Measuring and testing – Volume or rate of flow – Mass flow by imparting angular or transverse momentum to the...
Patent
1997-06-05
2000-03-28
Patel, Harshad
Measuring and testing
Volume or rate of flow
Mass flow by imparting angular or transverse momentum to the...
73861354, G01F 182
Patent
active
060416645
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and an apparatus for continuous, gravimetric metering and mass flow determination of flowable materials, with a flowmeter, especially a Coriolis measuring wheel, for determining the instantaneous mass flow and a metering device downstream of the flowmeter.
Such an installation for continuous, gravimetric feeding and/or mixing of bulk material is known from DE 4 023 948 A1, wherein a metering rotor balance according to DE 3 217 406 A1 or EP-A 0 198 956 is utilised. A collector device supported on force measuring cells with a bucket wheel gate is connected in a closed pneumatic conveyor passage downstream of this metering device following a bulk material feed line. Through this the bulk material mass located therein can be continuously determined and either the speed of rotation of the bucket wheel gate or the total air flow amount of the feed blower can be influence by this, so that the bulk material throughput can be influenced by varying the amount of air supplied per unit time. A computer controlled central metering control system is used for corresponding regulation of the desired mixing ratio or the desired feed amount per unit time (feed rate), as is described in DE 3 217 406 A1 for example, wherein the weighing signal of the bin weighing cells serves as the input signal and the speed of rotation of the metering rotor in particular and optionally of the bucket wheel gate for the bulk material feed are regulated. However a certain regulation dead time can occur up to the regulation to the set-point feed rate.
This regulating system is described in more detail in EP-A 0 198 956 cited above, wherein the bulk material mass acting instantaneously in the rotor weighing path is detected in the metering rotor balance, from which the bulk material mass flow rate is given by multiplying by the angular velocity of the metering rotor. The weighing electronics store the instantaneous bulk material mass located on the rotor balance path (measuring path), so that shortly before the discharge of the bulk material to the pneumatic feed line, the rotor angular velocity can be varied in accordance with the predetermined set-point feed rate, so that the metering rotor is accelerated or slowed down. A relatively high metering accuracy results from this, which is very well suited to metering finely divided bulk material, for example in coal dust metering for rotary cement kilns or metering additives in flue gas purification.
With certain feed materials however, such as additives for mixing in for flue gas purification in power stations, furnace installations and the like, account has to be taken of the fact that these bulk material can tend to "ball" or even form bridges, depending on the degree of moisture, fluidization, fineness and the like, so that random or strongly pulsating mass flow fluctuations can occur in the bulk material feed. In this case the previously described metering apparatus is hardly able to compensate any more for the short-term mass flow fluctuations, since the metering rotor has a substantial self mass of some hundreds of kilograms, especially in a shock-resistant design, so that the changes in angular velocity needed to keep the feed rate constant with strongly fluctuating mass flows and thus strong acceleration or retardation of the metering rotor are hardly possible any more, because of the inertial mass.
These positive and negative fluctuations can be partially compensated in the first-mentioned installation for feeding and/or mixing bulk material, in the form of a mean value formation, in that a collecting container supported on force measuring cells is provided. However, such a compensating container substantially increases the cost of the structure and the demand on space. The discharge through the output device in the form of a bucket wheel gate is in addition relatively inaccurate, because of the volumetric measuring principle in the pockets of the bucket wheel gate.
A Coriolis measuring wheel is described in DE-PS 1 211 415, following which is connected
REFERENCES:
patent: 2598220 (1952-05-01), Dodds
patent: 3308662 (1967-03-01), Maurer
patent: 4528848 (1985-07-01), Hafner
patent: 5301555 (1994-04-01), Hafner
patent: 5359900 (1994-11-01), Hafner
Patel Harshad
Pfister GmbH
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