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Specialist Chemical Engineering Solutions
To meet stringent health and safety requirements for steam raising at an existing chlorine gas producing plant, Gee & Company has developed one of the most complex chemical dosing systems of its type, incorporating unusually high engineering standards. Housed within a large self-contained kiosk, the packaged dosing system was factory- built and tested so as to minimise the level of site installation skills and work.
Runcorn boiler plant is being provided by Alstom Power Turbo Systems on a turnkey basis, and will produce steam, demineralised and high-grade water.
The steam-raising portion consists of three 110 t/h boilers that burn a mix of hydrogen and natural gas. Demineralised water is produced in three streams, each of 222.55 t/h gross flow.
A particularly demanding specification for the injection of chemicals was set partly by the health and safety requirement posed by the hazardous nature of the operations at Runcorn and partly by the intention to operate the plant on a continuous, year-round basis. Together, these requirements also dictated the need for a degree of equipment and system redundancy.
Commenting on the selection of Gee to engineer the chemical dosing system, Bill Harris, Alstom’s engineer responsible for the dosing said, “The choice of Gee was a natural one for us, as our two companies have worked together successfully in the past on projects such as Ling Ao nuclear power station in China, the combined cycle gas turbine system at Black Point in Hong Kong and the CHP project at Shotton in the UK”.
The chosen approach was for Gee to manufacture and pre-assemble a large purpose-designed dosing kiosk within its Birmingham factory, where there was access to skills and equipment that would not be available on site. Here - after being connected up electrically – comprehensive functional testing was also carried out. The client witnessed this testing programme before the entire unit was partially disassembled, shipped to site, re-assembled and finally commissioned.
Basic construction of the 7 metres x 4 metres kiosk is of fibreglass, incorporating an integral floor. The chemical storage day/measurement tanks are all manufactured by Gee from polypropylene and the kiosk itself is fully pre-cabled in the factory. Amongst its more unusual features is that it incorporates a greater number of dosing pumps than any other single container supplied by the company.
It also has a polypropylene GRP-coated BS4994 Cat 1 bulk ammonia storage tank. This, together with associated piping and a safety shower, are the only components that are not housed within the kiosk. The scrubber incorporates a pull-ring packed column to remove any dangerous fumes and is supplied with a spray water storage tank and pump. Dilution and transfer of bulk concentrated ammonia and hydrazine to the chemical day/measurement tanks located within the kiosk is by eductors.
Three primary chemical dosing functions are provided, each housed within dedicated cabinets inside the main kiosk. These dose ammonia, hydrazine and sodium phosphate respectively. For reasons of both safety and performance, all three systems are equipped with high specification dosing pumps.
These are Signal S300 metering pumps, a feature of which is a double diaphragm to provide additional safety, together with a rupture detection system that would pre-empt and warn of any pump failure before it happened. The hydrazine and ammonia dosing skids have a primary and stand-by facility, and the phosphate skid is fitted with a common stand-by dosing pump.
Hydrazine is dosed to the high-grade water feed pumps and boilers. A further dedicated dosing pump can be brought into service to deliver hydrazine to the high-grade water feed pumps discharge when the high-grade water de-aerator is out of service.
Ammonia is dosed to the feed to the boilers and high-grade water de-aerators, as well as high-grade water feed pump and boilers’ feed pumps suction. Ammonia can also be dosed to the high-grade water feed pumps discharge when the high-grade water de-aerator is out of service.
In total, the three skid units comprise of a total of fifteen dosing pumps – giving the necessary redundancy to meet Ineos Chlor’s critical objective of ensuring that the system runs to a continuous 24/7 programme.
All control and protection features are available locally at the dosing kiosk control panel. Remote pump selection, together pump servo setting, is available remotely via the plant control system. An operator terminal within the dosing kiosk enables human/machine communication, in addition to which graphical operator panels within the HMI permit system monitoring and control. Equipment status and alarm signals are also communicated to the plant control system via a serial link.
Gee has spearheaded the use of factory-built package plant for chemical dosing.
