Development of a generalized numerical framework for simulating biomass fast pyrolysis in fluidized-bed reactors

Canadian report voices concern over PVC plasticizer

A CFD model for biomass fast pyrolysis in fluidized-bed reactors

Multi-fluid modeling biomass fast pryolysis with particle shrinkage model for complex reaction kinetics

This numerical study investigates the effects of operating conditions on the product yields of a biomass fast pyrolysis reactor. A numerical approach that combines a multifluid model and pyrolysis reaction kinetics was applied to simulate the biomass fast pyrolysis process in a bubbling fluidized-bed reactor. The model was first validated using experimental data, and a parametric study was conducted. Operating parameters were varied to characterize their effects on the final product yields. For the reactor studied, it was found that the maximum tar yield could be obtained by maintaining both the wall temperature and the inlet temperature of nitorgen at approximately 800 K. The inlet velocity of nitrogen at about 0.6 m/s also produced favorable results. Simulations indicated that the optimal biomass particle diameter and the feeding rate were 900 μm and 1.92 kg/h, respectively, for tar production. Larger sand particle diameter and deeper initial sand bed also favored the tar yield.

Reaction of volatiles – A crucial step in pyrolysis of coals

With the increasing concern on fossil fuel storage and environmental problems, the utilization of renewable lignocellulosic biomass resources will play an increasing important role in the future. Biomass can be converted to a variety of fuels and chemicals by different technologies, one of them is fast pyrolysis which has received extensive interests in recent years (Bridgwater & Peacocke, 2000; Mohan et al., 2006). Fast pyrolysis of biomass is a thermal decomposition process that occurs in the absence of oxygen, with quickly biomass decomposition and rapid vapor condensation, to convert biomass mainly into a liquid product (know as bio-oil) with the yield as high as 70~80 wt%. The essential principles to obtain high bio-oil yield include moderate pyrolysis temperature (around 500 °C), very high heating rates (103 – 105 °C/s), short vapor residence time (< 2 s) and rapid quenching of pyrolysis vapors. A number of pyrolysis reactors have been developed for the bio-oil production, including bubbling fluidized bed, entrained bed, circulating fluidized bed, rotating cone, screw pyrolysis reactor, vacuum pyrolysis reactor, etc. In recent years, several research institutes (BTG, Dynamotive) have already established demonstration biomass fast pyrolysis plants, suggesting that the fast pyrolysis technique is near commercial. Crude bio-oils, also referred to as biomass pyrolysis liquids, pyrolysis oils, or bio-crude oils, are dark brown, free flowing liquids with an acrid or smoky odor. Chemically, bio-oils are complex mixtures of water and hundreds of organic compounds that belong to acids, aldehydes, ketones, alcohols, esters, anhydrosugars, furans, phenols, guaiacols, syringols, nitrogen compounds, as well as large molecular oligomers (holocellulose-derived anhydrooligosaccharides and lignin-derived oligomers). There are many valuable compounds, and thus, bio-oils have the potential for useful chemicals recovery. However, most of the chemicals are in low contents, making their recovery not only technically difficult but also economically unattractive at present. Therefore, the commercialization of bio-oils for valueadded chemicals requires the production of specific bio-oils with high contents of target products. Selective fast pyrolysis, differed from conventional fast pyrolysis which is usually aimed at the maximum bio-oil yield, is to drive the pyrolysis of biomass towards the products of interest. Since the biomass pyrolytic pathways and the subsequent products are influenced by various factors, and thus, selective fast pyrolysis can be performed in different ways, mostly by catalyst utilization, to (1) maximize the yield of target products and (2) obtain target products with high purity. This manuscript is divided into two sections. The first

Numerical study of hydrodynamics with surface heat transfer in a bubbling fluidized-bed reactor applied to fast pyrolysis of rice husk

The purpose of this project was to prepare and operate a fast pyrolysis process development unit (PDU) that can validate experimental data generated at the bench scale. In order to do this, a biomass preparation system, a modular fast pyrolysis fluidized bed reactor, modular gas clean-up systems, and modular bio-oil recovery systems were designed and constructed. Instrumentation for centralized data collection and process control were integrated. The bio-oil analysis laboratory was upgraded with the addition of analytical equipment needed to measure C, H, O, N, S, P, K, and Cl. To provide a consistent material for processing through the fluidized bed fast pyrolysis reactor, the existing biomass preparation capabilities of the ISU facility needed to be upgraded. A stationary grinder was installed to reduce biomass from bale form to 5-10 cm lengths. A 25 kg/hr rotary kiln drier was installed. It has the ability to lower moisture content to the desired level of less than 20% wt. An existing forage chopper was upgraded with new screens. It is used to reduce biomass to the desired particle size of 2-25 mm fiber length. To complete the material handling between these pieces of equipment, a bucket elevator and two belt conveyors must be installed. The bucket elevator has been installed. The conveyors are being procured using other funding sources. Fast pyrolysis bio-oil, char and non-condensable gases were produced from an 8 kg/hr fluidized bed reactor. The bio-oil was collected in a fractionating bio-oil collection system that produced multiple fractions of bio-oil. This bio-oil was fractionated through two separate, but equally important, mechanisms within the collection system. The aerosols and vapors were selectively collected by utilizing laminar flow conditions to prevent aerosol collection and electrostatic precipitators to collect the aerosols. The vapors were successfully collected through a selective condensation process. The combination of these two mechanisms has created the ability to effectively fractionate the bio-oil into distinct fractions with improved characteristics. The fractions of bio-oil each contained different properties. Bio-oil properties that were improved included the energy content, water content, acid content and distribution of certain carbohydrates (levoglucosan and acetic acid). The improved properties that are associated with the fractionated bio-oil could allow bio-oil to be used in new markets, preferably without further upgrading. The decreased water and acid contents in the first four (of five) fractions could allow for easier upgrading of the bio-oil into transportation fuels or other valuable products. Char and solid particulate content of bio-oil must be minimized. Solid particulate can erode surfaces, leading to decreased equipment and component life and increased maintenance. Char can contribute to the instability of bio-oil by acting as a catalyst and causing secondary reactions. To continuously remove char from the pyrolysis reactor product stream, two cyclonic gas separators (cyclones) were designed and constructed. The design of the two gas cyclones was based on gas flow rate, particulate density, desired efficiency and desired pressure drop.

A second look at fast pyrolysis of biomass—the RTI process

Chapter 7 - Fast Pyrolysis of Biomass: Recent Advances in Fast Pyrolysis Technology

This paper presents results on the primary pyrolysis products of organosolv lignin at temperatures between 360 and 700 °C. To study the primary products, a vacuum screen heater (heating rate of 8000 °C/s, deep vacuum of 0.7 mbar, and very fast cooling at the wall temperature of −100 °C) was used. The effect of the temperature on the primary and secondary lignin products was studied with a fluidized-bed pyrolysis reactor (Treactor between 330 and 580 °C) with pine wood. The results obtained with the screen heater show that the primary products of lignin were oligomers. Between 450 and 700 °C, the yield of these oligomers was very high, between 80 and 90%. After formation, the oligomers left the particle by evaporation or thermal ejection. Monophenols and other light compounds were formed by secondary reactions inside the particle or in the vapor phase. In the fluidized-bed reactor, significant quantities of lignin oligomers were formed along with monophenols, water, and other light compounds. The changes o...

Zeolite-based cracking catalysts for bio-oil upgrading: A critical review

The techno-economic performance analysis of biofuel production and electric power generation from biomass fast pyrolysis and bio-oil hydroprocessing is explored through process simulation. In this work, a process model of 72 MT/day pine wood fast pyrolysis and bio-oil hydroprocessing plant was developed with rate based chemical reactions using Aspen Plus® process simulator. It was observed from simulation results that 1kgs−1 pine wooddb generate 0.64kgs−1 bio-oil, 0.22kgs−1 gas and 0.14kgs−1 char. Simulation results also show that the energy required for drying and fast pyrolysis operations can be provided from the combustion of pyrolysis by-products, mainly, char and non-condensable gas with sufficient residual energy for miniature electric power generation. The intermediate bio-oil product from the fast pyrolysis process is upgraded into gasoline and diesel via a two-stage hydrotreating process, which was implemented by a pseudo-first order reaction of lumped bio-oil species followed by the hydrocracking process in this work. Simulation results indicate that about 0.24kgs−1 of gasoline and diesel range products and 96W of electric power can be produced from 1kgs−1 pine wooddb. The effect of initial biomass moisture content on the amount of electric power generated and the effect of biomass feed composition on product yields were also reported in this study. Aspen Process Economic Analyser® was used for equipment sizing and cost estimation for an nth plant and the product value was estimated from discounted cash flow analysis assuming the plant operates for 20years at a 10% annual discount rate. Economic analysis indicates that the plant will require £16.6 million of capital investment and product value is estimated at £6.25/GGE. Furthermore, the effect of key process and economic parameters on product value and the impact of electric power generation equipment on capital cost and energy efficiency were also discussed in this study.

Some agro-industrial wastes are currently untreated, resulting in an increase in greenhouse gas emissions. Therefore, in relation to the pollution generated by fossil fuels, the study of the obtained fuels from agro-industrial and forestry residues has been promoted. Rice is a basic product for several families in the world, and its residue is a component that has enormous potential in Colombia due to its consumption. The objective of the present study is to conduct an exergoeconomic evaluation of the production of fuel from rice husks as agro-industrial waste by means of the slow and fast pyrolysis process. Using simulators like Aspen Plus, the simulation of the two processes was carried up, implementing a rigorous kinetic model. The yield values were validated with data from the literature, obtaining values of 42.3% and 41.4% for slow and fast pyrolysis, respectively, for pyrolytic oil. The total investment cost of the process is 2146.45 kUSD. According to the thermodynamic parameters of the simulator, an exergy analysis was conducted for the two processes. Overall exergy percentages of 73.84% and 78.19% were obtained for the slow and fast pyrolysis, respectively. The economic and exergy analysis was coupled to implement a specific exergy costing. The exergoeconomics factors obtained values of 72.21% and 76.78%, for the slow and fast pyrolysis reactors, respectively. The contribution of the present research is related to the rigorous kinetic model, in addition to its implementation in slow pyrolysis, involved in the exergoeconomic study of biomass pyrolysis processes.

Numerical simulation and structural optimization of multi-compartment fluidized bed reactor for biomass fast pyrolysis