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The project has demonstrated results above expectations concerning different aspects and all the expected results have been achieved.
The Technology Assessment (Action 4), developed to assess the prototypes, has proven the effectiveness of SFE and SCWO processes under real conditions by the treatment of selected contaminated sediment samples.
At the beginning, a comprehensive testing plan describing each step and including all parameters that require evaluation (as temperature, pressure, energy consumption, emission, etc.) has been planned, in particular the areas in which have been developed the principal procedures were:
1) Selection, collection and chemical characterization of contaminated samples;
2) Starting run and blank test of the two prototypes;
3) Process optimization of the integrated system.
The SFE and SCWO pilot plants, because of their high level of innovation and the absence of other similar plants, have required a meticulous start-up procedures in order to verify the hold of the reactors and the endurance and pressure tight of the individual parts (pipes, joints, valves, gaskets, etc.). The application of ”starting run” testing, through which all the functionalities of the systems have been verified, and the application of ”blank” testing, in which controlled inert samples (made of demineralized water and sand) have been used to evaluate the load capacity, temperatures and pressures reachable in the reactors, have been crucial to attest the functionality of systems and alarm sensors and to pass at the subsequent tests with real contaminated samples.
The data analysis of the contamination of the Venice Industrial Harbor area (regarding both soil and sediment) has pointed out that the most representative pollutants in sediments are primarily PAHs, which reach very high concentrations. Therefore it was disposed to collect samples with these contaminants and use them to realized homogenized “ad hoc” samples of desired concentration levels of PAHs.
SFE experimentation test results
Regarding the extraction phase with the SFE pilot plant, 8 different trials have been performed with samples of about 2,5 kg with contamination levels relative at class “over C”. This Class of sediment has been chosen since it necessary required to be disposed in landfill or treated as stated by the Protocol regarding “Environmental safety criteria for the excavation, transport and reuse operation of sediment dredged from the canals of Venice” emanated in 1993. Starting from a collected sample with very high concentration of PAHs, two types of homogenized samples have been obtained in laboratory, Sample 1with about 50 mg/Kg d.w. and Sample 2 with 75 mg/Kg d.w. of PAHs, so respectively about 2 and 4 times the concentration limit of class “C“ (20 mg/Kg d.w.).
At the beginning, the extraction phase was executed for 90 minutes, after some tests it was decided to take only 60 minutes for each extraction, thanks to the good results obtained by the first group of tests. As shown in the Table 1, the high percentages of reduction were obtained in both 90 and 60 minutes tests, so we can assume that it is possible to obtain the desired results (90% of abatement of organic compounds) in shorter kinetics of 30-40 minutes.
The graphs in Figure 1 illustrate the results achieved: starting from a sediment in class “over C” through the super critic fluid extraction it is possible to obtain a sediment in class “A”, this type of sediment can be reused directly for the restoration of the typical sandbanks called “barene” into the Venice Lagoon.
The analysis of the extracted liquids have been performed each 15 minutes in order to verify their concentration of pollutants. In the graph below is shown an example of the concentration (µg/L) found on the extracts achieved in the second test with the Sample 2.
This results are particularly of interest because one of the more complex issues on the sediment and other contaminated matrices treatment is the water content reduction which presents technological complications and an elevate energy requirement, that made drying particularly expensive. Indeed, many different treatment technologies on market and also the landfill disposal, require dried material or low humidity content of the waste. The fine fraction and the presence of clay, silt and colloidal composts in sediments makes dehydration complex and expensive. Instead, the SFE process has the enormous advantage to not require that pretreatment.
SCWO experimentation test results
Regarding the oxidation phase with the SCWO pilot plant, two trials have been performed with concentrated liquid obtained by all the different extractions realized with the SFE plant in order to verify the integrated system. Since the “blank” testing have highlighted that was necessary, to stoke the hydrothermal flame, oxidase an extract with a minimum concentration of organic substances around the 7%, concentrated samples by the extracts obtained during the SFE phase (with a concentration of around 68 g/L) has been used for the oxidation tests lasted around 50 minutes. The results of the liquid obtained after the oxidation, see Table 2, demonstrate the high efficiency of the process which can destroy the 99.9% of the contaminants. The liquid can be easily discharged in the civil sewage after only a correction of its pH.
Finally, in the second trial, also the gasses generated during the oxidation have been sampled and analyzed to demonstrate the good performance of the SCWO. As shown in the Table 3, the oxidation, obtained with the contaminated extract, appears to be enhanced compared with that obtained with the specific alcohol at the beginning used to stoke the flame. This is proven by the lower concentration of O2 and CO and the higher level of CO2. Also the undesirable substances as PCDD/PCDF were analyzed to confirm that their formation does not occur during the oxidation as the results in the table below confirm which are compared with the emission limits of a generic plant (Dlgs 152/2006).
These encouraging results lead to candidate the SCWO plant as an very attractive treatment solution for countless types of contaminated liquids with high concentration levels.
As above reported, all the expect outputs has been achieved, in particular:
the extraction efficiency has been higher than 90% (SFE) and over 90 % of efficiency in oxidation (SCWO) of target organic compounds;
the pilot plants are expected to have kinetic rates of extraction and oxidation of the target organic compound in the order of 60’;
the end-products generated (solid, liquid and gaseous) are easily managed and discharged without further treatment.
Finally, it has been possible to verify that these processes can be realized with compact equipment, easy to transport and to install in the intervention sites. Some aspects still require improvements such as the energy recovery of the heat produced by the oxidation, phase that can turn this process in an energetically self-sufficient plant.
River and marine sediments play a fundamental role in the protection of the ecosystems belonging to a large portion of European territory. Every year in the EU around 200 million cubic meters of sediments are dug out: of these, 15 to 20 % are contaminated by organic compounds (PAHs, PCB, pesticides, etc.) and/or by heavy metals.
Research in the field of environmentally sustainable and compatible, above all rapid, technological solutions for the reclamation of soil and sediments has led to the experimentation of solutions of the biotechnological and physical-chemical type, often integrated together.
Green Site Project is a 30 months long running (October 2011 – December 2013) project aiming at demonstrating the effectiveness of innovative technologies for the reclamation of sediments coming from the excavation of the canals located in the industrial area of Porto Marghera (Venice, Italy). The technologies involved the use of fluids at the supercritical state for the extraction and the use of supercritical water for the oxidation of hydrocarbons and organic compounds having a high environmental impact.
The aim of this sub-action has been the assembly of the pilot plant in tight accordance to the project design. The construction of the skid is started on 27 September 2012. The assembly is started on the 24th January and ended on the 28th March 2013.
The supporting structure of plant was studied considering the following requirements:
Small dimension and easy to transport;
Arrangement of process equipment that facilitates the control and the operations management;
Easy to read and calibration of test equipment.
The skid has plan dimensions 6.05 x 2.45 m, total height 2.5 m. The total weight of the structure including mounted equipment is about 3.7 t. The skid consists of structural elements in Stainless Steel AISI 304 tubular framework with high thickness, reinforcement sections and sheet metal. Under the basement 18 supports to calibrate the level. Main front includes the process equipment and separation of pollutants, such as accumulation tank CO2, extractor, separator gravimetric, cyclonic separator. There are pressure gauges with a large diameter. There are the main valves for regulating the process. Front Back includes equipment such as oxidizer, heaters, process pumps, flowmeters.
Aisle with aluminium gangway for access to circuit hydraulic lines to process, cooling water circuit, control valves and adjustment process (linked operation to the logic of automation), pressure transmitter, under the gangway is installed conduit for electrical. Front Cabinet: in the short side of the skid, on the opposite side of the inlet of gangway, is obtained the position for housing electrical panel In the final stage of construction of the skid, with the skid still in the workshop of construction, were mounted major equipment such as storage of CO2, extractor E1, gravimetric separator S1, cyclone separator S2, heaters H1, H2, H3, H4, H5, condensation units C1, C2, C3, C4, C5, C6, collectors of the cold water feed and return.
In assembly phase were mounted in succession: process pumps, flow meters, safety valves, valves for manual adjustment, regulation valves to control automatic slaved to instrumentation for controlling and adjusting the process parameters (analyzers-temperature transmitters, gauges-flow transmitters, etc.), pressure transmitters.
Being a pilot plant with special features and unusual has studied the construction of piping “in the field” according to the hydraulic diagram, the location of equipment and instrumentation, with the constant support of process engineer and of technical department. The way of the piping has been studied in order to optimize the spaces, choosing the shortest distance, thinking of maintaining a space of accessibility to the electrical system. Has been adopted a tubing ¼ “ thickness 1.24 mm with two different materials: a) AISI 316 L (ASTM A269 – EN10216), for the lines at high pressure (300 bar) and temperatures below 260 °C b) INCONEL (ASTM B444, UNS N066255) for the lines at high pressure (300 bar) and temperatures until to 410 ° C (line oxidation process)
Particular attention was taken to the construction of the pipe, taking care of the cleaning of the end of the tubing after cutting and blowing compressed air to inside of the pipe ensuring the internal cleaning of the pipe to avoid the presence of small metal shavings, which can prevent the regular operation of valves and process equipment. The fixing of the pipes has been achieved with specific media to be fixed to the frame with platelet support.
We have realized the cooling circuit with copper pipe and installation of valves and solenoid valves. The pipes, where provided, were coated the thermal insulation material: polyurethane insulation for no very hot pipe; rock wool for pipe working at high temperature. Been included in the vessel are special seals U with internal spiral wire. The following hydraulic tests were successful.
It was still tested another type of seal in extractor E1 because the former have determined some difficulty in extraction of the head of the vessel.
The panel has been mounted on head of the skid and secured with additional structural support. Then It was connected all the electromechanical equipment, valves and instrumentation. Special metal sheaths have been provided for the wiring of electrical cables coming out of the heater. Electric cables high heat resistance have been used for the connection of heating resistances of oxidiser O1. Were performed on all hydraulic TEST vessel under pressure. One at a time, all of the vessel were filled with water and brought to pressure. The test was attended by an inspector certification of SGS. All tests were positive. After the hydraulic and electrical assembling the technical department completed the assembly drawings with indication of the final equipment position and the reference to P&I.