In a regulatory environment in which renewable energies and the conversion of energy in cogeneration processes would seem to be responsible for the €30,000 million tariff deficit, there are still companies committed to the environment and with sufficient “common sense” to build renewable energy fired CHP plants, thereby preventing the only combustible gas produced in our country from been burnt by flare systems. This is the case of the Abrera and Igualada WWTPS, where projects developed by acciona agua and CPI, and executed by Micropower Europe, gave rise to the installation of a total of 11 capstone micro-turbines to enable energy recovery from the biogas produced in the sludge digestion and co-digestion processes implemented at the two plants.
The Abrera and Igualada WWTPs have treatment capacities for population equivalents of 115,000 and 290,000 respectively (design flow of 34,500 and 20,000 m3/day). As a result of this activity, they generate a large quantity of sludge on a daily basis and this requires treatment to prevent damage to the environment. This treatment consists of anaerobic digestion of of the sludge in the digesters at the plants. The digestion of this sludge, along with the co-digestion processes implemented, results in a biogas output of around 175 and 210 Nm3/h respectively.
Because the biogas is a renewable resource, which comes from a process that benefits the environment, it is of vital importance to recover its energy so that electrical power can be generated for self-consumption at the WWTPs (drastically reducing the energy costs associated with water treatment), along with thermal energy to maintain optimum conditions for the digestion process, (which in turn produces more biogas to enable ongoing energy recovery).
The biogas produced at the Abrera and Igualada WWTPs is sufficient to feed up to five and six Capstone CR65 BIO Digester micro-turbines, respectively, at full load, taking into account a methane concentration of around 65%.
Article published in: FuturENVIRO December 2013