In what appears to be yet another step towards its goal of operating the safest car factory in the industry, Tesla has been granted a patent that could pave the way for a safer process in battery production. Published today, the electric car maker’s recent patent describes a system to treat and recycle Dichloromethane (DCM), which is among the materials used in the production of electric car batteries.
DCM is utilized in a variety of industrial processes, particularly in chemical plastic welding, wherein softened plastic pieces or surfaces are welded together. The material is also used to soften plastic sheets for stretching or shaping, and as a solvent to remove unwanted compounds. In Tesla’s case, DCM is among the materials used in the forming of a separator base film for an electric car’s battery system. While DCM is invaluable in manufacturing, though, the material carries some health risks.
Dichloromethane is the least toxic among the simple chlorohydrocarbons, but its high volatility makes it an inhalation hazard nonetheless. Prolonged skin contact with DCM could also result in the material dissolving some of the skin’s fatty tissues, causing irritation or chemical burns. With these risks in mind, the manufacturing industry employs ways to recover DCM. Tesla notes that current systems for DCM treatment and recovery are capital intensive, particularly since the process involves expensive components such as activated carbon beds, condensers, steam boilers and distribution systems, density separation vessels, and waste water treatment systems.
Tesla’s diagrams outlining its Dichloromethane recovery system. [Credit: US Patent Office]
Tesla describes conventional DCM treatment systems as follows:
“The DCM itself may then be removed through a heating and/or evaporation process with the exhaust collected. This exhaust containing DCM is then combined with the exhaust from other tools and systems used in the manufacturing process. The combined exhaust may then be fed to a recovery plant to recover DCM. In the recovery plant, the waste exhaust stream is typically treated with activated carbon. This scrubbing process requires high capital expenditure (many expensive components), high operating cost (extensive steam and cooling water consumption which accounts for >20% of total process cost), large footprint requirements, and large amounts of waste water that need to be processed. In order to address these cost and environmental-remediation issues, an improved process for the removal of DCM from exhaust streams is needed.”
Tesla’s take on DCM treatment and recovery utilizes a wet scrubber and a density separator vessel as key components of the system. The wet scrubber in Tesla’s patent has a scrubbing chamber, where water is utilized to scrub the waste exhaust stream containing the DCM. Tesla notes that the wet scrubber could adopt a variety of designs to remove DCM from the waste exhaust stream, including a venturi scrubber design, a condensation scrubber design, an impingement-plate scrubber design, or a packed bed tower design, among others.
Tesla’s use of a density separator vessel is described in the following section from the patent.
“The density separator vessel has an inlet to receive the liquid water and DCM mixture, an outlet to expel DCM, and an outlet to expel waste water. The DCM may be routed back to the industrial process for reuse and/or collected for later use. The waste water may be routed back to the wet scrubber, as shown along (the) waste water return loop. Waste water may also or alternately be routed to waste water treatment system for processing for subsequent treatment by (the) waste water treatment system.
“Typically, a large portion of the waste water is returned to the wet scrubber via (the) waste water return loop and a small portion of the waste water is treated by the waste water treatment system. Even though the waste water may contain small amounts of DCM, the waste water will still retain its ability to scrub the exhaust containing DCM. An advantage of the wet scrubber over the activated carbon beds is that all or most of the water used by the wet scrubber is the waste water from the density separator vessel, resulting in substantial savings of water and energy, and resultantly, substantial cost savings.”
Tesla states that compared to more traditional exhaust treatment systems, the DCM treatment and recovery model outlined in its patent effectively eliminates the use of steam and cooling, while also reducing the amount of throughput needed by a waste water system. With these efficiencies in mind, Tesla notes that it could reduce capital expenditures and operating costs “for the same amount of DCM processed processing.” The increased simplicity of the system and reduced airflow rates are expected to help the company get more savings in both capital expenditures and operating costs as well.
More than a way to optimize its operations, Tesla’s recent patent is also a notable way for the company to keep its battery production lines safer for its employees. Such a system would definitely be invaluable for the company, particularly as Tesla is now preparing the Model 3 for a global rollout. With the Model 3 ramp ever-expanding, and with high-volume vehicles like the Model Y and possibly the Tesla pickup truck in the pipeline, optimizations such as a better DCM treatment and recovery system are all but necessary.
Tesla’s recently published patent on its DCM treatment system could be accessed here.
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