Biomass Gasification - Process analysis and dimensioning aspects for downdraft units and gas cleaning lines

In such territories where food production is mostly scattered in several small / medium size or even domestic farms, a lot of heterogeneous residues are produced yearly, since farmers usually carry out different activities in their properties. The amount and composition of farm residues, therefore, widely change during year, according to the single production process periodically achieved. Coupling high efficiency micro-cogeneration energy units with easy handling biomass conversion equipments, suitable to treat different materials, would provide many important advantages to the farmers and to the community as well, so that the increase in feedstock flexibility of gasification units is nowadays seen as a further paramount step towards their wide spreading in rural areas and as a real necessity for their utilization at small scale. Two main research topics were thought to be of main concern at this purpose, and they were therefore discussed in this work: the investigation of fuels properties impact on gasification process development and the technical feasibility of small scale gasification units integration with cogeneration systems. According to these two main aspects, the present work was thus divided in two main parts. The first one is focused on the biomass gasification process, that was investigated in its theoretical aspects and then analytically modelled in order to simulate thermo-chemical conversion of different biomass fuels, such as wood (park waste wood and softwood), wheat straw, sewage sludge and refuse derived fuels. The main idea is to correlate the results of reactor design procedures with the physical properties of biomasses and the corresponding working conditions of gasifiers (temperature profile, above all), in order to point out the main differences which prevent the use of the same conversion unit for different materials. At this scope, a gasification kinetic free model was initially developed in Excel sheets, considering different values of air to biomass ratio and the downdraft gasification technology as particular examined application. The differences in syngas production and working conditions (process temperatures, above all) among the considered fuels were tried to be connected to some biomass properties, such elementary composition, ash and water contents. The novelty of this analytical approach was the use of kinetic constants ratio in order to determine oxygen distribution among the different oxidation reactions (regarding volatile matter only) while equilibrium of water gas shift reaction was considered in gasification zone, by which the energy and mass balances involved in the process algorithm were linked together, as well. Moreover, the main advantage of this analytical tool is the easiness by which the input data corresponding to the particular biomass materials can be inserted into the model, so that a rapid evaluation on their own thermo-chemical conversion properties is possible to be obtained, mainly based on their chemical composition A good conformity of the model results with the other literature and experimental data was detected for almost all the considered materials (except for refuse derived fuels, because of their unfitting chemical composition with the model assumptions). Successively, a dimensioning procedure for open core downdraft gasifiers was set up, by the analysis on the fundamental thermo-physical and thermo-chemical mechanisms which are supposed to regulate the main solid conversion steps involved in the gasification process. Gasification units were schematically subdivided in four reaction zones, respectively corresponding to biomass heating, solids drying, pyrolysis and char gasification processes, and the time required for the full development of each of these steps was correlated to the kinetics rates (for pyrolysis and char gasification processes only) and to the heat and mass transfer phenomena from gas to solid phase. On the basis of this analysis and according to the kinetic free model results and biomass physical properties (particles size, above all) it was achieved that for all the considered materials char gasification step is kinetically limited and therefore temperature is the main working parameter controlling this step. Solids drying is mainly regulated by heat transfer from bulk gas to the inner layers of particles and the corresponding time especially depends on particle size. Biomass heating is almost totally achieved by the radiative heat transfer from the hot walls of reactor to the bed of material. For pyrolysis, instead, working temperature, particles size and the same nature of biomass (through its own pyrolysis heat) have all comparable weights on the process development, so that the corresponding time can be differently depending on one of these factors according to the particular fuel is gasified and the particular conditions are established inside the gasifier. The same analysis also led to the estimation of reaction zone volumes for each biomass fuel, so as a comparison among the dimensions of the differently fed gasification units was finally accomplished. Each biomass material showed a different volumes distribution, so that any dimensioned gasification unit does not seem to be suitable for more than one biomass species. Nevertheless, since reactors diameters were found out quite similar for all the examined materials, it could be envisaged to design a single units for all of them by adopting the largest diameter and by combining together the maximum heights of each reaction zone, as they were calculated for the different biomasses. A total height of gasifier as around 2400mm would be obtained in this case. Besides, by arranging air injecting nozzles at different levels along the reactor, gasification zone could be properly set up according to the particular material is in turn gasified. Finally, since gasification and pyrolysis times were found to considerably change according to even short temperature variations, it could be also envisaged to regulate air feeding rate for each gasified material (which process temperatures depend on), so as the available reactor volumes would be suitable for the complete development of solid conversion in each case, without even changing fluid dynamics behaviour of the unit as well as air/biomass ratio in noticeable measure. The second part of this work dealt with the gas cleaning systems to be adopted downstream the gasifiers in order to run high efficiency CHP units (i.e. internal engines and micro-turbines). Especially in the case multi–fuel gasifiers are assumed to be used, weightier gas cleaning lines need to be envisaged in order to reach the standard gas quality degree required to fuel cogeneration units. Indeed, as the more heterogeneous feed to the gasification unit, several contaminant species can simultaneously be present in the exit gas stream and, as a consequence, suitable gas cleaning systems have to be designed. In this work, an overall study on gas cleaning lines assessment is carried out. Differently from the other research efforts carried out in the same field, the main scope is to define general arrangements for gas cleaning lines suitable to remove several contaminants from the gas stream, independently on the feedstock material and the energy plant size The gas contaminant species taken into account in this analysis were: particulate, tars, sulphur (in H2S form), alkali metals, nitrogen (in NH3 form) and acid gases (in HCl form). For each of these species, alternative cleaning devices were designed according to three different plant sizes, respectively corresponding with 8Nm3/h, 125Nm3/h and 350Nm3/h gas flows. Their performances were examined on the basis of their optimal working conditions (efficiency, temperature and pressure drops, above all) and their own consumption of energy and materials. Successively, the designed units were combined together in different overall gas cleaning line arrangements, paths, by following some technical constraints which were mainly determined from the same performance analysis on the cleaning units and from the presumable synergic effects by contaminants on the right working of some of them (filters clogging, catalysts deactivation, etc.). One of the main issues to be stated in paths design accomplishment was the tars removal from the gas stream, preventing filters plugging and/or line pipes clogging At this scope, a catalytic tars cracking unit was envisaged as the only solution to be adopted, and, therefore, a catalytic material which is able to work at relatively low temperatures was chosen. Nevertheless, a rapid drop in tars cracking efficiency was also estimated for this same material, so that an high frequency of catalysts regeneration and a consequent relevant air consumption for this operation were calculated in all of the cases. Other difficulties had to be overcome in the abatement of alkali metals, which condense at temperatures lower than tars, but they also need to be removed in the first sections of gas cleaning line in order to avoid corrosion of materials. In this case a dry scrubber technology was envisaged, by using the same fine particles filter units and by choosing for them corrosion resistant materials, like ceramic ones. Besides these two solutions which seem to be unavoidable in gas cleaning line design, high temperature gas cleaning lines were not possible to be achieved for the two larger plant sizes, as well. Indeed, as the use of temperature control devices was precluded in the adopted design procedure, ammonia partial oxidation units (as the only considered methods for the abatement of ammonia at high temperature) were not suitable for the large scale units, because of the high increase of reactors temperature by the exothermic reactions involved in the process. In spite of these limitations, yet, overall arrangements for each considered plant size were finally designed, so that the possibility to clean the gas up to the required standard degree was technically demonstrated, even in the case several contaminants are simultaneously present in the gas stream. Moreover, all the possible paths defined for the different plant sizes were compared each others on the basis of some defined operational parameters, among which total pressure drops, total energy losses, number of units and secondary materials consumption. On the basis of this analysis, dry gas cleaning methods proved preferable to the ones including water scrubber technology in al of the cases, especially because of the high water consumption provided by water scrubber units in ammonia adsorption process. This result is yet connected to the possibility to use activated carbon units for ammonia removal and Nahcolite adsorber for chloride acid. The very high efficiency of this latter material is also remarkable. Finally, as an estimation of the overall energy loss pertaining the gas cleaning process, the total enthalpy losses estimated for the three plant sizes were compared with the respective gas streams energy contents, these latter obtained on the basis of low heating value of gas only. This overall study on gas cleaning systems is thus proposed as an analytical tool by which different gas cleaning line configurations can be evaluated, according to the particular practical application they are adopted for and the size of cogeneration unit they are connected to.

Effect of rearing techniques and feed composition on productive traits, bird welfare and quality of poultry products

The PhD project was focused on the study of the poultry welfare conditions and improvements. The project work was divided into 3 main research activities. A) Field evaluation of chicken meat rearing conditions kept in intensive farms. Considering the lack of published reports concerning the overall Italian rearing conditions of broiler chickens, a survey was carried out to assess the welfare conditions of broiler reared in the most important poultry companies in Italy to verify if they are in accordance with the advices given in the European proposal COM (2005) 221 final. Chicken farm conditions, carcass lesions and meat quality were investigated. 1. The densities currently used in Italy are in accordance with the European proposal COM 221 final (2005) which suggests to keep broilers at a density lower than 30-32 kg live weight/m2 and to not exceed 38-40 kg live weight/m2. 2. The mortality rates in summer and winter agree with the mortality score calculated following the formula reported in the EU Proposal COM 221 final (2005). 3. The incidence of damaged carcasses was very low and did not seem related to the stocking density. 4. The FPD scores were generally above the maximum limit advised by the EU proposal COM 221 final (2005), although the stocking densities were lower than 30-32 kg live weight per m2. 5. It can be stated that the control of the environmental conditions, particularly litter quality, appears a key issue to control the onset of foot dermatitis. B) Manipulation of several farm parameters, such litter material and depth, stocking density and light regimen to improve the chicken welfare conditions, in winter season. 1. Even though 2 different stocking densities were established in this study, the performances achieved from the chickens were almost identical among groups. 2. The FCR was significantly better in Standard conditions contrarily to birds reared in Welfare conditions with lower stocking density, more litter material and with a light program of 16 hours light and 8 hours dark. 3. In our trial, in Standard groups we observed a higher content of moisture, nitrogen and ammonia released from the litter. Therefore it can be assumed that the environmental characteristics have been positively changed by the improvements of the rearing conditions adopted for Welfare groups. 4. In Welfare groups the exhausted litters of the pens were dryer and broilers showed a lower occurrence of FPD. 5. The prevalence of hock burn lesions, like FPD, is high with poor litter quality conditions. 6. The combined effect of a lower stocking density, a greater amount of litter material and a photoperiod similar to the natural one, have positively influenced the chickens welfare status, as a matter of fact the occurrence of FPD in Welfare groups was the lowest keeping the score under the European threshold of the proposal COM 221 final(2005). C) The purpose of the third research was to study the effect of high or low stocking density of broiler chickens, different types of litter and the adoption of short or long lighting regimen on broiler welfare through the evaluation of their productivity and incidence of foot pad dermatitis during the hot season. 1. The feed efficiency was better for the Low Density than for High Density broilers. 2. The appearance of FPD was not influenced by stocking density. 3. The foot examination revealed that the lesions occurred more in birds maintained on chopped wheat straw than on wood shaving. 4. In conclusion, the adoptions of a short light regimen similar to that occurring in nature during summer reduces the feed intake without modify the growth rate thus improving the feed efficiency. Foot pad lesion were not affected neither by stocking densities nor by light regimens whereas wood shavings exerted a favourable effect in preserving foot pad in good condition. D) A study was carried out to investigate more widely the possible role of 25-hydroxycholecalciferol supplemented in the diet of a laying hen commercial strain (Lohmann brown) in comparison of diets supplemented with D3 or with D3 + 25- hydroxycholecalciferol. Egg traits during a productive cycle as well as the bone characteristics of the layers have been as well evaluated to determine if there the vitamin D3 may enhance the welfare status of the birds. 1. The weight of the egg and of its components is often greater in hens fed a diet enriched with 25-hydroxycholecalciferol. 2. Since eggs of treated groups are heavier and a larger amount of shell is needed, a direct effect on shell strength is observed. 3. At 30 and at 50 wk of age hens fed 25 hydroxycholecalciferol exhibited greater values of bone breaking force. 4. Radiographic density values obtained in the trial are always higher in hens fed with 25-hydroxycholecalciferol of both treatments: supplemented for the whole laying cycle (25D3) or from 40 weeks of age onward (D3+25D3).

Pretrattamenti termo-meccanici ed enzimatici su scarti dell'industria enologica per la produzione di Biogas

A fundamental assumption for by-product from winery industy waste-management is their economic and commercial increase in value. High energetic value recovery from winery industry is an attractive economic solution to stimulate new sustainable process. Approach of this work is based about physic and biological treatment with grape stalks and grape marc to increase polysaccharides components of cell wall and energetic availability of this by-products. Grape stalks for example have a high percentage of lignin and cellulose and can’t be used, whitout pretreatment, for an anaerobic digestion process. Our findings show enzymatic and thermo-mechanical pre-treatments in combined application for optimise hydrolytic mechanism on winemaking wastes which represents 0,9 milion ton/year in Italy and on straw, cereal by-products with high lignin content. A screening of specifically industrial enzymatic complex for the hydrolysis lignocellulosic biomass were tested using the principal polysaccharides component of the vegetal cells. Combined thermo-mechanical and enzymatic pretreatment improve substrates conversion in batch test fermentation experiment. The conservation of the grape stalks, at temperature above 0°C, allow the growth of spontaneus fermentation that reduce their polysaccharides content so had investigated anarobic condition of conservation. The other objective of this study was to investigate the capability of a proprietary strain of L.buchneri LN 40177 to enhance the accessibility of fermentable forage constituents during the anaerobic conservation process by releasing the enzyme ferulate esterase. The time sequence study by batch tests showed that the L. buchneri LN-40177 inoculated grape stalk substrate was more readily available in the fermenter. In batch tests with grape stalk, after mechanical treatment, the L. buchneri LN41077 treated substrate yielded on average 70% more biogas per kg/DM. Thermo-mechanical, enzymatic and biological treatment with L. buchneri LN-40177 can increase the biogas production from low fermented biomasses and the consequent their useful in anaerobic biodigesters for agro-bioenergy production.

Il risparmio delle risorse alla scala abitativa e di insediamento. Tecnologie non convenzionali e valutazione ambientale attraverso metodologia LCA.

Nel corso del mio lavoro di ricerca mi sono occupata di identificare strategie che permettano il risparmio delle risorse a livello edilizio e di approfondire un metodo per la valutazione ambientale di tali strategie. La convinzione di fondo è che bisogna uscire da una visione antropocentrica in cui tutto ciò che ci circonda è merce e materiale a disposizione dell’uomo, per entrare in una nuova era di equilibrio tra le risorse della terra e le attività che l’uomo esercita sul pianeta. Ho quindi affrontato il tema dell’edilizia responsabile approfondendo l’ambito delle costruzioni in balle di paglia e terra. Sono convinta che l’edilizia industriale abbia un futuro molto breve davanti a sé e lascerà inevitabilmente spazio a tecniche non convenzionali che coinvolgono materiali di semplice reperimento e posa in opera. Sono altresì convinta che il solo utilizzo di materiali naturali non sia garanzia di danni ridotti sull’ecosistema. Allo stesso tempo ritengo che una mera certificazione energetica non sia sinonimo di sostenibilità. Per questo motivo ho valutato le tecnologie non convenzionali con approccio LCA (Life Cycle Assessment), approfondendo gli impatti legati alla produzione, ai trasporti degli stessi, alla tipologia di messa in opera, e ai loro possibili scenari di fine vita. Inoltre ho approfondito il metodo di calcolo dei danni IMPACT, identificando una carenza nel sistema, che non prevede una categoria di danno legata alle modifiche delle condizioni idrogeologiche del terreno. La ricerca si è svolta attraverso attività pratiche e sperimentali in cantieri di edilizia non convenzionale e attività di ricerca e studio sull’LCA presso l’Enea di Bologna (Ing. Paolo Neri).

Structure-property relations in polymers from renewable resources

The present research project focuses its attention on the study of structure-property relations in polymers from renewable sources (bio-based polymers) such as polymers microbially produced, i.e. polyhydrohyalkanoates (PHAs) or chemically synthesized using monomers from renewable sources, i.e. polyammide 11 (PA11). By means of a broad spectrum of experimental techniques, the influence of different modifications on bio-based polymers such as blending with other components, copolymerization with different co-monomers and introduction of branching to yield complex architectures have been investigated. The present work on PHAs focused on the study of the dependence of polymer properties on both the fermentation process conditions (e.g. bacterial strain and carbon substrate used) and the method adopted to recover PHAs from cells. Furthermore, a solvent-free method using an enzyme and chemicals in an aqueous medium, was developed in order to recover PHAs from cells. Such a method allowed to recover PHA granules in their amorphous state, i.e. in native form useful for specific applications (e.g. paper coating). In addition, a commercial PHA was used as polymeric matrix to develop biodegradable and bio-based composites for food packaging applications. Biodegradable, non-toxic, food contact plasticizers and low cost, widely available lignocellulosic fibers (wheat straw fibers) were incorporated in such a polymeric matrix, in order to decrease PHA brittleness and the polymer cost, respectively. As concerns the study of polyamide 11, both the rheological and the solid-state behavior of PA11 star samples with different arm number and length was studied. Introduction of arms in a polymer molecule allows to modulate melt viscosity behavior which is advantageous for industrial applications. Also, several important solid-state properties, in particular mechanical properties, are affected by the presence of branching. Given the importance of using ‘green’ synthetic strategies in polymer chemistry, novel poly(-amino esters), synthesized via enzymatic-catalyzed polymerization, have also been investigated in this work.

Sistemi per la produzione di enzimi industriali finalizzati alla valorizzazione di scarti agroalimentari

La demolizione idrolitica delle pareti cellulari delle piante tramite enzimi lignocellulosici è quindi uno degli approcci più studiati della valorizzazione di scarti agricoli per il recupero di fitochimici di valore come secondary chemical building block per la chimica industriale. White rot fungi come il Pleurotus ostreatus producono una vasta gamma di enzimi extracellulari che degradano substrati lignocellulosici complessi in sostanze solubili per essere utilizzati come nutrienti. In questo lavoro abbiamo studiato la produzione di diversi tipi di enzimi lignocellulosici quali cellulase, xilanase, pectinase, laccase, perossidase e arylesterase (caffeoilesterase e feruloilesterase), indotte dalla crescita di Pleurotus ostreatus in fermentazione allo stato solido (SSF) di sottoprodotti agroalimentari (graspi d’uva, vinaccioli, lolla di riso, paglia di grano e crusca di grano) come substrati. Negli ultimi anni, SSF ha ricevuto sempre più interesse da parte dei ricercatori, dal momento che diversi studi per produzioni di enzimi, aromi, coloranti e altre sostanze di interesse per l' industria alimentare hanno dimostrato che SSF può dare rendimenti più elevati o migliorare le caratteristiche del prodotto rispetto alla fermentazione sommersa. L’utilizzo dei sottoprodotti agroalimentari come substrati nei processi SSF, fornisce una via alternativa e di valore, alternativa a questi residui altrimenti sotto/o non utilizzati. L'efficienza del processo di fermentazione è stato ulteriormente studiato attraverso trattamenti meccanici di estrusione del substrato , in grado di promuovere il recupero dell’enzima e di aumentare l'attività prodotta. Le attività enzimatiche prodotte dalla fermentazione sono strettamente dipendente della rimozione periodica degli enzimi prodotti. Le diverse matrici vegetali utilizzate hanno presentato diversi fenomeni induttivi delle specifiche attività enzimatiche. I processi SSF hanno dimostrato una buona capacità di produrre enzimi extracellulari in grado di essere utilizzati successivamente nei processi idrolitici di bioraffinazione per la valorizzazione dei prodotti agroalimentari.

Methane production through anaerobic digestion of dedicated energy crops

Methane yield of ligno-cellulosic substrates (i.e. dedicated energy crops and agricultural residues) may be limited by their composition and structural features. Hence, biomass pre-treatments are envisaged to overcome this constraint. This thesis aimed at: i) assessing biomass and methane yield of dedicated energy crops; ii) evaluating the effects of hydrothermal pre-treatments on methane yield of Arundo; iii) investigating the effects of NaOH pre-treatments and iv) acid pre-treatments on chemical composition, physical structure and methane yield of two dedicated energy crops and one agricultural residue. Three multi-annual species (Arundo, Switchgrass and Sorghum Silk), three sorghum hybrids (Trudan Headless, B133 and S506) and a maize, as reference for AD, were studied in the frame of point i). Results exhibit the remarkable variation in biomass yield, chemical characteristics and potential methane yield. The six species alternative to maize deserve attention in view of a low need of external inputs but necessitate improvements in biodegradability. In the frame of point ii), Arundo was subjected to hydrothermal pre-treatments at different temperature, time and acid catalyst (with and without H2SO4). Pre-treatments determined a variable effect on methane yield: pre-treatments without acid catalyst achieved up to +23% CH4 output, while pre-treatments with H2SO4 catalyst incurred a methanogenic inhibition. Two biomass crops (Arundo and B133) and an agricultural residue (Barley straw) were subject to NaOH and acid pre-treatments, in the frame of point iii) and iv), respectively. Different pre-treatments determined a change of chemical and physical structure and an increase of methane yield: up to +30% and up to +62% CH4 output in Arundo with NaOH and acid pre-treatments, respectively. It is thereby demonstrated that pre-treatments can actually enhance biodegradability and subsequent CH4 output of ligno-cellulosic substrates, although pre-treatment viability needs to be evaluated at the level of full scale biogas plants in a perspective of profitable implementation.