Automation

System Investigations

ContentsIntroduction to Process................................................................................................................. 2

Specification of Problem............................................................................................................3

Proposal for solution..................................................................................................................3

System Design Specification.......................................................................................................4

Instrumentation and Control Devices........................................................................................5

Temperature Device...............................................................................................................5

PH Device................................................................................................................................7

Level Transmitter....................................................................................................................8

High and Low Level Switches................................................................................................10

Flow Meter...........................................................................................................................11

Process Control Design.............................................................................................................13

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Introduction to Process

I work in a pharmaceutical plant manufacturing Flu Vaccines for distribution globally. Due to the nature of the business and the live egg waste involved it must be suitably treated. We have classifications of liquid waste and all liquid waste falls into these two classifications. Contaminated and non-contaminated waste. Contaminated waste currently is treated through our waste facility on site and this system is fully automated. Non-contaminated waste can be distributed through the site main water drain. Recently we have had various complaints from the local water board in regards to condition of this waste during routine sampling and they have placed restrictions on the pH and temperature of outgoing waste. Currently our system Pipes all non-contaminated waste into local storage tank outside the plant and when it gets full (typically after a day’s production) it is discharged throughout the night.

The main cause of the excursion is deemed to be related to the pH. After each production day every product contact line must be cleaned and sanitised. This is first done by caustic in the Clean in place process. The next stage after the chemical mix removes residue left behind by the process is to clean steam sanitise the pipework ensuring all pathogens are killed at a very low level. The pH issues arise from this as all chemical waste must be disposed of and it is very high strength. Initially the discharge tank would just dilute due to the excess water waste from post clean flushes, however since these excursions an automated dilution method is required.

The issue we have now is to implement a system that will govern the discharge of waste to drain in regards to temperature and pH value and a suitable control system including automatic valves, PLC control (linked to the site Siemens PCS7 system) and condition monitoring equipment for temperature, level pH etc.

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Specification of Problem

As discussed earlier the defined issue is with the Environmental monitoring of the waste water systems to drain. The pH of the waste water can be too far below pH 7 and is drifting out of our agreed limits. The limits are set by local regulations and United Utilities and our limits are as follows

Limit Type Low Limit High LimitpH 6.0 10.0Temperature n/a 43.3°CFlow Rate n/a 12l/s

These are the control limits that the instrumentation I will choose will have to operate within and the control system in place to be robust enough to enable these tolerances to be controlled within and to block any discharge that it outside these limits. Also ensuring maintenance of the equipment in line with our requirements to the Food and Drug Administration (FDA).

The issue in hand has become far more prominent due to the increase in production waste chemicals from the cleaning. Previously the chemical would just mix within the tank and dilute after the flush had completed however this is not currently the case and the pH has been rising and without manual addition of water to dilute there is no control on this par of the process.

Proposal for solution

My proposal for a solution to this issue is to have an automatic dosing of clean water from site to bring down both temperature and pH. The project must conform to these basic standards;

Not allow discharge if process conditions are not met. Dose water to meet process conditions for temperature and pH Circulate/agitate liquid to ensure consistency. Automatically discharge after a hold time at defined process conditions.

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For the control system to stop discharge we must have interlock systems in place that will not allow the discharge valve to open until the temperature is < 43 degrees and the pH >6 and <10. As the whole site uses Siemens step 7 so any solution would have to be created to work with this system. Cards occupy both digital inputs/outputs and analogue inputs/outputs so either methods of feedback, inputs and outputs would be adequate.

A stand-alone system could be possible however there would be no visibility to the site monitoring system and if there was an issue nobody would be informed, if we cannot get rid of waste then production will grind to a halt.

Therefore the System would need a minimum of;

Temperature probe and transmitter pH probe and transmitter level transmitter In line flow meter 2 level switches (high and low for overspill and pump protection) Control valve Free slots on S7 Rack for IO cards. Agitator Dilution water pipework All instrumentation graphed and recorded for environmental monitoring

System Design Specification

1. The tank would be modified to add a pocketed temperature probe and transmitter, wired back into the Siemens AI terminal on the rack configured to feed 24v to the transmitter and receive a current readout of range 4-20 mA to 0 to 100 degrees C.

2. Suitable pH probe and transmitter would need to be selected and installed within tank taking note of orientation as some probes are not suitable for mounting upside down etc. This would then also be wired back to an input card and supplied with 24v power. There is also a possibility that this one probe could also do temperature so a decision could be made to try to reduce cost of the project by combining these into one probe.

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3.Active level transmitter sourced for reading a live level reading graphed back to the control system to give indication of usage and levels over time

4. Level switched for protection of pump and secondary high high level valve shut off.

5. Circulation pump to recirculate tanked liquid to aid with mixing and keeping liquid of uniform pH/temp.

6. Control valve for limiting flow rate of discharge

7. An agitator and motor would also help with the missing to ensure no pockets of high temperature or pH.

Instrumentation and Control Devices

Temperature Device

PT100 Endress TH13Temperature probes often used are PT100 or thermocouples, as thermocouples are often used for high temperature applications I would choose to opt for the PT100. It is accurate, repeatable and readily available. A requirement would be to have it enclosed within a pocket, for calibration purposes this is a must as there is no requirement to drain the tank to calibrate (also known as a thermowell). A company we use often is Endress and Hauser. They supply a TH13 temperature transmitter housing with thermowell for enclosing the PT100 probe.

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Fig (1)

In figure 1 I propose we use this housing with a socket weld for enhanced leak protection, the probe will then sit inside spring loaded onto the metal edge ensuring good contact and eat transfer (this can be enhanced with thermal Paste).

The probe is a PT100 and connects directly to the transmitter head mounted directly to the top. This will then be powered by a 24v supply direct from a local instrument junction box connected to a 2 wire Siemens analogue input card.

For calibration purposes temperature transmitters on site are HART compatible as the programming software we have available in both a laptop and a remote handheld device. This

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is used to make adjustments to range and calibration offsets. There are sometimes alarm set points settable within the transmitter software however as a site rule the Siemens PCS 7 does all the control and alarm points the only piece of information we receive on the input card is a 4-20 mA signal that is converted into a range on the PCS 7 Client.

Working Principal

The working principal of the PT100 Resistance Temperature Device is the use of a metal coiled wire typically platinum with a predictable resistance value for the temperature range. The PT100 is most common and its resistance value is 100Ω at 0 degrees C. The RTD is useful because it has low drift and is very accurate; it produces a graph that is almost a straight line, whereas say a nickel graph will have a curve associated with it.

An RTD is not commonly used above 600 degrees C and in these instances a thermocouple will be used. This is due to the higher temperature causing impurities to contaminate the element and cause it to become unusable. This is purely an application issue and at the design stage it is imperative that you asses the working range of the probe and determine which type to select for this application. In general anything below 500 degrees is an RTD PT100 and above it’s a range of thermocouple materials that can be selected depending on the top end on the temperature scale.

PH Device

pH used to be a particularly difficult process measurement to take, it required multiple probes into one line and was very prone to misreading’s and failures. Newer methods have come into the forefront now and reliability and calibration methods have really improved. Currently on our site we use a single probe method that proves with regular calibration to be reliable. The probe is connected into a local display and transmitter box that is modular. You can buy different modules for whatever application you require. Relays can be activated to trigger alarm points back to the control system or to local valves to enable one small sub system to complete some steps of control.

Endress and Hauser Liquiline CM442

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The selection I would choose to use is the CM442; it features a modular design so you can specify the way it is to be configured by modules insert able into the casing. They can be configured during ordering as to what modules you would like to be installed and these can be

changed at any time. I would suggest for this project that we use an analogue output module to supply a 4-20mA signal to the control software but also a 2 relay module to provide the outputs to signal for alarm points back to the control system so that it will react when the item goes out of specification. Although this will also be done in software to provide the control for dosing it is also handy to have the hard wired outputs for safety so we can ensure that the valves in question will not open regardless of the software. As discussed earlier it is also possible to receive the temperature from these devices, in this application the temperature is used for compensation of the pH in relation for temperature and could also be used as a reading back to remove the need for a PT100. I have chosen not to use this as within the industry my company operates calibration is mandatory and calibration of the temperature section of this probe is not possible, for temperature we must use a 3 point check and we would only be able to use a one point spot check.

Measuring principal

The pH analysis equipment used in this equipment uses the potentiometric measurement principle. The type of probe used is called a glass electrode, it has a buffer solution internally and a pH sensitive glass membrane. A gel layer develops on the inside of the membrane which is in contact with the buffer. Positive hydrogen ions either diffuse out or into the gel layer depending on the pH value of the measured solution. The internal buffer generates a potential differential between the gel layer and the buffer this is then compared to a reference sensor (now in newer probed inside the single unit) and it is proportional to the pH measured in the fluid. Figure 2 shows the two part probe.

Fig 2

Level Transmitter

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The level transmitter will be used to give constant reading of levels in the tank and will be graphed to show dropping level along with all other system parameters to ensure when dumping water it is at the correct temperature and pH.

Radar Micropilot FMR245

The Micropilot radar level system will be a good choice for this system; it is fairly maintenance free and has no parts that will need replacing as there is no product contact. All items that need replacing will be on the tank externals with the possibility of a clean of the radar face every so often to reduce erroneous readings. It is this reason I would choose a radar system for this application. We will have contact with a wide range of temperatures and pH values that could corrode and wear out other methods that use contact as a means of measurement. Capacitance would be out of the situation due to changes in the process medium and floats would degrade too often.

Measurement Principle

The Micropilot is a downward facing level measurement device that uses the time of flight method of measurement. Time of flight uses a known distance to empty value that is measured beforehand and uses radar impulses to reflect off the measured level and to be received by the measuring device. This time taken given the measured to empty distance gives a distance to level which can then be worked out to a live level as measured on the field as shown in figure 3 below.

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Fig 3

High and Low Level Switches

This part of my design is all about safety of both equipment and people. These switches offer another level of protection other than the radar level. The radar level will be used for control however the switches are used purely for safety.

Liquiphant M Tuning Fork Level

The FEL 52 (3 wire DC) Switched tuning fork level by Endress and Hauser is designed for this purpose, it connects into the process vessel and detects for liquid on the tip, on detection the transistor is switched giving a signal back to the control system. This signal will then be used for the protection of the pumps, when the level drops below this probe the level will be dangerously low and could cause pump cavitation so this signal will stop the pumps and enforce interlock conditions until the level in the vessel is higher. The pump will be stopped but the discharge valve will still be able to be opened as long as the discharge conditions are met. The

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unit is very versatile and can be mounted anywhere in practically any fluid or solid material see figure 4 below.

Fig 4

Measurement Principle

The level switch operated by using a tuning fork vibrating at their resonant frequency when the liquid touches the tip of the probe the frequency changes and this will then activate a limit and cause the switch to operate. This also provides a self-monitoring function, as corrosion builds up or fouling the frequency will also change generating an error and the probe will need to be replaced.

Flow Meter

The flow meter will be in line with discharge pipe to control the flow rate to keep it within specification of discharge amount per day. This flowmeter will enable the control system to throttle a control valve to keep the flow rate to the set point and our discharge within agreed limits.

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Proline Promag E100

This flowmeter is on the cheaper end of the scale, it is low cost but as this is waste water an electromagnetic flowmeter is ideal. It does not inhibit flow and allows for a full bore application straight to drain. It will also allow control of the flow from a local control valve. As we only need a reference reading and it is not a process parameter that we require to be accurate due to the process recipe or a metered service.

Measuring Principle

The electromagnetic flowmeter measuring principle is based on theory of voltage induction, the process medium is the moving conductor and the voltage induced through a magnetic field caused by this conductor is proportional to the flow velocity of the liquid. Figure 5 shows a graphical representation of this process with a full explanation and formulae

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Fig 5

Control ValveThe process flow will be governed by a control valve made by GEMU valves. It’s electronically positioned with feedback for current position. They are very accurate for rate control and provide very fine tuning for this type of application. The operate by controlling a diaphragm to modulate the valve, the input for this would come from the control system via an output signal of 4-20 mA 4 being closed and 20 fully open. This would effectively ensure no high flowrates on the outlet.

Process Control Design

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This section we will cover the design of the system and layout drawing. The design has been chosen to meet a specification that will solve the initial problem. We do not want water to be discharged to drain until it is within specification set by the local water board.

The specification I devised is as follows each step will be broken down to see if the chosen solution would be effective.

1. The tank would be modified to add a pocketed temperature probe and transmitter, wired back into the Siemens AI terminal on the rack configured to feed 24v to the transmitter and receive a current readout of range 4-20 mA to 0 to 100 degrees C.

The transmitter has been added to drawing at a location that would read the temperature and talk with the PCS7 control system to regulate the temperature if it is too high using the analogue input cards the software would then provide the conditions.

2. Suitable pH probe and transmitter would need to be selected and installed within tank taking note of orientation as some probes are not suitable for mounting upside down etc. This would then also be wired back to an input card and supplied with 24v power. There is also a possibility that this one probe could also do temperature so a decision could be made to try to reduce cost of the project by combining these into one probe.

PH probe and transmitter has been inserted into the vessel drawing (QT330004) this will also communicate with the control system and allow the system to take control using the pre-defined parameters for discharge interlocking bottom valve when out of specification.

3. Active level transmitter sourced for reading a live level reading graphed back to the control system to give indication of usage and levels over time

Lever transmitter has been placed into the top that would provide an active reading showing current level of the tank. The control system would then be able to provide a graph.

4. Level switched for protection of pump and secondary high high level valve shut off.

Two level switches have been placed onto drawing that would dictate interlock conditions for inlet and outlet valves and pump for protection of overspill and pump.

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5. Control valve for limiting flow rate of discharge

Control valve has been inserted into drawing to regulate the flow of the discharge keeping us within tolerance.

6. An agitator and motor would also help with the missing to ensure no pockets of high temperature or pH.

Agitator placed into drawing to allow mixing of the process waste medium keeping a constant process condition.

7. Flowmeter installed to allow control of flow

Flowmeter was added to drawing to allow control valve to control flow as to not breech conditions

As we can see there are no limitations on the implementation of this new automation system and it would meet all specifications I defined earlier. This system would work and would benefit the site as a whole in keeping within our environmental constraints

The outlines of these changes are that the process control system would be configured to allow the inlet of water/acid from internal process tanks up to 60% of the level of the tank. The pH (QT330004) would be monitored as well as the temperature (TT330005) and if there are any deviations from this it would dose water into the tank until pH and temperature are within tolerance.

This would then allow the discharge control valve (CV330007) to open and control depending on the measured flowrate (FT330006) to keep it below 12 liters/second. Then that would run until low level alarm is triggered from the level switch (LS330002), this will protect the pump from running dry. The same is true for high level (LS330003) if the transmitter for level is defective the there is some safety systems in place where the valve will fill only up to the high level point and interlock conditions would be initiated and the valve locked out.

Agitation will only be operational when low level is not initiated and level is measured above 30%.

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This system will fulfill the design and the problem and enable us to operate safely and within our agreed discharge parameters. Figure 6 shows a mock up drawing showing locations of instrumentation and a graphical display using on site PCS7 Graphics (readings would be underneath Tag Names).

Fig 6

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Bibliography

Promag Flowmeter Manual TI01159DEN_0114.pdf

http://www.omega.com/prodinfo/magmeter.html Omega Measuring principle electromagnetic

http://www.endress.com/ PH Analysis Sensor

Temperature sensor TI13 manual TI00110ren_1312.pdf

Level Switch Manual ftl50.pdf

Beamex Ultimate Calibration on site book

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