Fuel and Combustion

Fuel and Combustion

On a Numerical Model for Gasification of Biomass Materials: An Alternative Method to Combustion

Authors
Mahdi Vaezi
Mohammad Passandideh Fard
Mohammad Moghiman
Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad
Abstract
In this paper, a thermochemical equilibrium model is used to predict the performance of a downdraft biomass gasifier. Numerical results are shown to be in good agreement with those of the experiments. Different biomass materials are tested using the model, and forest residual is shown to be the most energetic one. For this material, the gasification temperature, syngas composition and calorific value are calculated. The effects of moisture content, air/fuel ratio, air inlet temperature and steam/fuel ratio are also investigated. The air inlet temperature is found to be the only way to increase syngas calorific value and cold gas efficiency. The steam/fuel ratio, on the other hand, plays a key role in controlling the gasification temperature and H2/CO ratio.

Highlights

A thermodynamic equilibrium model was developed for a biomass gasifier in order to calculate the composition of the produced syngas, and investigate the gasification characteristics. The predicted results agreed well with those of the experiments available in the literature. The model was then employed to evaluate the capability of different biomass materials to produce energy. Among twenty different biomass materials of five major families, forest residuals had the highest calorific value. The effects of moisture content, air inlet temperature, air/fuel ratio and steam/fuel ratio on gasification characteristics were investigated. Although the increase in air inlet temperature was the only way to increase the produced syngas calorific value and cold gas efficiency, it also increased the gasification temperature, which was not favorable. Steam injection was found to reduce the gasification temperature and increase the H2/CO ratio. The developed model in this study can be used to simulate gasification of other types of biomass materials and predict the effect of important variables in optimization of a biomass downdraft gasifier.

Keywords
Gasification
Thermochemical Equilibrium
Numerical Modeling
Renewable Energy
Biomass

مقاله حاضر به ارائه یک مدل عددی بر پایه تعادل ترموشیمیایی پرداخته و با بهره­گیری از آن، عملکرد یک رآکتور  گازی­سازی پایین­سو را پیش­بینی کرده است. داده­های عددی حاصل، در مقایسه با نتایج تجربی، از دقت قابل قبولی برخوردارند. در جریان شبیه­سازی فرایند گازی­سازی به کمک مدل عددی تولید شده، زیست توده­های متنوعی مورد ارزیابی قرار گرفتند که در میان آن­ها، پسماندهای جنگلی به عنوان انرژی­زاترین زیست توده برگزیده شدند و مطالعات مربوط به سنجش عملکرد رآکتور، بر روی آن­ها انجام گرفت. در جریان مطالعات، تاثیر شرایط عملیاتی شامل محتوای رطوبت، نسبت بخار به سوخت، نسبت هوا به سوخت و دمای هوای ورودی بر مشخصه­های گازی­سازی مورد سنجش قرار گرفت. مشخصه­های گازی­سازی مورد اشاره عبارت بودند از: دمای گازی­سازی، ترکیب مولفه­های گاز سنتزی و ارزش گرمایی گاز سنتزی. در این میان آشکار شد که تغییر دمای هوای ورودی، یگانه روش افزایش همزمان ارزش گرمایی گاز سنتزی و راندمان گازی­سازی است. از سوی دیگر مشخص شد که نسبت بخار به سوخت، نقشی کلیدی در کنترل دمای گازی­سازی و تنظیم نسبت هیدروژن به مونواکسیدکربن بر عهده دارد. مدل عددی تولید شده را می­توان به عنوان ابزاری برای طراحی شرایط اولیه و عملیاتی رآکتورهای گازی­سازی، هم­چنین به منظور بهینه­سازی عملکرد آن­ها به کار گرفت.

 

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