Automatic Control of Inhibitor Content in Cooling Water of Marine Engine

Transcription

1 Automatic Control of Inhibitor Content in Cooling Water of Marine Engine V. Ferrari 1,a, G. Raoli 2,b 1 Centro Sviluppo Materiali SpA, Via di Castel Romano 100, Roma, Italy, 2 Global Engineering Srl, Via Casilina km , Anagni (Fr), Italy, a v.ferrari@c-s-m.it, b giancarlo.raoli@global-engineering-srl.com

2 Objective of work To develop a simple and reliable system for the automatic control of the inhibitor concentration in water, applied to cooling circuits of marine engines.

3 Experimental Activity Laboratory Simulating Circuit

4 Experimental Activity Laboratory Simulating Circuit Sensors: Polarization Resistance Temperature Conductivity ph

5 Experimental Activity Electrochemical Sensor The electrochemical sensors operation is based on the polarization resistance technique. The polarization resistance (R p ) method is based on the Stern and Geary equation i corr = B/R p where i corr is the corrosion current and B is a factor depending on both the cathodic (b c ) and anodic (b a ) Tafel slopes of the electrochemical reaction involved in the corrosion process. The factor B is defined by the following equation: B = b a b c /2.303(b a +b c ) For most active metals in non turbulent water flow it can be assumed that the cathodic reaction is under diffusion control (b c ), which leads to B = b a /2.303 Assuming that the anodic Tafel slope is 60 mv, since the principal anodic reaction is the oxidation of iron (Fe Fe e ), the corresponding value used for B is nearly 26 mv.

6 Experimental Activity Experimental Tests Series of tests varying: Temperature, between 25 and 90 C Inhibitor concentration, between 0 and 3600 ppm And acquiring for each condition: Corrosion rate Temperature Conductivity ph C in = a T c + b T v corr + c ph c + d Algorithm linking the inhibitor concentration (C in ) to Corrosion rate (V corr ), Temperature (T), Conductivity (c), ph, through mathematical coefficients

7 inhibitor analysis, ppm Experimental Activity Confirmation of the algorithm validity Inhibitor concentration sensor/analyses comparison inhibitor algorithm, ppm

8 Experimental Activity On board tests Cruise ship under construction at Fincantieri Shipyards, Monfalcone PLC Sensors A complete system of sensors as well as a PLC unit were installed on a by-pass pipe derived on the cooling water circuit of the ship engines No.3 and No.4.

9 Experimental Activity On board tests IT DG: Engine IT: Inhibitor Tank S: Sensor System EV: Evaporating R: Cooling DG S PLC Scheme of the system installed on board EV R

10 Experimental Activity First on board campaign The experimental campaign was made during the preparation of the cooling water for the first ignition of the engine. The inhibitor was added step by step to have a number of conditions for testing the system. The chemical analysis of inhibitor concentration was made by using the analysis kit provided by the inhibitor supplier. Scope: check the agreement between the inhibitor concentration values derived by the algorithm and those from chemical analyses

11 Inhibitor (analysis), ppm Experimental Activity Results of first on board campaign Comparison of data from analyses and from sensors on-board campaign Inhibitor (sensors), ppm

12 Experimental Activity Second on board campaign A second on-board campaign of measurements was carried out in the last months of The variation of inhibitor concentration was obtained by removing increasing volumes of water with inhibitor from the inhibitor tank and adding identical volumes of distilled water. Scope: confirm the agreement between the algorithm and chemical analyses values check the restoring of inhibitor concentration

13 Inhibitor (analysis), ppm Experimental Activity Results of second on board campaign Comparison of data from analyses and from sensors 2 nd on-board campaign Inhibitor (sensors), ppm

14 Inhibitor concentration, ppm Experimental Activity Results of second on board campaign Trend of inhibitor concentration 3000 Pump on Pump on 2500 Optimal value Upper threshold limit Lower threshold limit Pump off Pump off Pump off Time, h

15 Further features of the automatic system (based on Rockwell technology) 1. Daily report on both average and total inhibitor consumption 2. Continuous monitoring of the parameters measured by sensors at pre-settable frequency 3. Trend of measured parameters, inhibitor concentration, inhibitor consumption, etc. 4. Auto diagnosis of components (valves, pump, pressure transducer, probes, supply system etc.); in event of malfunctions, alarms and corrective actions also to the main control room 5. Two-year storage of data 6. Monitoring of the inhibitor level in the storage tank and calculation of the exhaustion time

16 Conclusions An automatic system has been developed for controlling the inhibitor concentration in the cooling water circuit of marine engines. Such a system comprises: sensors to measure chemical and physical parameters of the water an algorithm that links such parameters to the inhibitor concentration. a PLC unit with a software able to compare the concentration value to those of the operating range and decide, when necessary, logical actions like turn a dosing pump on to restore inhibitor concentration.

17 Conclusions The system has been tested on a cruise ship under construction in the Fincantieri Shipyards in Monfalcone. Two measurements campaign were carried out on one of the three cooling circuits of the ship engines. The results were very promising and proved that the inhibitor concentration values derived by the algorithm are in very good agreement with those obtained by chemical analysis. The system, under patenting, is able to control automatically the inhibitor concentration by measuring it at preset intervals and keeping it within the operating range by acting on the feeding pump when necessary.

18 Multi-sensor system 2 nd World Congress on Corrosion GLOBAL-CONTROL in the Military Inhibitor and corrosion Naples, automatic Sept control 2007 system for marine engines cooling circuit Cooling circuit T V corr Cond. GLOBAL CONTROL For a longer life of marine engines Inhibitor tank