Environmental and economic assessment of switching from

1 IntroductionBoth household tasks and industrial activities are driven by economic and environmental constraints. Due to increasing greenhouse gas emissions, the limiting of global warming to below a 2°C increase is widely regarded as an imperative policy intervention. Industry has found affordable sources of electricity and heat generation in boilers, furnaces, and internal combustion engines. In order to reduce greenhouse gas emissions using a sector-by-sector regulatory approach, policymakers have generally recommended phasing out heavy fuel oil and coal boilers and furnaces (Heslin and Hobbs, 1989; De Almeida et al., 2004; Lopez and Mandujano, 2005; Zhang et al., 2016; Wilson and Staffell, 2018). There are several studies which have focused on the economic, technical, and environmental analysis of switching or substituting energy sources (Kaewboonsong et al., 2006; Ahmad and Puppim de Oliveira, 2015; Han et al., 2017; Fleiter et al., 2018; Gilbert et al., 2018; Rehfeldt et al., 2019; Moya et al., 2020; Shen et al., 2021).Park et al. (2019) investigated the substitution of heavy fuel oil with bioliquid fuel in a large furnace and boiler, and reported a significant decrease in nitro oxide (NOx) and sulfur oxide (Sox) emissions. Wilson and Staffell (2018) found that switching fuel from coal to natural gas with an appropriate incentives framework avoided 1 GtCO2 per year. RehfeldtFleiter et al. (2020) also reported that fuel switching is a valuable option for medium and long-term emissions reduction in German industrial.All these studies have concluded that fuel substitution is a promising alternative for minimizing industrial boiler emissions, particularly for waste oil, coal, or heavy fuel-oil powered boilers. A significant emissions reduction below the applicable carbon dioxide (CO2) emissions target has been recorded in the substitution of heavy fuel oil or coal by natural gas (De Almeida et al., 2004; Lopez and Mandujano, 2005).In the case of Cameroon, a developing country, several fuel-switching or substitution alternatives are feasible for its available energy resources, including biomass, biofuels, and natural gas. Before 2012, all thermal power plants, boilers, and furnaces were fueled by heavy fuel oil and waste oil, except for two biomass cogeneration plants which were powered by sugar cane bagasse and palm oil cob agricultural waste. Such a functioning mode was imposed by Cameroon’s energy sector, which lacked natural gas production until 2011. Based on the recommendations of the National Gas Development Master Plan, initiated in 1986 and updated in 2003 (Energy Sector Management Assistance Programme, 2001), the exploitation of natural gas was encouraged in 2012 by gas code legislation (Law N° 2012, 2012). Several industrials have opted for now-available natural gas due the attractive cost and environmental benefits of switching from heavy fuel oil and waste oil in industrial burners. Five years after, with fuel substitution occurring at different rates depending on the sector activity, it is essential to make an initial assessment to guide the consolidation or reorientation of ongoing fuel-switching. Can this replacement of heavy fuel and waste oil by natural gas help down drive emissions and offer a way of improving the efficiency of industrial boilers and furnaces?The purpose of this article is to analyze the environmental and economic impact of the ongoing energy transition in industrial boilers and furnaces. It first presents the study area and the gas consumption sector. It then highlights the emissions model and resulting emissions impacts based on avoiding heavy fuel oil usage. Finally, the article analyzes substitution in steam boilers of the brewing industry using environmental and energy performance metrics.2 Materials and methods2.1 Study areaThe study was carried out in Douala (latitude 4°02′ 53.77″N, longitude 9°42′15.41″E), Cameroon’s main harbor and its most energy-hungry city, a location of economic and industrial activity. Douala is located on the western seaboard and is the most important trade hub in Central Africa. The fuel demand and consumption of the city is 70% of the country’s total. The city’s industries are in two main locations. The first is around the natural gas production unit (within 10 km) and contains 85% of the city’s industrial activity; the second is in the city’s suburbs. This study area is the only city in Cameroon where natural gas is available and is sold to industrial customers. Figure 1, depicts the study area, including the gas production and distribution network.2.2 Gas consumption dataThe data used to perform the analysis are taken from official sources provided online by the natural gas supplier (Victoria Oil & Gas, 2018; Gaz du Cameroun, 2016; Gaz du Cameroun, 2017; Gaz du Cameroun, 2018; Gaz du Cameroun, 2021). Before the development of natural gas, boilers, furnaces, and heat production in the industrial sector were fueled by heavy fuel oil and waste oil. Figure 2 presents the evolution of heavy fuel oil consumption in the industrial sector before and after natural gas production. The substitution can be clearly observed in the decrease in fuel oil consumption since the year 2012. Some companies have opted to continue supplying burners with fuel oil due to difficulties in changing the necessary equipment.Data on natural gas consumption were collected over the decade 2012–2021. As depicted in Figure 3, natural gas consumption in industrial boilers is driven by five major applications: brewery and food processing (34%), steel manufacture (14%), dairy products (10%), and textile (10%) and salt manufacture (7%).The evolution of natural gas sales per day is depicted in Figure 4. The natural gas purchased is not stored by industrial customers but is directly provided to the boiler or furnace through a pipe network from the gas company wellhead. Thus, the amount of natural gas sold by the producer is equivalent to the amount consumed at the endpoint boilers and furnaces. Eq. 1 shows the assumption for estimated gas consumption.VNG_ sold=VNG_ consumed(1)where VNG solded is the volume of natural sold and VNG consumed is the volume consumed.FIGURE 4. Natural gas daily consumption.2.3 Emissions modeling approachIn this subsection, the impact of heavy fuel oil substitution on greenhouse gas emissions is assessed on a city level based on the total volume of gas consumed. It is assumed that the combustion of fossil fuels in boilers, heaters, and furnaces results in CO2, methane (CH4), SOx, and nitrous oxide (N2O) emissions.2.3.1 Carbon dioxide emissionsA fuel analysis approach is used to estimate CO2 emissions. This firstly involves determining the carbon content of fuel combusted and applying that to the amount of fuel burned to calculate CO2 emissions. The products of incomplete combustion are not taken into account. The simplified procedure used for the emissions calculation from the default fuel analysis approach is given by Eqs 2 and 3 respectively for fuel oil and natural gas (Eggleston et al., 2007).EmissionsFO=∑i=1nmFO,i×HCi×Ci×FOi×CO2(mw)C(mw),(2)EmissionsNG=∑i=1nQNG,i×HCi×Ci×FOi×CO2(mw)C(mw),(3)where mFO,i and QNG,i represent, respectively, the mass or volume of fuel combusted, HCi is the heat content of the fuel, Ci is the carbon content coefficient of fuel i, FOi is the fraction of fuel i oxidized, and CO2(mw) and C(mw) are the molecular weight of CO2 and carbon.2.3.2 CH4 and N2O emissionsThe estimation of CH4 and N2O emissions from stationary combustion is performed using Eq. 4 (Rehfeldt et al., 2019).Emissionsj,s=As×EFj,s,(4)where EF represents the emission factor, j is the pollutant type (CH4, N2O), A the activity level, and s is the source category. The appropriate factors in terms of fuel type and sector where the fuel is consumed for calculating CH4
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