Fuel tank cleaning
Above-ground fuel storage tanks require regular cleaning. The sludge is removed to eliminate fuel contamination and recover lost storage capacity. Removing the sludge by conventional methods requires an empty tank, which results in long downtimes. Cleaning oil storage tanks manually leads, in addition to working in a combustible, explosive, and toxic environment, to low efficiency and environmental pollution problems. Meanwhile, mostly customized systems have found their way into successfully cleaning tanks and tubes. Tank cleaning robots use a method of dilution; that does not require the tank to be emptied. Diluting the sludge and heating it (to approx. 60°C), they constantly control the sludge’s viscosity such that it reaches and maintains a consistency at which it can be pumped out of the tank. This method permits the recovery of fuel that is trapped in the sludge. Subsequent centrifugation separates small particles and frees them from the oil, which further reduces toxic waste. While operating inside the tank, tank cleaning robots – or robotic devices - can be guided from outside via remote control and light-sensitive cameras.
Removing rust
Removing rust from a gas tank can be accomplished by using abrasives, such as gravel or washers, acids (muriatic acid or vinegar), soda, or tank coating kits. For achieving this task, mobile robots can be equipped with tools for water jetting, power tools for rust and paint removal, or vacuum suction systems.
Water tank cleaning
A new and emerging market is the cleaning of fresh-water tanks. Water reservoirs need to be cleaned between one and five years to comply with specific national laws. Up until now, professional personnel certified for working in confined spaces have executed this task. Reservoirs are often emptied for up to two weeks to perform the work. Due to poor working conditions and high salaries, the potential for using robots has been explored. The basic principle is to deploy a vehicle that automatically traverses the water tank and can also work as an underwater vacuum cleaner. The vehicles are typically equipped with ultrasonic sonar for navigation. In addition, video is often provided to allow an operator to monitor the progress of the machines and document the cleaning process.
Pipe and duct cleaning
Pipe and duct cleaning has become quite common due to a lack of alternatives concerning the accessibility of pipes and ducts. Several designs have been suggested that typically share a wheeled or tracked mobile platform carrying a brush. Generally, teleoperated robotic devices dominate the market in this area. Robots are usually controlled via a cable connection transmitting a camera image.
Level of distribution
While remotely controlled vehicles for inspection of confined environments have existed since the 1990s, robots with a degree of autonomy are still uncommon and, in many cases, research prototypes. The Sprint Robotics Collaborative (an industry-driven initiative that promotes robotics techniques in technical inspections and maintenance of capital-intensive infrastructure) identified numerous application scenarios of robotics in the task, field inspection, cleaning, and maintenance. Current and particularly future product developments and scenarios are described in their roadmap.
Fuel tank cleaning
Numerous cleaning and maintenance service providers use robotic equipment as a part of their cleaning services for oil storage tanks, refineries, fuel transshipment terminals, chemical plants, and fuel tanks for oil-fired power plants. Typically, robot bases are teleoperated using a television monitor to clean from outside a vessel:
- A high-pressure stream of "cutter fluid" mobilizes the sludge.
- The sludge is pumped to a multi-phase separation and purification system.
The system separates tank-bottom contents into three streams – solids, recyclable water, and high-value oil or other separable liquids. Using robots for tank, tube, and pipe cleaning improves overall safety. Their sensors (for detecting waste, materials, pollution, etc.) are more suitable than visual observation and experience of human workers so that possible ignition sources, combustible fumes, and electrostatic charges are eliminated.
Manufacturers are, for example, Gerotto Federico and Koks Robotics. Wolftank Adisa offers a mobile platform with an extendable arm to clean the vertical surfaces of tanks.
Water tank cleaning
For cleaning water tanks, remotely controlled automated equipment, from Weda, as an example, eliminates the need to attract professional personnel and decommission the tank. The tracked vehicle allows the cleaner to move reliably in sandy conditions without getting stuck. Typically, the robot is tele-controlled, but it can be programmed for repeatable missions. Scantron Robotics and Deep Trekker offer similar systems. Large, heavy-duty systems are TechCor’s Track Driven Robotic Unit. An increasing need for underwater cleaning also arises from the growing number of fish farms.
Pipe and duct cleaning
Cleaning air conditioning ducts is essential for maintaining available airflow and preventing health risks. Many platforms follow a modular design so that various tools and instruments are provided for specific applications in maintenance, inspection, and cleaning tasks for tanks, pipes, and other infrastructure. It is especially the case in duct cleaning. An example is the Anatroller mobile robot, family by Robotic Design Inc., which features heating, ventilation, and air conditioning, as well as duct cleaning and inspection of different size categories. Other manufacturers are Danduct Clean and Environmental Solutions. Other applications include the cleaning of water pipes and sewers. A tracked system able to operate in pipes with diameters between 350 and 710 mm is, for example, available from JettyRobot and Ibak.
Cost-benefit considerations and marketing challenges
Fuel tank cleaning
In 2018, the petrol tank cleaning market was estimated at USD 895 million. The work, which is up to now, most conducted manually, bears high risks. Hazards are not only suffocation, contact with chemicals, and explosions, but also slipping and falling inside the tanks. Only in the UK alone, around 25 employees die every year while working in confined spaces. These risks seem to favor a wider usage of automated systems in the future. However, low tank cleaning frequencies, although it is increasing, are currently still a restriction in terms of making a robot acquisition financially viable. In "high-risk" tanks, for example, in those where emissions from the tank ventilation system or pyrophoric materials exclude the possibility of gas release, the robotic device can operate under a nitrogen blanket or in another inert atmosphere. It can be guided from outside via remote control and light-sensitive cameras, isolating workers from dangerous in-tank work. As robots are built small enough to pass through the tank opening or can expand themselves, in-tank robot assembly is no longer needed, further reducing in-tank man-hours. In addition, the manhole cover can be closed after the robot is installed, which reduces the release of gases and increases safety. The robotics method significantly reduces cleaning time (three to five times quicker than manual work). Firstly, the robots can stay in the tank longer than humans, which saves on long recovery breaks. Secondly, pumping the sludge out is much faster than the conventional method. In addition, the tank does not need to be completely emptied (it can even be used during operation), which significantly reduces downtime and reduces the need for additional storage tanks. There are high reductions of waste (up to 90%), partly owing to the high fuel recovery rates (up to 98%).
Water tank cleaning
An innovation challenge published by Singapore’s National Water Agency in 2020 indicates the expected benefits of using robots for cleaning water reservoirs. Firstly, there is no need for qualified personnel working in confined spaces. Furthermore, the personnel currently have to be tested regularly for water-borne diseases, such as typhus and cholera: while a robot can easily be cleaned and disinfected before being inserted into a new tank. The manual work must be carried out in unlit caverns, where surfaces are often slippery. Using robots thus also reduces the risk of tripping and falling.
Duct and pipe cleaning
Most duct cleaning robot manufacturers report very high returns on investments for many types of ducts. Navigating the robots through vertical ducts or ones with complex junctions remains still a central problem.