The integrated mercury sampling extension for the ASaP intermittent LNG Sampler system is designed as an add-on. On June 2021 Analytical Solutions and Products had a very successful Factory Acceptance Test (FAT). The LNG Sampler for an off-shore location in Mozambique, passed the FAT with flying colors.
Unique features of the LNG Sampler system
- The limited footprint available in the existing installation (replacement of a competitor LNG sampler).
- Integration of a mercury sampler according ISO 6978-2: 2003 Sampling of mercury by amalgamation on gold/platinum alloy.
Despite the footprint challenge and additional requirements of mercury sampling the ASaP craftsmen (or artists as we like to call them) did an outstanding job to build a very compact LNG sampler and still make everything easy to access for operation and maintenance.
Of course everything starts with good engineering and in-depth knowledge of the current International standards. The ASaP engineering team succeeded in a very challenging task and exceeded every expectation of the EPC, System integrator and ASaP team members involved.
Despite the “manual” sampling, the mercury system was fully integrated and automated by the user friendly ASaP LNG Sampler software.
Integrated Mercury sampling modes
The mercury sampling extension on the LNG Sampler system is designed as an add-on system with connection towards the PLC and HMI control system that controls the remainder of the system. The Mercury Sampler system is integrated into the heated LNG sampling cabinet, which has a nominal heating setpoint of 40°C.
The mercury sampling control system is connected to the PLC and HMI of the LNG sampler using Modbus TCP communications over Ethernet.
The Mercury Sampler can be operated in either of the following modes:
- Manual control (i.e., starting a of sample collection on demand of an operator)
- Automatic sequence (i.e., automatic sample collection following the start of an LNG sampling sequence)
Mercury sampling manual control
In manual control mode, the operator must make sure that the system is ready to start collection of sample and per-requisites of ISO 6978-2 sampling procedures are met, including purging. In case the system is not ready for sample collection, the operator needs to ensure that corrective measures are taken before sample collection. In manual sample control, the operator is enabled to enter a specific amount of gas to be passed over the sample trap at the HMI screen. As soon the start manual sample button is pressed, the operator is asked to confirm during the step “traps installed “that the following prerequisites for safe sampling are met:
- That the sample traps have been properly installed in the heated block
- That the flexible hoses have been properly connected to the glass sample traps
- That the sample block valves before and after the heated block are in the open position.
As soon this is confirmed, the sample collection for the specified amount of sample will be commenced at the flow rate set.
Mercury sampling automatic control
To ensure representative mercury sampling during the offload of the LNG, an automatic sampling option is built in. When the automatic mercury sampling is enabled in the HMI screen, automatic mercury sampling sequence will be started as soon as the intermittent LNG sampling is started or when LNG sampling is in progress immediately. The sampling in this case starts from the pre-purging step. In automatic control mode, the mercury sampling will follow the suspend and resume regime of the intermittent LNG Sampler.