In pyrolysis, oxygen containing compounds aldehydes, ketones, phenolics, and organic acids make the oil too unstable and acidic for introduction into existing pipelines, tankers, and refineries Bridgwater, a. Thus, a primary research goal in biomass thermochemical conversion is directed towards the optimization of these processes to reduce the amount of unwanted byproducts if the oil is the preferred product. The first facility using the fast pyrolysis principle in Brazil was described by Rocha et al.
Bioware Tecnologia has grown and is scientifically supported by the University of Campinas, Brazil. Its main aim is to develop and produce high addedvalue products from forest and agro-industrial waste, using state-of-the-art and environmentally friendly technologies.
Its research intends to develop biomass fast pyrolysis technology in a continuous atmospheric bubbling fluidized bed reactor in order to produce bio-oil and charcoal. The basic raw materials used are: elephant grass, cane trash and bagasse, which have already been processed with a measure of success. When the reactor operates under these conditions, the wet scrubber recovers an average of 40 wt. The pilot facility, which is fully automated, has a nominal capacity of kg.
The bio-oil could be used as an emulsifying agent for heavy petroleum, an additive for cellular concrete, a substitute of phenol in PF resin formulations and fuel for the generation of energy. Moreover, the charcoal produced could be used as fuel in furnaces, as a prereducer for iron ore pellets, activated carbon and catalytic substrate. The supply of cheap raw materials to be used in the Bioware process is plentiful and practically limitless. Specifically, great support and interest have been shown by the Brazilian sugarcane industry regarding this technology.
In addition, the pulp and paper sawmill and rice industries have expressed interest in becoming active partners. The company already cooperates with many national groups and companies Rocha et al. Wang et al. Even though different types of gasifier configurations have been developed, downdraft gasifiers are most often offered commercially, followed by fluid beds, updraft and other gasifier types Bridgwater, Fixed-bed, counter-current updraft , and concurrent downdraft gasifiers are, in general, of very simple construction and operation.
They also present high carbon conversion, long solid residence times, and low ash carryover. The updraft process is more thermally efficient than the downdraft process, but the tar content of the gas is very high Di Blasi et al. Performance of the air gasification depends on the initial air temperature supplied to the gasifier. The initial temperature of the feed gas determines the heating value of the dry fuel gas produced. In other words, the higher the air temperature the higher the heating value of the dry fuel gas that can be obtained.
Chars are formed as part of the biomass pyrolysis, and their formation involves the biomass drying, loss of volatiles and structural rearrangements in the solid phase. The char must then be converted efficiently to gas by a combination of gasification and combustion. In high-temperature oxygen-blown, entrained flow and fixed bed gasifiers this must occur during the short residence times, where the reactions are fast and efficient.
In lower-temperature gasifiers airblown fluidized and fixed bed , complete conversion in one reactor is difficult to achieve given that the reactivity of the char diminishes rapidly. An additional reactor is then needed to burn the remaining carbonaceous material.
In this type of gasifier, a greater understanding of the way the char reactivity changes with operating conditions can potentially be useful in maximizing the efficiency and economics of the overall system Cousins et al. In fixed-bed counter-current updraft and concurrent downdraft air gasifiers, different process are stratified along the bed height, such as biomass preheating, drying and pyrolysis, char gasification and char and volatile combustion.
For updraft gasification, it is essentially the exothermic gasification of char which provides the heat for the exothermic gasification processes. For the downdraft configuration, homogeneous combustion of volatile pyrolysis products predominates over char combustion, which is still important for the stabilization of the reaction front. Given the large particle sizes required by these technologies, heating rates during the devolatization stage are much slower than those of fluid bed reactors Di Blasi et al. The recent technological progress on cyclonic gasifiers, a type of entrained flow reactor, may increase the application and the efficiency of biomass gasification processes in relation to conventional gasifiers, besides eliminating the necessity of complex gas cleaning systems Gabra et al.
More recently, Wang et al. Production of syngas from coal, natural gas, and other carbonaceous sources is well established. The greatest challenge in producing syngas from biomass in entrained flow pressurized gasifiers is biomass feeding. For relatively short residence times of fuel particles in the reactor, the biomass particles must be sufficiently small, relatively dry and they should be transported from atmospheric conditions to pressurized conditions in the entrained flow reactor.
The pulverized fuel feeding system for coal feeding to this type of reactor can be applied to biomass wood under the assumption that the properties of biomass particles are similar. As described by Svoboda et al. Pneumatic transport systems are not suitable for fibrous and needle-like biomass materials.
Screw feeding of wood powder suffers from fluctuations of flow rates Joppich and Salman, and some corrections e. Due to problems with high energy consumption and feeding of small wood particles, conceptions of feeding bigger wood particles about 1 mm have been suggested van den Drift et al.
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Pressurizing of biomass fuels to high pressures over approximately 2 MPa is mediated by lock hoppers, pressurized usually by an inert gas N 2 or CO 2. Another possibility for pressurizing to relatively lower pressures less than approximately 1. Another challenge is the need to avoid poisoning the noble metal catalysts used in the subsequent downstream conversion to fuels and chemicals Devi et al.
Potential problematic products are the alkali metals, halides, sulfur gases, and especially the tars. A high quantity of tar is produced during the pyrolysis step as the organic components of biomass decompose. Catalytic conversion of tar in raw syngas to CO and H 2 is practiced, but the quantities of tar that must be converted are large, and robust catalysts that are insensitive to alkali metals, halides, sulfur, and nitrogen need to be developed Ragauskas et al.
Besides deactivating catalysts, the tars that are entrained with the vapor can plug transfer lines and damage compressors Phillips, Also presented by these authors, chloride, the predominant halide in biomass, is converted to HCl or sub-micrometer aerosols of potassium and sodium during gasification, which pose a corrosion issue.
Most of the alkali metal chlorides are removed by filtering the cooled syngas. Sulfur gases can be removed by absorption. Remaining alkali metal chlorides and sulfur gases are removed by reaction with ZnO in a packed-bed filter. Beside problems with slagging behavior of ash in high temperature biomass gasification Coda et al. Especially because of the fibrous nature of the biomass, it does not fluidize and fluffs are formed that plug the piping Joppich and Salman, ; Zwart et al. Additionally, there are important requirements of disintegration of wood biomass and separation of the pressurized conditions in the gasifier from atmospheric conditions in the feeding line.
In the context of integrating biomass pyrolysis to bio-oil gasification and catalytic synthesis, the feeding of bio-oil and the possibilities for production of slurries of bio-oil and char such as previously presented in Tab. Char from fast pyrolysis of biomass can be used either for heating the process of pyrolysis or can be ground and mixed with bio-oil. As proven experimentally by Henrich and Weirich and later on described by Svoboda et al. Due to the content of carbonaceous char in the slurry, the average content of oxygen in such a fuel is lower than in the original bio-oil and the carbon and oxygen demand in entrained flow gasification is higher.
Other possibilities include mixing ground pulverized wood, torrefied wood or biochar with other bio-liquids, particularly waste liquids, to prepare pumpable slurries. Raw glycerol from production of biodiesel Demirbas, ; Fernando et al. Its relatively high viscosity at lower temperatures can be reduced by heating to higher temperatures or by addition of alcohols. In spite of many years of research and commercial endeavors, cost effective and reliable methods of biomass gasification on the commercial scale remain elusive.
Various gasification technologies have been developed and commercialized, but have been focused on gasification for power generation, where high calorific value gas is the target and impurities less of an issue than for Fischer-Tropsch synthesis IEA, Although advances in syngas purification technologies are necessary for the catalytic conversion of syngas to other fuels or chemicals, they add further complications and increase the overall cost.
Crop wastes, agroindustrial, forest and wood residues, byproducts from biofuel production such as the press cake from seeds, fruit bodies, empty fruit bunches as well as the leaves of the plant with low or no commercial value and crude glycerol, are amongst the many residues available in Brazil, offering great opportunities for interesting product outlets, representing a potential and highly available option to increase the bioenergy share in the country.
A moving from residues towards alternative energy sources and high value products can also represent an option to improve the sustainability of the bioenergy chain, reducing negative environmental impacts related to inappropriate disposal. These residues frequently are not used as energy sources due to their poor energy characteristics low density, low heating value, and high moisture content , which can incur high costs during collection, transportation, handling, and storage.
Additionally, the inappropriate removal of agricultural residues from fields may give rise to concerns of soil quality, decrease in soil organic carbon, soil erosion, crop yields and other environmental implications. Even though some research on these subjects can be found, it is important to increase the efforts on the development and implementation of the biorefinery concept, which requires multi-institutional and multidisciplinary networks in Brazil to carry out research, development and innovation activities in this field.
Higher value-added products than fuels offer the most challenging opportunities. The main issue to making the biorefinery concept a reality is the establishment of the logistics for biomass collection, pretreatment, transportation and storage, which should be modeled in order to integrate them into the current industrial infrastructure and serve as the basis for further developments. Thermochemical processes are becoming more accepted as emerging technology with commercial potential and can be used to support the biorefinery development and improve the Brazilian bioenergy sector. Pyrolysis emerges as a great opportunity.
The biochar is proposed as a soil improver and the bio-oil can be used as a source of renewable chemicals through various upgrading routes. This pyrolysis-gasification arrangement may provide a competitive way to convert diverse, highly distributed and low-value lignocellulosic biomass to syngas and, from this product, a wide range of value added products can be obtained through catalytic synthesis.
The research opportunities appear in the entire bioenergy chain: biomass production; logistics for collection, transportation and storage; pretreatment and processing. Additionally, further research and development of the fundamental science is required for successful exploitation of the full biomass potential, thus providing the tools for the design engineers to achieve the requisite technological development and performance improvements.
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Waste Management 32, No. Walter, A. The product gas also contains a considerable amount of unreacted steam along with CO, CO 2 , H 2 , and some higher molecular hydrocarbons. The product gas can then be converted into various fuels or chemical products. The impurities in the flue gas is significant during the steam hydrogasification.
Cui et al. The feedstock is turned into a slurry through a hydrothermal pre-treatment process HTP and is transported into the steam hydrogasification reactor SHR using a slurry pump. A portion of the necessary steam enters the reactor as water that is part of the slurry along with additional superheated steam and recycled hydrogen. The methane-rich gasifier product gas is then subjected to warm gas clean-up in order to remove contaminants such as sulfur and other species. This is an important aspect of the process: Even though the steam hydrogasification process needs hydrogen, it does not require an external source of hydrogen.
The hydrogen is separated and fed back into the gasifier, making the process self-sustained in terms of the hydrogen supply. The process is currently undergoing demonstration [ 31 ]. Gasification, which implies incomplete combustion also commonly referred to as partial oxidation of the carbonaceous feedstock, is one of the most attractive options to convert biomass into various high value products such as liquid and gaseous fuels, chemicals and electricity.
Gasification is the most popular among the thermochemical conversion processes with the exception of direct combustion. Gasification processes have several advantages and disadvantages over other conversion technologies. The main advantages are that the gasification feedstock can be any type of biomass including agricultural residues, forestry residues, by-products from chemical processes, and even organic municipal wastes.
Moreover, gasification typically converts the entire carbon content of the feedstock, making it more attractive than enzymatic ethanol production or anaerobic digestion where only portions of the biomass material are converted to fuel. The second advantage is that the product gas can be converted into a variety of fuels H 2 , Bio-SNG, synthetic diesel and gasoline, etc. The other benefit of the biomass gasification process is lowered CO 2 emissions, compact equipment setup with higher thermal efficiency [ 32 ].
Thus gasification is most suitable to produce chemicals that can be alternatives to petroleum based products. Gasification technology for biomass conversion is commercially applied in China: in , China built more than 70 biomass gasification projects for household cooking and each of them can supply energy for — families [ 32 ] whereas in India, a perspective way of electricity generation is gasification. Gasification processes are primarily designed to produce synthesis gas syngas, a mixture of hydrogen and carbon monoxide by converting the feedstock under reducing oxygen deficient conditions in the presence of a limited amount of gasifying agent such as air or oxygen [ 5 ].
Gasification consists of three major steps. The first step is devolatilization of the dried feedstock to produce the fuel gas for the second step, which is combustion. The combustion step produces the necessary heat and reducing environment required for the final step. The final step so-called reduction step, char gasification step or syngas production step , is the slowest reaction phase in gasification, and often governs the overall gasification reaction rate.
A detailed discussion of gasification, including minor steps and considerations is available elsewhere [ 5 ]. The dual fluidized bed reactor configuration is a well-known option for the gasification of biomass feedstock. This configuration uses two separate reactors, one for the combustion and the other for the reduction reaction. Other fuel sources can be used for the combustion step to overcome the low heating value of the biomass feedstock. These fuels include char by-product from the reduction reactor or other designated fuels such as methane.
Air is only used in the combustion reactor and does not enter the reduction reactor, thereby preventing nitrogen dilution of syngas, a major problem in air blown gasifiers [ 34 ]. The heat required for the reduction reaction is supplied through the bed material typically sand from the combustion reactor. The bed material is continuously circulated between the two reactors while the ash is removed from the bed material using cyclones and the gases from the two reactors are not allowed to mix.
The Milena project gasifier uses the two reactor configuration [ 35 ]. Cao et al. The factors that affects the biomass gasification process most are: the reaction temperature, residence time and oxygen to biomass ratio [ 37 ]. According to this study, the optimum residence time is 1. A major challenge of biomass gasification is to overcome the higher specific capital and operating costs.
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This is due to the much smaller plant sizes normally less than tons per day compared to coal gasification plants tens of thousands of tons per day. The plant size is determined by biomass availability and related logistic issues and transportation costs inherent to any distributed resource. Other challenges include the presence of undesirable species such as alkali compounds in biomass ash. Alkali materials such as sodium and potassium cause slagging and fouling problems [ 38 ].
Most biomass gasifiers operate below the ash softening temperature to avoid ash melting. The lower temperatures also lead to lower capital cost requirement, resulting in favorable process economics. However, lower temperatures often result in the formation of undesired tar, which leads to severe operational problems. A number of catalysts and process configurations have been developed to address this issue, but tar problems still persist [ 39 ].
Addition of a catalytic tar cracker to the outlet of the gasifier to decompose the tars into smaller molecules has been considered [ 40 ]. Washing out the tars while the product gas is cooling down has also been proposed, but this approach requires rigorous treatment of the washing water. These issues are not to be underestimated and careful attention is required in the design and operation of biomass gasifiers. The study performed by van de Kaa, Kamp and Rezaei [ 41 ], investigated the technology dominance of the three different dry thermochemical conversion of biomass.
They found that the gasification technology has the highest potential of becoming the commercial technology for biomass conversion in the Netherlands. Bio-SNG is a fuel made from syngas produced by biomass gasification with major constituent of natural gas for potential use in household or transportation. Dutch ECN [ 44 ] has already performed feasibility study on production of SNG from biomass gasification since with fluidized bed gasifier consisting of gas purification system, and subsequent methanation and SNG upgrading processes.
Besides, they are planning to exclude reliance on fossil fuel sources in national transport system by The methane concentration and calorific value of the SNG thus produced were Pyrolysis is the thermal decomposition of the feedstock in the absence of oxygen. The products of biomass pyrolysis are char, bio-oil also referred to as bio-crude and gases including methane, hydrogen, carbon monoxide, and carbon dioxide.
Pyrolysis can be further classified into slow and fast pyrolysis based on the residence time of the solid biomass in the reactor. The objective of the process is to maximize the liquid yield and minimize the production of char and gases. On the other hand, slow pyrolysis takes several hours to complete with bio-char being the main product. Pan et al. Fast pyrolysis has attracted considerable attention in recent years. Fast pyrolysis efficiency, in addition to the residence time and operating temperature, is strongly dependent on the particle size of the feedstock as rapid and efficient heat transfer through the particle is critical.
Pyrolysis processes can be built in relatively small scales and are well suited for lignocellulosic feedstocks. Efficient thermal energy input to the reactor is critical since the pyrolysis process is endothermic and heat transfer rates play a major role in the conversion process. High moisture content biomass must be dried prior to the conversion process. Besides oil and gas, bio-char is an important pyrolysis product. Oxygen and water are major by-products during fast pyrolysis and these components degrades the fuel quality to the low-grade fuel compared to conventional hydrocarbon fuel [ 51 ].
Duman et al. Flash pyrolysis is an emerging technology and there are several key issues that need to be addressed. Some of these problems are discussed below. Ideally, bio-oil should be interchangeable with petroleum crude oil so that the transportation and refining infrastructure can be used in existing form or with minor modifications.
Based on this reasoning, the properties of bio-oil are often compared to that of petroleum crude oil. However, bio-oil has serious physical and chemical property issues and it is difficult to use it in existing petroleum refineries [ 15 , 16 , 17 , 18 , 21 , 22 , 23 ]. Bio-oil is known to be extremely corrosive and this nature causes serious problems related to handling and transportation. Typical bio-oil TAN values range from 50 to as high as [ 24 ]. Besides water, components present in high concentrations are hydroxyl-acetaldehyde and acetic and formic acids.
These oxygenated compounds along with various other species such as phenolic compounds contribute toward the acidity of the bio-oil. Typical pH of the bio-oil is in the range of 2. The viscosity of bio-oils increases during storage and the physical properties undergo considerable changes [ 21 ]. The changes in the physical properties are attributed to the self-reaction of various compounds in the bio-oil including polymerization reactions [ 22 , 25 ]. These reactions, occurring during storage, increase the average molecular weight of the bio-oil and also lead to other storage related issues such as phase separation.
The resulting corrosive nature presents serious obstacles to any efforts aimed at the transportation and centralized refining or upgrading of the bio-oils. Also, the unstable nature of bio-oils often necessitates minimizing storage times and local upgrading, instead of transportation to a centralized facility. Such local upgrading is done by means of hydro-deoxygenation using hydrogen, often in the presence of catalysts. This normally adds capital and operating cost to the bio-oil production process.
Gasification and co-gasification of bio-crude to syngas have been tried, with reasonable success [ 5 ]. These processes are regarded as pre-commercial, or demonstration stage technologies. Direct combustion of biomass is the oldest energy production process in human history. It is still by far the most widely used biomass conversion process.
It is the most common biomass to power generation method commercially available [ 41 ]. Co-firing of biomass with coal is the effective way for lowering the greenhouse gas emissions. A wide range of technology options ranging from the simple fire stove to the advanced boiler system with fluidized furnace using pulverized fuel are available.
Precise control of mixing between the biomass fuel and oxygen source generally, air is a critical aspect of advanced combustion systems in order to achieve improved thermal efficiency and minimize of criteria pollutant emissions including particulate matter PM , nitrogen oxide NOx , carbon monoxide CO and hydrocarbons. Recently, development of combustion systems with pressurized fluidized beds have enabled direct electricity production without requiring steam generation, since process utilizes the fluidized bed as combustion chamber of the gas turbine [ 55 ].
Pulverized coal combustion technology is well established and co-firing is an attractive option that can reduce the carbon dioxide emissions from coal. However challenges associated with co-firing with biomass such as changes in ash properties, fouling of heat exchanger, etc. The resulting biomass fuel is a desirable feedstock for entrained-flow reactors or in pulverized coal fired boilers with co-firing of biomass [ 57 ]. Arce et al. According to the study, the ignition front propagation speed and the highest temperature that is reached at the fixed bed combustor affects the combustion process most.
Oxy-combustion is an emerging technology that uses pure oxygen in the combustor. The advantage is that after the cooling of flue gas, nearly pure carbon dioxide is produced without any nitrogen or nitrogen oxides. However, the use of pure oxygen or oxygen enriched air results in higher capital and operating costs.
This technology is still in the research and demonstration stage. As more cost effective processes for oxygen production such as membrane separation are developed, oxy-combustion will presumably become a more attractive option for both biomass and fossil feedstocks. Energy sources from the renewable carbon are critical to address future energy needs, in the all energy consuming sector. Biomass is the largest and most widespread carbon source for producing renewable energy, fuels and chemicals and can be a constant, reliable resource compare to other renewable sources such as solar or wind energy.
A wide range of biomass conversion processes are available and are under development. Among these, thermochemical processes offer several advantages, including product versatility, and high conversion rates and efficiencies, although challenges to commercialization still remain. Wet thermochemical processes including hydrothermal conversion, supercritical gasification and steam hydrogasification are still under development, but have many attractive aspects for use in decentralized, low cost applications, especially for high moisture content biomass.
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Dry thermochemical conversion processes including direct combustion, gasification and pyrolysis have several specific technology options that are mature. However, economic viability issues and technical challenges related to tar formation and alkaline ash presence still need to be addressed.
New emerging approaches such as the bio-refinery concept which synergistically combines different conversion technologies and generate multiple products are expected to play a key role in addressing the technical and economic barriers of the current thermochemical biomass conversion processes. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications.
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