**4. Socio-environmental impact**

the small size of feedstock particle required much more energy input during the biomass pre-preparation process. In addition, it is also effective by applying an optimal design of gasification reactor. A collaborative project between Switzerland and India demonstrated that an open-top fixed bed would produce much less tar and particulates than a closed-top fixed bed [15]. The reason behind this is that the open-top fixed bed could introduce dual air from the

Secondly, in many processes, tar is removed as a downstream step after gasification, including mechanical method, thermal cracking and catalysis. The details of some common technologies have been listed in **Table 1**. Wet gas cleaning method has been accepted at an early stage. Its equipment investment is relatively low and the operation is also easy to handle. But this technology would also create a lot of waste water and bring serious environmental issues. Therefore, dry gas cleaning method becomes more widespread via various types of filters, rotating particle separators and dry cyclones. Although the dry method avoids waste water issues, its efficiency of tar removal is not good enough if compared with wet method. On the other hand, the replacement, renewal or disposal of filter materials reduces the financial effectiveness of the entire gasification system. This similar situation could also be applied to thermal cracking method and higher operation temperature requires much more energy input.

In the recent two decades, catalytic cracking has attracted more and more attention and has already become the central branch of research. Catalytic cracking is more like a downstream catalytic reforming unit and could easily degrade comparative stable tar to a significant extent. The previous research indicated that the catalytic cracking unit could promote gas yield by 10: 20 vol% and increase the heating value by c.a. 15% [23]. Ni-based catalyst is applied most widely and especially preferred for hydrogen or syngas production. Nickel has a very good catalytic activity and a preferable price advantage. While the application of Ni catalysts needs to avoid extremely high heavy-tar content flue gas, which will form a serious carbon deposition over the catalyst surface and lead to a quick deactivation. The other transition metal-based catalysts, such as co, Fe and cu, also have similar issues. Thus, some applications used the two-stage catalytic reforming process: the first stage used dolomite to

Electrostatic precipitator, wet cyclone, wet scrubber

activated carbon adsorber, sand filter

Usage of appropriate catalyst Tar cracking catalysts are divided into five major groups, namely

catalysts and activated carbon-based catalysts

Cyclone, rotary partial separator, fabric filter, ceramic filter,

Ni-based, non-Ni-based, alkali metal-based, acid catalysts, basic

Maximum tar destruction was found at 1250 ° *C* and 0.5 s

top and nozzles actually increase the residence time for degrading tar.

12 Gasification for Low-grade Feedstock

**Method Technique used Details/examples**

Usage of mechanical device

Usage of mechanical device

or equipment

or equipment

**Table 1.** Post-gasification tar removal methods [15].

Application of high temperature with long residence time

Wet gas cleaning

Dry gas cleaning

[21]

[21]

Thermal cracking [21, 22]

Catalytic cracking [21] Biomass gasification could exploit an abundant variety of waste materials as feedstock such as agricultural residues and food waste. It actually achieves resource recovery and mitigates CO2 emission as an environmental benefit. However, power generation from biomass gasification poses several key hazards and socio-environmental impacts.

#### **4.1. Health and safety hazard**

One of the major risks is the potential emission of toxic producer gas and particulates. The production of CO, SOx , NOx and volatile organics involves incomplete combustion and oxidation of trace elements in feedstock [24]. As one of the most dangerous constituent, CO can permeate into human blood system and combine with hemoglobin to stop oxygen adsorption and distribution. Long-term exposure to CO causes asthma, lung inflammation, schizophrenia and cardiac defects. Toxic gases like SOx , NOx and volatile organics could also destruct inhalation, ingestion and dermal system of human [25]. Hence, the entire gasification process should prevent leakage and an efficient gas clean-up system is essential. In recent years, the hazard of particles emission (PM2.5) attracts public attention increasingly, due to its carcinogenicity. PM2.5 particles can adsorb many soluble organic compounds including alkanes, carboxylic acid and aromatic compounds, which will damage human organs like lung and liver [26]. For control of these particles' emission, an efficient gas clean-up system with conditioning unit is necessary, as well as avoiding insufficient combustion and gasification. In addition, ashes and condensate from biomass gasification also contribute to environmental problems if they are not disposed properly. Especially the toxic condensate with high content of tar is very difficult to deal with and has higher risk of hazards.

to its low energy density. However, in some small communities, with large amount of local biomass materials, using biomass to replace polluting fossil fuels is a competitive way for

Biomass Gasification: An Overview of Technological Barriers and Socio-Environmental Impact

http://dx.doi.org/10.5772/intechopen.74191

15

This chapter provides the current technique status and development condition in China. It concludes that the gasification of biomass waste with distributed power generation would be a potential market. The properties of biomass feedstock have been analyzed and both advantage and disadvantage of biomass utilization were pointed out. Consequently, highly dispersed property and the low volumetric of biomass limit its large-scale application. Apart from that, this chapter also detailed some common types of gasifiers, except some emerging technologies, for meeting special requirements such as supercritical water gasification (SCWG) for wet biomass and plasma gasification for toxic organic waste. The tar issue, one of the most baffling problems in biomass gasification, is introduced briefly as well as its removal technologies. In our view, the socio-environmental impact is not the primary factor for restriction of biomass gasification development, while an objective financial return can actually attract investors and accelerate commercialization; in the meantime, it will also contribute to

and Yusen Rao3

providing reliable and clean power and heat.

other technical breakthroughs.

Xiang Luo1,2\*, Tao Wu1,2, Kaiqi Shi1,2, Mingxuan Song3

Nottingham Ningbo China, Ningbo, China

source Technology. 2002;**83**:37-46

source Technology. 2002;**83**:47-54

Revue de Métallurgie Paris. 2009;**106**:410-418

\*Address all correspondence to: xiang-luo@nottingham.edu.cn

1 A Key Laboratory of Clean Energy Conversion Technologies, The University of

2 New Materials Institute, The University of Nottingham Ningbo China, Ningbo, China

3 Department of Chemical and Environmental Engineering, The University of Nottingham,

[1] Asadullah M. Barriers of commercial power generation using biomass gasification gas:

[2] McKendry P. Energy production from biomass (part 1): Overview of biomass. Biore-

[3] McKendry P. Energy production from biomass (part 2): Conversion technologies. Biore-

[4] Fallot A, Saint-André L, Le Maire G, Laclau J-P, Nouvellon Y, Marsden C, Bouillet J-P, Silva T, Piketty M-G, Hamel O. Biomass sustainability, availability and productivity.

A review. Renewable and Sustainable Energy Reviews. 2014;**29**:201-215

**Author details**

Nottingham, UK

**References**

Besides the risk of health hazards and environment, gasification is also confronted with risk of fire and explosion. Because the gasification system is normally operated at relatively high temperature and pressure, it also produces flammable gas mixture with a great portion of hydrogen gas. However, explosion is not easy to be created even air leakage into the gasification system, which could raise a partial combustion. This will only lead to lower quality and higher temperature of producer gas [1], unless there is a large amount of air which enters with feedstock from the feeding system or massive leakage of flammable outlet gas occurs.

#### **4.2. Social impact**

The development of bioenergy will need a lot of land for energy-growing crops. This requirement will clash with other applications of farmland, like food and other cash crops. The competition with food agriculture must be intensive. The food shortage is still a big global issue nowadays. According to the data of World Hunger Education Service, the world's hungry population was 925 million in 2010. Besides this, the world population is still growing by rate of 1.2%. The natural disasters and climate change also affect agriculture. These three factors will decide that the demand of the farmland in the future will expand. Thus, transferring farmland for energy crop planting in a large scale would be difficult, especially in Europe.

#### **4.3. Ethical issues**

The bioethics report by Nuffield council points out that deployment of bioenergy should not violate the human right which is reflected in the Universal Declaration of Human Right (UDHR). In the UDHR, it states that every people can share and enjoy the protection of the moral and the any product from any scientific, literary or artistic which is owed by them. There are a lot of ethical issues referring bioenergy, like human rights, solidarity and sustainability. Biofuel production application will require land use, water supply and labor from local community. Destruction to the land and local ecosystem cannot be avoided. Also, land displaced for energy crops will not only bring food price increases; some local residents may face migration. All these could be regarded as the actions, which violate the human rights of citizens and non-citizens.
