The approach used for evaluating the improvement techniques is described in the following sections.
4.2.1 Evaluation definitions
Table 2.49 below describes the two key criteria assessed for each technique and a descriptor of how a ‘Red, Amber, Green’ rating was applied to each of the two criteria.
Table 2.49: Evaluation and rating definitions (see Section 4.2.1.1 for a detailed explanation of +, ++ and +++ notes)
Criteria Rating
1. Net annual average energy efficiency
Reduced efficiency: No change in efficiency:+
on location Some restrictions on location which
in some instances Can be retrofitted in the majority of installations
52 ISWA CE Report 5 Table 5 – Based on gross efficiencies corrected to net efficiencies. It is assumed that in electricity only mode, electrical parasitic load is 10% of power recovered. Available at:
http://www.iswa.org/fileadmin/galleries/Task_Forces/Task_Force_Report_5.pdf.
53 ISWA CE Report 5, Table 2 – Methane output represents increased efficiency.
4.2.1.1 Net annual average energy efficiency
It is important to note a WtE plant producing power only, or one producing heat only, or a CHP plant cannot be compared in terms of energy efficiency.
+ The middle column ('No change in efficiency') represents the baseline or, in other words, the average value in the range that we encounter in practice today. 'Reduced efficiency' applies to techniques which are below the expected level of energy efficiency (there are limited numbers of these techniques) and, at the other end of the spectrum, 'Increased efficiency' represents techniques which deliver above average performance.
++ In the calculation of annual average heat-only energy efficiency, it is assumed that this category applies to cement/lime kilns, waste heat boilers combusting hazardous/non-hazardous waste and industrial boilers where the heat-producing plant only runs when it is required and therefore all the heat recovered is sold. It should also be noted that cement/lime kilns included in this category directly consume the heat recovered in their material production process (rather than recovering heat via a steam boiler). Pretreatment is required to produce the SRF and the process produces a material product as a result of combustion54. An estimation of the energy consumption required to pretreat waste is provided below in Section 4.2.1.3.
+++ In the calculation of net annual average CHP energy efficiency, it is assumed that 80% of the heat recovered per annum can be sold for heating or cooling purposes55. This is calculated as shown in Annex 456. It should be noted that electrical output is reduced when a thermal plant is run in CHP mode (80% of the time) and that the electrical output will improve again during periods when heat is not supplied (the remaining 20% of the time). This is reflected in the calculation.
4.2.1.2 Applicability
A key aim of this study is to understand how the technical potential of waste-to-energy can be further exploited. In order to do this, an evaluation of the applicability of different techniques has been carried out. The applicability of each technique has been considered as the combination of three subcriteria:
location dependence;
waste streams; and
opportunity for retrofitting to existing installations.
Location
In general, the main restriction on the location of techniques is the viability of district heating/cooling. Other factors relating to location are considered the same across Member States. Therefore, the location criterion has been evaluated in a qualitative way. Some examples of location dependence are shown below:
54 CEMBUREAU interviews, January - April 2016.
High dependence on
location Some restrictions on
location which may restrict be little or no demand for district heating in southern
This has been assessed using a quantitative method, based on the amount of energy (in PJ) currently being recovered from each waste stream; this assessment takes account of both the quantity and calorific value of the waste stream. For example, for the wastes that already contribute higher amounts of energy, there is more potential to increase the efficiency of the energy recovery from these waste streams. For waste streams with smaller volumes, or those that contain less energy, there is less potential. Each technique was assessed as to which of the 18 wastes the technique was applicable to, and therefore also the percentage of potential energy in PJ that was applicable.
The scoring assigned is set out below:
Applicable to <33% of
total potential energy Applicable to 34-66% of
total potential energy Applicable to 67% of total potential energy
Opportunity for retrofitting to existing installations
To enable the WtE landscape to be changed in the short to medium term, it is important to identify techniques which can be more easily retrofitted to existing WtE installations. Scoring was assigned as follows:
New installations only Can be retrofitted in some
instances Can be retrofitted in the majority of installations Combining the applicability subcriteria
As there are three subcriteria which are used to evaluate the overall applicability of each technique, to get an overall score, the RAG scores (R=1, A=2, G=3) for location, waste streams and retrofitting are multiplied together. The rounded cube root of each score is then calculated to determine the overall score of Red, Amber, or Green. This process is in line with the guidance set out by the JRC for aggregating non-numerical indicators57.
This will result in the lowest score being 1 (i.e. Red in each applicability subcriterion) and the maximum being 27 (i.e. Green in each applicability subcriterion).
Multiplied scores of 1,2 or
Multiplied scores of 18 or 27
= a rounded root value of 3
57 Available at: https://ec.europa.eu/jrc/en/coin/10-step-guide/step-7.
Two red subscores automatically lead to a red overall score, whereas at least two subscores of green and one amber are needed for an overall green score.
The overall applicability score will still be a qualitative indicator, rather than a quantitative indicator, but gives a good idea of how much of the actual market can be affected by the energy efficiency gain delivered by a given technique. The most relevant techniques today will be those that can be implemented in existing installations, without geographical limitations and for an important fraction of waste materials. The subscoring for applicability (Location / Waste streams / Retrofittability) is provided in detail within Annex 5 for each technique.
4.2.1.3 Energy input required for the production of Solid Recovered Fuel (SRF)
In order to be able to compare different WtE techniques objectively, it is necessary to take into account the energy input required to pretreat the waste, where pretreatment is necessary. There are different levels of pretreatment, ranging from simple metals removal and shredding (which has a very small effect on process electrical efficiency) to the production of SRF which requires significantly more effort and should be taken into account. Processes which require SRF include cement and lime kilns, many forms of co-incineration in large combustion plants and some advanced conversion technologies.
SRF is a high-quality recovered fuel with a CV of around 20.2MJ/kg58 (which equals 5,611kWh of energy per tonne) when derived from MSW; this is due to the significant contribution of paper, cardboard and plastics. Nasrullah also calculated that, to produce 1 tonne of SRF from MSW, the ‘in plant’ energy input was 97kWh (where ‘in plant’ energy is the energy required for the sorting process). Therefore the percentage of the total energy input taken up by the pretreatment (in plant) process is calculated as 1.7%.
The ‘out plant’ energy is more significant than the ‘in plant’ energy input and refers to waste collection and transportation etc. but, as this applies equally to any waste treatment process, this element is not considered.
Another aspect which impacts total energy recovery is the energy content of material lost during the SRF sorting process, i.e. material which is not suitable for inclusion within the tight specification of an SRF product (which, for example, requires halogens such as chlorine to be strictly limited to ensure the IED compliance of the CL plant).
Nasrullah estimates that this equates to 15% of the energy content of the waste, with 8% lost to rejects and 6% to the fine fraction. A high mass fraction of rubber material, plastic (PVC plastic) and inert elements (stone/rock and glass particles) was found in the reject material stream. Although the halogenated elements of this reject fraction are high in energy, the inert elements have no energy value and are generally best excluded from most WtE processes.
As such, the lost fraction (15% of the waste energy content) may be of more significance than the energy directly consumed in the SRF production process (1.7%
of the waste energy content).
4.2.1.4 Other considerations
In addition to the two rated criteria, for each technique further comment is provided on:
Exclusion criteria – the technique could be excluded for further consideration if it causes possible conflicts with the waste hierarchy, has a negative effect on emissions or for other specific reasons.
Technology Readiness Level – each technique is rated for Technology Readiness Level as described in Section 4.2.2 below.
4.2.2 Approach and Technology Readiness Level
Where possible, each technique and system has been assigned a Technology Readiness Level (TRL) as shown below in Table 2.50. The TRL indicates how close the technique is to commercial deployment, and this has been recorded in the scoring notes for each technique. A technique with a high TRL should have low residual risks and good availability of operational data. Many highly innovative techniques have a low TRL and there is likely to be very little operational data available.
Table 2.50: Technology Readiness Level Technology
Readiness Level Description
1 Basic principles observed and reported
2 Technology concept and/or application formulated
3 Analytical and experimental critical function and/or proof of concept 4 Basic validation of technology in laboratory environment
5
Basic validation technology in a laboratory environment, where basic technological components are integrated together with realistic supporting elements
6 Technology model or prototype demonstration verified in a relevant environment
7 Technology prototype demonstrated in an operational environment
8 Actual technology completed and qualified through testing and demonstration
9 Actual technology qualified through successful commercial operation 9 + More than one commercial-scale plant and over five years' operational
experience