools it is possible to study dynamics of CSP field under changing weather conditions, find optimum control strategies, and plan and predict the performance of the field. CSP technology considered in this paper, linear Fresnel reflector (LFR), is a proven line focusing technology, having simpler design but suffering in optical performance compared to more mature parabolic trough (PT) technology. Apros dynamic simulation software is used to configure and simulate the solar field. Apros offers a possibility to dynamically simulate field behavior with varying collector configuration, field layout and control mode under varying irradiation conditions. The solar field applies recirculation (RC) as a control mode and direct steam generation (DSG) producing superheated steam. DSG sets challenges for the control scheme, which main objective is to maintain constant steam pressure and temperature at the solar field outlet under varying inlet water and energy conditions, while the steam mass flow can vary. The design and formulation of an entire linear Fresnel solar field in Apros is presented, as well as the obtained control scheme. The field includes user defined amount of collector modules, control system and two modules describing solar irradiation on the field. As two-phase water/steam flow is used, an accurate 6-equation model is used in Apros. Irradiation on the solar field under clear sky conditions is calculated according to time, position and Linke turbidity factor. Overcast conditions can be created by the clear sky index. For LFR single-axis sun tracking system is applied. In order to test the model functionality and to investigate the field behavior, thermal performance of the field was simulated at different dates at two different locations, and the results were compared. Similar field dimensions and control schemes were applied in each case, and simulations were done for full 24 hours in order to study the daily operations and ensure process stability. Control scheme functionality is evaluated based on the plant behavior in simulation cases having different operational conditions. The proper operability of the configured LFR model is evaluated. Obtained performance results show differences between locations and variation depending on season and time. The importance of a proper control system is revealed. The results show that the dynamic model development of a solar field is necessary in order to simulate plant behavior under varying irradiation conditions and to further develop optimal field control schemes and field optimizing process. The future work in the development of the LFR model presented will focus on dynamic response behavior development under transient conditions and field start-up and shut down procedure development.

A novel acetylated anhydroglucose oligomer (AGU-oligomer), prepared by acid catalyzed transglycosida- tion of potato starch triacetate and ethylene glycol, was used as a multifunctional coinitiator for the ring-opening poly- merization of -caprolactone (-CL). The polymers were synthesized using different weight ratios of the starting materials and were characterized by NMR, SEC, and MALLS. The results confirmed the expected P(AGU/CL) polymer structure, namely a 'comb-like' graft-copolymer having the AGU oligomer as backbone with PCL grafts of variable chain lengths (LCL 4 -21). Thermal and mechan- ical properties of graft-copolymers with different -CL block lengths were examined. By changing the graft length, crys- tallinity was controlled and amorphous polymers were ob- tained with AGU-oligomer contents higher than 50 wt %. The tensile properties varied with the composition and a copolymer having 40 wt % of AGU-oligomer behaved like soft elastomer, showing high elongation at break. © 2006

The aim of this study was to evaluate film-formation properties of a novel, organic solvent-free aqueous dispersion of potato starch acetate (SA; degree of substitution 2.8) and its ability to control drug release from a coated tablet. Initially, film-formation mechanisms and drug permeabilities of both organic solvent and dispersion-based SA free films (prepared by cast or spraying techniques) were investigated. The SA dispersion was suitable for the fluid-bed coating process, forming strong films with complete coalescent polymeric spheres. The model compounds predominantly permeated via the micro-pores of SA free films, which resulted from the leaching of water-soluble excipients from the dispersion. Thus, the permeation rate depended on the film structure rather than the physico-chemical properties of the penetrant. In the case of SA-coated tablet, drug release was sustained when the coating level was increased (from 12% to 20%, stated as a weight gain), and also as lipophilicity of the drug increased. When compared to the reference polymer dispersion (Surelease®), SA coatings showed better mechanical properties against the osmotic pressure caused by a hydrophilic core tablet. These results clearly demonstrate that SA dispersion has high utility as a novel aqueous coating material for controlled release products.

In the present work, measurement experience of oxy combustion in a pilot scale circulating fluidized bed (CFB) combustor is summarized. The aim was to study combustion dynamics under air-and oxygen-firing conditions in order to develop and validated combustion controls for Flexi-Burn™ CFB combustion technology. Dynamic CFB-pilot combustion tests were carried out including various step and ramp tests in both air and oxy combustion and different operation strategies for oxy combustion.

Sequential extraction method was applied to lignins from hardwood and softwood isolated by kraft and VTT organosolv processes. Solvent extraction was found to fractionate lignin according to the molecular weight: small molecular weight lignin is dissolved in the organic solvents and the lignin with higher molecular weight is enriched into the residue. Isolated acetone fractions of lignin are more homogeneous with narrow molecular weight distributions. Based on the31P NMR results, both total hydroxyl content and the content of phenolic hydroxyl units are higher in the acetone fraction than in the residue. Pyrolysis-GC/MS of all lignins showed thatp-hydroxy phenols are enriched to the residues. Preferential dissolution of syringyl type lignin in acetone was observed for hardwood kraft lignin, whereas the opposite behavior was seen for the hardwood organosolv lignin. Glass transition temperatures of all acetone soluble fractions were notably low compared to starting and residue lignins, which gives possibilities for future applications as a material with specific properties.

Graft copolymers of acetylated starch oligomer (AS) and poly(methyl methacrylate) (PMMA) were polymerized by atom transfer radical polymerization (ATRP). AS was converted to an ATRP macroinitiator by converting a part of the hydroxyl groups of AS to 2-bromoisobutyryl groups. Macroinitiators with varying degrees of substitution for the 2-bromoisobutyryl group were prepared. The polymerizations were conducted using CuBr/BiPy catalyst system, either in bulk or in 1:1 v/v THF solution. They proceeded with first-order kinetics and the molecular weights of the polymers increased linearly with conversion. Graft copolymers with different graft densities and graft lengths were prepared in a controlled manner. The hydrophobicity of these copolymers was studied by contact angle measurements.

The preparation of highly porous starch acetate particles suitable for filler for paper was studied using solution precipitation techniques. Chemically cleaved starch acetate with a DS value of 2 to 3 and glass transition temperature of +158-160 °C was used as starting material for the preparation of ideally spherical particles in diameter as one half of the wave length of the visible light.Particle shape and size take form spontaneously when solvated (e.g., acetone-ethanol mixture) starch polymer is mixed with non-solvent (e.g., water).The refractive index of the starch pigment is 1.47 and an ISO brightness value as high as 94 has been measured.The preparation of starch pigment dispersion of 20-30% solid contents has been carried out on a semi-industrial scale by using 0.25 m3 DRAISS reactor in combination with 0.2 micron cut-off continuous filtering unit.Starch pigment has improved affinity to paper surface and it can be used as such or mixed with other pigments to enhance optical or printing properties of paper.

Purpose: The aim of this study was to investigate the ability of n-alkenyl succinic anhydrides (n-ASAs) to improve the film-forming characteristics of a novel coating polymer, potato starch acetate degree of substitution 2.8 (SA). n-ASAs were also applied to improve the otherwise brittle properties of ethyl cellulose (EC) aqueous dispersion (Aquacoat®) and EC solvent-based films. Methods: The effectiveness of two n-ASAs, 2-octenyl succinic anhydride (OSA) and 2-dodecen-1-ylsuccinic anhydride were evaluated as plasticizers. Mechanical properties, both water vapor and drug permeabilities, and glass transition temperatures of the cast free films were measured. Triethyl citrate and dibutyl sebacate were used as reference plasticizers. Results: The long hydrocarbon chain of n-ASA, with its accessible carbonyl groups, enabled a strong plasticization effect on the tested polymers. Due to the excellent mechanical properties (i.e., a tough film structure with considerable flexibility) and low permeability of the plasticized films, n-ASAs, and especially OSA proved to be an ideal plasticizer particularly for EC based coatings. Also, the EC aqueous dispersion plasticized with n-ASAs resulted in a markedly enhanced coalescence of the colloidal polymer particles, even at low drying temperatures. Conclusions: In applications where a coating with high flexibility is required, n-ASAs can be used as plasticizers at moderately high concentrations (up to 60–70%, w/w) without losing the high tensile strength, excellent toughness and low permeability of EC and SA films.

The hydroxyl groups of conifer tree tannins can be readily converted to quaternary ammonium ether derivatives having a N-content as high as 4 percent and reagent incorporation of about 90 percent. While such a cationic tannin is an effective flocculant, its performance can still be improved by crosslinking reactions of the A-ring with formaldehyde or epichlorohydrin. The flocculation ability of cationic tannins can readily be evaluated in the laboratory by a conventional jar test or by a photometric dispersion analyzer, which records the relative floc sizes. Many times the best flocculation behavior of the cationic tannin in a real wastewater treatment situation is achieved by a combination dosage, which contains cationic tannin as an inexpensive charge neutralizer of the colloidal particles and a more costly macromolecular linear polymer as a bridging agent.

The results from the coating trials show that after calendering, the starch pigment is as good as the reference carbonate and clay pigments in brightness, opacity, gloss and roughness. Mixtures AP-Clay and AP-GCC-Clay give even better opacity and gloss than any of these pigments alone.