RU2605530C1 - Method for metering liquefied hydrocarbon gases during storage in tanks - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to metering liquefied hydrocarbon gases (hereinafter LHG) and, in particular, to measurements of weight of LHG during storage on automobile gas-filling stations (hereinafter AGFS) and multifuel filling stations (hereinafter MFS). Method of metering liquefied hydrocarbon gases (LHG) stored in a tank comprises steps of: determining component composition of LHG by means of chromatographic analysis and determining molecular weight µ of certain components using a processing unit. Then measuring density value ρ_l of liquid phase of components included in composition of LHG by means of measuring density; determining level H of interface of LHG in tank by means of measurement of level of interface. Further, temperature t_l of liquid phase of LHG is determined and temperature t_u of LHG vapour phase in tank by means of temperature sensors. Then measuring density ρ_p of vapour phase of components included in composition of LHG, by means of measuring density or determining density ρ_u of vapour phase of components, included in composition of LHG, from component composition and temperature of liquid phase of LHG in tank by means of a processing unit. Further, determining from level H of interface of LPG in tank corresponding to said level value of volume V_l20 of liquid phase of LHG in tank on measured level H using known calibration table of tank, composed at temperature 20 °C, by means of processing unit to calculate volume V_l(t_l) of liquid phase of LHG in tank at temperature t_l using formula V_l(t_l)=V_l20·[1+2·α_st·(t_l-20)] by means of processing unit, determining volume of LHG vapour phase in tank at determined temperature t_u of vapour phase of LHG as difference between full capacity of tank at said temperature and volume of liquid phase LHG in tank at said temperature by formula V_u(t_u)=V_D20 ^res·[1+2·α_st·(t_u-20)]-V_l(t_l), where V_D20 ^res is previously known actual capacity of tank at temperature 20 °C. Then calculating mass M_l of liquid phase LHG as product of volume V_l(t_l) of liquid phase in tank on measured density value ρ_l of liquid phase of LHG, c mass M_n of LHG vapour phase as product of volume V_u(t_u) occupied by vapour phase of LHG in tank, on measured or determined density ρ_u of LHG vapour phase, total mass M₀ of LHG in tank through summation of mass M_l of liquid phase and mass M_n of LHG vapour phase in tank.

EFFECT: high accuracy of metering LHG during storage in tanks.

4 cl, 7 tbl

Description

FIELD OF THE INVENTION

The invention relates to the field of accounting for liquefied petroleum gases (hereinafter - LPG) and, in particular, to measurements of the mass of LPG during storage at automobile gas filling stations (hereinafter - gas filling stations) and multi-fuel filling stations (hereinafter - MAZS).

State of the art

Hydrocarbon accounting has always been an important aspect in their storage and sale; therefore, many methods and means have been developed for its implementation.

The prior art it is known selected as a prototype solution (RU 115090 "Device for commercial accounting of hydrocarbon fuels, publ. 04/20/2012), which describes the method carried out by the device for commercial accounting of hydrocarbon fuels, this solution relates to means for simultaneous control of the physical and economic parameters of hydrocarbon fuel and allows you to improve the quality and completeness of control of hydrocarbon fuel transported through pipelines or stored in stationary tanks. A device for commercial accounting of hydrocarbon fuel is made on the basis of at least one programmable logic controller and contains input-output modules associated with the output of at least one sensor in contact with hydrocarbon fuel; a communication processor module connected via an industrial data network to the interface; a storage module, a central processor module based on a high-speed logical processor and including blocks of means for monitoring the measurement channels and generating accounting information related to hydrocarbon fuel. Moreover, the device for commercial accounting of hydrocarbon fuel is made on the basis of at least one programmable logic controller with mounting modules on a profile bus, it contains input-output modules connected with the output of at least one sensor in contact with hydrocarbon fuel and selected from the list including: volumetric flowmeter, mass flowmeter, temperature sensor, pressure sensor, humidity sensor, density sensor, viscosity sensor, level meter and / or hydrostatic pressure sensor.

However, this solution does not disclose the accounting for unequal temperatures of the liquid and gas components of LPG in tanks, which leads to a decrease in the accuracy of accounting for LPG during storage in tanks.

Also known from the prior art the solution disclosed in patent RU 2262667 "Method for determining the physical parameters of liquefied gas in a tank" (publ. 20.10.2005), the proposed invention can be used in various technological systems associated with filling and draining of liquids, in particular liquefied hydrocarbon gases in gas supply systems. The purpose of the invention is the expansion of the measuring range towards the lower boundary. The device contains three capacitors 1-3, rigidly fixed in the neck 5 of the tank 6, and a measuring unit 7. The capacitors 1 and 2 are used to calibrate the device, and the capacitor 1 is located in the vapor space of the tank 6, and the capacitor 2 is placed in a liquid medium. In this case, the capacitors 1, 2 are made flat, mounted horizontally and rigidly fixed on the upper and lower ends of the capacitor 3. A vertically located coaxial capacitor 3 is located between the calibration 1 and 2 and changes its capacitance depending on the filling level of the reservoir 6. Device for measuring the liquid level can operate in continuous measurement over the entire filling range of the tank 6 from minimum to maximum values.

However, this decision does not disclose the accounting for unequal temperatures of the liquid and gas components of LPG in tanks, which leads to a decrease in the accuracy of accounting for LPG when stored in tanks

Disclosure of the invention.

In one aspect of the invention, there is disclosed a method for accounting for liquefied petroleum gases (LPG) stored in a tank, comprising the steps of:

- determine the component composition of LPG using means of chromatographic analysis;

- determine the molecular masses µ of certain components using the processing unit;

- measuring the density ρ _g of liquid phase components included in the LPG via density measurement means;

- determine the level H of the phase separation of LPG in the tank using a means of measuring the level of phase separation;

- determine the temperature t _{W of the} liquid phase of the LPG and the temperature t _{p of the} vapor phase of the LPG in the tank using temperature sensors;

- measure the density ρ _{p of the} vapor phase of the components included in the LPG using a density measuring tool or determine the density ρ _{p of the} vapor phase of the components included in the LPG by the composition and temperature of the liquid phase of the LPG in the tank using the processing unit ;

- determine by the value of the H level of the LPG phase section in the tank the corresponding value of the volume _{Vh20 of} the LPG liquid phase in the tank corresponding to this level at the measured level H using a previously known calibration table of the tank, compiled at a temperature of 20 ° C, using the processing unit;

- calculate the volume V _W (t _W ) of the liquid phase of the LPG in the tank at a temperature t _W according to the formula V _W (t _W ) = V _{W 20} · [1 + 2 · α _St · (t _W -20)] using the processing unit,

where α _article - the temperature coefficient of linear expansion of the material of the tank wall, taken equal to steel α _article = 12.5 · 10 ^-6 1 / ° C;

- determine the volume of the vapor phase of the LPG in the tank at a certain temperature t _{p the} vapor phase of the LPG as the difference in the total capacity of the tank at the mentioned temperature and the volume of the liquid phase of the LPG in the tank at the temperature by the formula

V _p = (t _p ) = V _D20 ^res · [1 + 2 · α _st · (t _p -20)] - V _W (t _W ),

where V _D20 ^rez is the previously known actual tank capacity at a temperature of 20 ° C;

moreover, the temperature of the liquid t _W and the steam t _p phases of the LPG in the tank is measured using temperature sensors installed at three levels of the tank: upper, middle and lower;

calculate the mass M _{W of} the LPG liquid phase as the product of the volume V _W (t _W ) of the liquid phase in the tank and the measured density ρ _{W of} the LPG liquid phase,

calculate the mass M _{p of the} vapor phase of the LPG as the product of the volume V _p (t _p ) occupied by the vapor phase of the LPG in the tank by the measured or determined density ρ _{p of the} vapor phase of the LPG,

determine the total mass of M ₀ LPG in the tank by summing the mass M _{W of the} liquid phase and the mass M _{p of the} vapor phase of LPG in the tank.

In additional aspects, it is disclosed that when calculating the volume of the liquid phase, the correction for the thermal expansion of the material of the means for measuring the level of the phase separation of LPG in the tank is additionally taken into account; calculate the volume V _W (t _W ) of the liquid phase of the LPG in the tank at a temperature t _W using the formula V _W (t _W ) = V _{W 20} · [1+ (2 · α _st + α _si ) · (t _W -20)], moreover, α _si is the correction for the temperature expansion of the material of the measuring instrument for the level of the phase separation of LPG in the tank, taken equal to steel α _si = 12.5 · 10 ^-6 1 / ° C.

In further aspects, it is disclosed that

a) if the level of the liquid phase of the LPG is equal to the upper level, t _W and t _p calculated as follows:

,

,

t _p = t _in

where t _cy is the temperature measured at a level corresponding to the middle of the height of the tank;

t _in - temperature measured at the upper level,

t _n - temperature measured at the lower level,

b) if the level of the liquid phase of the LPG in the tank is less than the upper level, but greater than or equal to half the inner diameter of the horizontal tank, t _W and t _p calculated as follows

,

,

t _p.cp = t _in ,

c) if the level of LPG in the tank is less than half the internal diameter of the horizontal tank, but greater than or equal to the lower level, t _W and t _p calculated as follows

t _W = t _n

,

,

g) if the level of the liquid phase of the LPG in the tank is less than the lower level, t _W and t _p calculated as follows

.

.

, где P - давление, измеренное датчиком; R - газовая постоянная, Z - фактор сжимаемости, причем фактор сжимаемости Z является известной функцией приведенного давления Р_пр и приведенной температуры

, где Р_пр - приведенное давление, которое вычисляется как отношение давления Р к известному для конкретных компонентов СУГ критическому давлению P_кр; T_пр - приведенная температура, которая вычисляется как отношение абсолютной температуры T СУГ к известной для конкретных компонентов СУГ критической температуре T_кр.In additional aspects, it is disclosed that the volume of the LPG vapor phase in the tank is determined by the formula V _p (t _p ) = V _D20 ^res · [1+ (2 · α _st + α _si ) · (t _p -20)] - V _w ( t _g ), where α _si is the correction for the temperature expansion of the material of the measuring instrument for the level of the phase separation of LPG in the tank, taken equal to for steel α _si = 12.5 · 10 ^-6 1 / ° C; calculate the density ρ _{p of the} vapor phase of the LPG according to the formula

where P is the pressure measured by the sensor; R is the gas constant, Z is the compressibility factor, and the compressibility factor Z is a known function of the reduced pressure P _pr and the reduced temperature

where P _CR - the reduced pressure, which is calculated as the ratio of the pressure P to the critical pressure P _cr known for the specific components of the LPG; T _ol - the reduced temperature, which is calculated as the ratio of the absolute temperature T of LPG to the critical temperature T _cr known for specific components of LPG.

The main task solved by the claimed invention is to ensure high accuracy of accounting for LPG when stored in tanks.

The essence of the invention lies in the fact that when measuring the mass of LPG by determining the volume and density of LPG in the tank, the different temperature of the liquid and vapor phases of the LPG in the tank is additionally taken into account, which affects the different expansion of the parts of the tank in which these two phases are located, which must be taken into account for more accurate calculation of the total mass of LPG stored in the tank.

The technical result achieved by the solution is to increase the accuracy of accounting for LPG during storage in tanks and is ensured by taking into account the temperature differences between the liquid and vapor phases of LPG in the tank, which causes different expansion of the upper and lower parts of the tank.

The implementation of the invention

The proposed technical solution relates to horizontal cylindrical tanks used during accounting operations at gas filling stations (MAZS), while it is obvious that they are subject to calibration and verification and must have individual calibration characteristics.

In general, the following measurement methods are used to measure the LPG mass at the gas filling station:

- direct method of dynamic measurements;

- direct method of static measurements;

- indirect method of dynamic measurements;

- indirect method of static measurements.

The choice of the method for measuring the mass of LPG at the gas filling station is carried out taking into account the possibility of technical implementation of the method and economic feasibility.

This description describes a method for measuring the mass of LPG in the gas filling tanks, performed by the indirect method of static measurements using measuring systems for LPG parameters in horizontal cylindrical graduated gas filling tanks.

At least the following parameters are the initial data for determining the mass of LPG during storage in gas station tanks:

- the composition of the liquid phase of the LPG (according to the passport or the results of chromatographic analysis) x _mi ,% mass;

- molecular weights µ and critical parameters P _cr and T _{cr of} individual hydrocarbons included in the LPG;

- values of the density of the liquid phase ρ _W , kg / m ³ , hydrocarbons that are part of the LPG;

- values of saturated vapor pressure P _S , MPa, hydrocarbons that are part of the LPG;

- level of phase separation of LPG in the tank - H, mm;

- calibration table of the storage tank for LPG;

- the temperature of the liquid and vapor phases of the LPG in the tank - t _W and t _n , ° C;

- excess vapor pressure of the LPG in the tank - R _huts , kgf / cm ² (MPa);

- the density of the liquid phase of the LPG ρ _l , kg / m ³ (in the presence of a channel for measuring the density of the liquid phase of the LPG);

- the density of the vapor phase of the LPG ρ _p , kg / m ³ (in the presence of a channel for measuring the density of the vapor phase of the LPG).

The level of the phase separation of LPG N in the tank is measured (depending on the applied measuring instruments (SI)) using level converters known from the prior art, for example:

- magnetostrictive type (SiteSentinel, Struna, PMP-201);

- radio frequency type (SU-5D);

- microwave type (VEGAFLEX 65).

By the value of the level of the phase separation of LPG in the tank N, according to the calibration table, the volume value _Vh20 corresponding to this level is _determined .

The volume of the liquid phase of the LPG in the tank at the actual temperature is calculated by the formula

V _W (t _W ) = V _{W 20} · [1+ (2 · α _st + α _si ) · (t _WFr. -20)],

where V _W20 is the volume of the liquid phase of the LPG in the tank at the measured level H, determined by the calibration table of the tank, compiled at a temperature of 20 ° C, m ³ ;

α _v - temperature coefficient of linear expansion of the tank wall material, taken equal to α _v Steel = 12.5 · 10 ^-6 1 / ° C;

α _si - correction for the temperature expansion of the material of the measuring instrument for the level of the phase separation of LPG in the tank, taken equal to steel α _si = 12.5 · 10 ^-6 1 / ° С;

t _W - temperature of the liquid phase of the LPG in the tank, ° C.

Moreover, taking into account the correction for the thermal expansion of the material of the measuring instrument is optional.

The volume of the vapor phase of the LPG in the tank at the actual temperature is determined as the difference between the total capacity of the tank at the actual temperature and the volume of the liquid phase of the LPG in the tank at the actual temperature according to the formula

V _p (t _p ) = V _D20 ^res · [1 + 2 · α _st · (t _p -20)] - V _w (t _w ),

where V _D20 ^rez - the actual capacity of the tank at a temperature of 20 ° C (according to the passport of the tank), m ³ ;

t _p - temperature of the vapor phase of the LPG in the tank, ° C.

The value of t _{p is} calculated through the temperature values measured by at least one sensor located in the vapor phase of the LPG.

Preferably, the liquid temperature t _w and t _n vapor phase of LPG in the tank is measured via temperature sensors located at the three levels of the tank: the upper, middle and lower.

In one embodiment, the temperature of the liquid t _W and the steam t _p phases of LPG, measured along the temperature measuring channel, is averaged according to the following formulas:

a) if the level of the liquid phase of the LPG is equal to the upper level,

,

,

t _p = t _in

where t _cy is the temperature measured at a level corresponding to the middle of the height of the tank, ° C;

t _in - temperature measured at the upper level, ° C;

t _n - temperature measured at the lower level, ° C,

b) if the level of the liquid phase of the LPG in the tank is less than the upper level, but greater than or equal to half the inner diameter of the horizontal tank,

,

,

t _p = t _in

c) if the level of LPG in the tank is less than half the internal diameter of the horizontal tank, but greater than or equal to the lower level,

t _W = t _n

,

,

g) if the level of the liquid phase of the LPG in the tank is less than the lower level,

t _W = t _n

.

.

In one embodiment, the average density of the liquid phase of the LPG in the tank is determined using density converters of the liquid phase of the LPG (such as SiteSentinel, Struna, PMP-201, SU-5D).

In the absence or failure of the density measurement channel, the density of the LPG liquid phase in the tank is determined by the calculation method according to the component composition and the temperature value of the LPG liquid phase in the tank.

In the absence of SI density at the gas filling station, the density of the LPG liquid phase is determined by calculation by the component composition and temperature corresponding to the conditions for measuring the volume of the LPG liquid phase in the tank. The composition of the liquid phase of the LPG in mass% is taken according to the quality certificate of the LPG or the results of chromatographic analysis.

The density of a multicomponent mixture of the liquid phase of LPG at a temperature is calculated by the component composition in mass percent and the density of individual hydrocarbons by the formula

,

,

where x _mi is the mass fraction of the i-th component in the composition of the liquid phase of LPG,%;

ρ _Жi (t _Ж ) is the density of the i-th component of the liquid phase of the LPG at a temperature t _W , kg / m ³ ;

n is the number of components of the liquid phase of the LPG.

The density of the vapor phase of the LPG in the tank is determined using converters of the density of the vapor phase of the LPG (SU-5D).

In the absence or failure of the density measurement channel, the density of the LPG vapor phase in the tank is determined by the calculation method according to the component composition obtained from the equilibrium phase of the LPG in the tank and the temperature and gauge pressure of the LPG in the tank, measured using temperature and pressure transducers.

The density of the vapor phase of the LPG is calculated by the formula

,

,

where ρ _p - the density of the vapor phase of the LPG, kg / m ³ ;

P is the absolute pressure, MPa;

t _p - temperature of the vapor phase of the LPG, ° C;

R is the gas constant, J / (kg · K);

Z is the compressibility factor.

The compressibility factor Z is a function of the reduced pressure P _ol and the reduced temperature T _ol

,

,

where P _CR - reduced pressure, which is a dimensionless quantity and is calculated as the ratio of the absolute pressure P to the critical pressure P _cr ;

T _ol - the reduced temperature, which is a dimensionless quantity and is calculated as the ratio of the absolute temperature T to the critical temperature T _cr .

The critical pressure P _cr and the critical temperature T _{cr of} hydrocarbon gases included in the LPG are known from reference sources of the prior art.

The mass of the liquid phase of the LPG is calculated as the product of the volume of the liquid phase in the tank by the measured density of the liquid phase of the LPG or the calculated value of the density reduced to the conditions for measuring the volume of the liquid phase of the LPG, according to the formula

M _W = V _W · ρ _W ,

where M _W - the mass of the liquid phase of the LPG in the tank, kg;

ρ _W - the density of the liquid phase of the LPG at a temperature t _W in the tank, kg / m ³ .

The mass of the LPG vapor phase is calculated as the product of the volume occupied by the LPG vapor phase in the tank by the measured density of the LPG vapor phase or the density value of the LPG vapor phase obtained by the calculation, according to the formula

M _p = V _p · ρ _p ,

where M _p is the mass of the vapor phase of the LPG in the tank, kg;

ρ _p - the density of the vapor phase of the LPG at a temperature t _p in the tank, kg / m ³ .

The mass of LPG is composed of the masses of the liquid and vapor phases of the LPG in the tank

M = M _w + M _p ,

where M is the mass of LPG in the tank, kg

According to GOST P 52087-2003, five grades of SUG are produced: technical propane (PT), automotive propane (PA), automotive propane-butane (PBA), technical propane-butane (PBT), and technical butane (BT).

Requirements for the component composition and basic physical and chemical properties of the SUG grades are shown in Table 1 below.

Moreover, when using liquefied gases of the ПТ and ПБТ grades as a fuel for automobile transport, the mass fraction of the sum of unsaturated hydrocarbons should not exceed 6%, and the saturated vapor pressure should be at least 0.07 MPa for the ПТ and ПБТ grades at minus 30 ° C and minus 20 ° C, respectively.

LHG contains saturated and unsaturated hydrocarbons. The values of molecular mass µ and critical parameters T _cr and R _cr for individual hydrocarbons that are part of the LPG are shown in table 2.

The composition of the mixture of liquid hydrocarbons from mass percent x _m1 , x _m2 , ..., x _mn to molar percent x ₁ , x ₂ , ..., x _{n is} calculated according to the formula

where x _mi is the mass fraction of the i-th component in the composition of the LPG mixture,%;

x _i is the molar fraction of the i-th component in the composition of the LPG mixture,%;

µ _i is the molecular weight of the i-th individual hydrocarbon, kg / kmol.

LHG, in contrast to oil products, has an increased saturated vapor pressure, which is one of the standardized indicators of GOST P 52087-2003. The working pressure in the technological equipment for transportation, storage and distribution of LPG is 16 kgf / cm ² (1.6 MPa).

For the purpose of accounting for LPG in mass units, it is necessary to have reliable methods for determining the density of the liquid and vapor phases of LPG both by instrumental and calculation methods.

The density of a multicomponent mixture of the liquid phase of LPG at a temperature t is calculated by the component composition in mass percent and the density of the liquid phase of individual hydrocarbons by the formula

,

,

where x _mi is the mass fraction of the i-th component in the mixture,%;

ρ _Жi (t) is the density of the liquid phase of the i-th component of LPG at a temperature t, kg / m ³ (see data in table 1 in the range -50≤t≤ + 50 ° C);

n is the number of components of the liquid phase of the LPG.

The density of the vapor phase of the LPG is calculated by the formula

,

,

where ρ _n is the density of the vapor phase of the LPG, kg / m ³ ;

P is the absolute pressure, MPa;

t _n is the temperature of the vapor phase of the LPG, ° C;

R is the gas constant, J / (kg · K);

Z is the compressibility factor.

The compressibility factor Z is a function of the reduced pressure P _ol and the reduced temperature T _ol

and can be determined by known from reference graphs and tables.

Saturated vapor pressure is the pressure at which liquid and vapor in a closed (sealed) volume at a certain temperature are in equilibrium.

The saturated vapor pressure of LPG is among the indicators normalized by GOST R 52087 (see table 1).

The composition of the vapor phase in equilibrium with the liquid phase of the LPG in the tank is determined by the formula

,

,

where y _i , is the molar fraction of the i-th component in the vapor phase of the LPG,%;

x _i - molar fraction of the i-th component in the composition of the liquid phase of LPG,%;

P - absolute pressure, under which there is a mixture of LPG, MPa, is the sum of the partial pressures of the components included in the LPG

,

,

P _i - partial pressure of the i-th component of the mixture of LPG, MPa;

P _si is the saturated vapor pressure of the i-th component of the LPG, MPa;

n is the number of components that make up the LPG.

From reference sources of the prior art, it is possible to find out the saturated vapor pressure P _{s of the} individual hydrocarbons included in the LPG in the temperature range -50≤t≤ + 50 ° C (223.15≤T≤323.15 K).

For the multicomponent composition of the vapor phase of the LPG, the values of the average molecular weight μ _cm , pseudocritical temperature T _pc and pseudocritical pressure P _{pc are} calculated by the formulas

,

,

,

,

,

,

where T _pc , T _{cr i} - pseudocritical temperature and critical temperature of the i-th component of the vapor phase of the LPG, K;

P _pc , R _{cr i} - pseudocritical pressure and critical pressure of the i-th component of the vapor phase of LPG, MPa;

µ _i , µ _cm are the molecular weights of the ith component and the mixture of LPG vapor, respectively, kg / kmol;

y _i is the molar fraction of the i-th component in the vapor phase of the LPG,%;

n is the number of components of the vapor phase of the LPG.

Consider an example of calculating the parameters of multicomponent mixtures of liquid and vapor phases of LPG at temperatures:

t = -5 ° C - for the autumn-winter period;

t = 15 ° C - for the spring-summer period.

The composition of the liquid phase of the LPG in% mass:

The density of the liquid phase of LPG at temperatures of -5 ° C and 15 ° C is calculated by the formula (2)

When calculating the limits of the relative measurement error of the LPG mass, the volume expansion coefficient of the LPG liquid phase βt _{20 is used} , the value of which is calculated by the method of successive approximations from the expression

where CTL _ρ is a correction factor that takes into account the effect of temperature on the volume of the liquid phase of the LPG;

βt ₂₀ - coefficient of volume expansion of the liquid phase of the LPG, 1 / ° C.

Table 3 presents the results of calculating the coefficient of volume expansion of the liquid phase of the LPG, the component composition of which is indicated above.

At the critical point, the specific volumes of the liquid and vapor phases are equal; therefore, the density of the liquid phase of ethane C ₂ H ₆ at temperatures above the critical T _cr = 305.4 K is taken to be inversely proportional to the critical volume ρ _cr = 1 / v _cr = 1 / ( 4.992 · 10 ^-3 ) = 203.2 kg / m ³ .

We will recalculate the component composition of the liquid phase of the LPG from% mass to% molar according to the formula (1):

The saturated vapor pressure of a mixture of hydrocarbon gases at temperatures of -5 ° C and 15 ° C is calculated by the formula (4)

Let us calculate the density of the vapor phase of the LPG at a temperature t _p = -5 ° C and absolute pressure P _{s cm} (-5 ° C) = 0.284 MPa according to the formula (3)

By the values of the reduced pressure P _CR = P _{s cm} / P _pc = 0.284 / 4.21 = 0.068 and the reduced temperature T _CR = (273.15 + t _p ) / T _pc = (273.15-5) / 374.2 = 0.717 from the reference tables we find the compressibility factor Z = 0.933.

The density of the vapor phase of the LPG is calculated by the formula (3)

Calculation of the density of the vapor phase of LPG at a temperature t _p = 15 ° C and absolute pressure P _{s cm} (15 ° C) = 0.522 MPa according to the formula (3)

According to the above pressure values P _ave = P _{s cm} / P _nc = 0.522 / 4.20 = 0.124, and the present temperature T _ave = (273,15 + t _n) / T _pc = (273.15 + 15) / 375.2 = 0.768 from the reference tables find the compressibility factor Z = 0.880.

The density of the vapor phase of the LPG is calculated by the formula (3)

From the above calculations it is clear that all of them can be partially or fully automated, that is, implemented using software and hardware.

Embodiment 1

In the first embodiment, the proposed technical solution is a method in which the component composition of LPG is determined. The determination can be carried out by measuring chromatographic analysis methods known from the prior art, as well as on the basis of previously known information (as a rule, the component composition of LPG is known from one or another documentation). This step can be automated, for example, by means of a PC, processor, controller, or other computing tool that is functionally connected by the corresponding communication lines to chromatographic analysis tools and / or a memory unit that stores data on the component composition of the LPG.

At the next stage of the method, the molecular weights of the components that make up the LPG are determined. It is understood that the molecular weights of certain components are easily determined by reference literature containing information on the molecular weights of the chemical elements that make up the components. This stage can be automated, for example, by means of a PC, processor, controller, or other processing unit (computing means), functionally connected by corresponding communication lines to a memory unit that stores data on the molecular weights of the components included in the LPG.

In the next step of the method, the density value of the liquid phase of the components included in the LPG is measured using a density measuring means, for example, one of the above or another known from the prior art. This step can be automated by means of a processing unit functionally connected by corresponding communication lines to a density measuring means.

In the next step of the method, the level H of the phase separation of the LPG in the tank is determined by means of measuring the level of the phase separation. This step can be automated by means of a processing unit functionally connected by corresponding communication lines with a means for measuring the level of phase separation.

The next step of the method determines the temperature t _{W of the} liquid phase of the LPG and the temperature t _{p of the} vapor phase of the LPG in the tank using sensors. This step can be automated by means of a processing unit that is functionally connected to the respective communication lines directly or via corresponding transducers with sensors. One sensor for the liquid phase and one for the gaseous can be installed in the tank. However, there may be more sensors: several for each phase. Sensors can be installed at different levels of the tank, for example at the lower, middle, upper; a plurality of sensors can be installed uniformly in height of the tank or unevenly, for example, a larger number of sensors can be installed at the middle level of the tank or in the upper and lower levels of the tank.

In the next step of the method, the density ρ _{p of the} vapor phase of the components included in the LPG is measured using a density measuring tool or the density ρ _{p of the} vapor phase of the components included in the LPG is calculated by the component composition and the temperature of the liquid phase of the LPG in the tank using processing unit.

.The implementation of the measurement option using the density measurement tool is described above. The formula by which the vapor phase density can be calculated is given earlier:

.

where x _mi is the mass fraction of the i-th component in the composition of the liquid phase of LPG,%; ρ _Жi (t _ж ) is the density of the i-th component of the liquid phase of the LPG at a temperature t _l , kg / m ³ (see table 1); n is the number of components of the liquid phase of the LPG.

Obviously, the calculation of this formula can be easily implemented by means of a processing unit functionally connected with temperature sensors, if necessary, with other measuring means and a memory unit with the necessary information on LPG introduced in advance.

At the next step of the method, the value of the volume _{Vh20 of the} liquid phase of the LPG in the tank corresponding to this level is determined by the value of the H level of the LPG phase section in the tank at the measured level H using a previously known calibration table of the tank compiled at a temperature of 20 ° C.

To automate this step, the calibration table is preloaded into the memory from which the processing unit takes the necessary data and, based on the value of H, this block determines the value of V _x20 .

The next step of the method calculates the volume V _W (t _W ) of the liquid phase of the LPG in the tank at a temperature t _W using the formula V _W (t _W ) = V _{W 20} · [1 + 2 · α _St · (t _W -20)] using processing unit, where α _st - the temperature coefficient of linear expansion of the material of the tank wall, taken equal to steel α _st = 12.5 · 10 ^-6 1 / ° C.

To automate this stage, many linear expansion coefficients for various materials are preloaded into the memory from which the processing unit takes the necessary value and, based on the obtained values of temperature t _W and volume V _{W 20} , calculates V _W (t _W ) using the formula.

The next step of the method determines the volume of the vapor phase of the LPG in the tank at a certain temperature t _{p the} vapor phase of the LPG as the difference in the total capacity of the tank at the mentioned temperature and the volume of the liquid phase of the LPG in the tank at the temperature by the formula

,

,

where V _D20 ^rez is the previously known actual tank capacity at a temperature of 20 ° C.

To automate this stage, the processing unit, on the basis of the temperature obtained from the sensor and the coefficient α _st extracted from the memory and the value V _Д20 ^rez , using the above formula, calculates the volume of the LPG vapor phase V _p (t _p ).

In the next steps of the method, the processing unit, based on previously obtained information on the volume and density of the liquid and vapor phases, finds the masses of the liquid and vapor phases, as well as the total mass of LPG as the sum of the masses of the liquid and vapor phases.

In general, the method can be implemented by means of an accounting device comprising a tank body; a processing unit integrated in the tank body, functionally connected with sensors installed in the tank, and with a memory containing information about the parameters of the tank; chromatographic analysis tool; means for measuring the density of liquid and vapor phases; means for measuring the level of the phase separation, and all measuring and other hardware-software, software and hardware can be built into the tank body and functionally connected to the processing unit.

The device operates as follows. The processing unit collects from all sensors, measuring instruments and memory the necessary information, processes it according to the algorithm described above, and provides the exact mass value of the LPG in the tank.

In the proposed technical solution, the temperature expansion of the material of the means for measuring the level of the phase separation of LPG in the tank can be additionally taken into account according to the formula: V _W (t _W ) = V _{W 20} · [1+ (2 · α _st + α _si ) · (t _W -20 )], where α _si is the correction for the thermal expansion of the material of the measuring instrument for the level of the phase separation of LPG in the tank, taken equal to for steel α _si = 12.5 · 10 ^-6 1 / ° C.

A specific arrangement of sensors may be as follows: upper, middle, and lower level of the tank.

In a preferred embodiment, if the level of the liquid phase of the LPG is equal to the upper level, t _w and t _p are calculated as follows:

, t_п=t_в, где t_cy - температура, измеренная на уровне, соответствующем середине высоты резервуара; t_в - температура, измеренная на верхнем уровне, t_н - температура, измеренная на нижнем уровне.

, t _p = t _in , where t _cy is the temperature measured at a level corresponding to the middle of the height of the tank; t _in - temperature measured at the upper level, t _n - temperature measured at the lower level.

, t_п.ср=t_в.If the level of the liquid phase of the LPG in the tank is less than the upper level, but greater than or equal to half the inner diameter of the horizontal tank, t _W and t _p calculated as follows

t _t.sp. = t _in .

.If the level of LPG in the tank is less than half the inner diameter of the horizontal tank, but greater than or equal to the lower level, t _W and t _p calculated as follows t _W = t _n ,

.

.If the level of the liquid phase of the LPG in the tank is less than the lower level, t _W and t _p calculated as follows t _W = t _n

.

Embodiment 2

As can be seen from formula (5), to determine the volume of the tank occupied by the gas phase, find the total volume of the tank at a temperature t _p and subtract from this total volume of the tank the volume occupied by the liquid phase having a temperature t _g . However, this approach does not take into account the fact that different parts of the tank under the influence of different temperatures (t _p and t _g ) are deformed in different ways. Obviously, a higher temperature (for example, t _p ) causes greater expansion than a lower one (for example, t _g ).

To account for this non-uniform deformation, in one embodiment, it is proposed to determine the volume V _{CP of the} tank at a temperature of the lower part of the tank equal to t _W and a temperature of the upper part of the tank equal to t _p . To do this, determine the actual capacity V _{D_tzh} ^cut tank at a temperature t _W (according to the formula V _{D_tzh} ^cut = V _D20 ^cut [1 + 2 · α _article (t _W -20)]) and the actual capacity V _{D_m} ^cut tank at a temperature t _p ( _{D_m} formula v ^res = v _D20 ^Res [2 + 1-α _v (t -20 _n)]), calculating an average value of v _{D_SR} ^cut as the average of v and v _{D_tzh} ^Res _{D_tp} ^Res _{D_CP} formula v ^res = (v _{D_tzh} ^{Res Res} _{D_tp} + V) / 2.

In the future, this value is used to determine the volume of the vapor phase V _p (t _p ) by the formula:

V _p (t _p ) = V _{D_СР} ^rez -V _w (t _w ).

Obviously, this approach reduces the maximum error that occurs when calculating the volume of the vapor phase.

Further determination of the mass of LPG in the tank is carried out according to the method described above.

Embodiment 3

The difference of another embodiment from embodiment 2 is that it takes into account not two areas of different deformation of the tank, but as many areas as there are sensors in the tank.

Consider an example for three sensors: lower, middle and upper.

Having readings from three sensors, it is possible to build the distribution of the temperature field along the height of the tank. For example, the following readings were obtained from three sensors: t ₁ , t ₂ , t ₃ , where t ₁ is the temperature received from the lower sensor, t ₂ is the temperature received from the middle sensor, t ₃ is the temperature received from the upper sensor. It should be clear here that the physical location of the “upper”, “middle”, “lower” is associated with the geometry of the tank and its location relative to the surface of the earth, the upper sensor is physically above the middle and lower sensors relative to the direction of gravity.

Preferably, the sensors are arranged uniformly along the height of the tank, in which case the height of the tank is divided into uniform parts, each of which is deformed in accordance with its temperature.

The previously known actual capacity V _D20 ^cut tank at a temperature of 20 ° C can be found as the sum of the capacities of the parts of the tank:

V = V _D20 ^{Res Res} _{D20_1} + V + V _{D20_2} ^Res _{D20_3} ^Res,

where V _{D20_1} ^rez - capacity at the lower level, V _{D20_2} ^rez - capacity at the middle level, V _{D20_3} ^rez - capacity at the upper level.

Since the shape of the tank is known in advance, the capacity of the individual parts of the tank can be determined without any creative effort.

Knowing the temperature of the LPG in individual parts of the tank, you can determine the deformation of the individual parts of the tank and find the total capacity V _{D_KORR} ^cut tank, taking into account temperature correction:

V = V ^res _{D_KORR D20_1} ^Res [1 + 2 · α _st (t ₁ -20)] + V _{D20_2} ^Res [1 + 2 · α _st (t2-20)] + V _{D20_3} ^D [1 + 2 · α _st ( t ₃ -20)] ³ .

In the future, this value is used to determine the volume of the vapor phase V _p (t _p ) by the formula:

V _p (t _p ) = V _{D_CORR} ^rez- V _w (t _w ).

Obviously, this approach further reduces the error that arises when calculating the volume of the vapor phase.

Further determination of the mass of LPG in the tank is carried out according to the method described above.

For a known shape of the tank, and, as a rule, it is a circle, it is easy to construct a map of the distribution of the temperature field t (l) over the tank even for three temperature values (in the upper, middle and lower parts of the tank).

Knowing the distribution t (l) of the temperature field over the tank, where the tank has a total surface length L, it is possible to determine the exact temperature deformation of the tank by its surface. Obviously, the variable l defines a specific point on the surface of the tank and can take values from 0 to L.

.

.

In the future, this value is used to determine the volume of the vapor phase V _p (t _p ) by the formula:

V _p (t _p ) = V _{D_CORR} ^rez- V _w (t _w ).

Obviously, this approach further reduces the error that arises when calculating the volume of the vapor phase, since it uses a more accurate determination of temperatures along the surface of the tank.

Embodiments are not limited to the embodiments described herein, those skilled in the art based on the information set forth in the description and knowledge of the prior art will appreciate other embodiments of the invention without departing from the spirit and scope of the present invention.

The elements mentioned in the singular do not exclude the plurality of elements, unless specifically indicated otherwise.

The functional connection of elements should be understood as a connection that ensures the correct interaction of these elements with each other and the implementation of one or another functionality of the elements. Particular examples of functional communication may be communication with the possibility of exchanging information, communication with the possibility of transmitting electric current, communication with the possibility of transmitting mechanical motion, communication with the possibility of transmitting light, sound, electromagnetic or mechanical vibrations, etc. The specific type of functional connection is determined by the nature of the interaction of the above elements and, unless otherwise indicated, is provided by well-known means using principles well known in the art.

The methods disclosed herein comprise one or more steps or actions to achieve the described method. The steps and / or actions of the method can replace each other without going beyond the scope of the claims. In other words, unless a specific order of steps or actions is defined, the order and / or use of specific steps and / or actions can be changed without departing from the scope of the claims.

The application does not always indicate specific software and hardware for the implementation of the blocks in the drawings, but one skilled in the art should understand that the essence of the invention is not limited to a specific software or hardware implementation, and therefore, any software and hardware may be used to implement the invention, known in the art. So hardware can be implemented in one or more specialized integrated circuits, digital signal processors, digital signal processing devices, programmable logic devices, user programmable gate arrays, processors, controllers, microcontrollers, microprocessors, electronic devices, and other electronic modules configured to carry out the functions described in this document, computers or a combination of the above.

Although not specifically mentioned, it is obvious that when it comes to storing data, programs, and the like, a computer-readable storage medium is meant, examples of computer-readable storage media include read-only memory, random-access memory, register, cache semiconductor storage devices, magnetic media such as internal hard drives and removable drives, magneto-optical media and optical media such as CD-ROMs and digital versatile disks (DVDs), as well as any other Gia known in the prior art storage media.

Although exemplary embodiments have been described in detail and shown in the accompanying drawings, it should be understood that such embodiments are illustrative only and are not intended to limit the broader invention and that the invention should not be limited to the particular arrangements and structures shown and described, since various other modifications may be apparent to those skilled in the art.

The features mentioned in the various dependent claims, as well as the implementations disclosed in various parts of the description, can be combined to achieve beneficial effects, even if the possibility of such a combination is not explicitly disclosed.

In the above description of examples, directional terms (such as “above,” “top,” “below,” “bottom,” “top,” “bottom,” etc.) are used for convenience. In general, “above,” “upper,” “up,” and similar terms refer to the direction toward the earth's surface.

Claims (4)

1. A method of accounting for liquefied petroleum gases (LHG) stored in a tank, comprising the steps of:
- determine the component composition of LPG using means of chromatographic analysis;
- determine the molecular mass µ of certain components using the processing unit;
- measuring the density ρ _g of liquid phase components included in the LPG via density measurement means;
- determine the level H of the phase separation of LPG in the tank using a means of measuring the level of phase separation;
- determine the temperature t _{W of the} liquid phase of the LPG and the temperature t _{p of the} vapor phase of the LPG in the tank using temperature sensors;
- measure the density ρ _{p of the} vapor phase of the components included in the LPG using a density measuring tool or determine the density ρ _{p of the} vapor phase of the components included in the LPG by the composition and temperature of the liquid phase of the LPG in the tank using the processing unit;
- determine by the value of the H level of the LPG phase separation in the tank the corresponding value of the volume _{Vh20 of} the LPG liquid phase in the tank corresponding to this level at the measured level H using the tank’s previously known calibration table compiled at a temperature of 20 ° C using the processing unit;
- calculate the volume V _W (t _W ) of the liquid phase of the LPG in the tank at a temperature t _W according to the formula V _W (t _W ) = V _{W 20} · [1 + 2 · α _St · (t _W -20)] using the processing unit,
where α _article is the temperature coefficient of linear expansion of the material of the tank wall;
- determine the volume of the vapor phase of the LPG in the tank at a certain temperature t _{p the} vapor phase of the LPG as the difference in the total capacity of the tank at the mentioned temperature and the volume of the liquid phase of the LPG in the tank at the temperature by the formula
V _p (t _p ) = V _D20 ^res · [1 + 2 · α _st · (t _p -20)] - V _w (t _w ),
where V _D20 ^rez is the previously known actual tank capacity at a temperature of 20 ° C;
moreover, the temperature of the liquid t _W and the steam t _p phases of the LPG in the tank is measured using temperature sensors installed at three levels of the tank: upper, middle and lower;
calculate the mass M _{W of} the LPG liquid phase as the product of the volume V _W (t _W ) of the liquid phase in the tank and the measured density ρ _{W of} the LPG liquid phase,
calculate the mass M _{p of the} vapor phase of the LPG as the product of the volume V _p (t _p ) occupied by the vapor phase of the LPG in the tank by the measured or determined density ρ _{p of the} vapor phase of the LPG,
determine the total mass M ₀ LPG in the tank by summing the mass M _{W of the} liquid phase and the mass M _{p of the} vapor phase LPG in the tank. 2. The method according to p. 1, in which when calculating the volume of the liquid phase, the correction for the thermal expansion of the material of the means for measuring the level of phase separation of the LPG in the tank is additionally taken into account. 3. The method according to p. 1, in which
a) if the level of the liquid phase of the LPG is equal to the upper level, t _W and t _p calculated as follows:

,
t _p = t _in
where t _su is the temperature measured at a level corresponding to the middle of the height of the tank,
t _in - temperature measured at the upper level,
t _n - temperature measured at the lower level,
b) if the level of the liquid phase of the LPG in the tank is less than the upper level, but greater than or equal to half the inner diameter of the horizontal tank, t _W and t _p calculated as follows

,
t _p = t _in
c) if the level of LPG in the tank is less than half the internal diameter of the horizontal tank, but greater than or equal to the lower level, t _W and t _p calculated as follows
t _W = t _n

,
g) if the level of the liquid phase of the LPG in the tank is less than the lower level, t _W and t _p calculated as follows
t _W = t _n

. 4. The method according to p. 1, in which
calculate the density ρ _{p of the} vapor phase of the LPG according to the formula

,
where P is the pressure measured by the sensor,
R is the gas constant
Z is the compressibility factor,
wherein the compressibility factor Z is a known function of the reduced pressure P _ol and the reduced temperature T _ol

where P _CR - the reduced pressure, which is calculated as the ratio of the pressure P to the critical pressure P _cr known for specific LPG components; T _CR - the reduced temperature, which is calculated as the ratio of the absolute temperature T LPG to the critical temperature T _cr known for specific components of LPG.