Techno-Economic Assessment of a Combined Heat and Power Technology based on a Reciprocating Gas Spark Ignition Engine in Waste Water Treatment Plant of El Karma, Oran, Algeria

Abstract

This study concerns energy analysis in the waste water treatment plant (WWTP) of El Karma in Oran which is the largest municipal wastewater treatment plant in Algeria and second largest in Africa. This plant is designed to treat 270,000 m3/day of waste water. It is, also, equipped with four digesters, each of 9,600 m3, to produce up to 324,000 Nm3/month of biogas. The plant covers its electricity needs from the network. Most of the produced biogas is burned in a boiler to generate heat for the anaerobic digestion and the remained biogas is flared. The aim of this study is to assess the viability of a cogeneration in this plant using the whole amount of biogas produced. Cogeneration, also called combined heat and power (CHP), is an efficient approach for generating electric power and useful thermal energy for heating or cooling from a single fuel source with high efficiency. The investigation is conducted in the case of a CHP technology based on a gas spark ignition engine. The techno-economic performance of the CHP is compared to the current energetic situation of the plant. The methodology applied uses technical and economic inputs from the biogas plant as well as the CHP. The most important parameters retained in the economic appraisal of the CHP technology are the following: Payback Period (PBP), Net Present Value (NPV), Internal Rate of Return (IRR), and Profitability Index (PI) using two alternatives (constant and escalated costs of energy, amount of biogas produced and operating/maintenance) The results show that the energy output of the CHP meets the electrical and thermal needs of the plant with an excess in electricity production as the bulk source of income for the plant. The outcome of the techno-economic assessment indicates that the project is profitable (PI = 2.5) with a short payback period (PBP = 5 years) and interesting internal rate of return (IRR = 18%). This study clearly emphasizes how CHP, as a technological innovation, can impact the economic viability of WWTP El Karma by building an energy integrated system and saving money. Keywords: Combined Heat and Power Technology- Reciprocating Engine- Techno Economic Analysis Module- Net Present Value-Internal Rate Of Return - Payback Time-Profitability Index.