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4.1 The impregnation plant for the waterlogged wood finds 

The impregnation plant for the waterlogged wood finds has the function to help the impregnation solution to enter the wood objects thanks to an shake-up of the fluids at room pressure and constant temperature.

The plant is composed by: 

✔  a tank with a capacity of 1000 litres (about 600 useful lt) made of stainless steel, with a warm jacket in which diathermic oil circulates, that is externally insulated with mineral lamina to minimize the thermal consumption of the process; 
✔  a heating system of the diathermic oil of the jacket, with 6 electrical resistances, thermocouples for the temperature control and for the non-stop registration of the temperature of the water and the oil, electronic systems controls and supervision of the process; 
✔  an high speed stirring system for the disintegration of the starch clots during the phase of the solution preparation; 
✔  a slow speed stirring system, adjustable with an inverter, to keep the starch and polysaccharides particles in suspension during the impregnation o the objects; the two areas – the mixer one and the samples submersion one – are separated by one movable and adjustable grid; 
✔  a system of closure of the treatment chamber studied for the reuse and re-circulation of liquids evaporated during the heating, useful to avoid concentration of the impregnating solution; 
✔  an electric and control panel with a PC for the managing of the impregnation process. 
The plant is predisposed to be connected with an external acquisition data system, extendable till 16 analogical channels with a sampling frequency of 250ksample/sec, based on the National Instruments technology and checkable by software (Labview). 

The plant can impregnate waterlogged wood samples with maximum dimensions of 120*30*30cm and can work non stop; thanks to the acquisition data system its working is checkable also by remote control (i.e via Internet). 

The plant, that is shown in some pictures, has been completed in May 2000 and has been sent to La Rochelle Centre in the first days of September 2000.

Figure 1: Starch dissolution tank – Complete sight

Figure 2: Starch dissolution tank – Detail of the impregnation chamber

4.2 The thermal treatment and desiccation plant 

The thermal treatment and desiccation plant is used to carry out the polymerisation of the starch and polysaccharides existing in the wood after the impregnation treatment and to give the treated sample the humidity level requested for the application, using the DDS process. 

This plant is composed by: 

✔   a treatment chamber in stainless steel with 400 l of useful volume, able to work at temperatures till 190°C and with pressure till 10     bar, with a semi automatic system for closing and opening and with a large door; 
✔   a heating system of the treatment chamber constituted by some external heating electric sheets controlled by an electric temperature regulator connected o thermocouples; 
✔   a quick throttle valve, with big dimensions, for the instantaneous decompression of the treatment chamber, controlled by pneumatic actuators and electric valves; 
✔   a vacuum reserve in stainless steel with capacity of 4,5m3 connected with the treatment chamber through the quick valve; 
✔   a vacuum generation system with suction capacity of about 380 m3/h, able to reach pressures of 30-40mbar, constituted by a vacuum um with liquid ring and vapour ejector at single stadium; 
✔   loading truck for the wood samples with an automatic weighing system of the object during the treatment phase; 
✔   control systems and electronic scheduling of the temperature levels and pressure in the treatment chamber; 
✔   command and control electric panel of the whole plant to be managed with Pc. 

The treatment chamber is connected to a system for the vacuum generation to be used for the thermal mechanical treatment of starches polymerisation. 

Moreover the chamber is connected to a plant for the generation of compressed air for the DDS treatment. 

The system is predisposed to be connected to the acquisition data system and elaboration data system to National Instruments with 16 channels (already described for the impregnation plant). 

The plant is able to impregnate wood samples both of fresh and waterlogged with maximum dimensions of 140*50*50cm and can work non-stop for very long periods; thanks to the acquisition data system its working is checkable also by remote control (i.e. via Internet). 

The plant, that is shown here below, was completed in March 2000 and is actually installed by the Centre of La Rochelle.

Figure 1: Thermomechanical plant - general 1

Figure 2: Thermo-mechanical plant - general 2

During the final inspection of the plant some problems, already described, have been evidenced in the vacuum generation system, that required the modification and the strengthening both of the vacuum pump and of the injecting steam system. 

Particularly it’s necessary to add other steam ejectors to reach pressure levels of about 3mbar and the support of a new pump to the old one to reach a suction capacity of 3500m3/h.

4.3 Economical evaluation of the Arkè process on waterlogged wood 

The main cost items of a waterlogged wood consolidation with the Arkè process are (normally): 

✔    the laboratory cost for initial characterisation of the wood sample; 
✔    the purchasing of starch based products for the impregnation phase; 
✔    the supply of electric energy for pumps used in the impregnation phase. 
✔    the supply of thermal energy (steam) for the intermediate thermal treatment; 
✔    the supply of electric energy for DDS functioning (air compressor, vacuum pump). 

Among these cost items, the most important is surely the last one, because the power consumption of the DDS treatment is not negligible and can have a relatively long duration (till to several days for big size elements). 

These cost can appear important if compared with those normally used for fresh wood drying but are quite negligible if compared with the impregnation with highly expensive resins (i.e. the PEG or the PPG) or if compared with highly expensive drying processes like freeze drying. 

On a preliminary evaluation, only the use of sugar impregnation and classical drying techniques (i.e. hot air drying) can lead to processing cost lower than those obtainable with the Arkè process: but considering the cost/benefits ratio it’s obvious that the technology developed in this project is preferable. 

This evaluation has been only made on a general level, we have to underline that both the Arkè process and the other should normally adapted case by case to the specific problems of the archaeological wood finds to be treated . A more detailed economical analysis should thus be done considering all the particular aspects required by each applications (i.e. ASE value to be obtained, durability to be guaranteed, mechanical stability to be reached, etc.) But in any case, will be very difficult that an objective evaluation could lead to results different from the above mentioned.

4.4 Development and market perspectives for the process on waterlogged wood 

The development of the Arkè process will surely continue after the end of WEST project. 

The sectors in which the research is still active (to optimise the Arkè method) are: 

✔   transfer of the lab results in the pilot plant; 
✔   verification and increasing of the physical chemical stability and resistance to micro biological aggressions of the wood treated objects;
✔   adaptation of the Arké method for the consolidation of the very ruined waterlogged wood objects (low pressure DDS). 

From the technical point of view the perspectives are surely encouraging , but anyway there are still aspects that should be more studied, such as: 

✔    the influence of the dimensions of the object to be treated on the kinetic of the impregnation process; 
✔    the influence of the dimensions of the object on the kinetic o the DDS treatment and on the parameters to be adopted (i.e. using of DDS processes at variable pressure); 
✔    the possibilities to combine a quick preliminary freezing process with the DDS technology to use this treatment also on very ruined archaeological finds; 
✔    the dimensional stability of the treated object exposed to different hygrometric conditions; 
✔    the resistance of the treated objects to microbiological aggressions. 

From the point of view of the plant, it will be necessary to verify the correspondence of the pilot plant to the necessities of the process and, though, the investments costs for an industrial plant could be precisely evaluated. 

Moreover it could be directly verified the existence of problems on the dimensions of the objects to be treated and will be determined with more accuracy duration and costs of the complete process. 

As concerns the market of Arkè method we can say that, even if the consolidation of waterlogged wood is a small part of the sector of Arts, this new method is having a great success both in terms of recovery of finds and on opening of special dedicated museum areas 

The technologies actually existing in this sector are not able to satisfy the exigencies of restorers and have high costs that weigh upon the plant costs and upon the managing of exposition areas. 

So it’s a very favourable situation for the penetration of Arkè process on the market. 

A fundamental role in the development of the Arké process will be done by the Technical Scientific Committee created within the project WEST, with supervision and evaluation roles on the obtained results. The indications and the opinions of his Committee, constituted by experts of the waterlogged wood sector, museums responsible and artistic supervisors, will be utilized to optimise the results obtained in the experimentation phase on a pilot plant and will constitute a fundamental base for the future presentation of the technology on the market. 

Moreover a series of initiatives to increment the visibility of the project in the waterlogged wood sector has been carried out, for example: 

✔  participation to the 4th European Commission Conference on Research for Protection, Conservation and Enhancement of Cultural Heritage: Opportunities for European Enterprises – Strasbourg (FR) - 22-24 November 2000, that has been the first official presentation of the results of the project to a public of experts in the managing and restoration of cultural heritage; 
✔  the presentation of the post-doctorate thesis of Mr Emile Sanya, responsible of the research WEST for waterlogged wood for Gradient – LMTAI; 
✔  the realisation of this Internet site dedicated to the project. 

Moreover we are actually studying many other activities for the future diffusion of the results obtained till now. The first objective will be the centralization of the know-how developed in the project in order to create a single operating centre able to carry out all the steps needed by the Arkè process, that are: 

✔   waterlogged wood characterisation analysis; 
✔   waterlogged wood samples treatment (directly); 
✔   treatment plants production; 
✔   advice supply to potential customers; 
✔   process licensing. 

This centre has been recently created in the south of Italy (Salerno) and the name of the firm is Legni & Segni della Memoria srl. This firm, participated by the main part of SME proposer of Craft WEST, is now in charge for all the commercial activities related to the Arkè process, for the diffusion of the obtained results and for the further development of the technology.