(144a) Thermochemical Characterization of Bran for Conversion in Energy

Introduction

The biomass is considered the source of renewable energy with a high potential to assist the energy demand of the modern society. The biomass is the fourth energy source in the world, it gives around 14% of primary energy (Demirbas, 2006), it presents a closed cycle of CO2,  null sulfur emissions, good opportunities for the use of ashy and potential to save the resources of fossil energy.

The industries should modify their processes so that their residuals can be recycled and to use them as matter prevails for other processes to reduce the contamination, the industry brewer generates big quantities of by-products and residuals being the trash of malt (bran) the most abundant since corresponds around 85% of the total of generated by-products, this is around 31% of the original weight of malt and it represents 20 kg approximately for each 100 liters of produced beer (Mussatto et al., 2006).

The thermochemical characterization of  bran to evaluate its heating potential as alternating source of energy to cover important part of the energy is the objetive.

The gasification of biomass has attracted the biggest interest among the technologies of thermochemical conversion; it converts the biomass through a partial oxidation toward a gas mixture (synthesis gas) (Wang et al.  2008), this gas possesses a heating value that can replace the fossil fuels with a high efficiency to generate heat (Yassin et at the 2008).

Experimental

Chemical, Thermal and Lignocellulosic Characterization.

The chemical characterization was carried out by means of a bromathological analysis, with application of the procedures ASTM to determine humidity content (D 2867-99), ash (E1755-01), volatile matter (D2866-83) and fixed coal (by difference), likewise it was carried out a thermal analysis to know the variation of different properties of the matter as function of the temperature carrying out a thermogravimetry study using a thermobalance Pyris TG/DTA  Perkin Elmer, the method marks to weigh the sample in alumina panels, heating from 25 to 800ºC, using three heating conditions at 10, 15 and 20 ºC/min. The kinetics of decomposition was obtained using a thermobalance Mettler Toledo 851, with the same conditions applying the ASTM E698.

The elementary analysis was carried out under the  ASTM D5373/D1989 specific conditions. This is a destructive technique, a quantity is weighed between 2 and 4 mg is subjected to a thermal oxidation among 1.600-1.800 ºC, in atmosphere of oxygen, with the total and quantitative conversion of the components was gotten in CO2 (Carbon), H2O (Hydrogen) and N2 (Nitrogen).

The lignocellulosic analysis was made whit procedures of TAPPI to determine the cellulose content (T 203 os-74), lignin (T 222 om-88) and hemicellulose (for difference) carrying out a previous extraction of the waxes  (T-12 -75), it was determined in sample virgin and   300 ºC, 400 ºC and 500 ºC. These temperatures were extracted from DSC results.

Results

The bromathological analysis was carried out triplicated for all the samples, it is presented in Fig. 1, the average of the obtained results.

Fig. 1.  Bromathological analysis

A content of volatile material was observed bigger than 80% and a smaller percentage than 10% of ashy, these characteristics present the appropriate bran to use it in a gasifier.

Differential scanning calorimery (DSC) 

The obtained results by means of a DSC, they represent the differential heat contributed to a sample (regarding the one contributed to the reference), expressed as flow of heat (dQ/dt) in function generally of the temperature. The results obtained of the analysis they are in Table 1.

Table 1. DSC results

The temperatures were determined for the analysis of the lignocellulosic content of the bran, it was demonstrated that at temperatures lower than 200 ºC comes off the humidity of the sample, of 220 at 315 ºC the decomposition of the hemicellulose is observed, of 315 at 400 ºC the decomposition of the cellulose is presented and to temperatures higher than 400 ºC the decomposition of the lignin is observed. Data compared with the contained lignocelluosic of the palm oil (Yang et al., 2005) 

Elementary Analysis 

It was determinated the content of Carbon, Hydrogen, Nitrogen, Sulfur and Oxygen; since it influences in the proportion agent-oxidizer / residual-optima, besides defining the production of pollutants of the type of nitrogen oxides and / or sulfur, or  chloride of hydrogen. It is shown in the Fig. 2

Fig. 2 . Elementary analysis

Combustion energy 

It's gross energy of combustion that possesses the bran which is transferred in form of heat, it is denominated to be able of heating, it is determined in a theoretical way using the obtained values of the carried out elementary analysis using the following formula:

 It presents 2.1 % of the value measured to the calculated value (Reed and Das, 1988).

 Thermogravimetric Analysis

This measure is the variation of the mass of a sample when it undergoes a change of temperature in a controlled atmosphere. The record of these changes gives information on the sample breaks down or reaction with other components generating volatile components, that originate physical and chemical changes. For most of these chemical reactions it has been found that the dependent factor of the temperature is adjusted to the equation of Arrhenius (2)

where K0 is the factor of frequency and Ea is the energy of activation of the reaction. This expression is adjusted to the experimental results in a wide range of temperatures and it is considered like a first appropriate approach for the study of the effect of the temperature on the kinetic equation.  Of the previous expression it can be seen that to constant temperature as much as bigger is the Ea, smaller it will be the constant of speed and therefore slower it will be the reaction speed. The obtained value of the kinetics of the decomposition of first order, it is shown in Table 2, which corresponds to the obtained determination of the application of the Star software version 6.2 of the thermobalance used.