Small-scale Gasifier Research Articles

Investigation of the utilization of forest woodchips in a commercial small-scale open-top gasifier

The present work investigates the gasification of forest woodchips, which also contain needles, branches and cones, in an 85-kW open-top gasifier with 60 %–100 % load. This lower quality fuel has higher contents of ash, bark and fines compared to typical requirements of commercial small-scale gasifiers. The woodchips were utilized in unsieved and sieved (>10 mm) fraction. By using gas analysis and temperature measurements at a high local and temporal resolution, three main novel results were found: 1) The results of this work confirm that preferential paths in the fuel bed, caused by the fines content, led to a worse gas quality. The positive effects of a load reduction (i.e., increasing hydrogen and decreasing tars contents) were not found with the unsieved fuel. 2) Opposite trends for the methane concentration with the load were found with unsieved and sieved fuel. The preferential paths probably prevented the complete decomposition of longer-chain hydrocarbons and increased the intermediate product methane, while the non-methane hydrocarbon content reduced at a similar rate with both fuel fractions. 3) When using unsieved fuel, reducing the load massively decreased the fluctuations of the air mass flow and the total hydrocarbon content. With sieved fuel, however, a satisfying process stability was already achieved in all loads. Therefore, an appropriate load management was identified to enable the utilization of fuels with higher fines contents. With these new findings, forest chips in unsieved and sieved form can be successfully used in small-scale open-top gasification.

Reducing energy poverty in small rural communities through in situ electricity generation

Energy is key in achieving sustainable societies. There have been great efforts towards improving energy access worldwide. Despite the advances in energy access, energy poverty remains a major problem in many parts of the world, particularly in rural communities. Modern energy, in particular electricity, can help rural communities develop through improving education and health. During the last two decades, there have been improvements on bioenergy technological innovations, e.g. electricity generation from bioenergy from residual biomass from several agricultural crops in biorefineries. Most research has focussed on large biorefineries, with limited research on small-scale gasifiers’ location and contribution to energy poverty. This paper is aimed at assessing technological options to generate electricity in situ from biomass to reduce energy poverty of rural communities. This is done using four analysis methods: (1) crops availability data; (2) poverty and marginalisation data; (3) electricity provision/distribution; and, (4) GIS/Geographical latitude and longitude to locate municipalities in Mexico. The results shows that the generating potential for electricity using residual biomass with gasifiers could improve the welfare of almost 10 million people communities using residual biomass from crops harvested in such communities. This research provides location solutions on the best places to locate small-scale biorefineries. The research also provides systemic analysis to reduce energy poverty through in situ electricity generation using cheap accessible small plant technologies and biomass as raw material, as well as their location. Generating electricity in a decentralised way through agricultural residual biomass can help lift rural communities from poverty and improve their well-being, and, thus, make societies more sustainable.

Design of a biomass-heating network with an integrated heat pump: A simulation-based multi-objective optimization framework

The integration of compression heat pumps is a promising technology to recover waste heat from exhaust gases of a biomass-based heating network. This requires, however, the consumption of additional electricity, which has a high emission factor or a high price in many countries. In this context, the integration of small-scale gasifier cogeneration is supposed to be superior technology to provide the necessary power for heat pumps. Nevertheless, the multiple possibilities of integrating these components imply a high degree of system complexity and, therefore, higher design requirements. To maximize the benefits of the integrated system, development of an optimization approach at the system level is necessary, so that the connection variants of the heat pump, the installation of gasifier cogeneration, and their optimal design can be adequately planned. This work introduces a multi-objective simulation–optimization framework for the design of the proposed integrated system based on the genetic algorithm, taking into account the complex thermodynamic processes as well as the techno-economic performances and environmental impacts of the concepts. As a case study, an existing biomass heat network located in Germany is investigated to test the capabilities of the proposed approach. The analysis of the optimization results demonstrates that it is possible to ensure the effective utilization of biomass resources while simultaneously achieving the economic and environmental compatibility of the system through an appropriate optimization design. The proposed simulation–optimization framework allows decision-makers to achieve an optimal system design under the given constraints and the chosen objectives.

Perspectives of decentralised gasification of residual municipal solid waste

In the European Union (EU), the dominant technology for high-temperature thermal treatment of residual Municipal Solid Waste (i.e., the unsorted waste where source separation is performed) is the moving grate incineration. The process of combustion in this sector has been optimised thanks to the introduction of stringent criteria of operation both in the combustion chamber and in the treatment of the generated off-gas. However, the costs of treatment can be sustainable only if the tariff to be applied for the service is coherent with the average value found in the sector. The literature demonstrates that, under a capacity threshold, the grate system is out of market, thus limiting the implementation of small decentralised plants. This paper discusses the potential benefits of small-scale and decentralised thermo-chemical treatment plants replacing a single large-scale one. In addition, the present article analyses the consequences of the results of a recent survey that zoomed in on the availability of small-scale gasifiers for implementing such a strategy. The results of this analysis show that small-scale gasification is preferable to other technologies (e.g., incineration and pyrolysis) in terms of scale effect and flexibility/modularity. Compared to other thermal treatments, the local environmental impact could be reduced by converting syngas into fuels or chemicals rather than burning it for direct energy recovery. The paper also shows that small-scale gasification is able to respond to different needs in both EU and non-EU countries, like the management of progressively lower amounts of residual waste requiring treatment/management of uncontrolled dump sites.

Sustainable utilization of bamboo through air-steam gasification in downdraft gasifier: Experimental and simulation approach

This study presents a detailed analysis to utilize bamboo which is a widely available feedstock in North-Eastern states of India, via air-steam gasification with an estimated potential to generate 23.92 PJ energy. The study was carried out in a downdraft gasifier (10 kWe) to produce hydrogen-rich syngas. The effect of the steam to biomass ratio (0.1–0.4) on the gas composition and performance parameters is studied. The maximum H2 yield (37.12%) is found in the steam to biomass ratio of 0.35. The lower heating value and cold gas efficiency are in the range of 4.72–5.71 MJ/Nm3 and 62.1–85.7%, respectively. The higher steam to biomass ratio of above 0.35 led to cooling of combustion and reduction zone and negatively affected the performance parameters of the gasifier. The experimental data of the present study is validated with model data and root mean square error is found in the range of 4.24–7.76 and 2.88–10.08 from experimental data from literature with the developed model. Results show that it is economical and viable to use small-scale gasifiers to produce syngas from bamboo to meet the local energy demand. This is of importance in small and isolated communities that are near bamboo forest.

Carbon dioxide removal potential from decentralised bioenergy with carbon capture and storage (BECCS) and the relevance of operational choices

Bioenergy with carbon capture and storage (BECCS) technology is expected to support net-zero targets by supplying low carbon energy while providing carbon dioxide removal (CDR). BECCS is estimated to deliver 20 to 70 MtCO2 annual negative emissions by 2050 in the UK, despite there are currently no BECCS operating facility. This research is modelling and demonstrating the flexibility, scalability and attainable immediate application of BECCS. The CDR potential for two out of three BECCS pathways considered by the Intergovernmental Panel on Climate Change (IPCC) scenarios were quantified (i) modular-scale CHP process with post-combustion CCS utilising wheat straw and (ii) hydrogen production in a small-scale gasifier with pre-combustion CCS utilising locally sourced waste wood. Process modelling and lifecycle assessment were used, including a whole supply chain analysis. The investigated BECCS pathways could annually remove between −0.8 and −1.4 tCO2e tbiomass−1 depending on operational decisions. Using all the available wheat straw and waste wood in the UK, a joint CDR capacity for both systems could reach about 23% of the UK's CDR minimum target set for BECCS. Policy frameworks prioritising carbon efficiencies can shape those operational decisions and strongly impact on the overall energy and CDR performance of a BECCS system, but not necessarily maximising the trade-offs between biomass use, energy performance and CDR. A combination of different BECCS pathways will be necessary to reach net-zero targets. Decentralised BECCS deployment could support flexible approaches allowing to maximise positive system trade-offs, enable regional biomass utilisation and provide local energy supply to remote areas.

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.

Potential to retrofit existing small-scale gasifiers through steam gasification of biomass residues for hydrogen and biofuels production

This work investigates the opportunity of retrofitting existing small-scale gasifiers shifting from combined heat and power (CHP) to hydrogen and biofuels production, using steam and biomass residues (woodchips, vineyard pruning and bark). The experiments were carried out in a batch reactor at 700 °C and 800 °C and at different steam flow (SF) rates (0.04 g/min and 0.20 g/min). The composition of the producer gas is in the range of 46–70 % H2, 9–29 % CO, 12–27 % CO2, and 2–6 % CH4. A producer gas specific production factor of approx. 10 NLpg/gchar can be achieved when the lower SFs are used, which allows to provide 80 % of the hydrogen concentration required for biomethanation and MeOH synthesis. As for FT synthesis, an optimal H2/CO ratio of approx. 2 can be achieved. The results of this work provide further evidence towards the feasibility of hydrogen and biofuels generation from residual biomass through steam gasification.

Techno-economic study of a small scale gasifier applied to an indoor hemp farm: From energy savings to biochar effects on productivity

The hemp market is fast growing due to demand for cannabidiol, nutraceutical and hemp fiber products. This work demonstrates the economical advantage of biomass gasification application to indoor hemp production. Gasifiers provide electrical energy, heat and biochar: these are highly valuable products for indoor growers where lights and thermal management are key costs of the business. Energy produced in an autonomous and renewable way increases the sustainability and in the facility. In this paper a small scale gasifier is fueled with certified “A1 plus” wood pellets to test its behavior and its biochar production rate. Biochar is used for hemp growing tests in an indoor hemp production facility. Results show how a 22 kW power plant is sufficient to guarantee almost complete sustainability in a 80 m2 facility. In the best case scenario where energy saving, biochar and thermal energy selling are considered, the gasifier investment has a payback time of about 3.5 years. At the end of the gasifier lifespan, the Net Present Value reaches 249 k€ considering a discount rate of 6%. Consequential results were also obtained from biochar application to pot growing substrates: there was a 7.7% increase in dry flower production and a 33.9% increase in total plant fresh biomass. Cannabinoids profiles resulted not affected by biochar application.

Analysis of the performance of an integrated small-scale biomass gasification system in a Canadian context

Small-scale downdraft biomass gasification is a promising technology for off-grid combined heat and power generation utilizing Canada’s vast biomass resources. As small-scale gasifiers are currently emerging into the Canadian market, the current study investigates the required feedstock characteristics for stable operation using Canadian softwood, along with the quality of the biochar produced as a byproduct. It was found that reducing feedstock moisture from 20 to 9% increased overall system efficiency from 8.2 to 12%. Equilibrium simulations were utilized to evaluate the deviation from ideal conversion when using feedstock outside the gasifier feedstock specifications. These showed the gasifier was operating close to equilibrium, with the lower heating value of the actual producer gas deviating by an average of 9% from simulated results. This study provides a novel methodology for the quantification of reliability and efficiency of these systems which can be used to evaluate the economic benefit of these systems in Canada.

Energy and biochar co-production from municipal green waste gasification: A model applied to a landfill in the north of Italy

This work discusses the advantages that can be obtained from the integration of landfill gas with biomass gasification. The case study presented consists of a landfill located in the province of Reggio Emilia, in the north of Italy. Landfill gas from municipal-waste fuels four internal combustion engines with overall nominal power of 2 MW, the electricity is sold back to the grid, while the thermal power is used for the heating of an industrial greenhouse compartment for basil production. Within the same facility, green waste is collected from the surrounding municipalities then chipped and sieved. Fine particles are disposed into a composting plant close by, while the sieved fraction is sold to the market for electricity production in large-scale boiler-based power plants. The idea here presented and discussed consists of the implementation of a gasifier to convert the sieved fraction of green waste into a syngas fuel directly on site. Syngas is blended with the landfill gas and then fed to the gas engines. In this work green waste gasification is tested in a commercial small-scale gasifier, proving that sifted green waste is a suitable fuel for this application. A specific consumption of 1.2 kg/kWh and a total electrical efficiency of 16.22% were measured. The sizing of the full-scale gasification facility is based on both the experimental results and data about the local availability of green waste. The economic return of the investment is then discussed. Finally, a further level of integration between gasification and the existing site is proposed: gasification-derived biochar is investigated as soil amendment for the on site company at the landfill that grows basil commercially. Results of 55 days in vivo tests show an increase in the biomass production of the basil of 53% compared to the control test group.

Modeling and optimization of industrial internal combustion engines running on Diesel/syngas blends

The paper presents a numerical analysis of combustion, carried out on a compression ignition indirect injection engine fueled by both Diesel and syngas, the latter obtained from biomass gasification and introduced in the intake manifold. The computational fluid dynamics model includes an improved chemical kinetics scheme, tailored on the syngas-diesel dual fuel combustion. The model was validated by an experimental campaign, on the same engine. The syngas fuel was produced by a small scale gasifier running on wood chips. Several simulations were performed varying both the share of syngas and the Diesel start of injection angle. The total amount of heat released by combustion can increase up to 50%, along with the indicated work and the cylinder peak pressure. The start of injection angle should be modified in order to preserve the mechanical integrity of the engine, as well as to maximize its brake efficiency. The numerical analysis provides the guidelines for setting the injection strategy, as a function of the syngas share.

Advanced Concepts in Modular Coal and Biomass Gasifiers

The program involves the application of a novel gasification concept, termed a modular allothermal gasifier (MAG) to produce syngas from coal, biomass, and waste slurries. The MAG employs a steam-driven gasification process using a pressurized entrained flow reactor wherein the external wall surfaces are catalytically heated to 1000 °C via heterogeneous combustion of a portion of the produced syngas. The MAG can be fed by a hydrothermal treatment reactor for biomass and waste feedstocks, which employs well-developed hydrothermal processing technology using the addition of heat and water to provide a uniform slurry product. The hydrothermal treatment reactor requires no preprocessing and a clean syngas is produced at high cold gas efficiency (80%). Importantly, the MAG can operate over a wide range of positive pressures up to 3 MPa (30 bar) which provides process control to vary the output to match end-use needs or feedstock rate. The system produces minimal emissions and operates at significantly higher efficiency and lower energy requirements than pyrolysis, plasma gasification, and carbonization systems. The system is compact and modular, making it easily transportable, for example, to a variety of sites, including those where remoteness, inaccessibility, and space limitations would preclude competing systems. The system can be applied to small gasification systems without the increase in heat losses that plague conventional small scale gasifiers. Test results and model simulations are presented on a single tube system and analyses of a variety of configurations presented.

Modeling the emissions of a dual fuel engine coupled with a biomass gasifier-supplementing the Wiebe function.

There is a growing market demand for small-scale biomass gasifiers that is driven by the economic incentives and the legislative framework. Small-scale gasifiers produce a gaseous fuel, commonly referred to as producer gas, with relatively low heating value. Thus, the most common energy conversion systems that are coupled with small-scale gasifiers are internal combustion engines. In order to increase the electrical efficiency, the operators choose dual fuel engines and mix the producer gas with diesel. The Wiebe function has been a valuable tool for assessing the efficiency of dual fuel internal combustion engines. This study introduces a thermodynamic model that works in parallel with the Wiebe function and calculates the emissions of the engines. This "vis-à-vis" approach takes into consideration the actual conditions inside the cylinders-as they are returned by the Wiebe function-and calculates the final thermodynamic equilibrium of the flue gases mixture. This approach aims to enhance the operation of the dual fuel internal combustion engines by identifying the optimal operating conditions and-at the same time-advance pollution control and minimize the environmental impact.

Tar Tolerant HCCI Engine Fuelled with Biomass Syngas: Combustion Control Through EGR

Abstract The filtration of condensable tars is a necessary step before biomass syngas can be used in spark ignition engines. In small scale gasifiers, this step represents one third of the investment cost and create several issues of maintenance. Since tar related problems occur primarily due to tar condensation, an alternative system is being developed where a Homogeneous Charge Compression Ignition (HCCI) engine is operated at intake temperatures above the tar dew point, thereby eliminating the need for tar filtration. Based on a conservative estimate of tar dew points, HCCI combustion has been studied at an intake temperature of 250 °C. This paper presents a comprehensive study of the first HCCI engine operated with syngas. In particular, it addresses a control technique based on Exhaust Gas Recirculation (EGR). Simulated biomass syngas and simulated EGR were used on a 500cc mono-cylinder HCCI engine operated at 1000 RPM. The effects of charge dilution, thermal and kinetic damping as a consequence of EGR and the consequential combustion control have been discussed. In addition to being an effective control, the use of EGR decreases the Maximum Pressure Rise Rate and allows increasing the upper limit of the Indicated Mean Effective Pressure from 2.8 bar at EGR=0% to up to 3.5 bar at EGR=25%, a rise of about 25%.

Introduction of an energy efficiency tool for small scale biomass gasifiers – A thermodynamic approach

Modern gasification plants, should be treated as poly-generation facilities because, alongside the production of electricity and heat, valuable or waste materials streams are generated. Thus, integrated methods should be introduced in order to account for the full range and the nature of the products. Application of conventional hybrid indicators that convert the output into monetary units or CO2 equivalents are a source of bias because of the inconsistency of the conversion factors and unreliability of the available data. Therefore, this study introduces a novel thermodynamic-based method for assessing gasification plants performance by means of exergy, entransy and statistical entropy. A monitoring campaign has been implemented on two small scale gasifiers and the results have been applied on the proposed method. The energy plants are compared in respect to their individual thermodynamic parameters for energy production and materials distribution. In addition, the method returns one single value which is a resultant of all the investigated parameters and is a characteristic value of the overall performance of an energy plant.

Utilisation of biomass gasification by-products for onsite energy production.

Small scale biomass gasification is a sector with growth and increasing applications owing to the environmental goals of the European Union and the incentivised policies of most European countries. This study addresses two aspects, which are at the centre of attention concerning the operation and development of small scale gasifiers; reuse of waste and increase of energy efficiency. Several authors have denoted that the low electrical efficiency of these systems is the main barrier for further commercial development. In addition, gasification has several by-products that have no further use and are discarded as waste. In the framework of this manuscript, a secondary reactor is introduced and modelled. The main operating principle is the utilisation of char and flue gases for further energy production. These by-products are reformed into secondary producer gas by means of a secondary reactor. In addition, a set of heat exchangers capture the waste heat and optimise the process. This case study is modelled in a MATLAB-Cantera environment. The model is non-stoichiometric and applies the Gibbs minimisation principle. The simulations show that some of the thermal energy is depleted during the process owing to the preheating of flue gases. Nonetheless, the addition of a secondary reactor results in an increase of the electrical power production efficiency and the combined heat and power (CHP) efficiency.

Energy recovery from human faeces via gasification: A thermodynamic equilibrium modelling approach

Non-sewered sanitary systems (NSS) are emerging as one of the solutions to poor sanitation because of the limitations of the conventional flush toilet. These new sanitary systems are expected to safely treat faecal waste and operate without external connections to a sewer, water supply or energy source. The Nano Membrane Toilet (NMT) is a unique domestic-scale sanitary solution currently being developed to treat human waste on-site. This toilet will employ a small-scale gasifier to convert human faeces into products of high energy value. This study investigated the suitability of human faeces as a feedstock for gasification. It quantified the recoverable exergy potential from human faeces and explored the optimal routes for thermal conversion, using a thermodynamic equilibrium model. Fresh human faeces were found to have approximately 70–82wt.% moisture and 3–6wt.% ash. Product gas resulting from a typical dry human faeces (0wt.% moisture) had LHV and exergy values of 17.2MJ/kg and 24MJ/kg respectively at optimum equivalence ratio of 0.31, values that are comparable to wood biomass. For suitable conversion of moist faecal samples, near combustion operating conditions are required, if an external energy source is not supplied. This is however at 5% loss in the exergy value of the gas, provided both thermal heat and energy of the gas are recovered. This study shows that the maximum recoverable exergy potential from an average adult moist human faeces can be up to 15MJ/kg, when the gasifier is operated at optimum equivalence ratio of 0.57, excluding heat losses, distribution or other losses that result from operational activities.

Gasifier as a cleaner cooking system in rural Kenya

Global demand for wood fuel energy is high and rising due to population increases, particularly in sub-Saharan Africa, where firewood and charcoal are the main sources of cooking energy. Inefficient cooking techniques consume large amounts of fuel and create indoor pollution, with negative health impacts particularly among women and small children. Efficient cooking stoves can potentially save fuel and reduce the health risks of smoke in the kitchen. This study compared the ease of use, energy consumption, fuel use efficiency and gas and particle emissions of a small-scale gasifier cooking stove with that of a traditional three-stone stove and an improved Hifadhi stove in a smallholder farming setting in Kenya. This was done by participatory evaluation of these cooking techniques by women on smallholder farms, assessing fuel consumption, time used in cooking and indoor air concentrations of carbon monoxide and fine particulate matter. It was found that compared with traditional and improved cooking stoves, the gasifier domestic cooking system saved 27–40% of fuel, reduced cooking time by 19–23% and reduced emissions by 40–90%. Thus the gasifier system has potential to alleviate energy and time poverty among small-scale farmers, while improving kitchen air quality. These new findings can assist in development of cleaner biomass cooking technologies in developing countries. Women who cooked using the gasifier preferred it to current cooking practices due to perceived benefits. Thus the gasifier is appropriate for rural areas; it constitutes a cleaner cooking system that saves fuel, produces charcoal for another round of cooking, cooks rapidly, and reduces indoor air pollution from cooking with biomass fuel. However, there is a need to improve the design to make it more stable and safer.

Thermodynamic modeling of small scale biomass gasifiers: Development and assessment of the ‘‘Multi-Box’’ approach

Modeling can be a powerful tool for designing and optimizing gasification systems. Modeling applications for small scale/fixed bed biomass gasifiers have been interesting due to their increased commercial practices. Fixed bed gasifiers are characterized by a wide range of operational conditions and are multi-zoned processes. The reactants are distributed in different phases and the products from each zone influence the following process steps and thus the composition of the final products. The present study aims to improve the conventional ‘Black-Box’ thermodynamic modeling by means of developing multiple intermediate ‘boxes’ that calculate two phase (solid–vapor) equilibriums in small scale gasifiers. Therefore the model is named ‘‘Multi-Box’’. Experimental data from a small scale gasifier have been used for the validation of the model. The returned results are significantly closer with the actual case study measurements in comparison to single-stage thermodynamic modeling.