CN104535128A - Precise low-pressure saturated wet gas flow metering method - Google Patents

Abstract

The invention provides a precise low-pressure saturated wet gas flow metering method which aims to solve the problems that in the prior art, an existing low-pressure saturated wet gas flow metering method ignores the temperature change, and thus the metering error is larger due to change of the density of saturated steam. According to the precise low-pressure saturated wet gas flow metering method, a temperature sensor and an absolute pressure transmitter are arranged on a metering point, and the temperature of the low-pressure saturated wet gas and the current absolute pressure value of the metering point are detected in real time; the saturated steam pressure and the saturated steam density are worked out according to the temperature detection result; the corrected low-pressure saturated wet gas flow is worked out by the adoption of the formula (please see the formula in the specification). The precise low-pressure saturated wet gas flow metering method has the advantages that the temperature of the low-pressure saturated wet gas is detected in real time, real-time compensation is conducted on the influence on the flow metering accuracy of the low-pressure saturated steam density change caused by the temperature change, and the metering accuracy of the low-pressure saturated wet gas flow is guaranteed.

Description

Low pressure saturated with moisture body flow accurate measurement method

Technical field

The present invention relates to low pressure saturated with moisture flowmeter body amount technology, be related specifically to a kind of low pressure saturated with moisture body flow accurate measurement method.

Background technology

The gas of low pressure saturated with moisture body general reference after water at low temperature cleaning dust cooling, as coke-oven gas, blast furnace gas, coal gas of converter, rock gas, acetylene etc.Through the gas of cleaning dust, its relative humidity is state of saturation.Along with country is more and more stricter to the requirement of energy management, the accuracy requirement of business unit to low pressure saturated with moisture flowmeter body amount is more and more higher.Usually, temperature and pressure is adopted to compensate low pressure saturated with moisture flowmeter body amount.Its compensation formula is:

When differential pressure transmitter be set to not evolution time, adopt following formula (1):

$Q=Q_{\max }\×\frac{I-4}{16}\×\sqrt{\frac{(P_g+P_0)(t+273.15)}{(P+P_0)(t_g+273.15)}}---\left(1\right)$

When differential pressure transmitter be set to evolution time, adopt following formula (2):

$Q=Q_{\max }\×\sqrt{\frac{I-4}{16}}\×\sqrt{\frac{(P_g+P_0)(t+273.15)}{(P+P_0)(t_g+273.15)}}---\left(2\right)$

In formula, Q is current mark condition lower volume flow, and unit is Nm ³/ h; Qmax is full scale flow, is as the criterion with the calculated description of flowmeter, and unit is Nm ³/ h; I is differential pressure transmitter output current, and unit is mA; for the relative percentage of flow; for the flow of design, unit is Nm ³/ h; P _gfor current pressure, unit is kpa; P is design pressure, is as the criterion with the calculated description of flowmeter, and unit is kpa; P ₀for local annual mean atmospheric pressure, unit is kpa; t _gfor Current Temperatures, unit is DEG C; T is design temperature, is as the criterion with the calculated description of flowmeter, and unit is DEG C; Differential pressure transmitter range is the △ P value that calculated description is finally determined.

Above-mentioned compensation formula carries out computing by the Ideal-Gas Equation, when not considering temperature variation, and the change of saturation vapor pressure and saturated steam density.But in low-pressure gas flow metering, the working pressure of medium is low, density is little, the variable quantity of the saturation vapor pressure that temperature variation causes and density, larger on the impact of gas current pressure and density.This impact will bring larger measuring error.Usually, the working temperature of low pressure saturated with moisture body is generally decided to be 20 DEG C or 30 DEG C, pressure 4 ~ 6KPa, the low density 0.4kg/m of mark condition ³left and right, high only 0.6kg/m ³left and right.Such as, when temperature variation brings up to 30 DEG C by 14 DEG C, saturated steam density is by 0.0121kg/m ³bring up to 0.0304kg/m ³, difference 0.0183kg/m ³.When Media density is 5kg/m ³time, its percentage is 0.366%; When Media density is 0.5kg/m3, its percentage is 3.66%.Therefore, in low-pressure gas flow metering, ignore the larger error in dipping that saturated steam variable density that temperature variation causes is brought.Obviously, prior art low pressure saturated with moisture flowmeter body metering method also exists and ignores the saturated gas density that temperature variation causes and change the problems such as the error in dipping greatly brought.

Summary of the invention

For problems such as the larger error in dippings that ignoring of solving that prior art low pressure saturated with moisture flowmeter body metering method exists saturated steam variable density that temperature variation causes is brought, the present invention proposes a kind of low pressure saturated with moisture body flow accurate measurement method.Low pressure saturated with moisture body flow accurate measurement method of the present invention, at stoichiometric point set temperature sensor and absolute pressure transmitter, the temperature of low pressure saturated with moisture body and the current absolute pressure value of stoichiometric point are detected in real time, saturation vapour pressure and saturated gas density is calculated, the low pressure saturated with moisture body flow after adopting following formula (3) to calculate correction according to temperature detection result:

In formula, q _vN2for low pressure saturated with moisture body flow after correction, unit is Nm ³/ h; q _vN1for low pressure saturated with moisture body flow before correction, unit is Nm ³/ h; ε ₁ε ₂be respectively design load and the currency of inflatable coefficient. be respectively relative humidity design load and currency; For saturated with moisture body, humidity calculates by 100%, and value is 1; Z ₁z ₂be respectively compressibility coefficient design load and currency; Because low-pressure gas pressure is little, to Z ₂impact can ignore; P _smax1.P _smax2be respectively saturation vapor pressure design load and currency, its currency P _smax2record current temperature value by temperature sensor to calculate; T ₁t ₂be respectively kelvin degree design load and currency, its currency is by temperature sensor measurement; ρ ₁ρ ₂be respectively saturated gas density design load and currency, its currency ρ ₂tried to achieve by the temperature computation of temperature sensor measurement; P ₁for design absolute pressure, P ₁=P _a+ P _g, i.e. P ₁equal stoichiometric point area atmospheric pressure annual mean P _athe gauge pressure value P current with stoichiometric point _gsum; P ₂for current absolute pressure value, measured by absolute pressure transmitter;

Further, above-mentioned computation process is that real-time continuous calculates, and the signal input flow rate integrating instrument, computing machine or the arithmetic processor that temperature sensor and absolute pressure transmitter are exported in real time calculate.

The Advantageous Effects of low pressure saturated with moisture body flow accurate measurement method of the present invention is the temperature detecting low pressure saturated with moisture body in real time, real-Time Compensation is carried out on the impact of the low pressure saturated steam variable density flow meter amount degree of accuracy that temperature variation causes, ensure that low pressure saturated with moisture flowmeter body accuracy of measurement.

Accompanying drawing explanation

Accompanying drawing 1 is low pressure saturated with moisture body flow accurate measurement method schematic diagram of the present invention.

Below in conjunction with the drawings and specific embodiments, low pressure saturated with moisture body flow accurate measurement method of the present invention is further described.

Embodiment

Accompanying drawing 1 is low pressure saturated with moisture body flow accurate measurement method schematic diagram of the present invention, as seen from the figure, low pressure saturated with moisture body flow accurate measurement method of the present invention, at stoichiometric point set temperature sensor and absolute pressure transmitter, the temperature of low pressure saturated with moisture body and the current absolute pressure value of stoichiometric point are detected in real time, saturation vapour pressure and saturated gas density is calculated, the low pressure saturated with moisture body flow after adopting following formula (3) to calculate correction according to temperature detection result:

In formula, q _vN2for low pressure saturated with moisture body flow after correction, unit is Nm ³/ h; q _vN1for low pressure saturated with moisture body flow before correction, unit is Nm ³/ h; ε ₁ε ₂be respectively design load and the currency of inflatable coefficient. be respectively relative humidity design load and currency; For saturated with moisture body, humidity calculates by 100%, and value is 1; P _smax1.P _smax2be respectively saturation vapor pressure design load and currency, its currency P _smax2record current temperature value by temperature sensor to calculate; Z ₁z ₂be respectively compressibility coefficient design load and currency; Because low-pressure gas pressure is little, to Z ₂impact can ignore; T ₁t ₂be respectively kelvin degree design load and currency, its currency is by temperature sensor measurement; ρ ₁ρ ₂be respectively saturated gas density design load and currency, its currency ρ ₂tried to achieve by the temperature computation of temperature sensor measurement; P ₁for design absolute pressure, P ₁=P _a+ P _g, i.e. P ₁equal stoichiometric point area atmospheric pressure annual mean P _athe gauge pressure value P current with stoichiometric point _gsum; P ₂for current absolute pressure value, measured by absolute pressure transmitter;

Further, above-mentioned computation process is that real-time continuous calculates, and the signal input flow rate integrating instrument, computing machine or the arithmetic processor that temperature sensor and absolute pressure transmitter are exported in real time calculate.

Low pressure saturated with moisture body flow accurate measurement method of the present invention adopts the temperature of temperature sensor to low pressure saturated with moisture body to detect in real time, and try to achieve saturated gas density by temperature, then compensate with the saturated gas density saturated with moisture flowmeter body amount of change, thus obtain the metering of precision.Because temperature sensor can dynamically, continuously to the temperature detection of low pressure saturated with moisture body, in real time, the temperature variation of low pressure saturated with moisture body is reacted exactly, therefore, can fully reflect temperature variation bring saturated gas density to change impact, thus obtain flowmeter value accurately.

Obviously, the Advantageous Effects of low pressure saturated with moisture body flow accurate measurement method of the present invention is the temperature detecting low pressure saturated with moisture body in real time, real-Time Compensation is carried out on the impact of the saturated gas density change flow meter amount degree of accuracy that temperature variation causes, ensure that low pressure saturated with moisture flowmeter body accuracy of measurement.

Claims (2)

1. a low pressure saturated with moisture body flow accurate measurement method, is characterized in that, at stoichiometric point set temperature sensor and absolute pressure transmitter, to low pressure saturated with moisture body stoichiometric point current temperature and absolute pressure value detect in real time, and

2. calculate saturation vapour pressure and saturated gas density according to temperature detection result, the low pressure saturated with moisture body flow after adopting following formula (3) to calculate correction:

In formula, q _vN2for low pressure saturated with moisture body flow after correction, unit is Nm ³/ h; q _vN1for low pressure saturated with moisture body flow before correction, unit is Nm ³/ h; ε ₁ε ₂be respectively design load and the currency of inflatable coefficient. be respectively relative humidity design load and currency; For saturated with moisture body, humidity calculates by 100%, and value is 1; P _smax1.P _smax2be respectively saturation vapor pressure design load and currency, its currency P _smax2record current temperature value by temperature sensor to calculate; Z ₁z ₂be respectively compressibility coefficient design load and currency; Because low-pressure gas pressure is little, to Z ₂impact can ignore; T ₁t ₂be respectively kelvin degree design load and currency, its currency is by temperature sensor measurement; ρ ₁ρ ₂be respectively saturated gas density design load and currency, its currency ρ ₂tried to achieve by the temperature computation of temperature sensor measurement; P ₁for design absolute pressure, P ₁=P _a+ P _g, i.e. P ₁equal stoichiometric point area atmospheric pressure annual mean P _athe gauge pressure value P current with stoichiometric point _gsum; P ₂for current absolute pressure value, measured by absolute pressure transmitter;

Further, above-mentioned computation process is that real-time continuous calculates, and the signal input flow rate integrating instrument, computing machine or the arithmetic processor that temperature sensor and absolute pressure transmitter are exported in real time calculate.