Flowmeters critical to operation of terephthalic acid centrifuges

Paul Boughton

Krohne VA40 variable area flowmeters are performing a critical role to ensure the reliable operation of the world's largest pure terephthaltic acid (PTA) centrifuges.

The instruments are being used to monitor the flow of demineralised water that lubricates and cools mechanical seals on centrifuges designed and manufactured by Thomas Broadbent.
The company has been awarded contracts worth £27million to supply in excess of 30 centrifuges into
India, China and Thailand, where they are used in the manufacture of the PTA from which polyester fibre is made.
The centrifuges are used at the primary dewatering stage of production, where they can process up to 50tonnes of dry PTA powder per hour.

Overheating

The seals are vital to the effective operation of the centrifuges and can operate at temperatures in excess of 140°C. Insufficient water flow within the seals could lead to overheating and failure, which would result in costly downtime and repairs.
Nine VA40s are installed on each centrifuge (Fig.1). The instruments are fitted to the input and output of the water supply to the mechanical seals where they measure the flow of water in and out.
Any difference in the input and output values could indicate a water leak, which would affect lubrication and cooling and potentially damage the seals.
The flowmeters are fed with demineralised water from a centralised supply system flowing at rates of between three and 18litres per minute.
Product qualitycompetitive pricing and the ability to provide strong after-sales support were the key reasons why we awarded this contract to Krohne explained John Wright, business manager for Thomas Broadbent.
Our success in this market is based on our ability to offer the most cost-effective and technically advanced centrifuge packages.
"To enable us to do this we need suppliers that can also meet these criteria."

Moving to bottom loading

Shell's Lubricant Centre at Stanlow in Ellesmere PortEnglandproduces a wide range of lubricants such as motor oilaviation turbine oilcutting fluids and soluble oil. Worldwidethe company supplies and distributes more than 700 grades of lubricant and 1500 brand packs to a multitude of customersfrom local garages and farmers to large industrial plants.
When the company required a new loading bay for bulk finished productsmainly hydraulic and engine oilsit also wanted to increase loading efficiency. This meant moving away from traditional top loading of tankers to the more afety-conscious bottom loading method.
Endress+Hauser suggested using ten Promass 83F coriolis mass flowmeters with a Profibus DP communication network (Fig.2).
By using the Profibus systema wealth of additional application information is made availableincluding density and temperature data. Cabling and I/O requirements are significantly reduced too.
As Shell loads tankers by volume (litres)density is a key factor as it changes with temperature. Promass coriolis meters were installed as they offer accurate and reliable density measurement and feature a self-monitoring health check for optimum performance.
They are also secure and tamper-proof and account for all product transfers from the storage tanksallowing seamless integration into Shell's inventory control system.
The main benefit of Shell's new loading system is that it supports driver-initiated loading. This meets the increased efficiency objectiveas drivers no longer have to wait for manual link-up to the pumps.
Chris TurnerShell Lubricant E and I engineer commented: "Driver-initiated loading has proved a real benefit all round.
"All the data provided by the Profibus networksuch as diagnostic informationhas helped us maintain smooth operation and system integrity and the Promass flowmeters are low maintenanceaccuratesecure and user-friendly."

Oil reception

The Clair onshore facilities at the Sullom Voe Oil Terminal on Shetland are concerned with the reception and storage of oil from the Clair reservoir. AMEC is principal designer of these facilities.
Oil reception from the platform is via an emergency shutdown valve skidthen on to a pig reception skid. The oil is then routed to two large storage tankers.
While one storage tank acts as the oil reception tankthe other is used for tanker loading. Once the reception tank is filledthe tank duties are switched.
Able Instruments has been working with AMEC on the supplyinstallation and commissioning of a 12-inch diameter Rheonik coriolis meterthe largest available worldwide.
The Rheonik coriolis range is characterised by its novel and patented Omega tube elementwhich allows the most challenging of applications to be solved.
The Omega tube has a torsional or swinging movementrather than the bending motion traditionally associated with coriolis. This allows increased tube wall thicknesswhich means exceptional resistance to abrasionoperation under high pressuresplus it eliminates the requirement for the secondary containment associated with other element designs.
The meter has been installed on the onshore pig reception skid to monitor the supply of oil to the storage tanktherebycrucially monitoring the oil flow received from the platform.
The Coriolis flow signal is also employed in the pipeline integrity monitoring system tied to the offshore platformensuring there is no loss of inventory between offshore supply and onshore reception.

Small line measurement

According to Fluid Components International (FCI)engineers tasked with improving small line size gas and air flow measurement and control for industrial processes will find that the ST75 series flowmeter sets a new price-performance standard by offering a simple and more reliable solution at the lowest cost in its class.
Blending high accuracy with extensive featuresit measures and monitors air or gas flows in line sizes from 6-51mm with a single instrument and provides three outputs of the mass flow ratetotal flow and media temperature (Fig.3).
Combining a non-cloggingsmall-size thermal dispersion sensing element with sophisticated microprocessor-based electronics and precision calibrationthe ST75 delivers fastdirect mass flow measurement without the need for any other sensors -- reducing installation complexity and eliminating maintenance scheduling.

Low cost

FCI developed the ST75 to be the lowest costsmall-line mass flow solution for use in processes using natural gasmethaneother fuel gasescombustion air as well as oxygennitrogen and all inert gases and compressed air.
The company says it is ideal for use in fuel and air feed lines to furnacesburnersindustrial ovensheat treating systemsboilersand power co-gen equipment found in a wide variety of manufacturing and process industries.

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