Cleaning of tanks and vessels
Problems associated with oil slime
All the processes associated with the transportation and storage of oil in reservoirs lead to the formation of sediments at the bottom, called oil slime. They are composed of particles of mineral origin (non-petroleum) in combination with the heaviest hydrocarbons, related mainly to the paraffin series, with a specific weight exceeding those of water and oil. Physical deposits are dense, non-flowing mass, very unevenly located on the surface of the bottom of the tanks. The sediment can be located at a level in the range of 03 – 3 meters, and the volume can be 300 – 6000 cubic meters.
Owing to sediment, obstacles are created for moving the oil and mixing the layers in the reservoir tank. In this connection, concentrated aggressive salt solutions are localized and the corrosion process develops both in the bottom region and in the first zone of the reservoir. At the same time, the working (useful) volume of the tank is significantly reduced. These problems lead to a decrease in the operational characteristics of the object and a deterioration in the quality of petroleum products and oil, which end up in these tanks. In 2004, the requirements systematized in the Rules for the Technical Operation of Tanks were developed. According to them, a partial survey of reservoirs together with its cleaning should be performed at least once every five years, and a full survey should be performed at least once every 10 years. Regarding the frequency of cleaning such containers should be familiar with the requirements of GOST 1510-84. Terms of stripping should correspond to the type of oil products, technical condition of tanks, storage conditions and frequency of changing the grade of oil products. Due to the timely cleaning of tanks and high-quality control of petroleum residues, highly viscous resinous sediments, moisture and mechanical impurities, uninterrupted functioning is ensured at oil depots, fuels and lubricants storage facilities, thermal power plants and gas stations.
The requirements indicate the following period of cleaning:
– at least 2 times a year – for the fuel used in jet engines. The same period is intended for aviation gasoline, aviation oils and its components, straight-run gasoline; if the injection line is equipped with cleaning agents, the filtration fineness of which does not exceed 40 microns, it is allowed to clean the tanks at least annually;
– at least once a year – for tanks with oils with additives used with lubricating oils;
– at least once every 2 years – for tanks with other oils, motor gasolines, diesel fuels, paraffins and petroleum products that have similar physical and chemical properties.
Cleaning of metal and reinforced concrete tanks in which oil, fuel oil, motor fuels and oil products with similar physicochemical properties are stored should be made in accordance with the need, which depends on quality assurance conditions, and guarantees reliable operation of equipment and tanks.
Cleaning of tanks is carried out using three methods: manual, mechanical (mechanized) and mechanized method of cleaning with detergents (chemical-mechanized).
The procedure for manual cleaning of the tank is to remove solid residues, steaming, rinsing with hot (from 30° to 50°) water from the fire bore under pressure from 0.2 to 0.3 MPa. Then, the flushing water and the remaining sludge is pumped out with a pump. The manual method by which oil tanks are cleaned has several important disadvantages:
- A huge risk to the safety and health of people involved in cleaning tanks using manual methods;
- Personnel performing tank cleaning is usually distinguished by substantially worse preparation than the personnel who serve the main equipment at the enterprises related to the production, refining and transportation of oil. Due to these problems, the inevitable multiple increase in the risk of human error and even such manifestations as criminal negligence. It is widely known that in Russia such work is entrusted to unskilled low-paid workers;
- Such cleaning methods invariably lead to environmental pollution (we are talking about water and air basins and the soil of the earth);
- When carrying out such cleaning, a huge amount of oil waste is generated. This makes its transportation, disposal, recycling and / or neutralization problematic.
When performing a mechanized cleaning method, hot water is supplied under pressure using special washing machines (hydro monitors), then the surface of the tanks is steamed for several days with the help of superheated steam. Only after this mechanical cleaning is performed using abrasive blasting machines. Through the use of such a cleaning method, a significant reduction in the time of work, reduction of tank idle time, reduction in the volume of complicated operations hazardous to human health, and reduction in the cost of the tank cleaning procedure are achieved. Among the shortcomings inherent in the mechanized method of treatment, it should be mentioned the large consumption of thermal energy required for heating water, the need for pumping dirty water and the use of treatment plants, the relatively large losses of light fractions in oil residues.
In the chemical-mechanized method of cleaning tanks, detergent solutions are used, thanks to which the walls, bottom and internal structures of tanks are better freed from sediment. The use of these solutions improves the quality of cleaning, accelerates the intensity of the procedure. At the same time, the use of manual labor can be considered insignificant. Among the shortcomings of the method, limiting its practical application, it is necessary to mention the high cost of the reagents used, as well as the work related to the further solution purification of the means used and the utilization of the reagent.
Among the mechanized complexes that perform tank cleaning, we note:
Installation MKO-1000 produced by Clean World M Company
Installations are made by Clean World M Company. Today it is the most common installation produced by Russian manufacturers. They are based on 20 and 40-foot shipping containers. The installation design is represented by three technical segments – the engine compartment, the capacity of technical detergents and the open emulsion tank.
Technospas Technological Complex
The principle of operation of the installation is fully consistent with the principle of operation used in MKO-1000 installation. The assembly of the complex is carried out from containers of 20 and 40-foot volume. The installation package includes gas control devices that help prevent hazards associated with ignition or explosion, as well as a fan that performs forced degassing.
The installation package that performs tank cleaning includes imported membrane pumps with a long service life.
BLABO system manufactured by Oreko Company
We represent a very efficient and at the same time extremely complicated import system. It is constructively represented by 4 and more than 20-foot containers discharged in the vicinity of the customer’s tank.
The equipment of the installation includes a powerful 2-phase decanter, which provides the possibility of high-quality separation of solid fractions. In consequence of this, the separation of hydrocarbons from the washing solution and water occurs, for which a centrifugal separator is used. This technology contributes to the quality of separation, unattainable in Russian counterparts. The customer receives a certain amount of dry slime, water with detergent solution and hydrocarbons in separate form.
MegaMAX complex manufactured by KMT International Company
This installation is rightly unofficially called the “killer of slime”. It is characterized by mobility, high speed of unfolding and folding, high-speed cleaning of tanks and complete independence from the conditions at the customer’s site. It operates without electricity, hot water and steam.
2 trailers with a unique design, approximately corresponding to a 40-foot container in size, are used for the installation. The layout of the installation allows to effectively use even the free space between the axles of the semi-trailer.
Comparative characteristics table
|Country of origin||Russia||Russia||Denmark||USA|
|Maximum capacity of cleaned tanks||50 ths. cubic meters||50 ths. cubic meters||No rest||No rest|
|System deployment rate||3 days**||3 days**||1 week*|
2 to 4 weeks*
6 to 8 hours**
|Performance when cleaning 50 ths. cubic meters of tank after running complex||2 months**||2 months**||2 weeks**||2 weeks**|
|Number of containers||1 x 40 ft||1 x 40 ft||4 x 20 ft||2 semi-trailers|
|Filtration||Filters||Filters||Filters||Vibroseparator + Filters|
|Centrifugal separation||Cyclone||Cyclone||2-f decanter + separator + cyclones||3-f decanter|
* manufacturer information
** expert evaluation.