1 Domestic and foreign development present situation
Pipeline CO2 transport has been applied abroad, with about 6,000 km of CO2 pipelines in the world, with a total capacity of more than 150 Mt/a. Most of the CO2 pipelines are located in North America, while others are in Canada, Norway and Turkey. The majority of long-distance, large-scale CO2 pipelines abroad use supercritical transport technology.
The development of CO2 pipeline transmission technology in China is relatively late, and there is no mature long-distance transmission pipeline yet. These pipelines are internal oilfield gathering and transmission pipelines, and are not considered CO2 pipelines in the real sense.
2 Key technologies for CO2 transport pipeline design
2.1 Requirements for gas source components
To control the gas components entering the transmission pipeline, the following factors are mainly considered: (1) to meet the demand for gas quality in the target market, such as for EOR oil recovery, the main requirement is to meet the requirements of mixed-phase oil drive. ②To meet the requirements of safe pipeline transmission, mainly to control the content of toxic gases such as H2S and corrosive gases, in addition to strictly controlling the water dew point to ensure that no free water precipitates during the pipeline transmission. (3) Comply with national and local laws and regulations on environmental protection; (4) On the basis of meeting the first three requirements, reduce the cost of gas treatment upstream as much as possible.
2.2 Selection and control of transport phase state
In order to ensure the safety and reduce the operating cost of CO2 pipeline, it is necessary to control the pipeline medium to maintain a stable phase state during the transmission process. In order to ensure the safety and reduce the operating cost of CO2 pipelines, it is necessary to first control the pipeline medium to maintain a stable phase state during the transmission process, so the gas phase transmission or supercritical state transmission is generally chosen. If gas-phase transport is used, the pressure should not exceed 4.8 MPa to avoid pressure variations between 4.8 and 8.8 MPa and the formation of two-phase flow. Obviously, for large volume and long distance CO2 pipelines, it is more advantageous to use supercritical transmission considering engineering investment and operation cost.
2.3 Routing and area hierarchy
In the selection of CO2 pipeline routing, in addition to conforming to local government planning, avoiding environmentally sensitive points, cultural relic protection zones, geological disaster areas, overlapping mine areas and other areas, we should also focus on the relative location of the pipeline and the surrounding villages, towns, industrial and mining enterprises, key animal protection zones, including wind direction, terrain, ventilation, etc. While selecting the routing, we should analyze the high consequence areas of the pipeline, and at the same time take corresponding protection and early warning measures. When choosing the route, it is recommended to use satellite remote sensing data for terrain inundation analysis, so as to determine the high consequence area of the pipeline.
2.4 Principles of valve chamber design
In order to control the amount of leakage when the pipeline rupture accident occurs and to facilitate pipeline maintenance, a line cut-off valve chamber is generally set at some distance on the pipeline. The valve chamber spacing will lead to a large amount of pipe storage between the valve chamber and a large amount of leakage when an accident occurs; the valve chamber spacing is too small will lead to an increase in land acquisition and engineering investment, while the valve chamber itself is also prone to leakage area, so it is not easy to set too much.
2.5 Selection of coating
According to foreign experience in CO2 pipeline construction and operation, it is not recommended to use internal coating for corrosion protection or resistance reduction. The selected external anticorrosion coating should have better low temperature resistance. During the process of putting the pipeline into operation and filling the pressure, the growth rate of the pressure needs to be controlled to avoid a large temperature rise due to a rapid increase in pressure, resulting in coating failure.
2.6 Special requirements for equipment and materials
(1) Sealing performance of equipment and valves. (2) Lubricant. (3) Pipe stop cracking performance.
Contact Person: Miss. Catlin Zeng