Sustainable ethanol production from lignocellulosic biomass - Application of exergy analysis

The sustainability of the second-generation biofuels requests to confirm that the energy produced from lignocellulosic biomass is significantly greater than the energy consumed in the process. As lignocellulosic biomass does not affect the food supply, sugarcane bagasse was analyzed as a raw material for second-generation biofuels production. Exergy analysis serves as a unified and effective tool to evaluate the global process efficiency. Exergy analysis evaluates the performance of sugarcane bagasse and its sustainability in the bioethanol production process. In this work, four ethanol production topologies using the typical daily amount of residual biomass produced by the sugar industry were compared. The exergy analysis concept is effective in screening design alternatives with the lowest environmental impact for second-generation bioethanol fuel production from renewable resources. This study was executed by the use of the Aspen Plus^® program and other software developed by the authors.     

Potential of bioethanol production from agricultural wastes in Iran

The production of bioethanol from agricultural residues such as wheat, barley, sugar cane, corn and rice in Iran is investigated in this paper. In Iran, agricultural residues are not commonly used for energy application. This paper aims to cover several perspectives on the size of the bioethanol feedstock resource in Iran. Crop residues and sugar cane bagasse are included in feedstock for production of bioethanol. There are approximately 17.86 MT of wasted crops in Iran that can potentially produce 4.91 GL of bioethanol per year. Wheat, sugar cane bagasse, rice, barely and corn are the most favourable bioethanol production source in Iran. Agricultural waste materials can be used for production of bioethanol fuel. Bioethanol can be considered as the optimum alternative fuel for gasoline. Bioethanol is an environmentally friendly fuel and has the potential to provide comparable engine performance results.     

Optimizing ethanol and bioelectricity production in sugarcane biorefineries in Brazil

In sugarcane biorefineries, the lignocellulosic portion of the sugarcane biomass (i.e. bagasse and cane trash) can be used as fuel for electricity production and/or feedstock for second generation (2G) ethanol. This study presents a techno-economic analysis of upgraded sugarcane biorefineries in Brazil, aiming at utilizing surplus bagasse and cane trash for electricity and/or ethanol production. The study investigates the trade-off on sugarcane biomass use for energy production: bioelectricity versus 2G ethanol production. The BeWhere mixed integer and spatially explicit model is used for evaluating the choice of technological options. Different scenarios are developed to find the optimal utilization of sugarcane biomass. The study finds that energy prices, type of electricity substituted, biofuel support and carbon tax, investment costs, and conversion efficiencies are the major factors influencing the technological choice. At the existing market and technological conditions applied in the upgraded biorefineries, 300 PJ y⁻¹ 2G ethanol could be optimally produced and exported to the EU, which corresponds to 2.5% of total transport fuel demand in the EU. This study provides a methodological framework on how to optimize the alternative use of agricultural residues and industrial co-products for energy production in agro-industries considering biomass supply chains, the pattern of domestic energy demand, and biofuel trade.     

Production of anhydrous ethanol using oil palm empty fruit bunch in a pilot plant

Bioethanol production from lignocellulosic biomass for use as an alternative energy resource has attracted increasing interest, but short-term commercialization will require several technologies such as low cost feedstock. The huge amount of oil palm empty fruit bunches (EFB) generated from palm oil industries can be used as a raw material for cheap, renewable feedstock for further commercial exploitation. Using a pilot-scale bioethanol plant, this study investigated the possibility of utilizing oil palm empty fruit bunches as a renewable resource. All bioethanol production processes such as pretreatment, hydrolysis, fermentation, and purification were constructed as automatically controlled integrated processes. The mass balance was calculated from operational results. Changhae ethanol multiexplosion pretreatment with sodium hydroxide was conducted to improve the enzymatic hydrolysis process, and a separate hydrolysis and fermentation process was used for producing bioethanol at an 83.6% ethanol conversion rate. In order to purify the ethanol, a distillation and dehydration facility was operated. Distillation and dehydration efficiencies were 98.9% and 99.2%, respectively. The material balance could be calculated using results obtained from the operation of the pilot-scale bioethanol plant. As a result, it was possible to produce 144.4 kg anhydrous ethanol (99.7 wt%) from 1000 kg EFB. This result constitutes a significant contribution to the feasibility of bioethanol production from lignocellulosic biomass and justifies the pilot plant's scale-up to a commercial-scale plant.     

Syngas from sugarcane pyrolysis: An experimental study for fuel cell applications

The use of biomass for the production of electrical energy is a promising technological solution for those countries where there are problems with the disposal of agricultural waste and/or the production of low-cost energy. The gasification and/or pyrolysis of the biomass produces a gas rich in hydrogen that can be used in a fuel cell system to produce electrical energy with reduced environmental impact and significant energy recovery.In this work, a study of the pyrolysis of Brazilian sugarcane bagasse was carried out. The experimental process consisted of the pyrolysis of the biomass material in a batch pyrolysis reactor. In some runs the biomass was dry, while in others it was pre-treated by the addition of water. It was noted that the water added to the biomass before the pyrolysis process resulted in a decrease in the quantity of steam added to the fuel cell feeding gas, necessary to avoid carbon deposition, and in an increase in cell power, but, at the same time, caused a decrease in the quantity of syngas produced.Then, the composition of the gas obtained from the experimental pyrolysis of the sugarcane was inserted in a simulation tool of a molten carbonate fuel cell system in order to estimate the feasibility of the entire process in terms of operating conditions and electrical performance.The present study indicates that the syngas obtained from the sugarcane biomass (about 40%) can be converted into electricity using a fuel cell system with a high efficiency.     

Key prospects and major development of hydrogen and bioethanol production

Cheap Production of bioethanol from renewable lignocellulosic waste has the imperative potential to economically cut burgeoning world dependency on fossils while reducing net emission of carbon dioxide (CO₂), a principal greenhouse gas (GHGs). This paper highlights key benefits and status of bioethanol production technologies, aiming mainly on recent developments and its key potentials in Pakistan. Most sector of Pakistan economy heavily rely on the energy and power that is being produced using traditional approaches like from oil and hydel. However, the sedimentation in dams cut-down the energy generation and overwhelmed severe energy crisis that are witnessed since last decade. Thus, Pakistan must go to avail alternative sources of energy like hydro, biomass and solar so that energy security can be ensured to recover the tremendous loss of economy. Renewable biomass is abundantly available in Pakistan which can be used to produce bioethanol and electricity. Currently, 22 distilleries are producing the ethanol from sugar cane bagasse and out of these only 8 distillation units are producing motor fuel grade ethanol. The current bioethanol production of country is about 403,500 tons/year along with 2423 tons of biodegradable waste available in major cities. In addition, Pakistan produces 6.57, 0.5, 0.66, and 2.66 million tons of sugarcane, corn, rice, and wheat straw per annum, respectively. This biomass can produce 1.6 million liters of bioethanol which can produce approximately 38% of Pakistan's electricity annually. Despite having large potential, Pakistan is still producing a few volumes of ethanol from sugarcane bagasse. The production of bioethanol can be boosted using (I) pretreatment of agricultural biomass by alkali (II) enzymatic and bacteria-based hydrolysis of the biomass (III) post-hydrolysis using pressurized steam above 100 °C (IV) Fermentation of the biomass@ 7–10 h and (V) and (VI) distillation of bioethanol. This study recommends (1) increase R&D capacities mainly in the west and central regions of Pakistan, (2) initiate mega-projects to promote integrated bio-ethanol production at agriculture farms by providing 1/3 subsides, (3) purchase of bioethanol directly from the major agricultural farms, (4) produce bioethanol related manpower from the key research institutes as specified in this study.     

Solar-driven steam-based gasification of sugarcane bagasse in a combined drop-tube and fixed-bed reactor – Thermodynamic,kinetic, and experimental analyses

Syngas production via steam-based thermochemical gasification of Brazilian sugarcane bagasse, using concentrated solar energy for process heat, was thermodynamically and experimentally investigated. Energy and exergy analyses revealed the potential benefits of solar-driven over conventional autothermal gasification that included superior quality of syngas composition and higher yield per unit of feedstock. Reaction rates for the gasification of fast pyrolyzed bagasse char were measured by thermogravimetric analysis and a rate law based on the oxygen exchange mechanism was formulated. In order to provide residence times long enough for adequate char conversion, a laboratory-scale entrained flow reactor that combines drop-tube and fixed-bed concepts was developed. Testing was performed in an electric furnace with the final aim to supply heat by concentrated solar radiation. Experimental runs at reactor temperatures of 1073–1573 K and a biomass feed rate of 0.48 g/min yielded high-quality syngas of molar ratios H₂/CO = 1.6 and CO₂/CO = 0.31, and with heating values of 15.3–16.9 MJ/kg, resulting in an upgrade factor (ratio of heating value of syngas produced over that of the feedstock) of 112%. Theoretical upgrade factors of up to 126%, along with the treatment of wet feedstock and elimination of the air separation unit, support the potential benefits of solar-driven over autothermal gasification.     

Waste biomass to liquids: Low temperature conversion of sugarcane bagasse to bio-oil. The effect of combined hydrolysis treatments

This article describes the influence of different sugarcane bagasse hydrolysis pretreatments on modifications to biomass feedstock and the characteristics of the resultant pyrolysis products. Sugarcane bagasse was pretreated with acid, alkaline or sequential acid/alkaline solutions and pretreated samples were then subjected to a low temperature conversion (LTC) process under He or O₂/He atmospheres at 350-450 °C. Both pretreated samples and sugarcane bagasse in natura were analyzed by determination of their chemical composition and by thermogravimetric, FTIR and SEM analyses. The gases yielded during LTC were monitored on-line by quadrupole mass spectrometry, and the liquid fractions obtained were characterized by FTIR and ¹H and ¹³C NMR. Irrespective of the sugarcane bagasse pretreatment applied, the main bio-oil component obtained was levoglucosan. However, the LTC yield of bio-oil depended on the hydrolysis treatment of the biomass and decreased in the presence of O₂. The acid hydrolysis pretreatment increased the LTC bio-oil yield notably.     

Improving bioethanol production from sugarcane: evaluation of distillation, thermal integration and cogeneration systems

Demand for bioethanol has grown considerably over the last years. Even though Brazil has been producing ethanol from sugarcane on a large scale for decades, this industry is characterized by low energy efficiency, using a large fraction of the bagasse produced as fuel in the cogeneration system to supply the process energy requirements. The possibility of selling surplus electricity to the grid or using surplus bagasse as raw material of other processes has motivated investments on more efficient cogeneration systems and process thermal integration. In this work simulations of an autonomous distillery were carried out, along with utilities demand optimization using Pinch Analysis concepts. Different cogeneration systems were analyzed: a traditional Rankine Cycle, with steam of high temperature and pressure (80 bar, 510 °C) and back pressure and condensing steam turbines configuration, and a BIGCC (Biomass Integrated Gasification Combined Cycle), comprised by a gas turbine set operating with biomass gas produced in a gasifier that uses sugarcane bagasse as raw material. Thermoeconomic analyses determining exergy-based costs of electricity and ethanol for both cases were carried out. The main objective is to show the impact that these process improvements can produce in industrial systems, compared to the current situation.     

Life cycle assessment and life cycle costing of bioethanol from sugarcane in Brazil

Brazil has always been the pioneer in the application of bioethanol as a main fuel for automobiles, hence environmental and economic analyses of the Brazilian ethanol industries are of crucial importance. This study presents a comparative life cycle assessment (LCA) on gasoline and ethanol as fuels, and with two types of blends of gasoline with bioethanol, all used in a midsize car. The focus is on a main application in Brazil, sugarcane based ethanol. The results of two cases are presented: base case—bioethanol production from sugarcane and electricity generation from bagasse; future case—bioethanol production from both sugarcane and bagasse and electricity generation from wastes. In both cases sugar is co-produced. The life cycles of fuels include gasoline production, agricultural production of sugarcane, ethanol production, sugar and electricity co-production, blending ethanol with gasoline to produce E10 (10% of ethanol) and E85 (85%), and finally the use of gasoline, E10, E85 and pure ethanol. Furthermore, a life cycle costing (LCC) was conducted to give an indication on fuel economy in both cases. The results show that in the base case less GHG is emitted; while the overall evaluation of these fuel options depends on the importance attached to different impacts. The future case is certainly more economically attractive, which has been the driving force for development in the ethanol industry in Brazil. Nevertheless, the outcomes depend very much on the assumed price for crude oil. In LCC a steady-state cost model was used and only the production cost was taken into account. In the real market the prices of fuels are very much dependent on the taxes and subsidies. Technological development can help in lowering both the environmental impact and the prices of the ethanol fuels.     

Energy recovery by fast pyrolysis of pre-treated trommel fines derived from a UK-based MSW material recycling facility

In this experimental study, a physically pre-treated trommel fines feedstock, containing 44 wt% non-volatiles (ash and fixed carbon) and 56 wt% volatile matter (dry basis), was subjected to fast pyrolysis to recover energy from its organic load, using a 300 g h⁻¹ bubbling fluidized bed (BFB) fast pyrolysis rig. A physical pre-treatment method (including crushing, grinding and sieving) was used to prepare a 0.5–2 mm sized trommel fines feedstock to make it suitable for fast pyrolysis in the BFB reactor. Experimental results from the fast pyrolysis process showed that the highest yield of organic liquid was obtained at around a temperature of 500 °C. However, both char and gas yields increased dramatically at temperatures above 500 °C, as a result of enhanced cracking of organic vapours, which reduced the yield of liquid products. Overall, energy recovery from the pyrolysis products (liquid and gas products as well as char pot residues) ranged from 63 to 70%, generally increasing with temperature. A large proportion of the high ash content (36 wt%) of the feedstock was found in the char pot (>62%), while smaller proportions were found in the reactor bed and some liquid products. The char pot ash residues composed mostly of non-hazardous earth materials and may be applied in bulk construction materials e.g. cement manufacture. Although, there was no problem with the pyrolysis rig during 1 h of operation, longer periods of operation would require periodic removal of accumulated solid residues and/or char pot modification to ensure continuous rig operation and process safety.     

A comparative techno‐economic assessment of three bio‐oil upgrading routes for aviation biofuel production

The aviation industry continues to grow, and consequently, more fuel is needed. With the intention of decarbonising the aviation sector, sustainable routes that have the potential to mitigate emissions, such as biomass fast pyrolysis, can positively contribute to this direction. Within this context, the present study performs a comparative techno‐economic evaluation of aviation biofuel manufacture via the main bio‐oil upgrading pathways, namely, hydroprocessing (HP), gasification followed by Fischer‐Tropsch synthesis (G+FT), and zeolite cracking (ZC). The research constitutes the first endeavour to investigate and compare the feasibility of producing biojet fuel via pyrolysis‐based routes. The presented work provides an inclusive evaluation that comprises process modelling and financial assessment. Based on the simulations, overall energy efficiencies of 48.8%, 45.73%, and 45.38% and jet fuel energy efficiencies of 23.70%, 21.45%, and 20.53% were calculated, while the implementation of a discounted cash flow analysis estimated minimum jet fuel selling prices (MJSPs) of 1.98, 2.32, and 2.21 $/L for the HP, the G+FT, and the ZC, respectively. Sensitivity analysis revealed that the processes are capital and feedstock intensive while an increase to the bio‐oil yield will favour the economic performance of the examined biorefineries. An increase of the plant size from 100 (base case) to 150 dry tonnes per hour of feedstock will decrease the selling prices by approximately 25% for all cases. Monte Carlo simulations exhibited that without establishing and/or maintaining appropriate policy schemes, there is no pragmatic prospect for the examined biorefineries to beat the competition against the prevailing oil infrastructures.     

Removal of K and Cl by leaching of straw char

A pretreatment process to remove potassium from straw fuel may be based on pyrolysis followed by char wash. The straw is pyrolysed at moderate temperatures at which the potassium is retained in the char. Potassium and residual chlorine are extracted from the residual char by water. Char and pyrolysis gases may then be used in a conventional boiler without problems due to the high straw potassium content. To evaluate this pretreatment process knowledge about the char wash process is needed. In this study wheat straw chars were experimentally investigated in the laboratory to determine the extraction time of potassium and chlorine during char wash with water. The influence of particle size, water temperature, straw type, potassium content in water and pyrolysis conditions were investigated. Based on the experimental data a mathematical model describing the extraction, was developed. The laboratory experiments showed that three fractions of potassium in the straw reacted differently: 35–58% of the char potassium was dissolved very fast, followed by a secondary slow potassium release that was strongly influenced by particle sizes, water temperature, char type and water KCl content. The residual 5–10% of the char potassium remains in the char and could not be removed with pure water.     

Developments in the scale-up of the vortex-pyrolysis system

Fundamental and applied research and engineering development over the past 13 years has demonstrated that continuous reactors could be used with very fast heating rates and short residence times to produce high yields of liquids from biomass. The National Renewable Energy Laboratory developed the ablative pyrolysis system and Interchem Environmental is commercializing this technology. Interchem designed and built a first generation, 32.7 tonnes (36 tons) per day, prototype ablative pyrolysis system in Missouri. The system was operated for 15 months with varying degrees of success. A second generation plant was designed based on the operating data collected from the first plant and on NREL's design for the vortex reactor. This facility is currently being built in Kansas City, KS. This paper discusses the design and operation of the first generation prototype facility and the design of the second generation system. The second plant is designed to produce 70% oil, 15% char and 15% non-condensible gases from the incoming wood. The oil will be sold as boiler fuel, the char sold as a feedstock to charcoal briquette manufacturers and the gases burned to provide process heat. Upon successful commercialization of this process, agricultural and forest residues can be converted into valuable products. In addition, the process offers a mechanism to use biomass as a feedstock for chemical production rather than relying on petroleum feedstocks.     

Efficient sugar production from sugarcane bagasse by microwave assisted acid and alkali pretreatment

Sugarcane bagasse represents one of the best potential feedstocks for the production of second generation bioethanol. The most efficient method to produce fermentable sugars is by enzymatic hydrolysis, assisted by thermochemical pretreatments. Previous research was focused on conventional heating pretreatment and the pretreated biomass residue characteristics. In this work, microwave energy is applied to facilitate sodium hydroxide (NaOH) and sulphuric acid (H₂SO₄) pretreatments on sugarcane bagasse and the efficiency of sugar production was evaluated on the soluble sugars released during pretreatment. The results show that microwave assisted pretreatment was more efficient than conventional heating pretreatment and it gave rise to 4 times higher reducing sugar release by using 5.7 times less pretreatment time. It is highlighted that enrichment of xylose and glucose can be tuned by changing pretreatment media (NaOH/H₂SO₄) and holding time. SEM study shows significant delignification effect of NaOH pretreatment, suggesting a possible improved enzymatic hydrolysis process. However, severe acid conditions should be avoided (long holding time or high acid concentration) under microwave heating conditions. It led to biomass carbonization, reducing sugar production and forming ‘humins’. Overall, in comparison with conventional pretreatment, microwave assisted pretreatment removed significant amount of hemicellulose and lignin and led to high amount of sugar production during pretreatment process, suggesting microwave heating pretreatment is an effective and efficient pretreatment method.     

利用微藻热化学液化制备生物油的研究进展

微藻是制备生物质液体燃料的良好材料,利用微藻热化学液化制备生物油在环保和能源供应方向都具有非常重要的意义。目前国内外研究者主要采用快速热解液化和直接液化两种热化学转化技术进行以微藻为原料制备生物油的研究。快速热解生产过程在常压下进行,工艺简单、成本低、反应迅速、燃料油收率高、装置容易大型化,是目前最具开发潜力的生物质液化技术之一。但快速热解需要对原料进行干燥和粉碎等预处理,微藻含水率极高,会消耗大量的能量,使快速热解技术在以微藻为原料制备生物油方面受到限制。直接液化技术反应温度较快速热解低,原料无需烘干和粉碎等高耗能预处理过程,且能产生更优质的生物油,将会是微藻热化学液化制备生物油发展的主流方向,极具工业化前景。国内外研究者还尝试利用超临界液化、共液化、热化学催化液化、微波裂解液化等多种新型液化工艺进行微藻热化学液化制备生物油的实验研究。今后的主要研究方向应是将热化学液化原理研究、生产工艺开发、反应器研发、反应条件优化、产品精制等有机地结合起来,进行深入研究。同时应努力节约成本、降低能耗。     

Nitrogen explosion pretreatment of lignocellulosic material for bioethanol production

A novel method for the pretreatment of lignocellulosic material is investigated in this work, using floodplain meadow hay as a feedstock for bioethanol production. Pressurized nitrogen (N₂) pretreatment is combined with explosive decompression to achieve high glucose yields with simple technology and low energy input. Results show that N₂ explosion yields hydrolysis efficiencies up to 71.8%. The highest hydrolysis efficiency was achieved at a temperature of 210°C with a cellulose to glucose conversion rate of 195.1 g kg^?1 of biomass.     

Production of bio-oil and activated carbon from sugarcane bagasse and molasses

In this study, the production of bio-oil and activated carbon from sugarcane bagasse and molasses was investigated via pyrolysis and CO₂ activation. The pyrolysis process yielded char, bio-oil, and gases in 25.90, 41.11, and 32.99 wt%, respectively. The properties and characteristics of obtained bio-oil are comparable with the proposed specifications of the various grades of pyrolysis oils and could find potential application as fuel or source of a number of valuable chemicals. The activation process with CO₂ showed it was possible to obtain activated carbon with surface area up to 900 m² g⁻¹ over 4.5 h activation time with a predominance of micro- and mesopores. The bagasse-based activated carbon was found to be efficient in comparison to commercial activated carbon in removing molasses color, and might provide a lower-cost alternative adsorbent for use in sugar decolorization in raw sugar refining.     

Catalytic fast pyrolysis of sugarcane bagasse pith with HZSM-5 catalyst using tandem micro-reactor-GC-MS

Fast pyrolysis of biomass is praised as an efficient and feasible process to selectively convert lignocellulosic biomass into bio-fuels and bio-chemicals. Pith of sugarcane bagasse could be an attractive lignocellulosic waste from depithing process from pulp and paper mill, which can utilize for production of biofuel and added value products. In this study, we employed a tandem micro-reactor coupled with gas chromatography-mass spectroscopy to investigate the products distribution from pith of sugarcane bagasse via catalytic fast pyrolysis. In the operating conditions, pyrolysis temperature and HZSM-5 catalyst had significant effect on products and distributions. An increase in the pyrolysis temperature from 400°C to 550°C led to an increase in the yield of phenolic compounds (6.3%, w/w%), followed decrease at higher temperature. The maximum carboxylic acids (10.6%) and furfural (3.5%) were obtained at lower temperature. At presence of HZSM-5 catalyst, the selectivity of aromatics such as benzene, toluene, indene, and naphthalene were improved.     

A techno-economic comparison of power production by biomass fast pyrolysis with gasification and combustion

This paper presents an assessment of the technical and economic performance of thermal processes to generate electricity from a wood chip feedstock by combustion, gasification and fast pyrolysis. The scope of the work begins with the delivery of a wood chip feedstock at a conversion plant and ends with the supply of electricity to the grid, incorporating wood chip preparation, thermal conversion, and electricity generation in dual fuel diesel engines. Net generating capacities of 1–20 MW_e are evaluated.The techno-economic assessment is achieved through the development of a suite of models that are combined to give cost and performance data for the integrated system. The models include feed pretreatment, combustion, atmospheric and pressure gasification, fast pyrolysis with pyrolysis liquid storage and transport (an optional step in de-coupled systems) and diesel engine or turbine power generation. The models calculate system efficiencies, capital costs and production costs. An identical methodology is applied in the development of all the models so that all of the results are directly comparable.The electricity production costs have been calculated for 10th plant systems, indicating the costs that are achievable in the medium term after the high initial costs associated with novel technologies have reduced. The costs converge at the larger scale with the mean electricity price paid in the EU by a large consumer, and there is therefore potential for fast pyrolysis and diesel engine systems to sell electricity directly to large consumers or for on-site generation. However, competition will be fierce at all capacities since electricity production costs vary only slightly between the four biomass to electricity systems that are evaluated.Systems de-coupling is one way that the fast pyrolysis and diesel engine system can distinguish itself from the other conversion technologies. Evaluations in this work show that situations requiring several remote generators are much better served by a large fast pyrolysis plant that supplies fuel to de-coupled diesel engines than by constructing an entire close-coupled system at each generating site. Another advantage of de-coupling is that the fast pyrolysis conversion step and the diesel engine generation step can operate independently, with intermediate storage of the fast pyrolysis liquid fuel, increasing overall reliability. Peak load or seasonal power requirements would also benefit from de-coupling since a small fast pyrolysis plant could operate continuously to produce fuel that is stored for use in the engine on demand.Current electricity production costs for a fast pyrolysis and diesel engine system are 0.091

1. Download : Download full-size image

/kWh at 20 MW_e and 0.199

1. Download : Download full-size image

/kWh at 1 MW_e in the base case studied here reducing to 0.073

1. Download : Download full-size image

/kWh at 20 MW_e and to 0.146

1. Download : Download full-size image

/kWh at 1 MW_e when learning effects are included. These systems are handicapped by the typical characteristics of a novel technology: high capital cost, high labour, and low reliability. As such the more established combustion and steam cycle produces lower cost electricity under current conditions.The fast pyrolysis and diesel engine system is a low capital cost option but it also suffers from relatively low system efficiency particularly at high capacities. This low efficiency is the result of a low conversion efficiency of feed energy into the pyrolysis liquid, because of the energy in the char by-product. A sensitivity analysis has highlighted the high impact on electricity production costs of the fast pyrolysis liquids yield. The liquids yield should be set realistically during design, and it should be maintained in practice by careful attention to plant operation and feed quality. Another problem is the high power consumption during feedstock grinding. Efficiencies may be enhanced in ablative fast pyrolysis which can tolerate a chipped feedstock. This has yet to be demonstrated at commercial scale.In summary, the fast pyrolysis and diesel engine system has great potential to generate electricity at a profit in the long term, and at a lower cost than any other biomass to electricity system at small scale. This future viability can only be achieved through the construction of early plant that could, in the short term, be more expensive than the combustion alternative. Profitability in the short term can best be achieved by exploiting niches in the market place and specific features of fast pyrolysis. These include:

• •countries or regions with fiscal incentives for renewable energy such as premium electricity prices or capital grants;
• •locations with high electricity prices so that electricity can be sold direct to large consumers or generated on-site by companies who wish to reduce their consumption from the grid;
• •waste disposal opportunities where feedstocks can attract a gate fee rather than incur a cost;
• •the ability to store fast pyrolysis liquids as a buffer against shutdowns or as a fuel for peak-load generating plant;
• •de-coupling opportunities where a large, single pyrolysis plant supplies fuel to several small and remote generators;
• •small-scale combined heat and power opportunities;
• •sales of the excess char, although a market has yet to be established for this by-product; and
• •potential co-production of speciality chemicals and fuel for power generation in fast pyrolysis systems.