Operation year-round 24-hour

The facility will be one of the largest biomass plants to be built in the world and is scheduled to enter commercial operation in late 2012. Young trees will be grown as a crop to produce wood chips. The plant will use 2.5 million tonnes of wood chips each year to produce 300 MW of electrical energy. The plant will operate 24 hours a day, all year round to meet some of the National Grid base load. 

Availability or operating reliability is the actual operating time of a plant in relation to overall time. Usually it is stated as a percentage and relates to 8760 hours/ year, which correspond more or less to a year-round 24-hour-operation. Here, scheduled plant downtimes, e.g. for inspections, have to be taken into account Therefore, an availabiUty of 98% means that the plant may have a total downtime of 175 hours, i.e. 7.3 days. It is logical that the operator is interested in as much plant availability as possible. S/he will commit the plant constructor to adhere to availability. As a rule, penalties are provided in the case of non-compUance. Therefore, high demands on availability lead to increasing procurement and maintenance costs. In this comiection, redundancies and multi-line plants also have to be taken into consideration. 

Figure 3 shows the DDS UF-plant at the above mentioned Feta cheese factory. It comprises a total of 20 DDS UF modules, type 35, each with 27 m (approx. 297 ft ) membrane area. The membrane applied is of synthetic material with a nominal cut-off value of 20,000. The plant can operate round the clock, and the cleaning time is approx. 2 hours every 24 hours. The cleaning is carried out with a solution of hot 0.5% sodium hydroxide, followed by a solution of hot 0.3% nitric acid, and sterilization if necessary with CI2. The membrane life time is approx. 1 year. 

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