Материал: Scientific Herald of the Voronezh State University of Architecture and Civil Engineering

HEAT AND GAS SUPPLY, SEWERAGE, BUILDING CONSTRUCTION

OF WATER RESOURCES PROTECTION

UDC 711.4:697.3:711.8

B. N. Kuricyn1, N. N. Osipova2, S. S. Kuznecov3

ON THE DEFINITION OF OPERATIONAL PARAMETERS OF TANK INSTALLATIONS IN COMBINED REGASIFICATION

OF LIQUEFIED PETROLEUM GAS

Saratov State Technical University Named after Yu. A. Gagarin Russia, Saratov, tel.: (8452)99-88-93, e-mail: osnat75@mail.ru

1D. Sc. in Engineering, Prof. of Dept. of Heat and Gas Supply, Ventilation,

Water Supply and Applied Fluid Dynamics

2PhD in Engineering, Assoc. Prof. of Dept. of Heat and Gas Supply, Ventilation,

Water Supply and Applied Fluid Dynamics

3PhD student of Dept of Heat and Gas Supply, Ventilation, Water Supply and Applied Fluid Dynamics

Statement of the problem. Combined regasification of liquefied petroleum gas is characterized by different operating conditions of the reservoir system. Varied selection of the vapor and liquid phases of the reservoir causes a significant trend component composition of the liquefied gas in the tank, which may adversely affect the efficiency of gas-powered equipment. This led to the need for additional research to determine the operating parameters of the reservoir installation with natural and artificial re-gasification of liquefied natural gas.

Results. A mathematical model allowing one to determine the content of propane at the beginning of the cycle and regasification before the next refueling, the amount of gas produced in the combined mode selection, the amount of gas produced in the natural mode regasification liquefied petroleum gas.

Conclusions. The efficiency of the combined cycle liquefied petroleum gas regasification providing significant savings of energy consumed in the evaporation plant. The contribution of natural evaporative capacity feed tank to the overall steam production plant is 33—58 %.

Keywords: liquefied petroleum gas, tank installation, combined regasification, natural evaporative capacity.

Introduction

Gas is commonly supplied to users residing remotely from natural gas pipelines based on liquefied hydrocarbon gas.

© Kuricyn B. N., Osipova N. N., Kuznecov S. S., 2016

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Scientific Herald of the Voronezh State University of Architecture and Civil Engineering. Construction and Architecture

The use of gas in household applications (heating, cooking and hot water supply) is possible if tank setups of liquefied hydrocarbon gas. Gas supply systems using underground gas tank setups with artificial regasification are most common. Tank sets are thus fitted with special heat exchangers using hot water or water vapor, gas fuel combustion products, electrical energy for regasification [1, 2].

Studies of heat exchange in underground tank setups showed that natural evaporative capacity of tank setups has a large influence on the overall steam capacity.

Therefore the authors put forward a scheme of a combined regasification of liquefied hydrocarbon gas allowing one to fully account for natural evaporative capacity of tanks [3, 4].

An underground tank setup is thus fitted with a switch-on valve which while maintaining the pressure of a steam blanket Р0 provides alternate selection of vapor and liquid phases of liquefied hydrocarbon gas. The vapor phase of liquefied hydrocarbon gas is regenerated in the suction tank due to heat coming in from the subbase and the liquid phase undergoes regasification in the evaporator.

The operation of an underground tank setup means there are the following modes:

––mode of cooling of liquid down to a calculation state that corresponds with the pressure of adjusting the switch-on valve Р0 = 0,15 МPа (absolute) (natural regasification of liquefied hydrocarbon gas);

––a combination of selection of liquid and gaseous phases (combined regasification of liquefied hydrocarbon gas).

1. Developing a mathematical model describing a combined regasification of liquefied hydrocarbon gas. Combined selection of liquid and gas phases in the suction tank due to heat and mass exchange there is intensive dynamics of physical processes, quantitative evaluation of which is necessary to predict operational parameters of tank setups.

Let us express a rate of change of operational parameters of tank setups of liquefied hydrocarbon gas through a rate of change of its filling levels σ:

where F is a moistened surface of the tank setup; МГ is the mass of liquefied gas in the tank setup; ММ is the mass of a metal body contacting the liquid; σ is a level of filling of the tank setup; t is the temperature of the liquefied gas; τ is the time.

According to [5, 6], a rate of change of the parameters F / , M Г / , M М / in a range of change in filling of the tank setup from 15 to 85 % with no significant effect on the accuracy of calculations can be assumed to be constant with the maximum error of 4—5 %.

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Issue № 1(29), 2016 ISSN 2075-0811

This equally applies to a rate of change in the temperature of liquefied gas t / and level of its filling / .

Considering the accepted admissions let us write the equation of a heat balance of the tank setup with a cooling mode of the liquid:

where k is the coefficient of heat transfer of the tank setup (according to [5] depending on the volume of a tank setup and heat conductivity of the base); dependences on the volume of the tank setup and heat conductivity of the base course); СГ, СМ are heat conductivity of liquefied gas and metal body of the tank setup; r is latent hear of vapor of liquefied gas; tгр is a natural temperature of the base course on the axes of laying of the tank setup; g is the consumption of liquefied gas.

Letter indices «b» and «e» stand for the beginning and ending of cooling of the liquid in the underground tank setup.

As the initial temperature of liquefied gas following the filling of the tank setup is assumed to be the temperature of the air outside, i.e. tн = tв.

Calculation parameters MГН , MМН , FН correspond to the initial level of filling of the tank setup σн = 85 %. The parameters M ГК , M МК , FК are assumed depending on filling of the tank

setup at the end of cooling τохл.

The temperature of the liquefied gas at the end of cooling tК is determined according to the diagrams: the composition temperature [7] for corresponding parameters of liquefied gas РК and ΨК:

––РК = Р0 is the pressure of gas in the tank setup corresponding to the beginning of combined regasification;

––ΨК is the amount of propane in the liquid phase at the end of cooling.

The amount of propane in the liquid phase of gas ΨК in the tank setup at the end of cooling depends on the initial amount of propane ΨН and relative percentage of vaporized gas φ according to the formula [7]

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Scientific Herald of the Voronezh State University of Architecture and Civil Engineering. Construction and Architecture

where m is the ratio of the elasticity of propane vapors and n-butane. It is accepted according to thermodynamic tables depending on the average temperature of liquid in the tank setup. Equation (3) is solved using the iteration method by choosing the corresponding values τохл, at which the left and right part of the equation are linked with a specified accuracy. As the tank setup switches off a combined regasification, the latter provides the user with only that part of vapor that is due to natural heat coming in from the base course. The rest is generated by the evaporator.

The amount of vapor obtained in the tank setup during a combined regasification:

where tо is the temperature of the liquefied gas prior to another filling; Fо is a moisturized surface of the tank setup prior to another filling; τо is the length of a combined regasification. The length of the regasification mode is as follows

The relative percentage of liquefied gas obtained due to natural evaporative capacity of the tank setup:

Equation (5) is solved by the iteration method by linking the left and the right parts with a necessary accuracy. Specifying a range of values of tо we get the amount of vapor Gо. Hence using the values of Gо according to the formulas (7) and (8) we get the relative percentage of evaporated gas obtained due to natural evaporative capacity of the tank setup φ and using the formula (4) the residual amount of propane in liquid prior to another filling ΨК = Ψ0. Then according to the diagrams [7], knowing the composition of the liquid phase in the tank setup Ψ0 and the pressure in a combined regasification Pо, we determine the temperature of liquefied gas tо prior to another filling of the tank setup.

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