Mejdi Jeguirim

Pyrolysis characteristics and kinetics of Arundo donax using thermogravimetric analysis.

The increase of the price of fossil means, as well as their programmed disappearing, contributed to increase among appliances based on biomass and energy crops. The thermal behavior of Arundo donax by thermogravimetric analysis was studied under inert atmosphere at heating rates ranging from 5 to 20 degrees C min(-1) from room temperature to 750 degrees C. Gaseous emissions as CO(2), CO and volatile organic compounds (VOC) were measured and global kinetic parameters were determined during pyrolysis with the study of the influence of the heating rate. The thermal process describes two main phases. The first phase named active zone, characterizes the degradation of hemicellulose and cellulose polymers. It started at low temperature (200 degrees C) comparatively to wood samples and was finished at 350 degrees C. The pyrolysis of the lignin polymer occurred during the second phase from 350 to 750 degrees C, named passive zone. Carbon oxides are emitted during the active zone whereas VOC are mainly formed during the passive zone. Mass losses, mass loss rates and emission factors were strongly affected by the variation of the heating rate in the active zone. It was found that the global pyrolysis of A. donax can be satisfactorily described using global independent reactions model for hemicellulose and cellulose in the active zone. The activation energy for hemicellulose was not affected by a variation of the heating rate with a value close to 110 kJ mol(-1) and presented a reaction order close to 0.5. An increase of the heating rate decreased the activation energy of the cellulose. However, a first reaction order was observed for cellulose decomposition. The experimental results and kinetic parameters may provide useful data for the design of pyrolytic processing system using A. donax as feedstock.

Thermogravimetric analysis and emission characteristics of two energy crops in air atmosphere: Arundo donax and Miscanthus giganthus

The aim of this work was to study the thermal behavior of two herbaceous crops (Miscanthus giganthus, Arundo donax) obtained from energy plantations. Thermogravimetric analyses were performed at 5 degrees C min(-1) under air atmosphere. The thermal degradation rates in devolatilization and combustion steps, the initial degradation temperature, and the residual weight were determined. The gas emissions and Particle Matter (PM) were also quantified. The thermal behavior of energy crops depends on the chemical composition. In fact, the initial degradation temperature for A. donax under air atmosphere was lower than for M. giganthus. However, the thermal degradation rate was higher for M. giganthus. Kinetic expressions for the degradation rate in devolatilization and combustion steps have been obtained for both energy crops. The comparison of the gas and PM emissions showed the same order of magnitude for both energy crops. In fact, 26.8 mmol/g of CO, CO(2), VOC and 1.8 x 10(13) particles/g were mainly emitted.

Combined process for the treatment of olive oil mill wastewater: absorption on sawdust and combustion of the impregnated sawdust.

Olive oil mill wastewater (OMWW) generated by the olive oil extraction industry constitutes a major pollutant, causing a severe environmental threats because of the high chemical oxygen demand and the high content of polyphenol. This work studied a combined process of absorption on sawdust, a low-cost renewable absorbents, and an energetic valorisation via combustion was studied. The thermal behaviour of different OMWW/sawdust blends was studied under inert and oxidative atmosphere from 20 to 900 degrees C using thermogravimetric analysis (TGA). Gaseous emissions such as CO(2), CO and volatile organic compounds (VOCs) were measured under oxidative conditions at 600 degrees C in a fixed-bed reactor. Kinetic parameters were obtained and compared for the different mixtures of OMWW and sawdust. The absorption of the organic content of OMWW on sawdust improves the decomposition of cellulosic compounds at low temperatures in both atmospheres. Compared to sawdust, absorption of the organic content of OMWW on sawdust favours a combustion process with lower molar ratio of CO/CO(2) in the exhaust. Combustion of an impregnated sawdust containing 40 wt.% of the organic content of the OMWW generates the same amount of gas in the exhaust as sawdust. OMWW/sawdust blends may therefore be a promising biofuel with low environmental impacts.

Devolatilization kinetics of Miscanthus straw from thermogravimetric analysis.

The thermal degradation, reactivity, emission characteristics, and kinetics of Miscanthus straw under inert atmosphere were studied using thermogravimetric analysis (TGA) at different heating rates. The thermal decomposition of Miscanthus straw occurs within a temperature ranging between 180°C and 600°C. Miscanthus has the highest reactivity compared to different agriculture residues tested in the same sequence. Assuming the addition of three independent parallel reactions corresponding to three pseudocomponents linked to the hemicellulose, cellulose, and lignin, three-pseudocomponent models were used to simulate the Miscanthus straw devolatilization. The presented data may have a contribution in developing energy recovery systems using Miscanthus straw as a feedstock.

Experimental investigation on gaseous emissions from the combustion of date palm residues in laboratory scale furnace

Emissions characteristics from the combustion of five date palm residues, DPR, (Date Palm Leaflets, Date Palm Rachis, Date Palm Trunk, Date Stones and fruitstalk prunings) in a laboratory scale furnace were investigated. Release of gaseous products such as CO2, CO, VOC, NOx and SO2 were measured at 600-800°C. The main goal was to analyze thermal behaviors and gaseous emissions in order to select the most convenient biofuel for an application in domestic boiler installations. Regards to biofuel characteristics, date stone have the highest energy density (11.4GJ/m(3)) and the lowest ash content (close to 1.2%). Combustion tests show that among the tested date palm residues, date stone may be the promising biofuel for the design of combustion processing system. However, a special attention to the design of the secondary air supply should be given to prevent high emissions of CO and volatile matters.

Thermochemical conversion of waste tyres—a review

A review of the energy recovery from waste tyres is presented and focuses on the three thermochemical processes used to valorise waste tyres: pyrolysis, gasification, and combustion/incineration. After recalling the chemical composition of tyres, the thermogravimetric behaviours of tyres or their components under different atmospheres are described. Different kinetic studies on the thermochemical processes are treated. Then, the three processes were investigated, with a particular attention given to the gasification, due to the information unavailability on this process. Pyrolysis is a thermochemical conversion to produce a hydrocarbon rich gas mixture, condensable liquids or tars, and a carbon-rich solid residue. Gasification is a form of pyrolysis, carried out at higher temperatures and under given atmosphere (air, steam, oxygen, carbon dioxide, etc.) in order to yield mainly low molecular weight gaseous products. Combustion is a process that needs a fuel and an oxidizer with an ignition system to produce heat and/or steam. The effects of various process parameters such as temperature, heating rate, residence time, catalyst addition, etc. on the energy efficiency and the products yields and characteristics are mainly reviewed. These thermochemical processes are considered to be the more attractive and practicable methods for recovering energy and material from waste tyres. For the future, they are the main promising issue to treat and valorise used tyres. However, efforts should be done in developing more efficient technical systems.

Characterization of coffee residues pellets and their performance in a residential combustor

ABSTRACT Spent coffee grounds (SCG) and coffee husks (CH) were evaluated as biofuels, after densification, for energy production. CH represent a specific problem for the coffee industry due to a low calorific value, high ash content, and a very low bulk density. Hence, the energetic potential of SCG (95 wt%)/CH (5 wt%) blend and pure SCG (100%) were examined. The blend of SCG and CH was limited to 5 wt% of CH because of the low bulk density of CH. Therefore, physicochemical and energetic characterizations of the produced pellets were performed. Thermogravimetric analyses were performed under nitrogen and air atmospheres to evaluate the CH behavior in the blend. Characterization study shows that both produced pellets could reach the French Agropellets standard (AQI). Thermal degradation showed that the mean reactivity of the SCG/HC pellets was higher than pure SCG. Then, combustion experiments were performed in a domestic combustor, after modification of the boiler power in order to improve its energetic performances. The presence of CH led to a rise of CO, NOx, VOC’s, and particle emissions. Nevertheless, the performances of the biofuels are almost in agreement the NF EN 12809 standard.

Activated Carbon Prepared from Date Pits for the Retention of NO2 at Low Temperature

Abstract Activated carbons were prepared from date pits by physical activation with CO2 and the textural properties were investigated by BET and D-R methods with N2 and CO2 adsorption isotherms. The interaction of the NO2 with activated carbon was examined at ambient temperature and the effect of operating conditions such as temperature and inlet gas compositions was also examined. It was observed that the development of porosity with increasing time of activation favours the adsorption capacity of NO2. The maximum adsorption capacity reached was about 107 mg/g, which is higher than several activated carbon prepared from classical lignocellulosic biomass. However, a slight decrease of NO2 adsorption capacity was observed with increasing temperature. The addition of oxygen into the inlet gas gave rise to an increase in amount adsorbed of NO2.

Process engineering for pollution control and waste minimization

The Biomass Energy, Environment and Sustainable Development workshop has been successfully organized in the frame of the International Renewable Energy Congress (IREC) conference which was organized in Hammamet (Tunisia) from March 22 to 24 2016. Approximately, 50 scientists joined the workshop to discuss the challenges of waste minimization and recovery, pollution analysis and treatment. IREC covers a wide range of topics concerning renewable energies from solar thermal energy to biomass energy and others. During this congress different scopes are approached such as materials and technologies, modelling and simulation, optimization, energy efficiency, sustainability... The seventh edition of IREC offered the possibility to organize a workshop dedicated to the chemical engineering community, which works specifically on applications for biomass treatment, transformation and valorisation. This event offers the possibility to build new collaborations between foreign research teams but also benefit from a convenient environment to welcome researchers. The workshop mostly focused on two research fields: water treatment and energy production from biomass. Protection of environment as well as the energetic valorisation of biomass resources has become crucial since more than 20 years. The world faces to a complex situation with the emergence of developing countries, which lead to an increase of fossil fuel demand, to an acceleration of feedstock consumption and to the generation of large amount of wastes and pollutions. The latter has led to a lot of researches, in order to minimize the impact of wastes and pollutants on the environment. Among the different processes which are used to remove pollutant from wastewater, adsorption is one of the more studied. To reach high pollutant abatement without a prohibitive cost, new cheap materials were developed these last years mainly from biomass and waste solids. Biomass may origin from different sources: sawmill industry, agriculture, agro-industry... Depending on its origin, biomass compositionmay be different in composition and in structure. Raw biomass can be used as biosorbent, but generally, a thermal treatment is applied (torrefaction, pyrolysis) in order to increase the surface area and the porosity of the biomass, offering higher adsorption capacities for organic and mineral compounds. At this stage, the adsorbent is called biochar. To obtain higher adsorption properties and to obtain sorbents with high selectivity, biochars can be activated by chemical or physical routes. The activated carbons present important surface areas (sometimes more than 2000 m/g) and their porosities can be designed depending on the final application (micro and/or mesoporosity). These materials are often used for the removal of organic pollutants present in wastewater at low concentration, as it is described in several papers of the special issue. Water treatment can be also investigated by filtration process. Depending on the nature of the compounds present in the feed solution (organics, salts, bacteria, particles), the process has to be adapted in order to reach the best performance with high durability. The main problem which is encountered when using filtration membranes corresponds to fouling due to the adsorption of molecules and bacteria at the surface of the filtration layer. Different treatments have to be applied to recover good performances of the membranes, they are at the origin of additional costs (chemical reagents, process stop, etc.) and environmental impacts. These aspects Responsible editor: Philippe Garrigues

Thermal degradation kinetics and mechanisms of Posidonia Oceanica under inert and oxidative atmospheres

ABSTRACT The thermal degradation characteristics of Posidonia Oceanica (PO), a marine biomass abundantly available on the coastal zone of the Mediterranean Basin, were investigated using thermogravimetric analysis under inert and oxidative atmospheres. The kinetic parameters of the both thermal degradations conditions were determined using n-reaction order model. Coats–Redfern and Phadnis–Deshpande methods were used to discuss the probable degradation mechanisms. Results showed that PO is an attractive alternative for energy production owing to its elevated heating value. Moreover, PO thermal degradation follows the usual shape of biomass decomposition. Hence, under inert atmosphere, its thermal degradation had two different stages after moisture release. The first stage corresponded to the volatiles release while the second stage corresponded to the char formation. The solid-state decomposition mechanisms followed by the devolatilization step of PO were two or three dimensional diffusion controlled reaction. However, the decomposition mechanism during PO char formation corresponded to a nucleation and growth mechanism. Under oxidative atmosphere, two stages were also observed corresponding to volatiles release and char combustion, respectively. The solid-state mechanism of volatiles release followed three dimensional diffusion controlled reaction while the char combustion mechanism corresponded to a contracting area phase boundary controlled reaction.