New technologies & applications
POWER PLANT PRODUCTS1 September 2007
Fast alignment of critical machinery
A production stoppage can in many ways be compared to an auto-racing pit stop, says Fixturlaser. If you do not use fast, top-of-the-line tools in the pit, you can’t expect to win the race. This is true also of maintenance of rotating machinery. In today’s competitive environment long production stops are unacceptable, and a way of reducing them, says the company, is to use its XA 4th generation laser based tools, which include features, together known as Express Alignment, that promote extra fast shaft alignment.
This wireless system can now be upgraded with what Fixturlaser says is a unique function for measuring dynamic movements such as thermal growth and process effects. This is designated Fixturlaser OL2RXA (Offline-to-running) and the XA is the only shaft alignment system on the market that includes this function. Other suppliers offer separate systems, using multiple software, which do not facilitate the shaft alignment process. The Fixturlaser OL2R, which is protected by patent, has been developed to match the shaft alignment procedure without involving additional evaluation software.
Hardware for the laser units includes a point laser to enable easy mounting of the fixtures. The included software is based upon the characteristic user interface from the Fixturlaser XA shaft alignment programs and also includes 3D flash animations to guide the user through the measurement step-by-step. It is then possible to perform alignment and compensate for the actual dynamic movement in a fast and flexible way.
The user can measure several machines with a single system. It is also possible to carry out several ‘hot’ measurements in succession, and then save them separately in the system, to be paired later with the relevant ‘cold’ measurements taken separately. The results from an OL2RXA measurement are machine-unique target values that can be retained and used to accomplish precision shaft alignment.
Improved vortex flowmeter
Emerson Process Management has introduced a new version of its Rosemount MultiVariable 8800 vortex flowmeter. Users have traditionally preferred vortex technology in saturated steam applications because of its reliability and wide rangeability. However, users also prefer a compensated mass flow output. It is claimed that by incorporating multivariable technology, this new unit can deliver all the benefits of proven vortex technology and a temperature compensated mass flow output directly from the meter, reducing process variability.
Standard multivariable vortex designs integrate the vortex and temperature sensors into the same assembly. This requires process shutdown for verification or replacement and an extensive spare part inventory. The new 8800 has isolated, independent vortex and temperature sensors, allowing both sensors to be verified or replaced independently without breaking the process seals, and eliminating the need for process shutdown for verification of the temperature sensor.
This is claimed to lower the total installed cost of temperature compensated measurement points by 25% compared to externally compensating a traditional vortex, by eliminating the need for an external thermowell, temperature sensor and transmitter, and a flow computer or control system compensation program.
The device can also be used to output the variables independently, allowing users to obtain additional temperature monitoring points where it was previously cost prohibitive. It an intelligent digital field device that can be incorporated in the PlantWeb digital plant architecture.
In situ robot welders for turbines
A new laser welding technique has been used to repair low-pressure steam turbine blades in minutes – rather than days – by exploiting advances in understanding of the way repair metals adhere.
Called In Situ Laser Surfacing, the development is the product of a collective effort by several research institutions and power station operators.
As the name implies, In Situ Laser Surfacing allows flaws from wet steam erosion on the blades of low-pressure steam turbines to be repaired in place. Some power station operators have reported that current blade repair, or replacement, costs $AU250,000 per turbine per day in downtime, or up to $AU2.5 million in total per turbine. A typical low-pressure steam turbine rotor has 180 last-row blades, each about a metre long, with a replacement cost of $AU10,000 each if they cannot be repaired to the level of their original aerodynamic precision.
The new method, developed at Australia's Commonwealth Scientific and Industrial Research Organisation, uses high-power laser energy to fuse a metal alloy powder to the turbine blade’s surface, and the work can be done without the need to deblade the rotor. It only has to be removed from its casing. The laser is a portable unit that is taken to the power station, and the operation is performed by a robotic arm.
The process is technically not welding. The laser supplies a high-energy stream into which a metal alloy powder is directed. The laser fuses the metal to the blade’s surface, in contrast to conventional repair methods that have used TIG (tungsten inert gas) welding. But it has been found that when using this method the blade temperature is difficult to regulate and blades can suffer thermal damage.
The technology has been trialled at TRUenergy’s Torrens Island power station in Adelaide, Australia. TRUenergy’s asset strategy manager, Ralph Villarosa, says the initial field trial last year on six blades was successful and the company completed earlier this year a second trial on a further 17 blades. He believes the technique has significant commercial application.
Shutdown protection for critical machinery
The new Series 684 multi-purpose indicator alarm module from IMI Sensors (a subsidiary of PCB) is intended to provide an economical solution to machine shutdown protection when increased vibration levels signal a potential failure. These modules are available in various sizes and include up to eight channels in a single NEMA 4X enclosure. ICP (IEPE) piezo-electric or 4-20 mA sensors interface directly with the system, which is universally powered and provides appropriate excitation voltages. Within each indicator channel are up to four form C relays, for alarm and shutdown control. Time delays and push button programmable settings allow for simple set-up with no false alarms. Indicator lights on the front of each unit display relay status.
Each meter has the ability to integrate an acceleration signal and display the units in acceleration, velocity, or displacement on the highly visible, bright display. The raw vibration signal can be accessed via BNC connections on the front of the module for convenient interface with data collection equipment. Also available is the capability to retransmit a signal for straightforward interface with existing PLC, DCS, and SCADA systems.
Diesel engine combustion monitoring
PCB Piezotronics has introduced a new dynamic pressure sensor, designated Model 175A01and described as ‘ideal’ for measuring dynamic combustion pressure in gasoline (petrol) or diesel engines. The high temperature (up to +600 °F/+315 °C) piezoelectric charge output sensor, structured with naturally stable quartz sensing elements, can measure rapidly-changing pressure fluctuations over a wide amplitude and frequency range.
The uncooled design measures pressure with low thermal shock error, and ground isolation avoids electrical interference from electronic ignition systems, making the sensor equally well-suited for research and development or monitoring applications. A solid-state construction, hermetically-sealed housing, and laser-welded flush diaphragm help ensure durability in harsh engine testing environments. The sensor is available with a dynamic range to 4000 psi (275 bar). A range of models and mounting adaptors is available for various engine types.