Introduction
A client came to iGAS with a requirement for gas generation and mixing which would be on an offshore pipe lay vessel. The vessel needed a continuous supply of acetylene which would be used for various cutting tasks on board. The vessel, shown in Fig. 1, would be in operation 24/7 and the client wanted a Mobile Acetylene Generation to eliminate their dependency on cylinder supplies which have been previously problematic.
The System
The acetylene plant was designed to ensure the vessel had a continuous flow of gas. This gas had to be produced safely and efficiently and meet the require flow rate specified by the client. The acetylene once produced was distributed around the vessel using a ring main piping system which had over 20 individual points of use to allow the user to access the gas throughout the vessel.
The system was designed to produce acetylene at 8kg/h at 1.4bar to ensure the supply would meet demand. The acetylene is produced in two generators which mix water and carbide to produce the gas. The generation of the acetylene gas used a pneumatic control system to load the generators from the carbide hoppers. Each hopper stored 75KG calcium carbide which meant the generator could produce 25kg of gas. The system uses two tanks to allow the user to be refilling one carbide store whilst the other is in use therefore allowing continuous operation.
The generator had a nitrogen purge system to ensure safe working conditions. Great care was taken when designing an Acetylene generator as the gas is flammable in concentrations as low as 2.5% therefore all equipment in the container and in the immediate vicinity had to be 2G Eex-d IIC T2 rated.
The process flow diagram for the acetylene generators is shown below in Fig 4.
Conclusion
The decision to move away from the traditional cylinder supply and look to generate acetylene and oxygen on board the vessel has led to eliminating the need for cylinder deliveries. Once the generators were installed the system was fully operational within a few days. Time for installation was reduced considerably due to the generators being containerised, factory built and tested before being sent to the vessel.
