Table of Contents
1 INTRODUCTION
The oil and gas industry faces a serious challenge due to the high volume of oil residue and sludge during the storage and processing of crude oil. The purpose of this article is to examine the most state of the art tank bottom cleaning techniques currently on the global market and to determine the best effective, safest, cost-effective, and ecologically friendly clean-up procedure. This investigation examines the most commonly used, efficient and effective applied techniques of oil tank bottom cleaning [1].
There are many different types of containers, tanks, and pits used in the oil and gas sector to store or treat fluids that include oil. The crude oil tank is one of them, and it is used to store crude oil. It’s commonly composed of carbon steel, painted outside and inside, galvanised, or coated with a polymer coating to prevent corrosion. The tank’s sort, size, and composition are determined by the oil’s storage conditions like operating temperature and pressure, the characteristics of the crude oil like its contents and toxicity, and the storage capacity required. The shell, roof, bottom, valves, piping, instrumentation, cathodic protection system, and steel structure are an oil tank field’s key components held[2].
Removing petroleum residues from the bottom of the oil tanks is an unavoidable procedure that the oil and gas industry has to deal with. The major cause for cleanup is the residue left behind by the denser components in crude oil settled over the period. This residue takes up much volume in the oil tanks, limiting their storage and affecting the quality of petroleum products. Besides, several periodic inspections are mandated by the operating standards. These actions are impossible to carry out if there are leftovers in the tank. Cleanup methods targeted at safety procedures, cleaning effectiveness, time and money reduction, and ecological preservation have all been emphasised by corporations. Cleaning a tank can be done in various ways, such as manual, automatic and robotic Fields[3].
Workers entry into the oil tank is usually necessary to accomplish the task. Still, the amount of time consumed in the tank and the human resource required varies depending on the technique. Several objectives for a successful cleanup include reducing the number of people who enter a restricted space that requires permission, as exposure to hazardous conditions involves various dangers. Studies suggest a rise in the frequency of fatalities in recent times. In addition, the desire to cut maintenance costs while still improving safety has shifted the focus to more mechanised systems that involve less workforce and have shown to be safer [4].
Another key objective is to extract the oil that has been accumulated at the bottom of the oil tank in huge quantities as sludge residue. Many case studies have also proven that the revenue obtained by sludge oil recovery surpasses the cleanup expenditures. Furthermore, with ecological rules strengthening with time, the secure carriage and disposal of sludge and related clean-up waste in the oil tank to a designated site and then to waste treatment plants is a critical component of an efficient cleanup procedure. Therefore, experts strive to find out the most state of the art and efficient ways to clean the bottom of the oil tanks. This paper discusses the most advanced processes of cleanup. The methodology, along with merits and demerits of the three most commonly used processes, is given under:
Figure 1 Oil Tank Bottom
2 BALBO SYSTEM
BLABO is a compact and portable automated cleanup system, which is a cleaning technique that does not involve human entry and can extract almost the total amount of the hydrocarbon contained in the sludge mixture [5]. The procedure works in a closed-loop, with the sludge at the bottom of the tank being dissolved, vacuumed, segregated, and released. The whole process is illustrated in Figure 2.
The tank’s inside surface is then cleansed with water to provide a clean oil tank for assessment and servicing. The procedure would not need human intervention in the oil tank. Firstly, the workforce transfers and deploys the instruments outside the tank by a plan devised by the experts and cleanup firm employees. For easy shipping and deployment, all apparatus is incorporated into container-based units. The vacuum piping network is linked to the tank’s preexisting nozzles.
In contrast, the jet nozzles and nitrogen delivery pipelines are put onto the roof employing the secure method called cold tapping. The tank’s inside is supplied with nitrogen until the oxygen concentration falls to around 7% to prevent any explosion. The monitoring panels are continually monitoring this number to ensure that it remains consistent at this moment. If this value surpasses the allowable limits due to any reason, the procedure will immediately halt until the standard security configuration is attained.
The procedure is then undertaken by the control panels mounted on the module at a safe location and a reasonable distance from the oil tank, provided the equipment has been correctly installed. The firm’s skilled staff to verify the process’s integrity, performance, and security is a critical precondition for the machinery’s shipping, deployment, and functioning. The system includes a vacuum module, separating module, recirculating module, skimming module, jet nozzles, and ancillary equipment. The vacuum module’s primary function is to extract sludge off the tank’s bottom employing vacuum and rotary pumps and transfer it to the recirculating module. The vacuum module is placed near the tank bottom as feasible to achieve the most efficient functioning.
Additionally, two parallel filters are fitted before pump operation to prevent any obstruction in the flow. On it is mounted the control panel, through which the module’s functioning may be regulated. The recirculating module is used for desludging, which is accomplished by circulating the cleanup medium until all of the sludge has been disintegrated and evacuated from the tank’s interior. It is a key part of the operation since it comprises the first segregation of the heavy sludge particles via the three powerful hydro cyclones. The jet nozzles placed on the tank’s roof are critical to the operation since they move the cleaning medium to the tank’s bottom and break down the sludge, allowing it to be readily vacuumed. The oil initially present in the sludge and was retrieved throughout the separation procedure is referred to as a cleanup medium. The control panel regulates the pressure on the output and regulates the jet nozzles. A heat exchange mechanism is used to increase the cleaning medium’s temperature and improve flow to produce more effective circulation. To ensure the process’s safety and conform to safety rules, lower explosive limits and oxygen levels must be reached.
The separating module and the recirculating module work in tandem. They perform the ultimate sludge removal according to the specifications. The silt may be segregated into oil, liquid, and solid leftovers, allowing nearly all hydrocarbon contents to be recovered. After the tank has been thoroughly cleaned, it must be flushed with water to remove any remaining oil from the sides and bottom. The cleanup material for this technique is hot water, which is pushed via the jet nozzles. The water used is recycled and purified from the oil and solid particulates combined during purification to guarantee a more cost-effective procedure and lower usage. The skimming module, utilised primarily at this step, does this separation. Coalescing plates, which filter water from particles and grease in two phases, are used for separation.
Figure 2 BLABO System Process
3 MEGAMACS SYSTEM
MEGAMACS is a portable, power-independent system that stores its components in 2 transportable containers. It may be utilised to remove hydrocarbon containing materials from containers, vessels, pits, tankers, lakes, ponds and other reserves. Petroleum, water, and solid remnants are separated from the sludge. The oil collected from the sludge is sold to the tank owners, resulting in net profit. The equipment may be put up to 140 meters far from the oil tank to be cleaned, which solves the challenge of space constraints.
Furthermore, the treatment is carried out more securely. Because of its adaptable hydraulic framework for adjusting to harsh topography, the apparatus takes relatively less space and do not need specific ground preparation for installation. The apparatus can be moved by six persons and installed in around 4 hours without cranes. Heat exchange system, vibration separator, process tank, washing pump, suction system, centrifuge, oil collection tank, water pump and water collection tank, sludge separator, automatic cannon, ancillary equipment, washing heads, and booster pump are among the components of the system [6].
The main process tank is filled with water heated to 90 °C by a helical pipe heat exchange system after all of the apparatus has been moved and put in the proper location. A single-step centrifuge pump known as a washing pump can recycle water. When the water or other cleaning medium reaches the proper temperature, this pump shifts to clean mode and transports the water to the oil tank to be cleaned. The tank cannon and the boost pump are then installed within the tank because the amount of sludge in the tank is below the level of the maintenance hole. Instead, the tank cannon can be installed on the tank’s roof. If the sludge level is higher than the maintenance hole, the hole is opened up to a limit and steps are taken to extract the sludge as much as feasible to provide room for the booster pump and tank cannon deployment. The autonomous tank gun may need to be temporarily installed at the maintenance hole outlet as part of this operation.
When the autonomous tank cannon is positioned in the tank, it begins to discharge hot water or another cleaning medium at a pressure of around 25 bar to break down the sludge that has hardened or solidified, allowing it to be readily drawn from the booster pump. The driving system is hydraulic, and the fluid flow may be controlled from the tanks outside. The boost pump is installed within the tank and pulls the sludge and the solid residue to the main cleanup unit. Because the pump is powered by hydraulic pressure, it may be immersed in the sludge without incurring any damages. The sludge is then transported to the vibration separator, where the bigger solid particles are separated. Such particles are placed in specific containers before being delivered to be processed and stored. The residual water–oil combination, together with tiny particles, is pumped into the main process tank. The second separation begins with solid components settling on the bottom, and a lighter proportion of 60% oil and 40% water remains on the surface.
In terms of system security, this process is meant to work from a distance of up to 140 meters. Furthermore, there is no requirement for power, lowering the possibility of a tank explosion due to a spark or fire. To avoid any accidents, all moving and rotating parts are protected. The cleanup system’s control panel is directly linked to the tank, allowing it to supervise specific operating criteria at all times. The cleanup immediately shuts down once the alarms have been triggered if one or more operational parameters have crossed the acceptable operating parameters due to its automated control system. Furthermore, the oil tank does not need to be inserted because the system does not generate a static charge.
Figure 3 MEGAMACS System Process
4 MARTin SYSTEM
Automated cleaning is a relatively new technique that has been used to clean oil tanks, containers, pits, and other reservoirs in the oil and gas sector in recent times. This technique is still in developing stages, and its numerous benefits have not been widely highlighted to acquire trust in-tank owners. Nonetheless, there is much opportunity for improvement. It arose from a common desire to eliminate exhausting physical human labour in cramped areas surrounded by a hazardous environment that offers several risks. This approach replaces human labour with an autonomous cleanup process that does not require people’s persistent presence within limited spaces such as an oil tank because the device is managed externally. The automated cleaning system is normally detachable, with the essential equipment housed in truck-transportable containers. The remote-control robotic vehicle that enters the tank and is used to break down and remove sludge from the tank’s bottom is crucial to the [7].
The robot enters the tank maintenance hole and can suction or carry the sludge out of the oil tank by moving through the bottom surface of the oil tank. The robot is driven by a trained specialist from a remote-control panel outside the tank to a safe location. The tank does not need to be gas-free to enter when using this approach. As a result, all equipment installed to the robot are anti-explosive and hydraulically propelled to remove any danger of fire or explosion. The hydraulic pressure is created from the external tank and delivered to the robot via high-pressure nozzles fitted within the robot to move its equipment. The whole system can be dismantled and reassembled quickly to enter and exit the tank with ease. The sludge from the tank is separated into petroleum water and solid remnants after many treatment steps. It is a detachable system consisting of equipment mounted outside the tank and equipment that enters the tank.
MARTin is a cutting-edge autonomous cleanup system for oil tanks. This technology differs from all earlier cleanup systems in that it is automated. MARTin pioneered this ability by inventing a mechanised scavenger shown in Figure 4 with video monitoring and illumination systems, a discharge system, and a chemical supply device that can be controlled from outside the tank via a purpose-built facility in the control room by an operator. In a nutshell, this cleanup system’s sophistication comprises four blocks. The first block removes bottom sedimentation and scrubbing oil deposits’ interior surfaces. The second block is for sediment cleaning and processing. Other equipment can be stored and transported in the third block. A fourth block is for oil waste disposal and water treatment.
The blocks are of the same weight and size and are delivered to the deployment location by trucks that can be up to 160 meters distant from the oil tank to be cleaned. The sludge recycling process is similar to the approach described before by studying the MEGAMACS process. Thus it will not be discussed further. As per MARTin, the autonomous excavator can extract sludge from the oil tank at a higher rate and based on the process design while assuring high quality of separation of the recovered oil sludge into oil, water, and solid at a great speed.
Figure 4 MARTin System
5 REFERENCES
[1] B. Islam, “Petroleum sludge, its treatment and disposal: A review,” Int. J. Chem. Sci, vol. 13, no. 4, pp. 1584-1602, 2015.
[2] R. Heidersbach, Metallurgy and corrosion control in oil and gas production. John Wiley & Sons, 2018.
[3] H. Sarma, K. L. T. Bustamante, and M. N. V. Prasad, “Biosurfactants for oil recovery from refinery sludge: Magnetic nanoparticles assisted purification,” in Industrial and Municipal Sludge: Elsevier, 2019, pp. 107-132.
[4] Q. Sun, H. Li, J. Yan, L. Liu, Z. Yu, and X. Yu, “Selection of appropriate biogas upgrading technology-a review of biogas cleaning, upgrading and utilisation,” Renewable and Sustainable Energy Reviews, vol. 51, pp. 521-532, 2015.
[5] M. M. Maru et al., “Biodiesel compatibility with carbon steel and HDPE parts,” Fuel Processing Technology, vol. 90, no. 9, pp. 1175-1182, 2009.
[6] A. Chrysalidis and G. Z. Kyzas, “Applied Cleaning Methods of Oil Residues from Industrial Tanks,” Processes, vol. 8, no. 5, p. 569, 2020.
[7] T. A. Hamad et al., “Hydrogen recovery, cleaning, compression, storage, dispensing, distribution system and end-uses on the university campus from combined heat, hydrogen and power system,” International journal of hydrogen energy, vol. 39, no. 2, pp. 647-653, 2014.
