Electricity and heating energy are two vital and essential energy types utilized in several industrial and household applications, and solid fuel plays a critical role as a fuel source for producing these energies [
1,
2]. The technique of solid fuel combustion is especially critical to the power and heat demand in the world. The world produced over 80% of its electricity by utilizing fossil fuel-based sources in 2020 [
3]. Even though coal is also a highly environmentally polluting non-renewable energy source, 35% of global electricity energy demand was fulfilled by coal in the year 2024, producing 10,704 terawatt-hours of electricity [
4]. However, the world has identified the requirement to phase out coal consumption due to the unhealthy environmental impact of coal combustion [
5,
6]. Climate analytics and scientists have shown that coal combustion needs to end by at least 2040 to reduce further environmental pollution and move into a sustainable and renewable alternative, such as the utilization of biomass [
5,
6]. Biomass is a renewable and clean energy source that can be used for the combustion process to produce electricity and heat energy; sources such as wood, agricultural residue, animal waste, and forestry waste can be utilized as sustainable alternatives to coal [
7,
8]. Furthermore, biomass utilization has shown a promising future in replacing non-renewable coal consumption; the global biomass market was worth around USD 46.98 billion in 2021, and it is expected to increase to USD 84.78 billion in 2030 [
9]. The Sun’s energy is stored in the chemical bonds of plant materials and can be extracted as biomass energy from combustion applications [
10]. Henceforth, biomass combustion emits roughly the same amount of carbon dioxide to the environment, which is absorbed during the plant growth period, neutralizes the carbon cycle, and does not add additional carbon dioxide to the atmosphere [
10]. Therefore, in climate change and environmental pollution reduction perspectives, biomass utilization is preferred over coal. However, the low calorific values, the provision of sustainable biomass feed, and the preprocessing of the biomass are some areas that need to be developed further to completely replace coal. The technological advancement of biomass conversion is a vital factor; technologies such as cofiring of biomass with coal, applying pyrolysis process for biomass to produce biofuels, gasification of biomass to produce syngas, and conversion of biomass to ethanol or methanol are some of the techniques that are being used at the moment to utilize biomass in a more effective manner [
11,
12]. Furthermore, efficient utilization of fuel in combustion operation is a critical factor in power generation. Techniques such as CCCHP provide efficient operation while reducing the environmental impact [
13]. Moreover, several regulations and policies were introduced to enhance CCCHP utilization and support CHP adoption [
8]. Especially in the USA, Energy Regulation and Policy, environmental regulation, state climate change plans, and incentives like Electric Utility rates, Feed-in-Tariff, and tax rates are assisting in promoting CCCHP operation [
8].
Several large-scale power and heat generation projects have been established in the world, especially in developing countries, to fulfill the increasing energy demand. As an example, a 150 MW renewable energy project was proposed to Sri Lanka to fulfill the energy demand in the southern area. Henceforth, the selection of 125 MW electric power generation was chosen for this simulation by considering the stability and integration with existing infrastructures, available demand, and realistic operation conditions [
14]. Furthermore, the 25 MW heating power generation was chosen by targeting the industrial processes and other thermal applications while ensuring efficient operation. This study presents a feasibility study of biomass and coal–biomass combustion CCCHP systems, specifically considering real-world constraints such as energy efficiency, exergy efficiency, environmental impact, and operational stability at different biomass moisture contents. Furthermore, the investigation considers the realistic assessment of utilizing biomass as a sustainable alternative to coal. The contribution of this finding through the identification of optimum biomass moisture content for CCCHP energy generation applications for large-scale energy projects will help in developing an efficient biomass-to-energy conversion approach.
1.1. Combined Cycle Combined Heat and Power (CCCHP) Operation
Producing several types of energy integrating heat and power generation is crucial for improving energy efficiency and sustainability in the current domain; the key benefit of this operation is gaining higher energy and exergy efficiency with significant power output [
13]. Combined Heat and Power (CHP) operation, also known as cogeneration, is the simultaneous utilization of electricity energy and heat energy from a power generation plant [
15,
16]. The CHP process provides a more efficient, economically beneficial, and low environmental impact operation since it utilizes the waste heat and consumes both heat and power energy generated through a single combustion process [
15]. The CHP is an ideal operation condition for rising energy demand with limited resources globally. Moreover, the CHP operation reduces fuel consumption compared to traditional power generation due to the higher energetic and energetic CHP efficiency [
17]. The utilization of biomass for CHP combustion systems provides a great solution by attaining significant emission reduction while utilizing renewable biomass sources [
15]. However, the supply of sufficient and continuous biomass feed to the combustion system is critically important to achieving optimum operation [
16]. The CHP systems consist of several components based on the fuel type and the design, such as a combustion unit, gas turbine, steam turbine, combined cycle systems, electric generator, and steam generator with heat recovery units [
15,
18]. Moreover, the different fuel types can be fed to the CHP system to enhance efficiency, especially when integration with renewable energies, such as biomass and biomethane, is highly beneficial from an environmental perspective. The CHP operation combined with combined cycle power generation affords the production of more electricity by consuming the same fuel source and gaining more efficient operation [
19,
20]. Compared with single-cycle operation, the combined cycle power plant can have higher efficiency. Generally, a combined cycle can consist of a combination of gas turbine and steam turbine operations, which can reach an efficiency level of over 60% [
20]. The gas turbine system employs the Brayton cycle to generate electricity, and the exhaust heat-recovered steam turbine system employs the Rankine cycle to produce extra electricity; therefore, the overall electricity efficiency is the summation of both cycle efficiencies due to the consumption of the same fuel source for both cycle operations [
21]. The gasification of solid fuels such as coal, coke, or biomass can also deliver combined cycle operations called integrated gasification combined cycle (IGCC) plants [
20,
21]. Moreover, the IGCC of coal causes lower environmental pollution compared to normal combustion, with lower environmental impact [
21].
1.3. Research Objective
This research study aims to develop a system model using Ebsilon Professional 16 software to evaluate the effective outputs of different material inputs such as biomass, coal, and coal–biomass mix with different moisture contents in a CCCHP system. This simulation was conducted in three different ways. The first simulation uses coal as the input material with 10% moisture content, the second one uses biomass (bagasse) with a moisture content of 10% to 40%, and the third one uses a coal–biomass mix with varying moisture content. The bagasse moisture content can be varied from 40 to 55% (
w/
w) range, and dried bagasse was used for the combustion activities [
25]. Henceforth, the 10% to 40% range was selected for the simulation.
System energy and exergy (maximum theoretical useful work obtainable from an energy conversion system) efficiency are parameters used to evaluate the effective output of the developed system [
26]. The quality of energy is a vital factor for analyzing an energy-associated system. The energy analysis describes only the quantitative part of the energy, but the exergy analysis describes both the quantity and quality of energy and provides information about individual components. Hence, exergy analysis is the best way to evaluate an energy-based system [
27]. The system utilizes two power generation units consisting of a combined gas turbine and steam turbine cycle operation, and the power generation was compared and analyzed for different fuel feed systems with different fuel moisture content frameworks. Then, a comprehensive energy and exergy analysis was executed for the systems to analyze the system performance with different fuel feed conditions. Ultimately, the exhaust conditions were investigated for different combustion systems to identify the environmental impact of different solid fuel combustions. A key finding from this research study was the analysis of the performance variation in solid fuel combustion systems in non-renewable coal, renewable biomass, and coal–biomass cofiring processes. Moreover, a comprehensive analysis was performed based on the energetic and environmental perspectives to identify the possibility and importance of replacing non-renewable coal with renewable biomass and cofiring systems.