Directive 2008/98/EC, implemented in Italy by Legislative Decree 205/2010, introduces a criterion to calculate energy efficiency which makes it possible to classify a municipal waste incineration plant as an energy recovery plant. This criterion makes it possible to calculate the energy efficiency of the incineration process on the basis of the energy introduced with the waste, the amount of energy consumed and the amount of energy produced (thermal and electrical). In order to ensure that the methods of applying this criterion are consistent, a reference document has been issued at European level to calculate energy efficiency.
The formula used to calculate energy efficiency provided by Directive 2008/98/EC is, in fact, a performance index. Therefore, it does not match the plant performance calculated using the classical thermodynamic criteria, but is an indicator of energy recovery capacity aimed at comparing different plants.
In addition, a decree of the Italian Ministry of the Environment and for the Protection of Land and Sea, no. 134 of 19 May 2016, added a “climatic factor” to the formula to account for the climate type of the plant’s location. This factor was added to offset climate-related effects both on electricity generation and on the quantity of unused heat produced; in fact, the energy performance of plants located in countries with warm climates are “physiologically” lower than those of plants located in colder areas. As well reflecting the quality of the investments made over the years to upgrade the plants to use the best available techniques, the status of “recovery plant” also makes it possible to attribute to the plant a role of primary importance in the waste management system.
In fact, while the municipal waste to be disposed of is subject to the “principle of self-sufficiency in the water and waste regulatory area (ATO)”, the municipal waste to be recovered is subject to the “principle of proximity”, meaning that it can be sent to the nearest recovery plant, not necessarily located in the same ATO it is in.
After having determined compliance with the energy efficiency criterion, as set by the regulation, the authorization that governs its activities (Integrated Environmental Authorization) must be modified so that an incineration plant can be operated as a recovery plant. These changes to the authorization are not substantial since they do not increase the plant’s potential nor change to previously authorized emission levels.
All the recovery plants operated by the Herambiente Group (including those of Herambiente in Padua and Trieste) are R1 plants, except for the Ravenna special waste plant. In this regard, an evaluation process is being initiated in European round-tables to define a common criterion to assign R1 operation also to special waste plants.
The total installed capacity of the waste-to-energy plants managed by the Group (besides that of Ravenna) is approximately 140 MWe (equivalent to a medium-small thermoelectric power plant) and about 884 GWh of energy was recovered in 2016.
Recently, the Community framework further investigated the matter, determining at European level a climate correction factor (CCF) applicable to the R1 energy efficiency formula, in Commission Directive (EU) 2015/1127 of 10 July 2015; with a measure of the Ministry of the Environment (decree 134 of 19 May 2016). The factor has therefore been implemented, so the coefficient has been reduced from 1.38 to 1.25. Herambiente Group’s plants retain the R1 qualification they have acquired.
This plant network makes it possible to manage the flows of non-separated municipal waste beyond the so-called municipal-derived waste in the region, in the event of a shutdown of the reference plant, this waste can be sent, either in full or in part, to the closest energy recovery plant, thus limiting the use of landfills and, by doing so, pursuing the goals set by European and national regulations on the hierarchy of waste treatment.
For example, with regard to the non-separated municipal waste collected in the Province of Rimini, if the Coriano (Rimini) plant were to shut down or the quantities of waste produced were to exceed its treatment capacity – as often occurs during peak tourism periods, for example – the waste could be sent to the closest available plants (e.g. Ravenna) for energy recovery and no longer disposed of in landfills.
Concerning the performance assessment of in terms of efficiency, there are two “structural” aspects. The first concerns the process related to the conversion of energy released by the combustion of waste, the second to the external users that can make productive use of the waste heat generated by the combustion. In the first case, the assessment is plant related: The heat generated by combustion of the waste is used to produce steam, and depending on its characteristics (pressure and temperature) achieves different performance of the steam turbine, (the higher the temperature of the steam, the greater the efficiency of the cycle). The choice to opt for more or less advanced solutions takes into account not only performance but also economic factors (for example, to work with steam temperatures particular attention must be paid to the issue of acid corrosion of the pipes in which the steam flows, which increases costs due to a greater thickness of the pipes or due to coating them with materials such as Inconel, effective against corrosion but very expensive) and management factors (for example, work in more critical conditions may result in the need to increase both the duration and the frequency of ordinary and extraordinary maintenance).
In the second case, finally, it is necessary to capability of recovering the waste heat produced by the combustion processes. The greater the ability to recover this waste by users outside the waste-to-energy plant, the greater the efficiency of the plant, also in terms of the R1 index.
Lastly, waste-to-energy plants not only ensure significant energy recovery (electrical and thermal), but also produce heavy slag (called IBA, Incinerator Bottom Ash), for which there are well-established recovery processes whereby the slag is sent to organizations that work in this specific sector. With a production of about 250,000 tonnes of such slag in the group’s plants, more than 80% is routinely used for material recovery (only a small portion is used in landfills as technical material for cultivation). The most important recovery chain is the production of artificial aggregates used to produce cement, as well as the production of cement mixes and (in one case) directly for the production of cement.
Therefore, waste-to-energy plants not only guarantee energy recovery but also contribute significantly to the recovery of building materials from the point of view of a circular economy.