Small-scale Gasification System Research Articles

A preliminary evaluation of different residual biomass potential for energy conversion in a micro-scale downdraft gasifier

Residual biomass can be a promising alternative to replace fossil fuels for energy production. Through small-scale gasification systems it is possible to obtain a fuel gas from solid biomass that can be used for electrical and thermal energy generation. In this work, six different biomasses (five agro-industrial residues and A1 ENplus pellets) were tested in a lab-scale prototype. For each tested feedstock, elemental and ash analyses were carried out. The contaminant amount in the produced gas was measured as well as the mass and energy fluxes to calculate the gasification efficiency. The ratio between the pressure drop across the reactor and the gas flow raised to the square was introduced to compare the gasifier behavior at different power outputs. The results showed that with the exclusion of the tests run with cork, the other tested agro-industrial residues (pistachio shell, hemp and driftwood) performed acceptably in terms of efficiency, providing also a char with a carbon content over 70% as by-product.

Barriers to Success: A Technical Review on the Limits and Possible Future Roles of Small Scale Gasifiers

Literature and manuals refer to biomass gasification as one of the most efficient processes for power generation, highlighting features, such as residual biomass use, distributed generation and carbon sequestration, that perfectly incorporate gasification into circular economies and sustainable development goals. Despite these features, small scale applications struggle to succeed as a leading solution for sustainable development. The aim of this review is to investigate the existing technological barriers that limit the spreading of biomass gasification from a socio-technical point of view. The review outlines how existing technologies originated from under feed-in-tariff regimes and highlights where the current design goals strongly differ from what will be needed in the near future. Relevant market-ready small-scale gasification systems are analyzed under this lens, leading to an analysis of the reactor and filtration design. To help understand the economical sustainability of these plants, an analysis of the influence of capital expenditures and operating expenditures on the return of investment is included in the discussion. Finally, a literature review on prototypes and pre-market reactors is used as a basis for spotting the characteristics of the system that will likely resolve issues around fuel flexibility, cost efficiency and load variability.

Numerical and experimental evaluation of flue gas recirculation for syngas combustion

Biomass gasification can be an interesting solution for the energy production to fight global warming and the environment pollution. The flare apparatus is an essential component of gasification systems, but considering small scale ones, it is often quite simple and not very optimized. A way to minimize the NOx production during the combustion is recirculating the flue gas into the flames, making the combustion zone cold and inhibiting the nitrogen oxides formation. In this work different flare designs were numerically evaluated through OpenFOAM software to find the best flare shape that can guarantee the flue gas recirculation. Simulations results were verified building and testing a flare with an optimized geometry for a small-scale gasification system. Numerical simulation and experimental tests shown that it can be possible to design a simple flare for syngas combustion that guarantee low combustion temperature through flue gas recirculation.

A review of recent developments and future prospects in gasification systems and their modeling

Gasification is receiving a renaissance in response to global warming mitigation. Total gasification installation, construction and planning energy capacity has increased from 42 GWth to 400 GWth between 1999 and 2020. One of the drivers of gasification technologies that has influenced their increase is their capability to accommodate low-value feedstock and organic wastes. Another driving factor is the technology prospect for enhanced power efficiency and environmental performance when used in Integration Combined Cycle (IGCC) with carbon capture. Although gasification has been at the forefront of many studies, it is missing comprehensiveness and organization of the vast information in the literature. There are more than 600,000 studies that focus on gasification and they are mostly very chaotic for their usage for further research development and policy decision making. For instance, the field of modeling and simulation of reactive flow has expanded and high fidelity analyses have been utilized in addressing gasification challenges significantly. Moreover, there had been new developments in areas such as plasma gasification, supercritical water gasification, small scale gasification systems developments, co-gasification and coupling of gasification with other technologies such as anaerobic digestion. Hence, in this work we present a systematic organization of the reported findings, recent developments and future prospects. Recent developments on feed material characteristics of different fuels utilized for gasification in order to evaluate their potential is reported herein. In addition, literature survey of gasification processes, classifications of gasification and influence of process parameters and technologies were also reported. The effect of different parameters like pressure, catalyst, and temperature on the gasification efficiency and gas composition were extracted and presented. At the end, some areas that have witnessed recent progress were highlighted and future prospects in this continually growing thermochemical conversion field was presented.

Techno-Economic Assessment of the Use of Syngas Generated from Biomass to Feed an Internal Combustion Engine

The focus of this study is to provide a comparative techno-economic analysis concerning the deployment of small-scale gasification systems in dealing with various fuels from two countries, Portugal and Brazil, for electricity generation in a 15 kWe downdraft gasifier. To quantify this, a mathematical model was implemented and validated against experimental runs gathered from the downdraft reactor. Further, a spreadsheet economic model was developed combining the net present value (NPV), internal rate of return (IRR) and the payback period (PBP) over the project’s lifetime set to 25 years. Cost factors included expenses related to electricity generation, initial investment, operation and maintenance and fuel costs. Revenues were estimated from the electricity sales to the grid. A Monte Carlo sensitivity analysis was used to measure the performance of the economic model and determine the investment risk. The analysis showed an electricity production between 11.6 to 15 kW, with a general system efficiency of approximately 13.5%. The viability of the projects was predicted for an NPV set between 18.99 to 31.65 k€, an IRR between 16.88 to 20.09% and a PBP between 8.67 to 12.61 years. The risk assessment yielded favorable investment projections with greater risk of investment loss in the NPV and the lowest for IRR. Despite the feasibility of the project, the economic performance proved to be highly reliant on the electricity sales prices subdue of energy market uncertainties. Also, regardless of the broad benefits delivered by these systems, their viability is still strikingly influenced by governmental decisions, subsidiary support and favorable electricity sales prices. Overall, this study highlights the empowering effect of small-scale gasification systems settled in decentralized communities for electric power generation.

Assessment of the Behaviour of a Commercial Gasification Plant During Load Modulation and Feedstock Moisture Variation

Fixed-bed biomass gasification coupled with internal combustion engines allows an efficient exploitation of biomass for the combined production of heat and power (CHP) at small scale with increased economic viability with respect to combustion-based CHP systems. The main barrier on the way towards a wider market distribution is represented by the fact that a robust practical operation of state-of-the-art fixed-bed biomass gasification systems is limited to very specific fuel properties and steady-state operation. The aim of this work is twofold. On the one hand, it presents the results of a series of test runs performed in a monitored commercial plant under different process conditions, in order to assess its behaviour during load modulation and fuel property variations. On the other hand, an in-house developed thermodynamic equilibrium model was applied to predict the behaviour of the gasification reactor. This gasification model could be used for the development of a model-based control strategy in order to increase the performance of the small-scale gasification system. To assess the general operational behaviour of the whole gasification system an experimental one-week-long test run has been performed by BIOENERGY 2020+ and the Free University of Bozen-Bolzano as round robin test. The plant has been tested under different operating conditions, in particular, varying the load of the engine and the moisture content of the feedstock. The outcomes shown in the present work provide a unique indication about the behaviour of a small-scale fix-bed gasifier working in conditions different from the nominal ones.

Modelling of advanced gasification systems (MAGSY): Simulation and validation for the case of the rising co-current reactor

This study presented a new model (named MAGSY) for the simulation of advanced small-scale gasification systems. These novel designs can be complex and may combine several features that are not typical for conventional systems. MAGSY is a vis-à-vis and process-based model that has been able to account for the excess air in the combustion sub-process (zone) which is conveyed to the pyrolysis zone creating practically a coupled system of sub-stoichiometric combustions. Onsite monitoring results from a rising co-current gasifier are used for the validation of the model. Simulations have been performed for excess air regimes between 11% and 20% and the produced gases from the “oxidation reactions” system were reformed by the “char-gas reactions” system. The model calculated a hydrogen molar fraction of 19.53% and carbon monoxide molar fraction of carbon monoxide 24.45% while the case study values were 19.19% and 24.02% respectively. Both gases were shown to have inverted correlation with equivalent air ratios at values bigger than 99.3%, which is a notable point. For equivalent ratios of 0.l7–0.25 the model returned char yields of 1.2–1.7% and the measurement from the case study showed that the char yield was 1.5%. Finally, a detailed exergy analysis of the gasifier is presented and validated with the values that were retrieved from the monitoring. MAGSY is able to adjust and model reactors with different levels of complexity.

Applying modern automotive technology on small scale gasification systems for CHP production: A compact hot gas filtration system

Cost-effective and durable producer gas cleaning is a necessary step towards the promotion of sustainable gasification systems for electricity production. The automotive industry has vast technological experience on gas filtration both at experimental and theoretical level. In this study hot producer gas cleaning was attempted with the use of ceramic Diesel Particulate Filters (DPF) initially designed to operate in automotive applications. Different types of DPFs were used as downstream hot gas filters in two atmospheric air blown bubbling fluidized bed gasifiers. The experiments included short and long duration tests conducted with olive kernels under various gasification temperatures and air ratios. Being the first attempt on the application of “narrowly structured” ceramic DPF in a gas heavily loaded with particulate matter (PM), main objective was to investigate the operation performance in terms of overall collection efficiency, loading and pressure drop profile, as well as regeneration performance and structural robustness. The results showed high PM filtration efficiency, and highlighted fields for further research. Poor operation performance was experienced due to inlet surface plugging and in some cases limited structural robustness under uncontrolled regeneration conditions. Insight into the overall behavior of the DPF's was gained via axial tomography and imaging analysis. Further research is needed in order to adapt different geometrical structures and obtain better control of loading and regeneration processes.

Indicator-based economic, environmental, and social sustainability assessment of a small gasification bioenergy system fuelled with food processing residues from the Mediterranean agro-industrial sector

Small-scale gasification systems coupled with internal combustion engines could be innovative alternatives for combined heat and power production when fuelled with agricultural residues, providing benefits related to both food processing waste management and sustainable agriculture. In the present study, an indicator-based estimation of sustainability was performed for a gasification-based bioenergy system considering not only economic but also environmental and social issues. The analysed scenario consisted of an installed capacity of 40kWel, with an investment cost estimated to be approximately 1520€/kWhel and a net profit up to 20,000€/year. However, commercial success depends on instruments of reducing capital investment, such as subsidies, electricity feed-in tariffs, and biomass prices. Additional benefits such as low- or zero-cost feedstock and zero-cost biomass logistics suggest that small-scale gasification systems based on agricultural residues are likely to play an important role in future energy supplies for Mediterranean countries.

Study of a downdraft gasifier and externally fired gas turbine for olive industry wastes

Olive mill technology generates a variety of biomass wastes: olive pits/stones and remaining pomace resultant from olive oil extraction. Solid wastes are also generated during the pruning of olive trees (leaves and small branches). This renewable biomass could be a feasible option in gasification technology. Thermodynamic calculations evaluate the optimum operating parameters of a small scale gasification system. The product gas obtained from the downdraft gasifier has low calorific values: 4.35 MJ kg − 1 for exhausted pomace, and around 5.20 MJ kg − 1 for olive pits and leaves and prunings. The power system provides 70 kW e and 150 kW th with a biomass consumption of 80–85 kg h − 1 . Simulation results show the most important operating parameters are turbine inlet temperature ( TIT), pressure ratio ( Π) and hot side temperature difference of the heat exchanger (HTHE). High electric efficiency (20%) and overall efficiency (65%) are achievable with such a system.

Distributed gasification and power generation from solid wastes

A small-scale gasification system for solid wastes has been developed and tested. In this innovative system, known as the STAR-MEET system, a fixed-bed pyrolyzer combined with a high temperature steam/air reformer is employed. From the experimental results using wood chips and polyolefin sheets as feedstocks, it has been demonstrated that injection of high temperature steam/air mixture into the pyrolysis gas can effectively decomposes tar components in the pyrolysis gas into CO and H 2, resulting in an almost tar-free, clean product gas. A 900 °C class compact metallic heat exchanger has been successfully developed, which serves as the high temperature steam/air generator for the STAR-MEET system. Finally, power generation experiments using a complete STAR-MEET plant have been successfully carried out. These results demonstrate small-scale gasification and power generation system using solid wastes is quite feasible.

P12-05 小型廃棄物ガス化発電の研究開発

An innovative small-scale gasification system for solid wastes is proposed which is known as STAR-MEET system. In this system, a fixed-bed pyrolyzer combined with a high temperature reformer using high temperature steam/air mixture is employed. From the experimental results using rubber chips as a fuel, it has been demonstrated that injection of high temperature steam/air mixture into the pyrolysis gas effectively decomposes tar and soot components in the pyrolysis gas into CO and H_2,and almost dust and tar free clean reformed gas can be generated. The STAR-MEET system requires high temperature steam/air generator, and a 900℃ class metallic type compact heat exchanger has been successfully developed. Finally, power generation experiments using a complete STAR-MEET plant has been successfully done. These results demonstrates small-scale gasification and power generation system using solid wastes is quite feasible.

F117 マイクロごみ発電の研究開発 : 着想、基礎実験、実証実験そして実用化(新技術フォーラム-6 : グリーンエネルギーへの周辺技術 : 反応・改質・相変化を活用した高効率変換)

An innovative small-scale gasification system for solid wastes is proposed which is known as STAR-MEET system. In this system, a fixed-bed pyrolyzer combined with a high temperature reformer using high temperature steam/air mixture is employed. From the experimental results using rubber chips as a fuel, it has been found that injection of high temperature air into the pyrolyzer significantly increases the heating value of the pyrolysis gas. It has been also demonstrated that injection of high temperature steam/air mixture into the pyrolysis gas effectively decomposes tar and soot components in the pyrolysis gas into CO and H_2, and almost dust and tar free clean reformed gas can be generated. This gasification system generates low BTU gas from solid wastes. Thus power generation experiments using a small spark ignition engine were done employing low BTU gas as a fuel. Compared with natural gas driven, low BTU gas driven engine shows similar thermal efficiency while significantly low NOx and hydrocarbon emissions.