Sampling,characterisation and processing of solid recovered fuel production from municipal solid waste: An Italian plant case study

Abstract

This article presents the classification of solid recovered fuel from the Massafra municipal solid waste treatment plant in Southern Italy in compliancy with the EN 15359 standard. In order to ensure the reproducibility of this study, the characterisation methods of waste input and output flow, the mechanical biological treatment line scheme and its main parameters for each stage of the processing chain are presented in details, together with the research results in terms of mass balance and derived fuel properties. Under this study, only 31% of refused municipal solid waste input stream from mechanical biological line was recovered as solid recovered fuel with a net heating value (NC=HV) average of 15.77 MJ kg⁻¹; chlorine content average of 0.06% on a dry basis; median of mercury <0.0064 mg MJ⁻¹ and 80th percentile <0.0068 mg MJ⁻¹. The solid recovered fuel produced meets the European Union standard requirements and can be classified with the class code: Net heating value (3); chlorine (1); mercury (1).

Keywords

Mechanical biological treatment municipal solid waste separate collection refused derived fuel solid recovered fuel

Introduction

The growth of energy prices and the unfavourable forecast of world economic crisis have significantly increased stakeholders’ interest in the energetic valorisation of waste. The European Union (EU) provides specific regulations for waste management, generally defining targets for its recycling and recovery. According to the EU Waste Framework Directive aimed at an overall landfill waste reduction by 2020, the current target is reaching 50% in recycling, composting, thermal-treatment or reuse of the total amount of municipal solid waste (MSW) generated. For mixed waste treatment, there are still technological, economic and social impediments, especially for its recycling or composting (Ciuta et al., 2015; Ionescu et al., 2013, 2015; Rada et al., 2014a, 2014b; Zhou et al., 2015). As already demonstrated in the literature (Ciudin et al., 2014; Consonni and Viganò, 2011; Ranieri et al., 2014a, 2014b; Rovetta et al., 2009), the efficiency of MSW separate collection (SC) plays an important role in potential waste recovery by reducing the refused municipal solid waste (RMSW) stream and increasing its heating value. Depending on its properties, RMSW can be subject to an advanced mechanical and biological treatment and classified as refused derived fuel (RDF) or solid recovered fuel (SRF), a sustainable alternative, a shift from landfilling towards waste for energy recovery. By comparison with fossil fuels, this renewable material is significantly beneficial in terms of its utilisation as an alternative energy source, incorporating a high fraction of biogenic matter, which is considered as carbon dioxide (CO₂)-neutral, thereby reducing the total global inventory of greenhouse gas emissions (Cioca et al., 2015; Kim et al., 2013; Petrella et al., 2013; Ragazzi et al., 2017; Ranieri and Gikas, 2014; Ranieri and Swietlik, 2010; Séverin et al., 2010; Van Lienden et al., 2010).

In this context, mechanical biological treatment (MBT) and co-combustion are seen as useful processes to comply with the EU requirements. After years of research and trials, under this study, science meets practice. The survey presented in this article focuses on the pathways used and the crossover of RDF (EWC Code 191210) to SRF (UNI EN 15359:2011) from the Massafra MSW treatment plant located in Southern Italy.

Materials and methods

Waste stream and determination of residual MSW composition

This case study concerns three municipalities (study area) within the regional territory of Puglia in Southern Italy, where the RDF/SRF production line is located. The average annual production of MSW in the study area has risen to 1,895,753 t y⁻¹ (approximately 474 kg cap⁻¹ year⁻¹) with a medium composition as presented in Figure 1 (PR-MSW, 2014). The SC rate has increased in recent years, reaching 27.56% in 2013. Paper, cardboard, glass, plastic, wood, metal, textile, organic and mixed packaging waste (multimaterials), waste electrical and electronic equipment (WEEE) and street wastes (garden waste, public bins, etc.) are separately collected.

Three samples, coming from different areas within the region, were used to determine the RMSW stream composition that was sent to the waste treatment plant for derived fuel production. The samples were collected from three vehicles that gather unsorted MSW from different areas (Massafra, Taranto and Castellaneta), which supply the treatment plant with RMSW. In these three areas, the MSW generation annual average only represents 7.4% of the total MSW production of the entire region. In these areas the average SC rate reaches up to 10%.

Each sample underwent separation by waste fraction. At the beginning, each sample analysed was weighted using a digital MICRON LINE ATHENA mod. MKW 150, which can support up to 150 kg (±10 g). The undersized materials were separated by first using a plastic grate with a 2 cm mesh and manually sorted. After the separation, individual product fractions were taken as samples for laboratory analysis.

The moisture content by type of RSMW fraction was determined according to ASTM standard method E 871-82 (ASTM, 2013). The samples were placed in open trays, in an oven at 105 ºC for 24 h in order to ensure complete moisture loss. At the end of the process, the samples were cooled in desiccators at room temperature. After reaching room temperature, the samples were immediately weighed in order to avoid moisture gain from the atmosphere, subsequently assessing the total calorific value on the dried.

Plant and process description

The plant under study is owned by CISA S.p.A and it is able to process 220,000 t y⁻¹ of RMSW coming from surrounding municipalities. The plant is located in Southern Italy, near the town of Massafra (Taranto, Puglia).

The following paragraphs detail the phases and treatments used for RDF production (Spinosa and Carella, 2011).

Reception area

The RMSW is downloaded in the ‘reception area’ of the plant. The building is encapsulated, thanks to a lower pressure system preventing emissions from escaping. The reception area is also the place for the first rough manual routine visual inspection of waste loads, which takes place before their mechanical and biological treatment.

Primary shredding and iron removal

The first step of the process is the ‘bag opener’, by means of a 50 t h⁻¹ slow-speed shredder fitted with a hydraulic control. During this phase, a magnetic separator in the head of the conveyor belt used for shredded material discharging, already eliminates ferrous materials content in the waste, which is then sent for recycling. The shredded waste is then transferred to storage boxes and moved into the bio-stabilisation tunnels with the aid of a wheel loader.

Bio-stabilisation

Bio-stabilisation takes place in large tunnels that are filled and hermetically closed. Here waste is activated by micro-organisms, such as bacteria, yeasts and moulds, under aerobic conditions, a process of degradation of organic matter present included in the RMSW stream. The resulting product is a sanitised and stabilised material and therefore has a dynamic respirometric index of less than or equal to 800 mg O₂/kg_VS*h. Bio-stabilisation plays a fundamental role in waste-derived fuel production. During the process air/oxygen, temperature and humidity are monitored.

RDF production

The bio-stabilised material obtained is sent to the RDF production line, which is equipped with:

a sieve disc;

a hydraulic separator;

two secondary single rotor shredders at low speed of rotation;

a magnetic separator and two flat paralleled extruders.

Flue gas cleaning system

The equipment used for the RDF production is monitored for possible dust formation. Dust is collected by means of an exhausted air suction system and, if need be, sent to an air treatment system.

Air bio-filtration

The saturated air from the bio-stabilisation process is humidified and sent to a bio-filtration system in order to be purified before its emission into the atmosphere. RMSW under this study underwent advance mechanical and biological treatment for RDF production, as presented in Figure 2. The 13 bio-tunnels installed at the plant in Massafra are made of reinforced concrete and equipped for blowing air into the material in order to guarantee the uniformity of the aerobic treatment – which runs longitudinally along the floor. Under this study, the treatment air flow was higher than 40 m³ h⁻¹ t_waste⁻¹, so the total time of treatment could be conveniently reduced. In order to ensure the hygienisation cycle, the temperature is controlled by varying the air supplied in the process, which for this study was continuously higher than 55 ºC for at least 3 days. After hygienisation, temperature is maintained at about 50 ºC, which is favourable for the development of microflora and micetes working on organic substance degradation. Furthermore, the optimal humidity level must be ensured during the aerobic process, which depends on the composition and the aeration degree of the material. The bio-stabilised material then undergoes a mechanical treatment line for RDF/SRF. By using the screening process, dry waste fuel (DWF) is produced and destined to RDF/SRF production. The DWF product (oversized) is then deprived of its heavy fraction and any ferrous impurities possibly still present, through the passage in a hydraulic separator first and then through and a magnetic separator (only ferrous metals). Subsequently, the material is finely ground and thickened to reach the correct size and moisture. The conveyor belt of an automatic loading system transports the RDF/SRF obtained into the electricity production plant. As presented in Figure 2, further non-recoverable waste from the RMSW pre-treatment line, bio-stabilisation and production of RDF/SRF is sent to landfill.

Waste-derived fuel analysis and sampling methodology

Sampling methodology

In order to analyse a representative sample and determine the input and output process stream properties from the waste-derived fuel production plant, several standards methods were used. The sampling of input and output streams was done in compliancy with UNI EN 15442: 2011 standard. The preparation for the laboratory analysis was performed in compliancy with UNI EN 15443: 2011 standard.

For the classification as SRF, all sampling and analytical stages used for the RDF characterisation were performed in compliancy with the criteria, procedures and methods described hereafter (UNI 9903-14: 1997, UNI 10802: 2004, UNI EN 14899: 2006, UNI EN 15400: 2011, UNI EN 15403: 2011, UNI EN 15408: 2011, UNI EN 15411: 2011, UNI EN ISO 11885: 2009, UNI EN 15414-3: 2011, UNI EN 15415-1: 2011, DIN 51730, 1976).

Determination of SRF classes

The purpose of this study is to characterise and define the waste-derived fuel produced by the plant as RDF or SRF. In the sampling period, the plant was officially producing RDF. In the EU, the classification of fuel from MSW is covered by technical documents, where SRF is divided into 125 SRF classes and mainly depends on key combinations of three properties: Lower Heating Value (LHV), chlorine (Cl) and mercury (Hg) (Rada and Ragazzi, 2014).

At present, the plant is in a transition situation, awaiting the authorisation for the classification of fuel from MSW under the new regulation. In order to classify the main parameters (LHV, mercury, chlorine), the class limit value of the following parameters should be compared with the 95% confidence interval. The UNI EN 15359: 2011 standard defines the classes for each parameter mentioned above. The 95% confidence interval ensures that any samples that are statistical outliers will have less of an impact on the arithmetic mean resulting in a more representative figure. For the calculation of the upper and lower limits of the confidence interval at 95% of the average, the following equation must be used:

X = \bar{X} \pm 1, 96 * \frac{s}{\sqrt{n}}

(1)

where:

- X is the lower/upper limit of the 95% confidence interval of the average arithmetic mean;

- $\bar{X}$ average arithmetic mean of the 10 measurements;

- 1,96 is the functional characteristic of the normal distribution (for the 95% confidence interval);

- s is the standard deviation (based on all the 10 measurements);

- n is the number of measurements (in this case n = 10).

Therefore, in the waste-derived fuel classification, the main parameters considered are as follows.

- LHV: Lower limit value of the 95% confidence interval of arithmetic mean.

- Chlorine: Upper limit value of the 95% confidence interval of arithmetic mean.

- Mercury: The class code for mercury, cadmium and heavy metals are determined using median and 80th percentile and again they represent a conservative approach. This method is used in order to comply with the emission limits imposed so the facility can operate.

The RDF under study can be classified as improved derived fuel, in terms of SRF, if it meets regulation UNI EN 15359: 2011 as presented in Table 1.

Table 1.

SRF classification (UNI EN15359: 2011).

Properties	Statistical measure	Unit	Solid recovered fuel classes
Properties	Statistical measure	Unit	1	2	3	4	5
HHV	Mean	MJ/kg (a.r.)	⩾ 25	⩾ 20	⩾ 15	⩾ 10	⩾ 3
Cl	Mean	% (d.m.)	⩽ 0.2	⩽ 0.6	⩽ 1.0	⩽ 1.5	⩽ 3
Hg	Median	mg/MJ (a.r.)	⩽ 0.02	⩽ 0.03	⩽ 0.08	⩽ 0.15	⩽ 0.50
Hg	80th percentile	mg/MJ (a.r.)	⩽ 0.04	⩽ 0.06	⩽ 0.16	⩽ 0.30	⩽ 1.00

HHV: Higher Heating Value; d.m.: dry matter; a.r.: as received.

Results and discussions

Residual MSW composition

The classification of RMSW and the determination of its composition represent a crucial stage of any integrated municipal solid waste scheme. In the case study presented in this article, three RMSW waste streams were used for the determination of the waste flow input composition that is sent for MBT for derived fuel production. The samples were chosen from three vehicles that collect the unsorted MSW from different areas (Massafra (RMSW₁), Taranto (RMSW₂) and Castellaneta (RMSW₃), which supply the treatment plant with RMSW. The amount of each batch was approximately 150 kg. The RMSW categorisation by type of waste fraction is described in Table 2. In this study, the RMSW is classified into 13 categories, in order to have a clearer view on the waste treatment chain inputs and outputs. The amount of recyclable packaging waste is split into aluminium, cellulosic and plastic packaging waste. As demonstrated in previous studies carried out by the authors (Ionescu et al., 2013; Ranieri et al., 2014b), the SC rate strongly dictates the RMSW composition and, therefore, the RDF/SRF combustible properties. The latter statement is also confirmed by the slight variation of the weight waste fractions in the areas studied, as shown in Table 2.

Table 2.

RMSW categorisation, by type of fraction in the reported case study.

Waste fraction	Waste fraction details	RMSW₁ (kg)	RMSW₂ (kg)	RMSW₃ (kg)	Total average
Waste fraction	Waste fraction details	RMSW₁ (kg)	RMSW₂ (kg)	RMSW₃ (kg)	(kg)	(%)
Aluminium packaging waste	Rigid, semi-rigid, flexible, poly laminate	0.20	0.50	0.40	1.10	0.2
Cellulosic packaging waste	Solid cardboard, Rippled cardboard, poly laminate	10.56	7.56	8.34	26.46	5.6
Plastic packaging waste	Rigid, flexible, poly laminate	12.16	11.06	10.88	34.10	7.3
Recyclable packaging waste		22.92	19.12	19.62	61.66	13
Steel packaging waste		3.46	2.16	4.00	9.62	2
Wood packaging waste		0.00	0.00	0.00	0.00	0
Glass packaging waste		7.98	6.16	11.42	25.56	5
Others	Cardboard	21.10	19.70	25.30	66.10	14
Others	Plastics	9.62	12.40	8.40	30.42	6
Organic waste	Kitchen waste	55.16	47.38	50.00	152.54	33
Organic waste	Green waste	0.00	2.84	0.00	2.84	1
Textile		9.10	3.08	5.10	17.28	4
Inert		8.18	14.10	9.42	31.70	7
Undersized waste		8.34	12.22	10.68	31.24	7
Other types of waste		13.28	15.32	11.52	40.12	9
Total		159.14	154.48	155.46	469.08	100%

RMSW: refused municipal solid waste.

In Figure 3 the RMSW composition is presented.

Residual MSW moisture and energetic content

The total moisture content of any solid waste is one of the most significant properties, because it impacts on the heating value (energy content) of the material, and it also determines the choice of the waste treatment option and its process parameters.

The RMSW moisture content as received and by type of combustible waste fraction is presented in Figure 4. The variability ranges from 4% for polymers up to 40% for cellulosic, lignocelluloses materials and undersized waste fractions. The total RMSW moisture content is 29.02%.

The average energy content, lower heating value on dry and wet basis, of the RMSW is 13.83 MJ kg⁻¹ and 9.09 MJ kg⁻¹, respectively, as presented in Table 3.

Table 3.

RMSW low heating value.

RMSW waste	RMSW₁ (kJ kg⁻¹)	RMSW₂ (kJ kg⁻¹)	RMSW₃ (kJ kg⁻¹)	LHV average(kJ kg⁻¹)
RMSW waste dried	13,718	13,788	13,998	13,835
RMSW waste wet basis	8637	9127	9530	9098

It can be concluded that the almost 30% of moisture content of the RMSW as received (wet basis) decreases the RMSW energetic potential in dry basis to 65.7%.

RMSW: refused municipal solid waste; LHV: Lower Heating Value.

RMSW processing plant mass balance

The overall mass balance of the RMSW treatment line for RDF/SRF production is presented in Table 4.

Table 4.

RMSW processing plant mass balance.

Type of stream	Quantity
Primary input	(t y⁻¹)	(%)
RMSW stream	160,538.4	100
Unprocessed waste	6384.5	4
Effective input
Waste stream input (bio-stabilisation)	154,153.9	96
Output
Landfilled waste from the bio-stabilisation process	4682.6	3
Landfilled waste from SRF production line (inert)	75,748	49
Wastewater	2742.3	2
Recyclable metals	328	0
Dust from filter sleeves	1.5	0
Processes losses	20,659.5	13
RDF/SRF stream	49,991.7	32

RMSW: refused municipal solid waste; SRF: solid recovered fuel; RDF: refused derived fuel.

Considering the input RMSW composition and properties, the present treatment line scheme and the efficiency of each process stage, it can be concluded that only 31% of the RMSW stream input flow is recovered as RDF/SRF and 0.2% is sent to a recyclable metals facility.

The RDF/SRF composition, presented in Figure 5, is mostly covered by a combustible reliable recovered fraction from the RMSW input stream of 39.21% (cellulosic, wood, plastics). A further undersize fraction of 55.80% represents a mixture of different types of waste.

Waste-derived fuel class

The laboratory analysis of process streams produced in RDF/SRF production plant produced from RMSW are presented in Table 5.

Table 5.

Characterisation of the RDF/SRF samples.

Parameter	Standards methods^a	Concentration determinate										Average	Unit of measurement	Quality limits
Parameter	Standards methods^a	S₁	S₂	S₃	S₄	S₅	S₆	S₇	S₈	S₉	S₁₀		Unit of measurement	Quality limits
Nature	Organoleptic	Mixed	Organic	Organic	Organic	Organic	n.d	n.d	n.d	n.d	n.d	Organic
Physical status	Organoleptic	Solid	Solid	Solid	Solid	Solid	n.d	n.d	n.d	n.d	n.d	Solid
Colour	Organoleptic	Varied	Varied	Varied	Varied	Varied	n.d	n.d	n.d	n.d	n.d	Varied
Odour	Organoleptic	Unpleasent	Unpleasent	Unpleasent	Unpleasent	Unpleasent	n.d	n.d	n.d	n.d	n.d	Unpleasent
LHV	C	23.014	20.388	18.697	19.559	18.794	n.d	n.d	n.d	n.d	n.d	20.0904	MJ kg⁻¹	>15
NCV	C	28.99	28.18	23.28	24.57	23.07	18.80	18.7	19.1	18.8	19.7	22.319	MJ kg⁻¹_d.m.
NCV	C	23.01	24.67	18.70	19.56	18.79	14.78	14.52	15.78	14.80	15.47	18.008	MJ kg⁻¹
Moisture	G	20.64	17.64	19.67	20.39	18.55	21.38	22.33	17.40	21.44	21.48	20.092	g% (m m⁻¹)	25
Glass (quantity)	A	<0.010	<0.010	<0.010	<0.010	<0.010						<0.010	g% (m m⁻¹)
Ash	E	13.15	17.40	13.62	17.21	17.45	17.59	17.20	17.11	18.4		16.57	g% (m m⁻¹) _d.m	20
Ash softening temperature	L	1234	1250	1238	1236	1270						1245.6	ºC
Cl	F	0.013	0.011	0.19	0.012	0.19	0.013	0.010	0.014	0.010	0.010	0.0473	g% (m m⁻¹)	0.9
Br	E	<0.10	<0.10	<0.10	<0.10	<0.10	<0.10	<0.10	<0.10	<0.10	<0.10	<0.10	mg kg⁻¹_d.m.
F	F	<0.010g% (m m⁻¹)	<0.010g% (m m⁻¹)	<0.010g% (m m⁻¹)	<0.010g% (m m⁻¹)	<0.010g% (m m⁻¹)	<0.10mg kg⁻¹_d.m	<0.10mg kg⁻¹_d.m	<0.10mg kg⁻¹_d.m	<0.10	<0.10	<0.10mg kg⁻¹_d.m
S	F	0.012	0.012	0.08	0.015	0.012	0.012	0.013	0.015	0.010	0.013	0.0194	g% (m m⁻¹)	0.6
Sb	G	<0.50	10.5	<0.50	1.37	<0.50	23.2	<0.50	71.6	4.36	69.4	18.043	mg kg⁻¹_d.m.
Al	G	268	711	510	699	2442						926	mg kg⁻¹_d.m.
As	G	<0.50	<0.50	<0.50	<0.50	<0.50	0.54	<0.50	1.06	<0.50	1.15	0.275	mg kg⁻¹_d.m.
Ba	G	12.4	36.0	27.9	50.9	58.4	18.7	39.3	60.3	35.9	51.0	39.08	mg kg⁻¹_d.m.
Be	G	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	mg kg⁻¹_d.m.
Cd	G	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	mg kg⁻¹_d.m.
Cd+Hg	G	<0.30	2.02	<0.30	<0.30	<0.30						<0.30	mg kg⁻¹_d.m.	7
Co	G	<0.50	1.32	<0.50	1.08	<0.50	24.2	<0.50	<0.50	<0.50	<0.50	<0.50	mg kg⁻¹_d.m.
Cr	G	2.79	31.7	5.80	14.1	11.0	2.68	6.12	9.45	7.38	8.20	9.922	mg kg⁻¹_d.m.	100
Fe	G	384	1027	1276	1288	5387	n.d	n.d	n.d	n.d	n.d	1872.4	mg kg⁻¹_d.m.
Mn	G	11.1	36.2	85.8	32.0	80.4	18.4	24.3	30.2	29.0	21.4	36.88	mg kg⁻¹_d.m.	400
Hg	G	<0.10	1.77	<0.10	<0.10	<0.10	<0.10	<0.10	<0.10	<0.10	<0.10	<0.10	mg kg⁻¹_d.m.
Hg	G	<0.0043	0.072	<0.0053	<0.0051	<0.0053	<0.0068	<0.0069	<0.0063	<0.0068		0.0052	mg MJ⁻¹
Mo	G	0.35	1.09	<0.50	5.17	<0.50	<0.50	<0.50	<0.50	1.11	<0.50	<0.50	mg kg⁻¹_d.m.
Ni	G	1.53	3.24	3.87	4.16	2.67	1.12	2.07	2.14	3.72	1.30	2.582	mg kg⁻¹_d.m.	40
Pb (volatile)	G	<0.50	<0.50	<0.50	<0.50	<0.50						<0.50	mg kg⁻¹_d.m.	200
Pb	G	25.9	61.1	36.2	937	107	25.9	166	161	342	121	198.31	mg kg⁻¹_d.m.
Cu (soluble compost)	G	11.4	32.3	26.8	40.0	39.9						30.08	mg kg⁻¹_d.m.	300
Cu	G	14.4	32.3	26.8	40.0	39.9	15.8	32.5	142	44.5	130	51.82	mg kg⁻¹_d.m.
Sn	G	0.30	0.95	<0.50	1.18	<0.50						0.243	mg kg⁻¹_d.m.
Se	G	0.65	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	mg kg⁻¹_d.m.
Tl	G	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	<0.50	mg kg⁻¹_d.m.
V	G	0.25	1.32	<0.50	0.97	1.66	0.61	<0.50	<0.50	0.88	<0.50	0.569	mg kg⁻¹_d.m.
Zn	G	41.6	80.6	255	100.0	307	39.0	99.7	76.6	70.9	<0.50	107.04	mg kg⁻¹_d.m.
Sb+As+Pb+Cr+Co+Cu+Mn+Ni+V	Computation	58	178	160	1031	244	112	231	417	432	352	321.5	mg kg⁻¹_d.m.
Size distribution – Fraction passing the sieve
200 mm	I	0.61	0.71	1.01	0.84	0.59	0.64	0.77	0.76	0.82	0.64	0.7	%
125 mm	I	5.41	5.87	8.36	4.12	4.89	6.59	5.44	11.92	11.50	6.59	7.1	%
100 mm	I	6.92	8.47	33.72	7.12	8.94	8.47	9.54	26.83	25.98	8.47	14.4	%
50 mm	I	2.21	4.59	1.57	4.88	6.79	4.59	5.94	4.76	5.21	4.59	4.5	%
25 mm	I	2.14	2.87	11.52	4.01	4.51	2.48	2.22	2.37	3.44	2.48	3.8	%
12.5 mm	I	2.27	2.00	18.53	1.81	2.19	1.44	1.18	30.64	31.06	1.40	9.3	%
6.3 mm	I	0.92	0.84	12.05	0.79	0.89	0.58	0.69	9.43	8.41	0.62	3.5	%
3.15 mm	I	31.60	30.58	3.19	32.49	31.49	31.44	32.15	1.26	1.20	31.44	22.7	%
1.6 mm	I	1.72	1.21	5.06	1.59	1.51	1.12	1.29	1.69	1.77	1.12	1.8	%
800 µm	I	12.59	12.66	0.67	11.49	11.25	11.08	11.32	3.23	2.29	11.08	8.8	%
400 µm	I	19.52	16.29	1.30	19.29	14.29	17.51	15.99	2.04	1.45	17.51	12.5	%
200 µm	I	14.09	13.91	3.02	11.57	12.66	14.06	13.47	5.07	6.87	14.06	10.9	%

Standards: A. UNI 9903-14: 1997; B. UNI 10802: 2004; C. UNI EN 14899: 2006; D. UNI EN 15400: 2011; E. UNI EN 15403: 2011; F. UNI EN 15408: 2011; G. UNI EN 15411: 2011 Method C+ UNI EN ISO 11885: 2009; H. UNI EN 15414-3: 2011; I. UNI EN 15415-1: 2011; J. UNI EN 15442: 2011; K. UNI EN 15443: 2011; L. DIN 51730.

d: ; LHV: ; NCV: net calorific value; d.m.: dry matter.

Looking at the results obtained from the application of the criteria for the determination and classification of SRF, set out in the UNI EN 15359: 2011 standard, it can be can concluded that the classification of the SRF is characterised by:

net calorific value average of 15.77 MJ kg⁻¹;

chlorine (Cl) content average of 0.06% on a dry basis;

median of mercury (Hg) <0.0064 mg MJ⁻¹ and 80th percentile <0.0068 mg MJ⁻¹ and the following – Class code: NHV3; Cl 1; Hg 1.

Therefore, the waste-derived fuel meets the requirements established by the standards and can be categorised as a waste-derived fuel in terms of SRF.

Owing to the MBT line, the average SRF moisture content reaches up to 20%, from 30% of the RMSW wet basis input flow. The 10% drop of the moisture content offers a notable advantage during the combustion process by a lower content of the water vapour fraction in the flue gas, as the dew point of the flue gas is 36 °C–40 °C, where the latent heat of water vapour is difficult to recover.

Owing to the bio-stabilisation process and non-combustible waste removal, the energetic potential reports an increase by 58% in wet basis, compared with the RMSW input flow. The average calorific value obtained is similar to the results reported in other studies that have similar solid waste input flow composition and an MBT treatment line or computational simulations in: Turkey 14.360 MJ kg_RDF⁻¹ (Kara, 2012), Canada 15.84 MJ kg_RDF⁻¹ (Reze et al., 2013) or Greece 14.78 MJ kg_SDF⁻¹ (Agraniotis et al., 2010). Moreover, Wagland et al. (2011) compared the performance of SRF and RDF for energy production purposes. They concluded that the use of a coal and SRF fuel mixture in fluidised bed reactor releases less emissions compared with a coal and RDF mixture.

In combined heat and power (CHP) plants, the use of SRF is a challenging task, owing to their heterogeneous nature and their wide particle size distribution. In our case study, the SRF size distribution varies between 200 µm up to 125 mm. The particle size distribution dictates the main SRF to energy process parameters: Design of the power plant, type of reactor, temperature control, flexibility of the thermal conversion process choice (pyrolysis, gasification or combustion), process agent (air,O₂, inert, H₂O), residence time, heating rate or by-products formation. Lacking a CHP plant, according to Samolada and Zabaniotou (2014), the application of a SWOT (strengths, weaknesses, opportunities, threats) analysis proved the benefits of using SRF in cement kilns compared with the construction of new combustion plants for electricity production.

Conclusions

This article presents the production of SRF from a RMSW treatment plant located in Southern Italy. In order to ensure the reproducibility of this study, sampling and characterisation methods of waste input and output flow, the MBT line scheme and its main parameters for each stage of the chain are presented in detail, together with the research results in terms of mass balance and derived fuel properties. According to the results obtained on RMSW composition, as expected, organic waste was the most predominant fraction, with a value of 33.11%, a RMSW total moisture content of 29.02% and an energetic potential of 13.83 MJ kg_{dry basis}⁻¹. Under this study, only 31% of the RMSW input stream from the MBT line was recovered as SRF, and 0.2% sent to a recyclable metals facility. The SRF produced meets the EU standard requirements and can be classified with the class code: NHV3; Cl 1; Hg 1.

A further publication is planned to describe the SRF usage in the existing power generation facility considering the energy and environmental complete balance.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work has been partly funded by University Politehnica of Bucharest, through the ‘Excellence Research Grants’ Program, UPB – GEX. Identifier: UPB–EXCELENȚĂ–2016, Research project title Asigurarea alimentării cu energie în regim continuu printr-un Sistem hibrid Integrat cu utilizarea Deșeurilor cu potențial energetic, surselor Eolione și Fotovoltaice [Continuous power supply through an integrated hybrid system using wastes with high energetic content, photovoltaic and wind energy], Contract number: 90/26.09.2016 (acronym:SIDEF).

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