RU2569782C2 - Transfer of thick hydrocarbon fluids via pipeline - Google Patents

Abstract

FIELD: transport.

SUBSTANCE: claimed process aims at transfer of thick hydrocarbon fluids via pipeline. This process consists in prevention of freezing of said fluids caused by decrease in thickness owing to heating. Note here that heating of transferred fluids is effected by transfer rate whereat the following terms are complied with: W₁≥W₂, where W₁ is heat released at fluid friction, W₂ is heat losses at transfer of fluids.

EFFECT: higher efficiency of transfer.

Description

The invention relates to the transportation of viscous hydrocarbon fluids through pipelines.

Known methods for pumping viscous fluids through pipelines, based on reducing the viscosity of the pumped fluids, can be divided into three groups:

1. Decrease in viscosity due to preliminary heating of a liquid. A known method of transporting pipelines of preheated non-Newtonian paraffin-containing hydrocarbon liquids ("hot" pumping). The initial flow temperature is chosen so that at the end of the pipeline a temperature is maintained 3-5 ° C higher than the pour point of a non-Newtonian paraffin-containing hydrocarbon liquid. Its heating is carried out at special thermal stations (see V.I. Chernikin. Transfer of viscous and solidifying oils. M: Gostoptekhizdat, 1958 [1]). The disadvantages of this known method of transporting non-Newtonian paraffin-containing hydrocarbon liquids include: burning part of the pumped oil in heating furnaces, air pollution by combustion products, the inability to use "hot" pumping on subsea pipelines without special expensive thermal insulation, pumping with stops, etc.

2. Decrease in viscosity due to the treatment of the liquid with ultrasound or electromagnetic radiation. An example of such a method can serve as RF patents No. 2346206 "Method for pumping viscous liquids" [2], RF Patent No. 2232124 "Method for melting and lowering the viscosity of chemical products, mainly oil and oil products, and a device for its implementation" [3], RF Patent No. 2103211 "A method for heating thickened products in a container and a device for its implementation" [4]. The disadvantage of such methods can be considered the need to install emitters.

3. Decrease in viscosity due to the introduction of additives into the liquid. Additives include diluents (Application for invention No. 92010884 “Method for the production of highly viscous oil” [5]), depressant additives (RF patent No. 2141460 “Method for the transportation of non-Newtonian paraffin-containing hydrocarbon fluid through a pipeline” [6]). The disadvantages of these methods include the high cost of the process due to the need to add an additional product to a viscous liquid and in most cases the inability to reuse a diluent or additive.

The aim of the invention is to develop a new method for pumping viscous hydrocarbon fluids through a pipeline while reducing their viscosity as a result of heating, achieved by the corresponding pumping speed.

The technical result of the invention is to increase the efficiency of the process of pumping viscous hydrocarbon fluids through pipelines by reducing their viscosity as a result of heating, achieved by the corresponding pumping speed.

Reducing the viscosity of the transported fluid is achieved by increasing the temperature of the fluid due to the heat of internal friction. To achieve this effect and compensate for heat loss during transportation of the liquid, it is necessary to ensure an appropriate pumping speed, due to which the release of energy from friction will occur more intensively. In this case, the necessary condition for the implementation of this method of pumping is the condition:

where: W ₁ - heat released during friction of the liquid;

W ₂ - heat loss during pumping.

Based on the equality W ₁ = W ₂ , the pumping parameters are determined.

The calculation procedure, as an example, may be as follows. The differential equation of thermal energy, in which the influence of friction is taken into account by the dissipative term, is represented as (see Valeev A.R. Thermal regimes of pipelines. The issue of accounting for oil and gas heating in pipelines // Electronic scientific journal "Oil and Gas Business". 2009. No. 2 C.URL: http://ogbus.ru/authors/Valeev/Valeev_1.pdf [7]; Kraus Yu.A. Design and operation of main oil pipelines Part 1: The main factors affecting the features of operation and the choice of design parameters of main oil pipelines . - Omsk. Publishing house OmSTU, 2010 [8]):

- диссипативный член;Where

- dissipative member;

w is the oil velocity;

c _po is the isobaric heat capacity;

k is the heat transfer coefficient from oil flow to the environment;

d is the inner diameter of the pipeline;

T is the temperature in section x;

T ₀ - ambient temperature;

- гидравлический уклон;

- hydraulic bias;

λ is the coefficient of friction

Having solved this equation, considering the fluid motion to be stationary, the Shukhov equation with the Leibenzon correction taking into account the heat of friction [7; 8]:

G is the mass second flow rate;

- коэффициент Шухова;

- Shukhov coefficient;

L - pipeline length

Further, the calculation is based on the equality of the quantities of heat released due to internal friction and released into the environment (W ₁ = W ₂ ), which means achieving a constant temperature throughout the pipeline. In this case, the temperature of the liquid at the beginning of the pipeline (T _n ) will be equal to the temperature of the liquid at any point (T):

Transforming (3) using (4), we obtain the following expression:

Now the task is reduced to the selection of parameters that satisfy this equation. They will establish the required mode of operation of the pipeline, in which the oil temperature throughout the entire pipeline will not be lower than the initial one.

Case Study 1

Suppose that it is necessary to pump high-viscosity oil (ρ = 800 kg / m ³ , ν ₄₀ = 20 cSt) with a flow rate of Q = 9500 m ³ / h with a temperature of at least 40 ° C over the entire length of the pipeline. The pipeline is laid underground without thermal insulation. The average soil temperature at a laying depth of 2 ° C. It is required to determine the diameter of the pipeline at which the indicated pumping temperature will be ensured.

The problem should be solved by the method of successive approximations. That is, having asked the diameter of the pipeline d, it is necessary to determine the parameters necessary to determine the minimum mass flow rate so that the condition W ₁ = W _{2 is} satisfied, according to the formula (5):

For the first approximation of the diameter of the pipeline, you can use technical or regulatory documentation, for example, RD 153-39.4-113-01 "Norms for the technological design of main oil pipelines". The specified pumping flow rate (Q = 9500 m ³ / h) corresponds to the oil pipeline capacity of 63.9 million tons / year (at a given density ρ = 800 kg / m ³ and the condition of the pipeline working 350 days a year). Based on table 5.1 RD 153-39.4-113-01, such a productivity of the pipeline corresponds to a diameter (outer) of 1220 mm. Given that the proposed pumping method is based on heat generation due to the increased pumping speed, a smaller diameter, i.e. 1020 mm, should be used for calculations. For calculations, we take the pipe wall thickness of 15 mm, so the inner diameter of the pipeline is d = 990 mm. We take the absolute roughness equal to Δ = 0,0002 m.

We calculate the flow rate of oil in the pipeline:

We calculate the Reynolds number by the formula:

We calculate the coefficient of hydraulic resistance by the Altshul formula

We calculate the minimum mass flow rate that is required to ensure the conditions W ₁ = W ₂ , after having taken k = 1.9 W / m ² ° C (taken from the reference literature or calculated by known methods):

The minimum volumetric flow rate will be equal to

Since the specified pumping capacity Q = 9500 m ³ / h is greater than the calculated minimum capacity Q _min = 9065.7 m ³ / h, the adopted diameter of the pipeline d = 990 mm will ensure oil pumping while maintaining the oil temperature not lower than the specified (40 ° C) the entire length of the pipeline.

If the calculated minimum productivity Q _min exceeds the specified Q, then the diameter should be reduced and calculations should be carried out again.

Thus, the proposed method of pumping ensures the transportation of oil through the pipeline with maintaining the temperature not lower than the set value due to the heat generated as a result of internal friction of the oil layers, thereby preventing an increase in the viscosity of the oil, thus, the pumped liquids are heated without using heating furnaces or other devices, due to the pumping speed at which condition (1) is satisfied:

where: W ₁ - heat released during friction of the liquid;

W ₂ - heat loss during pumping.

Case Study 2

An external oil transport of 250 m ³ / h was implemented at the existing field via a 325 × 7 mm pipeline with a length of 95,000 m. Underground pipeline construction (soil temperature -3 ° C) in thermal insulation with a thickness of 100 mm. The density of oil is 900 kg / m ³ . Initial oil temperature 34 ° C (kinematic viscosity at 34 ° C 150 cSt). The required oil temperature at the receiving point is not lower than 30 ° C. Oil cooling below 20 ° C is unacceptable, since this leads to a sharp increase in viscosity and the precipitation of paraffins in the pipe (kinematic viscosity at 20 ° C 230 cSt). For this purpose, an oil heater is installed at the 57th kilometer of the route. The parameters of the existing pumping mode are shown in table 1.

Consider the application of the proposed pumping method for this case. Calculations carried out by a method similar to that adopted in example 1, give the results shown in table 2.

The calculation results allow us to draw a conclusion about the economic efficiency of the proposed pumping method in comparison with the implemented method due to:

1. Reducing capital and operating costs for construction by reducing the diameter of the pipeline and eliminating the heating point.

2. Lower operating costs by reducing total power consumption by 46%.

Claims (1)

A method of pumping viscous hydrocarbon fluids through a pipeline with preventing them from solidifying in the pipeline by reducing their viscosity as a result of heating, characterized in that the heating of the pumped liquids is carried out due to the pumping speed at which the condition is met:

where W ₁ is the heat released during friction of the liquid;
W ₂ - heat loss during pumping.