**1. Introduction**

Currently, a substantial portion of the world's energy supply is derived from fossil fuels, whose reserves are unsustainable. High carbon fuel consumption and concomitant greenhouse gas emissions are currently the most pressing and wellconsidered challenges [1]. To address these encounters, renewable energy seems quite promising. Among all, biomass wastes are one of the renewable energy sources which can potentially substitute fossil fuels for heat and energy generation [2]. As biomass waste is virtually everywhere, it is an excellent resource for distributed heat and power generation, which reduces dependence on fossil fuels and central power generation, which is hugely challenged by global energy politics. It also promotes a circular economy as local resources can be converted to useful products and energy [3]. It can also be coupled with carbon capture, and bio-remediation through special biomass sources to have a greater impact on the environment [4]. Also, the utilization of biomass waste such as municipal and agro-industrial waste as feedstocks in large quantities resolves the concerns associated with waste management, aiding to curb environmental pollution and severe health effects [5].

There are various biomass-to-end-use (bio-based products and heat/power) conversion pathways. Thermo-chemical and biochemical conversion of biomass is the major conversion route yielding a wide range of products and subsequent applications. Thermochemical conversion is a widely employed means of biomass conversion through combustion, pyrolysis, gasification, and liquefaction [6]. Among those pathways, gasification is gaining increased attention for its better conversion efficiency, accommodation of a variety of feedstocks, and yield of a variety of products for versatile applications [7]. Fluidized bed gasification is a very matured and efficient coal and biomass conversion pathway mostly limited to industrial applications to date. Due to high solid-to-gas contact and excellent heat transfer in the fluidized bed, it is considered very suitable for controlling operating conditions (such as reaction temperature, residence time, and solid gas heat transfer) and the end product distribution compared to other gasification and thermo-chemical conversion pathways [8]. In addition, it is also suitable for a wide range of feedstocks. **Figure 1** shows a typical gasification process with respect to the operating temperature. Even though fluidized bed gasification is one of the most promising technologies used for the thermochemical conversion of coal and biomass materials, it comes up with challenges and limitations [10]. Particularly, the low energy density of biomass waste and challenges like syngas quality. In terms of heating value and the amount of contaminants like tar, particulates, and heavy metals present in the syngas, the downstream processes like upgrading and cleaning have a direct impact on investment and operational costs. In addition, transporting raw biomass residue over a long distance is not feasible technically or economically because of the very low volumetric energy density of biomass, which may require more fuel energy than it can produce [3].

In a frontier to design optimized fluidized bed gasifiers for typical end-products, experimental and computer models have been extensively employed. Experimental works are highly limited to lab-scale reactors and fail to represent actual-scale gasification processes due to cost and complex processes which makes the experiment difficult. Although computer models are widely employed to simulate the fluidized bed phenomena, it comes with severe limitations as fluidized bed gasification involved complex multi-phase, multi-step, multi-scale processes, which are very expensive to be dealt with in great detail at the same time.

*Opportunities and Challenges of Harnessing Biomass Wastes for Decentralized Heat… DOI: http://dx.doi.org/10.5772/intechopen.112533*

**Figure 1.** *Typical steps in gasification [9].*

In addition, due to a lack of well-formulated strategies and policies towards renewable energy, biomass waste is highly under-exploited, and often times it is dumped and burned in the open air, which has been a common trend in many developing countries. A comprehensive approach combining the technical, economic, strategic, and policy frameworks should be followed to address the existing challenges.

In this book chapter, the opportunities and challenges of the existing fluidized bed gasification technology as a potential candidate for biomass to heat and energy conversion pathways will be discussed.
