FLUIDIZED BED GASIFICATION OF BIOMASS: A SUBSTANCE FLOW ANALYSIS

A natural biomass was fed in a pilot scale bubbling fluidized bed gasifier, having a maximum feeding capacity of 100kg/h. Measurements included the syngas composition, the mass flow rate and composition of entrained fines collected at the cyclone and purge material from the wet scrubber, and the bed material characterization. The performance of the whole gasification plant and of its specific components as well as the validity of some design solutions and operating criteria have been quantitatively assessed by means of a substance flow analysis

Hydrothermal Carbonization of Oat in a Lab-Scale Batch Reactor

Biomass as feedstock for renewable energy and biomaterials production is of great importance to tackle energy, economic and environmental issues. Biomass can be processed in several ways depending on its composition, moisture content and availability. Hydrothermal Carbonization (HTC) is one possible option to deal with the biomass streams. In this study, oat was processed in a lab-scale stirred-batch HTC reactor to evaluate the effect of reaction temperature and residence time on the composition and yield of hydrochar obtained during the process. The results demonstrate that these operating parameters strongly affect the characteristics and the amount of the hydrochar produced. The results indicate that the increasing of the HTC severity conditions produces an enrichment of hydrochar in carbon content up to 72.8%. On the other hand, the hydrochar yield decreases from 0.85 to 0.56 g/g as the severity factor increases from 0.11 to 0.37

Effect of operating conditions on hydrochar production from digestate

Hydrothermal carbonization (HTC) is a thermo-chemical process that uses water under subcritical conditions to convert biomass into a C-rich product known as hydrochar. HTC process takes place at relatively low temperature (generally in the 180–250°C range) under autogenous pressure. The process conditions promote the hydrolysis and dehydration reactions generating condensed aromatic structures having a high concentration of oxygenated functional group (OFG); these characteristics make hydrochar a promising candidate in several high-value applications [1–3]. HTC can be applied to a number of feedstocks, ranging from simple carbohydrates (i.e. glucose, cyclodextrins, fructose, sucrose, cellulose, starch, etc.) to more complex biomasses (such as lignocellulosic biomass, agricultural residues, municipal biowaste, etc.). Please click Additional Files below to see the full abstract

Assessment of Integration between Lactic Acid, Biogas and Hydrochar Production in OFMSW Plants

Biological treatments such as anaerobic digestion and composting are known to be the most widespread methods to deal with Organic Fraction of Municipal Solid Waste (OFMSW). The production of biogas, a mix of methane and carbon dioxide, is worth but alone cannot solve the problems of waste disposal and recovery; moreover, the digestate could be stabilized by aerobic stabilization, which is one of the most widespread methods. The anaerobic digestion + composting integration converts 10% to 14% of the OFMSW into biogas, about 35–40% into compost and 35–40% into leachate. The economic sustainability could be rather increased by integrating the whole system with lactic acid production, because of the high added value and by substituting the composting process with the hydrothermal carbonization process. The assessment of this integrated scenario in term of mass balance demonstrates that the recovery of useful products with a potentially high economic added value increases, at the same time reducing the waste streams outgoing the plant. The economic evaluation of the operating costs for the traditional and the alternative systems confirms that the integration is a valid alternative and the most interesting solution is the utilization of the leachate produced during the anaerobic digestion process instead of fresh water required for the hydrothermal carbonization process

Fluidized-Bed Gasification of Plastic Waste, Wood, and Their Blends with Coal

The effect of fuel composition on gasification process performance was investigated by performing mass and energy balances on a pre-pilot scale bubbling fluidized bed reactor fed with mixtures of plastic waste, wood, and coal. The fuels containing plastic waste produced less H2, CO, and CO2 and more light hydrocarbons than the fuels including biomass. The lower heating value (LHV) progressively increased from 5.1 to 7.9 MJ/Nm3 when the plastic waste fraction was moved from 0% to 100%. Higher carbonaceous fines production was associated with the fuel containing a large fraction of coal (60%), producing 87.5 g/kgFuel compared to only 1.0 g/kgFuel obtained during the gasification test with just plastic waste. Conversely, plastic waste gasification produced the highest tar yield, 161.9 g/kgFuel, while woody biomass generated only 13.4 g/kgFuel. Wood gasification showed a carbon conversion efficiency (CCE) of 0.93, while the tests with two fuels containing coal showed lowest CCE values (0.78 and 0.70, respectively). Plastic waste and wood gasification presented similar cold gas efficiency (CGE) values (0.75 and 0.76, respectively), while that obtained during the co-gasification tests varied from 0.53 to 0.73

Fuel Gas Production from the Co-Gasification of Coal, Plastic Waste, and Wood in a Fluidized Bed Reactor: Effect of Gasifying Agent and Bed Material

In this study, the effect of gasifying agent and bed material on the performance of the co-gasification of a mixture of coal, plastic waste, and wood was investigated. The experimental runs were carried out in a lab-scale bubbling fluidized bed reactor utilizing air, oxygen-enriched air, a mixture of air and steam, and a mixture of oxygen and carbon dioxide as reactant gases, while silica sand, olivine, and a mixture of olivine and dolomite as bed materials were used. The results indicated that both gasifying agent and bed material strongly affect the gas composition and, as a consequence, the process performance. In particular, the test with oxygen-enriched air and silica sand provided a producer gas with the highest heating value (9.32 MJ/Nm3), while the best performance in terms of gas yield (2.98 Nm3/kg) and tar reduction (−94.5%) was obtained by utilizing the air/steam mixture and olivine. As regards tar composition, it was observed that the most abundant and recalcitrant tar substance groups are naphthalenes and PAHs. On the other hand, phenols and furans appear to be the most sensitive groups to the effect of gasifying agent and bed material

Fluidized-Bed Gasification of Plastic Waste, Wood, and Their Blends with Coal

The effect of fuel composition on gasification process performance was investigated by performing mass and energy balances on a pre-pilot scale bubbling fluidized bed reactor fed with mixtures of plastic waste, wood, and coal. The fuels containing plastic waste produced less H2, CO, and CO2 and more light hydrocarbons than the fuels including biomass. The lower heating value (LHV) progressively increased from 5.1 to 7.9 MJ/Nm3 when the plastic waste fraction was moved from 0% to 100%. Higher carbonaceous fines production was associated with the fuel containing a large fraction of coal (60%), producing 87.5 g/kgFuel compared to only 1.0 g/kgFuel obtained during the gasification test with just plastic waste. Conversely, plastic waste gasification produced the highest tar yield, 161.9 g/kgFuel, while woody biomass generated only 13.4 g/kgFuel. Wood gasification showed a carbon conversion efficiency (CCE) of 0.93, while the tests with two fuels containing coal showed lowest CCE values (0.78 and 0.70, respectively). Plastic waste and wood gasification presented similar cold gas efficiency (CGE) values (0.75 and 0.76, respectively), while that obtained during the co-gasification tests varied from 0.53 to 0.73

The Crucial Role of the Process Modelling During the Design of a Bubbling Fluidised Bed Gasifier of Plastics

Gasification is a thermochemical process that aims to convert solid fuels into a synthetic gas that can be addressed to an end-use apparatus to produce electric energy and heat or can be further refined to be transformed in chemical valuable products. Many solid fuels, included waste (wood, biomass, plastics, municipal solid waste, etc.), can be gasified under different operating conditions (pressure, temperature, reactants) in different kind of reactors. This paper aims to correlate the descriptive model for the gasification of a mixture of commodity plastic waste to the basic design of a bubbling fluidized bed gasifier on the basis of experimental data and mathematical calculations

Gasification of Sewage Sludge in a Bench-Scale Reactor

The handling of sewage sludge is one of the most significant issues of wastewater treatment plant due to its potential harmful environmental impact and remarkable disposal costs. As a consequence, a proper handling of this biowaste is needed. In the present study, a bench-scale fixed bed gasifier was operated with a sewage sludge coming from a drying facility. The experimental runs have been carried out using for each test 30 g of dried sewage sludge, steam as gasifying agent and by varying the reactor temperature in the range of 700 – 850 °C. The results indicated that the gasification test conducted at a temperature of 700 °C produced the highest concentration of hydrogen, 58.2%. In addition, the increase of reaction temperature determined a reduction of char and tar from 11.4 to 9.7 g and from 9.1 to 0.7 g, respectively. On the other hand, the cold gas efficiency increased from 11 to 50%

THERMAL PLASMA SYSTEM APPLIED TO DESTROY C-BASED POLLUTANTS

Air pollution resulting from engines fueled by low quality oils (e.g. HFO) is considered responsible for around 400,000 premature deaths per year worldwide, at an annual cost to society of more than €58 billion. Moreover, the utilization of fossil fuels increases the GHG gases emission in the atmosphere. In relation to maritime sector, the main sources of C-based pollutants and GHGs gases, other than particulate matter (PM), are incinerators and engines. Engines fueled by HFO emit carbon dioxide, hydrocarbons and C-based particulate this latter with an emission factor of 0.56-2.21 g/kWh; engines fueled by LNG or LNG/HFO emit carbon dioxide, a reduced amount of C-based particulate but a larger amount of other methane, due to the methane slip phenomenon. The release of methane into atmosphere results in an increase of GHG impact, larger than the case of LFO use. This paper reports a quantitative assessment of the GHG impact due to methane slip for a commercial 18.3 MW engine and proposes a system to promote the oxidation of unconverted hydrocarbons downstream the turbocharger exit. The proposed system is based on the thermal plasma conversion: the size of an industrial equipment and that of the corresponding down-scaled experimental set-up is described. The plasma converting reactor (PCR) is applicable to flue gas with a good effectiveness in hydrocarbons conversion abatement but the electricity cost necessary to run it with large gas flow rates should be economically unfeasible. Thus, an estimation of electricity cost and capex is given