Reducing Material Waste in Flexible Pet (Polyethylene Terephthalate) Production

Polyester is very popular because it is a light, soft, flexible, low-maintenance material that keeps you warm. Making it this way poses diverse challenges to PET producers.

A chemical plant specializing in producing PET was looking for a solution to reduce the waste resulting from product variance. The factory produces 25,000 tons of polyester annually, which is then provided to other manufacturers to produce a vast range of end products.

The SITRANS FC430
monitors the glycol flow.

This vast range requires different PET grades, which are achieved by slight variations in the synthesis procedures. In order to investigate possible options to upgrade their primary processing, understanding the complete process is vital. In the case of PET production, this process starts with mixing three key ingredients – PTA and IPA powder along with glycol liquid – in specific ratios to make a paste.

These source materials are stored in stainless steel bins with a volume of 2649 ft3. Rotary feeders move the mate- rial from these bins to a batching vessel along with glycol to make the polyester paste. The batching vessel is agitated to ensure that the mixture is always consistent. Monitoring tank levels, precisely controlling the dosing, the efficient use of raw materials and ensuring a consistent mix are the key parameters

SIWAREX WP251

when it comes to improving the primary processing. When Siemens designed a new system for the chemical plant from the bottom up, the Siemens S7-1200 PLC controller was the first product that was installed to set up a compact and flexible automation solution, which keeps track of the key parameters and the process efficiency.

Don’t get mixed up during mixing

Each raw material bin is mounted on Siwarex WL280 ring torsion load cells to achieve optimum weighing accuracy. These load cells are connected to two Siwarex WP251 weighing modules, which are specifically designed for batching applications. The advantages of this solution are that the WL280 load cells feature a C3 class rating for accuracy as well as an IP68 rating for protection against dust and direct high-pressure cleaning – ideal for handling powder materials such as PTA. In connection with the Siwarex WP251, a customer-specific application was engineered with a resolution of up to +/- 4 million parts.

SITRANS TS500

The glycol as the liquid component in this process is monitored by a Sitrans FC430 coriolis mass flowmeter providing a 4-20 mA output, which varies based on the flow rate of the material. This signal is fed into an analog S7-1200 input module. A Sipart PS2 positioner controls the valves to regulate the flow rate. In such flexible processes as this one, the operator individually sets the setpoint for total production. At the field level, this flexibility is achieved using Sinamics variable frequency drives, which independently adjust the flow rate of each material. To close the loop, the discharge rates from the raw material bins are monitored by the WP251. The output is then processed by the S7-1200 controller, sent through an analog module to control the Sipart PS2 positioner – which in turn allows more or less glycol to flow into the batching vessel. The downstream Sitrans FC430 flow meter additionally verifies the flow rate to ensure a high-quality mix.

How powder and liquid become PET

Pointek CLS200

The temperature of the paste is another crucial factor when it comes to producing high-quality PET. If the agitation causes too much heat, the whole mixture could be lost, causing unwanted waste. In this configuration, a TS500 controls the temperature to the optimum level. To further cut down on product loss, a Pointek CLS200 capacitance- based switch acts as a backup device to ensure that the material discharges completely, and does not build up or overflow. Its high frequency oscillation makes it insensitive to product buildup, therefore guaranteeing reliable level monitoring in the PET paste vessel. For integrated control and alarm management, the level switch is connected to the S7-1200 controller. With 13 sensors, 2 VFDs, 3 geared motors, 4 modules and 1 HMI installed and connected to the control system, the plant managers reap the benefits of a comprehensive portfolio from one supplier. The new equipment is reliable and efficient and – together with the DCS solution – offers excellent process and data control.

Less material waste and reduced downtimes

SIPART PS2

Where did this leave the chemical company? After the equipment had been running for 3 months, the first estimates were made as to whether the initial goals of reduced waste and increased efficiency had been met. The result: plant efficiency had increased by 27 % due to the reduced material waste and product loss. Further, the more reliable process measurements and diagnostics help the company to service their equipment on a preventive basis instead of a reactive one, resulting in reduced downtimes and in- creased reliability.

Simplified diagram showing the customer’s process.

So the next time, you put on your running gear, take a sip out of a plastic bottle or attach your safety belt, maybe you will remember the effort that goes into producing the PET that is needed to manufacture these types of products. By the way – they have another important characteristic in common as they can be completely recycled.

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You can download the PDF version of this application note from this page on the Ives Equipment web site.

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Ives Equipment
877-768-1600
https://ivesequipment.com

Beverage Container Manufacturer Improves Production Inventory Control with Radar Level Transmitter

SITRANS LR560 Radar Level Transmitter

A company in the southeastern United States produces and supplies beverage containers to a large number of bottling plants. The company produces a wide size range of polyethylene terephthalate (PET) bottles for both carbonated soft drinks and water. PET bottles are formed in a two-step process that includes both injection-molding and blow-molding equipment.

Challenge

The customer has a need to monitor the level in storage tanks containing crystallized PET plastic pellets used in the production of plastic soft drink bottles. The crystallized pellets range in density from 30 pounds per cubic feet to 56 pounds per cubic feet, and the tanks can be up to 60 feet in height.

The level measurement is used for inventory control, and it is important to maintain material supply during production periods. Production needs to know if they will need to switch tanks if the inventory is running low.

The customer had been using a plumb-bob for the level measurements and had also tried ultrasonic level measurement instruments, from a different vendor, in the past. The plumb bob cable became a mechanical nuisance, and because of high dust levels, the customer had experienced periodic loss of echo using the ultrasonic level devices.

Solution

The local Siemens representative convinced the customer to install a trial unit of the SITRANS LR560 radar level transmitter. The LR560 transmitter provided a continuous, repeatable and low-maintenance level measurement solution. The SITRANS LR560 unit’s plug and play performance is ideal for most solids level measuring applications, including those with extreme dust and high temperatures.

Its unique design allows safe and simple programming using the intrinsically-safe handheld programmer without having to open the instrument’s lid.

Results

The customer tested the trial unit for almost a year, and because of their confidence in the reliability of the level measurements, the customer placed an order for an additional 9 instruments for use in their storage silos.

Benefits

Time savings: No maintenance required. Because the SITRANS LR560 radar transmitter is a non-contacting instrument, the risk of product contamination is eliminated and no extended delays are caused as when plumb-bob cables get caught or broken.

Improved process reliability: Continuous level measurement is a real time indicator of how much is in the silo. A plumb-bob cable getting stuck at a certain distance can lead to misinterpretation of the actual level. After the cable gets stuck, there is no level history prior to the last request on demand from the instrument.

Easier to use: The SITRANS LR560 transmitter was set up using the quick start wizard and no further tuning or maintenance is required.

Unique product features: The local user interface allows for ease of con-figuration and set-up. Since the customer is only using the removable, local display during setup, the custom-er can save money by moving the display from unit to unit as needed. The narrow, 4-degree beam angle enables reliable depth penetration into the silo and ignores potential silo wall interference.

About the SITRANS LR560 Radar Level Transmitter The SITRANS LR560 2-wire, 78 GHz FMCW radar level transmitter is used for continuous monitoring of solids in silos to a range of 100 meters or 328 feet. Its plug and play performance is ideal for most solids applications, including those with extreme dust and high temperatures to +392ºF. Its unique design provides safe and simple programming using the intrinsically-safe handheld programmer without having to open the instru-ment’s lid.

The SITRANS LR560 transmitter includes an optional graphical local display interface (LDI) that improves setup and operation using an intuitive Quick Start Wizard, and echo profile display for diagnostic support. Startup is easy using the Quick Start wizard with a few parameters required for basic operation. The SITRANS LR560 instrument measures virtually any solids material level up to a range of 328 feet.

To discuss this, or any process instrument application, contact Ives Equipment by calling (877) 768-1600 or visit https://www.ivesequipment.com.