Moisture and Solid Mass as Indicators of the Ideal Transformation Technology

Abstract

The waste generated from human activities consists of molecules composed of hydrogen, carbon, minerals, metals, and water, representing the moisture content of the biomass. This moisture content plays a crucial role in determining the most suitable technology for extracting its potential. This chapter proposes a technological route based on the humidity content, offering optimal alternatives for biomass transformation. Additionally, a quantitative method is presented to aid in the selection of the ideal transformation technology.

1. Introduction

Efforts must be made to recover and repurpose biodegradable organic waste, minimizing its quantity and promoting a circular economy where nothing is discarded. With the growing reality of climate change, it becomes imperative to establish a self-sustaining and environmentally friendly economy to protect soils and ecosystems from the impact of industrial and urban waste.

Biomass naturally degrades and changes its chemical composition, providing an opportunity to direct this process toward obtaining a valuable end product. By defining the guidelines and characteristics of this chemical transformation, a new resource or raw material can be obtained with practical applications.

2. Characterization and outline of the technological route

Grande [1], fully characterizing the chemical composition of waste and having specific data on production volume, physical state, stability, and storage conditions are essential when considering waste as a potential raw material. When deciding on waste transformation, options include biodigestion, fermentation, mechanical methods, and thermal methods to extract desired molecules or by-products. It is crucial to ensure that all substances involved in the process do not pose a threat to human health and the environment [2].

Considering the workplace’s needs and circumstances, various technologies can be employed to achieve the desired final product. A selection process becomes necessary to evaluate and qualify the technologies and conditions for biomass transformation (Figure 1).

Figure 1.

Technological routes for the transformation of biomass into bioenergy according to their moisture content. Source: [3].

Given the variations in waste production percentages among countries, a strategy based on biomass humidity becomes even more crucial. This technological route can be extended by considering specific technologies suitable for treating particular biomass based on its moisture content.

2.1 Humidity greater than 75%

2.1.1 Wet and dry biodigestion

When dealing with high humidity content, wet and dry biodigestion are the recommended options. Wet biodigestion requires less thermal and mechanical intervention and is suitable for urban waste, while dry biodigestion is more convenient for residual biomass from agro-industries. Mathematical expressions can provide a better understanding of the transformation process and the production of by-products, according to [4].

$$\mathit{Vol}{\mathit{CH}}_4{\mathit{Nm}}^3=\frac{\left(\mathit{\text{Methane molar mass}}\frac{g}{\mathit{mol}}\right)\left(\mathit{dry}\mathit{\text{weight mass}}\mathit{kg}\right)}{\left(\mathit{\text{molar mass}}\mathit{dry}\mathit{\text{weight}}\frac{g}{\mathit{mol}}\right)\left(\mathit{\text{Methane density}}\frac{\mathit{kg}}{m^3}\right)}$$E1

Where:

${\mathit{Nm}}^3$ = Normal cubic meter.

Methane molar mass = 234 $\frac{g}{\mathit{mol}.}$

Molar mass dry weight = 521 $\frac{g}{\mathit{mol}}$

Methane density = 0.717 $\frac{\mathit{kg}}{m^3}$

Additionally, carbon dioxide is produced during this process.

$$\mathit{Vol}{\mathit{CO}}_2{\mathit{Nm}}^3=\frac{\left({\mathit{CO}}_2\mathit{\text{molar mass}}\frac{g}{\mathit{mol}}\right)\left(\mathit{dry}\mathit{\text{weight mass}}\mathit{kg}\right)}{\left(\mathit{\text{molar mass}}\mathit{dry}\mathit{\text{weight}}\frac{g}{\mathit{mol}}\right)\left({\mathit{CO}}_2\mathit{\text{density}}\frac{\mathit{kg}}{m^3}\right)}$$E2

Where:

${\mathit{Nm}}^3$ = Normal cubic meter

Carbon dioxide molar mass = 589 $\frac{g}{\mathit{mol}}$

Molar mass dry weight = 521 $\frac{g}{\mathit{mol}}$

Carbon dioxide density = 1.978 $\frac{\mathit{kg}}{m^3}$

A continuous model for receiving high-moisture residual biomass and producing biogas at a corresponding rate for electricity generation is proposed (Figure 2).

Figure 2.

Scheme for the use of residual biomass to produce three by-products (3).

While the general scheme is illustrated, variations may be necessary depending on the specific case, such as rural or urban environments (Figure 3).

Figure 3.

Model of the biomass use system to produce energy, heat, and agricultural amendment.

2.2 Humidity less than 50%

2.2.1 Combustion

For lower humidity levels, other technologies are considered for biomass transformation. These technologies are more suitable for biomass containing carbohydrates, starches, sugars, fats, and lignocellulosic fibers, indicating forest residues (Figure 4).

Figure 4.

Biomass combustion process for electricity generation.

If the biomass moisture content exceeds 50%, a drying process is necessary prior to incineration. The energy required to reduce the humidity can be estimated by subtracting the current content from 50% and multiplying it by the water vaporization value (2250 kJ/kg).

Pelletizing the biomass for improved transport and presentation may be an option, although it incurs additional costs. The energy delivered can be estimated using the lower calorific power (LCP) formula.

$$\mathit{PCI}=\mathit{PCS}\ast \frac{1-w}{100}-2.447\ast \frac{w}{100}-\left(\frac{h}{100}\ast 2\right)\ast 18.02\ast 2.447\ast \left(\frac{1-w}{100}\right)⟦\mathit{MJ}⟧$$E3

Where:

$\mathit{LCP}=$ Lower calorific power $⟦\mathrm{65,460}\mathit{MJ}⟧$

$\mathit{HCP}=$ Higher calorific power$⟦\mathit{MJ}⟧$

$w=$Moisture (%)

$h=$Hydrogen content (% weight)

Subtracting the costs of humidity reduction and pellet production from the obtained value provides the useful energy for electricity generation through a turbine (Figure 4). The biomass combustion scheme is presented in Figure 5.

Figure 5.

Scheme of operation of the combustion as a technology of energetic transformation of the residual biomass.

The choice of technology depends on the specific circumstances, such as geographical location and temperature conditions. Cold areas have different combustion efficiencies compared to tropical or desert areas due to heat dissipation and bacterial activity during biodigestion.

2.2.2 Gasification

According to (Probiomasa, FAO [5]), the following are the stages of gasification within an industrial plant.

Conditioning of the biomass: The gasifiers can run powered by different types of biomasses.

1. Fine biomass: peel of rice, peanuts, pomace, etc.

2. Biomass derived from wood: chips, pellets, briquettes.

Gasification: It takes place in reactors or gasifiers, where they carry out a complex process with thermochemicals.

Adequacy of synthesis gas (syngas): For its transformation into electric power, gasification gas must be cleaned to remove tars, and cool down. If one has to use internal combustion motors (ICM), they must be treated in ultracool systems.

Energy generation, thermal or electric: On generators or turbo-steam cogenerators, internal combustion engines or cycle engines must be combined.

Water treatment process: Current gasification systems operate in a closedcycle pattern, pointing to the maximum utilization of the resources.

The gasification process yields 2.5 to 3 normal $m^3.$ of gas per kilogram of dry biomass, with a calorific value ranging from 1000 to 1300 normal kcal/$m^3$.

Gasification offers an economical option for many, producing synthesis gas (syngas) with specific chemical compositions, which are presented in the following Table 1.

$N_2$	44–55%
$\mathit{CO}$	15–20%
$H_2$	15–20%
${\mathit{CO}}_2$	8–12%
${\mathit{CH}}_4$	1–4%

Table 1.

Chemical composition of synthesis gas (syngas).

2.2.3 Other energy and non-energy products

Fermentation, a part of bioethanol production, yields by-products and useful raw materials depending on the biomass type and composition. Major bioethanol producers like Brazil and the United States primarily, close to 60% [1], utilize sugar cane and cereals (such as corn and wheat), respectively.

Fermentation of biomass results in the production of by-products, such as processing of cassava, and this must go through a hydrolysate with enzyme α-amylase, which is a pretreatment before fermentation. After this, dextrins and maltodextrins are produced, useful for the production of antibiotics such as penicillin, cephalosporin, and streptomycin, and other organic acids (citric, lactic, gluconic, and itaconic), some amino acids, xanthan gum, glucans, dietary fibers, flavorings, dietary supplements, aroma compounds, acetone, enzymes [1], etc.

2.3 Selection of the appropriate technology as the case may be

With a wide range of technologies available, the chemical composition of biomass becomes a crucial factor in the transformation process. Theoretical estimates and mathematical expressions that represent biomass characteristics and energy potential help determine the ideal technology. Selection methods, such as the analytical hierarchical process developed by Professor Thomas Satty, aid in quantitative decision-making by considering independent criteria or variables that may conflict. Comparative matrices and pairwise comparison tables assist in evaluating and prioritizing alternative technologies.

This selection method is very useful in decision-making, having both quantitative and qualitative aspects at hand, which makes it a multi-attribute method, being widely used in the field of business, economics, or operations research [6], like in this particular case of choosing the most appropriate technology to transform biomass into electricity.

Select an alternative among several proposals based on a series of criteria or variables, normally hierarchical, see Figure 6 [6].

Figure 6.

Hierarchy of importance of selection criteria with respect to the alternatives.

It is important that criteria are independent of each other, which makes it easier for the comparative matrices to yield more reliable results, with the support of the comparison Table 2 between pairs, see Figure 2, which is essential when qualifying the selection priorities of the alternatives.

Worth	Definition	Comments
1	Equal importance	Criterion A is just as important as Criterion B
3	Moderate importance	Experience and judgment slightly favor Criterion A over B
5	Great importance	Experience and judgment strongly favor Criterion A over B
7	Very great importance	Criterion A is much more important than criterion B
9	Extreme importance	The greater importance of Criterion A over B is beyond any doubt
2, 4, 6, and 8	Intermediate values in previous ones, when it is necessary to clarify

Table 2.

Matrix of qualifiers between pairs to be compared of the analytical hierarchical process (AHP).

3. Conclusions

It is the same biomass with its physical and chemical characteristics, which gives indications of the best transformation and recycling treatments, whether in energy conversion or in new organic products useful in the food, cosmetics, and medicine industries, among others.

The energetic potential of the residual biomass resides in its solid mass, where the organic elements based on carbon are found, susceptible to decompose and later become fuel. If the biomass is very humid, this characteristic can help this transformation through biodigestion, water being the environment that allows bacteria to perform this task.

The alternative to transform the residual biomass into electricity with less humidity and the greatest amount of solid mass to be seen is gasification, which offers a synthesis gas (syngas), being an accessible option of economic production for many people.

Another method that takes advantage of bacterial activity in energy transformation is the production of bioethanol, with fermentation, the latter is also crucial in the production of other products, also biologically based, useful as inputs for other industries.

Acknowledgments

I express my sincere gratitude to the district university and its academic community for teaching me what I know about engineering and having the power to provide solutions to humanity’s challenges.

Conflict of interest

The authors declare no conflict of interest.