Pyrolysis Model of Single Biomass Pellet in Downdraft Gasifier

By coupling the heat transfer equation with semi-global chemical reaction kinetic equations, a onedimensional, unsteady mathematical model is developed to describe the pyrolysis of single biomass pellet in the pyrolysis zone of downdraft gasifier. The simulation results in inert atmosphere and pyrolysis zone agree well with the published experimental results. The pyrolysis of biomass pellets in pyrolysis zone is investigated, and the results show that the estimated convective heat transfer coefficient and emissivity coefficient are suitable. The mean pyrolysis time is 15.22%, shorter than that in inert atmosphere, and the pellet pyrolysis process in pyrolysis zone belongs to fast pyrolysis. Among the pyrolysis products, tar yield is the most, gas the second, and char the least. During pyrolysis, the temperature change near the center is contrary to that near the surface. Pyrolysis gradually moves inwards layer by layer. With the increase of pyrolysis temperature and pellet diameter, the total pyrolysis time, tar yield, char yield and gas yield change in different ways. The height of pyrolysis zone is calculated to be 1.51—3.51 times of the characteristic pellet diameter.

Development of Advanced Biomass Cookstove and Performance Comparisons Using the Modified Star Rating Methodology

A disruptive approach to a fundamental process has been applied in a biomass combustion device with two variable speed fans to supply air for gasification and another for combustion processes,separately.Besides,the preheating of secondary air,required for combustion process was also ensured through annulus chamber before being fed into the combustion chamber.The turbulent flow and homogenous mixing were also ensured by controlling the flow rate resulting in the reduced emissions of carbon monoxide(CO)and fine particulate matter(PM 2.5,particulate matter having aerodynamic diameter<2.5 micron).The design approach applied here has also ensured the homogeneous mixing of preheated air with the volatiles,resulted in cleaner combustion.This arrangement has led to the emissions of PM2.5 and CO much better than those of the earlier cookstove models,and very close to that of a liquefied petroleum gas(LPG)stove.Further,the comparative analysis based on the modified star rating of total 15(14 are biomass and another LPG)cookstove models tested using the same standard methodology has been done and presented in this study.Based on the star rating,the performance of the LPG stove was found to be best and assigned as a 5-star product followed by the IITD model(4-star),while the other 13 models got different ratings starting from 1-star to 3-star,respectively.Also,the thermal performance of the IITD cookstove model is found to be the highest,while the emission characteristics are found to be the least among all biomass cookstove models,presented here.

Effect of binder addition on combustion characteristics of cotton straw pellets and kinetic analysis

In this study,the combustion characteristics and kinetics of cotton straw(CS)particles mixed with polyethylene(PE)film and coal gangue(CG)were investigated.The co-combustion characteristics of CS mixed with PE and CG at different heating rates were revealed by the thermogravimetric method and differential thermogravimetric method.The ignition temperature,burnout temperature,and maximum weight loss rate were measured,and the comprehensive combustion and flammability indexes were calculated.The results showed that the composite combustion characteristic index and flammability index increased with the increase in heating rate.The addition of PE and CG additives could effectively extend the combustion time.The Coats-Redfern(C-R)reaction model and N-order reaction model were used to evaluate the kinetic parameters of the blends.The results showed that 12.5%PE+12.5%CG particles had the lowest activation energy(Ea=103.73 kJ·mol^(-1))at the volatile combustion stage.The dynamics conform to the third-order dynamics model.In addition,the applicability of C-R model,Flynn-Wall-Ozawa(FWO)model,and Starink model in the calculation of activation energy was explored,and it was found that the FWO model is not suitable for the calculation of activation energy of biomass pellet combustion kinetics.This study provides a new method for the development and utilization of mixed fuel particles of cotton stalk and solid waste and expands the application prospect of biomass.

Optimized design and experiment on ring mold pelletizer for producing biomass fuel pellets

The forming process of biomass fuel pellets using a ring mold pelletizer was analyzed,optimized,tested and evaluated in this study.The effects of stress amplitude and the stress ratio on the fatigue failure of the ring mold under 4-,3-,and 2-roller designs were investigated.Depending on the calculation of stress amplitude acting on the ring mold,the 4-roller design was chosen for having the smallest value of stress amplitude in this condition.After determining the main design parameters,a three-dimensional model of the ring mold pelletizer was established based on the Pro/Engineer software,and the model was transferred into ADAMS software through Mechanism/Pro which is a dedicated interface software.The ADAMS software was used to run simulations.In order to obtain the highest efficiency and the lowest power consumption,the optimal result was the 4-roller design.Finally,a prototype of the ring mold pelletizer with four rollers was designed and manufactured for biomass fuel pellet production.Corn stover biomass was used as material for experimental manufacturing of fuel pellets.Test and evaluation showed that the optimized pellet durability was 99.79%with ground corn stover particles passing a screen size of 1.97 mm,moisture content of 21.2%w.b.and a material moisture conditioning time of 3.82 h.Pellets formed in the prototype ring mold pelletizer using corn stover had acceptable durability according to European standards.

Potential availability of non-woody biomass feedstock for pellet production within the Republic of Ireland

The threat of increasing fuel prices and climate change necessitates the need for clean,renewable and independent energy sources.A GIS(Geographical Information Systems)model was developed using ArcGIS 9.2 to analyze the availability of non-woody biomass(wheat,oat,barley and rape straw,willow and miscanthus)for pellet production in Ireland.Utilization within the heating and electricity sector would displace currently used fossil fuels with cleaner,carbon neutral non-woody residues.The aim of the analysis was to determine the total hectares of biomass within Ireland and compute the potential non-woody biomass yield.The greatest potential source of biomass for pelleting is cereal straw.Within the Republic of Ireland the South-East,South-West and Mid-East of Ireland have the greatest biomass yield for pellet production and likely to be most economically viable.Non-woody biomass has a realistic potential to displace fossil fuels within the heating and electricity sector resulting in CO2 mitigation.

Predicting the true density of commercial biomass pellets using near-infrared hyperspectral imaging

The use of biomass is increasing because it is a form of renewable energy that provides high heating value.Rapid measurements could be used to check the quality of biomass pellets during production.This research aims to apply a near-infrared(NIR)hyperspectral imaging system for the evaluation of the true density of individual biomass pellets during the production process.Real-time measurement of the true density could be beneficial for the operation settings,such as the ratio of the binding agent to the raw material,the temperature of operation,the production rate,and the mixing ratio.The true density could also be used for rough measurement of the bulk density,which is a necessary parameter in commercial production.Therefore,knowledge of the true density is required during production in order to maintain the pellet quality as well as operation conditions.A prediction model was developed using partial least squares(PLS)regression across different wavelengths selected using different spectral pre-treatment methods and variable selection methods.After model development,the performance of the models was compared.The best model for predicting the true density of individual pellets was developed with first-derivative spectra(D1)and variables selected by the genetic algorithm(GA)method,and the number of variables was reduced from 256 to 53 wavelengths.The model gave R_(cal)^(2),R_(val)^(2),SEC,SEP,and RPD values of 0.88,0.89,0.08 g/cm^(3),0.07 g/cm^(3),and 3.04,respectively.The optimal prediction model was applied to construct distribution maps of the true density of individual biomass pellets,with the level of the predicted values displayed in colour bars.This imaging technique could be used to check visually the true density of biomass pellets during the production process for warnings to quality control equipment.

Producing durable pellets from barley straw subjected to radio frequency-alkaline and steam explosion pretreatments

Pelletization,a form of densification,increases bulk density and improves the convenience and accessibility of biomass feedstock due to the uniform shape and size.Pretreatment of biomass enhances the breakdown and accessibility of the cross-linking lignin,which acts as a binding agent.In this study,pelletization of radio frequency-alkaline and steam explosion pretreated barley straw was performed.Three levels of temperature(70oC,80oC,and 90oC),five levels of the mass ratio of biomass to NaOH solution(1:4,1:5,1:6,1:7,and 1:8),one hour equilibration time,biomass screen size of 1.6 mm,1%NaOH concentration,and 20 min residence time in the radio frequency chamber were used for the radio frequency-alkaline pretreatment.Three levels of steam temperature(140oC,160oC,and 180oC),three levels of moisture content of 8%,30%,and 50%(mass fraction of total mass),and 5 min and 10 min exposure to steam were tested for the steam explosion pretreatment.The effects of both pretreatment methods were evaluated by pelletizing the pretreated and non-pretreated barley straw samples in a single pelleting unit.The pellet density,tensile strength,durability,dimensional stability,and color of the pellets were determined.Radio frequency-alkaline pretreatment with the use of 1%NaOH solution and a ratio of biomass:NaOH solution of 1:8 has significant effect(P<0.05)on the breakdown of the lignified matrix,resulting in pellets with superior physical characteristics.The steam exploded samples pretreated at higher temperatures(180ºC)and retention time of 10 min resulted into pellets with good physical qualities.