Cleaning of processing oil pipelines from oil residues and ARPD
During the operation of oil pipelines, water, paraffin, mechanical impurities and other sediments accumulate in its cavities, which reduce the capacity of the pipeline, combined with an increase in costs associated with pumping oil.
Due to the presence of asphaltic-resinous substances in crude oil, dense deposits may occur on the surfaces of the walls of oil pipelines. In order to get rid of paraffin deposits in pipelines, it is necessary to take care of preventive and cleaning measures. There are significant differences between all kinds of cleaning, but the essence of all of them is the cleaning and removal of paraffins.
Before organizing regular cleaning of oil pipelines, pre-cleaning is carried out to get rid of foreign objects that are in the cavity, and to determine the installation defects.
When pre-cleaning is carried out, an intermediate type of pumping station must be stopped when a cleaning device is passed or received.
If the cleaning is performed at first time or cleaning has not been carried out for a long time, before starting the cleaning device, the parameters of serviceability, ease of closing and opening, as well as the possibility of full opening of the linear valve are checked. Also, the launch chambers, reception and pass quality in the cleaning devices are checked. Measures to eliminate all faults must be taken.
To prevent ARPD, two main areas are used, consisting in work to prevent sediments and remove formed sediments. In order to determine the most rational and optimal ways of combating ARPD and evaluate various methods, many factors are guided, including the fractional composition of solid hydrocarbons in the composition of oil, its physical and rheological properties, temperature transfer mode, duration of waxing, high molecular weight components flow, pipeline design features (especially in offshore fields), etc.
Prevention of ARPD in the cavities of oil pipelines is carried out today using various methods:
- mechanical (scrapers and pistons of different materials and construction are used);
- heat (flushing with hot heat carriers, electric heating);
- chemical (solvents and inhibitors are used for injection, detergents and gel pistons are used for cleaning).
The use of mechanical methods in the cleaning of oil pipelines from ARPD provides for the use of cleaning units (CU). For this purpose, special reception and launch chambers are included in the pipeline.
Thermal methods are based on the ability to melt paraffin at a temperature of more than +50 degrees, as a result of which it drains from heated surfaces. Today, it is practiced to use technologies that use water or hot oil, which are heat carriers, as well as to use direct steam, electric furnaces, electrical dewaxing unit (induction heaters).
There are a lot of methods used to get rid of the sediments. The common intensifying method, which consists in the use of solvents, should be mentioned among them. But the problem associated with the selection of solvent for specific conditions, has not be completely solved. Paraffin deposition inhibitors function on the processes of adsorption occurring at the boundary between the metal surface of the pipeline and the liquid medium.
Based on the cleaning technology, the sequence of actions required to remove ARPD and oil residues from the internal surfaces of the processing pipeline is determined.
The technology is represented by the following steps:
- Oil is being forced out of the processing pipelines of the oil pipeline system.
- The surface of auxiliary and main and processing pipelines in combination with the pump station equipment is prepared.
- ARPD solvent is pumped through the main and auxiliary processing pipelines of the oil pipeline system.
- A wind tunnel is pumped to remove residual paraffin solvent from the internal surfaces of the pipeline.
- A column fume stack is pumped in order to assess the quality of cleaning of the internal surfaces of the processing piping and equipment of the oil pipeline system.