SUMMARY OF WORK SINCE THE START OF THE PROJECT UNTIL NOVEMBER 30, 2014
This report summarizes the actions B1-B2-B3-B4-B5-B6-B7, and C1-C2-D1-D2 that have been developed over the period considered.
With reference to the following description, are explained some definitions used in the text of the report:
BACKSHEET: the photovoltaic panel behind the surface exposed to the sun and consists of plastic material in polyester or chlorinated or fluorinated compounds.
SANDWICH: is the set of glass + backsheet + eva + wafer of silicon metal.
SILICON WAFER: is the heart of the photovoltaic panel that converts sunlight into electricity.
PLOT: series of connectors generally in aluminum that connect the various wafers to bring the generated current to the connector of the panel.
WARP: number of connections perpendicular to the plot, on the surface of the wafer exposed to the sun, which generally consist of a glass frit containing silver.
RA: expected results
IP: progress indicators
It’s the action carried out by the partner PV CYCLE who oversaw the procurement of samples of panels used for the characterization of the same and for testing the process in subsequent actions.
IM/1: due to the variability of the panels characterized by PV Cycle will get an additional sample to have more data for the comparison.
OB/1: procure the panels at the beginning and then the sample panels for tests on prototypes developed during the project.
RA/1: to provide 20 panels 1 x 1,67 m sufficiently diversified to have average data of composition to be used in the actions B2-B3-B4-B5.
IP/1: supply of panels for characterization took place October 15, 2013 and for testing expected by December 2015.
The action was developed by SSV and consisted of the complete characterization of the sample panels received by PV CYCLE.
Based on these results, Sasil began the work of development of various process technologies provided by the project.
IM/2: the quality of the panels is variable depending in particular on the quality of the backsheet, which may contain chlorinated and fluorinated plastics that require a different approach in the pyrolysis phase.
OB/2: fully characterize the various panels and in particular to determine the metals present in the wafer to modulate the actions of acid attack and pyrolysis.
RA/2: provide useful indications on the most suitable technology for the recovery of the various components that constitute the photovoltaic panel.
IP/2: the close cooperation between Sasil and SSV has allowed a remarkable synergy that has allowed to proceed according to the flow chart provided by the project and to have immediately useful results to Sasil to optimize the subsequent actions of its competence.
The problem of the separation of the glass from the sandwich was solved brilliantly by Sasil with a method that has been the subject of patent application filed in September 2014. This system plans to remove the glass from the sandwich in a qualitative way with a progression of 1 cm per second.
The pre-prototype is able to process strips of the panel (obviously devoid of aluminum profiles and the connector) of the width of 250 mm, equal to ¼ of the total width of the panel.
It has been tested and is still being optimized, in particular in relation to the quality of the backsheet, the variability of which required an additional modulation on the positioning of the source of infrared, not initially provided by the patent.
It is during the optimization phase, the system for continuous bonding of the panels, prior to insertion in the detachment device, so as to give continuity to the system.
The final prototype will be sized to handle continuously about 22 panels/hour, the standard size of 1000 x 1660 mm.
The heat treatment preliminary to the detachment was made with a mixed system for medium and short wave infrared, assisted by a maintenance phase with diathermic oil.
The separation occurs by means of a device with a high frequency knife button and modulated in amplitude and speed.
On the glass recovered in the millimeter size was noted at times the presence of the organic black parts, due to the adhesion to the glass of the seals on the edge of the panel.
Furthermore, on the fine fractions of glass, less than a millimeter, however constituents only 5% of the stemmed glass, has occurred the incidental presence of silicon metal coming from the silicon wafer.
To overcome these two drawbacks, Sasil adopted a unique technology of optical treatment, after a sieving to 1 mm. Practically a channel of optical separator treats the fraction> 1 mm containing organic compounds, and a channel treats separately the fraction <1 mm to remove residual silicon metal from the glass.
IM/3: the greater difficulty involved the search of the optimal thermal system that would allow a temperature differential between “EVA” and glass, flaking, and this was done through a detailed analysis of the behavior in curing of the heated EVA, so as to ensure a margin of work sufficiently wide to allow the detachment at temperatures close to the temperature of crosslinking without reaching the same cross-linking.
This work was developed brilliantly by SSV.
The choice of infrared system was made after evaluating the option laser and microwave, with the advice of CNA respectively of Sesto Fiorentino and of the University of Rome Tor Vergata.
RA/3: the solution of the pre-prototype, including the section of optical separation, allowed to remove any unknown for the actual design of the prototype that is in an advanced stage of selection.
– Achievement of 97% of recovery of pure glass;
– Power consumption less than 50 kWh/t of the panel;
– Excellent level of homogeneity and particle size of the recovered glass;
– Very low level of emissions on warming phase and within the limits of the law; in any case, such emissions test will be repeated once developed the system of heat sealing of the panels prior to insertion into the car behind.
– Prototype in definitive design phase according to the operational directions of the pre-prototype.
This action has been carried out by Sasil and SSV according to a similar pattern, ie with pyrolysis treatment in batches, but with use of different gases (argon for SSV, nitrogen for SASIL).
The temperature conditions were the same even if it is seen that, according to analysis thermo-ponderal, already at 450 °C all organic compounds pyrolise completely.
As it was not possible to do is to obtain significant results on the quality of fuels obtained as the instrumentation provided for the analysis will be available at the SSV only in January 2015. In any case, the pyrolysis has provided the ashes sufficient, from the point of view of quality and quantity, for the subsequent acid etching process, object of the action 5.
Before the process of acid leaching (Action B5) the ashes were milled and screened under 0,5 mm obtaining residue subgrid free from metal particles, and a overscreen consisting predominantly of particles of aluminum and other metal conductors.
In fact, the advantage of this process is to break the silicon metal, which is very fragile, and leave intact the metals, which are elastic and with a particular grinding technique for compression tend to flatten and not to break, thereby enhancing their recovery by sieving .
With regard to the analysis of plastics from pyrolyze (polyester, Tedlar, PVC) as constituents of the backsheet, the data so far available on the 20 types of panels have provided a frequency of about 30% of fluorinated plastic and/or chlorinated on the total of panels examined.
This is an aspect that should be investigated further as it will be a decision about the treatment of the panels with the presence of chlorinated or fluorinated plastic as you can choose two options:
A- treat the sandwich before the pyrolysis, with a technology patented by an Italian company who has already made some tests with positive results with the goal of separating the organic solvent in the autoclave, the backsheet from the rest of the sandwich, so sent for disposal fluorinated or chlorinated plastics. This is to avoid sending in pyrolysis chlorine and/or fluorine (note that the weight of the backsheet accounts for only 1,5% of the total weight of the panel).
B- Studying, downstream of the pyrolysis, a system that inerted the fluorinated and/or chlorinated compounds that are generated in phase induced heating, in order to knock them down as fly ash, with a scrubbing at the end of the process of condensation of the fuel generated by the process of thermal cracking in an inert environment.
RA/4: from laboratory tests showed that the pyrolysis at 600°C is able to completely demolish the organic compounds present in the sandwich and not to produce carbon residues on the residual ashes, formed only from silicon metal, glass and metals. Therefore are evaluating the most effective system for use in the discontinuous pyrolyzer present in Sasil, and that choice will be made in March 2015 based on the results of the analysis that will SSV fuels recovered from pyrolysis.
IP/4: the quality of the residual ash has already been judged as optimal as a function of the subsequent step of acid attack hot and electrolysis.
This action has been divided into two sections:
– section of acid attack;
– electrolysis section.
The acid etching was conducted with different modes and different topologies of acids and bases but in the end the best results are obtained with nitric acid.
This choice was carefully evaluated also in function of the environmental impact because of the main drawback of this technology is that, however, we must eventually neutralize a residual acid polluted in part by metals.
However we have already achieved an environmentally sustainable because, by means of the killing with calcium hydroxide, is possible to obtain a calcium nitrate that, for the low content of residual metals may still be used in agriculture as a nitrogen fertilizer.
In any case, this aspect is still being in analytic investigation phase because the electrolysis process that generates acid residues to be salified is still under development and will be completely defined by the month of March 2015. Thus, even the environment appearance will be further investigated.
RA/5: through a first acid leaching is possible to obtain a good quality of metal silicon as residue of acid solubilization of ashes. This quality can be further improved through a basic attack with KOH that dissolves any residue from the oxidation of silicon.
The final choice of whether or not this additional operation depends on the market value of more or less pure silicon and this market survey is being developed on the basis of samples significant that we are producing with experimental tests on large quantities.
IP/5: indicators for the quantity and quality of silicon recovered from the leaching of metals recovered by electrolysis and fertilizer from salification acid residues were positive both in terms of energy consumption and environmental impact, and value of the end products .
An important issue that we have yet to investigate is the recovery of the residual glass present together with the metal silicon as filtered of the acid and alkaline attack, or acid attack alone, for which we are still evaluating gravimetric, centrifugal and chemical-physical systems.
– the recovery of the metal silicon is total (no problems of oxidation to SiO2);
– the silver recovery is total at the cathode of the electrolysis;
– the recovery of lead and copper is total at the cathode together with the silver;
– the recovery of aluminum is partial to the cathode because a part remains in solution and is then salified with calcium hydroxide but without incompatibility problems as fertilizer.
Since at the cathode of spongy graphite will be present different metals in minor amounts compared to silver, it will do so to orient the electrolysis in a way as to leave in solution those metals which do not give problems in the residual nitrate salts, and to retain at the cathode the heavy metals which may still be selectively removed by melting at different temperatures in the final process of recovery of the metals contained in the spongy cathode of graphite.
The design of the robot system for the separation of aluminum profiles and the connector is already well under way and does not reserve any problems because it uses standard robots, adapted to the particular function required.
The design of the prototype for the system of separation of the glass from the sandwich is in an advanced planning stage, based on the experience made on the pre-prototype already in operation for months.
The only problem yet to be determined is the bonding system of the panels once released from aluminum and the connector, to insert in the apparatus of detachment of glass from EVA which needs continuity of operation.
At first it seemed that the simple drawing of a tape on the two edges of the sandwich (backsheet side) was enough but then it is seen that, in phase of continuity of the process, the heat reached of the backsheet causes the detachment of the junction in the point dedicated to the inclusion in the apparatus of detachment at knife button.
It’s already found alternative means of a heat sealing tape itself but we are evaluating with a producer of backsheet the material type best suited to speed the operation automatically and avoid delays in the ongoing process, which would lead to discontinuities in the production of sandwich to start at pyrolysis.
The monitoring of the environmental impact is constantly followed by both Sasil that SSV and is based on that monitoring that we make the design decisions to be taken in the development of the prototypes that need to perform the functions required of the various actions.
The LCA study is done jointly by SSV and SASIL with free advice of ISPRA, Research Institute for Environmental Protection, which, being very interested in the development of this project, entered it as a reference project among the various options with the recovery of photovoltaics.
A first draft of the environmental impact assessment has already been completed on the basis of the results from the various actions carried out so far and, by January 2015, will be updated in line with subsequent tests to be carried out.
As regards the general Dissemination, SSV has prepared a mailing list to send the newsletter (at the time, one for the month of June and one for October).
With regard to international conferences, this year there have been two important conferences simultaneously on 23 September to which Sasil and SSV participated by presenting the project FRELP:
- 29th Conference on Solar Energy and Photovoltaic (EU PVSEC 2014) at Amsterdam in the section “PV life cycle management & recycling”;
- 12th ESG (European Society of Glass) Conference, at Parma.
Both have attracted much interest because, in the recovery of the panels with silicon technology, there are currently no active treatment processes at industrial level; also at the level of research is still in the recovery phase little selective for the enhancement of the individual components.
SASIL has prepared a NOTICE BOARD with the description of the project (objectives, actions and results) and a TECHNICAL SCHEME precisely with the outline of the project.
SASIL also updated regularly on his website a special page devoted to the project FRELP (http://www.sasil-life.com/index.php?option=com_content&view=article&id=85&Itemid=83&lang=it) and preparing two sections: one dedicated to the technical advances of the project and one to download newsletters, press releases and presentations of the conference.
In order to come to meet the request of the Commission to improve the site and given the technical limitations of its current location by the end of the year will be built a website specifically dedicated only to the FRELP project, made over to the SASIL website that enclosed already updates and sections of FRELP.