Operation & Maintenance of Power Plants 


Experience has enabled the power industry to specify allowable concentrations of SiO2


in steam to avoid


turbine damage. For a 180 bar operating pressure, in order to get a maximum of 5 ppb of SiO2


Any minor deviation of silica concentration


on a power plant can have serious and expensive consequences in relation to performance, reliability, efficiency and safety, it is logical that this parameter should be monitored closely. Silica concentration can be measured at the


following process steps (which may vary from one plant to another depending on plant architecture and management methods):


l Boiler blow down (drum boilers only). l Economiser outlet. l Steam. l Make-up water. l Condensate polishing. l Demineralisation plant.


Increase in steam production Today, power plant processes have changed and steam usage has increased. Te steam cycle is now more complex, it has to go through a higher number of application steps, such as heat transfer, cleaning and pressurising vessels to finally maintaining steam purity to recover heat in the main steam/water cycle.


Te production of huge quantities of steam in the energy conversion process is also universal. For example, a typical fossil-fuel power station converts around 650tons of water into steam per hour, in each of four 160MW boilers. Tis represents around two million tons of water usage per month. With such a large output of water in the steam process, the chemical quality of the water is critical.


A beneficial practice that should be considered when measuring silica in power plants is during the performance of anion exchangers and mixed-beds. Both the resin efficiency and exhaustion (break- through) can be monitored with high sensitivity and reliability here.


Tis practice allows operators to:


l Follow-up on the demineralisation process performance


l Make better use of resin capacity. l And optimises regeneration cycles.


So, measuring silica in steam/water processes today is ‘a must’ for sustaining and increasing power plant process efficiency.


in the steam, the boiler


water should not contain more than 100ppb of SiO2 ideal boiler conditions are met.


if


Measuring silica easily Hach Lange, a supplier and producer of water analysis technology, recently launched the POLYMETRON 9210 Silica analyser. Tis analyser provides operators’ the right means to measure silica in power plants. It detects early stages of resin saturation due to its


low 0.5 ppb detection limit which in turn reduces resin generation costs. Te analyser’s built-in sequencer (1 to 6 channels) optimises plant investments and favours the implementation of resin monitoring ‘best practices’. Te innovative ‘zero method’ operation determines potential Silica deposits on turbine segments; it is performed automatically without the need of calibration solutions or resin cartridges – eliminating any potential human error. Te unique grab sample feature ensures on the spot checking with reliable calibrations. To maintain measurement accuracy an air bubble elimination in the photometric cell has been integrated and for smaller power stations that are not constantly running, to return on-line with the sample after interruptions is also an option now. In order to reduce operating and maintenance costs to a minimum, this analyser has been designed to allow reagents to be made locally and only needs replenishment every 55 days (10 minutes cycle) or 84 days (15 minutes cycle). Today, Hach Lange has 3500 POLYMETRON


Silica analysers installed. Power plant operators are interested in analysers that can measure silica and run by themselves, having them be reliable and optimise plant process performance.


Operator feedback Te POLYMTERON 9210 Silica analyser meets all these criteria. Direct operator feedback confirms that many users appreciate the following advantages this analyser has to offer: zero method, using less reagents; built-in sequencer of one to six channels which optimises plant investments; unique grab sample feature allowing on the spot checking; easy to navigate menu structure; measurements are accurate and reliable. Te POLYMTERON 9210 can now easily be integrated into a nuclear or fossil power plant and will measure silica accurately, reduce demineralisation water plant costs and optimise overall plant process efficiency. l


Enter 21 or ✔ at www.engineerlive.com/ipe


Pierre Guillou is Global Product Manager and Katrien Verhassel is Communications Manager with HACH LANGE Sàrl, Vésenaz, Switzerland. www.hach-lange.ch


www.engineerlive.com 21


Paying attention to the so-called utility plant can also yield attractive returns. Improving water treatment programmes by preventing the formation of insulating boiler scale, namely silica, could save a typical power plant facility 10–12 per cent in steam-realted costs.


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