Chemring Marine is a member of the Chemring Group of companies, which is also home to Chemring Defence – one of the world’s leading suppliers of military pyrotechnics and explosives. The marine division produces the renowned Comet brand of SOLAS-approved smoke markers and handheld rocket flares, which are used extensively by the world’s navies, lifeboat and rescue services, merchant fleets and airlines, as well as fishing vessels and leisure craft.
Part of Chemring Marine’s rocket flare manufacturing process at Bremerhaven involves forcing propellant into the plastic body of the flare; at the end of each production batch, the tray beneath the filling area is flushed clear of any stray propellant by an operator, in preparation for the next batch. In order to ensure that the propellant is thoroughly dissolved and does not form a safety hazard, the acidic flushing agent needs to be delivered to the point of use at exactly +60 degrees Celsius. Since the entire process takes place within an Ex (ATEX) classified zone, Chemring Marine developed an explosion-proof method of heating the flushing agent, involving a special double-walled heat exchanger which transfers heat from a hot water source system to the bulk supply of flushing agent.
However, maintaining the entire supply of flushing agent at this temperature proved expensive, so Chemring Marine sought Intertec’s help in investigating whether the company could supply a more cost-effective solution, based on its Flattherm heater blocks. These small, electrically-powered modular conduction heaters provide a very flexible means of configuring explosion-proof fluid heater systems – multiple units can be operated in a master-slave arrangement to provide the required power output level, and they can be sandwiched around a tube of any appropriate material to create a highly efficient heat exchanger. An intrinsically safe temperature sensor on the outlet pipe provides feedback to a digital PID controller, facilitating fast and accurate temperature control. These types of heater system are ideal for applications where varying levels of heat energy need to be transferred accurately and quickly into the fluid, in order to compensate for changes in flow rates or inlet temperatures, or to accommodate different demanded outlet temperatures.
In this case, Intertec chose to base the fluid heater system on a master-slave configuration comprising a single 500 W and a single 400 W Flattherm heater block, using stainless steel tubing to accommodate the aggressive flushing agent. The outlet sensor is connected to the company’s TC D digital temperature controller, which is an ATEX-approved unit with fully encapsulated solid state circuitry; it uses zero-voltage switching techniques and a Triac power switching element to minimise radio frequency interference and power losses, and provides fully proportional control. Designed specifically for use in hazardous and potentially explosive atmospheres, the TC D controller incorporates a number of high reliability safety features, including local monitoring of the heater block’s surface temperature, with automatic limiting and fault shutdown. The entire heater system is housed in a standard Intertec enclosure, which is certified for use in Zone 1 environments.
According to Uwe Eggers, the Safety Officer in charge of waste management at Chemring Marine’s Bremerhaven facility, "Intertec’s explosion-proof fluid heater has proved to be an exceptionally cost-effective solution to our needs. All our work here is carried out in compliance with international safety standards, including the German Explosives Act, which in respect of pyrotechnic products and explosives is one of the most rigorous in the world. Most commercially-available explosion-proof heating systems involve wrap-around heating cables which require costly and time-consuming inspection and certification processes, so being able to install what is effectively a completely self-contained custom ATEX-approved heater was a huge advantage. What’s more, we are now able to heat the flushing agent to exactly the right temperature on an as-demand basis, which is much more efficient and far less expensive to operate."