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Providing problem solving and educational information for topics related to industrial steam, hot water systems, industrial valves, valve automation, HVAC, and process automation. Have a question? Give us a call at (800) 892-2769 | www.meadobrien.com
Common Ways to Measure Steam Flow
For steam, energy is primarily contained in the latent heat and, to a lesser extent, the sensible heat of the fluid. The latent heat energy is released as the steam condenses to water. Additional sensible heat energy may be released if the condensate is further lowered in temperature. In steam measuring, the energy content of the steam is a function of the steam mass, temperature and pressure. Even after the steam releases its latent energy, the hot condensate still retains considerable heat energy, which may or may not be recovered (and used) in a constructive manner. The energy manager should become familiar with the entire steam cycle, including both the steam supply and the condensate return.
When compared to other liquid flow measuring, the measuring of steam flow presents one of the most challenging measuring scenarios. Most steam flowmeters measure a velocity or volumetric flow of the steam and, unless this is done carefully, the physical properties of steam will impair the ability to measure and define a mass flow rate accurately.
Steam is a compressible fluid; therefore, a reduction in pressure results in a reduction in density. Temperature and pressure in steam lines are dynamic. Changes in the system’s dynamics, control system operation and instrument calibration can result in considerable differences between actual pressure/temperature and a meter’s design parameters. Accurate steam flow measurement generally requires the measurement of the fluid’s temperature, pressure, and flow. This information is transmitted to an electronic device or flow computer (either internal or external to the flow meter electronics) and the flow rate is corrected (or compensated) based on actual fluid conditions.
The temperatures associated with steam flow measurement are often quite high. These temperatures can affect the accuracy and longevity of measuring electronics. Some measuring technologies use close-tolerance moving parts that can be affected by moisture or impurities in the steam. Improperly designed or installed components can result in steam system leakage and impact plant safety. The erosive nature of poor-quality steam can damage steam flow sensing elements and lead to inaccuracies and/or device failure.
The challenges of measuring steam can be simplified measuring the condensed steam, or condensate. The measuring of condensate (i.e., high-temperature hot water) is an accepted practice, often less expensive and more reliable than steam measuring. Depending on the application, inherent inaccuracies in condensate measuring stem from unaccounted for system steam losses. These losses are often difficult to find and quantify and thus affect condensate measurement accuracy.
Volumetric measuring approaches used in steam measuring can be broken down into two operating designs:
For steam three differential pressure flowmeters are highlighted: orifice flow meter, annubar flow meter, and spring-loaded variable area flow meter. All differential pressure flowmeters rely on the velocity-pressure relationship of flowing fluids for operation.
Historically, the orifice flow meter is one of the most commonly used flowmeters to measure steam flow. The orifice flow meter for steam functions identically to that for natural gas flow. For steam measuring, orifice flow flowmeters are commonly used to monitor boiler steam production, amounts of steam delivered to a process or tenant, or in mass balance activities for efficiency calculation or trending.
The annubar flow meter (a variation of the simple pitot tube) also takes advantage of the velocity-pressure relationship of flowing fluids. The device causing the change in pressure is a pipe inserted into the steam flow.
The spring-loaded variable area flow meter is a variation of the rotameter. There are alternative configurations but in general, the flow acts against a spring-mounted float or plug. The float can be shaped to give a linear relationship between differential pressure and flow rate. Another variation of the spring-loaded variable area flow meter is the direct in-line variable area flow meter, which uses a strain gage sensor on the spring rather than using a differential pressure sensor.
The two main type of velocity flowmeters for steam flow, turbine and vortex shedding, both sense some flow characteristic directly proportional to the fluid’s velocity.
A multi-blade impellor-like device is located in, and horizontal to, the fluid stream in a turbine flow meter. As the fluid passes through the turbine blades, the impellor rotates at a speed related to the fluid’s velocity. Blade speed can be sensed by a number of techniques including magnetic pick-up, mechanical gears, and photocell. The pulses generated as a result of blade rotation are directly proportional to fluid velocity, and hence flow rate.
A vortex-shedding flow meter senses flow disturbances around a stationary body (called a bluff body) positioned in the middle of the fluid stream. As fluid flows around the bluff body, eddies or vortices are created downstream; the frequencies of these vortices are directly proportional to the fluid velocity.
For more information on process steam management, contact Mead O'Brien by visiting http://www.meadobrien.com or call (800) 892-2769,
When compared to other liquid flow measuring, the measuring of steam flow presents one of the most challenging measuring scenarios. Most steam flowmeters measure a velocity or volumetric flow of the steam and, unless this is done carefully, the physical properties of steam will impair the ability to measure and define a mass flow rate accurately.
Steam is a compressible fluid; therefore, a reduction in pressure results in a reduction in density. Temperature and pressure in steam lines are dynamic. Changes in the system’s dynamics, control system operation and instrument calibration can result in considerable differences between actual pressure/temperature and a meter’s design parameters. Accurate steam flow measurement generally requires the measurement of the fluid’s temperature, pressure, and flow. This information is transmitted to an electronic device or flow computer (either internal or external to the flow meter electronics) and the flow rate is corrected (or compensated) based on actual fluid conditions.
The temperatures associated with steam flow measurement are often quite high. These temperatures can affect the accuracy and longevity of measuring electronics. Some measuring technologies use close-tolerance moving parts that can be affected by moisture or impurities in the steam. Improperly designed or installed components can result in steam system leakage and impact plant safety. The erosive nature of poor-quality steam can damage steam flow sensing elements and lead to inaccuracies and/or device failure.
The challenges of measuring steam can be simplified measuring the condensed steam, or condensate. The measuring of condensate (i.e., high-temperature hot water) is an accepted practice, often less expensive and more reliable than steam measuring. Depending on the application, inherent inaccuracies in condensate measuring stem from unaccounted for system steam losses. These losses are often difficult to find and quantify and thus affect condensate measurement accuracy.
Volumetric measuring approaches used in steam measuring can be broken down into two operating designs:
- Differential pressure
- Velocity measuring technologies.
DIFFERENTIAL
For steam three differential pressure flowmeters are highlighted: orifice flow meter, annubar flow meter, and spring-loaded variable area flow meter. All differential pressure flowmeters rely on the velocity-pressure relationship of flowing fluids for operation.
Orifice Flow Meter (courtesy of Foxboro) |
Differential Pressure – Orifice Flow Meter
Historically, the orifice flow meter is one of the most commonly used flowmeters to measure steam flow. The orifice flow meter for steam functions identically to that for natural gas flow. For steam measuring, orifice flow flowmeters are commonly used to monitor boiler steam production, amounts of steam delivered to a process or tenant, or in mass balance activities for efficiency calculation or trending.
Differential Pressure – Annubar Flow Meter
The annubar flow meter (a variation of the simple pitot tube) also takes advantage of the velocity-pressure relationship of flowing fluids. The device causing the change in pressure is a pipe inserted into the steam flow.
Differential Pressure – Spring-Loaded Variable Area Flow Meter
The spring-loaded variable area flow meter is a variation of the rotameter. There are alternative configurations but in general, the flow acts against a spring-mounted float or plug. The float can be shaped to give a linear relationship between differential pressure and flow rate. Another variation of the spring-loaded variable area flow meter is the direct in-line variable area flow meter, which uses a strain gage sensor on the spring rather than using a differential pressure sensor.
VELOCITY
The two main type of velocity flowmeters for steam flow, turbine and vortex shedding, both sense some flow characteristic directly proportional to the fluid’s velocity.
Velocity – Turbine Flow Meter
A multi-blade impellor-like device is located in, and horizontal to, the fluid stream in a turbine flow meter. As the fluid passes through the turbine blades, the impellor rotates at a speed related to the fluid’s velocity. Blade speed can be sensed by a number of techniques including magnetic pick-up, mechanical gears, and photocell. The pulses generated as a result of blade rotation are directly proportional to fluid velocity, and hence flow rate.
Vortex Flowmeter (courtesy of Foxboro) |
Velocity – Vortex-Shedding Flow Meter
A vortex-shedding flow meter senses flow disturbances around a stationary body (called a bluff body) positioned in the middle of the fluid stream. As fluid flows around the bluff body, eddies or vortices are created downstream; the frequencies of these vortices are directly proportional to the fluid velocity.
For more information on process steam management, contact Mead O'Brien by visiting http://www.meadobrien.com or call (800) 892-2769,
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Limitorque QX Electronic Actuator User Instructions
Limitorque QX |
The QX design builds on more than 10 years of experience with proven Limitorque MX technology - the first generation double-sealed electronic valve actuator from Flowserve designed to provide control, ease of use and accuracy. The QX includes all the user-preferred features of the MX in a quarter-turn smart actuator package. It is the only non-intrusive, double-sealed quarter-turn actuator to display the Limitorque brand.
For more information on any Limitorque actuator, visit Mead O'Brien at http://www.meadobrien.com or call (800) 892-2769.
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Common Industrial and Commercial Process Heating Methodologies
Fuel boiler producing steam. |
- Steam
- Fuel
- Electric
- Hybrid systems
STEAM
Tube heat exchanger. |
FUEL
Fuel-based process heating systems generate heat by combusting solid, liquid, or gaseous fuels, then transferring the heat directly or indirectly to the material. Hot combustion gases are either placed in direct contact with the material (i.e., direct heating via convection) or routed through radiant burner tubes or panels that rely on radiant heat transfer to keep the gases separate from the material (i.e., indirect heating). Examples of fuel-based process heating equipment include furnaces, ovens, red heaters, kilns, melters, and high-temperature generators.
ELECTRICITY
Electricity-based process heating systems also transform materials through direct and indirect processes. For example, electric current is applied directly to suitable materials to achieve direct resistance heating; alternatively, high-frequency energy can be inductively coupled to suitable materials to achieve indirect heating. Electricity-based process heating systems are used for heating, drying, curing, melting, and forming. Examples of electricity-based process heating technologies include electric arc furnace technology, infrared radiation, induction heating, radio frequency drying, laser heating, and microwave processing.
HYBRID
Hybrid process heating systems utilize a combination of process heating technologies based on different energy sources and/or heating principles to optimize energy performance and increase overall thermal efficiency. For example, a hybrid boiler system may combine a fuel-based boiler with an electric boiler to take advantage of access to lower off-peak electricity prices. In an example of a hybrid drying system, electromagnetic energy (e.g., microwave or radio frequency) may be combined with convective hot air to accelerate drying processes; selectively targeting moisture with the penetrating electromagnetic energy can improve the speed, efficiency, and product quality as compared to a drying process based solely on convection, which can be rate-limited by the thermal conductivity of the material. Optimizing the heat transfer mechanisms in hybrid systems offers a significant opportunity to reduce energy consumption, increase speed/throughput, and improve product quality.
The experts at Mead O'Brien are always available to assist you with any process heating application. Visit http://meadobrien.com or call (800) 892-2769 for more information.
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