Packaged dosing system for Ineos steam plant

London -- To meet stringent health and safety requirements for steam raising at an existing chlorine gas producing plant, Gee & Company has developed a complex chemical dosing system. 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.

The boiler plant was provided by Alstom Power Turbo Systems on a turnkey basis, and will produce steam, demineralised and high-grade water for the existing Ineos Chlor chlorine plant at Runcorn. The steam-raising portion consists of three 110t/h boilers that burn a mix of hydrogen and natural gas. Demineralised water is produced in three streams, each of 222.55t/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.

Gee manufactured and pre-assembled a large purpose-designed, dosing kiosk within its Birmingham factory, where comprehensive functional testing was also carried out. The unit was then partially disassembled, shipped to site, re-assembled and finally commissioned.

Basic construction of the 7m x 4m kiosk is in fibreglass, incorporating an integral floor and supplied fully pre-cabled. The chemical storage day/measurement tanks were all manufactured from polypropylene by Gee and the kiosk incorporates more dosing pumps than any previous container supplied by the company.

The installation has a GRP-coated polypropylene BS4994 Cat 1 bulk ammonia storage tank.

This, together with associated piping and a safety shower, is the only component 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, and, for reasons of both safety and performance, are equipped with high specification dosing pumps. These Signal S300 metering pumps feature 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 water feed pumps discharge when the water de-aerator is out of service.

Ammonia is dosed to the feed to the boilers and water de-aerators, as well as water feed pump and boilers’ feed pumps suction. Ammonia can also be dosed to the water feed pumps discharge when the water de-aerator is out of service. Phosphate, in the form of a pre-blended liquid, is dosed directly into each of three boiler drums.

In total, the three skid units comprise a total of 15 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 with 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 communicated to the plant control system via a serial link.