October 22, 2019

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chlorine ›   Chlorine dioxide ›   water ›  


Kemio, the best instrument for disinfection monitoring!

Repeatable, reliable results Kemio reduces complexity and subjectivity for the user, minimizing chances for error, and delivering repeatable results for any operator. Multiparameter testing platform Kemio can test for free chlorine, total chlorine, chlorine dioxide, chlorite and peracetic acid (PAA), with new sensors added to the same device. Kemio also allows for simultaneous measurement of free and total chorine. View full article →

How can a cooling tower spread Legionnaires' Disease?

It really should be one of the happiest, most carefree destinations on the planet; however perennial family favourite, Disneyland, found itself at the epicentre of an outbreak of Legionnaire’s disease just before Christmas, as you might have read elsewhere. As well as being an obvious PR disaster for the globally-renown resort behemoth, any possible risk presented by the presence of the potentially deadly respiratory infection could spell more far-reaching bad news for those directly affected by an episode.  View full article →

Brewing up success!

Amperometric methods are traditionally the domain of large laboratory instrumentation which require high levels of user care and maintenance of the electrodes, both of which have been overcome with the ChlordioX Plus, in an instrument a fraction of the size and a fraction of the capital investment. View full article →
November 28, 2017

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chemicals ›   chlorine ›   Chlorine dioxide ›  


Chlorine vs. Chlorine Dioxide different features against biofilm growth

Biofouling growth may be partly prevented during the design phase, by using suitable materials (i.e. copper, AISI 316 stainless steel or treatment of the surfaces with special polymers) and by dimensioning the pipes in such a way as to obtain a flow rate (> 1 m/s) which will hinder adhesion of the organisms and to avoid stagnant points as much as possible. View full article →

Industrial Water Analysis

Boiler water analysis

If you supervise a limited-attendance or unattended boiler then Lenntech can assist you with your water testing requirements.

Boiler water tests available

The specific method of chemical treatment used varies with the type of boiler and the specific properties of the water from which the boiler feed is derived. This is very site specific but Lenntech has the testing capability to cover all your requirements.

A boiler requires testing of three different water types as shown below:

Feedwater

Boiler feedwater is sourced from many different places. Some supplies come from industry owned bores and treatment plants, while others come directly from a council supply, however all feedwater should be analysed in order to correctly determine dose rates of treatment chemicals.

Water quality can change as it passes through a delivery or reticulation system, so it is important to check for various parameters at point of use - ie where it enters the boiler or pre-treatment system.

Boiler feedwater is usually a combination of returned condensate plus pre-treated makeup water from a softener, reverse osmosis, or other purification system. Typical tests used for boiler feedwater include:

  • Chloride or salinity
  • Conductivity
  • Dissolved Oxygen
  • Hardness
  • Iron and Manganese  
  • pH
  • Silica
  • Sulphide
  • Suspended Solids
  • Total Dissolved Solids
  • Turbidity

Not all water supplies will require all the tests shown here, and if the supply is constant the tests will not need to be repeated very often.

Boiler Water

The boiler water itself must be dosed in order for the boiler to run efficiently and safely. A chemical imbalance can lead to corrosion and damage to the system and this damage can ultimately lead to boiler failure and injury.

Boiler water analyses are basically aimed at keeping the parameters within established limits.

Tests include

  • Chloride
  • Hydroxide P2 Alkalinity
  • Nitrate
  • pH
  • Phenolphthalein P1 Alkalinity
  • Phosphate
  • Silica
  • Sulphite
  • Total Alkalinity
  • Total Dissolved Solids

Condensate

Good condensate is the best quality, least expensive water most systems can generate. You do not want to lose it, or contaminate it unnecessarily.

Steam condensate analysis should include

  • Ammonia
  • Conductivity
  • Copper
  • Iron
  • pH

Test

Description

Make-up, Raw Water pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Silicate, Sulphur, Chloride, Ortho-Phosphate, Total Inorganic Phosphate
Clarifier, Softener, Filter-Alum pH, P/M-Alkalinity, Conductivity, Total Aluminium, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Silicate, Sulphur, Chloride
Clarifier, Softener, Filter-Lime pH, P/M-Alkalinity, Conductivity, Total Hardness, Filtered Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Silicate, Sulphur, Chloride, Total Inorganic Phosphate
Sodium Zeolite, Dealkalizer, Desilicizer, Softened Make-up pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Silicate, Sulphur, Chloride
Hydrogen Zeolite, Strong Acid Cation pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Silicate, Sulphur, Chloride
Mixed Bed Exchanger, Degasifier, Anion Exchanger, Demineralizer Conductivity, Filtered Hardness, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Silicate, Reactive Silicate, Sulphur, Chloride
Deaerating Heater, Feedwater, Condensate Polisher pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Silicate, Reactive Silicate, Sulphur, Chloride, Total Phosphate.
Blowdown – Expected Conductance >300 µS/cm pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Silicate, Sulphur, Chloride, Nitrate, Ortho-Phosphate
Blowdown – Expected Conductance >300 µS/cm pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Silicate, Silica Reactive, Sulphur, Chloride, Nitrate, Ortho-Phosphate
Steam Condensate Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Silicate, Reactive Silica, Sulphur, Chloride

Cooling water analysis

Cooling tower is a heat removal devices used to eliminate waste heat of air released to atmosphere. This process allows airborne contaminants, organic matters and particles to become deposited into the cooling water. This, combined with the contaminants in the feed water, creates an environment for microorganism growth, solid deposits and scaling.

Improper treated cooling tower water could be an amplifier of biological hazardous agent. The warm and moist environment of a cooling tower favors the growth of Legionella bacteria which causes the outbreak of the deathly Legionnaires' disease. Thus, cooling tower water quality must be monitored in a regular basis to prevent spreading of diseases to users.

Test

Description

Make-up, Raw Water pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Total Manganese, Sodium, Total Silica, Sulphur, Chloride, Ortho-Phosphate, Total Inorganic Phosphate, Total Zinc
Cooling Tower, Air Washer pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Total Manganese, Sodium, Total Silica, Sulphur, Chloride, Ortho-Phosphate, Total Zinc
Sea water/Brine pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Manganese, Total Iron, Total Copper, Total Silica, Sulphur, Ortho-Phosphate, Total Zinc
High Cycle Tower, Jacket, Brine pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Manganese, Total Iron, Total Copper, Total Silica, Sulphur, Ortho-Phosphate, Total Zinc
Closed System, Glycol pH, Specific Gravity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Total Silica, Sulphur, Chloride
Closed System, Non-Glycol pH, P/M-Alkalinity, Conductivity, Total Hardness, Total Calcium, Total Magnesium, Total Iron, Total Copper, Sodium, Total Silica, Sulphur, Chloride



Read more: https://www.lenntech.com/products/boiler-water-analysis.htm#ixzz4x5ZX3UHF

Methods for determining chlorine dioxide and its oxychlorine by-products in water

The analysis of chlorine dioxide and its oxychlorine by products in water is a difficult topic due to the volatility of chlorine dioxide and to the interferences from other species with standard test methods. In the real samples, this is further complicated as chlorine dioxide is often used in a system which is dynamic and therefore sampling is also important.

USEPA Regulations

The USEPA require that both chlorine dioxide (ClO2) and chlorite (ClO2-) are monitored daily at the start of a distribution network and that chlorite is measured less frequently at various points throughout a network. Chlorate is not required, although is included under the Information Collection Rule.

The following are methods that have been approved by the USEPA for ClO2 monitoring:

  • Amperometric titration (Standard Method 4500 - ClO2 E)
  • Colorimetric DPD (Standard Method 4500 - ClO2 D)
  • Colorimetric Lissamine Green (USEPA Method 327.0 V1.1)
  • ChlordioX Plus Sensor System

As DPD has been removed as a standard method for determining ClO2 by the AWWA Standard Methods committee, the EPA will also probably remove it sooner rather than later.

As for chlorite, there are a few methods (such as ion chromatography) approved for chlorite monitoring. None of them are truly portable as the ChlordioX Plus is making it the only portable USEPA approved method for determining chlorite.

Methods in detail

  • Iodometric titration (Standard Method 4500 - ClO2 Method B) - Iodometric titration of ClO2, Cl2, ClO2- and ClO3- is possible with although it is a very difficult and time consuming procedure to separate all the oxychlorine species. It is a better method for standardising chlorine dioxide solutions.
  • Amperometric methods

Standard Method (4500 -ClO2 Method C) - Amperometric titration is an electrochemical method that measures current flow when a fixed voltage is applied to an electrode. By measuring the current whilst carrying out a titration with phenylarseine oxide, each oxychlorine species can be separated out and quantified. However, Method C has now been removed as an EPA approved method for measuring chlorine dioxide in drinking water due to inherent weaknesses in the test method.

Amperometric Method (4500 - ClO2 Method E) - Principle is as per Method C and the procedure is also similar but the inherent test weaknesses are avoided. This method is the standard method which all the ChlordioX Plus evaluations were compared to and is the industry standard method. In theory, as well as chlorine dioxide, chlorine and chlorite, chlorate can also be carried out using this method but it is complicated and therefore usually carried out via ion chromatography.

  • DPD method Colorimetry (4500 - ClO2 Method D - Reserved) - The industry standard for portable testing of chlorine dioxide (and to a degree chlorite) but according to recent research is not selective enough in the presence of both chlorine dioxide and chlorite and also suffers from other interferences such as chromate and oxidised manganese. It is no longer a standard method (AWWA) but is still an EPA approved method.
  • Lissamine (LGB) Green - Not a standard method but an EPA approved method for measuring chlorine dioxide (and chlorite in the presence of horseradish peroxidase). It is temperature dependent as it removes colour from the lissamine green indicator and, therefore, is not easy to use in the field and at its best in a laboratory environment.
  • Ion Chromatography (4110 Determination of Oxyhalides using Ion Chromatography) - The standard method for chlorite and chlorate determination and a USEPA requirement although obviously not a field test.
  • Spectrophotometry - Chlorine dioxide can be measured photometrically at 360nm using a standard spectrophotometer although the detection limit is relatively high and solutions containing chlorine dioxide and chlorite can be susceptible to interference (especially at longer wavelengths) so again it is best used as a tool for standardisation of solutions. Some field test kits also use this method but at wavelengths in the visible region.

Other colorimetric methods

Other colorimetric methods are available however none are approved for compliance testing.

This summary of methods is based on White’s Handbook of Chlorination and Alternative Disinfectants by the Black and Veatch Corporation, published by Wiley in 2010.

See here for a list of EPA methods approved for chlorine dioxide and chlorite monitoring under the alternative test methods program

Diseno de succion y descarga de bombas de dosificacion de quimicos

Sistema de tubería de succión de la bomba

 La tubería debe ser distribuido de modo no hay puntos altos ocurren donde pueden formar vapor bolsillos. bolsas de vapor reducen el área de flujo efectiva de la tubería y por lo tanto hacen cebado y funcionamiento de la bomba difícil. Vent cualquiera de los puntos altos inevitables y proporcionar calibre y drenar las conexiones adyacentes a la bomba.

 Tamaño de línea

Muchos de los problemas de la bomba de resultado de una línea de succión que es demasiado pequeño en el diámetro, o demasiado largo. La tubería de succión debe ser del siguiente modo para proporcionar una transición suave del flujo de fluido y dar lugar a pérdidas de tuberías de fricción reducidos:

Ser corta y directa

  • Ser de una a dos veces más grande que la bomba conexión de aspiración. Utilice reductores de tubería tipo excéntricas en la bomba con el lado plano hacia arriba para evitar una bolsa de vapor posible.
  • Contener un número mínimo de vueltas. Cumplir con las vueltas necesarias con los codos de radio largo o laterales.

 

 Sistema de bomba Tubería de Descarga

 A continuación se enumeran los requisitos fundamentales para un sistema de tuberías de descarga.

La tubería no debe ser menor que la conexión de descarga de la bomba, y debe:

  • Ser lo más corta y directa posible.
  • Sea uno a dos tamaños más grandes que la conexión de descarga de la bomba con multiplicadores utilizados en la bomba.

Contener un número mínimo de vueltas. Llevar a cabo cualquier vueltas necesarias con los codos de radio largo o laterales.

  • Estar provisto de calibre y de drenaje conexiones adyacentes a la bomba.

 

Todo alternativo de desplazamiento positivo bombas suministran fluido y construir presión hasta que se tomen medidas para controlar y estabilizar el trabajo de la bomba o se produce un fallo. Para proteger la bomba, tuberías, y personal de los peligros asociados con el funcionamiento de una bomba de “desplazamiento positivo” contra una “cabeza muerta” una válvula de alivio de seguridad siempre debe ser proporcionado entre la bomba y la válvula de descarga.

 

La válvula de seguridad debe estar dimensionado para pasar toda la capacidad de la bomba y la presión de apertura debe ser fijado en el 10 por ciento sobre la presión de descarga de trabajo especificado y tienen una presión de acumulación no superior a 110 por ciento de agrietamiento presión.

La conexión de salida de la válvula de alivio de seguridad ideal sería que se canaliza de vuelta al recipiente de suministro de aspiración. Tubería de nuevo a la tubería de succión puede causar discontinuidades en el flujo de la tubería de succión que puede resultar en un mal funcionamiento de la bomba y daños. En caso de que sea necesario tubería de la válvula de seguridad de nuevo a la tubería de succión, la conexión en el tubo de succión debe tener un mínimo de diámetros de tubería 10 de aspiración de longitud de vuelta hacia el recipiente de suministro de aspiración alejado de la conexión de aspiración de la bomba. Esto permitirá que cualquier discontinuidad de flujo creado por el flujo de la válvula de alivio en la succión

tubería para ser suavizadas por el tiempo y efecto viscoso.

 

Una línea de derivación de descarga de la tubería de descarga de la bomba de vuelta al recipiente de suministro de aspiración permite la lubricación para llegar a las partes críticas de la bomba y duro durante el inicio, sin someterlos a cargas altas y permite que todas las cámaras de bombeo cilindro de fluido a convertirse totalmente cebadas.

Una línea de derivación con una válvula de cierre se debe instalar en la tubería de descarga entre la bomba y la válvula de retención de vuelta a la fuente de suministro de aspiración, no en la línea de succión de la bomba para evitar la discontinuidad del flujo.

Instalar una válvula de retención de descarga allá de la conexión de derivación para proteger la bomba de presión del sistema de descarga durante los periodos de inactividad de la bomba y el arranque de la bomba.

Las descargas piping “puntos muertos” deben ser evitados o provisto de dispositivo de amortiguación. Este tipo de característica puede ser responsable de los armónicos de tuberías indeseables y puede contribuir a niveles elevados de vibración y ruido.

Para algunos servicios las fluctuaciones de presión de la bomba o de flujo naturales pueden no ser apropiados. En estos casos, es prudente utilizar un amortiguador de pulsaciones de la instalación. Para una eficacia máxima del amortiguador debe ser montado adyacente al cilindro de fluido de la bomba. Recomendaciones para el tamaño de amortiguador y el tipo pueden obtenerse de fabricantes mojadores basado en detalles de tipo de bomba y tamaño, las condiciones de servicio, y el sistema de tuberías.

Instalar bridas o uniones como cerca de la bomba como sea práctico para permitir la eliminación cilindro de fluido durante el mantenimiento.

se requieren válvulas de cierre en ambas líneas de succión y descarga para aislar la bomba cuando se requiere mantenimiento. Ellos deben ser de diseño apertura completa, tal como una válvula de compuerta. Cuando la conexión de dos o más bombas a una aspiración común

y / o línea de descarga de cuidado ejercicio para prevenir una onda de presión mutuallly de refuerzo que se produzcan durante el funcionamiento. Esto se puede lograr mediante la adición de las capacidades de todas las bombas que operarán simultáneamente para determinar las velocidades de línea para el dimensionamiento de la tubería y el cálculo de la cabeza de aceleración. La mejor manera de evitar una onda de presión de refuerzo mutuo es instalar las líneas de succión y de descarga independientes para cada bomba.

La Figura 31 proporciona un ejemplo de las recomendaciones esbozadas en la sección anterior para un sistema de tubería de la bomba apropiada, mientras que la Figura 32 proporciona un ejemplo de una configuración no apropiado sistema de tubería de la bomba.

 

Metering pump suction and discharge design

Pump Suction Piping System

 

Piping should be laid out so no high points occur where vapor pockets may form. Vapor pockets reduce the effective flow area of the pipe and consequently make pump priming and operation difficult. Vent any unavoidable high points and provide gauge and drain connections adjacent to pump.

 

Line Size

 

Many pump problems result from a suction line that is too small in diameter, or too long. Suction piping should be as follows to provide a smooth transition of fluid flow and result in reduced piping friction losses:

 

Be short and direct

  • Be one to two sizes larger than pump suction connection. Use eccentric type pipe reducers at pump with flat side up to avoid a possible vapor pocket.
  • Contain a minimum number of turns. Accomplish necessary turns with long radius elbows or laterals.

 

 

Pump Discharge Piping System

 

Listed below are the fundamental requirements for a discharge piping system.

Piping should not be smaller than pump discharge connection, and should:

  • Be as short and direct as possible.
  • Be one to two sizes larger than pump discharge connection with increasers used at pump.

Contain a minimum number of turns. Accomplish any necessary turns with long radius elbows or laterals.

  • Be provided with gauge and drain connections adjacent to pump.

 

All positive displacement reciprocating pumps deliver fluid and build pressure until action is taken to control and stabilize the pump’s work or a failure occurs. To protect pump, piping, and personnel from hazards associated with operating a “positive displacement” pump against a “dead head” a safety relief valve should always be provided between the pump and discharge valve.

 

The safety relief valve should be sized to pass the entire pump capacity and the cracking pressure should be set at 10 percent over the specified working discharge pressure and have an accumulation pressure not exceeding 110 percent of cracking pressure.

The safety relief valve outlet connection should ideally be piped back to the suction supply vessel. Piping back to the suction pipe can cause discontinuities in the suction pipe flow that can result in poor pump operation and damage. Should it become necessary to pipe the safety relief valve back to the suction piping, the connection into the suction pipe should be a minimum of 10 suction pipe diameters in length back toward the suction supply vessel away from the pump suction connection. This will allow any flow discontinuity created by the relief valve flow into the suction

pipe to be smoothed out by time and viscous effect.

 

A discharge bypass line from pump discharge piping back to the suction supply vessel permits lubrication to reach critical pump and drive parts during startup without subjecting them to high loads and allows all fluid cylinder pumping chambers to become fully primed.

A bypass line with a shut-off valve should be installed in discharge piping between pump and check valve back to suction supply source, not into the pump suction line to prevent flow discontinuity.

Install a discharge check valve beyond the bypass connection to protect pump from discharge system pressure during pump idle periods and pump startup.

Discharges piping “dead ends” are to be avoided or provided with dampening device. This type of feature can be responsible for undesirable piping harmonics and can contribute to elevated levels of vibration and noise.

For some services the natural pump pressure or flow fluctuations may not be appropriate. In these cases it is prudent to use a pulsation dampener for the installation. For maximum effectiveness the dampener should be mounted adjacent to the pump fluid cylinder. Recommendations for dampener size and type can be obtained from dampener manufacturers based on details of pump type and size, service conditions, and piping system.

Install flanges or unions as close to the pump as practical to allow for fluid cylinder removal during maintenance.

Shut-off valves are required in both suction and discharge lines to isolate pump when maintenance is required. They should be of full opening design, such as a gate valve. When connecting two or more pumps to a common suction

and/or discharge line exercise care to prevent a mutuallly reinforcing pressure wave from occurring during operation. This can be achieved by adding the capacities of all pumps that will operate simultaneously to determine line velocities for sizing pipe and calculating the acceleration head. The best way to avoid a mutually reinforcing pressure wave is to install independent suction and discharge lines to each pump.

Figure 31 gives an example of the recommendations outlined in the previous section for an appropriate pump piping system, while Figure 32 provides an example an inappropriate pump piping system configuration.

Fundamentals of corrosion control in water systems

Liquid analysis systems and sensors are cost effective tools against corrosion.

Water plus metal equals corrosion. This reality attacks the bottom line of every steam driven power generation plant in the world.

In a steam power plant, high purity water is heated and boiled to make steam, which energizes and powers a turbine to produce electricity.

Water and steam are in constant contact with metal surfaces threatening the integrity of plant equipment like condensers, heaters, pumps, piping, boilers, and turbines.

Fortunately, water purification and chemical treatment greatly reduce and control the corrosion in the plant. Ensuring good cycle chemistry to prevent corrosion, however, requires accurate and continuous analytical measurements in the demineralization train, cooling water, condensate, and boiler feed-water and steam systems.

While the guidelines given below address the needs of a steam driven power generation facility, they can also be useful in other manufacturing facilities where water plays an important role.

Corrosion occurs when metal ions transfer from a base metal to water and combine with oxygen to become hydroxides and solid metal hydroxides. Resultant particles often travel to other parts of the system and are deposited.

Rust reaction
Rust reaction

Deposit is a poor conductor

Once a deposit forms, it attracts more suspended solids and the deposit grows. Deposits frequently accumulate on heat exchange surfaces, boiler tubes, and heaters.

The deposit is a poorer conductor of heat than metal and therefore interferes with heat transfer across the tube. This lowers the overall cycle efficiency and can cause local tube overheating failures. Deposits can also significantly lower the efficiency of the turbines and, in turn, become corrosion sites when dissolved solids trapped in the deposit concentrate as the liquid boils away. Eventually, the concentration reaches highly corrosive levels and severe under-deposit corrosion occurs.

A tough oxide film that protects the base metal is the best way to defend iron and copper from corrosion. For iron and carbon steel, the protective film is magnetite.

For copper and copper alloys, the protective film is cuprous oxide. This film works only in the presence of properly controlled water chemistry.

Proper water chemistry also ensures that the film won't wear away and, if a break occurs, the film quickly repairs itself.

Controlling water chemistry requires maintaining high purity water, controlling pH, monitoring for trace quantities of dissolved oxygen, and, if necessary, controlling the feed of a scavenging agent like hydrazine.

Demineralization train

The first line of defense against corrosion in a steam power plant is the use of high purity water. Producing that water is the function of the demineralization train, which converts raw water containing between 100 and 1,500 ppm dissolved solids into water that contains no more than 10 to 20 ppb dissolved solids. Treatment steps may include filtration, softening, chlorine removal, reverse osmosis, degasification, and ion exchange.

Efficient reverse osmosis (RO), in which water forces through a semi-permeable membrane, can remove approximately 98% of the dissolved salts and silica in raw water and nearly all large organic molecules. Contacting conductivity sensors placed in the feed water and the permeate of the RO let plant operators monitor the water quality and overall efficiency of the RO system.

Conductivity measurements in RO permeate and high purity water are not simple, however. Calibration of sensors is complex and must take place by comparing the sensor against a National Institute of Standards and Technology (NIST) traceable calibrated cell of a known cell constant or by calibrating the sensor in a certified solution. However, upon exposure to the atmosphere, high purity conductivity standards and water foul through the absorption of carbon dioxide from the surrounding air and any residue in the sample container. To prevent contamination, it may be desirable to use sensors pre-calibrated to NIST standards. Conductivity validation instruments are available that connect to the process via tubing, eliminating the effects of the atmosphere on the measurement.

Typically, feed-water to an RO system will undergo treatment and will already contain chemicals to ensure optimum operation. These chemicals, however, require careful monitoring, or they may attack the RO membranes. This is particularly true if the feed-water is outside the desired acidic range. Plant operators require general-purpose pH sensors to maintain mild acidity in the feed-water. Chlorine may be in the feed water in some plants as a biocide or need removal in others by means of a carbon bed because it attacks the RO membranes. However, carbon beds reach saturation over time, therefore, chlorine monitors detect breakthrough of chlorine.

Reverse osmosis alone can rarely produce water of sufficient purity for make-up. The RO permeate is usually polished using an Ion Exchanger (IX). These systems consist of tanks containing resin beads selectively treated to adsorb either cations or anions. A cation bed exchanges positively charged ions (such as calcium, magnesium, and sodium) for hydrogen, and the anion bed exchanges negatively charged ions (such as chloride, sulfate, and bicarbonate) for hydroxyl. The displaced hydrogen and hydroxyl combine to form pure water. After a certain amount of use, these systems become exhausted and must be regenerated using sulfuric or hydrochloric acid for cation resin and sodium hydroxide for anion. The monitoring of the concentration of both of these substances must happen continuously with conductivity sensors measuring the regenerant as it enters the tank. During rinse, toroidal conductivity measurements made on the bed effluent determine how well rinsed the regenerants are.

Ammonia, Conductivity, and pH

Variations in cooling tower design

In the condenser, recirculating cooling water converts turbine exhaust steam into condensate. Cooling water usually contains high levels of dissolved solids, and leakage of cooling water into the steam cycle is a major source of contamination.

Leaks introduce ions that raise the conductivity and increase the corrosiveness of the feed-water, boiler-water, and steam. To give early indication of leakage and to monitor the overall condenser performance, the cation conductivity of the condensate pump discharge registers on a flow-through conductivity sensor.

In addition, monitoring condensate and feed-water purity requires measuring cation conductivity. After the condensate passes through the cation column, the conductance of the contaminating salt increases as it converts to a significantly more conductive acid.

There is an increased emphasis in the industry on the re-use of cooling water using cooling towers. The cooling effect comes by the evaporation of a small fraction of water and heat exchange with the air passing through the cooling tower. As the water evaporates, however, the dissolved solids concentrate, ultimately causing scale and corrosion in the heat exchange equipment. While there are many variations in cooling tower design, a common feature is the control of water quality with the use of continuous pH and conductivity measurements to maintain a given set of conditions. A contacting conductivity sensor measures the relative concentration of the impurities in the water. The analyzer for that sensor initiates the opening of a blowdown valve when the conductivity becomes too high. Higher purity make-up water is then introduced which lowers the conductivity.

Since most impurities in cooling water are alkaline, a small quantity of sulfuric acid adds in to the circulating water to lower the pH and thus prevent the formation of scale. Measuring this sulfuric acid concentration and keeping the pH below seven, where scaling is less likely to occur (as indicated by the Langelier Index), is best accomplished by a general-purpose pH sensor. Cooling water that contains a high level of suspended solids, however, requires the use of more specialized pH sensors more resistant to fouling.

Liquid analysis in steam power generation

Condensate feed-water

The cooling tower turns steam into water after leaving the turbine. Make-up water from the demineralization train adds to this water to become feed-water, which pumps through a series of heaters to the boiler. Controlling corrosion in the condensate and feed-water system is usually accomplished in one of two ways-all volatile treatment (AVT) and oxygenated treatment (OT). AVT uses ammonia to control pH and hydrazine to provide a reducing environment for protection of copper alloys. AVT requires measurement of ammonia, dissolved oxygen, and hydrazine. Ammonia measurement can happen either directly or indirectly from pH and conductivity. The indirect method is useful because ammonia reacts in water to produce hydroxide ion. Both conductivity, which is a measurement of ions in solutions, and pH, which is an indirect measurement of hydroxide ion, can combine to yield the ammonia concentration.

OT uses ammonia to control pH and trace oxygen to provide a slightly oxidizing environment that promotes formation of a tough modified oxide film. Water quality for OT is more stringent than for AVT, requiring cation conductivity of less than 0.15 micro Siemens/centimeter. It is necessary to measure dissolved oxygen, pH, and cation conductivity in feed-water systems using the OT method. pH measurement can be difficult in low conductivity water and requires the use of flowing reference technology. A pH measurement requires electrical continuity between the reference and glass electrodes and a path to the solution ground. High purity water does not provide enough conductivity to reliably complete these paths and causes junction potential that registers as erratic drift and offset in the pH measurement. A flowing reference eliminates this effect by stabilizing the junction potential. This measurement takes place in a bypass line in order to preserve the quality of the feed-water and preferably in a stainless steel measurement chamber to dissipate the electrostatic current generated by the high purity water. Since high purity pH is flow sensitive, flow rates should be very low and constant.

Boiler water steam treatment

The boiler is the final collection point for all the corrosive and scale-producing contaminants generated upstream. Solid corrosion lands on the boiler tube surfaces and grows by collecting more suspended matter. Eventually, overheating and tube failure occur. Maintenance of a protective oxide film is the optimum way to limit water corrosion, and this more readily happens when maintaining a low concentration of dissolved solids in a slightly alkaline pH environment. To accomplish this, continuous measurement of both pH and conductivity needs to happen. Conductivity measures the concentration of dissolved solids and a long-life conductivity sensor is required. To maintain the alkaline environment required, power plants commonly buffer the boiler water with sodium hydroxide and sodium phosphate salts. Overfeeding or underfeeding of these chemicals can be damaging, however, and therefore accurate pH and phosphate measurements are critical.

Boiler water also undergoes treatment in order to produce high purity steam. Impurities enter this boiler water from the boiler drum and from vaporous carryover, which deposits on the turbine and causes erosion damage. Silica is the most notorious contaminant, and it is necessary to measure it in the boiler water and steam. Salts such as sodium hydroxide and ammonia salts also vaporize in the steam and flow into the turbine where they precipitate, concentrate, and become highly corrosive. To control contamination in the steam, the conductivity measurement of the boiler water must happen, which indirectly measures the dissolved solids. Then, blowdown controls the amount of contamination.

So, to avoid the uncontrolled corrosion that costs the power industry billions of dollars every year, monitor water quality rigorously and control that quality continuously.

Liquid analysis systems and sensors are hard working, easy-to-use, cost effective tools when measured against the impact of corrosion on plant costs and operations.

While every plant is different, generally an array of pH and conductivity sensing instruments is required for virtually every step of the steam-power generation process.

Beyond that, individual plants will require dissolved oxygen, ozone, chlorine, and other more specialized measurements.

Many plants are opting for centralized digital control systems to continuously monitor the output of analyzers and automate many control functions. This reduces impact on staff and allows corrosion control management to run like a well-oiled machine.

Most important, the key to successful corrosion control is the continuity of measurement.

Grab samples and other periodic measurement techniques are inadequate to the task. Only continuous, real-time analysis offers the assurance of water quality that corrosion control requires.

Sensing pH a venerated pursuit

In the sixteenth century, alchemist Leonard Thurneysser discovered that the hue of violet sap changed with the addition of either sulfurous or sulfuric acids. This early indicator was widely used through the subsequent centuries to detect acids.

With Svante Arrhenius's introduction of ionic theory in the 1880s, the first theories concerning disassociation of acids and bases were developed. Johannes Bronsted, who postulated that acids and bases are substances capable of either donating or accepting hydrogen ions, further refined these initial theories.

By 1904, Hans Friedenthal had successfully established the first scale for classifying acids by determining the dissociation constants for weak acids, according to conductivity and correlating color changes corresponding to different hydrogen ion concentrations using 14 indicating dyes.

The hydrogen ion concentration numbers from Friedenthal's calculations were small and awkward to manipulate. Thus, Lauritz Sorensen suggested using the negative logarithm of these numbers, which he dubbed the "hydrogen exponent" or "pondus Hydrogennii."

This led to the development of the term pH and the creation of the modern pH scale.

Modern pH Scale
The modern pH scale

 

 

Originated published at: https://www.isa.org/standards-and-publications/isa-publications/intech-magazine/2005/may/sensing-ph-controlling-ph/

Prueba de biocidas en el fracturamiento hidráulico

Resumen

Fractura hidráulica o 'fracking' es un proceso utilizado en la industria de petróleo y gas para mejorar la productividad de un aceite o de gas bien. Implica la fracturación de roca con agua (mezclada con arena y algunos productos químicos) inyectado en un pozo bajo alta presión y se utiliza comúnmente en shale gas y otras fuentes 'no convencionales' de petróleo y gas.

No convencionales de petróleo y Gas fuentes

Fracturamiento hidráulico se utiliza generalmente en camas de gas de esquisto, gas de aceite apretado camas o camas de gas de carbón. Todos son fuentes de petróleo o de gas que se encuentran en diferentes tipos de formación rocosa y son por lo general difícil para una empresa hacer económico sin fracturación hidráulica de perforación de gas o petróleo. Por esta razón que se conoce como una técnica de 'estimulación bien'. Aunque el proceso ha sido utilizado en los últimos 50 años, recientemente es prominente en el debate público debido a la expansión de la técnica en los Estados Unidos y las preocupaciones sobre las consecuencias de su uso generalizado.

Agua utilizada en el 'Fracking'

El proceso de 'fracking' implica la perforación de que un pozo agujero subterráneo profundo, a menudo con una etapa horizontal cuando un lecho de roca es particularmente bajo. La roca es fracturada luego utilizando explosivos que crean pequeñas fisuras en la roca que ayudan el flujo de petróleo y gas fuera de la cama en el pozo. Es la baja porosidad de la roca que requiere el fracturamiento hidráulico para hacer un bien económico. Sin fracturación hidráulica, el pozo no produciría suficiente petróleo y gas a hacer vale la pena hacer.

Agua, arena y algunos productos químicos son inyectados al pozo bajo presión para garantizar estas fisuras que abren bajo la enorme presión causada por las formaciones de roca por encima de la cama de roca blanco. Es la arena que sostiene las fisuras abiertas a menudo unos pocos milímetros de ancho. Una gran cantidad de agua (millones de galones) se utiliza en una sola frack y el agua puede provenir de muchas fuentes diferentes, por ejemplo, agua dulce, agua saladas o reciclado de agua de un anterior proceso de fracturamiento hidráulico.

 

Los productos químicos que pueden agregarse al agua y el propósito detrás de su adición se enumeran en el Apéndice E del informe de la EPA en el fracturamiento hidráulico de 2011. Puede encontrar una versión resumida en el cuadro 4.

 

 

Figura 6 se tiene el informe de la EPA en fracturamiento hidráulico, página 13.

 

 

Figura 7 se tiene el informe de la EPA en fracturamiento hidráulico, página 13

 

La mayoría de los productos químicos agregados son los normalmente utilizados en otros procesos industriales que utilizan agua y se añaden para mantener la integridad del pozo, por ejemplo, tensioactivos, inhibidores de corrosión, reguladores de pH y reductores de fricción.

Los biocidas se añaden al agua para evitar la acumulación de bacterias en el agua que puede llevar a la corrosión ácida o la creación de compuestos de sulfuro en. Crecimiento bacteriano puede afectar la producción de pozos de petróleo y gas y puede ser introducido en el fluido de fracturamiento hidráulico de diversas fuentes como la fuente de agua y el apuntalante. Apuntalante es que el término usado para la arena (o de otros compuestos) espera que abren las fisuras.

                                   

La tabla 4 se enumeran los tipos de productos químicos agregados al agua y su propósito. Se toma del informe de la EPA, página 29.

  

Prueba de agua dulce utilizado en el fracturamiento hidráulico

De los productos químicos añadidos al agua, el analito principal que se debe probar en el sitio antes de la inyección es el biocida. Ellos son probados en sitio debido a su volatilidad inherente que hace muestreo y fuera del sitio de prueba inadecuado.

Biocidas que se utilizan incluyen isotiazolona, glutaraldehído, cloro y dióxido de cloro. Otra vez estas son biocidas de uso frecuente en otros procesos industriales utilizando agua como torres de refrigeración.

La tasa de dosificación de biocidas es a menudo automatizada usando un método amperométrico en línea que añade el biocida en cantidades controladas, dependiendo de la velocidad de flujo del agua a introducirse al pozo de la fuente de agua. Secundario de método se realiza generalmente para calibrar la línea en la punta de prueba y como cheque aguas abajo del punto de inyección para biocida está presente en la concentración correcta en el líquido antes de que finalmente se inyecta en el pozo.

 

Pruebas de biocidas en el agua la puede ser difícil debido en parte a la tendencia creciente del uso de agua reciclada para núcleos de frack. Más tradicionales métodos colorimétricos de la prueba (como el método DPD para la cuantificación de cloro o concentraciones de dióxido de cloro) pueden ser desperdiciador de tiempo y difícil para los ingenieros; no pueden dar resultados consistentes donde el agua es alto en sólidos disueltos/suspendido. Otros métodos como ORP (potencial de oxidación-reducción) son fácil de usar pero sufren de una falta de selectividad y a menudo no se puede utilizar como una herramienta cuantitativa.

Ha habido una tendencia creciente dentro de las empresas de tratamiento de agua (que tienden a ser subcontratado por la empresa de perforación para administrar la dosificación de biocidas en el agua) a utilizar nuevos métodos como los sensores amperométricos desechables ya utilizados por el ChlordioXense. Estos métodos tienen la ventaja de ser fácil de utilizar y no son susceptibles a resultados inexactos, como se ha visto con métodos colorimétricos.

Prueba de agua 'Producidos' en el fracturamiento hidráulico

Reflujo de agua es el agua que fluye a la superficie durante y después de la terminación de fracturamiento hidráulico. Consiste en el fluido utilizado para fracturar la pizarra y contiene arcillas, aditivos químicos, los iones metálicos disueltos y sólidos totales disueltos (TDS). El agua tiene un aspecto turbio de altos niveles de partículas en suspensión. La mayor parte del reflujo se produce en las etapas iniciales del proceso de fracturamiento hidráulico mientras que el resto puede ocurrir más de una semana tres periodo de tiempo. El volumen de recuperación es generalmente menos de la mitad del volumen que se inyectó inicialmente en el pozo. El resto del líquido sigue siendo absorbido en la formación de la pizarra.

En cambio, ' agua ' es producida naturalmente agua que se encuentra en formaciones de esquisto que fluye a la superficie durante toda la vida entera del gas bien. Esta agua tiene altos niveles de TDS e iones metálicos como el calcio, hierro y magnesio. También contiene hidrocarburos disueltos junto con el natural materiales radiactivos (norma).

Históricamente, esta aguas residuales del proceso de fracturamiento hidráulico fue eliminada en estanques de evaporación grande. Esto sin embargo se ha convertido en socialmente inaceptable y las aguas residuales deben ser tratadas como residuos industriales de la misma manera que se trata el agua de otros procesos industriales. Las opciones disponibles para empresas de tratamiento de agua la industria del petróleo y el gas son bien 'inyección directa' en el suelo a profundidades por debajo de la mesa de agua y entre las capas de roca impermeable, o el tratamiento y la disposición del agua en la superficie del agua. Ambos métodos a menudo emplean tratamiento de agua con biocidas.

Prueba de concentración de biocidas en las aguas residuales puede ser imposible sin filtrar el agua que generalmente conduce a una reducción en el biocida para determinar la verdadera concentración en el líquido es difícil. La demanda de biocida del líquido también es muy alta debido a la cantidad de metales disueltos presentes. Por lo tanto, biocidas como el dióxido de cloro son generalmente mezclados con agua en concentraciones de hasta 20 mg/l y dosificados en el agua producido o reflujo. Como con el tratamiento de agua dulce que se describe en la página anterior, un método de sonda amperométrica en línea se utiliza para controlar la tasa de dosificación y un método secundario tales como el Palintest ChlordioXense utilizado para calibrar la sonda y proporcionar un método de comprobación secundaria.

Hay una tendencia creciente dentro de la industria de tratamiento de agua para recuperar el hydocarbons que están presentes en el agua de producción y venderlos en el mercado abierto. El uso de biocidas como el dióxido de cloro ayuda a aumentar la tasa de recuperación de aceite como tratamiento hace que los sólidos a precipitado fuera de solución y los hidrocarburos para instalarse en la parte superior del líquido tratado.

El dióxido de cloro actúa como un Desemulsificante para romper emulsiones a través de oxidación química, permitiendo que el agua separar hidrocarburos residuales, productos químicos y la materia particulada presente.


El agua suele ser de una buena calidad suficiente para ser reutilizada en otro sitio de frack o eliminarse mediante inyección directa. Los hidrocarburos pueden despumados y vendidos a las compañías petroleras, mientras que el lodo sólido es retirado y transportado a una planta de aguas residuales estándar.

La imagen de agua de producción (a la derecha) tratados con dióxido de cloro (a la izquierda).

 

Resumen

El uso de fracturamiento hidráulico como un proceso para incrementar los rendimientos de los núcleos de gas y petróleo está aumentando, especialmente en los Estados Unidos, y su uso casi con toda seguridad se extenderá a otros países.

Los biocidas son parte fundamental del fluido de fracturamiento hidráulico sí mismo y el tratamiento de las aguas residuales del proceso.

Principalmente se han adoptado métodos de prueba para la cuantificación de las concentraciones de biocida en el agua dulce y las aguas residuales de la industria de agua potable donde la matriz de agua es de una composición mucho 'más limpia'. Métodos colorimétricos y ORP, aunque útiles, tienen sus inconvenientes y así nuevos métodos como la ChlordioXense son ser fácilmente adoptados por la industria de petróleo y gas.

      

 

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