Water / Wastewater Treatment Reduced Maintenance Costs and Safe Operation of a Waste Water Treatment Plant
Explosion-proof plug-in connectors from Cooper Crouse-Hinds (UK) are helping to minimise maintenance time and costs at the Dokhaven waste water treatment plant. The eXLink connectors ensure that the site’s 12 gas detectors are fully operational at all times, ensuring the safety of the plant, employees and the surrounding environment.
Explosion protection plays a crucial role in waste water treatment. Substances dissolved in waste water can sometimes chemically react, potentially causing an explosive atmosphere. For this reason, gas detectors are installed at Dokhaven, which guarantee the safety of the plant and employees at all times.
Unlike conventional waster water treatment plants, Dokhaven has a two-stage waste water purification system with a processing time of 12 hours during dry
weather. During the first stage, after any coarse particles have been removed (wood, plastic, sand, etc.) the water is biologically purified, by enriching it with oxygen. This process breaks down the bacteria in the sludge and any contaminants. Next, the remaining sludge is separated and some of this fed back into the biological purification stage. The remaining sludge is taken to a nearby sludge treatment plant.
Next, the constituent parts of the waste water are broken down further in a second purification stage. The nitrate content is reduced again and the sludge is separated. The water – now biologically ‘clean’ – is fed into the Nieuwe Maas River via a run-off channel. This water that is fed into the river is often cleaner than the river water itself.
The complete system is ventilated by an overpressure system. The air pressure in the processing chambers is lower than that in the tunnels, which means that the contaminated air cannot escape uncontrolled, but is fed back into the atmosphere in a controlled manner after being purified in filter systems.
During the first biological treatment stage (when oxygen is added to the waste water) the safe operation of the plant is guaranteed by the 12 LEL (lower explosion limit) gas detectors. These Ex-de explosion- protected devices are protected to IP 66/67 and have a 3-pole connection, 24V DC at 3.5W and a 4-20mA signal output.
The eXLink plug-in connections supplied by Cooper Crouse-Hinds enable these 12 gas detectors to be replaced and serviced by a maintenance engineer without requiring a ‘Hot Work Permit’. eXLink is a range of connectors that enable the connection and disconnection of electrical apparatus in potentially explosive gas (or dust) atmospheres without the use of tools and without an engineer having to isolate the apparatus from the mains or disconnect the terminals.
This plug-in version of the gas detector has several advantages. In the event that an LEL meter is contaminated or faulty, the detector can be isolated electrically and replaced within a very short time – even in a potentially explosive atmosphere, by the eXLink’s simple disconnection procedure. There is no need for an engineer to isolate the apparatus from the circuit or to disconnect it at the terminals.
In the event of a fault with a gas detector and to enable the maintenance of a detector to be carried out with a minimum amount of effort and in the fastest possible time, the detectors use plug-in connections. A connection cable with an explosion-protected eXLink coupler, 4-pole plus PE, is fitted via an M20 Ex-e cable gland. The counterpart to this is a socket with an eXLink inlet, 4-pole plus PE, which is mounted directly adjacent to the gas detector. The gas detector can be connected and disconnected at any time thanks to this IP66/68 protected, EX-e plug and socket connection. The advantages here are the compact dimensions of the eXLink connectors (30mm diameter by 96mm or 60mm in length) and an M20 thread of the inlet, whereby, similar to a cable gland, the latter can be integrated into any type of enclosure.
The rapid replacement of this type of apparatus is of great benefit to the plant, because if the LEL meters are faulty, the pumps are automatically shut down and the complete water treatment process is disrupted. In certain cases, long term delays or disruptions can have serious consequences for the surrounding environment, and so minimising process downtime is critical. Another key advantage is the higher degree of operational safety. Due to the plug-in connections, manual errors that may occur when disconnecting or connecting electrical equipment are prevented, particularly when work is being carried out under time pressures or when wires are contaminated. Furthermore, longer operating cycles without shutdowns and eliminating manual errors when connecting apparatus effectively improves the overall safety of the installation.
Reader Reply Card No 39
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info@ps-pubs.com New Versatile Device Management Tool
Yokogawa Electric (The Netherlands) has released the FieldMateTM R2.03 versatile device management tool: an upgraded version intended for use in plants and other production-related sites. In response to rapid growth in the Chinese market, Chinese language support has been included as a standard feature. Support for the ISA100.11a field wireless communications standard is also provided.
Digital communications standards play an increasingly important role in communications between plant central control systems and field sensors. With conventional field communications, only measured values from sensors are sent to the central control systems. With digital communication technologies, however, additional data such as sensor settings and maintenance information can be sent, and operators in a central control room are also able to remotely configure and adjust the sensors.
Plants using sensors from multiple vendors that rely on more than one communications standard require versatile software tools for device
configuration, adjustment, and management. FieldMate, an open standard software package that supports FDT/DTM as well as all other major field communications standards, is ideally suited for such requirements. Yokogawa has released this upgraded version of FieldMate to capitalise on opportunities for growth in the device maintenance market.
FieldMate is a PC-based device configuration tool with an intuitive, user-friendly interface that is used to perform initial setup, routine maintenance, and device replacement. It supports all major industry-standard communication protocols such as FOUNDATION Fieldbus, PROFIBUS, BRAIN, and HART, as well as the FDT/DTM open framework for setting and adjusting any vendor’s network-capable field device, regardless of which communications protocol is used. In addition, support for the ISA100.11a field wireless communications standard enables configuration, adjustment, and management of a wider variety of field devices in plants.
Field Device Tool (FDT) is a communications interface that links control systems with field sensors such as pressure transmitters and flowmeters. Device Type Manager (DTM) is an FDT-based device application that is provided by a vendor of a device or a control system.
The target markets include facility maintenance divisions in process industries such as oil, petrochemicals, chemicals, pulp and paper, pharmaceuticals, foods and beverages, and iron and steel. Applications include sensor configuration, adjustment, and inspection and device information management in plants and other production facilities.
Reader Reply Card No 40
California City Upgrades Water Treatment Plant to Ease the Burden on Its Water Table
A growing demand for water is taking a heavy toll on the water table under the central California city of Visalia. To ease this burden, the city is upgrading its wastewater treatment plant, which will increase the amount of water that can be recycled and help reduce the need for pumping groundwater. The upgraded plant will feature GE’s (USA) membrane bioreactor (MBR) technology and will be the largest MBR plant in California when it enters service in 2013.
Currently, the treated water from the wastewater plant is discharged into a nearby stream, Mill Creek. Water discharge requirements limit the flow to 20 million gallons per day (mgd) on average, which is 2 mgd below the rated capacity of the existing treatment plant.
The upgrade of the plant’s wastewater treatment processes with the GE MBR technology will include de-nitrification of the plant’s effluent and a substantial improvement in water quality, enabling the city to divert water for local recycling. This will expand both the plant capacity and the city’s range of recycled water applications.
“The upgrade will provide the city with an additional source of water and will ease the demand on the water table, which we are concerned about reaching lower levels,” said Andrew Benelli, public works director for Visalia. “The treatment plant now will have the capability to provide recycled water for a number of additional uses such as golf courses and agricultural areas.”
Under a contract with Visalia, GE will supply MBR technology featuring ZeeWeed* reinforced, hollow-fiber membranes, which have been proven in more than two decades of wastewater treatment and water reuse. ZeeWeed (ZW) 500 technology is an advanced filtration technology that separates particles, bacteria and viruses from water or wastewater. Nearly 1,000 plants worldwide use this technology to produce superior quality drinking water and to meet or exceed stringent wastewater treatment and water reuse standards.
ZW500 MBR technology is certified under ecomagination, GE’s corporate-wide commitment to address challenges such as the need for cleaner, more efficient sources of energy, reduced emissions and abundant sources of clean water.
Reader Reply Card No 85
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www.pollutionsolutions-online.com • February / March 2011
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