Objective 5: Sampling and Testing Flashcards
What measuring units are typically used?
Metric units
PPM
Parts per million
What is the relationship between PPM and mg/L?
PPM x solution density = mg/L
What is the relationship between PPM and mg/L for water?
PPM = mg/L
Since water’s density is taken to be 1.0.
What are 11 Guidelines for Monitoring and Testing of Boiler Water?
- Identified critical points in the boiler system from which to take and test samples
- Time schedule for sampling and testing
- Clear, detailed procedure and interpretation for each test
- Established acceptable limits for each tested parameter
- Comparison of test results against acceptable limits
- Guidelines to maintain each tested parameter within acceptable range.
- Schedule and procedures for control chemical injections
- Acceptable training for relevant personnel
- Regular reporting procedure of results
- Forecasting steam production and corresponding make-up requirements
- Emergency troubleshooting procedures for severe excursions
What are the Typically Monitored Parameters?
- Phosphate
- Sulphite
- Alkalinity
- Total Dissolved Solids
- pH Measurement
- Chloride
- Iron
- Dissolved Oxygen
- Steam Purity
- Sampling
What is the most common method to determine Phosphate Residual in the water?
Ortho-Phosphate Test
What may be considered an acceptable Phosphate Residual?
Depending on the plant, anywhere from 2.0 mg/L (for complex equilibrium program) to 20 or 30 mg/L (for coordinated program).
Ortho-Phosphate Test
A measured amount of boiler water is mixed in a tube with specific amounts of reagents (one of which is molybdate). The water will turn a blue colour, with the depth of colour corresponding to the amount of phosphate in the water. The tube colour is then compared against standard coloured tubes, which are each marked to represent a specific mg/L or ppm of phosphate.
What instrument can be used for a more sophisticated and complete determination of all phosphate components?
Spectrophotometer
Where is the feed point for sulphite?
- Deaerator
2. Between the deaerator and the boiler
What is the typical sulphite residual maintained?
10-20 mg/L
What is the Sulphite Test Process?
- Get a fresh sample of boiler water which has had as little exposure to air as possible, cooled to room temperature
- Phenolphthalein indicator is added to the water, turning it red
- Sulphite indicator is added until the water becomes clear, indicating an acceptable pH
- Sample is titrated with potassium iodide-iodate solution until a faint permanent blue colour appears
- The mL of titrant used is multiplied by a factor
What are the 3 Alkalinity Tests?
- P Alkalinity
- M Alkalinity
- OH Alkalinity
P Alkalinity
P stands for Phenolphthalein, which is a titrating indicator that changes colour at a pH of 8.3 and used to indicate half of the carbonates plus all hydroxides in the water.
M Alkalinity
M stands for Methyl, which is a titration indicator that changes colour at a pH of 4.3 and is used to indicate the TOTAL amount of alkalinity (i.e. carbonates + hydroxides + bicarbonates) in the water.
OH Alkalinity
OH stands for Hydroxide and is a calculated alkalinity: 2P - M = OH. It gives only the amount of hydroxide alkalinity in the water and is often referred to as the caustic alkalinity.
Which Alkalinity Reading is generally used for control?
M Alkalinity
What are the methods of controlling Alkalinity?
- Adjusting Phosphate Feed
- Adding Caustic Soda
- Boiler blowdown
What are the acceptable limits of Total Alkalinity?
0-2 MPa: <350 mg/L
7-10 MPa: <100 mg/L
Explain the process of Alkalinity Testing
- Phenolphthalein indicator is added to a boiler sample which then turns red
- Sample is titrated with sulphuric acid until the sample becomes clear - the endpoint for P Alkalinity
- Methyl orange is added to the same sample, which then turns orange
- Sample is titrated with sulphuric acid until it turns red - the endpoint for M Alkalinity
Boiler Conductivity
The ability of water to conduct an electric current
Specific Conductance
The measure of the exact amount of electricity that can be conducted by a particular sample
What is relationship between the amount of dissolved solids and conductivity?
The specific conductance indicates the amount of total dissolved solids in the water.
What are the units of specific conductance?
µ mhos/cm: micro-mhos per cm
µ S/cm: micro-siemens per cm
What is the approximate mathematical relationship between the specific conductance and the actual total dissolved solids in the water?
1.0 µmho/cm of conductivity = 0.9 mg/L of dissolved solids
Explain the process of Conductivity Testing
A measured amount of filtered boiler water is placed in a flask and then a probe from a conductivity meter is placed into the water. The meter passes a current between electrodes in the probe and then measures and indicates the current on a display that is calibrated to read in µmhos. Some indicate the total dissolved solids directly.
What is the main value of pH testing?
As a backup when alkalinity is used for control.
Why is pH Testing important?
Control of corrosion and the effectiveness of scale-reducing reactions are very pH dependent.
What are the acceptable pH ranges for boilers?
6 MPa: 9.0 - 9.6
Where is pH testing prominent in the boiler system?
- Feedwater
2. Condensate Return Lines
How does pH testing work?
A special pH meter with a probe and electronic circuitry displays a direct pH readout, after being calibrated in a neutral buffer liquid.
In what form does Chloride exist in boiler water?
- Calcium Chloride
- Magnesium Chloride
- Sodium Chloride
- Iron Chloride
What is the effect of Chloride in Boiler water?
They are harmless except that they increase the dissolved solids.
How is the percentage of blowdown determined as it relates to Chloride?
Chloride in Feedwater/Chloride in Boiler Water = % Blowdown
How does the Chloride Test work?
- Boiler water sample is added to a flask along with phenolphthalein, turning it red
- Sulphuric acid is added until the sample turns clear, indicating a pH of 8.3
- Potassium chromate is added to the sample, followed by reiteration with silver nitrate, until the sample turns a rusty colour - chloride is calculated
How often is testing for iron done in a boiler system?
Occasionally
Why are iron tests performed at different locations in the system?
To determine the source of the iron, whether it is due to the water supply or to corrosion within the system and if so, if it is occurring inside the boiler itself, or the feedwater, or condensate systems.
How is the Iron Test performed?
A lab technician uses special equipment and adds an iron reagent to a sample of boiler water. If iron is present, an orange colour results. The sample is placed in a spectrophotometer where the absorbency of the sample is measured. The reading is transferred to a calculation which gives the iron content.
When is Dissolved Oxygen tested for?
Occasionally, usually as a check on the efficiency of deaeration equipment, to determine the amount of dissolved oxygen that may be getting into the boiler
What kinds of methods are used to test for Dissolved Oxygen?
- Titrations
2. Specialized Instruments such as Online Analyzers
Who normally tests for Dissolved Oxygen
Lab technician or consultant
How is Steam collected to be tested?
A sample of steam is collected and condensed upstream from the superheater and subjected to various tests.
What kinds of tests are performed to determine Steam Purity?
- Conductivity Test
- Sodium Tracer
- Anion Analyzer Test
Who tests for Steam Purity?
Lab technician or consultant
How is Sampling done?
- Sample is run through a cooler to reduce to ambient temperature
- Sample bottles are well-rinsed and flushed with the new sample to avoid interference from previous samples
- Sample line is run for several minutes before the sample is taken, to avoid contamination from sitting idle.
Where is Automatic Monitoring done?
In more sophisticated installations, particularly with higher pressure, higher capacity boilers where internal treatment is critical.
Automatic Monitoring
They provide continuous readings to a central location, including computer control systems, and relieve the testing responsibility from the operator, although occasional manual checks may be required. Some of these analyzers may be tied into control loops, e.g. with automatic blowdown.
What are 7 examples of automatic monitors?
- Specific Conductance Meters
- Corrosion Rate Analyzers
- Hardness Analyzers
- Fouling and Corrosion Monitors
- pH Meters
- Dissolved Oxygen Analyzers
- Turbidity Analyzers
