JPS5912573Y2 - Differential pressure flow measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flow rate measuring device for a fluid such as a mixed gas, and more particularly to a differential pressure type flow rate measuring device that accurately measures a flow rate using a differential pressure type flowmeter.

In a differential pressure type flowmeter, if the mass flow rate ω, the generated differential pressure Δp, and the flow coefficient (constant) a are expressed, the following equation A holds true.

ω=a r7τT7 (4) Therefore, when measuring the mass flow rate of fluid with a differential pressure flowmeter, the mass flow rate ω is a function of the density ρ, and correction is required according to density changes. becomes.

For this reason, it is difficult to accurately measure, for example, the flow rate of a mixed gas whose density changes several times with a single differential pressure type flowmeter.

Furthermore, when switching measurements using multiple differential pressure type flowmeters, chattering occurs, which adversely affects the control system that uses the flow rate.

The present invention has been devised in view of this point, and provides a differential pressure flow rate measuring device that uses a plurality of differential pressure flowmeters with different measurement ranges and can be switched accurately and smoothly.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of the differential pressure type flow measuring device of the present invention, and FIG. 2 is a diagram showing the relationship between flow rate and output signal.

1 is a differential pressure transmitter for large flow rates, and 2 is a differential pressure transmitter for small flow rates, which are provided at the same location in the mixed gas flow pipe.

The large flow rate differential pressure transmitter 1 mainly corresponds to mixed gases with low density, and the small flow rate differential pressure transmitter 2 corresponds to mixed gases with high density, and each has a measurement range corresponding to the mixed gas to be measured. It is determined.

Multipliers 3 and 4 output signals detected by the differential pressure transmitters for large flow rates and small flow rates [△p in equation (A)], and other density signals of the mixed gas measured separately [equation (A)]. This is a density correction computing unit that inputs and multiplies ρ].

Constant multipliers 5 and 6 are auxiliary arithmetic units for the density arithmetic units 3 and 4 in order to prevent the arithmetic unit outputs from exceeding the arithmetic unit processing signals.

The square root calculation units 7 and 8 are calculation units that square root the density-corrected large flow rate and small flow rate differential pressure signals, respectively, and linearize the output signal and the flow rate signal.

The constant calculator 9 converts the small flow rate system output signal level to the high flow rate system output signal level, and furthermore, as shown in FIG. 2, the relationship between the output signal and the flow rate in the small flow range is as follows for the same flow rate: This is to provide an output signal that is always slightly larger than the theoretical value.

To do this, the small flow rate system signal level is multiplied by a constant that is slightly smaller than the theoretical constant multiplied to convert the signal level to obtain the flow rate Q in FIG.

In order to match the output signal level of the large flow rate system and the output signal level of the small flow rate system, a small constant may be added, that is, the bottom may be raised.

The high selector 10 inputs and compares the large flow rate system output signal and the small flow rate system output signal converted to the high flow rate system output signal level, respectively, and outputs the larger one as the output signal.

This high selector 10 allows the flow rate Q shown in FIG.

In the range below the point (small flow range), the small flow range system is always selected, and the flow rate Q.

In the range above the point (large flow range), the large flow range system is selected, and when switching from the large flow range to the small flow range or from the small flow range to the large flow range, there is no so-called chattering phenomenon and smooth switching is possible. It will be done.

FIG. 3 is a block diagram of a mixed gas density measuring device which transmits a density signal to be input to the density correction multipliers 3 and 4.

11 to 15 are classified by gas type (G. to G5, assuming that the densities of G1 and G2 are equal, and the densities of G4 and 65 are also equal.

) is a differential pressure transmitter installed in the flow tube, and 16 to 20 are 11 to 20.
Based on the respective input signals from the 15 differential pressure transmitters,
A square root calculator is used as a flow rate calculator that calculates the gas flow rate by a predetermined calculation.

That is, a flow rate transmitter is constituted by a differential pressure transmitter and a square root calculator, and is provided for each flow tube for each type of gas to transmit the respective flow rates.

21 to 24 are addition calculators, 21 to 22 are for adding the flow rate for each gas type, 23 is for calculating the mixed gas total mass flow rate by multiplying the flow rate for each gas type by the density, and 2
Step 4 calculates the total volumetric flow rate value of the mixed gas by multiplying each type of off-gas by a coefficient for determining the volumetric flow rate value converted to the standard state.

The division calculator 25 divides the mass flow rate value, which is the output of the addition calculator 23, by the volumetric flow rate value, which is the output of the addition calculator 24, and calculates the density of the mixed gas.

When the division arithmetic unit 25 outputs an abnormal value for some reason, it is dangerous to use it as it is for the following control signals, so the limiter 26 sets a limit so that it does not exceed a certain upper limit and immediate lower limit.

The differential pressure signals for each gas type transmitted by the differential pressure transmitters 11 to 15 are input to the corresponding flow rate calculators 16 to 20, respectively, to output flow rate signals for each gas type, and the addition calculators 21.2
2, the total flow rate for each gas type is added.

Next, the addition calculator 23 calculates the mass flow rate of the mixed gas, and the addition calculator 24 calculates the mixed gas volumetric flow rate.

The division operation unit 25 is activated by the output signal of the addition operation units 23 and 24.
Calculate the density of the mixed gas.

The density signal of the division calculator 25 is transmitted by the limiter 26 under upper and lower limits so as not to exceed the set width, and the density value of the mixed gas is measured.

This density measuring device can measure the density of a mixed gas with better accuracy and responsiveness than conventional mechanical density meters, and the density signal of the mixed gas transmitted by this density measuring device is
Each of the multiplication units 3 and 4 shown in FIG. 1 is manually operated.

In this density measuring device, the total mass flow rate is determined by the mass flow rate addition calculator 23, but this flow rate is measured on the gas source side, and is not the flow rate used to control the gas usage side such as a boiler. However, it cannot be used because of problems such as time delay and accuracy.

By inputting the fluid density signal output from this density measuring device to the flow rate measuring device of the present invention, a flow rate that can be used for control etc. can be obtained.

Therefore, since the present invention has the above-mentioned structure, the high selector outputs the large flow rate system output signal as the flow rate signal for large flow rates, and outputs the small flow rate system output signal as the flow rate signal for low flow rates, and also for large flow rates. Mixed gas flow rate measurement control used in co-firing boilers of by-product gas (mixed gas) and liquid fuel (heavy oil) generated from petrochemical plants, etc., allows smooth switching between low-flow and low-flow systems, and eliminates chattering. This method can be effectively applied to a device, and even if there are large fluctuations in the mixed gas flow rate and density, boiler combustion control can be performed accurately and stably.

[Brief explanation of drawings]

FIG. 1 shows a block diaphragm of the differential pressure type flow rate measuring device of the present invention. FIG. 2 is a graph showing the relationship between the flow rate and output signal of the high selector according to the present invention. FIG. 3 shows a block diaphragm of a mixed gas density measuring device.

Claims (2)

[Scope of utility model registration request] (1) Input the differential pressure transmitters 1 and 2 for large flow rate and small flow rate installed at the same location in the fluid piping, and the differential pressure signal and fluid density signal output from the transmitters, and correct the fluid density respectively. It has square root calculators 7 and 8 that calculate the calculated flow rate signal, and a constant calculator 9 that combines the small flow rate signal with the large flow rate signal and at the same time makes the coefficient slightly higher than the theoretical coefficient. A differential pressure type flow rate measuring device comprising a high selector 10 which compares each flow rate signal of a flow rate system and outputs the larger one. (2) The fluid density signal outputs the total volumetric flow rate by adding the volumetric flow rates output by the flow rate transmitters 16 to 20 provided in the flow tubes for each type of gas using the flow rate adders 21 and 22, and outputs the total volumetric flow rate. The addition calculator 23 multiplies the volumetric flow rate of each gas type by the density of each gas and adds them to output the total mass flow rate, and the division calculator 25 outputs the total mass flow rate divided by the total volume flow value. A differential pressure type flow rate measuring device according to claim 1, which is obtained by registering a utility model.