Thermochemical Conversion of Biomass for the Production of Energy and Chemicals

Anthony Dufour

• Publisher: Wiley-ISTE
• Year: 2016
• ISBN:
  9781119137719
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Energy

This book highlights the processes of biomass thermochemical conversion, covering topics from combustion and gasification, to pyrolysis and liquefaction.

Heat, power, biofuels and green chemicals can all be produced by these thermochemical processes. The different scales of investigation are presented: from the bioenergy chains, to the reactors and molecular mechanisms.

The author uses current research and data to present bioenergy chains from forest to final use, including the biomass supply chains, as well as the life cycle assessment of different process chains.

Biomass conversion reactors are also presented, detailing their technologies for combustion, gasification and syngas up-grading systems, pyrolysis and bio-oil upgrading.

The physical-chemical mechanisms occurring in all these reactors are presented highlighting the main pathways for gas, char and bio-oil formation from biomass.

This book offers an overview of biomass valorization for students, engineers or developers in chemistry, chemical, environmental or mechanical engineering.

1
Bioenergy Chain and Process Scales

The outline of this book follows the different scales of investigation of biomass conversion which are presented in Figure 1.1. First the bioenergy routes are presented then followed by the reactor, particle and molecular scales.

Figure 1.1. The different scales of investigation in chemical engineering illustrated for biomass conversion: from electrons to routes

1.1. Biomass production and ecological issues

There are two different contexts on biomass production:

• – in some developing countries, biomass production may result in deforestation, a potential loss of biodiversity (especially in the rainforest), land-use competition and soil erosion (see Figure 1.2). Wood is often the main energy resource and is burnt in wood stoves with a very bad efficiency;
• – in developed countries, forest is aging and in expansion due to the lack of wood valorization. Wood energy should be promoted in some regions to better valorize the small stems in forests.

Figure 1.2. Two different contexts for wood valorization: (a) in developing countries (here in Madagascar), wood valorization results in deforestation and soil erosion; (b) in developed countries (as in France), wood is not well valorized and wood energy should be promoted to reduce the aging of trees and stems density in forests

Figure 1.3. Biogeochemical cycle of nitrogen in forests

A very important feature for ecosystems is the biogeochemical cycle that is represented in Figure 1.3 for forests. The main inputs (especially in nutrients such as N, P and K) are atmospheric deposition and rock mineralization. The outputs are soil leaching or erosion and biomass harvesting. Wood harvesting can considerably impact the cycle if it results in too high a flow of nutrient exportation (nutrients are present in the harvested wood) and thus in soil impoverishment.

For these reasons, a global assessment of the whole bioenergy chain (from forest to final use) is required to assess the sustainability of bioenergy. It is especially of high importance to assess the fate of carbon and nutrients in the whole bioenergy chain.

1.2. Modeling of bioenergy chains

1.2.1. Global model of the whole bioenergy chain

Lignocellulosic biomass such as wood waste represents the highest potential of renewable resources but the biomass-to-energy route has to be complementary to other wood uses such as timber and pulp and should not yield to detrimental nutrient exportation issues. For this reason, our group has developed a modeling strategy (presented in Figure 1.4) that combines a forest modeling platform, called CAPSIS [DUF 12c, FOR 12], and a process modeling simulator (Aspen Plus^®) [FRA 14].

Figure 1.4. Diagram of the approach developed at CNRS, Nancy, for bioenergy chain modeling: a forest management modeling tool (“CAPSIS”) is combined with a process modeling simulator (“Aspen Plus”) [FRA 14]

CAPSIS predicts the biomass growth and CAT handles the different uses of the tree logs. The logs are distributed as a function of their diameter and quality to different wood valorization chains (pulp, timber, energy and end-uses). The results from CAPSIS and CAT are generated in an excel file in the form of “kg of biomass hectare⁻¹ year⁻¹” including mineral flow rates (e.g. kg K hectare⁻¹ year⁻¹). These results are included in an advanced Aspen Plus model. Aspen Plus is a piece of software that is well adapted to modeling solids, such as biomass, and their chemical conversion to liquids or gases. It yields mass and energy balances of the process. The forest growth and tree log chains have been included as “process units” in Aspen Plus. The forest is considered as a “reactor” that produces biomass from CO₂, sun power and other nutrients, based on the results of CAPSIS. This approach helps the simulation of the whole biomass to energy chains under a unique “process” flow sheet.

In Aspen Plus, the photosynthesis process is modeled in a reactor with the following simplified equation [FRA 14]:

The flows in C, N, S, P and K (in kg ha⁻¹ yr⁻¹) as estimated by CAPSIS were used as input parameters for the Aspen Plus photosynthesis reactors. The scope of this work was not yet to model in details the forest biogeochemical process but to propose a simplified method to handle forest management under a process flow sheet such as Aspen Plus.1

The forest growth process provides the amounts of energy wood by hectare and year. Given a particular amount of electricity and heat power, this integrated forest-to-energy model made it possible to predict the annual flows in wood, carbon and nutrients, including N, S, P and K, from the forest to the air emissions (NOx, SOx, polycyclic aromatic hydrocarbons (PAHs), etc.) and ash flows. The model of the gasification plant is described in the following section. On the basis of this approach, the required surface area of forest and other utilities (e.g. fuel for harvesting and transport) are linked with the consumption of the gasification unit. For instance, a need of 1 MW power yields a flow rate of...

Table of contents

• Cover
• Table of Contents
• Title
• Copyright
• Acknowledgments
• Introduction on the Past, Present and Future of Biomass Conversion
• 1 Bioenergy Chain and Process Scales
• 2 Reactor Scale
• 3 Particle Scale and Mesoscale
• 4 Molecular Scale
• Conclusion
• Bibliography
• Index
• End User License Agreement