In process industry the effluent that is generated in the process is an important aspect particularly as regards to its disposal. Specifically effluents generated in Thermal Power Stations (TPS) exhibit acidic property causes harmful pollution in natural environment. It requires complete neutralization before its disposal. This paper gives idea about the automatic neutralization of effluent with highlighting the use of Programmable Logic Controller (PLC). It is combination of hardware and software in which mainly hardware consists designing of holding structure, tanks and electronic circuits like pH comparator unit etc. Whereas software gives idea about the logic commands given to system through PLC for completion of neutralizing process. Results for neutralization of different effluent with different normality of reagents are taken. With the help of results we conclude that effluents are neutralized automatically with appropriate addition of reagent and the time required to neutralize effluent is depend upon normality of the reagent used.
INTRODUCTION
Today industries are increasingly demand process automation in all sectors. Automation results in better quality and increase in products with reduced cost. In this concept, the Neutrapit Automation (NA) system plays an important role in industries for effluent treatment. The application of NA system, which has been discussed in this paper, is the development of Neutrapit base system for adjustment of pH of the process solution / liquid. This type of application that is adjustment of pH value is meet with in number of chemical industry such as paper wash in paper industry, waste water from textile processing house, dangerous effluent from dyes and pigment industries and waste water from sugar industries etc.
Thus treatment of effluent for these industries is a necessity and presently the employ manual treatment based on batch processes. Such processes can be continuously switch over to Neutrapit based neutralization process with minor adoption techniques depending upon characteristics of the industry concerned.
In TPS, equally large volume of effluent water is generated in the various processes such as cooling, coolant in condensers, slurry formation of fly ash and oil coolers associated with lubricant oil etc. This effluent water neither used in boilers as it is not treated nor it can be let free as it is, in the nearby river as they posses major pollution problems to the surrounding soil, water and locality.
The effluent treatment is basically theme of pH measurement and control. To facilitated discharge of industrial effluent it is essential to control pH value of the effluent using automatic neutralizing system. pH measurement and control is very much required in some of the following industrial processes such as water conditioning, pulp and paper industry, animal products, fermentation processes, sugar and starch industries etc.
The system for Neutrapit Automation has been designed to meet the demand for a robust and accurate pH measuring and controlling instruments. The system is based on a new approach incorporating fully solid-state circuitry where both the indications as well as control functions are carried out electronically without dependence on delicate moving parts. This system is test for neutralization of acidic effluents with different normality of reagents and results are found satisfactory.
SYSTEM HARDWARE
This section gives salient feature of Neutrapit Automation system, which is designed and implemented. This setup has been divided in to different parts for its easy explanation. Fig. (1) shows the complete system, which has been explained
below component wise.
1. Holding Structure: Holding structure consists of four tanks T1 to T4 with the control panel. It gives supports to the entire component in the system.
2. Tanks: The tanks consist of four different tanks as effluent tank (T1), acid tank (T2), alkali tank (T3) and process tank (T4). Tank T1 holds effluent, which has to be neutralized. Tank T2 and T3 holds the reagent as acid and base respectively. Tank T4 is process tank in which neutralization is carried out.
3. Solenoid Valves: These are output elements in Neutrapit automation system, which are directly ON/OFF control type of valves having high speed of response. Here we are using four solenoid valves SV1, SV2, SV3 and SV4, which provide ON/OFF control of liquid.
4. Water Level Controller: water level controller is generally used for filling tanks automatically. In Neutrapit automation it is used to fill process tank. Process tank consists of three electrodes C, B, A, for high level, low level and reference voltage respectively as shown in fig. (2). These three electrodes are mounted on wooden strip, which is dipped in process tank. Solenoid valves, which fill the tank, controlled by relay and PLC with electronic circuitry consists of transistors, diodes, and resistors.
5. pH Meter Circuit: Dgital pH meter is compact instrument designed for very accurate measurement of pH in the laboratory and industry. This pH meter is used for pH measurement of effluent. . Combine electrode has been used as sensor for pH meter. Here we used combine type of electrode having range 0-
14 pH.
6. pH Comparator Circuit: pH comparator circuit is used for comparing the pH value in terms of mili volts with reference voltage of corresponding pH value. This circuit it self tuned to adjust to internal reference voltage to obtain correct value of control set point or deadzone.
7. Programmable Logic Controller: Programmable Logic Controller’s (PLC’s) are vital components of modern automation systems. In its basic form, the PLC is a software based relay panel -purpose equivalent to general purpose. However, the typical PLC can do many things that plain Electro-mechanical relays cannot do such as timing and counting, etc. We use XMP-820 mini PLC as a controller in Neutrapit Automation System.
Software
Software is an integral part of any controller-based system and needs equal emphasis as that of hardware. PLC based setup is developed for a different rung. Software written consists of number of instructions in rungs and sub-rungs.
Operation:
1. Switch on the button or mains supply to run the system.
2. Fill the tank T4 up to high level controlled by level controller and PLC.
3. Start the stirrer to mix the effluent.
4. Measure the pH of the effluent in the tank T4 i.e. process tank with the help of pH meter
5. Depending upon the pH value of effluent add the reagent from tank T2 till the desired i.e. pH value 6.5 occurs so control gets exercised.
7. Drain the neutralized water of effluent from tank T4.
8. Repeat the same steps from 2 to 8 for next batch of effluent.
RESULTS
In this process to neutralize the effluent of acidic/alkaline nature it is necessary to add appropriate quantity of Alkaly or Acid as a reagent in effluent. Following tabular result show the details of neutralization in case of alkaline and acidic effluents. The dead zone of neutralization has been set as 6.5 to 7.5 pH as per process requirement.
CONCLUSION
Neutrapit Automation System can be conveniently employed for neutralizing effluents from T.P.S. The present system, which is of batch, type and carried out.
All these operations going on consciously hence necessitate employment of large number of skilled and unskilled workers to operate and control the process. Obviously it is costly prone to errors and involves dangerous associated with such chemical processes such as untreated/effluents with high acidic values outing the disposal bag.
PLC on the other hand when properly programmed and associated system is design, installed and tuned with Neutrapit can give very reliable service with minimum attention at very economical cost as the entire system involves only one time expenditure on development, installation and commissioning. More over such a system can be design to possess self-diagnostic properties such as level of effluent in the tanks, pH values, supply of neutralizing agent, etc. So that the operator can inventive in the process at the appropriate and correct place of fault to separate the system for normal operation.
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