Ammonia plant gets a load off its mind

A large complex in Chester owned by Kemira Ince is producing in the region of 3000 tonnes of agricultural fertiliser a day, and employs an Idec OpenNet Controller to automate the loading of tankers for improved efficiency

Kemira recently entered the anhy-drous ammonia market - this is the term used to describe ammonia which contains little or no water and is used in the manufacturer of products such as refrigerants and domestic cleaning fluids. Kemira produces a premium grade with only a few ppm of water.

A road tanker can be loaded at one of three loading bays at a rate of 4 tonnes an hour. The company recently needed a system to load its road tankers automatically as the ammonia is produced from the production line. An Idec OpenNet Controller (ONC) is used to control the operation. The correct routing valves are set up manually, then when the 'go' signal is given, the PLC takes over the sequencing operation, taking account of safety interlocks such as preventing the backfeed of liquid ammonia from the feed pipes to the vapour system. Vapour is used in the final sequence to clear the liquid ammonia from the feed pipes into the tanker.

The Idec controller employs a full local I/O configuration of 15 modules mounted adjacent to the CPU. For routing valve inputs, twelve 110V AC input modules are used, and three output modules are wired to the valve solenoids.

Safety issues An IDEC HG1B display module is connected to the ONC which shows trip diagnostic messages and valve states on 63 separate screens. The efficiency of the system has been improved tremendously, and safety issues have also been addressed as the whole operation can be monitored over CCTV, once automatic sequencing has been started.

Kemira officials say that a second phase is shortly to be put into action which introduces storage tanks at the end of the production line. This will allow a superior grade of liquid ammonia to be stored, and tankers will be fed from these at an increased rate of 40 tonnes per hour. The whole operation will be completely unmanned and will be controlled form a control room employing a Eurotherm SCADA system. This will communicate with the IDEC ONC PLC via a Modbus gateway.

• Idec
  e104@industrialnetworking.co.uk