**4. Existing challenges**

#### **4.1 Technical/technological bottlenecks**

One of the key challenges in developing commercial advanced waste gasification technologies is to improve the quality of the syngas produced, making it suitable for a range of applications, including energy generation in gas engines or turbines, hydrogen production, or chemical feedstock [10]. Compared to traditional fuels, syngas from biomass gasification has a low heating value. During gasification, various compounds are released, such as tars, heavy metals, halogens, and alkaline compounds, which can cause both environmental and operational issues. Generally, the acceptable limit for tar is around 50 � <sup>100</sup> *mg=Nm*<sup>3</sup> . While the amount of tar is important for engine applications, the dew point temperature of the tar is more crucial [13]. The heavy polyaromatic hydrocarbons primarily determine the dew point temperature of the total tar, even in small quantities.

As per recent research, both primary and secondary tar removal/reduction techniques are being widely used for advanced waste gasification technologies. Secondary methods like thermal or catalytic tar cracking and mechanical methods such as the use of cyclones, ceramic, fabric, or electrostatic filters, and wet scrubbers have been found to be highly effective in most cases, although they may not be economically feasible and can be particularly complex when very low tar content is required [85]. In-bed methods, which include the adequate selection of main operating parameters, use of proper bed additives or catalysts, and gasifier design and process optimization, are gaining more attention for waste gasification since they can significantly reduce the need for downstream cleanup [86].

Some in-bed tar treatment techniques are [13]:


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

*LHV* <sup>¼</sup> <sup>3</sup>*:*2*MJ=Nm*<sup>3</sup> ), higher carbon conversion efficiency (91.6%), higher thermal efficiency (75%), higher gas yield (2*:*7*m*3*=kg*) and reduced tar + SPM (solid particulate matter) (0*:*33*g=Nm*<sup>3</sup> ). But the upper ceiling of the working temperature (9000*C* in this case) is limited by the sintering of ash problem as rice husk has high ash content (18–20% in this case).


In addition to tars, unwanted products in the produced gas (dust, fry ash, tars, ammonia, sulfur compounds, and others) pose a serious problem in the heating or power generation components of the plant and may need to undergo intensive gas cleaning which results in higher plant investment and operation costs [10]. Maximizing gasifier performance and obtaining high-quality fuel is also a very important consideration as it affects the overall technical and economic feasibility of the biomass conversion system. Still, further development and optimization are required to maximize CCE, thermal efficiency, and CGE and minimize tar, char, and ash in the producer gas [3].

#### **4.2 Biomass availability and logistics**

The collection, storage, and transport of biomass need to be carefully evaluated as biomass have a poor volumetric energy density, and transporting it at a cost of high energy density fuel (fossil fuels) may not be worth the benefit. Even in the practical scenarios, processing, handling, and transporting biomass from production sites to conversion plants may contribute 20 to 50% of the total costs of bioenergy production [3, 88].

The wide range of power production scale of fluidized bed gasification (1*MW* � 1000*MW*) presents the flexibility of exploiting biomass in via fluidized bed gasification in local small-scale plants based on the local resource. Yet, factors are affecting the reliability of locally available biomass such as weather conditions, agricultural practices, regulations, and competing uses for local biomass [78]. As a result, it requires critical assessment and forecasting of technically and financially available biomass quantities on an annual basis with a well-structured and proven methodology.

Densification techniques, such as baling, pelleting, briquet, and pyrolysis/ torrefaction, help mitigate logistics costs associated with biomass transportation, storage, and handling, but the role of densification within the overall biomass-tobiofuel supply chain context is not yet well understood [89]. Densification by mechanical method increases the energy density of the biomass while torrefaction reduces the H/C and O/C ratio with the remaining 75–95% of total biomass energy


#### **Table 4.**

*Comparison of properties of Wood Pellets, Torrefied Biomass Pellets, and Coal.*

after removing moisture, hemicellulose, and partially cellulose [29]. CO and H2 production apparently increases with torrefaction [26, 90]. It results in near-complete degradation of its hemicellulose content while maximizing the mass and energy yield of the solid product [91]. It increases the calorific value, energy density, grindability and makes the biomass more hydrophobic so that it can be more suitable for storage [92]. **Table 4** compares the characteristics of torrefied biomass against wood pellets and coal. Such feedstock upgrading techniques are getting increasing attention, yet have their associated investment and operational costs.

#### **4.3 Lack of adequate policy frameworks and strategies**

Policy and regulatory barriers can significantly hinder the deployment of biomass waste for decentralized heat and energy generation. For the case of Europe, although there are some at the national and industry levels, there are currently no legally binding sustainability criteria for biomass at the EU level [2]. Several countries offer varying incentives and frameworks for biomass utilization, thereby creating disparities in policies and regulations [93]. These barriers come in the form of legal, regulatory, institutional, and economic constraints. Government regulatory policies may lack clarity, and inconsistent or overly restrictive policies can impede progress in this field.

For instance, a lack of uniformity in the requirements for emissions monitoring can make it much more difficult and expensive for project developers to advance [94]. Additionally, unclear feedstock requirements can make it challenging for suppliers to comply, which could prevent the facility from operating at full capacity or necessitate significant changes in the facility's design. Furthermore, it is less profitable than fossilbased power due to the lack of financial incentives and subsidies for decentralized heat and energy production facilities. Another significant obstacle is the unequal playing field between renewable and non-renewable energy sources. Potential investors may be deterred from investing as a result of these regulatory restrictions that

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

may make it more difficult to implement decentralized heat and energy generation facilities using biomass wastes.

In conclusion, there is a need for supportive policies and clear regulatory frameworks to encourage the deployment of decentralized heat and energy generation facilities that use biomass waste.

## **5. Techno economics**

The ability of fluidized bed gasification technology to effectively transform a variety of feedstocks into a clean and renewable form of energy makes it a desirable option for distributed heat and power generation. To determine a biomass conversion plant's economic viability, techno-economic considerations must be taken into account. In addition to end product application and feedstock availability, challenges such as cost-competitiveness and sustainability constrain bioenergy development [95]. The cost of fluidized bed gasification varies depending on factors like the region of the world, the type of feedstock, the cost of supplies for conversion processes, the size of the production, and the length of the production process.

Numerous academic institutions and international organizations recognize biomass as one of the most cost-effective renewable energy sources for power production [3]. Various biomass power technologies are mature and have production costs that are competitive with electricity generation rates in the OECD, particularly with lowcost agricultural or forestry waste sources like wood pellets, according to a recent report by the International Renewable Energy Agency (IRENA) [96]. Due to their low capital and operating expenses, small-scale gasification technologies have been shown to be both technically and economically viable for the production of heat. Industries that need process heat and have access to biomass resources should use these systems [3]. Additionally, by combining electrification with readily available biomass fuels from the local area, small-scale gasification systems have the potential to promote rural development [3].

Diego et al. [3], stated that the levelized cost of commercial bioenergy for electricity or combined heat and power ranges from US *cents*<sup>2005</sup> 3.5 to 25*=kWh* (*USD*<sup>2005</sup> 10*to*50*=GJ*) for liquid and gaseous biofuels and roughly *USD*<sup>2005</sup> 2 to 48*=GJ* for electricity or combined heat and power (CHP) systems larger than about 2*MW*. The estimated price for domestic or district heating systems is between *USD*<sup>2005</sup> 2 and 77*=GJ*, with feedstock costs between *USD*<sup>2005</sup> 0 and 20*=GJ* [3]. Appropriate gasifier systems with internal combustion engines can produce 1*kWh* of electricity from 1*:*1 1*:*5*kg* wood, 0*:*7 1*:*3*kg* charcoal, or 1*:*8 3*:*6*kg* rice husks [3].

A Cost Benefit Analysis framework can be used to evaluate the feasibility of fluidized bed gasification projects from an economic perspective. This framework aids in the technical and economic analysis of the bioprocess's domain data, including capital and operational costs, simulation, equipment installation costs, and project profitability [97, 98]. Truong et al. [99], studied the effect of plant size on the total capital investment (TCI), total production cost (TPC), and specific capital cost for a fluidized bed gasification plant with a gas engine, gas turbine, and combined gas and steam turbines. TCI and TPC increase linearly between 10 140\$*M* and between 1 12*:*5\$*M=year*, respectively for plant size from 10 to 550*t=d*. The gasification system with a gas engine has the lowest TCP while the gasification system with gas and steam turbines has the highest TCP, with a narrow difference between them. The SCC on the contrary, has a very steep decline in plant size between 10 and 50*t=d*, a medium decline between 50 and 150*t=d*, a slight decline between 150 and 300*t=d*, and almost no change beyond 300*t=d*. Also, the plant with steam and gas turbines has the least SCC (\$/(kWh/yr)).

State-of-the-art tools like Aspen Plus can be utilized to make TEA based on thermodynamic modeling, and energy and/or exergy analysis. In simulating and optimizing the biorefinery process flow, the size of the equipment and utilities can be calculated. Based on variables like equipment cost and material, raw material and utility costs, operating time, and product yield, the operational cost and investment are quantified. The discounted cash flow (DCF) method additionally aids in evaluating the project's profits, excises, internal rate of return (IRR), net present value (NPV), remuneration period, and lowest selling price [88]. It is also important to take into account the financial incentives if applicable. Antonio et al. [11] showed that the NPV is about four times when the financial incentives are considered in the technoeconomic analysis of a fluid bed gasifier and combined gas-steam cycle.

In order to account for uncertainties in the TEA of biorefineries and to take into account societal sustainability factors like employment, the Monte Carlo simulation can also be used. Financial metrics like revenue, lowest selling price, and profitability—which are frequently expressed are typically used to deliver the TEA's results [88]. **Table 5** summarizes some of the TEA conducted on fluidized bed biomass gasification plants.

## **6. Future prospects**

With the increasing global focus on climate change abatement and transition towards renewable energy sources, biomass gasification via fluidized bed gasification provides an opportunity to reduce greenhouse gas emissions while generating energy. Several research studies have outlined the future prospects of fluidized bed gasification technology.

According to the IPCC 2012 special report [1], advanced biomass integrated gasification combined-cycle (IGCC) power plants are among the technologies that are at a pre-commercial stage. With higher biomass to the power conversion efficiency of about 35–40%, the IGCC is a very competitive and attractive technology compared to conventional ones, especially in small-scale decentralized heat and power plants. For countries with existing huge small-scale decentralized plants, converting the conventional technology with a relatively small modification is considered a huge opportunity. Jesper et al. [102] showed the prospects of decentralized heat and power generation via gasification in the Case of Denmark where there are many existing small-scale heat and power plants with versatile technological options including FICFB (fast Internally Circulating Fluidized Bed) and LT-CFB (Low temperature circulating fluidized bed). The FICFB is designed for the cogeneration of electricity and bio-SNG and the LT-CFB is designed for the cogeneration of power, heat, and bio-fertilizer, with overall estimated efficiencies of 97 and 90% respectively.

The future prospect of fluidized bed gasification lies in leveraging key instruments such as advances in research and development, following proven methodologies in techno-economic feasibility and sustainability, and standardized and consistent policies and strategies at the regional, national, and global levels as depicted in **Figure 4**.

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


*DFB, Dual Fluidized Bed; CFB, Circulating Fluidized Bed; NPV, Net Present Value; IRR, Internal Rate of Return; PBP, Pay Back Period; TCI,Total Investment Cost; SNPC, Specific Net Production Cost; SCC, Specific Capital Cost; ASR, Annual Sale Revenue; ROI, Return on Investment; DCFROR, Discount Cash Flow Rate of Return.*

#### **Table 5.**

*Techno economic analysis conducted on different gasification plant designs.*

**Figure 4.**

*Leveraging comprehensive instruments for opportunities outweigh challenges.*
