Biomethane is a promising renewable energy carrier with the potential to diversify and decarbonise natural gas. It is produced from a range of waste sources and can be distributed into the natural gas grid or used as a vehicle fuel or converted into in cogeneration units. The economic evaluation of small plants for biomethane injection into the gas grid is not well defined in literature. This paper proposes a mathematical and economic model useful to evaluate the profitability of these plants in according to Discounted Cash Flow (DCF) method. The indicators used are Net Present Value (NPV), Discounted Payback Time (DPBT), Internal Rate of Return (IRR) and Profitability Index (PI). The baseline case studies analyse three different small-scale sizes (50 m³/h, 100 m³/h and 150 m³/h) concerning two typologies of substrates (organic fraction of municipal solid waste (ofmsw) and a mixture of maize and manure residues). Results define that the profitability is verified only for 150 m³/h ofmsw plant in baseline case study (NPV is 615,694 €, DPBT is 3 y, IRR is 33% and PI is 0.18). Furthermore, alternative case studies are conducted on the main critical variables (subsidies, investment costs of biogas production, transport costs of substrates and percentage of maintenance and overhead costs in biogas production). The economic feasibility can be reached in the following case studies: 100 m³/h ofmsw plant in sensitivity analysis, 50 m³/h ofmsw plant in scenario analysis, 150 m³/h mixed plant in scenario analysis with a new incentive scheme and 100 m³/h manure residues plant in scenario analysis. The biomethane can contribute to develop the circular economy recovering a wide range of waste.

生物甲烷是一种有前途的可再生能源载体，具有使天然气多样化和脱碳的潜力。它是由多种废物源产生的，可以分配到天然气网格中，或用作车辆燃料，或转化为热电联产装置。在文献中没有对将生物甲烷注入气网的小型工厂进行经济评估。本文提出了一种数学和经济模型，可用于根据贴现现金流量（DCF）方法评估这些工厂的盈利能力。所使用的指标是净现值（NPV），折现投资回报时间（DPBT），内部收益率（IRR）和盈利能力指数（PI）。基准案例研究分析了三种不同的小规模规模（50 m ³ / h，100 m ³ / h和150 m³ / h）涉及两种类型的基质（城市固体废物的有机部分（ofmsw）以及玉米和肥料残留物的混合物）。结果表明，在基准案例研究中，仅对150 m ³ / h的垃圾焚烧发电厂验证了盈利能力（NPV为615694€，DPBT为3年，IRR为33％，PI为0.18）。此外，还对主要的关键变量（补贴，沼气生产的投资成本，底物的运输成本以及沼气生产中的维护和间接费用百分比）进行了替代案例研究。经济可行性可以在下列情况下研究来达到：百米³ OFMSW在灵敏度分析植物/ h时，50米³ OFMSW在情景分析植物/小时为150m ³/ h混合工厂进行情景分析，并采用新的激励方案，并在情景分析中使用100 m ³ / h肥料残渣工厂。生物甲烷可以促进循环经济的发展，回收大量废物。