CONTROLLER DESIGN AND ANALYSIS FOR AUTOMATION OF CHEMICAL WATER TREATMENT SYSTEM

Transcription

1 International Journal of Electronics, Communication & Instrumentation Engineering Research and Development(IJECIERD) ISSN X Vol. 3, Issue 1, Mar 2013, TJPRC Pvt. Ltd. CONTROLLER DESIGN AND ANALYSIS FOR AUTOMATION OF CHEMICAL WATER TREATMENT SYSTEM T. SUDHA 1, KUMARA GURU DIDEROT 2, P. ALEXANDER 3 & M. OMAMAGESWARI 4 1 Department of Instrumentation & Control Engg., Sri Manakula Vinayagar Engg. College, Puducherry, India 2 Department of Electronics & Communication Engineering, Hindustan University, Chennai, India 3,4 Department of Instrumentation & Control Engg., Sri Manakula Vinayagar Engg College, Puducherry, India ABSTRACT The chemical water treatment is automatically controlled using the optimized controllers. The process control algorithmic approach is used to computerize the plant process. The system implements PID coupled with Dead Time Compensator for maintaining the concentration of harmful effluents under optimum level. Feed forward controller anticipates the temperature of the reactor by measuring the input concentration. A cascade controller is implemented to control the reactor core temperature by controlling the flow rate of cooling water. The concentration is continuously measured and the parameters of the controller are obtained and hence the efficiency of the system is improved. This system presents a fully automated solution for controlling chemical water treatment plant process. The design of the controllers with the parametric variation in the individual processes gives the well optimized design. KEYWORDS: Dead Time Compensator, Parametric Variation, Controllers, Algorithmic Approach, Automation INTRODUCTION In the present advanced & modernized industrial world almost all the manufacturing & chemical industries have waste water with harmful chemicals as its ingredients as waste. Thus it becomes necessary to treat this water so as to reduce the harmful effluents from it and to make it suitable to be used for further industrial and agricultural applications. The labor-intensive chemical water treatment plants which are used nowadays are manually operated and need to be automated so as to reduce the toxicity chemicals and also to save a large amount of time and money. The paper proposes an advanced process control algorithmic approach to computerize the plant processes. Controllers are applied to control the process steps of treating water including PID, feed forward & cascade controllers. These controllers are designed and simulated in real time platform Labview to control the flow rate of water and temperature of the plant including boiler and cooling water. The full plant is revolutionized with reliable & tested process control strategies leading to computerization of the system and will lead to high increase in efficiency of plant. Also, the health vulnerability will be abridged and lot of manpower and time will be saved. The concentration is continuously measured and when the set limit is reached the water is allowed to flow out. Full process is controlled manually with the opening and closing of valve, measuring of concentration using titration and chemical probes. This includes the continuous monitoring, resulting in high cost, large manpower & inefficiency. Also some of the entities of plant are inaccessible to humans, and the involvement of toxic chemicals is hazardous to health.

2 172 T. Sudha, Kumara Guru Diderot, P. Alexander & M. Omamageswari CHEMICAL PLANT Figure 1: Tank Process for Automation of the Chemical Water Treatment Plant SYSTEM SETUP Chemical treatment plant comprises of input pipeline embedded with flow meter sensors. PID,CASCADE & FEED FORWARD controllers along with reactor forms the water purifying unit. PID Controller Figure 2: Block Diagram of PID Controller A proportional integral derivative controller is a generic control loop feedback mechanism widely used in industrial control systems. A PID is the most commonly used feedback controller that calculates an "error" value as the difference between a measured process variable and a desired set point. The controller attempts to minimize the error by adjusting the process control inputs. Cascade Controller Figure 3: Block Diagram of Cascade Controller

3 Controller Design and Analysis for Automation of Chemical Water Treatment System 173 It controls the temperature of the reactor core so as to heat it at constant temperature. It has two controllers connected in cascade, one of which measures the change in temperature of reactor and other measures change in temperature of cooling water. Both controlling actions are added and given to the final control element to maintain the reactor temperature at set value. Controllers in cascade are P and PI. There gains are calculated using Cohen coon Method. For PI controller: kc = 2.927; ti = 2.018; For P controller: kc = Feed Forward Controller Figure 4: Block Diagram of Feed Forward Controller Water is treated by heating it in presence of chemicals to decrease the harmful effluents by reducing the concentration. The temperature of reactor is controlled by the feed forward controller. It measures the disturbance directly and then it anticipates the effect that it will have on the process output and changes the manipulated variable- temperature by such an amount so as to eliminate the impact of the disturbance concentration and feed flow rate on the process output. Its PID controller with input being initial concentration instead being measured output concentration. The gain values for Feed Forward controller are the same as used in PID feedback controller calculated using cohen-coon methodology. LABVIEW IMPLEMENTATION Chemical Plant Chemical water treatment system is a water purifier reducing the harmful waste effluents. The studied plant is a typical mechanical chemical water treatment plant using reagent for water processing. This paper presents a fully automated solution for controlling chemical water treatment plant process.the flow rate of water and heating temperature of boiler, and temperature & flow rate of cooling water are regulated depending on the input-output concentration of chemical water and heating temperature ( in case of cascade controller). Figure 5: Chemical Water Treatment Plant Implemented in Labview (Front Panel)

4 174 T. Sudha, Kumara Guru Diderot, P. Alexander & M. Omamageswari Circuit Design Figure 6: Chemical Water Treatment Plant Implemented in LabVIEW (Block Diagram) WORKING AND ANALYSIS General chemical treatment plant and its analysis without controlling action. The general system for chemical waste water treatment plant is third order and highly unstable. Its transfer function is expressed as [0.02s³ s² s +0.05] G P (S) = [s³ s² + 0.8s +0.5] For analysis this process transfer function is reduced to first order system. cohen-coon method is implied for reduction. PID gains are also calculated using Cohen-Coon formulae. PID Logic Cohen-hoon formula for PID controller Kc = (1/K)* (t/td)*(4/3 + Td/4t); ti= Td* ( 32+6Td/t) (13+8Td/t); td= 4Td (11+2(Td/t)); where ; Kc = proportional gain, Ki= 1/ti, ti=integral time constant Kd =td td= derivative time constant Thus for analysis the system is reduced to first order from third order.

5 Controller Design and Analysis for Automation of Chemical Water Treatment System 175 G(s) = 0.1 / (0.316s+1) Cascade Controller Cascade controller is implemented to control the reactor core temperature by controlling the flow rate of cooling water. Process transfer function is given by, G(s)=0.1/(0.316s+1) Here P controller is used and its gain is calculated by Cohen coon methodology. P controller : kc = The temperature process transfer function is given by, Gp(s) = 1 / (0.67s+1) Where, Γ=RA R is the resistance of the coil A is the area of the coil Here PI controller is used and the gain is calculated by Cohen coon methodology. PI controller: kc = 2.927; ti = Feed Forward Controller Feedforward controller transfer function is given by, G f (s) = 1 / (10s+1) Here Γ is determined by the response of the single tank system. PID controller: kc =4.46; ti=2.182; td=0.343 SIMULATION RESULTS PID Controller Figure 7: Output of PID Controller

6 176 T. Sudha, Kumara Guru Diderot, P. Alexander & M. Omamageswari Feed Forward Controller Cascade Controller Figure 8 : Output of Feed Forward Controller Figure 9: Output of CASCADE Controller CONCLUSIONS Computerization of plants will lead to a great revolution in the chemical waste water treatment industry. With real time Lab VIEW implementation we were able to find the values of controlling parameters and analyze the real time situation to perfection. The transfer function for feed forward & cascade controller can be derived using better modified techniques which will lead to better control. One can easily maintain the flow rate concentration and also the temperature of the reactor system so as to obtain the desired results using effective programmed design for systems. Other plant divisions like solid waste separator & drier can also be designed implementing advanced control algorithms and industrial techniques for full automation of treatment plant.. Future designs can be implemented in various industries beneficiating people in terms of chemical hazards, time, and efficiency by the Complete automation of chemical plants. REFERENCES 1. Handbook of PI and PID Controller Tuning Rules, Aidan O Dwyer Imperial College Press, London, 375pp, ISBN X, 20 Automatica, Volume 41, Issue 2, February 2005, Pages Qin- Guo Wang 2. Water Treatment Plant Design, Edward E. Baruth, American Water Works Association, American Society of Civil Engineers, American Water Work 3. Ruiter, J.B On-site wastewater management: a definition of alternatives. Master's thesis, Colorado State University, Fort Collin CO, June.

7 Controller Design and Analysis for Automation of Chemical Water Treatment System Corrections and comments from the author on the paper Simple analytic rules for model reduction and PID controller tuning, Journal of Process Control 13 (2003) , Journal of Process Control, Volume 14, Issue 4, June 2004, Page 465, Sigurd Skogestad. 5. A new controller including reference model and its relation to PID controller, Kitamori, T., SICE 2003 Annual Conference Volume 1, Issue 4-6 Aug S. Masiuk and J. Kawecka-Typek, Department of Chemical Engineering, Technical University of Szczecin, Al. Piastow 42, , Szczecin, Poland Transfer and weighting functions of a sewage treatment plant based on random input and output signal characteristics.g. Stephanopoulis, Chemical Process Control,1/e, Pearson 7. Programming, Tata McGraw Hill, New York, National Instruments, ni.com.dynamic classes in the PID control, Huba, M.; Bistak, P. American 8. Transfer and weighting function of a sewage water treatment plant based on random input and output signal characteristics,s.masiuk 9. Reid, G.W Innovation in on-site treatment systems. Individual On- site Wastewater Systems. Proc. Of the Sixth National Conf., McClelland, N.I. (ed.), Ann Arbor Science, Ann Arbor, MI.

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