RU2584628C2 - Method of preparation for transportation of liquefied hydrocarbon mixture via main pipelines under cool conditions - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to preparation for transportation of gas and gas condensate. Method includes cleaning of natural gas, multistep cooling to temperature from -30 to -50 °C with addition of cooled to temperature from -20 to -50°C condensate in amount of from 3 to 10 wt%. Obtained hydrocarbon mixture is cooled to temperature from -40 to -50 °C at pressure of 10-12 MPa to single-phase liquid state.

EFFECT: possibility of transportation of mixture of liquefied hydrocarbon gases with gas-condensate deposits of North by main pipelines.

1 cl, 4 dwg

Description

The invention relates to the field of preparation of a mixture of gas and gas condensate of gas condensate fields of the North for single-phase pipeline transport and can find application in the oil and gas industry.

A known method of pumping cryogenic liquid by gravity through a pipeline from the storage to the tank (patent RU No. 2006116911/22, publ. 11/27/2006) without loss of gas phase by removing it from the riser pipe and returning it to the storage.

The disadvantage of this method is that the pipeline is designed to transport cryogenic liquids, such as liquefied natural gas (LNG), nitrogen, oxygen, hydrogen (with a temperature below 120 K). Therefore, you will have to use expensive low-temperature nickel stainless steels for pumping. In addition, the authors propose pumping LNG through low-pressure pipelines, which will affect its productivity.

There is also a known method of pumping LNG through main cryogenic pipelines at a temperature of 153-173 K (minus 120 - minus 100 ° C) (Main pipelines of chilled and liquefied natural gas. Editor-in-chief is A.E. Polozov / N.P. Akulshina, V.A. Andrianov, V.I. Zorkaltsev et al., Ural Branch of the Russian Academy of Sciences, Komi Scientific Center, SYKTYVKAR, 1988, p. 158). In this case, it is proposed to use specially designed economically alloyed steels (for example, 10KHGNMAYU) or cryogenic nickel stainless steels. According to A.E. Polozov (AE Polozov. Strengthening the Strength of Low-Temperature Thermally Insulated Pipelines: Thesis for Doctor of Engineering Sciences: 25.00.19: Kursk, 2004. 348 pp.) The transition to LNG wires gives a great economic and environmental effect. The share of pipe steel in the cost of building a gas pipeline is 80%, and the transition to pumping LNG through pipelines, in his opinion, allows you to switch from 4 pipelines of a gas pipeline to 1 string of a cryogenic pipeline, which saves metal costs 75%. Taking into account the costs of thermal insulation of LNG wires and the increased cost of EL steel, we get a cost savings of 37%.

The disadvantage of this method is the need to use expensive cold-resistant nickel steels (at least 8% nickel) and expensive cryogenic vacuum insulation, as well as the need to maintain a low temperature (minus 161 ° C) at atmospheric pressure. In addition, LNG will have to be pumped through low-pressure pipelines, which will affect its productivity.

A known system for storing gas based on methane (patent RU No. 2224171, publ. 02.20.2004). It consists of a container for storing hydrocarbon solvent and dissolved gas, forming liquid and vapor phases and means for regulating the composition to maintain a predetermined phase ratio. The present invention relates to an improved system for liquefying and storing gas, and especially a system for storing gas, the main component of which is methane, by mixing with another hydrocarbon (organic solvent) for storage.

The disadvantage is that this methane-based gas storage system has limited use (only on a motor vehicle) and cannot be used when transporting liquefied hydrocarbons through pipelines.

The well-known "Method of bulk transportation and storage of gas in a liquid medium" ("Method of bulk transport and storage of gas in a liquid medium") (patent US 8257475 B2, publ. 04.09.2012). An integrated system with an installed vessel for loading a gas stream is intended for separating heavy hydrocarbons, compressing the gas, further cooling it, mixing the gas with a desiccant, mixing it with a liquid carrier or solvent, and then cooling the mixture to the conditions of processing, storage and transportation. After transporting the product to its destination, the hydrocarbon preparation line and the liquid transfer method provide for unloading the liquid into the storage system, separating the liquid carrier, and moving the gas stream to the storage or transportation system. Only methods for mixing and sorption of natural gas in a light hydrocarbon solvent (mainly propane) and devices for storage and transportation of liquefied petroleum gas carriers by gas carriers are considered.

The disadvantage is that the required amount of a light hydrocarbon solvent (mainly propane) in the mixture is practically impossible to obtain directly at the field.

As the closest analogue, the method of preparation for transportation of a mixture of hydrocarbons containing natural gas and condensate, known from patent RU 2476789 C1, priority 02/27/2013, was adopted.

When implementing the method according to the first embodiment, primary liquid is separated from the inlet stream, methanol is added to the primary separation gas, the resulting stream is cooled in an air cooling apparatus, in the first and second recuperative heat exchangers located in parallel, and gas in the cold reduction and recovery unit, separation is in a low temperature separator. The low-temperature separation gas is heated in the heat exchanger and in the unit for the reduction and recovery of cold, and then sent to the product gas pipeline. The primary separation condensate is directed to the degassing and separation of the aqueous or water-methanol phase into the first three-phase separator, from which the released gas is fed to the inlet to the low-temperature separator, and the condensate is heated in the third recuperative heat exchanger and still bottoms heater, and then sent to the lower separation part of the distillation column . The low-temperature separation condensate is heated in a heat exchanger and subjected to degassing and separation of the water-methanol phase in a second three-phase separator, after which the condensate is fed to the distillation column as irrigation. The gas from the distillation column and the degassing gas from the second three-phase separator are compressed in a compression unit and mixed with low-temperature separation gas. The condensate from the distillation column is cooled in the third recuperative heat exchanger and the second air cooling apparatus and sent to the separation of the water-methanol phase in the third three-phase separator, squeezed and fed into the product condensate pipeline.

The disadvantage of this technical solution is that the objective of this method of low-temperature preparation of natural gas and extraction of unstable condensate from the formation gas is the separation of natural gas and gas condensate (its extraction from the formation gas) and further transportation through separate pipelines. The objective of our technical solution is to mix natural gas and gas condensate and joint transportation of the hydrocarbon mixture through a low-temperature pipeline to the consumer.

The claimed invention is characterized in that it purifies natural gas, its multi-stage cooling it to a temperature of from -30 to -50 ° C with the addition of condensate cooled to a temperature of from -20 to -50 ° C in an amount of 3-10 weight. %, cooling the resulting hydrocarbon mixture to a temperature of from -40 to -50 ° C at a pressure of 10 to 12 MPa to obtain a single-phase liquid state.

The technical result is the possibility of transporting a mixture of liquefied petroleum gases, consisting of natural gas and gas condensate, through pipelines at a temperature of from -40 to -50 ° C and a pressure of from 10 to 12 MPa.

The technical result is achieved in that in order to ensure the transportation of the mixture in a single-phase liquid state through main pipelines from gas condensate fields, natural gas is cooled to a temperature of from -0 to -50 ° C with the addition of condensate cooled to a temperature of from -20 to -50 ° C in an amount from 3 to 10 weight. %, cooling the resulting hydrocarbon mixture to a temperature of from -40 to -50 ° C at a pressure of 10 to 12 MPa to obtain a single-phase liquid state.

The method is illustrated by the following figures: FIG. 1 is a diagram of a technology for producing a mixture of liquefied hydrocarbons; FIG. 2 - Р-Т-diagram (pressure - temperature) of various individual substances and mixtures (in mass percent):

1 - methane Tkr = -82.4 ° C, Pkr = 4.6 MPa,

2 - typical natural gas Tkr = -73 ° C, Pkr = 5.4 MPa,

3 - reservoir gas Tkr = -50.8 ° C, Pkr = 8.7 MPa,

4 - a mixture of gas and gas condensate in a ratio of 97: 3 Tkr = -39.6 ° C, Pkr = 10.03 MPa,

5 - a mixture of gas and gas condensate in a ratio of 95: 5 Tkr = -37.1 ° C, Pkr = 10.45 MPa,

6 - a mixture of gas and gas condensate in a ratio of 93: 7 Tkr = -34.96 ° C, Pkr = 10.81 MPa,

7 - a mixture of gas and gas condensate in a ratio of 90:10 Tkr = -28.9 ° C, Pkr = 11.72 MPa;

FIG. 3 - component composition of formation gas of the South Tambey gas condensate field (% by volume) and typical natural gas (% by mass);

FIG. 4 is a schematic diagram of a pipeline transport of liquefied petroleum gases:

1 - installation of integrated gas treatment,

2 - installation for producing a hydrocarbon mixture,

3 - pipeline

4 - head pumping station,

5 - intermediate cooling stations,

6 - intermediate pumping stations,

7 - low temperature storage,

8 - installation regasification,

9 - gas supply to consumers.

The method is as follows. Natural gas directly from the gas condensate field enters the drying unit, where water particles are extracted from it, passes through a filter (purification from acidic components, fine purification from mercury and nitrogen removal) (Fig. 1). After that, the gas goes through a multistage stage of cooling and pressure increase with the addition of gas condensate and high molecular weight compounds at each stage. The resulting mixture of liquefied hydrocarbons at a temperature of from -40 to -50 ° C and a pressure of not more than 12 MPa is brought into a liquid state. After liquefaction, it enters directly into the pipeline.

Taking into account the necessary margin of pressure and temperature to prevent gas formation during the justification and development of the technology, an initial temperature of minus 40 - minus 50 ° C and a pressure of 10-12 MPa are preliminarily taken. Higher pressure and lower temperature of the mixture will lead to higher construction costs due to the need to use expensive nickel steels and increase the thickness of the pipe wall. Existing grades of steel grade X70 and X80 are operational at the above pressures and temperatures.

The features of obtaining a mixture of liquefied methane and gas condensate are due to the need to obtain a relatively high liquefaction temperature at a relatively low pressure. Therefore, the standard scheme for the production of liquefied natural gas (LNG) can be significantly reduced by using only the first part of the scheme for the production of LNG (refusal from the unit to obtain a temperature of -160 ° C).

A favorable factor for obtaining a mixture of natural gas, condensate and oil in a single-phase state is that most of the fields Yamal are gas condensate. The mass content of oil and gas condensate reaches from 3 to 10%. Research was conducted on the example of the South Tambey gas condensate field. The total hydrocarbon reserves of the South Tambeyskoye gas condensate field according to the State Balance of 01.01.2008 are: gas of category C1 - 1,003.92 billion m ³ ; C2 - 252.186 billion m ³ ; condensate in category C1 - 47.48 million tons; C2 - 18.78 million tons. The total gas reserves (C1 + C2) are 1256.1 billion m. The total reserves of condensate (C1 + C2) are 66.26 million tons.

In FIG. 2 shows a phase diagram of a PT (pressure-temperature) mixture of natural gas and gas condensate. It shows that adding 3% by weight gas condensate to the produced natural gas leads to a critical mixture temperature increase from minus 73 ° С for typical natural gas and from minus 50.8 ° С for reservoir gas of the South Tambeyskoye field to minus 39.6 ° C (critical pressure is 10.03 MPa). The composition of a typical natural gas and formation gas of the South Tambeyskoye field is shown in FIG. 3. With the addition of 5%, the critical temperature shifts to minus 37.1 ° C at a critical pressure of 10.45 MPa. With a gas condensate content of 7 and 10%, the critical temperature is minus 34.96 and minus 28.9 ° C, and the critical pressure is 10.81 and 11.72 MPa, respectively. The phase diagrams PT (pressure-temperature) and critical parameters of the mixture at different gas condensate contents are shown in FIG. 2.

Thus, the addition of gas condensate to natural gas will allow transporting this mixture in a liquid single-phase state at a temperature of minus 40 - minus 50 ° C and a pressure of 10-12 MPa (taking into account the required pressure margin). Since the composition of the gas condensate produced from different wells of the gas condensate field is different, it is planned to control the temperature and pressure of the liquefaction by adding a small amount of special additives of high molecular weight compounds obtained in the developed field.

In FIG. 4 is a schematic diagram of pipeline transport of a mixture of liquefied hydrocarbons.

Natural gas from the gas condensate field of the North goes to the complex gas treatment unit (UKPG) 1, where it is purified, dried and separated from impurities.

Then, purified and cooled natural gas and cooled gas condensate are fed to the hydrocarbon mixture production unit (UPUS) 2, where the following processes occur: pressure increase simultaneously with gas cooling and high-pressure gas condensate injection into the lower part of the unit through a special nozzle until the necessary mixture parameters are reached liquefied hydrocarbons (pressure not more than 12 MPa and temperature from -40 to -50 ° C). Part of the gas, which does not have time to go into a liquefied state, flows back to the lower part of the mixing plant. The process of preparing the mixture is repeated until the entire mixture passes into a single-phase liquid state at the above temperature and pressure. The resulting mixture under pressure is fed into a pre-cooled pipe 3.

The fundamental difference between the complex liquefied hydrocarbon preparation unit and the LNG preparation unit is that we refuse the cycle of liquefying a hydrocarbon mixture from -50 ° C to -160 ° C, which significantly reduces costs.

Further, the resulting mixture enters the head pumping station (HPS) 4, which supports the necessary pumping conditions. The composition of the STS includes: receiving tanks, retaining and main pumping and metering unit. They serve to receive liquefied hydrocarbon gases and to store some of its reserves in order to ensure uninterrupted operation of the pipeline.

To prevent gas heating due to heat influx from the environment, pipelines are covered with thermal insulation (for example, from polyurethane foam with a thickness of 50-70 mm), and intermediate cooling stations (PSO) 5 are placed along the route.

Intermediate pumping stations (PNS) 6 are located at distances determined on the basis of hydraulic and thermal calculations. According to calculations, pumping and cooling stations should be installed at a distance of about 100 km.

At the end of the pipeline, a low-temperature storage (HX) 7 and a regasification unit (UR) 8 of the liquefied hydrocarbon mixture are placed. At the regasification unit, the mixture is divided into components: gas, gas condensate, high molecular weight compounds. Gas is supplied to the main gas pipeline, and gas condensate is transported through pipelines or by rail or road.

The proposed preparation method allows pumping a mixture of natural gas and unstable gas condensate through pipelines from gas condensate fields of the North. It follows from the study that the proposed method for the combined transportation of LNG along the Northern Sea Route and a mixture of liquefied hydrocarbons through underground pipelines will significantly reduce the cost of transporting gas and gas condensate, and reduce the number of icebreakers and tankers.

Claims (1)

A method of preparing for transportation of a mixture of liquefied hydrocarbons containing natural gas and condensate, including the purification of natural gas, creating a mixture of natural gas and condensate, characterized in that the multi-stage cooling of natural gas to a temperature of from -30 to -50 ° C with the addition of chilled to temperature from -20 to -50 ° C condensate in an amount of from 3 to 10 weight. % and cooling the resulting hydrocarbon mixture to a temperature of from -40 to -50 ° C at a pressure of from 10 to 12 MPa to a single-phase liquid state.

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