What is Mass Flow Meter in Bunkering , MFM Bunkering

Mass Flow Meter in bunker supply

A mass flow meter is a device which is used to measure the mass flow rate of a liquid fluid traveling through a tube. The mass flow rate is the mass of the fluid traveling past a fixed point per unit time. It is also known as inertial flow meter. The mass flow meter is not able to measure the volume per unit time passing through the device, it only measures the mass per unit time passing through the device. The volumetric flow rate is the mass flow rate divided by the fluid density. If the density of the fluid is constant than the relationship is simple but if the fluid density is not constant than the relationship is not so simple. The density of fluid generally may change with temperature, pressure or the composition. The fluid may also be a combination of phases such as a fluid with entrained bubbles. Actual density can be determined due to dependency of sound velocity on the controlled liquid concentration. There are basically two ways of measuring the flow, one on volumetric basis and the other on weight basis.

Solid materials are measured in terms of either weight per unit time or mass per unit time. Very rarely solid quantity is measured in terms of volume. Liquids are measured either in volume  rate or in weight rate. Broadly the fluids are classifies into two types which are incompressible and compressible. Fluids in liquid phase are incompressible whereas fluids in gaseous phase are compressible. Liquid occupies the same volume at different pressures where as gases occupy different volumes at different pressures. This point has to be taken care of while calibrating the flow meters.Flow meter is a device that measures the rate of flow or quantity of a moving fluid in an open or closed conduit.

Flow measuring devices are generally classified into four groups.

1. Mechanical type flow meters. Fixed restriction variable head type flow meters using different sensors like orifice plate, venturi tube, flow nozzle, pitot tube, dall tube, quantity meters like positive displacement meters, mass flow meters etc. fall under mechanical type flow meters.
2. Inferential type flow meters. Variable area flow meters (Rotameters), turbine flow meter, target flow meters etc.
3. Electrical type flow meters. Electromagnetic flow meter, Ultrasonic flow meter, Laser doppler Anemometers etc. fall under electrical type flow meters.
4. Other flow meters. Purge flow regulators, Flow meters for Solids flow measurement, Cross-correlation flow meter, Vortex shedding flow meters, flow switches etc.

The ability of the flow meter to accurately measure and control flow is important in maintaining the process conditions required to maximize plant production, efficiency and product quality. Generally flow measurements are used as indicators of overall process performance. This is due to the law of conservation of mass which states that the mass entering a system is equal to the mass leaving the system when both are measured over the same interval. Therefore, mass flow meters and mass flow transmitters become crucial in overall plant operations

The working principle of mass flow meter

A Mass Flow Meter operating on the "Coriolis principle" contains a vibrating tube in which a fluid flow causes changes in frequency, phase shift or amplitude. The sensor signal is fed into the integrally mounted pc-board. The resulting output signal is strictly proportional to the real mass flow rate, whereas thermal mass flow meters are dependent of the physical properties of the fluid. Coriolis mass flow measurement is fast and very accurate.

Coriolis mass flowmeters measure the force resulting from the acceleration caused by mass moving toward (or away from) a center of rotation. As related to flowmeters, the effect can be demonstrated by flowing water in a loop of flexible hose that is “swung” back and forth in front of the body with both hands. Because the water is flowing toward and away from the hands, opposite forces are generated and cause the hose to twist.

In a Coriolis mass flowmeter, the “swinging” is generated by vibrating the tube(s) in which the fluid flows. The amount of twist is proportional to the mass flow rate of fluid passing through the tube(s). Sensors and a Coriolis mass flowmeter transmitter are used to measure the twist and generate a linear flow signal.

The Coriolis force Fc is generated by the inertia of the fluid particles accelerated between points AC and of those decelerated between points CB.

This force causes an extremely slight distortion of the measuring tube that is superimposed on the fundamental component and is directly proportional to the mass flowrate.

This distortion is picked up by special sensors. Since the oscillatory characteristics of the measuring tube are dependent on temperature, the temperature is measured continuously and the measured values corrected accordingly.

Mass Flow vs Volumetric Flow

Mass is a measure of the amount of matter that makes up an object. The mass of an object is considered constant. Volume refers to the amount of space an object takes up. The volume of an object can change depending on pressure, temperature and other factors. In terms of flow, at room temperature and low pressures the volumetric and mass flow rate will be nearly identical, however, these rates can vary drastically with changes in temperature and/or pressure because the temperature and pressure of the gas both affect the volume. For example, assume a volumetric flow reading was used to fill balloons with 250 mL of helium, but the incoming line ran near a furnace that cycled on and off, intermittently heating the incoming helium. Because the volumetric meter simply measures the volume of gas flow, all of the balloons would initially be the same size. However, if all the balloons are placed in a room and allowed to come to an equilibrium temperature, they would generally all come out to be different sizes. If, on the other hand, a mass flow reading were used to fill the balloons with 250 standard mL of helium, the resulting balloons would initially be different sizes, but when allowed to come to an equilibrium temperature, they would all turn out to be the same size.

Advantage and disadvantages

This technology has high accuracy, can handle sanitary applications, is approved for custody transfer and is highly reliable and low maintenance. Mass flow is more important than volume for fluids intended for the production of energy. These include petroleum liquids and natural gas both compressed and liquefied. The cost is high, especially for line sizes above four inches. Pressure drop can be a consideration for “U” shaped tube designs and high viscosity fluids

How to Use Coriolis Mass Flowmeters

Coriolis mass flowmeters measure the mass flow of liquids. Be particularly careful when using Coriolis mass flowmeters to measure gas/vapor flows because flow rates tend to be low in the flow range (where accuracy is degraded). Also, in gas/vapor applications, large pressure drops across the flowmeter and its associated piping can occur.

This flowmeter can be applied to sanitary, cryogenic, relatively clean, and corrosive liquids and gases/vapors in pipes smaller than 6-12 inches. General applications are found in the water, wastewater, mining, mineral processing, power, pulp and paper, petroleum, chemical, and petrochemical industries. Materials of construction are generally limited to stainless steel and Hastelloy C. Straight-tube designs are available to measure some dirty and/or abrasive liquids.

Many applications for Coriolis mass flowmeters are found in chemical processes where fluids can be corrosive and otherwise difficult to measure. In addition, the relative insensitivity to density allows Coriolis mass flowmeters to be applied in applications where the physical properties of the fluid are not well known. These flowmeters can also be used in chemical feed systems found in most industries.

Industries Where Used

The industries in order of higher to lower are chemical, oil and gas, food and beverage, pharmaceutical, pulp and paper, power, metals and mining, and water and wastewater followed by all others in small amounts.

Application Cautions for Coriolis Mass Flowmeters

If the pressure drop is acceptable, operate a Coriolis mass flowmeter in the upper part of its flow range because operation at low flow rates can degrade accuracy. Note that high viscosity fluids increase the pressure drop across the flowmeter. For liquid flows, make sure that the flowmeter is completely full of liquid. Be especially careful when measuring gas/vapor flow with Coriolis mass flowmeters. Pay special attention to installation because pipe vibration can cause operational problems.

Thermal  mass  flow  meters  work  by  measuring  the  amount  of  heat  transfer  a  gas produces  as  it  flows  past  a  heating  element.  A  reference  probe  checks  the  ambient temperature  of  the  surrounding  gas,  while  a  measurement  probe  senses  the  heat transfer  from  the  heating  e lement.  The  amount  of  energy  required  to  keep  the measurement system in equilibrium depends directly on the mass of the passing gas or gas mixture.

The  third  type  of  mass  flow  technology  is  the  multivariable  DP  flow  meter  which measures  temperature and  pressure   as well as flow. This information  is  then used  to assess density and volumetric flow, from which a mass value can be derived. In contrast to  coriolis  and  thermal mass flow  meters,  which are  in  direct contact with the  gas or liquid, multivariable flow meters are considered an indirect method of measurement, as the mass flow information is inferred using temperature and pressure values.

The benefits of Coriolis mass flow meter include:

• Lower capital expenditures by using a multi-variable measurement device that provides direct, precision measurement of mass flow rate, density and temperature
• Improved process uptime and flexibility through high reliability, a wide range of operation, and bidirectional flow capability
• Improved product quality and tighter process control through higher accuracy and repeatability resulting in reduced waste, rework and scrap
• Reduced cost of installation, since there are no special mounting, flow conditioning, or straight pipe runs required
• Reduce maintenance costs because there are no moving parts, no calibration drift, and no need to adjust the factory zero in typical operating conditions
• Simplified work practices with Smart Meter Verification to confirm the meter components are operating correctly without disrupting the process or trips into the field
• Measurement accuracy for gases, fluids with entrained gas and slurries