Power generation boilers use fuels such as coal, oil or natural gas to heat water and therefore produce steam, which is in turn used to drive turbine generators. The economics of power generation rely to a great extent on the efficiency of the fuel to heat conversion process and therefore the power generation industry are amongst the most advanced users of efficiency techniques based on on-line process analysis.
Within the power station the aim of water and steam control is to minimize contamination of circuit, thereby reducing corrosion as well as cutting down the risk of the formation of harmful impurities. Therefore it is very important to control the quality of water to prevent the deposits on turbine blades by Silica (SiO2), reduce corrosion by dissolved oxygen (DO) or to prevent acid corrosion by Hydrazine (N2H4). Measurement of water conductivity gives an excellent initial indication of falling water quality, analysis of Chlorine (Cl2), Ozone (O3) and Chloride (Cl) used for control of cooling water disinfecting, indication of corrosion and detection of cooling water leaks in the condense stage.
The sampling system shall monitor key chemical parameters which relate to the quality of process fluids in the steam-condensate-feedwater cycle and the quality of various other process fluids. The system provides data to operating personnel for detection of deviations from control limits so that corrective action can be taken. As a minimum, the following components shall be included in each sample line:
- Inlet Isolation Valve
- Primary Sample Cooler
- Variable Pressure Reducing Valve
- Secondary Sample Cooler
- Blowdown Valve
- Pressure Indicator
- Temperature Indicator
- Total Sample Line Flow Indicator
- High Temperature Shutoff Valve
- Back Pressure Regulating/Relief Valve
- Grab Sample
- Analyzer Branch Lines and Valved Flow Indicators as appropriate
The water analysis equipment shall be designed complete with all sample conditioning devices, analyzers, transmitters, indicators, recorders, annunciators, interlocks, etc. The general arrangement of the water analysis equipment proposed shall be shown by the bidder. The sample points and components on each line will be shown on the water analysis system P&ID.
Under all sampling conditions, cells or analyzers not requiring minimum sample flow rate shall be designed with a flow rate of approximately 50-100 cc/min. If the analytical equipment requires some different flow rate, the analyzer minimum flow shall be the design basis. Total sample line flow should be at a rate of 6 feet/second (2 M/sec) to ensure a contemporary sample.
To ensure representative samples, each sample shall flow continuously. Bumpless transfer shall be incorporated so that the flow to the analyzer is undisturbed by grab sampling or maintenance of analyzers.
The sampling system will be designed to include the following sub-systems and skids as required:
- Sample Conditioning Rack
- Wet Analyzer Rack
- Control and Recorder Panel
- Temperature Control Unit (TCU)
The Wet Analyzer Rack shall be designed to be located in close proximity to the Sample Conditioning Rack and Control and Monitor Panel, and either mounted on the same base or bolted to it if possible. The analyzers will be surface mounted to this rack. Insofar as practicable, panel instruments, electrical devices, and conduit shall be arranged logically according to function. Panels shall be constructed of carbon steel and painted in accordance with this specification. Units shall be designed so that the wet analyzer(s) can be easily accessible from the front of the rack, with all drain, electrical and other connections located in the rear.
The Wet Analyzer Rack shall include the following, but not be limited to:
– Hydrazine analyzers
– Sodium analyzers
– Silica analyzers
– Other non-cell type analyzers, such as chlorides or phosphate analyzers 
Analyzer sample lines will originate from a dedicated bulkhead area near the top of the rack, or will continue from the attached conditioning rack.
Unless one is included with the analyzer, each measuring analyzer shall include a flowmeter with a needle valve for manual flow adjustment. The flow meter range
Sentry Equipment Technical Specification – Steam and Water Sampling System
shall be suitable for the flow requirements of the analyzer. A glass tubed flow meter is required, acrylic type flow meters are not allowed.
A drain line will collect all the liquids leaving the analyzers, and lead them to the conditioning rack drain or other drain as appropriate.
The analyzers on the Wet Analyzer Rack will be wired to the Control & Monitor Panel to terminate all the signals from the cells, analyzers, and power supply. The electrical enclosure, as well as the electronics enclosure of each analyzer, should have a NEMA Type 12 rating as a minimum.
The Control and Monitor Panel shall be designed to be located in close proximity to the Sample Conditioning Rack and Wet Analyzer Rack, and either mounted on the same base or bolted to it if possible.
The temperature control unit shall be a packaged, chilled water cooling and control system, mounted on a skid, with all necessary accessories included within the confines of the skid. Included are: a full-capacity circulation pump for the cooling water, full-capacity hermetically sealed compressor, and all necessary piping, valves and controls.
