W.P. Walawender

Activated carbons prepared from phosphoric acid activation of grain sorghum

The production of activated carbons from grain sorghum with phosphoric acid activation has been studied by means of two processes, i.e., one-stage and two-stage. The former comprises simultaneous carbonization and activation after impregnation; the latter, the carbonization of the precursor at 300 degrees C for 15 min, followed by the activation of the resultant char after impregnation with phosphoric acid. The preparation conditions, e.g., activation duration, phosphoric acid concentration, and activation temperature, have been varied to determine the optimal processing conditions. The optimal activation conditions for the highest surface areas have been determined to be 600 and 500 degrees C with a phosphoric acid concentration of 35% for the one-stage and two-stage processes, respectively. The two-stage process has been found to greatly enhance the porosity development, especially the microporosity.

Fluidized-bed steam gasification of rice hull

Steam gasification of grain by-products can be a significant biomass conversion technology because of the need to utilize agricultural waste for non-food applications including energy resources. The most obvious beneficiary will be the developing countries whose economies are often tied to agricultural produce and are lacking in conventional fuels. One agricultural by-product that shows promise is the rice hull; it is found in abundance in the rice mills of producer countries and is considered as a waste material. Although gasification of rice hull has been proposed as a potential waste disposal and energy recovery method, little has been done to fully realize this proposition. In the present work, data were obtained for steam gasification of rice hull in a bench-scale fluidized-bed gasifier, a technology which has proven to be feasible for other grain by-products. The produced gas, which is rich in hydrogen, has been found to have a heating value ranging between 12.1 and 11.1 MJ m−3 at the respective reactor temperatures of 700 and 800°C; energy recovery varies between 35 and 59%.

Gasification of waste tires in a fluid bed reactor

Abstract Shredded rubber tires were gasified with steam in a 0.23m I.D. fluidized bed reactor over a temperature range of 900–1060K. The results indicated that the gas produced is rich in olefins and the heating value and volumetric yield of the produced gas vary approximately linearly with the gasification temperature. The gas yield decreases and its heating value increases as the gasification temperature is decreased. In the temperature range investigated, the heating value of the produced gas ranged between 39.6 MJ/Nm3 (1060 Btu/SCF) and 22.2 MJ/Nm3 (595 Btu/SCF), and the gas yield ranged from 0.21 Nm3/kg DAF (3.5 SCF/lb DAF) to 0.76 Nm3/kg DAF (12.1 SCF/lb DAF). The results also indicated that the fluid bed gives a higher gas yield than other types of contactors.

EQUILIBRIUM MODELING OF A DOWNDRAFT GASIFIER I—OVERALL GASIFIER

A model, based on the thermodynamic equilibrium of the C-H-O-Inert system and mass and energy balances, has been applied to the air-blown downdraft gasification of wood. The model predicts the temperature, gas composition and char yield at the exit of the gasifier for a specified set of heat loss and input condition. A parametric study has been conducted to simulate the influences of the air/feed mass ratio and moisture/feed mass ratio on the gasifiers performance. The model predictions are compared with a comprehensive set of experimental data obtained from the gasification of wood in a commercial-scale downdraft gasifier; the air/feed ratios range from 1.1 to 2.1 and the moisture/feed ratios range from 0.05 to 0.3. The predicted trends for variations in the operating parameters are in general agreement with the experimental data. The results of comparisons also indicate that the performance of the wood gasifier can be approximated reasonably well by the equilibrium model.

Kinetics of rice hull char burnout in a bench-scale fluidized-bed reactor

Abstract Rice hull, also known as husk, is a by-product of the rice milling process; it is a significant alternative energy resource for the milling industries of rice producing countries. Apart from its high energy content, the residual ash from complete combustion of rice hull at moderate temperatures in a combustor, e.g., a fluidized-bed reactor, is also a potential cement extender. The regeneration of steam for parboil rice and for other process activities makes combustion an attractive means of disposing rice hull in the rice milling industries, which otherwise is a menace to the rice miller. In the present work, the combustion kinetics of Guyana rice hull char was studied in a bench-scale fluidized-bed reactor. The salient features of the combustion of the char were observed, and the temporal history of burnout was traced at temperatures of 973 and 1173 K. The oxygen concentrations of the inlet fluidizing gas were maintained at 2.3 and 4.6% by regulating the mixing of nitrogen and air. The rates of ...

Control of a downdraft gasifier for biomass conversion with a fuzzy controller

Abstract A fuzzy controller is proposed for solving difficulties involved in controlling a complex process under dynamic conditions. A knowledge base is one of the most important components of such a controller. It contains control know-how of a skilled human operator and consists of two elements: a rule base for fuzzy IF—THEN rules and a database comprising the operational definitions of the fuzzy sets for these rules. Construction of the knowledge base is not a trivial matter. To facilitate it, a new identification method has been developed based on a learning mechanism. By resorting to this method, a fuzzy knowledge acquisition system is linked to the rule base for self-generation of fuzzy IF—THEN control rules; simultaneously, a self-learning predictive system is linked to the database for updating the fuzzy sets for defining the control rules. The fuzzy knowledge acquisition and self-learning predictive systems are implemented by an expert system shell and a predictive module, respectively. A scheme is described for controlling a downdraft gasifier for biomass conversion with the proposed fuzzy logic controller based on the available empirical information on the performance of the gasifier.

Equilibrium modeling of a downdraft gasifier. II: Flaming-pyrolysis zone

An equilibrium model has been applied to the flaming-pyrolysis (FP) zone, the most important and active zone, in a downdraft biomass gasifier. The model predicts the temperature, gas composition and char yield at the exit of the FP zone for a set of specified fuel material, heat loss and input condition. Based on the model, a parametric study has been conducted to simulate the influences of the air/feed mass ratio (A/F), moisture/feed mass ratio (W/F), heat loss rate, and the volatility of the biomass fuel over feasible ranges of these parameters. It has been found: a) the A/F has a tremendous influence on the performance of the FP zone, and the minimum A/F required to completely pyrolyze the biomass fuel in the FP zone is approximately 1.2; b) high W/F and high heat loss rate result in a low temperature in the FP zone, which in turn may prevent the biomass fuel from being completely pyrolyzed in the FP zone, and c) biomass fuel with very low volatile content may result in an excessively high temperature ...

Material Balance Analysis of Prototype Commercial Downdraft Gasifiers

Complete material balance data have been published only recently for downdraft gasifiers. Generally, it is inconvenient to measure all stream rates; thus unknown stream rates are estimated from material balance. Typically the system is overspecified; this leads to various solution options; thereby leading to conflicting estimations. This paper presents an analysis of data from two prototype gasifiers which examines four solution options based on sensitivity considerations.