【Haichuan Explores the World】BASF’s acetylene plant: robot for cleaning carbon deposits in combustion chambers

The flare at the new acetylene plant (internally referred to as W148), located north of BASF’s production facility, often burns continuously well into the night. Residents in Ludwigshafen, Germany, were troubled by this new plant and called on this world’s largest chemical company to address the noise pollution it caused; however, BASF’s experts quickly reassured these neighbors. The operation of BASF’s three flares over the past few months indicates that the commissioning of the plant is progressing as planned. All components, control elements, and technical equipment throughout the factory are currently in the process of comprehensive testing, so as to ensure optimal coordination among them during the respective manufacturing steps. Once this currently most advanced acetylene plant comes online, there will be no longer a need for processes such as combustion during the commissioning phase.

BASF’s acetylene plant in Ludwigshafen, Germany, has an annual production capacity of 90,000 tons, and its production efficiency ranks first in the world. The new plant covers an area of about 40,000 m2, equivalent to roughly 8 football fields; its construction led to the retirement of an old plant that had been in operation since 1964. Acetylene is a highly reactive gas, and BASF uses this valuable raw material in around 20 plants in Ludwigshafen to produce a range of chemical products, including pharmaceuticals, vitamins and flavors, crop protection agents, plastics, elastomeric textile fibers, electronic chemicals, and solvents. Dr. Uwe Liebelt, manager of the production facilities at Ludwigshafen’s European and integrated production sites, said, “From this perspective, acetylene production is the cornerstone of the entire economic value creation network in our production facilities.” ”

Acetylene is a product of the incomplete combustion of natural gas and oxygen at temperatures as high as 1400°C. In addition to acetylene and hydrogen, this process also produces carbon monoxide, carbon dioxide, water, methane, and soot. Within a few thousandths of a second after the reaction, the pyrolysis gas rich in acetylene must be rapidly cooled – this sudden cooling step prevents the reverse decomposition of acetylene. The new acetylene plant at the Ludwigshafen production site has 10 reactors, and the quenching process utilizes the plant’s closed-loop circulating water. Compared to using oil for quenching in the past, a closed-loop circulating water system can reduce volatile organic compounds released into the atmosphere. Next, the N-methylpyrrolidone (NMP) solvent is added, and the pyrolysis gas is separated into two main components: acetylene and syngas, which is a mixture rich in carbon monoxide and hydrogen. After purification, acetylene and syngas are transported via pipelines to various factories for use as raw materials.

The combustion chamber must be cleaned regularly. In acetylene production, the formation of coking products is inevitable. Soot will coalesce into clumps of different sizes and accumulate layer by layer inside the combustion chamber, eventually causing severe blockages there. Therefore, the coke must be removed regularly. For a long time, this difficult and monotonous task was carried out by trained staff who had to regularly use long carbon rods to remove coke. Over the past few decades, the old factories in Ludwigshafen required two workers to clean each reactor at least once per hour. Sometimes the sediment is so thick that the carbon cleaning rod can hardly move. It is not hard to imagine how strenuous the task of \"poking coke in the dark\" must be, causing particularly severe damage to a person’s back and joints. To avoid this unpleasant task, BASF tested the first generation of carbon-clearing robots in the old factory. For the new plant, building on its existing experience, BASF has improved the performance of the robots – the 10 new carbon removal robots are equipped with the latest technology developed by BASF’s \"Robotics and Mechatronics\" team.

The carbon-clearing robot runs every 12 minutes. To prevent the carbon cleaning rod from burning out, only 15 seconds are available per carbon cleaning cycle to remove the coking products in the combustion chamber

Each of these 10 reactors is equipped with a carbon removal robot, which \"grasps\" the manual carbon removal rod through electromagnetic coupling. Its working principle is to control the carbon removal rod through 3 electric actuators, thereby achieving the carbon removal effect. During the carbon removal process, 7 carbon removal cycles must be run continuously. Each cycle should not exceed 15 seconds; otherwise, the carbon cleaning rod may be damaged by extreme temperatures or even burned up in the combustion chamber. Carbon cleaning is performed every 2 minutes, and the total time for 7 carbon cleaning cycles is approximately 20 minutes. The carbon removal robot moves the carbon removal rod in a spiral pattern to prevent any contact between the rod and the burner plate or the reactor walls. Ralf Bihl, Automation Manager at BASF Robotics and Mechatronics, said, “The use of robots is particularly effective, as this carbon removal task is extremely difficult to carry out – it not only has to be repeated every 2 minutes, but the time required for each carbon removal operation is also very short.” ” The applying force and rotational torque of the robotic system are designed to match human strength. If employees can manually remove coke using carbon removal rods, the robotic system will adjust itself based on that force, so that the robot can use this data for cleaning tasks in the future. If there is not enough manpower to remove the coke, the system will be set to an incorrect command – no further force will be applied, especially when the carbon removal rod enters the combustion chamber from the reactor stuffing box. Because excessive force applied by the robotic system may damage the robotic system, the carbon cleaning rod, or the combustion chamber. The electromagnetic coupling between the robot and the carbon-clearing rod is a key factor in protecting the entire system from overload, as excessive force can cause irreversible damage to the system.

When developing carbon-reduction robot solutions, BASF’s engineers compared conventional industrial robots with the carbon-reduction robots they had developed. BASF chose custom development for several reasons, with compactness being the most crucial one. Since carbon-removal robots do not require versatility, BASF engineers can carry out targeted mechanical design. Compared to standard six-axis robots, the BASF carbon-reduction robot system is compact and lightweight; components can be replaced manually when necessary, without the need for lifting equipment. The steering requirements for the carbon removal system are relatively low, thus simplifying the basic design. Furthermore, even in the event of a power outage, the robot can be operated manually. That is, in the event of a power failure, it is possible to manually operate the carbon cleaning rod to ensure that the combustion chamber is cleaned of carbon deposits. The carbon removal robot system solution is based on mature components, and its modular design facilitates rapid maintenance and component replacement to ensure high availability of the robot system. Following the “traditional” design concept, the control system is composed of discrete components that can be replaced individually as needed. With a few exceptions, all spare parts are standard items that can be obtained quickly. Due to the high flammability of acetylene, the entire plant is a potential explosion area, with an explosion protection rating of EEx zone 2 T2; where T2 specifies a maximum surface temperature of 300°C, corresponding to the auto-ignition temperature of acetylene at 305°C. Carbon removal robots also require explosion-proof design, with their control systems housed in separate positive-pressure explosion-proof enclosures: 3 for the main electronic equipment, and 10 for the control panels of the reactors.

The control units for the carbon removal robots are installed in 3 control cabinets, which are designed with an explosion protection rating of Exp-positive pressure type to ensure the safety of the equipment in hazardous environments

As expected, the initial operation results of the new plant continue to show the formation of large amounts of soot on the walls of the combustion chamber; therefore, carbon removal robots are absolutely necessary. Ralf Bihl said, “Manually removing coke is a monotonous and strenuous physical task.” ”He added, “Due to the large scale of the factory and the need for frequent carbon removal operations, this task is not only costly but also has adverse effects on workers’ health.” However, carbon-clearing robots are fully capable of handling this task. ” Therefore, carbon-cleaning robots can be regarded as new types of “steel workers” – they can work around the clock, all year long, without any complaints. These robots rest only during the maintenance of the combustion chamber. Due to the use of circulating water for quenching, the overhaul interval in the new plant is longer than that in the old plant. Nevertheless, each reactor is shut down for several days each year for mandatory safety inspections – the carbon-clearing robots also take short breaks in the darkness.