Conductivity Measurements for Boiler Blowdown

Introduction

To defray energy costs, many industrial plants have their own boilers to generate steam in order to produce a portion of their energy needs. In addition to generating power, the steam may also be used directly in plant processes or indirectly via heat exchangers or steam jacketed vessels. 

Challenges

The raw water used to feed the boilers contains varying levels of impurities that must be removed to protect the boiler and associated equipment. Pre-treatment processes such as reverse osmosis, ion exchange, filtration, softening, and demineralization may be used to reduce the level of impurities, but even the best pretreatment processes will not remove them all and will continuously carry some dissolved mineral impurities into the boiler.
These dissolved impurities accumulate in the boiler water when steam is made; only pure water leaves the boiler. The increasing concentration of dissolved solids leads to carryover of boiler water into the steam, damaging piping, steam traps, and other process equipment. The concentration of dissolved solids increases until the boiler water can no longer hold all of them in solution and a saturation point is reached. They then begin to drop out becoming suspended solids and forming a sludge or scale on the boiler walls and piping. 
Boiler problems are avoided by periodically discharging or “blowing down” water from the boiler to reduce the concentrations of suspended and total dissolved solids. Surface water blowdown is often done continuously to reduce the level of dissolved solids, and bottom blowdown is performed periodically to remove sludge or suspended solids from the bottom of the boiler. The frequency and level of blowdown required each day depends upon the concentration of impurities and the rate at which they build up in the boiler water. 
Boilers operating on soft water will require more top or skimmer blowdown to remove dissolved solids, whereas boilers operating on hard water will require more bottom blowdown to remove the settled solids. While control of suspended and dissolved solids in the boiler is critical, care must be taken to avoid excessive blowdown, as this would increase the demand for make-up (feed) water, treatment chemicals, and fuel.  

Solutions

The benefits of proper boiler blowdown control include the following: 

  • Reduced operating costs (less feedwater consumption, chemical treatment, and higher heating efficiency).
  • Reduced maintenance and repair costs (minimized carryover and deposits).
  • Cleaner and more efficient steam.
  • Minimized energy loss from boiler blowdown can save about 2% of a facility’s total energy use with an average simple payback of less than one year. 

The most common methodologies used for boiler blowdown control include: (1) continuous, (2) manual and (3) automatic. 
Continuous blowdown utilizes a calibrated valve and a blowdown tap near the boiler water surface. As the name implies, it continuously takes water from the top of the boiler at a predetermined rate to reduce the level of dissolved solids. The rate is usually set slightly greater than necessary to maintain safety protocols.
Manual blowdown is accomplished at most plants by taking boiler water samples once a shift and adjusting the blowdown accordingly. This grab sample approach means that operators cannot immediately respond to changes in feedwater conditions or variations in steam demand and scaling conditions can occur and go undetected until the next sample check. 
Automatic blowdown control is achieved by constantly monitoring the conductivity value of the boiler water, adjusting the blowdown rate, and the duration based on a specific conductivity set point. This provides control of the water chemistry.
Manual blowdown control cannot maintain this level of control more than 20% of the time. 
Upgrading from manual blowdown control to automatic control can reduce a boiler’s energy use by 2 – 5 percent and blowdown water losses by up to 20 percent.
Feed water usually contains one limiting component such as chloride, sulfate, carbonate, or silica. Even if the component is not conductive, as is the case with silica, its concentration is usually proportional to a component that can be measured by conductivity. Therefore, conductivity is a viable measurement for monitoring the overall total dissolved solids present in the boiler. A rise in conductivity indicates a rise in the “contamination” of the boiler water.

Summary

The frequency and duration required for boiler blowdown is significantly affected by the water quality. Improving feedwater quality through make-up water, chemical treatment and proper blowdown control can significantly reduce treatment and operational costs including:

  • Reduced operating costs 
  • Reduced maintenance and repair costs 
  • Cleaner and more efficient steam
  • Energy savings

Increased efficiency and reduced operating costs can be achieved by using the Yokogawa conductivity series line of products. Control configurations will carry with the application and the customer’s requirements. 

Product Recommendations

FLXA202 and FLXA402Conductivity Measurement System: 
Process Liquid Analyzer:
2-wire FLXA202 Conductivity Analyzer
4-wire FLXA402 Conductivity Analyzer

Sensor Selection: 
Analog and Digital SMART sensors are available. Analog options allow users to interface with a system that has been used historically. SENCOM technology, which allows sensors to transmit and receive data when connected to a transmitter/analyzer or a PC. The SMART digital sensors maintain specific measurement and calibration data on an integrated chip along that is an integral part of the sensor providing easy plug and play solutions. The data management software optimizes the performance of sensors for enhanced reliability and process safety.

Option #1: SC42-S*34 Large-bore conductivity sensor (fittings available for flow-thru, insertion, or immersion installations)

Option #2: SC4A Conductivity sensor (fittings available for insertion, sanitary, or retractable installations.)

isc40Another alternative would be Toroidal or Inductive Conductivity Sensor: 
ISC40 Inductive conductivity sensor (fittings available for flow-thru, insertion, or immersion installations)
 

Industrias

  • Alimentos y bebidas

    La industria de alimentos y bebidas debe producir alimentos y bebidas seguros y de alta calidad para los consumidores. Además del control de calidad, los procesos de manufactura incluyen muchos retos, como gestionar ingredientes, mejorar la eficiencia y atender cuestiones ambientales globales. Yokogawa aprovecha sus décadas de especialización tecnológica para ayudar a los clientes a construir y operar la fábrica ideal.

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  • Energía

    A mediados de la década de 1970, Yokogawa inició su participación en el negocio de la energía con el lanzamiento del Sistema de control eléctrico EBS. Desde entonces, Yokogawa ha continuado firmemente con el desarrollo de nuestras tecnologías y capacidades para proveer los mejores servicios y soluciones a nuestros clientes en todo el mundo.

    Yokogawa ha operado la red de soluciones de energía globales para jugar un papel más activo en el dinámico mercado de energía global. Esto ha hecho un posible un trabajo en equipo más unido dentro de Yokogawa, el cual conjunta nuestros recursos globales y nuestra especialización en la industria. Los expertos en el sector de energía de Yokogawa trabajan juntos para brindar a cada cliente la solución que se adapta mejor a sus requerimientos sofisticados.

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  • Papel y pulpa

    La industria del papel y la pulpa es altamente competitiva y debe satisfacer necesidades del mercado que están en constante cambio. Yokogawa ayuda a poner en operación plantas eficientes en el consumo de energía que son sostenibles globalmente.

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  • Petróleo y gas

    Yokogawa posee un caudal de experiencia en cada parte del negocio del petróleo y el gas, desde instalaciones en altamar y terrestres hasta ductos, terminales y operaciones en aguas profundas. Proveemos soluciones que mejoran la seguridad, garantizan una operación precisa y confiable y aumentan la eficiencia de la planta.

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  • Química

    Las plantas químicas dependen de procesos de producción continua y por lotes, cada una de los cuales impone diferentes exigencias para un sistema de control. Un proceso continuo exige un sistema de control robusto y estable que no falle y provoque el cierre de una línea de producción, mientras que en un proceso por lotes el énfasis se centra en tener un sistema de control que permita una gran flexibilidad para realizar ajustes a fórmulas, procedimientos y otros elementos. Ambos tipos de sistemas necesitan ser administrados en el historial de calidad del producto disponible, así como tener la capacidad de ejecutar operaciones no rutinarias. Con el respaldo de su extenso portafolio de productos, un equipo de experimentados ingenieros en sistemas y una red global de ventas y servicio, Yokogawa ofrece una solución para cada proceso productivo.

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  • Transporte, distribución y comercialización de petróleo y gas

    La industria de la refinación, comercialización y distribución de petróleo y gas ha estado enfrentando un número cada vez mayor de retos en años recientes. Entre ellos, las características cambiantes de la materia prima a procesar, el envejecimiento de las instalaciones y los equipos de procesos, el creciente costo de la energía, la falta de operadores de planta capacitados que puedan operar una refinería de manera segura y eficiente y los requisitos constantemente cambiantes del mercado y de los clientes.

    Con el paso de los años, Yokogawa ha formado alianzas con muchas compañías de refinación, comercialización y distribución para proveer soluciones industriales enfocadas en resolver estos retos y problemas. Las soluciones VigilantPlant de Yokogawa han ayudado a los propietarios de plantas a alcanzar una máxima rentabilidad y seguridad sostenible dentro de sus plantas.

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